Method and system for determining a characteristic of radioactive matter

Abstract

A method for determining a characteristic of radioactive matter. The method comprises detecting nuclear radiation emitted by the radioactive matter to gather detection information. The method comprises comparing the detection information to a signature decay characteristic of a known nuclear decay.

Description

Method and system for determining a characteristic of radioactive matterFIELD

[0001] The present invention relates to a method and system for determining a characteristic of radioactive matter. In particular, the method and system may be used to determine one or more characteristics such as identities one or more radionuclides present in the radioactive matter and associated quantities, identities of one or more types of nuclear radiation being emitted by the radioactive matter and associated quantities, spectroscopic information, radioactivity information, a degree of decay chain equilibration within the radioactive matter, and spatial and / or temporal changes in said characteristics.

[0001] The present invention may find particular usefulness in fields such as, for example, radiotherapeutics, nuclear energy generation and / or decommissioning. In the example of radiotherapeutics, ionising radiation has in many cases been shown to be a highly effective way to treat cancer, maximising cancer damage while limiting impact on healthy tissue. Targeted radiation therapy (TRT), a relatively new form of therapy, claims to accomplish this. In targeted radiation therapy (TRT) e.g. with Lu-177, and especially its subgroup targeted alpha therapy (TAT), e.g. with225Ac, radio-nuclei are attached to a targeting vector, e.g. a peptide. Through biochemical or other factors, this vector preferentially accumulates near or even inside the cancer cells. There, the radionuclei decay and cause a highly localised damage to cancer cells and leads to effective tumour control. It causes the death of cancer cells through various mechanisms while significantly reducing harm to the surrounding healthy tissue. What should be the optimum dose required to kill the cancer cell is one of the most critical questions for this treatment method. It is important to understand characteristics of the radiotherapeutics such as, for example, type, quantity, and / or radioactivity of radionuclides such as, for example, alpha-emitting radionuclides before the radiotherapeutics are utilized with patients. The method and system of the present invention may be used to facilitate a quality control procedure during production and / or use of such radiotherapeutics. It will be appreciated that this merely provides one example of a potential usage, and that the present invention may be used in fields other than radiotherapeutics. In the example of nuclear energy generation and / or decommissioning, the ability to characterise radioactive waste and / or characterise radioactive materials used in nuclear energy research, development, and / or production is of great importance.69634790-1BACKGROUND

[0002] Known nuclear radiation sensing systems require high resolution energy measurements and / or indirect measurement techniques (such as mixing the radioactive matter with a scintillator) which provide limited information (e.g. bulk radioactivites) and may involve contaminating radioactive matter in order to assess the radioactive matter.

[0003] It is an aim of the present disclosure to provide a method and system that address one or more of the problems above or at least provides a useful alternative.SUMMARY

[0004] According to an aspect of the present disclosure, there is provided a method of determining a characteristic of radioactive matter. The method comprises detecting nuclear radiation emitted by the radioactive matter to gather detection information. The method comprises comparing the detection information to a signature decay characteristic of a known nuclear decay.

[0005] The method advantageously enables radionuclides present in the radioactive matter to be distinguished and radioactive decay chains to be identified. Performing spectroscopic radiation (e.g., alpha particle) detection to allow identification of radiation emitters present in the radioactive matter based on their decay energy and / or temporal information may be useful in many applications such as, for example, streamlining quality control of radiotherapeutics, assessment of nuclear waste, etc.

[0006] The method of the above aspect may comprise any of the following features, including any combination of the following features.

[0007] The known nuclear decay may form part of a known nuclear decay chain. The signature decay characteristic may be an energetic and / or temporal characteristic of the known nuclear decay chain. That is, the signature decay characteristic may comprise a signature energy information and / or signature temporal information.

[0008] The detection information may comprise detected energy information. The signature decay characteristic may comprise signature decay energy information. The method may comprise comparing the detected energy information to the signature decay energy information.

[0009] The signature decay energy information may comprise a signature energy spectrum. The method may comprise determining a detected energy spectrum at least partially based on the detected energy information. The method may comprise comparing the detected energy spectrum to the signature energy spectrum.69634790-1

[0010] The method advantageously reduces a required energy resolution compared to known methods (e.g. having an energy resolution of approximately 1 MeV compared to an energy resolution of 10s of KeV).

[0011] The method may comprise comparing the detected energy spectrum to a plurality of signature energy spectra associated with a plurality of known nuclear decays. The method may comprise matching the detected energy spectrum to a most similar signature energy spectrum of the plurality of signature energy spectra.

[0012] The method advantageously improves an ability for different radionuclides to be identifies and / or distinguished. For example, the alpha energies from227Ac are different from those of225Ac, giving a spectroscopic distinction.

[0013] The signature decay energy information may comprise a signature decay energy. The method may comprise matching the signature decay energy to a corresponding decay feature of the detected energy spectrum.

[0014] The corresponding decay feature may be a step that forms part of the energy spectrum of the detected radiation. The corresponding decay feature may be a peak that forms part of the energy spectrum of the detected radiation. Steps may be converted to peaks by performing a numerical differentiation of the energy spectrum of the detected radiation.

[0015] Lower energy alphas may be more difficult to measure due to interactions in a sensor before detection occurs. As such, there may be a benefit to selecting higher energy signature alpha decays in identifying and / or distinguishing radionuclides, thereby informing choice of decay energies in the known decay chain to base a ‘signature’ on.

[0016] The method may comprise selecting a first region of the detected energy spectrum at least partially based on the signature decay energy. The method may comprise determining a number of detection counts associated with the first region.

[0017] Determining a number of detection counts associated with any region may comprise correcting for different stopping powers of the radiation emitted by the radioactive matter.

[0018] Determining a number of detection counts associated with any region may comprise determining an energy dependent correction. The energy dependent correction may at least partially account an efficiency of a nuclear radiation sensing system or method. The energy dependent correction may be referred to as an energy dependent efficiency correction. The energy dependent correction may be based on one or more Monte Carlo simulations, e.g. of a detection environment in which the69634790-1radioactive matter is located. Additionally or alternatively, the energy dependent correction may be based on one or more analytical calculations based on knowledge of a physical property of the detection environment. The energy dependent correction may at least partially account for a geometry of a nuclear radiation sensing system and / or the radioactive matter. The energy dependent correction may at least partially account for a stopping power of a nuclear radiation sensing system and / or the radioactive matter. The radioactive matter may be a radioactive fluid. A geometry and / or stopping power of the radioactive fluid may be at least partially accounted for. The radioactive matter may be a solid. A stopping power and / or geometry of the solid may be accounted for. The energy dependent correction may at least partially account for a low energy sensor threshold of a nuclear radiation sensing system.

[0019] The first region may comprise the corresponding decay feature.

[0020] Determining a number of detection counts associated with the first region may comprise determining a height of the corresponding step.

[0021] Determining a number of detection counts associated with the first region may comprise determining an area of the corresponding peak.

[0022] Determining the height of the corresponding step or determining the area of the corresponding peak may comprise performing a spectral fitting technique.

[0023] Determining the area of the peak may comprise performing numerical integration.

[0024] Determining the area of the peak may comprise performing a peak fitting technique.

[0025] Determining the height of the corresponding step or determining the area of the corresponding peak may comprise correcting for different stopping powers of the radiation emitted by the radioactive matter. The height of a step or the area of a peak may be approximately proportional to an inverse of the stopping power.

[0026] Determining the height of the corresponding step or determining the area of the corresponding peak may comprise correcting for an efficiency of the detection of radiation emitted by the radioactive matter. An efficiency of the detection may vary for different energies of radiation emitted by the radioactive matter. Correcting for an efficiency of the detection of radiation emitted by the radioactive matter may comprise correcting a detection efficiency of each alpha particle energy.

[0027] Summed detection counts from decay steps associated with different signature energies may advantageously provide spectroscopic information.69634790-1

[0028] The method may comprise selecting a second region of the detected energy spectrum. The method may comprise determining a number of detection counts associated with the second region. The method may comprise comparing the number of detection counts associated with the first region to the number of detection counts associated with the second region.

[0029] The comparison advantageously allows the radioactivity of a first radionuclide in the known decay to be determined relative to one or more other radionuclides in the known decay without necessarily assuming that a part of the decay chain is in an equilibrium state. The method advantageously allows assessment of a degree decay chain equilibration for a partly-equilibrated decay chain based on spectroscopic establishment of contributions from signature decay features.

[0030] The second region may be selected at least partially based on one or more other signature decay energies associated with a known nuclear decay chain.

[0031] An energy threshold corresponding to the signature decay energy may be used to define the first and second regions.

[0032] An energy threshold corresponding to an energy greater than the signature decay energy may be used to define the first and second regions.

[0033] The characteristic of the radioactive matter may comprise a decay chain present in the radioactive matter. The signature decay energy may be a greatest signature decay energy of the decay chain.

[0034] The characteristic of the radioactive matter may comprise a decay chain present in the radioactive matter. The signature decay energy may be associated with a radionuclide having a half-life that is greater than half-lives of subsequent radionuclides in the decay chain.

[0035] The characteristic of the radioactive matter may comprise a decay chain present in the radioactive matter. The characteristic of the radioactive matter may comprise a degree of nuclear decay equilibration e in the radioactive matter. The method may comprise using the following equation:NTwtotntote = - x - x -NtotWTnT where NT is a number of detection counts over the energy threshold, Ntot is a total number of detection counts in the detected energy spectrum, WT is a width of the spectral region above the energy threshold T, wtot is a total width of the detected energy spectrum, nTis a number of alpha decay steps above the energy threshold T, and ntot is a total number of alpha decay steps present in the detected energy spectrum.69634790-1

[0036] The method may comprise calculating a ratio of the number of detection counts associated with the first region to the number of detection counts associated with the second region. The method may comprise multiplying the ratio bywhere Ntotis a total number of detection counts of the first and second regions and t is a duration for which the detection information is gathered.

[0037] Calculating the ratio advantageously determines an absolute radioactivity of a first radionuclide in the known decay without necessarily assuming that a part of the decay chain is in an equilibrium state.

[0038] Calculating a ratio of the number of counts associated with the region to a total number of counts associated with all of the plurality of regions may comprise calculating a ratio of a height of the corresponding step of the energy spectrum of the detected radiation associated with the radionuclide to a total of the heights of the corresponding steps of the energy spectrum of the detected radiation.

[0039] Calculating a ratio of the number of counts associated with the region to a total number of counts associated with all of the plurality of regions may comprise calculating a ratio of areas of the corresponding peak of the energy spectrum of the detected radiation associated with the radionuclide to a total of the areas of the corresponding peaks of the energy spectrum of the detected radiation.

[0040] The method may comprise determining a radioactivity contribution associated with the first region relative to the second region. The method may comprise comparing the radioactivity contribution associated with the first region to an expected radioactivity contribution. The expected radioactivity contribution may be at least partially based on the signature decay characteristic.

[0041] The method may comprise determining a degree of nuclear decay equilibration present in the radioactive matter at least partly based on the comparison between the radioactivity contribution associated with the first region and the expected radioactivity contribution.

[0042] The method advantageously determines a degree of nuclear decay equilibration present in the radioactive matter. The expected radioactivity contribution may be at a nuclear decay equilibrium of the known nuclear decay chain.

[0043] The method may comprise determining a stopping power characteristic associated with the first region. The method may comprise calculating a radioactivity at least partially based on the stopping power characteristic and a result of comparing the number of detection counts associated with the first region to the number of detection counts associated with the second region.69634790-1

[0044] The method advantageously improves an accuracy with which the radioactivity is determined.

[0045] The stopping power characteristic may comprise a dimension of a detector and / or the radioactive matter. The stopping power characteristic may comprise a material property of the detector and / or the radioactive matter.

[0046] The method may comprise determining a radioactivity associated with the first region at least partially based on the stopping power characteristic.

[0047] The method may comprise comparing the numbers of detection counts in the first and second regions to a simulation of the known nuclear decay.

[0048] The simulation may comprise a Monte Carlo simulation. The simulation may be performed using software such as, for example, Geant4.

[0049] The method may comprise allowing the radioactive matter to reach a nuclear decay equilibrium at least partially based on the signature decay characteristic. The method may comprise detecting nuclear radiation emitted by the radioactive matter at the nuclear decay equilibrium.

[0050] The detection information may be gathered in a detection environment. The simulation may account for one or more characteristics of the detection environment. For example, the simulation may account for one or more physical properties of the detection environment, such as materials, dimensions (e.g. thicknesses), stopping powers, etc.

[0051] The simulation may at least partially account for a material of the detection environment and / or a dimension of the detection environment and / or a stopping power of the detection environment.

[0052] The method may comprise determining an energy dependent correction. The energy dependent correction may at least partially account an efficiency of a nuclear radiation sensing system or method. The energy dependent correction may be referred to as an energy dependent efficiency correction. The energy dependent correction may be based on one or more Monte Carlo simulations, e.g. of a detection environment in which the radioactive matter is located. Additionally or alternatively, the energy dependent correction may be based on one or more analytical calculations based on knowledge of a physical property of the detection environment. The energy dependent correction may at least partially account for a geometry of a nuclear radiation sensing system and / or the radioactive matter. The energy dependent correction may at least partially account for a stopping power of a nuclear radiation sensing system and / or the radioactive matter. The radioactive matter may be a69634790-1radioactive fluid. A geometry and / or stopping power of the radioactive fluid may be at least partially accounted for. The radioactive matter may be a solid. A stopping power and / or geometry of the solid may be accounted for. The energy dependent correction may at least partially account for a low energy sensor threshold of a nuclear radiation sensing system.

[0053] The energy dependent correction may advantageously contribute to allowing useful information (e.g. an identity of a radionuclide and / or decay chain present in the radioactive matter, and / or a degree of nuclear decay chain equilibration) to be determined from lower resolution energy measurements and / or spectra (e.g. the less well-resolved spectrum of Fig. 8). In contrast, prior art methods require higher resolution energy measurements and spectra having well-defined peaks in order to determine any conclusions, thereby limiting prior art methods to complex and expensive measurement equipment and / or highly controlled environments to ensure the provision of higher resolution energy measurements and spectra. As such, the method and system of the present disclosure may be successfully applied to a range of scenarios in which less well-resolved energy measurements and spectra may occur such as, for example, targeted alpha therapy radiopharmaceutical quality control, radiopharmaceutical spatial distribution mapping in in vivo and in vitro research, nuclear decommissioning isotope analysis in liquids, etc. In contrast, prior art methods are not suitable for, or have very limited applications to, said scenarios.

[0054] The method may comprise using the comparison to determine a degree of nuclear decay equilibration in the radioactive matter.

[0055] Determining a total number of counts associated with the energy spectrum of the detected radiation may comprise performing a numerical integration of the energy spectrum. When an identified radionuclide is a head radionuclide of the known nuclear decay chain, the method may comprise dividing a total number of detection counts associated with the spectrum of the detected energies of nuclear radiation by a number of corresponding decay features present in the detected energy spectrum.

[0056] The detection information may comprise detected temporal information. The signature decay characteristic may comprise signature decay temporal information. The method may comprise comparing the detected temporal information to the signature decay temporal information.

[0057] A combination of energy signature and temporal signature advantageously improves radionuclide identification and discrimination. An example69634790-1application of the present disclosure is to detect the presence of the225Ac decay chain (and distinguish it from the227Ac decay chain). These decay chains both consist of several alpha (and beta) decays, so by detecting multiple decays in the correct sequence with the appropriate relative decay times (e.g. characteristic of the half-lives of the radionuclides in the decay chains) the decay chains may be identified in the radioactive matter without requiring the higher resolution alpha spectroscopy needed to identify individual isotope decays.

[0058] The method may comprise determining a temporal sequence of decay events at least partially based on the comparison between the detected temporal information and the signature decay temporal information.

[0059] The method may comprise temporally segmenting the detection information. A first temporal period of the temporal segmentation may be at least partially based on the signature decay temporal information.

[0060] A second temporal period of the temporal segmentation may be at least partially based on signature decay temporal information associated with a different known nuclear decay.

[0061] The method advantageously improves the ability to distinguish radionuclides in radioactive matter comprising two different radionuclides having at least one similar signature decay chain characteristic.

[0062] Detecting nuclear radiation emitted by the radioactive matter may comprise detecting a first type of nuclear radiation and detecting a second type of nuclear radiation. The first and second types of nuclear radiation may be different.

[0063] The signature decay characteristic may comprise a first signature decay characteristic associated with the first type of nuclear radiation.

[0064] The signature decay characteristic may comprise a second signature decay characteristic associated with the second type of nuclear radiation.

[0065] Detecting nuclear radiation emitted by the radioactive matter may comprise detecting nuclear radiation emitted from different positions of the radioactive matter to gather position dependent detection information.

[0066] The method advantageously increases an accuracy of radionuclide identification and / or enables spatially dependent applications.

[0067] The method may comprise processing the detection information gathered from a first position of the radioactive matter independently of detection information gathered from another position of the radioactive matter.69634790-1

[0068] The method may comprise determining identities of a parent radionuclide and a daughter radionuclide of the parent radionuclide at least partially based on the comparison between the detection information and the signature decay characteristic. The method may comprise determining a position of the daughter radionuclide relative to a position of the parent radionuclide.

[0069] Detecting nuclear radiation emitted by the radioactive matter to gather detection information may comprise detecting one or more of alpha radiation emitted from an alpha-emitting radionuclide, and / or beta radiation emitted from a beta emitting radionuclide, and / or gamma radiation emitted from a gamma-emitting radionuclide, and / or neutron radiation emitted from a neutron-emitting radionuclide.

[0070] Detecting nuclear radiation emitted by the radioactive matter may comprise directly detecting the nuclear radiation.

[0071] Direct detection of radiation indicates that the sensor interacts with the radiation itself rather than interacting with a product of an interaction between the radiation and some other entity. For example, detecting light emitted by a scintillator in response to an interaction with the radiation is an example of indirect detection of the radiation, and cannot be considered to be direct detection of the radiation. This advantageously avoids one or more problems associated with indirect detection methods, such as scintillation. For example, the radioactive matter does not need to be mixed with a liquid that scintillates. As such, the to-be-measured radioactive matter is not affected by the detection.

[0072] The method may comprise determining a radiation dose in targeted alpha therapy.

[0073] According to another aspect of the present disclosure, there is provided a nuclear radiation sensing system. The nuclear radiation sensing system comprises a sensor configured to detect nuclear radiation emitted by radioactive matter. The nuclear radiation sensing system comprises a processor configured to compare detection information gathered by the sensor to a signature decay characteristic of a known nuclear decay to determine a characteristic of the radioactive matter.

[0074] The system described in the above aspect may comprise any of the following features, including any combination of the following features.

[0075] The sensor may be configured to directly detect the nuclear radiation. Direct detection of radiation indicates that the sensor interacts with the radiation itself rather than interacting with a product of an interaction between the radiation and some other entity. For example, detecting light emitted by a scintillator in response to an69634790-1interaction with the radiation is an example of indirect detection of the radiation, and cannot be considered to be direct detection of the radiation.

[0076] The sensor may comprise a photodiode.

[0077] The sensor may be configured to detect alpha radiation emitted by the radioactive matter. The sensor may be configured to detect an energy of the alpha radiation. The sensor may be configured to detect a quantity of the alpha radiation emitted by the radioactive matter.

[0078] The sensor may be configured to detect beta radiation emitted by the radioactive matter. The sensor may be configured to detect an energy of the beta radiation. The sensor may be configured to detect a quantity of the beta radiation emitted by the radioactive matter.

[0079] The sensor may be configured to detect gamma radiation emitted by the radioactive matter. The sensor may be configured to detect an energy of the gamma radiation. The sensor may be configured to detect a quantity of the gamma radiation emitted by the radioactive matter.

[0080] The sensor may be configured to detect neutron radiation emitted by the radioactive matter. The sensor may be configured to detect an energy of the neutron radiation. The sensor may be configured to detect a quantity of the neutron radiation emitted by the radioactive matter.

[0081] The processor may be configured to perform the method of the previous aspect of the disclosure.

[0082] The processor may be configured to identify an alpha emitting radionuclide that forms part of the radioactive matter. The processor may be configured to determine a quantity of the alpha emitting radionuclide. The processor may be configured to determine a radioactivity of the radioactive matter that is associated with the alpha emitting radionuclide. The processor may be configured to discriminate between different alpha emitting radionuclides that form part of the radioactive matter. The processor may be configured to determine quantities of the different alpha emitting radionuclides. The processor may be configured to determine radioactivites of the radioactive matter that are associated with the different alpha emitting radionuclides.

[0083] The processor may be configured to identify a beta emitting radionuclide that forms part of the radioactive matter. The processor may be configured to determine a quantity of the beta emitting radionuclide. The processor may be configured to determine a radioactivity of the radioactive matter that is associated with69634790-1the beta emitting radionuclide. The processor may be configured to discriminate between different beta emitting radionuclides that form part of the radioactive matter. The processor may be configured to determine quantities of the different beta emitting radionuclides. The processor may be configured to determine radioactivites of the radioactive matter that are associated with the different beta emitting radionuclides.

[0084] The processor may be configured to identify a gamma emitting radionuclide that forms part of the radioactive matter. The processor may be configured to determine a quantity of the gamma emitting radionuclide. The processor may be configured to determine a radioactivity of the radioactive matter that is associated with the gamma emitting radionuclide. The processor may be configured to discriminate between different gamma emitting radionuclides that form part of the radioactive matter. The processor may be configured to determine quantities of the different gamma emitting radionuclides. The processor may be configured to determine radioactivites of the radioactive matter that are associated with the different gamma emitting radionuclides.

[0085] The processor may be configured to identify a neutron emitting radionuclide that forms part of the radioactive matter. The processor may be configured to determine a quantity of the neutron emitting radionuclide. The processor may be configured to determine a radioactivity of the radioactive matter that is associated with the neutron emitting radionuclide. The processor may be configured to discriminate between different neutron emitting radionuclides that form part of the radioactive matter. The processor may be configured to determine quantities of the different neutron emitting radionuclides. The processor may be configured to determine radioactivites of the radioactive matter that are associated with the different neutron emitting radionuclides.

[0086] The sensor may comprise a first layer configured to detect a first type of nuclear radiation. The sensor may comprise a second layer configured to detect a second type of nuclear radiation. The first and second types of nuclear radiation may be different.

[0087] The first and second types of nuclear radiation may be any one of alpha, beta, gamma and neutron radiation.

[0088] The first and second layers may have different thicknesses. The first and second layers may comprise different materials.

[0089] The first and second layers may form a stacked multilayer structure.

[0090] The first and second layers may be arranged side-by-side.69634790-1

[0091] The first layer may be configured to detect alpha radiation. The first layer may have a thickness of about 50pm or more. The first layer may have a thickness of about 500pm or less. The first layer may comprise silicon.

[0092] The second layer may be configured to detect beta and / or gamma radiation. The second layer may have a thickness of about 1mm or more. The second layer may have a thickness of about 50mm or less. The second layer may have a thickness of about 25mm or less. The second layer may have a thickness of about 10mm or less.

[0093] An additional or alternative layer may be configured to detect neutron radiation. For fast neutrons, such a layer may comprise a neutron sensitive organic scintillator such as, for example, stilbene. For thermal neutrons, such a layer may comprise a lithium containing inorganic scintillator such as, for example, CLLBC (Cs2LiLa(Br,CI)6:Ce). A layer configured to detect neutron radiation may have a thickness of, for example, about 50mm.

[0094] The second layer may be configured to directly detect the second type of nuclear radiation. The second layer may comprise cadmium zinc telluride (CZT).

[0095] The second layer may be configured to indirectly detect the second type of nuclear radiation. The second layer may comprise a scintillator.

[0096] The nuclear radiation sensing system may comprise an array (e.g. a side-by-side arrangement) of different sensors having single and / or multilayer stacked structures. For example, a nuclear radiation sensing system according to the present disclosure may comprise multiple single-layer or multilayer (e.g. two or three-layer) sensors, which may be configured to detect different types of nuclear radiation, have different spatial segmentations and / or temporal segmentations, or a mixture thereof. A side-by-side arrangement of the same type of single-layer sensor may advantageously allow a larger area of contact between the radioactive matter and the sensor surface. For example, a side-by-side arrangement of an alpha radiation sensor and a beta and / or gamma radiation sensor may be simpler to produce and / or may be more appropriate for certain industrial applications.

[0097] The sensor may comprise a spatially segmented sensing area configured to detect nuclear radiation emitted from different positions of the radioactive matter. The processor may be configured to determine position dependent detection information.

[0098] The sensor may comprise an array of sensing elements configured to perform spatial radioactivity measurements.69634790-1

[0099] The processor may be configured to process detection information gathered from a first position independently of detection information gathered from another position.[000100] The sensor may comprise a passivation layer. The passivation layer may comprise PTFE.[000101] The passivation layer advantageously protects the sensor from harsh chemicals, such as acids, involved in chemical processing.[000102] Passivation layers other than PTFE may not survive the time period of the measurements. For example, most metals, particularly gold, may suffer through micro-cracks development and peels-off in a strong acid environment. The advantage of PTFE is it can be kept relatively thin and can be still be resistant to etching for the strong acids such as HNO3. Other passivation layers such as SiO2, a- SiN:H (amorphous silicon nitride or amorphous silicon oxynitride), alumina (AI2O3) could be used as passivation layer.[000103] The nuclear radiation sensing system may comprise a receptacle configured to receive the radioactive matter. At least part of the sensor may form at least part of the receptacle.[000104] At least part of the sensor and at least part of the receptacle may be a single piece. That is, at least part of the sensor may provide the dual functions of receiving the radioactive matter and detecting radiation emitted by the radioactive matter.[000105] The receptacle and / or the sensor may be spatially segmented to form separate sensing regions. The processor may be configured to process detection information gathered from one sensing region independently of other sensing regions.[000106] At least part of the passivation layer may form the at least part of the receptacle. That is, at least part of the passivation layer and at least part of the receptacle are a single piece. That is, the passivation layer provides the dual functions of receiving the radioactive matter and protecting one or more components of the sensor from potentially damaging chemicals (e.g. acids) that may form part of the radioactive matter.[000107] The receptacle may be arranged such that, when in use, the radioactive matter is in contact with the sensor.[000108] The receptacle may have a depth of about 10mm or less. The receptacle may have a depth of about 200pm or less, 100pm or less, 50pm or less, 20pm or less, or 10pm or less.69634790-1[000109] A depth of the receptacle (which may determine a maximum thickness of the radioactive matter under measurement) may at least partially determine an energy resolution of the nuclear radiation sensing system.[000110] Providing a relatively thin layer of radioactive material proximate to or in contact with the sensor advantageously reduces or limits an amount of energy lost by the nuclear radiation before reaching the sensor. For example, all alpha particles detected by the sensor may have lost an acceptable amount of energy. Energy loss is roughly proportional to the path length travelled by the nuclear radiation. For example, such an arrangement may ensure that the amount of energy lost by an alpha particle is less than about 1MeV or less.[000111] The receptacle may comprise a channel configured to receive a radioactive fluid. The channel may form part of a microfluidic system.[000112] The receptacle may comprise an elastomer. The elastomer may comprise PDMS.[000113] The receptacle may have a rectangular cross-sectional shape.[000114] The channel may form part of a fluid path. The fluid path may be arranged to form a tortuous path.[000115] The channel may be a microfluidic channel.[000116] The receptacle may comprise a mounting configured to receive a radioactive solid.[000117] The receptacle may be arranged such that the radioactive matter is proximate the sensor.[000118] The receptacle may be arranged such that a propagation distance between the radioactive matter and a sensing element of the sensor is about 10pm or less.[000119] The nuclear radiation sensing system may comprise a seal located between at least part of the receptacle and at least part of the sensor. The seal may comprise an elastomer. The elastomer may comprise PDMS.[000120] According to an aspect of the present disclosure, there is provided a method of forming a nuclear radiation sensing system. The method comprises providing a sensor configured to detect nuclear radiation emitted by radioactive matter. The method comprises providing a processor configured to compare detection information gathered by the sensor to a signature decay characteristic of a known nuclear decay to determine a characteristic of the radioactive matter.69634790-1[000121] The method may comprise forming a receptacle configured to receive the radioactive matter. Forming the receptacle may comprise performing lithography on a material that forms part of the receptacle. Forming the receptacle may comprise performing additive manufacturing.[000122] It will be appreciated that features of different aspects may be combined.BRIEF DESCRIPTION OF THE DRAWINGS[000123] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Fig. 1A schematically depicts a first portion of a nuclear radiation sensing system according to the present disclosure.Fig. 1B schematically depicts a second portion of the nuclear radiation sensing system according to the present disclosure.Fig. 2A schematically depicts the second portion of the nuclear radiation sensing system in accordance with the present disclosure.Fig. 2B schematically depicts two cross-sectional views of the second portion of the nuclear radiation sensing system in accordance with the present disclosure.Fig. 3A shows a partly assembled nuclear radiation sensing system in accordance with the present disclosure.Fig. 3B shows the first portion of the nuclear radiation sensing system including a sensor in accordance with the present disclosure.Fig. 4A shows the first and second portions of the nuclear radiation sensing system after having been assembled in accordance with the present disclosure.Fig. 4B shows a nuclear radiation sensing system in accordance with the present disclosure.Fig. 5A shows a spectrum of detected energies of alpha particles emitted by radioactive matter in accordance with the present disclosure.Fig. 5B shows a graph resulting from a numerical differentiation of the spectrum of Fig. 5A in accordance with the present disclosure.Fig. 6A shows a known nuclear decay chain of225Ac.Fig. 6B shows a known nuclear decay chain of227Ac.Fig. 7 shows simulated spectra for the known, fully equilibrated nuclear decay chains of225Ac and227Ac.69634790-1Fig. 8 shows another spectrum of detected energies of nuclear radiation emitted by radioactive matter in accordance with the present disclosure.Fig. 9A shows a histogram of the detection information of Fig. 5A in which the histogram is dominated by random, uncorrelated coincidences of alpha particles having an energy of about 5.4 MeV.Fig. 9B shows the same detection information as that shown in Fig. 9A, except that Fig. 9B includes the requirement that the difference in arrival times between the pairs of sequentially detected alpha particles must be within the range of 1 - 10 ms.Fig. 10A shows a spectrum of detected energies of beta particles emitted by radioactive matter in accordance with the present disclosure.Fig. 10B shows simulated spectra for the known, fully equilibrated nuclear decay chain of90Sr.Fig. 11 schematically depicts a nuclear radiation sensing system comprising a multilayer sensor according to the present disclosure.Fig. 12 shows a simplified level scheme showing the alpha decay of211Bi to the ground state of207TI and to an excited state at 351.1 KeV.Fig. 13 schematically depicts a sensor comprising a spatially segmented sensing area configured to detect nuclear radiation emitted from different of radioactive matter in accordance with the present disclosure.Fig. 14A shows a spectrum of detected energies of alpha particles emitted by radioactive matter comprising241Am in accordance with the present disclosure.Fig. 14B shows simulated spectra for the known decay of241Am.DETAILED DESCRIPTION[000124] Fig. 1A schematically depicts a first portion 100 of a nuclear radiation sensing system according to the present disclosure. The first portion 100 comprises a first recess 110 configured to receive a sensor (not shown) such that a sensing area of the sensor faces away from the first portion. The first recess 110 may comprise a first groove 120 configured to receive a first seal (not shown). The first groove 120 may, for example, be circular so as to receive a circular seal such as, for example, an O-ring (not shown). The first portion 100 comprises a first set of attachment points 130 configured to receive fastening elements (not shown) such as, for example, screws or bolts or the like. The first set of attachment points 130 may be configured to attach the first portion 100 to a second portion (not shown) of the nuclear radiation sensing system. The first portion comprises a first set of electrical connection points 14069634790-1configured to receive electrical connections (not shown) for the transmission of, for example, bias or power, signals, etc. The first set of electrical connection points 140 may be configured to allow electrical connection between one or more components of the nuclear radiation sensing system and one or more external systems such as, for example, a power supply, a digitizer, a controller, a processors, a readout, etc. The first portion 100 comprises sensor attachment points 112 configured to receive fastening elements (not shown) such as, for example, screws or bolts or the like. The sensor attachment points 112 may be configured to attach the sensor (not shown) to the first portion 100.[000125] Fig. 1B schematically depicts a second portion 150 of the nuclear radiation sensing system according to the present disclosure. The second portion 150 comprises a second recess 160 configured to receive the sensor (not shown) such that a sensing area of the sensor faces towards the second portion 150. When the first and second portions 100, 150 are attached to each other, the first recess 110 and the second recess 160 align with and oppose each other to house the sensor within the first and second portions 100, 150. The second recess 160 may comprise a second groove 170 configured to receive a second seal (not shown). The second groove 170 may, for example, be circular so as to receive a circular seal such as, for example, an O-ring (not shown). The second portion 150 comprises a second set of attachment points 180 configured to receive fastening elements (not shown) such as, for example, screws or bolts or the like. The second set of attachment points 180 may be configured to align with the first set of attachment points 130 such that fastening elements may be received through the aligned attachment points 130, 180 to thereby attach the first portion 100 to the second portion 150. The second portion 150 comprises a second set of electrical connection points 190 configured to receive electrical connections (not shown) for the transmission of, for example, bias or power, signals, etc. The second set of electrical connection points 190 may be configured to allow electrical connection between one or more components of the nuclear radiation sensing system and one or more external systems such as, for example, a power supply, a digitizer, a controller, a processors, a readout, etc. The first and second portions 100, 150 may be formed of, for example, PTFE. The PTFE may be machined to form the features of the first and second portions 100, 150.[000126] The second portion 150 comprises a receptacle 200. The receptacle 200 is configured to receive radioactive matter (not shown). In the example of Fig. 1 B, the receptacle 200 comprises a channel configured to receive a radioactive fluid. The69634790-1channel 200 may be a microfluidic channel that forms part of a microfluidic system (not shown). The channel 200 comprises an inlet 210 and an outlet 220. The inlet 210 is configured to receive a radioactive fluid supplied through an entrance 230 and the outlet 220 is configured to provide radioactive fluid to an exit (not shown). The entrance 230 and the exit may comprise a screw thread configured to receive tubing having a screw head connector (not shown). The tubing may be configured to provide the radioactive fluid from a source such as a vial (not shown).[000127] The first and second portions 100, 150 may be formed by performing lithography on a material that forms part of the receptacle 200. Alternatively or additionally, the first and second portions 100, 150 may be formed by performing additive manufacturing (e.g. 3D printing). It will be appreciated that the receptacle 200 may be configured to hold solid radioactive matter. That is, the inlet, outlet, entrance and exit may not be present or may not be utilised if the radioactive matter under measurement is a solid rather than a fluid.[000128] Fig. 2A schematically depicts the second portion 150 of the nuclear radiation sensing system in accordance with the present disclosure. A width 240 and length 250 of the channel 200 is shown in Fig. 2A. The width 240 of the channel 200 may be about 100 pm or more. The width 240 of the channel 200 may be about 1mm or more. The width 240 of the channel 200 may be about 50mm or less. The width 240 of the channel 200 may be about 1mm or less. The length 250 of the channel 200 may be about 1 mm or more. The length 250 of the channel 200 may be about 7mm or more. The length 250 of the channel 200 may be about 50mm or less. The length 250 of the channel 200 may be about 10mm or less.[000129] Fig. 2B schematically depicts two cross-sectional views of the second portion 150 of the nuclear radiation sensing system in accordance with the present disclosure. The view on the left side of Fig. 2B shows a cross-section along the width 240 of the channel 200 and the view on the right side of Fig. 2B shows a cross-section along the length 250 of the channel 200. A depth 260 of the channel is shown in Fig. 2B. The depth 260 of the channel 200 may be about 10pm or more. The depth 260 of the channel 200 may be about 10mm or less. The depth 260 of the channel 200 may be about 200pm or less. The depth 260 of the channel 200 may be about 100pm or less. The depth 260 of the channel 200 may be, for example, about 0.1mm. Different types of nuclear radiation experience different stopping. Where the depth 260 of the channel 200 is about 200pm or more, a detection performance for alpha particles may be substantially equivalent to that of a nuclear radiation sensing system having a69634790-1receptacle depth of about 200pm. However, for example, 2 MeV beta particles in water have a range of about 10mm. The depth 260 of the channel 200 may be selected in at least partial dependence upon a type or types of nuclear radiation that are to be detected. Inlet and outlet passages 270, 280 are shown in Fig. 2B. The inlet passage 270 is configured to receive radioactive fluid from the entrance 230 and direct the radioactive fluid to the channel 200. The outlet passage 280 is configured to receive the radioactive fluid from the channel 200 and direct the radioactive fluid to the exit.[000130] Fig. 3A shows a partly assembled nuclear radiation sensing system in accordance with the present disclosure. The first portion 100 is shown on the left side of Fig. 3A and the second portion 150 is show on the right side of Fig. 3A. O-ring seals 280 have been inserted into the first and second grooves of the first and second portions 100, 150. The O-ring seals 280 may comprise an elastomer such as, for example, FFKM. Fastening elements 290 have been inserted into the second set of attachment points of the second portion 150. Fig. 3B shows the first portion 100 of the nuclear radiation sensing system including a sensor 300 in accordance with the present disclosure. Fastening elements 310 have been inserted into the sensor attachment points of the first portion 100 to secure the sensor 300 to the first portion 100. The sensor 300 is configured to detect nuclear radiation emitted by radioactive matter held by the receptacle (e.g. a radioactive fluid in the channel that opposes the sensor 300 after assembly of the first and second portions 100, 150). At least part of the sensor 300 may form at least part of the receptacle 200. That is, at least part of the sensor 300 may provide the dual functions of receiving the radioactive matter and detecting radiation emitted by the radioactive matter.[000131] The sensor 300 and the receptacle 200 may be arranged such that the radioactive matter is in contact (e.g. continuous contact) with the sensor 300 during use of the nuclear radiation sensing system. The sensor 300 may comprise a photodiode. The photodiode may comprise silicon. The sensor 300 may comprise a passivation layer configured to protect the sensor 300 from chemically hazardous liquids such as acids. The passivation layer may comprise PTFE. Alternatively, the passivation layer may comprise other materials such as, for example, other plastic-based materials (e.g. polyimide), corrosion resistant metals (such as gold), or corrosion resistant oxides or nitrides (such as, for example, Ta2O5, SiO2, SiON:H, a-SiN:H, AI2O3, or ZnO). Alternatively, the sensor 300 may be uncoated. The sensor 300 may be configured to directly detect nuclear radiation emitted by radioactive matter. It will be appreciated69634790-1that direct detection of radiation indicates that the sensor interacts with the radiation itself rather than interacting with a product of an interaction between the radiation and some other entity. For example, detecting light emitted by a scintillator in response to an interaction with the radiation is an example of indirect detection of the radiation, and cannot be considered to be direct detection of the radiation. This advantageously avoids one or more problems associated with indirect detection methods, such as scintillation. For example, the radioactive matter does not need to be mixed with a liquid that scintillates. As such, the to-be-measured radioactive matter is not affected by the detection.[000132] Fig. 4A shows the first and second portions 100, 150 after having been assembled in accordance with the present disclosure. The first and second portions 100, 150 together form a sensing unit 320 of the nuclear radiation sensing system. Fastening elements 290 have been inserted through the first and second sets of attachment points to secure the first and second portions 100, 150 together. The first and second portions 100, 150 are fixed together such that the O-ring seals (not visible) press the sensor (not visible) against the channel (not visible). That is, the sensor is in contact with radioactive matter present in the channel during use. The nuclear radiation sensing system may be arranged such that there is no gap between the sensor and the radioactive matter in the receptacle during use.[000133] Fig. 4B shows a nuclear radiation sensing system 330 in accordance with the present disclosure. The sensing unit 320 is mounted to a housing 340. The housing 340 may be configured to suppress external light and electronic noise from influencing the sensor. A portion of the housing 340 is not present such that an internal space of the housing 340 is visible in Fig. 4B. Tubing 350 having screw head connectors 360 is connected to the entrance and exit of the sensing unit 320. The tubing 350 is fluidly coupled to a source of radioactive fluid such as, for example a vial (not shown). In the example of Fig. 4B, a syringe 370 is used to draw radioactive fluid from the vial via suction, through the tubing 350 and into the sensing unit 320. The radioactive fluid travels through the entrance and into the channel (not visible), and the sensor (not visible) detects nuclear radiation emitted by the radioactive fluid in the channel. The radioactive fluid then exits the sensing unit 320 and travels through tubing 350 into the syringe 370. Once radioactive fluid is in the channel, the sensing unit 320 may be disconnected from the tubing 350 and sealed at the entrance and exit. It will be appreciated that the arrangement of Fig. 4B is merely an example arrangement, and that other arrangements may be used. For example, the nuclear69634790-1radiation sensing system 330 may be integrated into a chemical processing stream, such as for quality control of medical radionuclides for the pharmaceutical industry. The chemical processing stream may involve either manual or automated filling of the channel whilst the sensor detects nuclear radiation emitted from the radioactive fluid at the channel.[000134] The nuclear radiation sensing system 330 comprises electronics 380 configured to receive detection information from the sensor and provide the detection information to a processor 390 via electronic outputs 400. The electronics 380 may connect to the sensor via electrical connections provided through the electrical connection points. The electronics 380 may form part of the processor 390. The nuclear radiation sensing system 330 may comprise a power supply 410 configured to provide power to the sensor (not visible) and / or the electronics 380. Alternatively, the nuclear radiation sensing system may receive power from an external source. The processor 390 is configured to compare detection information gathered by the sensor to a signature decay characteristic of a known nuclear decay to determine a characteristic of the radioactive matter. The following passages discuss various methods of determining characteristics of the radioactive matter, any (including combinations) of which the processor 390 may be configured to perform.[000135] Fig. 5A shows a spectrum of detected energies of alpha particles emitted by radioactive matter in accordance with the present disclosure. The spectrum may be referred to as a detected energy spectrum. The detected energy spectrum may be determined at least partially based on detection information (e.g. gathered by the sensor of the nuclear radiation sensing system). The sensor may be connected to a charge sensitive preamplifier configured to integrate the electric current produced when nuclear radiation (e.g. a charged particle) deposits energy within the sensor, thereby producing a voltage pulse that is proportional to the energy deposited in the sensor by the nuclear radiation. The amplitude of this voltage pulse may be measured using, for example, a digitizer or multi-channel analyser to produce a pulse height spectrum. The shape of the spectrum is characteristic of both the properties of the radioactive source (e.g. energies and intensities of the various radioactive decays within a decay chain) and the path that the nuclear radiation has taken e.g. due to energy loss in the fluid before reaching the sensor. The spectrum of Fig. 5A was produced by the nuclear radiation sensing system of Fig. 4B when radioactive fluid comprising Actinium-225 (225Ac) was provided to the channel of the sensing unit. The spectrum of Fig. 5A was obtained by detecting nuclear radiation emitted from a69634790-1radioactive fluid comprising 0.6 pL of 9.6 Bq / pL concentration225Ac over a period of 15 hours.[000136] Fig. 6A shows a known nuclear decay chain of225Ac. As shown in Fig. 6A,225Ac decays via a series of known alpha and beta decays. Fig. 6A shows a variety of known signature decay characteristics associated with the known decay of225Ac. The signature decay characteristics may comprise signature decay energy information and / or signature decay temporal information. For example, Fig. 6A includes the known signature half-lives of the various radionuclides present within the known decay chain of225Ac, the method (and intensity, where applicable) of decay (i.e. alpha or beta decay), and, in the case of alpha decays, the known signature decay energy of the alpha radiation emitted upon decay. Four of the signature alpha decay energies of the225Ac decay chain (i.e. the 5.8MeV, 6.4MeV, 7.1Mev and 8.4MeV from the decay of225Ac,221Fr,217At and213Po respectively) are evident as corresponding decay features 421 , 422, 423, 424 (which may be referred to as steps or edges) of the detected energy spectrum of Fig. 5A. In the example of Fig. 5A, the energies associated with the steps 421-424 in the detected energy spectrum correspond to the four signature alpha particle decay energies mentioned above. The steps 421-424 may correspond to decays that take place close to the sensor. To the left of each step 421-424 there is a substantially continuous, decreasing distribution of energies, corresponding to decays which take place at different depths within the receptacle of the nuclear radiation sensing system (i.e. different distances from the sensor), resulting in various amounts of energy loss before the alpha particles reach the sensor. By comparing the detection information (such as, for example, comparing the signature decay energy information of the corresponding decay feature steps 421-424) gathered by the sensor to a signature decay characteristic of the known nuclear decay chain (e.g. the signature decay energy information such as the abovementioned four known signature alpha decay energies of the225Ac decay chain), a characteristic of the radioactive matter present in the receptacle (such as the presence of one or more radionuclides225Ac,221Fr,217At and213Po) may be determined. For example, if the energies of the corresponding steps 421-424 substantially match the energies of the signature alpha decays, then it may be determined that225Ac,221Fr,217At and213Po are present in the radioactive matter.[000137] Fig. 6B shows a known nuclear decay chain of Actinium-227 (227Ac). The decay chain of Fig. 6B is a simplified decay chain of227Ac, with only the primary decay branches shown. As shown in Fig. 6B,227Ac decays via a series of alpha and69634790-1beta decays. Like Fig. 6A, Fig. 6B includes signature decay characteristics (including signature decay energy information and signature decay temporal information) such as, for example, the known half-lives of the various radionuclides present within the decay chain of227Ac, the method (and intensity, where applicable) of decay (i.e. alpha or beta decay), and, in the case of alpha decays, the signature decay energy of the alpha radiation emitted upon decay. As can be seen upon comparison between Fig. 6A and Fig. 6B, signature decay characteristics (e.g. signature decay energy information and signature decay temporal information) differ between the known decay chains of225Ac and227Ac, which offers the ability to identify and / or distinguish the presence of decay chains in a radioactive sample measured by the nuclear radiation sensing system of the present disclosure. That is, detection information gathered according to the method and system of the present disclosure may be compared to one or more signature decay characteristics of one or more known nuclear decays to determine a characteristic of the radioactive matter from which the detection information is gathered.[000138] Fig. 7 shows simulated spectra for the known, fully equilibrated nuclear decay chains of225Ac 500, 510 and227Ac 520, 530. The top spectra are the results of a simulation of a microfluidic nuclear radiation sensing system (such as that shown in Fig. 4B) having a channel depth of about 20pm. The bottom spectra are the results of a simulation of a microfluidic nuclear radiation sensing system (such as that shown in Fig. 4B) having a channel depth of about 100pm. The simulations are based on knowledge of the nuclear decays of225Ac 500, 510 and227Ac 520, 530. The spectra of Fig. 7 may be referred to as signature energy spectra. All simulations assumed that the sensor did not include a passivation layer. However, the presence of a passivation layer may also be simulated. The simulations may involve the use of Monte Carlo methods. The simulations of Fig. 7 were obtained through the use of Geant4. Other simulation software may be used. As can be seen, the shape of the spectrum depends on both the radionuclides present within the channel, and a depth of the channel. The depth of the channel may be adjusted to provide clearer detection of the signature decay chain characteristics. In general, a channel having a shallower depth may allow a greater resolution when detected the energies of nuclear radiation emitted by radioactive matter located in the channel. As can be seen upon comparison between the spectra of Fig. 7, signature decay characteristics (e.g. signature decay energies) of the known decay chains of225Ac and227Ac are visible in the spectra, which offers the ability to identify and distinguish the presence of decay chains in a radioactive sample69634790-1measured by the nuclear radiation sensing system of the present disclosure. By comparing detection information gathered by the sensor to signature decay characteristics of known nuclear decays, different decay chains and radionuclides may be identified and distinguished. For example, detection information gathered from an unknown radioactive sample within the nuclear radiation sensing system can be compared (e.g. numerically, or by inspection) to a library of known signature spectra (e.g. obtained either experimentally, or via simulation) in order to determine the identity of radionuclides present within the radioactive sample. This may involve matching the detected energy spectrum to a most similar signature energy spectrum of the plurality of signature energy spectra.[000139] Characteristics of the radioactive matter other than an identity (i.e. a presence or absence) of a radionuclide or decay chain may be determined. For example, the method and system of the present disclosure may be used to determine a radioactivity of the radioactive matter. How the radioactivity is determined may depend upon a degree of equilibration of the relevant nuclear decay chain that is present in the radioactive matter. When a parent radionuclide is synthesised, the parent radionuclide immediately begins to decay in accordance with signature temporal decay information (e.g. a half-life), populating the parent radionuclide’s daughter radionuclides. The daughter radionuclides will also begin decaying with their respective signature halflives, resulting in competing processes of generation and decay of the daughter radionuclides. As a result of this competition, the relative intensities of decays from different radionuclides in a nuclear decay chain will evolve over time until an equilibrium state is reached in which the production and decay rates of each radionuclide are in balance (which may typically occur after several half-lives have elapsed).[000140] Once the equilibrium state has been reached, a radioactivity of the radioactive matter may be determined by obtaining a detected spectrum such as the one shown in Fig. 5A and integrating the total counts within the spectrum. A radioactivity of a head radionuclide of the known nuclear decay chain may be calculated by dividing the total counts within the spectrum by a number of signature decays in the spectrum. In the example of the225Ac nuclear decay chain, this may be the integral of the spectrum of Fig. 5A divided by four due to the presence of four signature decay stages 421-424 of the known nuclear decay chain in the detected energy spectrum. Such a measurement may be achieved using a much shorter acquisition time (e.g. about 5 minutes) compared with the example spectrum shown in69634790-1Fig. 5A (which was obtained over the course of 15 hours) and without having to resolve the signature alpha decay energies. An energy dependent correction to at least partially account for an efficiency of the nuclear radiation sensing system or method may be used. For example, energy dependent efficiency corrections for the nuclear radiation sensing system and method may be based on Monte Carlo simulations, such as those shown in Fig 7, or may be analytically calculated based on knowledge of one or more of a geometry of the nuclear radiation sensing system, a stopping power of the radiation within the nuclear radiation sensing system (and liquid in the example of radioactive fluids), and / or a low energy sensor threshold (such as that shown in Fig. 5A at ADC channel 100).[000141] Before the equilibrium state is reached it may not be possible to determine a radioactivity of a radionuclide at the head of a decay chain solely by calculating the gross number of counts within the spectrum without also having knowledge of the age of the radioactive matter (i.e. being able to correct for the evolution of the radionuclide abundances within the decay chain). This is because the relative intensities of the different decays are changing as a function of time before the equilibrium state is reached. In such a situation (i.e. before a state of equilibrium is reached), evaluation of the characteristic decay features of the detected spectrum (e.g. heights of the steps 421-424) which correspond to the signature decay characteristics (e.g. the corresponding signature alpha particle decay energies) may be used to determine relative radioactivites of the radionuclides associated with the signature decay energies of the known nuclear decay. First and second regions of the detected spectrum may be selected at least partially based on the signature decay energy of the known nuclear decay, and a number of detection counts associated with the first and / or second regions may be determined. For example, one or more spectral fitting techniques may be used to determine the heights of the steps 421-424 (which may correspond to the number of detection counts associated with the steps) of the detected spectrum. The spectral fitting techniques may comprise one or more of, for example, chi-squared fitting, log-likelihood fitting, machine-learned fitting routines, etc. The number of detection counts associated with the first and second regions may then be compared to determine the characteristic of the radioactive matter.[000142] With reference to Fig. 5A and Fig. 6A, in the example of the225Ac decay chain, a radioactivity of225Ac may be determined from a ratio of a height of the 5.8 MeV signature alpha decay energy step 421 (which corresponds to the decay energy in the alpha decay of225Ac to221Fr), to the total height of all steps 421-424, multiplied by an69634790-1integration of the spectrum. In the example of Fig. 5A, the radioactivity of the225Ac radionuclide that forms part of the radioactive matter may be expressed as follows:whereare the heights of the steps 421-424 in the spectrum that correspond to the four identified signature alpha particle decay energies, Ntotis a total number of detection counts of the spectrum and t is a duration for which detection information is gathered.[000143] An energy dependent correction to at least partially account for an efficiency of the nuclear radiation sensing system or method may be applied to the heights H1, H2, H3,as discussed above. For example, this equation may be rewrittenH H H H by replacing each heightwith height and efficiency termswhere ei, 62, 63, 64 are efficiency correction terms at the signature decay energies of the steps 421-424 determined by, for example, Monte Carlo simulation. The same approach may be used to determine the radioactivity of other radionuclides of interest that have been identified in the radioactive matter and the associated spectrum.[000144] An alternative method of determining characteristics of the radioactive matter from the obtained spectrum involves performing a numerical differentiation on the spectrum. Fig. 5B shows a graph resulting from a numerical differentiation of the spectrum of Fig. 5A in accordance with the present disclosure. The y-axis of Fig. 5B is -dN / dE, where N is the number of detection counts (as in Fig. 5A) and E is the energy (i.e. Fig. 5B shows an additive inverse of the gradient of Fig. 5A). The numerical differentiation has converted the characteristic steps 421-424 of Fig. 5A into characteristic peaks 431-434 of Fig. 5B. The relative intensities of these peaks 431- 434 may be determined by, for example, integration or one or more peak fitting techniques (e.g., chi-squared minimisation in a, for example, Gaussian peak fitting on a, for example, linear background) to determine the relative areas of the peaks 431- 434. The extent of a peak may be determined by, for example, choosing points either side of the maximum within a selected percentage (such as, for example, 10%) of the peak maximum. Other approaches may be used and a user may exercise their judgment. The radioactivity of a given radionuclide associated with the characteristic peaks 431-434 may be calculated in a similar way as discussed above. In the example of Fig. 5B, the radioactivity of the225Ac radionuclide that forms part of the radioactive matter may be expressed as follows:69634790-1, Ni Ntot225Ac(Nt+ N2+ N3+ N4)Xt where N1,N2,N3,N4. correspond to the areas of the peaks 431-434. As before, the same approach can be taken, through identification of the signature alpha decay energies for the alpha decay energy of the radionuclide, to generalise this concept for identifying other radionuclides of interest such as, for example,227Ac (see Fig. 6B and Fig. 7), for which the signature alpha particle decay energies may be one or more of about 6.0 MeV, 5.7 MeV, 6.8 MeV, 7.4 MeV and 6.6 MeV (corresponding to the decays of227Th,223Ra,219Rn,215Po and211Bi respectively).[000145] The relative radioactivites of different radionuclides present in a decay chain will evolve according to the Bateman equation until the equilibrium state is reached. For example, with reference to the known decay chain of225Ac shown in Fig. 6A,213Bi has a half-life of about 46.6 minutes, whereas221Fr,217At and213Po each have a half-life of 4.8 minutes, 32.3 ms and 3.7 ps respectively. As such, the decays of221Fr,217At and213Po will reach equilibration relatively quickly compared to the213Bi decay. On the other hand,225Ac has a half-life of about 9.9 days, and will therefore decay relatively slowly compared to the213Bi decay. In the approximation that equilibration of the225Ac decay is relatively slow, and that equilibration of the221Fr,217At, and213Po decays in the225Ac decay chain are relatively fast (i.e. relatively well- equilibrated) compared to the decay of213Bi, over time t the radioactivites (A) of225Ac and213Po may be determined as follows:A225Ac(t) = A225AC * N225Ac(t) and,A213Po(t) = 213Bi * N213Bi(t), where the decay rates, A = ti / 2 / ln(2) are found from the associated radionuclide halflives (ti / 2), and the number of213Bi radionuclides in the radioactive matter, N2i3Bi(t), evolves as follows:N213Bi(t) = A225AC / (A225Ac+A213Bi) * N225Ac(t) * (©Xp(-A225Ac * t) - 6Xp(-A213Bi * t))[000146] Identification of the presence or absence of the equilibration state may be determined through spectral comparison of the combined or individual signature decay characteristics of the nuclear decay chain. The identification of an equilibration state in the decay chain of Fig. 6A may, for example, be determined through spectral comparison of the combined or individual characteristic alpha decay signatures of 5.8 MeV, 6.3 MeV, and 7.1 MeV decay energies (from the225Ac,221Fr, and217At decays, respectively) in comparison to the 8.4 MeV signature alpha decay energy from the213Po decay. A degree of nuclear decay equilibration (i.e. whether or not equilibration has been reached and, if not, how close to equilibration a part of the decay chain is)69634790-1may be determined by comparing the radioactivity of a radionuclide in the known nuclear decay chain to the total radioactivity detected from the radioactive matter. That is, a radioactivity contribution associated with a first region of the detected spectrum (selected at least partially based on the signature decay characteristic of the corresponding radionuclide) may be determined relative to a radioactivity of a second region (e.g. the entire spectrum) of the spectrum. The radioactivity contribution associated with the first region may be compared to an expected radioactivity contribution, which is determined at least partially based on the signature decay characteristic. Considering the example of the225Ac decay chain, this may be determined by comparing the radioactivity associated with the 8.4 MeV alpha decay from213Po (which is the last decay in the chain) to the radioactivity associated with all other decays in the decay chain. When in the equilibrium state, it is expected that the numbers of alpha decays from each of the radionuclides of225Ac,221Fr,217At and213Po (and thus the number of 8.4 MeV alpha particles detected) should be about a quarter of the total number of alpha particles detected (because only 2.14% of the decay of213Bi is alpha particles which may be considered to be negligible). As such, the expected radioactivity contribution in the equilibrium state would be a quarter of a total radioactivity. Any pre-equilibrium stage will yield less than this expected radioactivity contribution down to a minimum of zero. For a relatively well-resolved spectrum such as that of Fig 5A, the step-height methodology (or the peak area methodology) shown may be applied for any combination of steps 421-424 and, in particular, a comparison of the 8.4 MeV step 424 to any of the lower energy steps 421-423. The precision of the approximation that the221Fr decay is well-equilibrated may be evaluated using the corresponding formula for221Fr, i.e. s221Fr = H2 / H1 , where H1 and H2 are the heights of the corresponding steps 421 and 422 respectively.[000147] It will be appreciated that even with less well resolved spectra (i.e. when the characteristic features such as the steps 421-424 of Fig. 5A or the peaks 431-434 of Fig. 5B are less well defined) a similar approach (i.e. comparing selected spectral regions by, for example, determining a ratio of said regions) may be used to determine a characteristic of the radioactive matter. Fig. 8 shows another spectrum of detected energies of nuclear radiation emitted by radioactive matter in accordance with the present disclosure. The detected spectrum of Fig. 8 was obtained using fluid radioactive matter comprising a volume of about 0.06 pL of 0.8 Bq / pL225Ac solution. Like Fig. 5A, the spectrum of Fig. 8 was obtained experimentally using a nuclear radiation sensing system similar to that of Fig. 4B to detect the spectrum of radioactive69634790-1matter comprising225Ac. However, unlike Fig. 5A, the nuclear radiation sensing system used to obtain the spectrum of Fig. 8 comprises a PTFE passivation layer on the sensor (rather than no passivation layer being present) and detection only occurred for a duration of one hour (rather than 15 hours). The passivation layer increases the stopping of nuclear radiation propagating in the nuclear radiation sensing system, and the reduced detection duration reduces the measurement data available, both of which contribute to a reduction in the resolution of the spectrum of Fig. 8 relative to Fig. 5A. As can be seen upon comparison, the steps 421-424 of the spectrum of Fig. 5A are less well resolved in the spectrum of Fig. 8. However, through knowledge of a signature decay characteristic of a known nuclear decay that has been identified in the radioactive matter, a similar approach of comparing selected regions of the spectrum of Fig. 8 may be used to determine a characteristic of the radioactive matter. For example, the relative radioactivity of different radionuclides, and hence the degree of equilibration, may be determined by comparing suitable integration regions of the spectrum which are identified based on knowledge of the signature decay energies of the radionuclides present.[000148] In the example of the decay chain of225Ac shown in Fig. 6A, a spectral region can be chosen above the 7.1 MeV step which corresponds to decays from213Po only (i.e. the 8.4 MeV signature decay energy alpha particles). By integrating the number of counts in the spectrum below and above this region, a measure of the relative radioactivity of213Po to the total radioactivity of the radioactive matter may be obtained. As such, the resolution shown in the spectrum of Fig. 5A is not necessary if suitable integration spectral regions are selected through identification of a radionuclide and knowledge of its signature decay characteristics from its associated decay chain.[000149] It may also be desirable to account for a contribution to stopping power of the nuclear radiation sensing system, e.g. through statistical characterisation of the nuclear radiation sensing system and / or through simulation of the specific dimensions and properties (e.g. materials and associated stopping powers) of the nuclear radiation sensing system using, for example, Geant4. For example, with reference to Fig. 5A the height of each step 421-424 may be corrected to account for the different stopping powers (i.e. rates at which a material absorbs the kinetic energy of nuclear radiation) of the different energy alpha particles in the radioactive matter. That is, a method according to the present disclosure may comprise determining a stopping power characteristic associated with one or more regions of the detected spectrum. An accuracy of a radioactivity calculated based on said regions may then be improved by69634790-1accounting for the stopping power characteristics associated with the regions. In general, lower energy alpha particles may lose energy more rapidly than higher energy alpha particles. This may result in a lower step height 421-424 in the spectrum, for the same total number of decays, with the step height 421-424 being proportional to an inverse of the stopping power.[000150] The degree of equilibration present in the radioactive matter may, in the case of a relatively low resolution spectrum such as the one shown in Fig. 8, be determined at least partially based on the observed yields (i.e. number of detection counts) above a selected energy threshold 550. For example, in the case of225Ac, an energy threshold 550 of above 7.1 MeV is selected in Fig. 8. To ensure that the energy threshold is above the sensor response to a selected characteristic decay energy, a slightly greater energy threshold 550 may be selected. In the example of Fig. 8, an energy threshold 550 of 7.3 MeV is used to define first and second spectral regions. The first spectral region corresponds to the 8.4 MeV decay from213Po only (right of the dashed line 550) and the second spectral region corresponds to contributions from all other alpha particle decays in the decay chain of225Ac (left of the dashed line 550). The spectral region above the energy threshold 550 may be further limited by an upper bound above the 8.4MeV alpha decay energy, at 8.5MeV for example (Y7.3<E<8.S) . An integration of this region may then be compared to the yield across the 0.9 MeV region between 6.4 MeV and 7.3 MeV (Ye.4<E<7.3). The213Po radioactivity per micrometre of the radioactive matter in the receptacle of the nuclear radiation sensing system may be determined as follows:A213PO = Y7.3<E<8.5*S7.3<E<8.5 / W7.3<E<8.5, where W7.3<E<8.5 is the width of the integration region (i.e. 1.2 MeV) and S7.3<E<8.5 is the average alpha particle stopping power across the integration region (which may be determined through experimentation and / or simulation using, for example, Geant4). The average stopping power of a spectral region may be determined, for example, using the Bethe-Block formula and / or or extracted from known tables of stopping powers. The217At radioactivity may similarly be determined based on the yield between 6.4 MeV and 7.3 MeV (Ye.4<E<7.3). A yield of213Po may be accounted for in this region as follows:A radioactivity of217At per micrometre of radioactive matter perpendicular to the sensor (e.g. corresponding to the depth of the channel) may be found as follows:A217At = (Y7.3<E<8.5-Y’213PO) * S6.4<E<7.3 / W6.4<E<7.3.69634790-1The degree of equilibration in the213Bi equilibration point may be determined experimentally as £2i3Bi = A213P0 1 A2™, where a degree of equilibration £2i3Bi of zero corresponds to no equilibration past the213Bi decay point in the decay chain of Fig. 6A and a degree of equilibration £2i3Bi of one corresponds to a fully equilibrated decay past the213Bi decay point.[000151] As another example, consider the decay chain of227Ac shown in Fig. 6B. The half-lives of all radionuclides after223Ra are relatively short and so it may be assumed that they will be equilibrated with their parent radionuclides within a relatively short time. As a result, the radioactivites of any or all of these radionuclides may be used to determine the degree of equilibration of223Ra, given an appropriate choice of spectral regions for comparison. For example, by integrating the associated spectrum above an energy threshold of about 6.1 MeV, the number of counts is only dependent on the 6.6 MeV, 6.8 MeV and 7.4 MeV alpha decays from211Bi,219Rn and215Po respectively. As such, the degree of equilibration s of223Ra may be calculated as follows:where A>e.i is the radioactivity over the selected threshold energy of 6.1 MeV, Atot is the total radioactivity of the spectrum, wtot is the width of the spectrum, w>e.i is the width of the spectrum above the selected threshold energy of 6.1 MeV and the factor of 5 / 3 accounts for the three alpha decays present in the >6.1 MeV integration region, out of a total of five alpha decays in the227Ac decay chain. This equation may be generalised to give the following equation for determining a degree of equilibration:NTwtotntote = - x - x -NtotWTnT where NT is the number of detection counts over a selected energy threshold, Ntot is the total number of detection counts in the spectrum, WT is that width of the spectral region above the energy threshold T, wtot is the total width of the spectrum, nTis the number of alpha decay steps above the energy threshold T, ntot is the total number of alpha decay steps present in the spectrum.[000152] For a nuclear radiation sensing system in which a response function is known to blur otherwise well-resolved characteristic decay features (e.g. the relatively sharp steps shown in Fig. 5A) and / or for known nuclear decays in which at least some of the signature decay energy information (e.g. similar alpha decay energy steps) are similar and therefore more difficult to distinguish and / or for cases where geometric nonlinearities become significant in the sensor response of the nuclear radiation69634790-1sensing system, the degree of equilibration may be determined through comparison of the observed yields (i.e. numbers of detection counts) above and below the energy thresholds to a simulation (e.g. using a Monte Carlo method, such as Geant4) of the alpha particle response of the nuclear radiation sensing system (such as the simulations shown in Fig. 7). That is, the method according to the present disclosure may comprise comparing the numbers of detection counts in the first and second regions to a simulation of the known nuclear decay. The nuclear radiation sensing system response demonstrated in the225Ac spectrum observed in Fig. 8 is an example of this, where the response of 8.4 MeV alpha particles observed above the chosen energy threshold 550 of 7.3 MeV (i.e. only 8.4 MeV alpha particles) is compared to the observed alpha particles below this threshold.[000153] A signature decay characteristic of the known decay chain other than a signature decay energy or signature spectrum shape may be used to determine the characteristic of the radioactive matter. For example, the signature decay characteristic may comprise signature decay temporal information such as, for example, a temporal sequence of decays in the known decay chain and / or characteristic half-lives of the radionuclides present in the known decay chain.Temporal information may be used as an alternative to, or in combination with energy information, determined from the detection information gathered by the sensor of the nuclear radiation sensing system. That is, the detected temporal information may be compared to signature decay temporal information from the known decay to determine a characteristic of the radioactive matter. For example, a half-life of a radionuclide may be determined by measuring a change in a radioactivity (i.e. detection counts per second) of the radionuclide over time. A plot of radioactivity A against time 0-t may produce an exponential decay which may be fitted with a function of the form: A(t)=A(0)exp(-ln(2)t / ti / 2) which may be used to determine the half-life ti / 2 of the radionuclide. This technique may involve detecting radiation emitted by the radioactive matter for a significant fraction of one half-life (but ideally for several half-lives) and may assume only a single decaying radionuclide is present and thereby contributed to the gathered detection information.[000154] Using a combination of temporal information and energy information may vastly improve an accuracy of radionuclide identification and / or discrimination. This is particularly useful in cases where the radioactive matter comprises two different nuclear decay chains having at least some similar signature decay characteristics. For69634790-1example, the decay chain of225Ac (as shown in Fig. 6A) and the decay chain of227Ac (as shown in Fig. 6B) comprise some similar signature decay energies. For example, the 5.8 MeV decay energy associated with the decay of225Ac may be considered similar to the 6.0 MeV decay energy associated with the decay of227Th in the decay chain of227Ac. However, the two decay chains comprise different temporal signatures. For example, the half-life of225Ac is 9.9 days whereas the half-life of227Th is 18.7 days. Alternatively or additionally, a temporal sequence of decay events (e.g. parent and daughter radionuclide decay energy signatures) differs between the two decay chains, and may therefore be used to assist in identifying and / or distinguishing the decay chains. For example, the decay of225Ac is followed by the decay of221Fr which has signature decay energy of 6.4 MeV, whereas the decay of227Th is followed by the decay of223Ra which has a signature decay energy of 5.7 MeV. By comparing the detected temporal information and the signature decay temporal information, a temporal sequence of decay events may be determined, which may in turn allow for a radionuclide and / or decay chain present in the radioactive matter to be identified and / or distinguished. As such, by also using temporal decay information, two decay chains may be distinguished more easily and / or with lower energy resolution requirements than using energy decay information alone.[000155] Figs. 9A and 9B show two histograms representing the energies of pairs of sequentially detected alpha particles (energy 1 , energy 2) in accordance with the present disclosure. Fig. 9A shows a histogram of the detection information of Fig. 5A in which the histogram is dominated by random, uncorrelated coincidences of alpha particles having an energy of about 5.4 MeV. Fig. 9B shows the same detection information as that shown in Fig. 9A, except that Fig. 9B includes the requirement that the difference in arrival times between the pairs of sequentially detected alpha particles must be within the range of 1 - 10 ms. That is, the detection information of Fig. 9B has been temporally segmented at least partially based on signature decay temporal information, whereas the detection information of Fig. 9A has not been temporally segmented.[000156] The coincidence spectra shown in Figs. 9A and 9B demonstrate the enhanced identification and / or discrimination capabilities of combined temporal and energy information. In the example of Figs. 9A and 9B, enhanced identification of the decay chain of225Ac and discrimination compared to the decay chain of227Ac is based on their two millisecond decay coincidences (i.e. the approximately 32ms half-life associated with the decay of217At in the225Ac decay chain and the approximately 2ms69634790-1half-life associated with the decay of215Po in the decay chain of227Ac). The decay of221Fr to217At has a signature alpha decay energy of 6.4 MeV, and the subsequent decay of217At to213Bi has a signature alpha decay energy of 7.1 MeV. The decay of219Rn to215Po has a signature alpha decay energy of 6.8 MeV, and the subsequent decay of215Po to211Pb has a signature alpha decay energy of 7.4 MeV (see Figs. 6A and 6B).[000157] In the example of Figs 9A and 9B, identification of the decay chain of225Ac is based on the221Fr alpha decay (half-life of 4.9min and energy of 6.4 MeV) followed by the217At alpha decay (half-life of 32ms and energy of 7.1 MeV). As shown in Fig. 9A, sequentially detected alpha particles are generally dominated by random coincidences at the detection rates observed. However, as shown in Fig. 9B, with gathered detection information gated on a temporal period (or coincidence time window) of 1-10 ms (which is lower than the half-life of217At), the detection of a sequence of a 6.4 MeV alpha particle followed by a 7.1 MeV alpha particle is evident. A duration of the temporal period of the temporal segmentation of the detection information may be selected at least partially based signature decay temporal information such as, for example, a half-life of the radionuclide of interest. For example, the duration of the temporal period may be chosen to be as close as possible to the half-life of the radionuclide of interest, whilst ensuring that the temporal period is substantially below the typical random coincidence rate of (in the present example) about 300ms. The typical random coincidence may correspond to an inverse of radioactivity. For example, a radioactivity of 3 Bq may produce a typical random coincidence rate of 1 / 3=0.33 seconds. The dotted lines provided on both Fig. 9A and Fig. 9B are at energies 6.4 MeV and 7.1 MeV, which indicate the maximum expected decay energies if the detected pair of alpha particles originate from the221Fr ->217At ->213Bi cascade within the225Ac decay chain. As can be seen in Fig. 9B, the temporal information reveals that the detection of 6.4 MeV alpha particles is followed by the detection of 7.1 MeV particles in this temporal period, thereby indicating the presence of the225Ac decay chain in the radioactive matter. The diagonal locus of Fig. 9B is due to pairs of detected alphas originating from deeper within the receptacle of the nuclear radiation sensing system (e.g. the channel), hence their energy losses are correlated.[000158] For discrimination with the decay chain of227Ac (e.g. in the case of radioactive matter comprising both225Ac and227Ac), first and second temporal periods may be selected for the two decays and their relative contributions in the two temporal periods. That is, a first temporal period is selected at least partially based on the69634790-1signature decay temporal information of a known nuclear decay (e.g. of225Ac), and a second temporal period is selected at least partially based on the signature decay temporal information of a different known nuclear decay (e.g. of227Ac). For example, to discriminate between the abovementioned 2ms and 32ms decays, first and second temporal periods may be selected as 0.1 ms - 2ms for the227Ac decay chain and 6ms - 20ms for the225Ac decay chain, decided at least partially based on their respective exponential decays. This ensures that each decay chain is suppressed by approximately an order of magnitude in the temporal period selected for the other decay chain. In general, the greater the difference between half-lives, the greater the degree of suppression that is achievable.[000159] Temporal periods may be selected such that: (a) the temporal periods under comparison are chosen to be independent of each other (e.g. to ensure that the spectra are statistically independent); (b) overlap as much as possible with the first half-life of the decay in question (e.g. to ensure as many true positives as possible); (c) overlap as little as possible with the other decay (e.g. to reduce the number of false positives as much as possible); and (d) reducing the number of random coincidences by staying well below the average time difference between random coincidences, i.e. the inverse of the total decay detection rate. In the present example, the 1 ,8ms decay in the227Ac decay chain is substantially faster than the 32ms decay in the225Ac decay chain. By choosing a first temporal period of 0.1ms-2ms, the first temporal period covers more than half of the227Ac chain coincidences (i.e. true positives), while covering only approximately 10% of the225Ac chain decays (i.e. false positives). The second temporal period from 6-20ms, on the other hand covers approximately 25% of the225Ac chain coincidences (i.e. true positives), while covering only approximately 10% of the227Ac decay chain coincidences (i.e. false positives). At the same time, for the rate observed in the present data (i.e. 3 / s), the temporal period of maximally 20ms is well below the average random coincidence time difference of 1 / (3 / s) = 333ms.[000160] Whilst the focus thus far has been on alpha particles, the nuclear radiation sensing system and method according to the present disclosure may be used to detect other types of nuclear radiation, such as beta particles, gamma rays and / or neutrons. Fig. 10A shows a spectrum of detected energies of beta particles emitted by radioactive matter in accordance with the present disclosure. The spectrum of Fig. 10A was produced by a nuclear radiation sensing system similar to that of Fig. 4B when radioactive fluid comprising90Sr (which decays via a pair of beta decays) was provided to a channel of a sensing unit having a depth of 100pm. A radionuclide decaying via69634790-1beta decay may emit a range of beta particle energies, rather than the single characteristic energies associated with alpha decays. Nevertheless, the energy spectra measured from different radionuclides still have signature shapes which differ from each other.[000161] By comparing the shape of a measured spectrum to the shape of a known spectrum (determined either by experimentation or simulation) a beta decay chain (and associated radionuclides) may be identified and distinguished in a manner similar to the identification of alpha decay chains (such as those discussed above in respect of Figs. 5A, 5B and 7. For example, Fig. 10B shows simulated spectra for the known, fully equilibrated nuclear decay chain of90Sr. The spectra are the results of simulations of a microfluidic nuclear radiation sensing system (such as that shown in Fig. 4B) having a channel depths of about 10pm, 100pm and 200pm. All simulations assumed that the sensor did not include a passivation layer. However, the presence of a passivation layer may also be simulated. The simulations may involve the use of Monte Carlo simulation methods. The simulations of Fig. 7 were obtained through the use of Geant4. Other simulation software may be used. As can be seen, the shape of the spectra depends on both the radionuclides present within the channel, and a depth of the channel. As can be seen upon comparison between the spectra of Fig. 10A and Fig. 10B, a signature spectral shape offers the ability to identify and distinguish the presence of beta decay chains in a radioactive sample measured by the nuclear radiation sensing system of the present disclosure. By comparing detection information gathered by the sensor to signature decay characteristics of known beta decay chains, different beta decay chains and beta emitting radionuclides may be identified and / or distinguished. For example, detection information gathered from an unknown radioactive sample within the nuclear radiation sensing system can be compared (e.g. numerically, or by inspection) to a library of known spectra (e.g. obtained either experimentally, or via simulation) in order to determine the identity of radionuclides present within the radioactive sample.[000162] In general, to determine a degree of similarity between two spectra, the shape of a (e.g. normalised) spectrum may for example be compared to a (e.g. normalised) simulated or measured spectrum, e.g. using a (e.g. bin-by-bin) chi-squared hypothesis test with weights as inverse combined errors of the measured and known spectra. This may involve utilising either a run-test or a Kolmogorov-Smirnov test for which the quantifying statistic for the test may be determined by Monte-Carlo69634790-1simulation of the specific spectral shape, or by applying any other quantitative spectralbased hypothesis testing.[000163] The present system and method may be used to distinguish between different types of nuclear radiation emitted by the radioactive matter. Signature decay characteristics (e.g. signature energy and / or temporal information) of the different types of radiation may be used to identify and / or distinguish different decay chains present in the radioactive matter. An example of this is the microsecond beta-alpha coincidence decay of213Bi and213Po in the decay chain of225Ac. With reference to Fig. 6A, when multiple decay chains including the225Ac decay chain are present in the radioactive matter, coincident identification of the spectral signature from the213Bi beta decay (having known decay chain signatures such as a range of beta decay energies up to a maximum of about 1 .42 MeV and a half-life of about 45min) followed by the213Po alpha decay (having a signature alpha decay energy of 8.4 MeV and a half-life of 3.7ps). That is, the signature decay characteristic may comprise a first signature decay characteristic associated with the first type of nuclear radiation, and a second signature decay characteristic associated with the second type of nuclear radiation. Because of the relatively short half-life of213Po, the coincidence sensitivity is feasible, even at extremely high decay rates, and offers several orders of magnitude suppression of random coincidences, even at detection rates of about 1 kHz. As discussed above, the detection rate may be low enough such that the time between random coincidence detections does not coincide with the timing window chosen to select the decay of interest. This may be estimated as 1 / rate.[000164] This sequence of decays may be detected using a nuclear radiation sensing system comprising a multilayer sensor, such as the one schematically depicted in Fig. 11. In the example of Fig. 11 , the nuclear radiation sensing system is a microfluidic system comprising inlet and outlet tubing 350 connected to a channel 200. The tubing 350 provides radioactive fluid (i.e. a “sample”) to the channel 200. The arrows of Fig. 11 indicate the direction of travel of the radioactive fluid. The sensor 300 comprises a first layer 610 and a second layer 620 that are arranged to form a stacked structure.[000165] The first layer 610 is configured to detect alpha radiation and the second layer 620 is configured to detect beta and / or gamma radiation. To detect different types of nuclear radiation, the first and second layers 610, 620 may comprise different materials and / or thicknesses. The first layer 610 may comprise, for example, a silicon- based sensor. The first layer 610 may have a thickness of about 50pm or more. The69634790-1first layer 610 may have a thickness of about 500pm or less. The second layer 620 may, for example, comprise a cadmium zinc telluride (CZT)-based sensor. The second layer 620 may have a thickness of about 1mm or more. The second layer 620 may have a thickness of about 10mm or less. An additional or alternative layer (not shown) may be configured to detect neutron radiation. For fast neutrons, such a layer may comprise a neutron sensitive organic scintillator such as, for example, stilbene. For thermal neutrons, such a layer may comprise a lithium containing inorganic scintillator such as, for example, CLLBC (Cs2LiLa(Br,CI)6:Ce). A layer configured to detect neutron radiation may have a thickness of, for example, about 50mm. The first and / or second layers 610, 620 (and / or a neutron detecting layer) may be configured to perform spectroscopic measurements (e.g. to produce detected spectra such as those shown in Fig. 5A and Fig. 10A). The sensor 300 of Fig. 11 may be referred to as a two-component alpha-beta / gamma sensor. It will be appreciated that a multilayer sensor is not limited to use with microfluidic nuclear radiation sensing systems and may be used with any form of radioactive matter. It will be appreciated that in other embodiments of the present disclosure, radioactive matter may be introduced using hardware other than the microfluidic system shown in Figs. 4B and 11. The radioactive matter may not be a radioactive fluid and may, for example, be a solid. The radioactive solid may be disposed adjacent to the sensor.[000166] As another example, the decay chain of227Ac may be identified at least partially based on a combination of alpha and gamma-ray detection, e.g. using the nuclear radiation sensing system of Fig. 11. For example, a signature decay characteristic in the227Ac decay chain is the211Bi alpha decay. Fig. 12 shows a simplified level scheme showing the alpha decay of211Bi (from the227Ac decay chain, see Fig. 6B) to the ground state of207TI and to an excited state at 351.1 KeV. This decay involves a 16% decay via a 6.3 MeV alpha-emission. In most cases (13% of total decays), this results in a near-immediate 351.1 KeV gamma-ray emission in coincidence with the 6.3 MeV alpha-particle. This unique coincidence signature (similar to the alpha-alpha coincidence feature of Fig. 9B, but near-instantaneous) may be detected in a two-component alpha-gamma sensor (such as the one shown in Fig. 11). A temporal period for the alpha-gamma coincidence below the microsecond level furthermore ensures that no random coincidences are accepted. For low randomcoincidence rates, the coincidence timing requirement may be loosened to within approximately 1% of the random-coincidence time difference.69634790-1[000167] It may be desirable to determine position dependent detection information. Fig. 13 schematically depicts a sensor comprising a spatially segmented sensing area 700 configured to detect nuclear radiation emitted from different positions xi-8, yi-8 of radioactive matter 710 in accordance with the present disclosure. Such a sensor may be used to determine position dependent characteristics of the radioactive matter such as radioactivity and equilibration degree evaluation of radionuclides and / or decay chains. That is, detecting nuclear radiation emitted by the radioactive matter in accordance with the method and system of the present disclosure may comprise detecting nuclear radiation emitted from different positions of the radioactive matter to gather position dependent detection information. The sensor may be used to determine a position at which different radionuclides decay within the radioactive matter. For example, the radioactive matter may be a solid such as, for example, a frozen biological tissue sample, and position sensitive detection information may assist in identifying a spatial distribution of a radiotherapeutic within said sample. The spatial segmentation may be implemented as a spatially segmented-readout sensor 700, either through a pixelated readout or a strip-based readout (as shown in the example of Fig. 13). Coincident detection on, for example, readouts x3and ys constrains the observation to pixel A.[000168] In the combined decay energy and time information (e.g. temporally coincident spectroscopy) identification of, for example, the225Ac decay chain, as detailed in example of Fig. 9B, false positives (e.g. from random coincidences) may be further suppressed from the detection information gathered by the sensor 700 by requiring that the two subsequent decays take place in the same position within the radioactive matter 710. That is, the method and system of the present disclosure may comprise processing the detection information gathered from a first position of the radioactive matter independently of detection information gathered from another position of the radioactive matter. For example, the processor may be configured to process detection information gathered from a first position independently of detection information gathered from another position. In Fig. 13, random coincidences (e.g. those that dominate the histogram of Fig. 9A) may be present among all pixels xi-8, yi-8 of the radioactive matter 710. For example, the number of random coincidences detected in pixel A may be substantially equal to the number of random coincidences detected in pixel B. In contrast, true coincidences (e.g. those that are dominant in Fig. 9B) may only appear within a single pixel, such as A+A coincidences or B+B coincidences in the example of Fig. 13. In some experiments, it has been found that69634790-1this technique reduces the number of false positives by a factor of between about 25 and about 30, without compromising the sensor’s sensitivity to true positives.[000169] The position-sensitive spectroscopic evaluation (as either single-particle or coincident detections) furthermore allows an evaluation of a physical distribution of the decay-chain daughters of a radionuclide (e.g.225Ac), relative to the distribution of the original parent radionuclide within the radioactive matter 700. This facilitates an evaluation of whether or not the parent radionuclide and its daughter radionuclides move differently within the radioactive matter 710 during detection of the decays. That is, the method and system of the present disclosure may comprise determining identities of a parent radionuclide and a daughter radionuclide of the parent radionuclide at least partially based on the comparison between the detection information and the signature decay characteristic, and determining a position of the daughter radionuclide relative to a position of the parent radionuclide. For example, there may be a case where225Ac decays within the original region of radioactive matter 710, such as at pixels A, B in the example of Fig. 13, while some daughter radionuclides may be detected in other pixels such as those located outside of the original region of the radioactive matter 710. This technique facilitates evaluation of radionuclide-specific in-sample movement (e.g. flows), whether it be from diffusive transport, osmotic-driven flows, a micro-fluidic enforced flow within the nuclear radiation sensing system, etc. One possible application of this methodology includes monitoring diffusive transport of daughter radionuclides within a microfluidic system, or within movement-restricted radioactive matter, prior to the measurement in a context where movement of the parent radionuclide (e.g.225Ac) is restricted within the radioactive matter by a biochemical carrier. Another possible application of this methodology includes enforced microfluidic flow around movement-restricted biological cells, to which the original radioactive matter is attached by a biochemical targeting vector (e.g. molecule) for the biological cells, which may or may not retain the secondary emitters. Another possible application of this methodology is monitoring osmotic-driven flows, for which the flow of primary and secondary emitters differs, such as in a thin-layer alpha-chromatography in which the flow of radioactive matter takes place via transport paper held in the receptacle of the nuclear radiation sensing system, or by other means of osmotic flow, e.g. as used in chromatography. In all of these possible applications (i.e. diffusive, enforced, and / or osmotic flows), the position dependent detection information may also be determined with coincident detection of other types of nuclear radiation, such as beta particles, gamma rays and / or neutrons,69634790-1e.g. using a spatially segmented version of the multi-layered sensor of Fig. 11. The implementation of this combines the position dependent detection information (as shown in Fig. 13) in a multi-layer sensor (as shown in Fig.11) nuclear radiation sensing system. The position dependent detection information may be implemented on either (or both) of the two sensor components (e.g. alpha sensor and / or beta / gamma sensor) shown in Fig. 11. It will be appreciated that a spatially segmented version of a single layered sensor (e.g., the system shown in Fig. 11 without the beta and / or gamma sensor layer 620) may be used to carry out a position-sensitive spectroscopic evaluation of the radioactive matter.[000170] Whilst the method and nuclear radiation sensing system of the present disclosure has been exemplified by identifying the presence of the225Ac decay chain and / or distinguishing the225Ac decay chain from the227Ac decay chain, it will be appreciated that the method and nuclear radiation sensing system of the present disclosure are generally applicable to other decay chains. For example, Fig. 14A shows a spectrum of detected energies of alpha particles emitted by radioactive matter comprising241Am in accordance with the present disclosure. The spectrum of Fig. 14A was produced by the nuclear radiation sensing system of Fig. 4B when radioactive fluid comprising241Am was provided to the channel of the sensing unit. In the example of Fig. 14A, the channel has a depth of 10 pm. The spectrum of Fig. 14A was obtained by detecting nuclear radiation emitted from a radioactive fluid having a radioactivity per volume of 0.55 Bq / pL. As can be seen on comparison between the241Am spectrum of Fig. 14A, the225Ac spectrum of Fig. 5A and the simulated227Ac spectra of Fig. 7, each spectrum has its own signature shape which may be used to identify and / or distinguish the radionuclides.[000171] Fig. 14B shows simulated spectra for the known decay of241Am. The spectra are the results of a simulation of microfluidic nuclear radiation sensing systems (such as that shown in Fig. 4B) having channel depths of about 10pm, about 20pm, about 50pm, about 100pm and about 200pm. The data series with the lowest detection counts corresponds to a channel depth of about 200pm and the data series with the second lowest detection counts corresponds to a channel depth of about 100pm. All simulations assumed that the sensor did not include a passivation layer. However, the presence of a passivation layer may also be simulated. The simulations may involve the use of Monte Carlo methods. The simulations of Fig. 14B were obtained through the use of Geant4. Other simulation software may be used. As can be seen, the shape of the spectrum depends on both the radionuclides present within69634790-1the channel, and a depth of the channel. By comparing detection information gathered by the sensor to signature decay characteristics of known nuclear decay chains, different decay chains and radionuclides may be identified and distinguished. For example, detection information gathered from an unknown radioactive sample within the nuclear radiation sensing system can be compared (e.g. numerically, or by inspection) to a library of known spectra (e.g. obtained either experimentally, or via simulation such as those shown in Fig. 14B) in order to determine the identity of radionuclides (e.g.241Am in the example of Fig. 14A) present within the radioactive sample.[000172] Just as described above for the examples of225Ac and227Ac, the method and system disclosed herein may be used to determine one or more characteristics of radioactive matter comprising such as identities of other radionuclides present in the radioactive matter (e.g. the presence of241Am based on the spectrum of Fig. 14A and knowledge of the241Am decay) and associated quantities, identities of one or more types of nuclear radiation being emitted by the radioactive matter and associated quantities, spectroscopic information, radioactivity information, a degree of decay chain equilibration within the radioactive matter, and spatial and / or temporal changes in said characteristics.[000173] The nuclear radiation sensing system and method in accordance with the present disclosure may involve an array (e.g. a side-by-side arrangement) of different sensors. For example, a nuclear radiation sensing system according to the present disclosure may comprise multiple single-layer or multilayer (e.g. two or three- layer) sensors, which may be configured to detect different types of nuclear radiation, have different spatial segmentations and / or temporal segmentations, or a mixture thereof. A side-by-side arrangement of the same type of single-layer sensor may advantageously allow a larger area of contact between the radioactive matter and the sensor surface. For example, a side-by-side arrangement of an alpha radiation sensor and a beta and / or gamma radiation sensor may be simpler to produce and / or may be more appropriate for certain industrial applications.[000174] The skilled person will understand that in the preceding description and appended claims, positional terms such as ‘above’, ‘along’, ‘side’, etc. are made with reference to conceptual illustrations, such as those shown in the appended drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to an object when in an orientation as shown in the accompanying drawings.69634790-1[000175] The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another, but may be used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.[000176] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical, and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause sensors or other devices to interact with the physical world.[000177] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.69634790-1

Claims

CLAIMS:

1. A method of determining a characteristic of radioactive matter comprising: detecting nuclear radiation emitted by the radioactive matter to gather detection information; and, comparing the detection information to a signature decay characteristic of a known nuclear decay.

2. The method of claim 1, wherein the detection information comprises detected energy information, and wherein the signature decay characteristic comprises signature decay energy information, wherein the method comprises comparing the detected energy information to the signature decay energy information.

3. The method of claim 2, wherein the signature decay energy information comprises a signature energy spectrum, wherein the method comprises: determining a detected energy spectrum at least partially based on the detected energy information; and, comparing the detected energy spectrum to the signature energy spectrum.

4. The method of claim 3, comprising: comparing the detected energy spectrum to a plurality of signature energy spectra associated with a plurality of known nuclear decays; and, matching the detected energy spectrum to a most similar signature energy spectrum of the plurality of signature energy spectra.

5. The method of claim 3 or claim 4, wherein the signature decay energy information comprises a signature decay energy, wherein the method comprises matching the signature decay energy to a corresponding decay feature of the detected energy spectrum.

6. The method of claim 5, comprising: selecting a first region of the detected energy spectrum at least partially based on the signature decay energy; and, determining a number of detection counts associated with the first region.69634790-17. The method of claim 6, comprising: selecting a second region of the detected energy spectrum; determining a number of detection counts associated with the second region; and, comparing the number of detection counts associated with the first region to the number of detection counts associated with the second region.

8. The method of claim 7, wherein an energy threshold corresponding to the signature decay energy is used to define the first and second regions.

9. The method of claim 7, wherein an energy threshold corresponding to an energy greater than the signature decay energy is used to define the first and second regions.

10. The method of claim 8 or claim 9, wherein the characteristic of the radioactive matter comprises a decay chain present in the radioactive matter, and wherein the signature decay energy is a greatest signature decay energy of the decay chain.

11. The method of claim 8 or claim 9, wherein the characteristic of the radioactive matter comprises a decay chain present in the radioactive matter, and wherein the signature decay energy is associated with a radionuclide having a half-life that is greater than half-lives of subsequent radionuclides in the decay chain.

12. The method of claim 8 or claim 9, wherein the characteristic of the radioactive matter comprises: a decay chain present in the radioactive matter; and, a degree of nuclear decay equilibration e in the radioactive matter, wherein the method comprises using the following equation:NTwtotntote = - x - x -NtotWTnT where NT is a number of detection counts over the energy threshold, Ntot is a total number of detection counts in the detected energy spectrum, WT is a width of the spectral region above the energy threshold T, wtot is a total width of the detected69634790-1energy spectrum, nTis a number of alpha decay steps above the energy threshold T, and ntot is a total number of alpha decay steps present in the detected energy spectrum.

13. The method of any of claims 7 to 12, comprising: calculating a ratio of the number of detection counts associated with the first region to the number of detection counts associated with the second region; and, multiplying the ratio bywhere Ntotis a total number of detection counts of the first and second regions and t is a duration for which the detection information is gathered.

14. The method of any of claims 7 to 13, comprising determining a radioactivity contribution associated with the first region relative to the second region.

15. The method of claim 14, comprising comparing the radioactivity contribution associated with the first region to an expected radioactivity contribution, the expected radioactivity contribution being at least partially based on the signature decay characteristic.

16. The method of claim 15, comprising determining a degree of nuclear decay equilibration present in the radioactive matter at least partly based on the comparison between the radioactivity contribution associated with the first region and the expected radioactivity contribution.

17. The method of any of claims 7 to 16, comprising determining a stopping power characteristic associated with the first region.

18. The method of claim 17, comprising determining a radioactivity associated with the first region at least partially based on the stopping power characteristic.

19. The method of claim 17 or claim 18, comprising calculating a radioactivity at least partially based on the stopping power characteristic and a result of comparing the number of detection counts associated with the first region to the number of detection counts associated with the second region.69634790-120. The method of any of claims 7 to 19, comprising comparing the numbers of detection counts in the first and second regions to a simulation of the known nuclear decay.

21. The method of claim 20, wherein the detection information is gathered in a detection environment, and the simulation accounts for a characteristic of the detection environment.

22. The method of claim 21 , wherein the simulation at least partially accounts for one or any combination of: a material of the detection environment; a dimension of the detection environment; and, a stopping power of the detection environment.

23. The method of claim 21 or claim 22, wherein the method comprises determining an energy dependent correction based on one or a combination of: a Monte Carlo simulation of the detection environment; and, an analytical calculation based on knowledge of a physical property of the detection environment.

24. The method of any of claims 20 to 23, comprising using the comparison to determine a degree of nuclear decay equilibration in the radioactive matter.

25. The method of any preceding claim, wherein the detection information comprises detected temporal information, and wherein the signature decay characteristic comprises signature decay temporal information, wherein the method comprises comparing the detected temporal information to the signature decay temporal information.

26. The method of claim 25, comprising determining a temporal sequence of decay events at least partially based on the comparison between the detected temporal information and the signature decay temporal information.69634790-127. The method of claim 25 or claim 26, comprising temporally segmenting the detection information, wherein a first temporal period of the temporal segmentation is at least partially based on the signature decay temporal information.

28. The method of claim 27, wherein a second temporal period of the temporal segmentation is at least partially based signature decay temporal information associated with a different known nuclear decay.

29. The method of any preceding claim, wherein detecting nuclear radiation emitted by the radioactive matter comprises detecting a first type of nuclear radiation and detecting a second type of nuclear radiation, the first and second types of nuclear radiation being different.

30. The method of claim 29, wherein the signature decay characteristic comprises: a first signature decay characteristic associated with the first type of nuclear radiation; and, a second signature decay characteristic associated with the second type of nuclear radiation.

31. The method of any preceding claim, wherein detecting nuclear radiation emitted by the radioactive matter comprises detecting nuclear radiation emitted from different positions of the radioactive matter to gather position dependent detection information.

32. The method of claim 31 , comprising processing the detection information gathered from a first position of the radioactive matter independently of detection information gathered from another position of the radioactive matter.

33. The method of claim 31 or claim 32, comprising: determining identities of a parent radionuclide and a daughter radionuclide of the parent radionuclide at least partially based on the comparison between the detection information and the signature decay characteristic; and, determining a position of the daughter radionuclide relative to a position of the parent radionuclide.69634790-134. The method of any preceding claim, wherein detecting nuclear radiation emitted by the radioactive matter to gather detection information comprises detecting one or more of the following: alpha radiation emitted from an alpha-emitting radionuclide; beta radiation emitted from a beta emitting radionuclide; gamma radiation emitted from a gamma-emitting radionuclide; and, neutron radiation emitted from a neutron-emitting radionuclide.

35. The method of any preceding claim, wherein detecting nuclear radiation emitted by the radioactive matter comprises directly detecting the nuclear radiation.

36. A nuclear radiation sensing system comprising: a sensor configured to detect nuclear radiation emitted by radioactive matter; and, a processor configured to compare detection information gathered by the sensor to a signature decay characteristic of a known nuclear decay to determine a characteristic of the radioactive matter.

37. The nuclear radiation sensing system of claim 36, wherein the processor is configured to perform the method of any of claims 1 to 35.

38. The nuclear radiation sensing system of claim 36 or claim 37, wherein the sensor comprises: a first layer configured to detect a first type of nuclear radiation; and, a second layer configured to detect a second type of nuclear radiation, wherein the first and second types of nuclear radiation are different.

39. The nuclear radiation sensing system of claim 38, wherein the first and second layers have different thicknesses and / or comprise different materials.

40. The nuclear radiation sensing system of any of claims 36 to 39, wherein the sensor comprises a spatially segmented sensing area configured to detect nuclear radiation emitted from different positions of the radioactive matter, and wherein the processor is configured to determine position dependent detection information.69634790-141. The nuclear radiation sensing system of claim 40, wherein the processor is configured to process detection information gathered from a first position independently of detection information gathered from another position.

42. The nuclear radiation sensing system of any of claims 36 to 41 , wherein the sensor comprises a passivation layer comprising PTFE.

43. The nuclear radiation sensing system of any of claims 36 to 42, comprising a receptacle configured to receive the radioactive matter, wherein at least part of the sensor forms at least part of the receptacle.

44. The nuclear radiation sensing system of claim 43, wherein the receptacle is arranged such that, when in use, the radioactive matter is in contact with the sensor.

45. The nuclear radiation sensing system of claim 43 or claim 44, wherein the receptacle has a depth of about 10mm or less.

46. A method of forming a nuclear radiation sensing system comprising: providing a sensor configured to detect nuclear radiation emitted by radioactive matter; and, providing a processor configured to compare detection information gathered by the sensor to a signature decay characteristic of a known nuclear decay to determine a characteristic of the radioactive matter.

47. The method of claim 46, comprising forming a receptacle configured to receive the radioactive matter, wherein forming the receptacle comprises: performing lithography on a material that forms part of the receptacle, and / or performing additive manufacturing.69634790-1

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