Nuclear radiation monitoring circuitry and method

Abstract

There is disclosed circuitry for a first nuclear radiation monitoring apparatus, the circuitry comprising control logic configured to; receive first radiation data generated by a first nuclear radiation detector of the first nuclear radiation monitoring apparatus, the radiation data being indicative of nuclear radiation emitted from a target object and detected by the first nuclear radiation detector; wherein the control logic is further configured to: receive radiation data indicating characteristics of an interference radiation source different to the target object; analyse the radiation data indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source; modify the first radiation data generated by the first nuclear radiation detector based on the determined at least one characteristic to obtain modified first radiation data; and classify the nuclear radiation using the modified first radiation data to identify at least one radioactive isotope comprised in the target object.

Description

[0001] NUCLEAR RADIATION MONITORING CIRCUITRY AND METHOD

[0002] Field of the Disclosure

[0003] The present disclosure relates to a nuclear radiation monitoring circuitry and method.

[0004] Description of the Related Art

[0005] The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in the background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.

[0006] Radiation portal monitors (RPMs) are one class of nuclear radiation monitoring apparatus in current usage. There is currently a widespread use of RPMs at points of entry (POEs) into countries. These include drive-through RPMs for both containerised and non-containerised cargo. Air-freight and rail-freight RPMs are also used at border crossing points in order to detect undeclared radioactive materials concealed in cargo. In particular, such RPMs serve to help detect the presence of illicit Special Nuclear Materials (SNM). RPMs typically comprise a number of nuclear radiation detectors (e.g. gamma-ray and I or neutron detectors) through which nuclear materials, and SNMs in particular, can be detected and classified based on the radiation emitted by such materials.

[0007] Mobile radioisotope identification devices are another class of nuclear radiation monitoring apparatus in current usage, comprising sub-classes such as (i) handheld, (ii) backpack, and (iii) vehicle mounted nuclear radiation monitoring apparatus, configured for mobile deployment to areas of interest. Mobile nuclear radiation monitoring devices may be used to provide complementary functionality to fixed or semi-fixed nuclear radiation monitoring apparatuses such as RPMs. Thus, for example, personnel at a site where one or more RPMs are installed for vehicular inspection may use one or more mobile nuclear radiation monitoring apparatuses to conduct investigations of vehicles which have been identified as presenting a potential risk based on nuclear radiation monitoring conducted by an RPM.

[0008] Sites at which nuclear radiation monitoring apparatuses are in use may be subject to interference from active sources of radiation, such as X-ray sources. This may be, for example, because one or more X-ray imaging devices are installed at a point of entry I border crossing to carry out scanning of vehicles and I or cargo for illegal and / or hazardous objects and materials. X-ray signals can be detected by detectors used in nuclear radiation monitoring apparatuses, for example the plastic scintillator detectors (in particular, polyvinyl-toluene scintillator detectors) and crystal scintillator detectors often comprised in such apparatuses. The presence of interference from X-ray and other active radiation sources in the vicinity of nuclear radiation monitoring apparatuses may lead to misclassification of isotopes in the data collected by such apparatuses.

[0009] Approaches to mitigating the influence of interference radiation in the use of nuclear radiation monitoring apparatuses are therefore of interest.

[0010] SUMMARY

[0011] According to a first aspect of the present disclosure, there is provided circuitry for a first nuclear radiation monitoring apparatus, the circuitry comprising control logic configured to; receive first radiation data generated by a first nuclear radiation detector of the first nuclear radiation monitoring apparatus, the radiation data being indicative of nuclear radiation emitted from a target object and detected by the first nuclear radiation detector; wherein the control logic is further configured to: receive radiation data indicating characteristics of an interference radiation source different to the target object; analyse the radiation data indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source; modify the first radiation data generated by the first nuclear radiation detector based on the determined at least one characteristic to obtain modified first radiation data; and classify the nuclear radiation using the modified first radiation data to identify at least one radioactive isotope comprised in the target object.

[0012] According to a second aspect of the present disclosure, there is provided a nuclear radiation monitoring method comprising: receiving first radiation data generated by a first nuclear radiation detector of a first nuclear radiation monitoring apparatus, the radiation data being indicative of nuclear radiation emitted from a target object and detected by the first nuclear radiation detector; receiving radiation data indicating characteristics of an interference radiation source different to the target object; analysing the radiation data indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source; modifying the first radiation data generated by the first nuclear radiation detector based on the determined at least one characteristic to obtain modified first radiation data; and classifying the nuclear radiation using the modified first radiation data to identify at least one radioactive isotope comprised in the target object.

[0013] According to a third aspect of the present disclosure, there is provided a program for controlling a computer to perform a method according to the second aspect. According to a fourth aspect of the present disclosure, there is provided a recording medium storing a program according to the third aspect.

[0014] The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0017] Figure 1 schematically shows a Radiation Portal Monitor (RPM) according to an embodiment;

[0018] Figure 2 schematically shows gamma-ray spectra according to an embodiment;

[0019] Figure 3A schematically shows a nuclear radiation monitoring apparatus according to an embodiment;

[0020] Figure 3B schematically shows a signal processing chain between a nuclear radiation detector and a nuclear radiation monitoring apparatus according to an embodiment;

[0021] Figure 3C shows a front-end signal processing circuitry according to an embodiment;

[0022] Figures 4 and 5 schematically shows a count rates of radiation detection events with respect to time.

[0023] Figures 6 and 7 schematically shows an interference radiation source in a context of an arrangement of spatially separated nuclear radiation monitoring apparatuses

[0024] Figure 8 is a flow chart schematically showing steps of a method according to the present disclosure.

[0025] DESCRIPTION OF THE EMBODIMENTS

[0026] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.

[0027] The present technique relates to using radiation data indicating characteristics of an interference radiation source to modify radiation data generated by a nuclear radiation detector of a nuclear radiation monitoring apparatus. For the purposes of describing approaches according to the present disclosure in the context of a concrete use case, a radiation portal monitor (RPM) will be used herein an illustrative example of a nuclear radiation monitoring apparatus comprising circuitry or software configured to carry out the approaches. However, it will be appreciated that a RPM is only one embodiment of a nuclear radiation monitoring apparatus with which such circuitry and / or software configured to carry out approaches according to the present disclosure can be implemented, and the circuitry and I or software of the present disclosure is suitable for use with other nuclear radiation monitoring apparatuses comprising radiation detectors (e.g. gamma and I or neutron detectors). Thus, in addition to implementation in RPMs, it will be appreciated the circuitry and software described herein are suitable for use in mobile nuclear radiation monitoring apparatus such as (i) handheld, (ii) backpack, and (iii) vehicle mounted devices. Accordingly, any reference herein to an RPM can be substituted for a mobile nuclear radiation monitoring apparatus, and vice versa.

[0028] Figure 1 shows an exemplary Radiation Portal Monitor (RPM) 101 with which nuclear radiation monitoring circuitry may be implemented according to an embodiment of the present disclosure. The RPM comprises a first nuclear radiation detector 100. As shown in the example of Figure 1 , the nuclear radiation detector 100 can comprise a plurality of nuclear radiation detector panels 100A to 100D (which form respective portions of the nuclear radiation detector 100). Panels 100A and 100C form a right side R of the detector 100 and panels 100B and 100D form a left side L of the detector 100. The right R and left L sides of the detector 100 are placed apart (e.g. approximately 4 metres apart) on either side of a road, watercourse, or set of tracks so as to allow a vehicle 102 passing through the RPM to travel between the right R and left L sides of the detector 100. The panels of each of the R and L sides of the detector house one or more gamma ray detectors and / or one or more neutron detectors (thereby allowing gamma radiation and I or neutron radiation to be detected at each of the R and L sides of the vehicle).

[0029] The gamma-ray and neutron detectors are passive instruments that respond, respectively, to gamma-ray and neutron emissions emanating from both the target object being monitored I assessed (e.g. a cargo comprised in or transported by a vehicle passing through the RPM) and the surrounding environment. A dual-sided (in particular, a R and L sided) detection system is presented as an example in Figure 1. However, the present technique is applicable to other possible arrangements of detectors, including, but not limited to, single-sided deployments (e.g. R side or L side only) or multi-sided deployments (e.g. R and L side, as shown in Figure 1). In one example, the detector 100 may comprise detector panels above and / or below the cargo in addition to or instead of or in addition to detectors panels at the L and R sides of the cargo. The cargo being scanned is not limited to containerised cargo associated with a road vehicle, but could equally comprise pedestrian traffic, air-freight, rail-freight, non-containerised cargo, automobiles, watercraft, etc. It will be appreciated that, when the cargo is carried using an alternative method, the example RPM of Figure 1 will be adjusted accordingly (e.g. for rail freight, the R and L sides of the detector 100 will be either side of a railway rather than a road). Each gamma-ray detector, where present, is configured to record data indicative of an energyloss spectrum of gamma radiation (gamma-ray spectrum) over a given time interval. This data may be referred to as gamma-ray data, and is a sub-set of radiation data as described herein. Each gamma-ray detector may be, for example, a plastic scintillator detector (in particular, a polyvinyl-toluene scintillator detector), a garnet ceramic scintillator detector (and / or other detectors known to the skilled person based on garnet and I or ceramic technology), a crystal scintillator detector, or any other gamma-ray detector known to the skilled-person. The output of the gamma-ray detector will typically comprise a rate of detection events (referred to herein as a ‘count rate’), typically segregated into ranges of energy, such that separate rates are discriminated for different ranges of energy across a detectable range, enabling computation of a spectrum. The detectable energy range and noise floor of count rate will be a function of the detector design, and differs across different detector types. The determination of count rates associated with different energy levels is typically achieved using multi-channel analyser (MCA) circuitry and I or software connected to the detector hardware, and configured to process voltage pulses generated by the gamma-ray detector in response to excitation by incident radiation, converting them to a representation of count rate with respect to ranges of incident energy. MCA circuitry may be integrated into a gamma-ray detector unit (e.g. a detector panel), such that each gamma-ray detector (or panel) comprises an inbuilt MCA which analyses the raw data from each detector and returns radiation data comprising an indication of detection event count rate with respect to energy. Alternatively an MCA may be implemented as a standalone circuitry module configured to receive raw radiation data generated by one or more nuclear radiation detectors of a nuclear radiation monitoring apparatus (such as the RPM of Figure 1), and configured to pass processed radiation data to nuclear radiation monitoring circuitry configured to perform further processing steps such as classifying detected radiation using the radiation data to identify at least one radioactive isotope comprised in a target object from which the detected radiation is received. In embodiments, nuclear radiation monitoring circuitry as described herein may comprise MCA circuitry configured to receive radiation data indicating characteristics of an interference radiation source; analyse the radiation data indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source. The MCA circuitry (also referred to herein as ‘analyser’ circuitry) may be further configured to modify the first radiation data generated by the first nuclear radiation detector based on the determined at least one characteristic of the interference radiation source. In other embodiments, this modification may be carried out by classification circuitry downstream of the MCA / analyser circuitry in the signal chain, based on the at least one characteristic of the interference radiation source determined by the MCA / analyser circuitry

[0030] It will be appreciated that the functionality of the MCA / analyser circuitry used as described herein to analyse radiation data from one or more nuclear radiation detectors may be implemented by hardware control logic (e.g. one or more application specific integrated circuit (ASIC) or field programmable gate array (FPGA) modules), or may be implemented in software running on processor circuitry of a general purpose computing device. Thus the MCA / analyser circuitry may be implemented as and referred to as either a hardware analyser, or a software analyser.

[0031] Similar to the gamma-ray detector described above, each neutron detector, where present, is configured to record data indicative of a flux of incident neutrons over a given time interval. This data may be referred to as neutron data. The raw sensor output of one or more neutron detectors may, in a similar manner to the sensor output of one or more gamma-ray detectors, be processed by one or more MCAs to discriminate count rates by incident energy. Suitable gamma-ray and neutron detectors for nuclear radiation monitoring apparatuses are known in the art and are therefore not discussed further in detail here.

[0032] The gamma-ray data and neutron data acquired from one or more nuclear radiation detectors of a nuclear radiation monitoring apparatus together comprise radiation data associated with the nuclear radiation monitoring apparatus. The radiation data may be in the form of raw sensor output (i.e. voltage pulses requiring processing by MCA / analyser circuitry), or may be in the form of count rates assigned to relative or absolute energy ranges (i.e. the output of MCA / analyser circuitry). Where the nuclear radiation monitoring apparatus comprises both gamma-ray and neutron detectors, separate dedicated MCA / analyser circuitry may be used to process raw sensor output from gamma-ray and neutron detectors respectively. Alternatively, the same MCA I analyser circuitry may be configured to process raw sensor output from both gamma-ray and neutron detectors (i.e, the MCA I analyser circuitry may comprise discrete processing channels for gamma-ray and neutron data) and pass to classification circuitry processed radiation data comprising an indication of count rates with respect to energy.

[0033] It will be appreciated that MCA / analyser circuitry will in many embodiments reduce the timedomain resolution of the raw radiation data received from one or more detectors, in order to make the radiation data more tractable for further analysis and / or classification operations, where processing of the raw radiation data may be unfeasible (e.g. due to limitations on computational resources). Thus, for example, the temporal resolution of the count-rate data comprised in raw radiation data as initially digitised from the detector output may typically be of the order of microseconds, whereas the temporal resolution of processed radiation data output by the MCA I analyser circuitry may typically be of the order of milliseconds (noting that these are exemplary figures). As will be discussed further herein, where such down-sampling of temporal resolution is implemented by the MCA I analyser circuitry, it may be advantageous to carry out some radiation data analysis (and optionally modification) functions as described herein prior to temporal downsampling of the radiation data, such that these functions are performed at the point in the signal processing chain when the temporal resolution of the radiation data is finest. In the context of the RPM of Figure 1, each of the nuclear radiation detectors comprised in detector panels 100A to 100D is in data communication with nuclear radiation monitoring circuitry 200 so as to allow the generated nuclear radiation data to be provided to the nuclear radiation monitoring circuitry 200. This data transmission between each nuclear radiation detector and the nuclear radiation monitoring circuitry 200 is achieved using wired or wireless data communication approaches known to the person skilled in the art. Any visualisation data generated by the nuclear radiation monitoring circuitry 200 can be output to a display apparatus 201 (e.g. monitor comprising a liquid crystal display (LCD) or similar for displaying images) for display to a user.

[0034] Where the use context for the radiation monitoring circuitry of the present disclosure is an RPM, the RPM will typically also comprise a vehicle or pedestrian detection apparatus for detecting when a vehicle or pedestrian has entered the RPM. As shown in Figure 1, the vehicle detection apparatus has a pair of beam-break instruments (103A and 103B), each pair comprising a beam emitter 103A which emits a light beam and a beam detector 103B which detects that light beam. Beam emitters and detectors which perform such a function are known in the art and are therefore not discussed in detail here. The light beam may, for example, be a laser beam. One pair of beambreak instruments is typically positioned at the entrance to the RPM and one pair of bream break instruments is typically positioned at the exit of the RPM. The distance (d) between each pair of beam-break instruments is a known parameter stored in a memory of the nuclear radiation monitoring circuitry of the RPM. Figure 1 shows a pair of beam-break instruments at the exit of the RPM (exit beam-break pair). The exit beam-break pair includes beam emitter 103A and beam detector 103B. Although not shown, a similar arrangement (entrance beam-break pair) is present at the entrance to the RPM. The respective positions of the pairs of beam-break instruments need not necessarily be at the entrance and exit of the RPM. Rather, they may be at different positions of the RPM in the direction of travel of the vehicle, as long as the distance d between the pairs is known. It will be appreciated the use of break-beam instruments is described herein for the sake of providing a concrete example of a context in which approaches according to the disclosure may be implemented, and other ways of detecting the presence or not of a part of the vehicle 102 at a certain position along the RPM could also be used instead of the pairs of beam-break instruments. In this respect any form of occupancy and I or velocity detection approach known to the skilled person may be used in place of or in addition to the break-beam instruments 103A and 103B shown in Figure 1 and described herein. What is significant is that the RPM comprises a mechanism for triggering measurements to be recorded from the detector panels 100A to 100D, and subsequent radiation data processing steps to be implemented by nuclear radiation monitoring circuitry as described further herein (i.e. when occupancy of the RPM is detected), and halting the recording of measurements (i.e. when occupancy of the RPM is no longer detected). Where the nuclear radiation monitoring apparatus in which the nuclear radiation monitoring circuitry of the present disclosure is implemented is a different type / class of apparatus, such as a hand-held, backpack, or mobile nuclear radiation monitoring apparatus, it will be appreciated the triggering of measurement and data processing will typically not be implemented using beambreak or other occupancy-detection instruments, but by alternative user input devices (for example, suitable mechanical controls, or a user interface provided on a display panel of a general purpose computing device).

[0035] While Figure 1 schematically illustrates an RPM which comprises a plurality of nuclear radiation detectors, it will be appreciated approaches according to the present disclosure may be applied in respect of nuclear radiation monitoring circuitry configured to receive radiation data from a single nuclear radiation detector. Thus approaches according to the present disclosure may be applied separately for each nuclear radiation detector of a nuclear radiation monitoring apparatus which comprises a plurality of detectors, or may be applied in respect of a nuclear radiation monitoring apparatus comprising a single nuclear radiation detector. A module comprising nuclear radiation monitoring circuitry as described herein may therefore be provided on a per-detector basis, or on a per nuclear radiation monitoring apparatus basis. As described further herein, approaches according to the present disclosure may be applied to aggregated data from a plurality of nuclear radiation detectors (either comprised in a single nuclear radiation monitoring apparatus, or polled from nuclear radiation detectors distributed across a plurality of nuclear radiation monitoring apparatuses).

[0036] While not wishing to be constrained by any particular physical theory, radiation data captured by one or more nuclear radiation detectors of a nuclear radiation monitoring apparatus in proximity to a target object to be assessed is typically understood to comprise a plurality of components. These include (1) a measure of any radiation emitted from the materials comprised within the target object, and (2) a measure of other sources of radiation or noise which do not directly result from the radiation emission characteristics of the target object. It will be appreciated that this second component will typically comprise a plurality of sub-components, such as a background component, a noise component, and active interference component, and so on. The classification of detected radiation using first radiation data to identify at least one radioactive isotope comprised in a target object must thus take into account the presence of components which form part of the radiation data but are not associated with emission from the target object. While some such nontarget components result from natural, environmental radiation sources, active radiation sources such as X-ray scanners may also contribute to the non-target radiation components of radiation data collected by one or more detectors of a nuclear radiation monitoring apparatus. X-ray scanners are widely used for monitoring cargo at locations where security checks are required and / or desirable, such as points of entry / border crossings. Mobile or fixed X-ray scanners may be used as such sites to carry out scanning of vehicles and I or cargo for illegal and I or hazardous objects and materials. Since the locations where nuclear radiation monitoring apparatuses are installed or otherwise implemented are often also locations where X-ray scanners are in use, interference from X-ray scanners and other active radiation sources can present a particular issue in terms of managing non-target radiation components (sometimes collectively referred to as ‘background’ components) in radiation data acquired by nuclear radiation detectors of radiation monitoring apparatuses.

[0037] Figure 2 shows an exemplary gamma-ray spectrum obtained from a gamma-ray detector of an RPM, in which count rates of detection events are expressed in terms of the incident energy. Figure 2 shows two spectra, a non-target spectrum which comprises the contribution(s) of one or more components in the absence of radiation from a specific target or from active interference sources, and an ‘X-ray on’ spectrum which comprises the same non-target component(s) but including a component of interference radiation from an active X-ray source (e.g. comprised in an X-ray scanner) located in the vicinity of the RPM. The effect of the interference radiation is to elevate the count rate of the non-target radiation component of the radiation data. Interference radiation sources such as X-ray scanners may pose particular challenges to the successful classification of radiation data to identify radioactive isotopes comprised in target objects, beyond those posed by normal non-target components, such as noise and passive ‘background’ radiation components.

[0038] Thus, according to aspects of the present disclosure, there is provided circuitry for a nuclear radiation monitoring apparatus, the circuitry configured to; receive first radiation data generated by a first nuclear radiation detector, the radiation data being indicative of nuclear radiation emitted from a target object and detected by the first nuclear radiation detector; and classify the detected radiation using the first radiation data to identify at least one radioactive isotope comprised in the target object; wherein the circuitry is further configured to: receive radiation data indicating characteristics of an interference radiation source different to the target object; analyse the information indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source; and modify the first radiation data generated by the first nuclear radiation detector based on the determined at least one characteristic. It will be appreciated herein that references to circuitry may equally be taken to refer to software configured to carry out the functionality described by the software. As the skilled person is aware, control logic configured to carry out specific functionality can be implemented both in hardware (as in an ASIC), or in software configured to run on a general purpose computing device. Thus in some embodiments, the approaches described herein are implemented using hardware control logic implemented in an apparatus comprising application specific circuitry comprising the hardware control logic. In other embodiments, the approaches described herein are implemented in compiled software code configured to be run on a general purpose computer. Figure 3A schematically shows nuclear radiation monitoring circuitry 200 according to embodiments of the present disclosure, comprising a communication interface 202, an analyser 203, a classifier 204, a controller 207, and a storage medium 208. Optionally, in some embodiments, the nuclear radiation monitoring circuitry 200 may comprise a visualisation data generator 205, and a display output 206 configured to transmit display data to a display 201 .

[0039] The communication interface 202 is configured to send signals to and I or receive signals from the detector(s) 100 of the nuclear radiation monitoring apparatus 101 with which the nuclear radiation monitoring circuitry is configured for use (and in particular, for receiving nuclear radiation data from the nuclear radiation detector(s) 100). The communication interface 202 is also configured to receive the signals output by occupancy detection instruments (e.g. a beam detector (e.g. beam detector 103B) of each of one or more beam-break pairs, or alternative user input device for controlling the triggering and halting of detection by the nuclear radiation detector 100). Where the nuclear radiation monitoring circuitry 200 comprises MCA / analyser circuitry, the communication interface 202 is configured to receive radiation data in the form of raw sensor output data (e.g. voltage pulses) from the nuclear radiation detector(s) 100. Where the MCA I analyser circuitry is integrated into a detector 100 of the nuclear monitoring apparatus 101 (e.g. as part of detector-integrated front-end signal processing circuitry), or implemented as one or more standalone modules (e.g. standalone front-end signal processing circuitry), disposed between a nuclear radiation detector 100 and nuclear radiation monitoring circuitry 200, the communication interface 202 is configured to receive part-processed radiation data, for example in the form of detection event count rates for different absolute or relative ranges of energy.

[0040] In embodiments where it is included, the display output 206 is configured to transmit electronic information to the display apparatus 201 for display of that electronic information (in particular, for transmitting visualisation data generated by a visualisation data generator 205 to the display apparatus 201 for display of that visualisation data). The storage medium 208 (e.g. in the form of a hard disk drive, solid state drive, tape drive or the like) is for long-term storage of electronic information including radiation data and the results of analysis and classification steps applied to the radiation data. It will be appreciated that, rather than the nuclear radiation monitoring circuitry 200 comprising the storage medium 208, the storage medium 208 may be located in a separate apparatus (e.g. cloud server or local server) accessible to the nuclear radiation monitoring circuitry 200 over a network or the like (e.g. via the communication interface 202).

[0041] The controller 207 is configured to control the operation of each of the communication interface 202, analyser 203, classifier 204, storage medium 208, and in embodiments where they are included, visualisation data generator 205, and display output 206. The controller 206 may also control, via the communication interface 202, the operation of the nuclear radiation detector 100 (e.g. by controlling the communication interface 202 to send a control signal to the detector 100 to start and stop detection of nuclear radiation). Each of the communication interface 202, analyser 203, classifier 204, visualisation data generator 205, display output 206, controller 207 and storage medium 208 are implemented by appropriate circuitry, for example. The functionality of the analyser 203, classifier 204, visualisation data generator 205, display output 206, and controller 207, may be implemented by hardware control logic (such as by one or more ASIC or FPGA modules), and I or in software control logic implemented on one or more general purpose computing devices. In some embodiments, a first set of functions may be implemented in hardware control logic, and a second set of functions may be implemented in software control logic. For example, in embodiments where the nuclear radiation monitoring circuitry 200 is configured to carry out multi-channel analysis of raw sensor data to provide processed radiation data representing count rates of detection rates at different energy levels, this functionality may be implemented in an analyser 203 comprising hardware control logic as described further herein.

[0042] It will be appreciated that in embodiments, certain functions described herein as associated with the analyser 203 may optionally be implemented as part of front-end signal processing circuitry situated upstream on the signal chain from the nuclear radiation monitoring circuitry 200 as described in relation to Figure 3A. Figure 3B shows schematically a signal processing chain in which one or more detectors 100 are configured to pass radiation data (e.g. raw radiation count data) to front-end signal processing circuitry 150, which performs initial processing of the radiation data from the one or more detectors 100, and passes the modified radiation data to the nuclear radiation monitoring circuitry 200. The dashed line in Figure 3B is used to indicate tight integration between the one or more detectors 100 and the front-end signal processing circuitry 150 (where included). Thus the front-end signal processing circuitry 150 may be positioned close to one or more detectors 100 from which it receives radiation data, to reduce latency and maximise data integrity. Figure 3C shows schematically an exemplary set of functional modules comprised in the front-end signal processing circuitry 150, namely an optional signal conditioning module (e.g. implementing amplification and / or low or high pass filtering functions known to the skilled person), an analyser 152, and a communication interface 153 configured to transmit data processed I analysed by the analyser 152 to the communication interface 202 of nuclear radiation monitoring circuitry 200 as shown in Figure 3A. In embodiments where an analyser module 152 is situated in front-end signal processing circuitry 150 situated between one or more detectors 100 and nuclear radiation monitoring circuitry 200 on the signal processing path, the analyser 152 comprises functionality described herein in relation to the analyser 203 of the nuclear radiation monitoring circuitry 200. Accordingly, an analyser module may optionally be omitted from the nuclear radiation monitoring circuitry. Accordingly, radiation data analysed by the analyser 152 to determine at least one characteristic of radiation emitted by an interference radiation source may be passed to the communication interface 153 of the front-end signal processing circuitry 150 for transmission to a communication interface of nuclear radiation monitoring circuitry. The received radiation data may then be directly passed to a classifier module for identification of one or more radioisotopes in a target object associated with the radiation data, or may undergo further analysis (e.g. data modification steps) prior to classification, in an optional analyser module of the nuclear radiation monitoring circuitry.

[0043] In the embodiment of Figure 1, in which the nuclear radiation monitoring apparatus with which the nuclear radiation monitoring circuitry 200 is associated is an RPM, the collection of radiation data may be carried out as followed. When a vehicle, or other target object, enters the RPM and the front of the vehicle or target object aligns with the front of the detector 100, the beam detector 103B provides a beam-break signal to the controller 207 of the nuclear radiation monitoring circuitry 200 (though it will be appreciated other occupancy-detection approaches not based on breaking of a beam may be employed). In response, the controller 207 controls the detector 100 to start associating nuclear radiation data recorded by the nuclear radiation detector 100 with the vehicle or target object which has entered the portal. By “association”, it is meant that the recorded nuclear radiation data will be used to generate visualisation data associated with the vehicle or object. This is because the presence of the vehicle or object within the RPM means that the recorded nuclear radiation data will include the contribution of any nuclear radiation (in particular, gamma-rays and neutrons) emitted from the vehicle or other object. Nuclear radiation data is recorded by the detector 100 during each of a plurality of successive time intervals (referred to herein as capture intervals) as the vehicle travels past the detector 100 and is provided to the nuclear radiation monitoring circuitry 200 via communication interface 202. In non-RPM contexts, such as where the nuclear radiation monitoring circuitry 200 is implemented with a mobile nuclear radiation monitoring apparatus, a suitable user interface is used to provide the triggering signals to the controller 207 to cause the controller to control the detector 100 of the mobile nuclear radiation monitoring apparatus to start associating nuclear radiation data recorded by the nuclear radiation detector 100, and provide nuclear radiation data recorded by the detector 100 during each of a plurality of successive capture intervals to the nuclear radiation monitoring circuitry 200 via communication interface 202. The triggering of the controller in this manner may be effected by a user when in the vicinity of a particular target object to be assessed for the presence of radioactive isotopes.

[0044] In an RPM context, such as shown in Figure 1 , the speed v at which a vehicle travels past the detector 100 and the capture interval duration are determined so as to provide a balance between detector performance and vehicle throughput. In one example, the driver of the vehicle is instructed to drive the vehicle through the RPM at a speed v of 8 km.hr1and the capture interval duration is 100 milliseconds (ms). The detector 100 is reset at the beginning of each capture interval so as to record nuclear radiation data corresponding to the portion of the vehicle passing the detector 100 during that capture interval. The analyser receives the nuclear radiation data associated with a target object (e g. a vehicle and / or cargo) captured by one or more nuclear radiation detectors during each capture interval. In an embodiment, the nuclear radiation data from a plurality of adjacent time intervals is aggregated to improve the spectral classification performance. In one example, the nuclear radiation data of successive sets of plural adjacent capture intervals is aggregated. The successive sets of plural adjacent capture intervals over which the nuclear radiation data is aggregated are referred to as aggregated capture intervals. This means that, for example, for when the capture interval duration is 100ms and there are three plural adjacent capture intervals in a set over which nuclear radiation data is aggregated, the aggregated capture interval has a duration of 300ms. In the following description, the terms “capture interval” and “aggregated capture interval” are used interchangeably (since the aggregated capture interval is equivalent to a longer capture interval in terms of processing of the captured nuclear radiation data).

[0045] For neutron data captured by any neutron detectors during each capture interval, the analyser may likewise aggregate the neutron count detected by each neutron detector in order to determine a total neutron count for that capture interval.

[0046] For gamma-ray data captured by any gamma-ray detectors during each capture interval, the analyser combines the gamma-ray spectra detected from each gamma-ray detector in order to generate a higher intensity, combined gamma-ray spectrum (the data representing the combined gamma-ray spectrum is referred to as combined gamma-ray data). This allows the captured gamma radiation to be analysed even for a low gamma-ray source intensity. In order to maintain a combined gamma-ray spectrum of good quality for use in the subsequent signal processing stages, each gamma-ray detector is identical and is continuously stabilised and calibrated in order to avoid the impact of changing environmental conditions (e.g. temperature fluctuations). The combining of gamma-ray data from multiple detectors is known in the art (see e.g. [1] and [2]) and is therefore not described in detail here.

[0047] According to embodiments of the present disclosure, analyser circuitry (i.e. of nuclear radiation monitoring circuitry and I or front-end signal processing circuitry) is configured to receive radiation data indicating characteristics of an interference radiation source different to a target object, and to analyse the information indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source.

[0048] In embodiments, the radiation data indicating characteristics of an interference radiation source different to the target object comprises the first radiation data generated by the first nuclear radiation detector, and the analyser circuitry (herein also referred to as an ‘analyser’)is configured to analyse the first radiation data to determine the at least one characteristic of radiation emitted by the interference radiation source. Thus, in said embodiments, the radiation data indicating characteristics of an interference radiation source are the same radiation data which are to be classified by a classifier of the nuclear radiation monitoring circuitry to identify at least one radioactive isotope comprised in the target object.

[0049] Figure 4 shows schematically nuclear radiation data expressed in terms of counts of detection events per capture interval, where the width of each bar in the time axis corresponds to a capture interval, and the height of each bar corresponds to the frequency of detection events in the capture interval. In embodiments, the analyser (situated either in front-end signal processing circuitry or in nuclear radiation monitoring circuitry) is configured to generate data in the form shown in Figure 4, by combining for each capture interval the counts associated with all detected energies, to provide a total number of counts for a given nuclear radiation detector or plurality of detectors. The combining of counts for all energies may be implemented by MCA circuitry comprised in the analyser, according to approaches for configuring MCA circuitry, known to the skilled person. The total counts may be computed for each capture interval on a per-detector basis, providing a separate count for each detector, or the total counts for all detectors may be summed by the analyser to provide a measure of the total counts rate for an entire nuclear radiation monitoring apparatus.

[0050] Continuous interference detection

[0051] In embodiments, the analyser is configured to analyse radiation data of the form shown schematically in Figure 4 (i.e. indicating total counts per capture interval) to determine at least one characteristic of radiation emitted by the interference radiation source, wherein the at least one characteristic of radiation emitted by the interference radiation source comprises a time interval during which radiation from the interference radiation source is detected. Radiation data as shown in Figure 4 may be computed by an MCA integrated into an analyser of a front-end signal processing module upstream of the nuclear radiation monitoring circuitry, or integrated into an analyser of nuclear radiation monitoring circuitry.

[0052] The exemplary radiation data of Figure 4 shows the influence on counts per capture interval of a ‘continuous’ interference scenario, in which an interference radiation source is activated, continuously emits radiation for a period of time, and then is deactivated. Continuous interference may result, for example, from an X-ray scanner in the vicinity of a nuclear radiation monitoring apparatus, which is configured to produce a continuous beam of X-rays to support a specific form of imaging modality, such as for example two-dimensional projection imaging of objects passing along a conveyor or track. Figure 4 shows schematically a first period Tn, in which the radiation data is not influenced by interference from an active radiation source different to a target object under investigation by the nuclear radiation monitoring apparatus, and the variation in counts between successive capture intervals is below a threshold value. The degree of variation in the non-interference condition is influenced by fluctuations in non-target components, such as background radiation and the influence of noise, and variation in the intensity of any nuclear radiation detected from the target object under investigation, as the distance between the target object and detector varies during analysis (for example, as a vehicle drives past the detector 100 in an RPM context as shown in Figure 1). At a time ti, an interference radiation source different to the target object under investigation (e.g. an X-ray source) is activated, and the interference radiation begins to be detected by the nuclear radiation detector of the nuclear radiation monitoring apparatus. The influence of this interference radiation on the radiation data generated by the nuclear radiation detector is observed as an above-threshold variation in counts between the capture intervals immediately before and after time ti. During an interference time interval T, the interference radiation source is continuously emitting radiation, causing consistent elevated count rates in successive capture intervals from ti tot2. At time t2, the interference radiation source is switched off, and the counts per capture interval drop as the influence of the interference radiation on the radiation data generated by the nuclear radiation detector is removed. It will be appreciated that active interference radiation sources (such as X-ray sources) will typically have a very rapid switch-on time, which may be of the order of nanoseconds, and thus as set out further herein, a rapid rate of change in counts per unit time, which can be discriminated by comparing counts in neighbouring capture intervals, may be indicative of the presence of an active interference component in detected radiation.

[0053] In embodiments, the analyser is configured to determine a time interval T during which radiation emitted by an interference radiation is detected, based on determination of an increased radiation count rate in the first radiation data. With reference to the example of Figure 4, the analyser is configured in embodiments of the present disclosure to determine a time interval by detecting time points at which characteristics of the radiation data change, indicating the activation and deactivation of an interference radiation source. Thus, in embodiments, the analyser is configured to monitor changes in counts between successive capture intervals (or aggregated capture intervals), and to determine if the rise in counts between successive capture intervals exceeds a predefined threshold. A suitable threshold may be determined on the basis of modelling or experimentation, for example. Where the predefined threshold of increased count rate between successive capture intervals is met, the analyser is configured to determine that a period of interference has started. It will be appreciated that a predefined threshold may operate not on the basis of a change between successive single capture intervals, but on the basis of a change between a first plurality of capture intervals (e.g. a binned capture interval comprising 2, 3, 4, 5, or more capture intervals) and a successive second plurality of capture intervals (e.g. a further binned capture interval comprising 2, 3, 4, 5, or more capture intervals). In the example of Figure 4, the analyser may determine an interference initiation time ti based on an above-threshold count rate change between the capture interval immediately preceding ti and the capture interval immediately following ti. Having determined the initiation of interference (i.e. at ti), the analyser is further configured to continue monitoring the radiation data to detect an above-threshold fall in counts between successive capture intervals, indicating that the interference radiation source has been deactivated, such that the radiation from the interference source is no longer contributing to the non-target components of the radiation data. Thus, when initiation of a period of interference has been detected by the analyser, the analyser is configured to monitor changes in counts between successive capture intervals (or aggregated capture intervals), and to determine if a fall in counts between successive capture intervals exceeds a predefined threshold. Where this condition is met, the analyser is configured to determine that the period of interference has ended. Thus, in the example of Figure 4, the analyser determines an interference end time t2based on the magnitude of the count rate change between the capture interval immediately preceding t2and the capture interval immediately following t2. Determination of times ti and t2leads to determination of an interference period Tj, via the simple expression Ti= t2- t-i. Continuous interference may be distinguished from pulsed interference (discussed further herein) on the basis of the period of time Tj for which interference is detected (i.e. the number of consecutive capture intervals n between interference initiation and interference end). The presence of continuous interference may optionally be corroborated by comparing a previously recorded background spectrum, generated from radiation data collected during a period free from interference, to a spectrum generated from radiation data collected during the interference period Tj, and determining via approaches known to the skilled person that there is a statistically significant variation between the recorded background spectrum and the spectrum derived for the suspected continuous interference period Tj. This comparison may be implemented by the analyser, or by classifier circuitry of the nuclear radiation monitoring circuitry as described further herein. This approach may be carried out for a particular region of the energy spectrum, and the characteristic energy range of the interference source may optionally be detected by determining what region(s) of the energy spectrum display the largest variation. By way of non-limiting examples, this approach may be applied in a spectral region corresponding to ‘low’ energies (e.g. energies lower than approximately 100 keV), or to a spectral region corresponding to ‘high’ energies (e g. energies higher than approximately 1 MeV), though it will be appreciated any range of energy may be selected in dependence on characteristic emission energy of interference radiation sources which may be of particular concern. Thus energy characteristics of the radiation data may be used in detecting interference.

[0054] It will be appreciated that the switch-on time for an interference X-ray source may be very short compared to the capture interval timescale. For the sake of providing a concrete but non-limiting example, the switch-on time for an interference X-ray source may in some circumstances be of the order of nanoseconds, whereas the capture interval of the radiation data may be of the order of microseconds or faster (e.g. prior to processing by the MCA) or milliseconds (e.g. subsequent to processing by the MCA), it being understood that these orders of magnitude are only illustrative, and capture intervals will in practice depend on the specific detector(s) and MCA / analyser used. What will be considered of relevance is that where the capture interval duration is of a greater order of magnitude than the switch on time, a capture interval within which the interference X-ray source switches on will comprise a pre-interference sub-interval and an intra-interference subinterval. The counts in a capture interval within which an interference radiation source switches on will therefore represent the average of non-interference-affected and interference-affected periods of the capture interval. Thus in embodiments, comparison may be made between capture intervals or aggregated capture intervals separated by a predefined number of capture intervals or aggregated capture intervals (e.g. one capture interval). Thus for a current capture interval n, the counts may be compared to the value for capture interval n-2, such that where switch-on of an interference source occurs in a capture interval n-1 , the comparison in counts will be between capture intervals preceding and following the capture interval within which the interference source was switched on. This comparison may be carried out on a rolling basis for each capture interval.

[0055] It will be further appreciated that since the on-time associated with continuous interference is typically one or more orders of magnitude higher than the millisecond-order capture intervals characteristic of radiation data temporally down-sampled by MCA circuitry, interference detection can be carried out on radiation data either before or after the temporal down-sampling typically applied by MCA circuitry prior to classification. Where the analyser of the present disclosure is configured for both continuous and pulsed interference characterisation, it may be advantageous to carry out detection of all interference on radiation data which has not been temporally down- sampled, given that it is typically advantageous to detect pulsed interference prior to temporal down-sampling of the radiation data, and performing all interference detection (pulsed and continuous) at the same point in the signal processing chain may be more computationally efficient.

[0056] Where the analyser determines that continuous interference is present in radiation data received from a first nuclear radiation detector, based on determining characteristics of the radiation data comprising a start and end time of interference (and thus also an intervening interference period Tj), the analyser may be configured to modify the first radiation data generated by the first nuclear radiation detector based on at least one of the determined characteristics, or to provide the determined characteristics to a module of the nuclear radiation monitoring circuitry which is downstream on the signal processing path (e.g. a classifier) so that said module can carry out the modification of the radiation data based on the determined characteristics. For example, an analyser comprised in front-end signal-processing circuitry may transmit information indicating one or more interference periods to an analyser or classifier of nuclear radiation monitoring circuitry to enable said analyser or classifier to carry out modification of the radiation data based on the detected interference characteristics. For example, in embodiments modification of the radiation data comprises application of a background subtraction approach to modify the radiation data in the period T; to mitigate the effect of the interference on the spectral characteristics of the radiation data, before the modified radiation data with the background subtracted is classified by the classifier for identification of at least one radioactive isotope comprised in a target object associated with the collection of the radiation data (where ‘background subtraction’ is here used to refer to the subtraction of all non-target components of the detected radiation).

[0057] Background subtraction may be performed by using a sample of the background nuclear radiation (e.g. a background neutron count and / or a background gamma-ray spectrum) collected when a target object is not in the vicinity of the nuclear radiation monitoring apparatus, which preferably includes an interference radiation component from the interference source. Thus, the ‘background’ data may comprise radiation data collected during a previous interference period in which no target object is under investigation (i.e. in an RPM context, the RPM is unoccupied). Such ‘background’ data, representative of the captured background nuclear radiation, is stored in a storage medium (e.g. storage medium 208 shown in Figure 3A). Nuclear radiation data captured during each capture interval may be processed by the classifier 203 to remove the background radiation component during spectral deconvolution and subsequent determination of spectral features, using approaches known to the skilled person ([3]).

[0058] Pulsed interference detection

[0059] In addition to or as an alternative to being configured to determine the presence of continuous interference in radiation data by analysing the radiation data to determine at least one characteristic of radiation emitted by the interference radiation source, the analyser may be configured to determine the presence of a pulsed interference source based on analysing the radiation data to determine at least one characteristic of radiation emitted by the interference radiation source. Characteristically, pulsed sources (e.g. X-ray sources) have very short on- pulses (e.g. ~5 ps), with a frequency typically in the range of 100 to 1000 Hz. However this range is only illustrative, and the approaches set out herein to mitigate the effects of pulsed interference may be applied to interference from pulsed sources with different characteristics (e.g. having longer or shorter pulse durations, and higher or lower ranges of frequency). In some X-ray sources, the pulse-length and I or the frequency of operation are fixed, at least for a given period of operation (e.g. corresponding to a discrete scan performed using a pulsed interference source such as an X-ray source of an X-ray scanner). In other X-ray sources, the frequency of pulses may vary (e.g. in dependence on a time-varying velocity at which a sample passes through an X- ray scanning apparatus). The inventors have recognised that detecting periodic interference characteristics indicating a pulsed interference source in the vicinity of the nuclear radiation detector can enable particular forms of mitigation of said periods of interference to be carried out. This may reduce the latency with which mitigation can be carried out, in the form of radiation data modification.

[0060] Thus, in embodiments, the analyser (i.e. comprised in front-end signal processing circuitry or nuclear radiation monitoring circuitry) is configured to analyse radiation data indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source, wherein the at least one characteristic of radiation emitted by the interference radiation source comprises a pulse frequency. Figure 5 schematically shows nuclear radiation data expressed in terms of counts with respect to time, as may be computed by an MCA integrated into the analyser. The radiation data schematically shown in Figure 5 is characteristic of data generated by a nuclear radiation detector in a context where a pulsed interference radiation source is contributing to the non-target component of the radiation data. Pulsed or periodic interference may result, for example, from an X-ray scanner in the vicinity of a nuclear radiation monitoring apparatus, which is configured to produce a pulsed beam of X-rays to support a specific form of imaging modality, such as for example an X-ray computed tomography imaging scheme, in which a plurality of two-dimensional radiographs of an object are obtained along varied angular projections.

[0061] Figure 5 shows schematically a natural variation of counts per capture interval in the radiation data in a first period Tn, in which there is no interference from an active radiation source different to a target object under investigation by the nuclear radiation monitoring apparatus. The degree of variation in the non-interference condition is influenced by fluctuations in passive non-target components, and variation in the intensity of any nuclear radiation detected from the target object under investigation, as the distance between the target object and detector varies during analysis (for example, as a vehicle drives past the detector in an RPM context as shown in Figure 1). At a time ti, an interference radiation source different to the target object under investigation is activated, and the interference radiation begins to be detected by the nuclear radiation detector of the nuclear radiation monitoring apparatus. In the example of Figure 5, the interference source comprises periodic pulses of fixed pulse length and frequency, and the response of the nuclear radiation detector to the incident interference radiation is shown in the characteristic peaks centred at pulse times tp,i to tPi5. Five pulses are shown for simplicity, but it will be appreciated the number of pulses will vary, and will depend on the control protocol used to control the interference radiation source. In embodiments, the analyser is configured to determine the pulse frequency by analysing the radiation data comprising a measure of detection event counts with respect to time. This may be achieved using peak fitting algorithms known to the skilled person. In embodiments, timings corresponding to maxima of amplitude are determined to correspond to pulse centre timings. Thus, for example, the analyser may perform numerical differentiation of the radiation data indicating total pulse counts with respect to time, and determine timings at which the sign of the first derivative of pulse counts with respect to time switches from positive to negative.

[0062] Once the analyser has determined the timings of at least two pulses (i.e. an initial pulse tp,i and a subsequent pulse tp,2), the periodicity Tmof the pulses can be determined, based, for example, on Tm= tp,2- tp,i. Based on an assumption that the pulse frequency is fixed, the analyser may be configured to estimate the positions in time of future pulses centred at tp,3 to tp,nbased on characteristics of past pulses. A fixed frequency may be assumed when the inter-pulse period is determined to be constant for three or more detected pulses. Thus based on a timing of a pulse peak detected at tp,n, the timing of the subsequent peak (tp,n+i) can be estimated as tp,n+Tm. The analyser may be configured to modify the radiation data generated by the first nuclear radiation detector based on detecting pulse characteristics, including estimating future interference pulse positions. An advantage of the estimation of future interference pulse peaks is to reduce the latency of radiation data modification, by enabling the analyser to determine in advance periods of time during which radiation data modification will need to be applied, and allow real-time modification of the radiation data. The detection of pulses, and estimation of future pulse times and temporal widths, may be carried out in MCA circuitry comprised in the analyser, and the modification of the radiation data may also be carried out in MCA circuitry of the analyser according to approaches described herein, or may be carried out downstream of the analyser in the signal processing chain (e.g. in classifier circuitry of nuclear radiation monitoring circuitry). Integrating the detection of pulses and modification of data into MCA circuitry of the analyser can further reduce latency, as can implementing the detection of pulses and modification of data using hardware control logic (e.g. using ASIC and I or FPGA circuit modules).

[0063] In an embodiment, the analyser is configured to modify the first radiation generated by a nuclear radiation detector by removing data for time periods determined and I or estimated to correspond to interference pulses. The analyser may, for example, be configured to determine a pulse width for at least one interference radiation pulse (e.g. the interference pulse centred on time tp,i in the example of Figure 5), and use the determined pulse width to determine the time period either side of each estimated or determined interference pulse peak over which radiation data modification should be applied. As with peak detection, determination by the analyser of a numerical derivative of count rate with respect to time may be used to identify the temporal extent of the tails either side of a maxima (e.g. the maxima of a first pulse at tp,i). Thus, the analyser may use a determined pulse width and estimation of future pulse timings (e.g. timings of maxima in count rate with respect to time) to modify the radiation data generated by a first nuclear radiation detector during periods corresponding to the determined pulse width, centred around an estimated future pulse peak. These periods may be referred to as modification periods. Three modification periods 501 , 502, and 503 are shown schematically in Figure 5. The modification of the radiation data may comprise removing count data during modification periods, so that modified radiation data passed to the classifier 204 (for example in the form of a spectrum) for identification of at least one radioactive isotope comprised in a target object associated with the radiation data, exhibits an eliminated or substantially reduced non-target component associated with radiation from an active interference source other than the target object. Alternatively, during modification periods, a ‘background subtraction’ approach may be used to modify the radiation data, as described further herein.

[0064] It will be appreciated that the analysis of radiation data to determine pulse frequency is preferably carried out prior to any temporal down-sampling by the MCA I analyser of the raw count data generated by the one or more detectors of the nuclear radiation monitoring apparatus. This provides the highest likelihood of determining pulses of short duration, by maximising the temporal resolution at which pulse detection is carried out. Thus the determination of pulse times and widths to provide modification periods is preferably carried out before any temporal downsampling of the raw radiation data by the MCA I analyser circuitry.

[0065] With reference to Figure 5, the analyser may be configured to generate separate spectra for interference period(s) and non-interference periods. For example, a first spectrum may be generated based on radiation data collected during periods of time coinciding with the occurrence one or more interference pulses (i.e. periods of time corresponding to the modification periods as described above), and a second spectrum may be generated based on radiation data collected during periods of time not coinciding with interference pulses (i.e. periods of time between modification periods). In some embodiments, the first spectrum, comprising interference components, may be discarded, and the second spectrum only passed on for further classification. Where the interference pulses are sufficiently short that the cumulative ‘on’ time is a relatively low proportion of the total measurement interval, this approach may be advantageous given the relatively small loss of data, and the avoidance of more computationally intensive processing approaches. In other embodiments, background subtraction as described further herein may be applied only during the determined modification periods, for example using one or more stored interference spectra. The analyser may advantageously carry out pulse detection, determination of modification periods, and modification of radiation data, prior to temporal downsampling of the radiation data by MCA circuitry of the analyser, and may accordingly buffer radiation data during pulse detection and determination of modification periods, prior to temporal down-sampling, to allow the modification of the data at the raw temporal resolution once the modification periods are determined. Once the radiation data have been modified, they may then be temporally down-sampled by the MCA prior to spectrum generation.

[0066] Sharing of radiation data between nuclear radiation monitoring apparatuses In embodiments, the radiation data indicating characteristics of an interference radiation source different to the target object further comprises second radiation data generated by at least one second radiation detector spatially separated from the nuclear radiation monitoring apparatus, wherein the classification circuitry is configured to analyse the second radiation data generated by the at least one second radiation detector to determine the at least one characteristic of radiation emitted by the interference radiation source. In these embodiments, the analyser is configured to determine at least one characteristic of radiation emitted by an interference radiation source, and modify first radiation data generated by a first nuclear radiation detector based on the determined at least one characteristic, as described above. However, the radiation data on which this analysis is performed comprises (i) radiation data generated by a first nuclear radiation detector of a first nuclear radiation monitoring apparatus with which the analyser is configured for use, and (ii) radiation data generated by a second nuclear radiation detector comprised in a second nuclear radiation monitoring apparatus spatially separated from the first nuclear radiation monitoring apparatus.

[0067] In embodiments, each of the first and second nuclear radiation monitoring apparatus may comprise RPMs situated in different spatial locations (such as, for example, on different lanes of a road at a border crossing or other point of entry). In embodiments, the first nuclear radiation monitoring apparatus comprises an RPM, and the second nuclear radiation monitoring apparatus comprises a mobile nuclear monitoring apparatus such as a handheld, backpack, or vehicle mounted apparatus as described further herein. In embodiments where second radiation data is received by the analyser of a first nuclear radiation monitoring apparatus from a nuclear radiation detector of a second nuclear radiation monitoring apparatus, the analyser is configured to receive the second radiation data from an analyser of the second nuclear radiation monitoring apparatus, which may typically be configured as for the analyser of the first nuclear radiation monitoring apparatus shown schematically in Figures 3A and 3C, and as described herein. Thus a communication interface of second nuclear radiation monitoring circuitry comprising an analyser may transmit the second radiation data, comprising for example total detector counts with respect to time for one or more nuclear radiation detectors of the second nuclear monitoring apparatus, to the communication interface of nuclear monitoring circuitry of the first nuclear monitoring apparatus, comprising an analyser.

[0068] The communication interfaces of the respective nuclear radiation monitoring circuitry of each nuclear radiation monitoring apparatus may be configured to communicate the radiation data over a wired connection using a wired communication protocol known in the art such as Ethernet. This may be preferable when the first and second nuclear radiation monitoring apparatus are fixed installations such as RPMs. However, in other circumstances, such as where one or both of the first and second nuclear radiation monitoring apparatuses are mobile devices, the communication interfaces of the respective nuclear radiation monitoring circuitry may be configured to communicate radiation data over a wireless connection using a wireless communication protocol known in the art. For example, the communications interfaces may communicate using protocols defined in the 5G 3GGP standard, such as ultra-reliable low-latency communication (URLLC). Communications interfaces of nuclear radiation monitoring circuitry respectively associated with a plurality of nuclear radiation monitoring apparatuses may communicate radiation data to one another in real or near-real time using URLLC. To facilitate security and reliable quality of service (QoS), the plurality of nuclear radiation monitoring apparatuses may be networked together using a non-public 5G network such as a standalone non-public network (SNPN) in which physically distinct radio resources, subscriber database, and dedicated hardware are used, which are separate to those used by public 5G networks. A SNPN facilitating URLCC communication between communications interfaces of respective nuclear radiation monitoring apparatuses may be set up to support a coverage area in which the nuclear radiation monitoring apparatuses are to be primarily used, such as a border crossing or other point of entry where a plurality of RPMs are situated, with support from mobile nuclear radiation monitoring apparatuses. In such contexts, each communications interface can be part of a restricted subscriber set, to provide enhanced security.

[0069] Thus in embodiments, a communications interface of first nuclear radiation monitoring circuitry associated with a first nuclear radiation monitoring apparatus may be configured to receive in real or near-real time second radiation data generated by at least one second radiation detector comprised in at least one second radiation monitoring apparatus spatially separated from the first nuclear radiation monitoring apparatus. This second radiation data is passed from the communications interface to the analyser, which in some embodiments is configured to combine the second radiation data with the first radiation data (e.g. by summing the count rates with respect to time from first and second radiation data). The analysis of radiation data to determine at least one characteristic of radiation emitted by the interference radiation source may thus be carried out according to approaches described above (e.g. for continuous and I or pulsed interference determination) on third radiation data which is a combination of the first and second radiation data. In embodiments, the communications interface will be configured to receive timing synchronisation data to enable clocks associated with circuitry of the first and second radiation monitoring apparatuses to be synchronised, facilitating the alignment of capture intervals in radiation data acquired by the different radiation monitoring apparatuses.

[0070] Alternatively, the analyser of the nuclear radiation monitoring circuitry may separately analyse the first radiation data and second radiation data to determine at least one characteristic of radiation emitted by the interference radiation source, as described above, using discrete channels to perform the analysis. Where the first and second data are separately analysed, determined characteristics of the interference radiation source, such as the interference initiation time ti and period T; in a continuous interference scenario, and the pulse maxima timings and pulse widths, in a pulsed interference scenario, can be combined by the analyser (such as by averaging) before being used to modify the first radiation data generated by the first nuclear radiation detector as described herein.

[0071] The use of radiation data from multiple nuclear radiation monitoring apparatuses to determine characteristics of radiation emitted by an interference radiation source can advantageously improve the accuracy of detection of the interference radiation source, and / or improve the reliability with which radiation from interference radiation sources (for example active interference sources such as X-ray sources) can be detected and characterised, when compared to detection and characterisation of interference radiation using radiation data generated by the nuclear radiation detectors of a single nuclear radiation monitoring apparatus alone. Thus, in embodiments, regardless of whether an interference radiation source location is estimated by the analyser of a first nuclear radiation monitoring apparatus, the analyser is configured to use second radiation data received from a spatially separated second nuclear radiation monitoring apparatus to provide confirmation that what is detected as interference in first radiation data by the analyser is indeed interference, and not a detection artefact associated with characteristics of one or more nuclear radiation detectors of the first nuclear radiation monitoring apparatus, or is in fact the result of radiation received from a target object (e.g. a vehicle and / or cargo) with which acquisition of the first radiation data is associated. Thus with reference to the ‘continuous’ interference detection approach described in association with Figure 4, in embodiments the analyser may be configured to determine an interference period (Ti) for each of the first radiation data and the second radiation data. With reference to the ‘periodic I pulsed’ interference detection approach described in association with Figure 5, in embodiments the analyser may be configured to determine an interference pulse timing (e.g. tp,i) and pulse width for each of the first radiation data and the second radiation data. The analyser of the first nuclear radiation monitoring apparatus (i.e. a first RPM), having detected a period of continuous interference (Ti) or one or more pulses of interference, in first radiation data, may be triggered by this determination to check whether a corresponding period of continuous interference (Ti) or one or more corresponding pulses of interference (i.e. having the same maxima timing(s) and I or pulse width(s)) are present in second radiation data from a spatially separated second nuclear radiation monitoring apparatus (i.e. a second RPM), and optionally from a third spatially separated nuclear radiation monitoring apparatus (i.e. a mobile nuclear radiation monitoring apparatus). It will be appreciated this principle can be generalised to any number of further spatially separated nuclear radiation monitoring apparatuses. Where the same period of continuous interference T; is determined to be present in a plurality of instances of radiation data generated from different detectors of spatially separated nuclear radiation monitoring apparatuses, or where the same pulse maxima timings and I or pulse shapes are determined to be present in a plurality of instances of radiation data generated from different detectors of spatially separated nuclear radiation monitoring apparatuses, a higher degree of confidence may be assigned to the determination that the characteristics of interference radiation determined to be present in the first radiation data are indeed from an interference radiation source, and not from, for example, detector artefacts, or radioactive material present in a target object with which the first radiation data is associated.

[0072] It will be appreciated this approach of corroborating the presence of a period of continuous interference (Ti) and I or pulses of periodic interference, may be applied using radiation data obtained from any number of networked nuclear radiation monitoring apparatuses. The analyser of a given nuclear radiation monitoring apparatus in such a network may limit the comparison of radiation data from different spatially separated nuclear radiation monitoring apparatuses to neighbouring apparatuses which are within a certain threshold of distance.

[0073] Location estimation of interference radiation sources

[0074] In embodiments of the present disclosure, the circuitry is configured to determine information indicative of a relative position of the interference radiation source to the radiation monitoring apparatus based on analysing the first and second radiation data. Figure 6 shows schematically a plan view of an area 500, which may correspond, for example, to part of a border crossing or point of entry, or other location where the application of nuclear radiation monitoring for security and / or safety purposes is employed. Within the area 500 are at least two nuclear radiation monitoring apparatuses, each comprising at least one gamma-ray and I or neutron detector as described further herein, and each comprising nuclear radiation monitoring circuitry for processing, analysis, classification, and I or communication of radiation data generated by the at least one gamma-ray and I or neutron detector. The skilled person will appreciate any of these nuclear radiation monitoring apparatuses can be configured as described herein in respect of an RPM or mobile nuclear radiation monitoring apparatus. Thus the example of Figure 6 shows two spatially separated RPMs 510 and 520, which are configured as described herein for the RPM of Figure 1. Figure 6 further shows by way of example a mobile nuclear radiation monitoring apparatus 530, which may comprise a handheld, backpack, or vehicle mounted device as described further herein. Each of a first RPM 510, second RPM 520, and mobile nuclear radiation monitoring device 530, comprises nuclear radiation monitoring circuitry as described herein, comprising at least a communication interface, a controller and a storage medium as described herein, and may optionally comprise a classifier, a visualisation data generator, and a display output as described herein. The nuclear radiation monitoring circuitry may comprise analyser circuitry, or the analyser circuitry may be comprised in front-end signal processing circuitry situated upstream of the nuclear radiation monitoring circuitry in the signal chain. The respective communication interfaces of the nuclear radiation monitoring circuitry (or front-end signal processing circuitry) associated with each of first RPM 510, second RPM 520, and mobile nuclear radiation monitoring device 530, are configured to communicate radiation data between each other, using wired or wireless communication standards as described further herein. Thus in one embodiment, the respective communication interfaces of the nuclear radiation monitoring circuitry (or front-end signal processing circuitry) associated with each of first RPM 510, second RPM 520, and mobile nuclear radiation monitoring device 530, may communicate using URLLC communications protocols supported by the 3GPP 5G standard, and may be subscribers to a standalone non-public network (SNPN) covering the area 500. The respective communication interfaces associated with each of first RPM 510, second RPM 520, and mobile nuclear radiation monitoring device 530, may support more than one communication protocol, such that, for example, the respective communication interfaces associated with each of first RPM 510 and second RPM 520 (i.e. the fixed nuclear radiation monitoring apparatuses) may communicate with each other over a wired connection (e.g. an Ethernet connection), and respective communication interfaces associated with each of the first RPM 510 and second RPM 520 may communicate with the communication interface associated with the mobile nuclear radiation monitoring apparatus 530 via a wireless protocol (e.g. Bluetooth or 5G). What is significant is that the nuclear radiation monitoring circuitry (or front-end signal processing circuitry) associated with one of the nuclear radiation monitoring apparatuses is configured to receive radiation data from the nuclear radiation monitoring circuitry (or front-end signal processing circuitry) of at least one further nuclear radiation monitoring apparatus. In some embodiments, only one of a plurality of nuclear radiation monitoring apparatuses receives radiation data from at least one other nuclear radiation monitoring apparatus (e.g. RPM 510 may receive radiation data uni-directionally from each of RPM 520 and mobile nuclear radiation monitoring apparatus 530). In other embodiments, each nuclear radiation monitoring apparatus may transmit radiation data to each of the other nuclear radiation monitoring apparatuses, and receive radiation data from each of the other nuclear radiation monitoring apparatuses (e.g. RPM 510 may transmit radiation data to and receive radiation data from each of RPM 520 and mobile nuclear radiation monitoring apparatus 530, RPM 520 may transmit radiation data to and receive radiation data from each of RPM 510 and mobile nuclear radiation monitoring apparatus 530, and nuclear radiation monitoring apparatus 530 may transmit radiation data to and receive radiation data from each of RPM 510 and RPM 520).

[0075] In embodiments of the present disclosure, circuitry of a first one of a plurality of nuclear radiation monitoring apparatuses, forming a set of networked nuclear radiation monitoring apparatuses, is configured to determine information indicative of an absolute position of an interference radiation source, or a relative position of an interference radiation source with respect to two or more of the plurality of radiation monitoring apparatuses, based on analysing first radiation data generated by a detector of the first radiation monitoring apparatus, and analysing second radiation data generated by a detector of a second radiation monitoring apparatus, the second radiation data being radiation data transmitted to the nuclear radiation monitoring circuitry of the first nuclear radiation monitoring apparatus from nuclear radiation monitoring circuitry of a further at least one of the plurality of nuclear radiation monitoring apparatuses comprised in the network.

[0076] Thus, for example, in the example of Figure 6, circuitry (e.g. analyser circuitry) associated with first RPM 510 is configured to receive first radiation data from a detector of the first RPM 510, according to approaches described herein. The circuitry is further configured to receive second radiation data generated by a detector of the second RPM 520, with this second radiation data being received based on a communication interface of the second RPM 520 transmitting the second radiation data to the communication interface of the first RPM 510 according to wired or wireless communication protocols described herein. The communication interface of the first RPM 510 transmits the received radiation data to circuitry (e.g. analyser circuitry) of the nuclear radiation monitoring circuitry of the first RPM 510. Thus the circuitry of the first RPM 510 is configured to receive first and second radiation data, where the first radiation data is generated by a nuclear radiation detector of the first RPM 510, and the second radiation data is generated by a nuclear radiation detector of the second, spatially separated, RPM 520. Optionally, the circuitry of the first RPM may be further configured to receive third radiation data generated by a nuclear radiation detector of mobile nuclear radiation monitoring apparatus 530 in the same manner. It will be appreciated that radiation data may be received from any number of spatially separated nuclear radiation monitoring apparatuses which are connected to the first nuclear radiation monitoring apparatus (i.e. RPM 510), according to wired or wireless data transmission protocols described further herein.

[0077] Figure 6 schematically shows an interference radiation source 540 in the area 500 in which the first RPM 510, second RPM 520, and mobile nuclear radiation monitoring apparatus 530. The radiation emission characteristics and spatial separation of the interference radiation source from each of first RPM 510, second RPM 520, and mobile nuclear radiation monitoring apparatus 530, are such that the interference radiation forms a non-target radiation component of each of first radiation data generated by the first RPM 510, second radiation data generated by the second RPM 520, and third radiation data generated by the mobile nuclear radiation monitoring apparatus 530. Since the intensity of radiation with distance from the interference radiation source 540 decreases with distance from the interference radiation source 540 (i.e. typically according to an inverse square law in free space), determination of intensity characteristics of detected interference radiation in the first radiation data and the second radiation data can provide information about the absolute or relative distance of the interference radiation source 540 from each of the first RPM 510 and second RPM 520, and comparison of these characteristics, or determined distances, allows the position of the interference radiation source 540 to be triangulated.

[0078] The determination of the estimated distance of the interference radiation source 540 from each of the first RPM 510, second RPM 520, and mobile nuclear radiation monitoring apparatus 530, may be achieved by circuitry of the first RPM 510 in a number of different ways. Thus in an embodiment, the analyser of the nuclear radiation monitoring circuitry of the first nuclear radiation monitoring apparatus (i.e. RPM 510) is configured to analyse each of the first radiation data and second radiation data to determine at least one period of interference in each of the first and second radiation data (noting this approach is extendable to any number of instances of radiation data acquired from ones of a plurality of nuclear radiation monitoring apparatuses). For example, with reference to the ‘continuous’ interference detection approach described in association with Figure 4, an interference period T, may be determined for each of the first radiation data and the second radiation data. The estimated position of the interference radiation source may be determined based on characteristics of the first and second radiation data respectively during an interference period Tj according to the following approach.

[0079] It is assumed that the spatial position of each of the plurality of nuclear radiation monitoring apparatuses (e.g. first RPM 510, second RPM 520, and mobile nuclear radiation monitoring apparatus 530, in the exemplary context of Figure 6) is known at the analyser, for example by user input of such information, or transmission of such information to the analyser by each one of the plurality of nuclear radiation monitoring apparatuses. The analyser is configured to triangulate the position of the interference source using the inverse square law of signal attenuation, using approaches known to the skilled person, by converting a measure of interference radiation intensity sensed at each nuclear radiation monitoring apparatus to a measure of approximate distance of the interference radiation source from each nuclear radiation monitoring apparatus. The measure of interference radiation intensity sensed at each one of the plurality of nuclear radiation monitoring apparatuses may in embodiments be the total count rate for one or more capture intervals in which interference is determined to be present (e.g. one or more capture intervals during a period Tj of continuous interference, or during a modification period representative of an interference pulse). In embodiments, the interference component may be extracted from other components (e.g. background and noise components) using background subtraction approaches described herein, and the extracted interference component alone can thus be used to determine a measure of distance of the interference radiation source from each nuclear radiation monitoring apparatus. The latter approach may increase the accuracy with which distance can be approximated. Where the measure of interference radiation intensity is derived from a period of continuous interference in radiation data, capture intervals immediately following detected switch-on of the interference source may be used to provide the measure of interference radiation intensity, to minimise the influence of any foreground radiation source (e g. from a target object) on the measure.

[0080] Thus a distance d1 of the interference radiation source 540 from the first nuclear radiation monitoring apparatus (i.e. RPM 510) may be approximated, and a distance d2 of the interference radiation source 540 from the second nuclear radiation monitoring apparatus (i.e. RPM 520) may be approximated, both by the analyser of the first nuclear radiation monitoring apparatus. Optionally, a distance d3 of the interference radiation source 540 from the third nuclear radiation monitoring apparatus (i.e. RPM 530) may be approximated by the analyser of the first nuclear radiation monitoring apparatus. Estimation of the position of the interference radiation source can then be conducted by the analyser based on determining the intersections between an arc of radius d1 centred on a suitable point within the first nuclear radiation monitoring apparatus 510, of an arc of radius d2 centred on a suitable point within the second nuclear radiation monitoring apparatus 520, and optionally of an arc of radius d3 centred on a suitable point within the third nuclear radiation monitoring apparatus 530. A suitable point will typically be a centre of mass or volume of a detector of each respective nuclear radiation monitoring apparatus.

[0081] In addition to or as an alternative to being configured to estimate a relative position of an interference radiation source based on first radiation data and second radiation data generated by detectors of respective spatially-separated first and second nuclear radiation monitoring apparatuses, the analyser 203 of the first nuclear radiation monitoring apparatus may be configured to detect whether or not a position of an interference radiation source to a radiation monitoring apparatus is fixed. Figure 7 will be recognised from Figure 6, and shows the same arrangement of first nuclear radiation monitoring apparatus (i.e. RPM 510), second nuclear radiation monitoring apparatus (i.e. RPM 520), and optional third nuclear radiation monitoring apparatus (i.e. mobile apparatus 510), with the difference that the position of the interference radiation source 540 has changed relative to each of the nuclear radiation monitoring apparatuses. In embodiments of the present disclosure, the analyser of the first radiation monitoring apparatus is configured to periodically estimate the relative or absolute position of the interference radiation source according to one of the approaches set out above. For example, every time radiation from an interference radiation source is detected by the analyser according to analysis approaches set out herein, the analyser may be configured to calculate an updated estimate of the relative or absolute position of the interference radiation source, and compare this with a stored position previously calculated during a previous period of interference at an earlier point in time. More simply, suspected movement of the interference radiation source may be identified by the analyser detecting an above threshold change in the relative intensity of the interference radiation component between instances of radiation data received from different nuclear radiation monitoring apparatuses (where the threshold is set to allow for natural background variation and the influence of noise), and / or by determining an above threshold change in another characteristic such as an energy characteristic. A determination that the interference radiation source appears to have moved may be used to raise an alert to a user of the nuclear radiation monitoring apparatus, and I or to prompt an update in a ‘background subtraction’ approach used to mitigate the influence of interference radiation on the classification of first radiation to identify radioactive isotopes, according to approaches described herein.

[0082] Where the analyser determines there has been a change in the estimated absolute or relative position of the interference radiation source has changed between a first time taand a second time tb, the analyser may be further configured to determine an estimated velocity of the interference radiation source 530. This may be calculated by the analyser on the basis of subtracting coordinates representing the estimated position at time tafrom coordinates representing the estimated position at time tb. The estimated direction of travel and estimated magnitude of velocity of the interference radiation source may be reported to a user of the first nuclear radiation monitoring apparatus. This may enable the interference radiation source to be intercepted and investigated to determine if it is a threat.

[0083] Classification of isotopes from modified radiation data

[0084] Once the radiation data have been modified as set out above, to remove or reduce the influence of interference components, the classification of the modified radiation data to identify isotopes of interest in a target object under investigation by the nuclear radiation monitoring apparatus may be carried out using approaches known to the skilled person, such as those described in[4] or [5], which are not repeated here for the sake of brevity. More generally, it will be appreciated the subsequent classification of radiation data after it has been modified based on detected interference characteristics, is not of particular significance to the interference detection approaches set out herein, and accordingly any radiation data classification approach known to the skilled person may be applied to the modified radiation data.

[0085] In so far as embodiments of the disclosure have been described as being implemented, at least in part, by software-controlled data processing apparatus, it will be appreciated that a non- transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure.

[0086] It will be appreciated that the above description for clarity has described embodiments with reference to different functional units, circuitry and / or processors. However, it will be apparent that any suitable distribution of functionality between different functional units, circuitry and / or processors may be used without detracting from the embodiments. Described embodiments may be implemented in any suitable form including hardware, software, firmware or any combination of these. Described embodiments may optionally be implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of any embodiment may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the disclosed embodiments may be implemented in a single unit or may be physically and functionally distributed between different units, circuitry and / or processors.

[0087] Although the present disclosure has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in any manner suitable to implement the technique.

[0088] Figure 8 is flow chart schematically showing steps of a method according to the present disclosure, to be implemented by control logic of a nuclear radiation monitoring apparatus, wherein the method comprises a step S1 of receiving first radiation data generated by a first nuclear radiation detector of a first nuclear radiation monitoring apparatus, the radiation data being indicative of nuclear radiation emitted from a target object and detected by the first nuclear radiation detector; a step S2 of receiving radiation data indicating characteristics of an interference radiation source different to the target object; a step S3 of analysing the radiation data indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source; a step S4 of modifying the first radiation data generated by the first nuclear radiation detector based on the determined at least one characteristic to obtain modified first radiation data; and a step S5 of classifying the nuclear radiation using the modified first radiation data to identify at least one radioactive isotope comprised in the target object.

[0089] REFERENCES

[0090] [1] GB patent GB 2463707

[0091] [2] GB patent GB 2504771

[0092] [3] EP patent EP3715914

[0093] [4] EP patent EP3637150

[0094] [5] GB patent GB 2445578

Claims

CLAIMS1. Circuitry for a first nuclear radiation monitoring apparatus, the circuitry comprising control logic configured to; receive first radiation data generated by a first nuclear radiation detector of the first nuclear radiation monitoring apparatus, the radiation data being indicative of nuclear radiation emitted from a target object and detected by the first nuclear radiation detector; wherein the control logic is further configured to: receive radiation data indicating characteristics of an interference radiation source different to the target object; analyse the radiation data indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source; modify the first radiation data generated by the first nuclear radiation detector based on the determined at least one characteristic to obtain modified first radiation data; and classify the nuclear radiation using the modified first radiation data to identify at least one radioactive isotope comprised in the target object.

2. The circuitry of claim 1 , wherein the radiation data indicating characteristics of an interference radiation source different to the target object comprises the first radiation data generated by the first nuclear radiation detector, and wherein the circuitry is configured to analyse the first radiation data to determine the at least one characteristic of radiation emitted by the interference radiation source.

3. The circuitry of any preceding claim, wherein the radiation data indicating characteristics of an interference radiation source different to the target object comprises second radiation data generated by at least one second radiation detector spatially separated from the first nuclear radiation detector, and wherein the circuitry is configured to analyse the second radiation data generated by the at least one second radiation detector to determine the at least one characteristic of radiation emitted by the interference radiation source.

4. The circuitry of claim 3, wherein the at least one second radiation detector is comprised in at least one second radiation monitoring apparatus spatially separated from the first nuclear radiation monitoring apparatus.

5. The circuitry of any of claims 3 or 4, wherein the at least one second radiation detector comprises a nuclear radiation detector.

6. The circuitry of any of claims 2 to 5, wherein the at least one characteristic of radiation emitted by the interference radiation source comprises a time interval during which the radiation is detected.

7. The circuitry of claim 6, wherein the circuitry is configured to determine the time interval during which the radiation emitted by the interference radiation is detected based on determination of a period of increased radiation count rate in first and / or second radiation data.

8. The circuitry of claim 7, wherein the radiation count rate comprises a total count rate for all energies detected by the first and / or second nuclear radiation detector, with respect to capture intervals of fixed temporal width.

9. The circuitry of any of claims 6 to 8, wherein the circuitry is configured to modify the first radiation data generated by the first nuclear radiation detector by applying a background subtraction algorithm to portions of the first radiation data generated during at least one time interval during which radiation from the interference radiation source is detected.

10. The circuitry of any of claims 2 to 9, wherein the radiation data comprises a count rate of energies detected by the first and / or second nuclear radiation detector, with respect to capture intervals of fixed temporal width, and wherein the at least one characteristic of radiation emitted by the interference radiation source comprises a pulse frequency.

11. The circuitry of any of claims 2 to 10, wherein the radiation data comprises a count rate of energies detected by the first and / or second nuclear radiation detector, with respect to capture intervals of fixed temporal width, and wherein the at least one characteristic of radiation emitted by the interference radiation source comprises a pulse amplitude.

12. The circuitry of any of claims any of claims 2 to 11 , wherein the radiation data comprises a count rate of energies detected by the first and / or second nuclear radiation detector, with respect to capture intervals of fixed temporal width, and wherein the at least one characteristic of radiation emitted by the interference radiation source comprises a pulse shape.

13. The circuitry of any of claims 2 to 12, wherein the radiation data comprises a count rate of energies detected by the first and / or second nuclear radiation detector, with respect to capture intervals of fixed temporal width, and wherein the at least one characteristic of radiation emitted by the interference radiation source comprises a pulse duration.

14. The circuitry of any of claims 2 to 13, wherein the radiation data comprises a count rate of energies detected by the first and / or second nuclear radiation detector, with respect to capture intervals of fixed temporal width, and wherein the at least one characteristic of radiation emitted by the interference radiation source comprises an energy characteristic.

15. The circuitry of any of claims 10 to 14, wherein the circuitry is configured to modify the first radiation data generated by the first nuclear radiation detector by removing from the radiation data portions generated during at least one time interval corresponding to a determined interference pulse .

16. The circuitry of any of claims 10 to 14, wherein the circuitry is configured to modify the first radiation data generated by the first nuclear radiation detector by applying a background subtraction algorithm to portions of the first radiation data generated during at least one time interval corresponding to a determined interference pulse.

17. The circuitry of any of claims 15 to 16, wherein the at least one time interval is estimated in advance based on at least the pulse frequency.

18. The circuitry of any of claims 3 to 17, wherein the circuitry is configured to determine information indicative of an estimated spatial position of the interference radiation source based on analysing the first and second radiation data.

19. The circuitry of claim 18, wherein the circuitry is configured to determine the spatial position of the interference radiation source is not fixed.

20. The circuitry of claim 19, further configured to trigger an indication to a user based on determining the spatial position of the interference radiation source to the radiation monitoring apparatus is not fixed21. The circuitry of any preceding claim, wherein the circuitry is configured to classify the modified first radiation data by: (a) determining a nuclear radiation spectrum from the modified first radiation data; (b) identifying at least one peak in the nuclear radiation spectrum; (c) identifying a radioactive isotope comprised in the target object based on the at least one identified peak.

22. The circuitry of any preceding claim, wherein the interference radiation source comprises an X-ray source, and the circuitry is configured to determine at least one characteristic of X-ray radiation emitted by the interference radiation source.

23. The circuitry of claim 22, wherein the X-ray radiation has an emission energy of below 9 MeV.

24. The circuitry of any preceding claim, wherein the control logic is implemented as an application specific integrated circuit or field programmable gate array.

25. A system comprising a first nuclear radiation monitoring apparatus comprising a first nuclear radiation detector, the system further comprising the circuitry of any preceding claim.

26. A nuclear radiation monitoring method comprising: receiving first radiation data generated by a first nuclear radiation detector of a first nuclear radiation monitoring apparatus, the radiation data being indicative of nuclear radiation emitted from a target object and detected by the first nuclear radiation detector; receiving radiation data indicating characteristics of an interference radiation source different to the target object; analysing the radiation data indicating characteristics of the interference radiation source to determine at least one characteristic of radiation emitted by the interference radiation source; modifying the first radiation data generated by the first nuclear radiation detector based on the determined at least one characteristic to obtain modified first radiation data; and classifying the nuclear radiation using the modified first radiation data to identify at least one radioactive isotope comprised in the target object.

27. A program for controlling a computer to perform a method according to claim 26.

28. A recording medium storing a program according to claim 27.

Images