Improvements in Gamma-Activation Analysis Measurement

Abstract

A method and system for determining the concentration of one or more target elements in a sample using gamma activation analysis are disclosed, comprising: simultaneously irradiating the sample and a reference material containing at least two reference elements with X-rays; detecting deactivating gamma rays from the irradiated sample and the irradiated reference material; and determining the concentration of the target element or each target element in the sample by correcting the number of detected deactivating gamma rays from the at least two reference elements for the number of detected deactivating gamma rays present in the irradiated sample, wherein the at least two reference elements have variations in activation rate within predetermined X-ray endpoint energy ranges that are different from each other.

Description

Technical Field

[0001] This invention generally relates to improvements in gamma-activation analysis measurements, and more particularly to the use of gamma-activation analysis to measure the composition of unknown samples. Background Technology

[0002] Gamma-activation analysis (GAA), also known as photon activation analysis, is a technique for determining the concentration of certain target elements in a sample. GAA uses high-energy X-rays generated by an X-ray source to irradiate the sample, typically in the energy range of 6 MeV to 15 MeV or higher. The X-rays induce changes in some nuclei of the target element, which can lead to the formation of radioactive isotopes.

[0003] After a period of irradiation, the sample is transferred from the X-ray source to a detector system. The induced radioactive isotopes in the sample decay with characteristic half-lives and emit gamma rays with one or more characteristic energies. A suitable gamma-ray detector system counts the gamma rays emitted from the sample and measures their energies. The number of gamma rays emitted from the target element is proportional to the amount of that element in the sample.

[0004] The ratio constant between gamma-ray emission intensity and elemental mass depends on many factors; importantly, these include the intensity and energy spectrum of the X-rays emitted from the X-ray source.

[0005] Industrial gamma activation analysis is conveniently performed using X-ray sources, which include electron accelerators equipped with bremsstrahlung targets that convert a portion of the electron energy into X-rays. X-rays have a broad energy spectrum ranging up to the maximum electron beam energy, known as the endpoint energy. Electron accelerators are typically linear accelerators (LINACs), a widely used technique capable of generating high-intensity beams. For cost and compactness reasons, industrial LINAC sources typically do not include devices for stabilizing or monochromating the electron beam energy, such as magnetic separation. Therefore, such sources typically exhibit significant fluctuations in the intensity or energy of the electron beam, resulting in variations in the intensity and energy of the emitted X-ray beam. These variations can be caused by temperature changes in the accelerator, temperature changes in components within the power supply, or variations in the power supply voltage, and can be considered effectively random.

[0006] WO2015089580 describes a method for analyzing gold, which involves simultaneously irradiating and measuring a sample and a reference material containing a known amount of elemental bromine. The inventors determined that the activation of gold and bromine closely tracks each other over a wide energy range as the X-ray beam intensity or energy varies. Therefore, the standardization of the gold activation signal using the bromine activation signal provides a significant improvement in measurement accuracy.

[0007] Yagi and Masumoto ("A New Internal Reference Method for Activation Analysis and its Application", J. Radioanalytical and Nucl. Chem. 1984, 84(2), pp369-380) describe a method for analyzing target elements in an unknown sample by: first, adding a certain amount of a second element (reference element) to the unknown sample; second, irradiating the unknown sample and a second sample containing known amounts of the target and reference elements under the same activation conditions; and third, calculating the concentration of the target element in the unknown sample based on the ratio of the gamma ray intensities emitted by the target and reference elements from the unknown and second samples, and the known concentrations of these elements in the second sample. If the activation conditions (e.g., the energy of the X-ray beam) do not change between the two measurements, this method allows for precise determination of the concentration of the target element in the unknown sample.

[0008] Neutron activation analysis (GAA) is a related analytical method in which the formation of radioactive isotopes of a target element in a sample is induced by an incident neutron beam; similar considerations for correcting for neutron intensity or energy variations apply to GAA. In GAA, it has been previously proposed to simultaneously irradiate a sample and a reference containing the same target element. The sample and reference are then measured separately, and the relative intensities of gamma-ray emission for each element are compared to determine the concentration of each target element in the sample relative to a known concentration in the reference.

[0009] However, this method requires distinguishing gamma rays of the same energy emitted by the same elements in the sample and reference. Solutions include using separate detector systems to measure the sample and reference, measuring them sequentially in time, or using detector systems capable of resolving both the energy and origin position of gamma rays. These considerations increase the cost or complexity of the detector system, or reduce the rate at which samples can be analyzed. Therefore, they are not considered ideal for industrial analytical systems that require simplicity, low cost, and high throughput.

[0010] Any references or discussions of any document, action, or knowledge item in this specification are included solely for the purpose of providing context for the invention. No such references or discussions are recommended or implied as being part of common general knowledge or known at the priority date to be related to any attempt to resolve any problem addressed in this specification, or any combination thereof. Summary of the Invention

[0011] This invention relies on the simultaneous irradiation of an unknown sample and a reference material comprising two or more reference elements. The reference elements are selected from various considerations such that their sensitivities to changes in X-ray beam energy differ from one another. Based on these different responses, the response of a pseudo-element can be reconstructed to track the response of the target element in the sample.

[0012] In particular, the activation rate of one or more target elements in an unknown sample can be estimated by simultaneously irradiating and measuring the sample and a reference material containing two or more reference elements, which in turn allows the concentration of the target element or each target element to be calculated.

[0013] Therefore, one aspect of the present invention provides a method for determining the concentration of one or more target elements in a sample, the method comprising:

[0014] i. Simultaneously irradiate the sample and a reference material containing at least two reference elements with bremsstrahlung X-rays, such that activated nuclei are generated in any one or at least some of the target elements present in the sample, and activated nuclei are generated in the at least two reference elements;

[0015] ii. Detection of deactivated gamma rays from irradiated samples and irradiated reference materials;

[0016] iii. Determine the number of detected deactivated gamma rays from any one or each of the target elements present in the irradiated sample and the at least two reference elements;

[0017] iv. Determine the concentration of the target element or each target element in the sample, including correcting for the number of detected deactivated gamma rays present in the irradiated sample due to variations in the bremsstrahlung X-rays, based on the number of detected deactivated gamma rays from the at least two reference elements.

[0018] The at least two reference elements have variations in activation rates across different predefined X-ray endpoint energy ranges.

[0019] In one embodiment, at least one reference element exhibits a change in activation rate over a predefined X-ray endpoint energy range, the change being less than 3% different from the change of the target element or each target element.

[0020] In one embodiment, at least one reference element exhibits a change in activation rate over a predefined X-ray endpoint energy range, the change being greater than 20% different from the change of the target element or each target element.

[0021] In one embodiment, at least one of the reference elements exhibits a change in activation rate over the predefined X-ray endpoint energy range, the change being more than 20% different from the change in activation rate of the other reference element.

[0022] In one embodiment, at least two reference elements exhibit less activation rate variation than the target element or each target element over a predefined X-ray endpoint energy range.

[0023] In one embodiment, at least two reference elements exhibit greater activation rate variations over a predefined X-ray endpoint energy range than the target element or the activation rate variations of each target element.

[0024] In one embodiment, the activated nuclei of at least two reference elements exhibit a half-life of 1 second to 10 minutes, preferably less than 2 minutes.

[0025] In one embodiment, the activated nuclei of at least two reference elements emit one or more gamma rays with energies of 40 keV or higher, with a decay probability of 1% or greater per decay.

[0026] In one embodiment, the energy of the gamma rays emitted by the activated nucleus does not interfere with the measurement of gamma rays emitted by the target element or each target element.

[0027] In one embodiment, the energy of the gamma rays emitted by the activated nucleus does not interfere with the measurement of gamma rays emitted by any other element present in the sample.

[0028] In one embodiment, the target element and at least two reference elements have an X-ray induced activation reaction with a threshold energy below 15 MeV.

[0029] In one embodiment, at least two reference elements are activated nuclei produced by isotopes with a natural abundance of more than 90%, preferably more than 99%.

[0030] In one embodiment, if at least two reference elements are present in the sample, their mass in the sample should be less than 10% of the mass of the corresponding reference element in the reference material, preferably less than 1%.

[0031] In one embodiment, determining the concentration of the target element or each target element includes the following steps:

[0032] a. Calculate the time-corrected activation rate for each target element and the at least two reference elements;

[0033] b. Determine the target element signal value of the target element based on the ratio of the time-corrected activation rate of the target element to the time-corrected activation rate of the reference element.

[0034] c. To generate an attenuation-corrected signal value by applying an attenuation factor to correct the attenuation of incident X-rays and gamma rays of said or each target element in the sample; and

[0035] d. Multiply the signal value corrected by the attenuation factor by the normalization constant.

[0036] In one embodiment, the attenuation coefficient is experimentally determined by measuring gamma-ray signals from samples of different masses containing a target element of known concentration or by calculating using an readily available gamma-ray attenuation coefficient.

[0037] In one embodiment, the normalization constant is experimentally determined by comparing the attenuation factor-corrected signal value with the known mass value of the target element in a plurality of samples. Preferably, the normalization constant is the slope of the trend line of a curve of the attenuated signal versus the target element mass.

[0038] In one embodiment, there are two reference elements, and the target element signal value is ,in, , and These are the time-corrected activation rates of the target element, the first (main) reference element, and the second reference element, respectively, and among them... It is the ratio determined by experiment. with ratio Related functions.

[0039] In one embodiment, the function The following experimental results were obtained.

[0040] a. Simultaneously irradiate a sample containing a known amount of a target element and a reference material containing the first reference element and the second reference element with bremsstrahlung X-rays having a specific endpoint energy;

[0041] b. Detect deactivated gamma rays from irradiated samples and irradiated reference materials;

[0042] c. Determine the number of detected deactivated gamma rays from any target element present in the irradiated sample and the at least two reference elements;

[0043] d. Calculate the activation rates of the sample and the at least two reference elements;

[0044] e. Repeat steps (a) through (d) over a sufficiently large range with different endpoint energies to cover typical variations in the expected endpoint energy operation; and

[0045] f. Generation ratio and Related functions The lookup table.

[0046] In one embodiment, at least two reference elements include one of Br (bromine), Er (erbium), or Ir (iridium) and Tb (terbium).

[0047] In one embodiment, the target element, or each target element, has a reaction threshold energy of less than 10 MeV.

[0048] In one embodiment, at least two reference elements include one of Ge (germanium), Pd (palladium), or Rb (rubidium) and Tb (terbium).

[0049] In one embodiment, the target element, or each target element, has a reaction threshold energy for neutron emission between 10 MeV and 14 MeV.

[0050] A second aspect of the invention provides a gamma activation analysis system for determining the concentration of one or more target elements in a sample, comprising:

[0051] a. An X-ray source suitable for providing bremsstrahlung X-rays;

[0052] b. Gamma ray detection system;

[0053] c. Computing devices,

[0054] In this process, the sample and a reference material comprising at least two reference elements, the at least two reference elements having variations in activation rates within predetermined X-ray endpoint energy ranges different from each other, are simultaneously exposed to the X-ray source for bremsstrahlung X-ray irradiation before being provided to the gamma-ray detection system. In the gamma-ray detection system, detected deactivated gamma rays from any one of the target elements or each of the target elements present in the irradiated sample and the at least two reference elements are determined and provided to the computing device, wherein the computing device determines the concentration of the target element or each of the target elements in the sample, including correcting for the number of detected deactivated gamma rays from the at least two reference elements due to variations in the bremsstrahlung X-rays.

[0055] In one embodiment, at least two reference elements include one of Br (bromine), Er (erbium), or Ir (iridium) and Tb (terbium).

[0056] In one embodiment, the target element, or each target element, has a reaction threshold energy for neutron emission of less than 10 MeV.

[0057] In one embodiment, at least two reference elements include one of Ge (germanium), Pd (palladium), or Rb (rubidium) and Tb (terbium).

[0058] In one embodiment, the target element, or each target element, has a reaction threshold energy for neutron emission between 10 MeV and 14 MeV.

[0059] In one embodiment, the system further includes a sample delivery device for delivering the sample and reference material to the location to be irradiated by bremsstrahlung X-rays and a gamma-ray detection system.

[0060] A third aspect of the invention provides a gamma activation analysis system suitable for implementing the method provided in the first aspect of the invention.

[0061] The advantages of this invention include:

[0062] In the absence of a suitable single reference element, the accuracy of gamma activation analysis for determining elemental concentrations in samples is improved; and

[0063] Simultaneously measure the improvement capabilities of multiple target elements.

[0064] The intended application of this invention is to measure the concentration of elements in rock, mining, mineral ore, or process stream samples. Examples of target elements include, but are not limited to, gold, silver, copper, lead, zinc, and tin.

[0065] Other applications may include the measurement of soil, industrial materials, general or electronic waste, and other types of materials. Attached Figure Description

[0066] Several embodiments of the invention will now be described with reference to the accompanying drawings. It should be understood that these embodiments are given by way of illustration only, and the invention is not limited thereto. In the drawings:

[0067] Figure 1 This is a schematic diagram of a gamma activation analysis system utilizing at least one embodiment of the present invention;

[0068] Figure 2 It is a table of activation reactions and decay properties of potential reference material elements;

[0069] Figure 3 It shows the experimental measurement. 197M Au、 107M Ag and 109M The formation of Ag relative to 79M A graph showing the change in the activation rate of Br formation relative to the LINAC endpoint energy, where the ratio is normalized to one at an endpoint energy of 8.5 MeV.

[0070] Figure 4It shows the experimental measurement. 158M Tb, 167M Er and 191M The formation of Ir is relative to 79M A graph showing the change in the activation rate of Br formation relative to the LINAC endpoint energy, where the ratio is normalized to one at an endpoint energy of 8.5 MeV.

[0071] Figure 5 It shows the experimental measurement. 75M Ge 86M Rb、 109M Pd and 158M The activation rate of Tb formation relative to 62 A graph showing the change in Cu formation rate versus LINAC endpoint energy, where the ratio is normalized to one at a 12 MeV endpoint energy. Detailed Implementation

[0072] As previously stated, WO2015089580 discloses that when calculating the amount of gold in a sample using gamma-activation analysis (GAA), the main sources of uncertainty involve the flux and energy spectrum of X-rays from the source, which involve fluctuations in the intensity or energy of the electron beam that produces the X-rays.

[0073] Within the LINAC endpoint energy range of 8.0–9.0 MeV, the activation rates of gold and bromine exhibit remarkably similar variations with X-ray energy. Therefore, if a sample with an unknown gold content is simultaneously irradiated with a reference material containing a known amount of elemental bromine, the ratio of gold to bromine activation rates for X-rays is approximately constant within this endpoint energy range. The gold gamma-ray intensity was normalized by the bromine gamma-ray intensity, thus substantially correcting for variations in X-ray intensity and endpoint energy.

[0074] For clarity, the term "activation rate" used throughout this specification refers to the number of product nuclei produced per unit time for a given reaction. If nuclide X is converted into a second nuclide X by an incident X-ray beam... Then X is formed from the atoms of X. The reaction rate of the atoms, It is given by the following formula:

[0075]

[0076] in It is the number of X-type atoms present in the sample or reference material. It is expressed as X-ray energy. The average X-ray photon flux within the region containing X-type atoms, which is a function of . It is formed from X The microscopic reaction cross-section, which is also a function of X-ray energy, and the integral from the lower energy threshold of the reaction. Extending to the maximum X-ray energy or endpoint energy emitted by the source. .

[0077] In practice, the energy dependence of X-ray photon flux and microscopic reaction cross-section can be known with only limited precision. However, for a given X-ray source, the energy dependence of X-rays after X-ray radiation of a known amount can be experimentally measured. The emission of gamma rays from atoms is used to precisely determine the reaction rate.

[0078] GAA is suitable for detecting the concentration of any element with a suitable activation reaction, and in fact, when using GAA to calculate the concentration of any element in a sample, the main source of uncertainty involves the flux and energy spectrum of X-rays from that source.

[0079] However, it is uncommon to find two elements whose activation rates change sequentially with X-ray energy. Unlike gold, when measuring target elements such as silver and copper, there are no readily available reference elements. Therefore, the key factor in selecting a single reference element is that, as taught in WO2015089580, the change in the cross-sectional ratio of the reference element to the target element is the same or very similar (less than the predetermined measurement precision) within the electron beam energy range, which is impossible or impractical for many target elements.

[0080] Furthermore, simultaneously measuring multiple target elements in the same sample requires the reference material to contain multiple reference elements (typically one for each target element), which increases the probability of unwanted interference between gamma rays emitted by the reference and target elements.

[0081] Accelerators used for industrial gamma activation analysis conveniently generate electron beams with energies up to about 15 MeV. The minimum useful energy for effective activation is typically about 6 MeV. Within this energy range, there are two important classes of activation reactions that lead to the formation of radioactive isotopes from the target element: inelastic scattering producing nuclear isomeric states (also known as metastable states) and neutron emission. Examples of these two reaction types include:

[0082] Isomerization: Gold: 197 Au (g,g') 197M Au; half-life = 7.73 s; gamma-ray emission energy = 279 keV. Threshold < 1 MeV.

[0083] Neutron emission: Copper: 63 Cu (g,n) 62 Cu; half-life = 9.62 min; gamma-ray emission energy = 511 keV; threshold 10.9 MeV.

[0084] For energies above the reaction threshold, the production rate of a given radioactive isotope increases linearly with X-ray intensity, and is typically even stronger with X-ray energy (superlinear). Instruments performing gamma activation analysis must be able to accurately estimate or measure the activation rate of the target element during analysis to allow the measured gamma emission intensity of a given target element to be correlated with the concentration of that element in the sample.

[0085] Now refer to Figure 1 Embodiments of the present invention include a radiation station 100 and a gamma-ray detection system 110. Sample material with the elemental composition to be determined is loaded into a sample container 101. The sample container 101 is initially provided to the radiation stage 100 by a sample supply device 104 and is located near an X-ray source 102, which provides bremsstrahlung X-rays via an electron accelerator equipped with a bremsstrahlung target. The electron accelerator is preferably a linear accelerator (LINAC). The radiation stage 100 also includes radiation shielding (not shown for clarity) to protect the operator when the source is operating. A reference disk 103 containing reference material with two or more reference elements is detachably attached to the outside of the sample container 101.

[0086] Although the term "reference disk" is used throughout the specification, it should be understood that, for all embodiments, the reference material can be provided in any suitable manner, provided that the reference material can be irradiated simultaneously with the associated sample container intended to contain the target element, and that, for all embodiments described herein, the reference material is removably positioned in a consistent location relative to the sample. Therefore, the reference material can be contained in a container or package of any suitable shape. For example, the reference material can be arranged in the form of an annular ring surrounding sample container 101.

[0087] The gamma-ray detection system 110 includes one or more gamma-ray detectors 111, 112 arranged around the sample and reference disk 103 in the container 101. The gamma-ray detection system 110 includes means for collecting signals from the gamma-ray detectors 111, 112 and providing information relating to the energy and number of detected gamma rays to a computing device or analysis system 113, which processes the information to determine the elemental composition of the sample.

[0088] In operation, the sample container 101 containing the sample material is first loaded into the radiation stage 100. The X-ray source 102 operates for a period of time to activate the elements in the sample material in the sample container 101 and the reference material contained in the reference disk 103.

[0089] Once the radiation cycle is complete, the sample container 101 is transferred from the sample delivery device 104 to the gamma ray detection system 110. The sample delivery device 104 can be pneumatic, electric, or any other suitable device. The sample delivery device 104 is an optional aspect of the system, and sample delivery can be manual rather than automatic.

[0090] In detector station 110, sample container 101 is positioned adjacent to at least one gamma ray detector 111. A second detector 112 or other detector may be used to improve the efficiency of detecting gamma rays emitted from the sample.

[0091] Ideally, at least one detector 111 is positioned adjacent to the side of the sample container 101 to which the reference disk 103 is fixed. Thus, the detector 111 can detect gamma rays emitted from the reference disk 103 without the gamma rays needing to pass through the sample material in the sample container 101 and be attenuated therefrom.

[0092] Analysis system 113 records and counts gamma-ray signals from detectors 111 and 112. Analysis system 113 distinguishes the energies of the detected gamma rays, allowing signals from activated elements in the sample material in sample container 101 to be separated from signals from reference disk 103.

[0093] Sample container 101 remains in detector station 110 until sufficient time has elapsed to count the signals from the activated elements in sample container 101 and reference disk 103 to the desired level of accuracy. Sample container 101 can then be returned for further activation and measurement cycles, or ejected from the measurement system to allow analysis of new sample containers. Sample supply system 104 can allow simultaneous activation and measurement of different samples to improve throughput.

[0094] Reference panel 103 contains the reference elements selected when considering the following considerations:

[0095] Compared to the differences in activation rates of the target element and any reference element with respect to LINAC endpoint energy, the activation rates of the reference elements differ from each other. Most preferably, the activation rate of one reference element changes with energy similar to that of the target element, while the activation rate of another reference element changes significantly differently. Herein, similarity is defined as a change of less than 3% at a predetermined endpoint energy. Significance is defined as a change of more than 20% at a predetermined endpoint energy. Less preferably, the activation rate of at least one reference element changes significantly less with energy than that of the target element, and the activation rate of at least one reference element changes significantly more with energy than that of the target element. Alternatively, two or more reference elements may exhibit activation rate changes less than or greater than those of the target element, but the changes differ among the individual reference elements.

[0096] It is expected that the reference element will not be present in the sample material to be measured at a significant concentration. In particular, the mass of each element present in the sample should be less than 10% of the mass of the same reference element in the reference pan, preferably less than 1%.

[0097] The interaction of X-rays with all reference elements results in unstable isotopes with suitable half-lives, preferably in the range of 1 second to 10 minutes.

[0098] Unstable isotopes formed in X-ray induced reactions strongly emit one or more gamma rays. In particular, the unstable isotopes emit at least one type of gamma ray with an energy higher than 40 keV and a decay probability of 1% or greater, more preferably gamma rays with an energy higher than 60 keV or a probability of 10% or greater.

[0099] The energy of gamma rays emitted by unstable isotopes does not interfere with the measurement of gamma rays emitted by elements activated in the sample material.

[0100] The activation rates of the reference elements can be mathematically combined to determine an amount equal to the expected activation rate of the target element in an unknown sample, independent of variations in the intensity or energy of the X-ray source output. The calculated activation rate of the target element can then be used to derive the target element concentration from the measured intensity of gamma rays emitted by the radioactive isotopes formed in the X-ray reaction of the target element.

[0101] The criteria for selecting appropriate reference elements have been discussed above. Figure 2This is a table listing elements in the periodic table that have X-ray-induced activation reactions with threshold energies below 15 MeV, natural isotopic abundances of at least 1%, product half-lives of 1 second to 10 minutes, and emit at least one gamma ray with an energy above 40 keV and a probability of 1% or higher. Regarding natural abundance, higher natural abundances are preferred because fewer reference elements are needed to obtain a certain amount of the desired isotope, and the amount of unwanted isotopes of the same element is reduced, which decreases the significance of any potential interfering reactions. [The last sentence appears to be incomplete and possibly refers to a different topic: "for filling..."] Figure 2 Data in the tables, including isotopic abundance, reaction threshold, product half-life, and decay gamma-ray energy and intensity, are readily available in scientific literature. For example, some or all of the data can be accessed from the International Atomic Energy Agency Nuclear Data Service, which is available online at www.nds.iaea.org.

[0102] Figure 2 The columns in the table represent:

[0103] Target - potential reference elements and specific isotopes that have undergone activation;

[0104] Prop (%) - the natural abundance of this isotope;

[0105] Reac - Reaction type; neutron emission (g,n) or inelastic scattering (g,g);

[0106] Thr (MeV) - the reaction threshold energy of neutron emission reaction.

[0107] Products - Isotopes of the products of the capture reaction - Note that the products can be in the ground state or the off-state, the latter being indicated by the superscript 'm';

[0108] Half-life - Product half-life;

[0109] Intf. - indicates whether competing reactions on the same element that produce strong and / or long-lived gamma-ray emission can be excited using similar X-ray energies required for said reaction; and

[0110] Decay radiation - the energy and intensity (%) of the primary X-rays or gamma rays emitted from the product isotopes.

[0111] The optimal choice of reference element depends on the concentration and decay properties of other elements in the sample material (which will be measured using activation analysis) and the analysis time. For example, if the assay system measures 60 samples per hour, it is convenient to choose a reference element with a half-life of 2 minutes or less. The assay system can then sequentially select one of a small number of reference disks (typically 3-6), and the residual activity from the previous cycle using that reference disk will be significantly reduced.

[0112] Furthermore, the reference element will produce gamma rays with convenient energies that do not interfere with the gamma rays of the target element. Additionally, the reference element should not be expected to be present in a significant concentration in the sample being measured. The mass of each reference element present in the sample should be less than 10% of the mass of the same reference element in the reference disk. Preferably, the mass of each reference element present in the sample should be less than 1% of the mass of the same reference element in the reference disk.

[0113] Another factor influencing the selection of a reference element is the absence of unwanted radioactive products formed by reactions induced by other X-rays with the target isotope or other naturally occurring isotopes in the reference element. If these reactions have unfavorable decay characteristics, they may adversely affect the measurement of the desired decay products of the reference element and the analyte in the sample. A reference element in which the target isotope constitutes 100% or nearly 100% of the natural isotopic abundance is preferred to avoid or minimize such interfering reactions. Alternatively, a reference element may be selected where naturally occurring isotopes other than the target isotope do not produce unstable reaction products in X-ray induced nuclear reactions, or where the products of these reactions have extremely long or short half-lives, or where the products of these reactions do not emit strong gamma-ray radiation.

[0114] Two examples are provided to illustrate the selection of the best reference element.

[0115] The first example involves the simultaneous analysis of gold and silver through inelastic photon scattering. 197 Au(g,g') 197m The Au reaction produces the gold-197 isomer, which has a half-life of 7.73 seconds and decays to produce gamma rays with an energy of 279 keV. Two naturally occurring isotopes of silver can be activated in a similar manner, producing isotopes with half-lives of 44.3 and 39.8 s, respectively. 107m Ag and 109m The Ag isomers emit gamma rays with energies of 93.1 and 88 keV. The 8.5 MeV X-ray endpoint energy facilitates the activation of gold and silver.

[0116] Bromine was used as the reference element for gold because the gold / bromine activation ratio exhibits minimal energy dependence in the 8–9 MeV energy range. However, small residual energy variations exist, which can be important for very high-precision analysis, and the silver / bromine activation ratio varies more significantly with endpoint energy. Figure 3 The experimentally determined LINAC endpoint energies for gold / bromine and silver / bromine activation ratios were plotted in the approximate range of 7.5–9.5 MeV.

[0117] examine Figure 2The table in the table, which lists elements with activation thresholds below 8.5 MeV for measuring gold and silver, reveals the following reference possibilities: Br, Y, Tb, Er, Hf, W, and Ir. These elements undergo isomerization reactions with indeterminate thresholds (marked as "-" in the table) but typically become significant at X-ray endpoint energies above 6 MeV. In this example, Y is not considered further because its high gamma-ray emission energy (909 keV) introduces unwanted background below the lower-energy gold and silver lines, degrading the analytical performance of sample materials with low concentrations of the target element. Furthermore, W is not considered further because it typically occurs at perceptible concentrations in geological gold deposits, and Hf is not considered further because reactions producing other long-lived isotopes have thresholds below 8.5 MeV.

[0118] The choice among these possibilities depends on their activation rate relative to... 79M How the activation rate of Br varies (which in turn closely follows the isomer activation rate of gold, and quite closely follows the isomer activation rate of silver). High-quality reaction cross-sectional data for evaluating these activation rate ratios are generally unavailable. However, the relative activation rates can be readily determined experimentally by preparing samples containing the elements and then measuring the gamma-ray yields of different reactions using a LINAC that generates different endpoint energies. Figure 4 The activation rates of Tb, Er, and Ir relative to bromine were plotted as functions of the LINAC energy point energies. The activation rate ratios were arbitrarily normalized to one at the endpoint energy of 8.5 MeV.

[0119] from Figure 4 The results shown indicate that 167M Er and 191M The activation rate of Ir and 79M The activation rates of Br are very similar because the activation rate ratio is close to 1 across the entire energy range. Conversely, compared to the activation rate of bromine, 158M The activation rate of Tb increases sharply with increasing energy.

[0120] Therefore, elements Br, Er, or Ir, along with element Tb, will be the best reference elements for accurately measuring gold and silver in unknown samples. Elements from the first list (hereinafter referred to as the first or primary reference elements) track the activation rates of gold and silver fairly closely. Elements selected from the second list are hereby referred to as the second or secondary reference elements. The ratio of the activation rates of the secondary and primary reference elements is a strong function of the LINAC endpoint energy and can be used to correct for small deviations in the ratio of the activation rates of the target element (here, gold and silver) to the primary reference element using the procedure described later.

[0121] The second embodiment involves the analysis of copper ore. Through reaction... 63 Cu(g,n)62 Cu is the most convenient material for determining copper, where copper-62 decays with a half-life of 9.67 minutes by emitting positrons, which in turn produce a pair of 511 keV gamma rays. The neutron emission reaction of copper-63 has a threshold energy of 10.9 MeV and can be conveniently measured using LINAC, which operates to produce X-rays with an endpoint energy of approximately 12 MeV. The 511 keV gamma-ray emission from copper is caused by the annihilation of the positrons emitted when copper-62 decays; it is preferable to avoid using reference elements that also decay via positron emission to avoid interfering with the copper signal. With a throughput of approximately 60 samples per hour, reference elements will be selected with half-lives less than 1–2 minutes, as discussed in previous examples. Furthermore, at least one reference element should have an activation threshold within approximately 1.5 MeV of the copper threshold to ensure a substantially similar activation response relative to the endpoint energy. At least one reference element may have a lower activation threshold to ensure a significantly different response relative to the endpoint energy.

[0122] Taking these requirements into account, the reduction Figure 2 The list of possible reference elements in the table can be simplified to the following: Ge, Se, Br, Rb, Pd, Ag, Sb, Ce, Nd, and Tb. When using an endpoint energy of 12 MeV, elements Se, Br, Ag, Sb, Ce, and Nd are no longer considered undesirable product isotopes that compete for the production of strong gamma-ray emission (including gamma rays with energies of 511 keV in some cases).

[0123] For example, through from 142 Nd neutron emission formation 141M Nd inevitably comes with the passage from 150 Nd neutron emission formation 149 Nd. isotope 149 Nd is a strong gamma-ray emitter, and the much lower threshold energy of this reaction means that its gamma rays dominate the emission spectrum of Nd-containing reference materials. Despite containing almost pure Nd... 142 Materials with isotopic separation or enrichment of Nd are available, but they are very expensive for conventional industrial use.

[0124] Figure 5 The activation rates of the remaining elements Ge, Rb, Pd, and Tb were plotted divided by the activation rate of copper; at the target endpoint energy of 12 MeV, this ratio was arbitrarily normalized to a unit ratio.

[0125] In contrast to the previous examples, where the activation rates of Br, Er, and Ir closely followed those of gold and silver, all showing significant changes with LINAC endpoint energies when compared to copper. However, Ge and Pd exhibited relatively small changes, while Rb and Tb showed relatively larger changes. Therefore, elements Ge or Pd and Rb or Tb can be used for accurate analysis of copper, corrected for variations in X-ray intensity or energy as described below.

[0126] Once the primary and secondary reference elements are identified, recognizing that the designation of primary and secondary is often arbitrary, the method for correcting the activation rate of the target element in the sample is as follows.

[0127] Let the number of gamma rays measured from the target, the primary reference, and the auxiliary reference element be respectively. , and Let the half-lives of the decay products of the reactions on these elements be respectively... and through To define the relevant decay rate as :

[0128] Time-corrected activation rates of the target element, primary reference element, and auxiliary reference element (respectively) Calculate according to the following formula

[0129] (Equation 1)

[0130] in, , and These are the radiation, cooling, and measurement times used for activation analysis.

[0131] Then the signal of the target element, corrected for changes in LINAC energy and output, Then write it as

[0132] (Equation 2)

[0133] in It is an experimentally determined function that equals this ratio within any normalization factor. Here, the term "signal" refers to an intermediate mathematical quantity that is proportional to the mass of the target element in a given sample. By construction, this signal is independent of changes in X-ray intensity, because these changes cause... and The function changes proportionally. Correct for changes in LINAC endpoint energy.

[0134] Discover One procedure is as follows: A reference material containing a primary reference element and an auxiliary reference element is prepared. A sample containing a known amount of target element sufficient to produce a strong gamma-ray signature is prepared. The sample and reference material are activated together using an X-ray beam, and the number of gamma-ray counts from the reactions of the target element, primary reference element, and auxiliary reference element is measured and recorded using a gamma-ray detector system. Measurements are repeated, with the LINAC endpoint energy varying over a sufficiently large range to include typical variations in endpoint energy expected during normal operation of the source. The time-corrected activation rate is calculated according to Equation 1. Then, a process for making... and Ratio-related functions The lookup table. The step size between the LINAC endpoint energies used in the test should be fine enough to allow the use of linear or cubic spline interpolation to determine the intermediate points with at least the same accuracy as the design analysis of the target elements. value.

[0135] Preferably, the amounts of the primary and auxiliary reference elements should be selected such that the number of gamma rays observed from their reaction products allows the activation rates of these elements to be determined with a statistical precision of 5%. More preferably, the number of gamma rays should allow the activation rate to be determined with a precision of 3% or more preferably 1%. This ensures that the time-corrected activation rate of the primary element and the ratio of the time-corrected activation rates of the auxiliary and primary elements can be determined with high statistical precision. The appropriate amount of each reference element can be determined by scaling the mass in the experiment used to measure the activation rate ratio against the LINAC energy, wherein the scaling is performed by the ratio of the number of gamma rays of the target element measured during the experiment to the desired number of gamma rays measured during normal analytical operations.

[0136] For the first example with silver and gold as target elements, if the LINAC operates at a distance of 1 m with an endpoint energy of 8.5 MeV and an output of 160 Sv / min, then 200 mg Br and 400 mg Tb are appropriate amounts.

[0137] For the second example of the target element discussed above, which is copper, if the LINAC operates at a distance of 1 m with an endpoint energy of 12 MeV and an output of 40 Sv / min, then 400 mg Ge and 8 mg Tb are appropriate amounts.

[0138] By correcting for the attenuation of incident X-rays from the LINAC source and gamma rays from the target element in the sample, and finally multiplying by a normalization constant, the signal can be analyzed. The mass of the target element in the sample is calculated. The attenuation factor, which depends on the sample mass, can be determined experimentally by measuring gamma-ray signals from samples containing different masses of the target element at known concentrations, or calculated using readily available gamma-ray attenuation coefficients. Computerized radiative transfer simulations, such as Monte Carlo simulations, are convenient means of performing attenuation calculations. The value of the normalization constant can be determined experimentally by comparing the value of the attenuation factor-corrected signal with the known masses of the target element in a set of samples. The curve of the attenuation correction signal versus the target element mass should be a straight line with a slope equal to the value of the normalization constant. That is, the normalization constant is the gradient of the trend line of the curve of the attenuation correction signal versus the target element mass.

[0139] Finally, the concentration of the target element in the sample can be determined by dividing the measured mass of the target element in the sample by the sample mass.

[0140] In summary, the first (or primary) reference element for Br, Er, or Ir and the second (or secondary) reference element for Tb can generally be used to correct measurements of other elements that are available with LINAC endpoint energies below 10 MeV. Similarly, the first reference element for Ge, Pd, or Rb and the second reference element for Tb can be used for other accessible elements with LINAC endpoint energies in the range of 11–14 MeV.

[0141] Although the invention has been described in conjunction with a limited number of embodiments, those skilled in the art will understand that many substitutions, modifications, and variations are possible based on the above description. Therefore, the invention is intended to encompass all such substitutions, modifications, and variations that may fall within the spirit and scope of the disclosed invention.

[0142] Any references or discussions of any document, action, or knowledge item in this specification are included solely for the purpose of providing context for the invention. No such references or discussions are recommended or implied as being part of common general knowledge or known at the priority date to be related to any attempt to resolve any problem addressed in this specification, or any combination thereof.

[0143] In this specification, the terms “comprises / comprising,” “includes / including,” or similar terms are intended to indicate non-exclusive inclusion, such that a method, system, or apparatus that includes a list of elements does not individually include those elements, but may include other elements not listed.

Claims

1. A method for determining the concentration of one or more target elements in a sample, the method comprising: i. Simultaneously irradiate the sample and a reference material containing at least two reference elements with bremsstrahlung X-rays, such that activated nuclei are generated in at least some of the one or more target elements present in the sample, and activated nuclei are generated in the at least two reference elements; ii. Detection of deactivated gamma rays from irradiated samples and irradiated reference materials; iii. Determine the number of detected deactivated gamma rays from the one or more target elements and the at least two reference elements present in the irradiated sample; iv. Determine the concentration of the one or more target elements in the sample, including correcting for the number of detected deactivated gamma rays of the one or more target elements present in the irradiated sample due to variations in the bremsstrahlung X-rays, based on the number of detected deactivated gamma rays from the at least two reference elements. The at least two reference elements have varying activation rates over different predefined X-ray endpoint energy ranges, and the at least two reference elements are different from the one or more target elements.

2. The method of claim 1, wherein the first reference element of the at least two reference elements exhibits a change in activation rate over the predefined X-ray endpoint energy range, the change being less than 3% different from the change in each of the one or more target elements.

3. The method of claim 2, wherein the second reference element of the at least two reference elements exhibits a change in activation rate over the predefined X-ray endpoint energy range, the change being greater than 20% different from the change in each of the one or more target elements.

4. The method of claim 1, wherein at least one of the reference elements exhibits a change in activation rate over the predefined X-ray endpoint energy range, the change being more than 20% different from the change in activation rate of the other of the reference elements.

5. The method of claim 1, wherein at least two of the reference elements exhibit activation rate variations smaller than those of each of the one or more target elements within a predefined X-ray endpoint energy range.

6. The method of claim 1, wherein at least two of the reference elements exhibit a greater change in activation rate than each of the one or more target elements over a predefined X-ray endpoint energy range.

7. The method of any one of claims 1 to 6, wherein the activated nuclei of the at least two reference elements exhibit a half-life of 1 second to 10 minutes.

8. The method of any one of claims 1 to 6, wherein the activated nuclei of the at least two reference elements exhibit a half-life of less than 2 minutes.

9. The method of any one of claims 1 to 6, wherein the activated nuclei of the at least two reference elements emit one or more gamma rays with energies higher than 40 keV, and the probability of each decay is at least 1%.

10. The method of any one of claims 1 to 6, wherein the energy of gamma rays emitted by the activated nuclei of the at least two reference elements does not interfere with the measurement of gamma rays emitted by the one or more target elements.

11. The method of claim 10, wherein the energy of the gamma rays emitted by the activated nuclei of the at least two reference elements does not interfere with the measurement of gamma rays emitted by any other element present in the sample.

12. The method of any one of claims 1 to 6, wherein the one or more target elements and the at least two reference elements have an X-ray induced activation reaction with a threshold energy of less than 15 MeV.

13. The method of any one of claims 1 to 6, wherein the at least two reference elements that generate the activated nucleus have a natural isotopic abundance of greater than 90%.

14. The method of any one of claims 1 to 6, wherein the at least two reference elements that generate the activated nucleus have a natural isotopic abundance of greater than 99%.

15. The method of any one of claims 1 to 6, wherein if the at least two reference elements are present in the sample, the mass of the at least two reference elements in the sample is less than 10% of the mass of the corresponding reference element in the reference material.

16. The method of any one of claims 1 to 6, wherein if the at least two reference elements are present in the sample, the mass of the at least two reference elements in the sample is less than 1% of the mass of the corresponding reference element in the reference material.

17. The method of any one of claims 1 to 6, wherein determining the concentration of the one or more target elements comprises the following steps: a. Calculate the time-corrected activation rates of the one or more target elements and the at least two reference elements; b. Determine the target element signal value for each of the one or more target elements based on the ratio of the time-corrected activation rate of each of the one or more target elements to the time-corrected activation rate of the reference element. c. To generate an attenuation factor-corrected signal value by applying an attenuation factor to correct the attenuation of incident X-rays and gamma rays of one or more target elements in the sample; as well as d. Multiply the signal value corrected by the attenuation factor by the normalization constant.

18. The method of claim 17, wherein the attenuation coefficient is experimentally determined by measuring gamma-ray signals from samples of different masses containing known concentrations of the one or more target elements or by calculating using readily available gamma-ray attenuation coefficients.

19. The method of claim 18, wherein the normalization constant is experimentally determined by comparing the signal value corrected by the attenuation factor with the known mass values ​​of the one or more target elements in a plurality of samples.

20. The method of claim 19, wherein the normalization constant is the slope of the trend line of the curve of the attenuation correction signal versus the target element mass.

21. The method of claim 17, wherein two reference elements exist, and for each of the one or more target elements, the target element signal value is ,in , and These are the time-corrected activation rates of the corresponding target element, the first reference element, and the second reference element, respectively, and among them, It is the ratio determined by experiment. with ratio Related functions.

22. The method of claim 21, wherein the function f is derived experimentally as follows: a. Simultaneously irradiate a sample containing known amounts of one or more of the target elements and a reference material containing the first reference element and the second reference element with bremsstrahlung X-rays having specific endpoint energies; b. Detect deactivated gamma rays from irradiated samples and irradiated reference materials; c. Determine the number of detected deactivated gamma rays from the one or more target elements and the at least two reference elements present in the irradiated sample; d. Calculate the activation rates of the one or more target elements and the at least two reference elements; e. Repeat steps (a) through (d) over a sufficiently large range with different endpoint energies to cover typical variations in the expected endpoint energy operation; and f. Generation ratio with ratio A lookup table for the relevant function f.

23. The method of any one of claims 1-6, wherein each of the one or more target elements has an activation reaction threshold of less than 10 MeV, and the first reference element of the at least two reference elements is selected from Br (bromine), Er (erbium), or Ir (iridium), and the second reference element of the at least two reference elements is Tb (terbium).

24. The method of any one of claims 1 to 6, wherein each of the one or more target elements has a reaction threshold energy between 10 MeV and 14 MeV, and the first reference element of the at least two reference elements is selected from Ge (germanium), Pd (palladium), or Rb (rubidium), and the second reference element of the at least two reference elements is Tb (terbium).

25. A gamma activation analysis system for determining the concentration of one or more target elements in a sample, comprising: a. An X-ray source suitable for providing bremsstrahlung X-rays; b. Gamma ray detection system; c. Computing devices, In this process, the sample and a reference material comprising at least two reference elements, the at least two reference elements having variations in activation rates within predetermined X-ray endpoint energy ranges different from each other, are simultaneously exposed to the X-ray source for bremsstrahlung X-ray irradiation before being provided to the gamma-ray detection system. In the gamma-ray detection system, detected deactivated gamma rays from the one or more target elements and the at least two reference elements present in the irradiated sample are determined and provided to the computing device, wherein the computing device determines the concentration of the one or more target elements in the sample, including correcting for the number of detected deactivated gamma rays from the at least two reference elements due to variations in the bremsstrahlung X-rays, and wherein the at least two reference elements are different from the one or more target elements.

26. The gamma activation analysis system of claim 25, wherein each of the one or more target elements has a reaction threshold energy of less than 10 MeV, and the first reference element of the at least two reference elements is selected from Br (bromine), Er (erbium), or Ir (iridium), and the second reference element of the at least two reference elements is Tb (terbium).

27. The gamma activation analysis system of claim 25, wherein each of the one or more target elements has a reaction threshold energy between 10 MeV and 14 MeV, and the first reference element of the at least two reference elements is selected from Ge (germanium), Pd (palladium), or Rb (rubidium), and the second reference element of the at least two reference elements is Tb (terbium).

28. The gamma activation analysis system of any one of claims 25 to 27, further comprising a sample delivery device for delivering the sample and the reference material to a location to be irradiated by the bremsstrahlung X-rays and the gamma ray detection system.

29. A gamma activation analysis system suitable for implementing the method as described in any one of claims 1 to 24.

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