SGS efficiency calibration function model, construction method, calibration method and application
阅读说明：本技术 Sgs效率刻度函数模型及构建方法、刻度方法、应用 (SGS efficiency calibration function model, construction method, calibration method and application ) 是由 郑洪龙 苟家元 曾波 章航洲 李文钰 王力 吴耀 祝美英 肖峰 杨洪明 于 2021-07-22 设计创作，主要内容包括：本发明公开了SGS效率刻度函数模型及构建方法、刻度方法、应用,本发明首先通过MCNP计算不同线衰减系数和γ能量条件下的断层效率值；然后,通过多元非线性回归方法确定效率刻度函数及参数；再次,通过SGS透射测量放射性废物桶样品,获取断层介质的γ射线衰减系数；最后,将桶内出射γ射线衰减系数、出射γ射线能量和函数参数代入体源效率函数模型,计算得到介质不同断层的效率矩阵,实现断层的效率刻度。该方法准确快捷的实现了放射性废物桶SGS系统的效率刻度,不受SGS系统差异的影响,不受实验源和其他软件的局限,具有较强的通用性。(The invention discloses an SGS efficiency scale function model, a construction method, a scale method and application, and the method comprises the steps of firstly calculating fault efficiency values under different linear attenuation coefficients and gamma energy conditions through MCNP; then, determining an efficiency scale function and parameters by a multivariate nonlinear regression method; thirdly, measuring a radioactive waste barrel sample through SGS transmission to obtain a gamma ray attenuation coefficient of the fault medium; and finally, substituting the attenuation coefficient of the gamma rays emitted from the barrel, the energy of the emitted gamma rays and the function parameters into a source efficiency function model, and calculating to obtain efficiency matrixes of different faults of the medium, so as to realize the efficiency calibration of the faults. The method accurately and quickly realizes the efficiency calibration of the SGS system of the radioactive waste barrel, is not influenced by the difference of the SGS system, is not limited by an experimental source and other software, and has strong universality.)
The SGS efficiency scale function model construction method is characterized by comprising the following steps:
s1, establishing an MCNP model according to detection system parameters of the SGS system and a waste barrel medium sample;
s2, calculating fault discrete efficiency values under the conditions of different line attenuation coefficient values, characteristic energy and spacing layer numbers based on the MCNP model constructed in the step S1;
s3, utilizing the universal source efficiency function model to perform multiple nonlinear regression fitting on the fault discrete efficiency value obtained in the step S2 by Matlab, and determining a function parameter a in the universal source efficiency function modeli(i＝1,2,…,8)；
S4, converting the function parameter aiAnd (i is 1,2, … and 8) substituting the general source efficiency function model to obtain the SGS efficiency calibration function model.
2. The SGS efficiency scale function model construction method of claim 1, wherein the detection system parameters in step S1 include crystal size and cold finger size of the HPGe detector, collimator thickness and collimation space, shield thickness, distance from the collimator front end of the detector to the center of the waste bin, and collimator and shield materials.
3. The SGS efficiency scale function model construction method of claim 1, wherein in step S1, the sample height of the waste barrel is 80cm, the height of the fault in the barrel is 10cm, and the medium and nuclide are uniformly distributed in the fault in the barrel.
4. The SGS efficiency scale function model construction method of claim 1, wherein in step S1, the medium inside the waste bin comprises fiber, rubber, metal, soil, plastic and concrete.
5. The method for constructing the SGS efficiency calibration function model according to claim 1, wherein in step S4, the SGS efficiency calibration function model is as follows:
in the formula: e is gamma ray energy, and mu is a linear attenuation coefficient; wherein, ai(i ═ 1,2, …,8) are the function parameters determined by step S3.
6. An SGS efficiency scale function model constructed by the construction method as claimed in any one of claims 1 to 5.
7. The method for calibrating the segmented gamma scanning efficiency of the SGS efficiency calibration function model constructed based on the construction method of any one of claims 1 to 5 is characterized by comprising the following steps of:
step one, adopting a transmission source to carry out direct transmission measurement on a waste barrel sample, and calculating the gamma ray attenuation coefficient mu of each fault medium under different energiesj(E)；
Secondly, acquiring the energy E of gamma rays emitted from the barrel through emission measurement of a detector;
step three, the gamma ray attenuation coefficient mu obtained in the step onej(E) Substituting the energy E of the gamma rays emitted from the barrel obtained in the step two into an SGS efficiency scale function model to calculate to obtain an efficiency matrix epsilon of different faults of the mediumij(E)。
8. The method for calibrating the efficiency of a segmented gamma scan according to claim 7, wherein in the first step, the attenuation coefficient μ of gamma raysj(E) The calculation model of (2) is as follows:
in the formula I0(E) Intensity of incident gamma rays of energy E, Ij(E) Intensity of gamma ray after penetration of fault, muj(E) The gamma ray attenuation coefficient of the j layer medium of the waste barrel, and d is the diameter of the nuclear waste barrel; according to the calculated linear attenuation coefficient mu of different energies Ej(E) Establishing muj(E) Relation f with gamma ray energy Ej(E)：
μj(E)＝fj(E)＝a1 exp(-E/a2)+a3 exp(-E/a4)+a5
In the formula, ai(i-1, 2, …,5) is a function parameter.
9. The method for calibrating the efficiency of a segmented gamma scan according to claim 7, wherein in the second step, the detector is an HPGe detector.
10. An SGS efficiency scale function model constructed according to the construction method of any one of claims 1 to 5 is used for the SGS system efficiency scale.
Technical Field
The invention relates to the technical field of gamma nondestructive testing of radioactive waste barrels, in particular to an SGS efficiency scale function model, a construction method, a scale method and application.
Background
With the development of nuclear energy and nuclear technology industry in China, a large amount of barreled radioactive wastes are generated and accumulated in the running and scientific research production processes of nuclear facilities of nuclear power stations, nuclear waste disposal plants, nuclear-related scientific research units and the like. The type and activity of the radioactive waste in the barrel are important bases for accurately judging and classifying the radioactive waste, and the detection of the radioactive waste barrel is a necessary link in nuclear safety monitoring and nuclear waste treatment. A Segmented Gamma Scanning (SGS) based on the Gamma nondestructive testing principle is a fast and effective method for testing radioactive waste barrels, and SGS systems are widely used in nuclear power plants, nuclear waste disposal plants and other places.
Basic flow of SGS detection of radioactive waste buckets: (1) rotating the waste barrel at a constant speed to enable the medium in the barrel to be equivalently and uniformly distributed with nuclides; (2) dividing the waste barrel longitudinally into a plurality of fault layers with equal height; (3) performing transmission scanning on each fault by using a transmission source, and calculating a fault line attenuation coefficient; (4) emission scanning is carried out on each fault, and the pixel types and projection data in the barrel are obtained; (5) calculating an efficiency matrix by combining the attenuation coefficient of the fault line and the gamma ray energy; (6) and analyzing the equation set by using a nuclide activity reconstruction algorithm, and reconstructing the activity of the core element in the bucket. The SGS detection principle is shown in fig. 1, and according to the principle of detecting radioactive waste barrels by the SGS system, the nuclide activity reconstruction equation is as follows:
in the formula: e is the energy of gamma-rays,. epsilonij(E) For the efficiency of the detector at the i-layer position for the j-th layer sample, Aj(E) Activity of sample at layer j, pi(E) Projection values, p, obtained for the detector at the i-layer positioni(E)＝ni(E)/[f(E).t]，ni(E) The net count of the full energy peak of the detector at the ith layer position, f (E) the gamma ray emissivity branch ratio, t the scanning time of a single fault, and N the total longitudinal layer number of the whole barrel.
The radioactive waste barrel is detected by using the SGS system, the activity of the core element in the barrel is rebuilt, the efficiency scale is a very important function, and as can be seen from the formula, the efficiency scale matrix epsilonij(E) The method is of great importance to a nuclide activity reconstruction equation, and the calibration result is directly related to the nuclide activity reconstruction accuracy. At present, a Monte Carlo simulation method is time lag, an experimental efficiency calibration method and a shell source equivalent calibration method are limited by experimental sources, domestic and foreign efficiency calibration software is represented by ISOCS, LabSOCS, Angle software and Gamma Clib, the software can calculate fault efficiency in a targeted manner, cannot be effectively combined with independently developed SGS system analysis software, and is still limited in practicability. The SGS efficiency calibration method based on the efficiency function can quickly and conveniently calculate fault efficiency, and can be embedded into an SGS system to complete efficiency calibration. In SGS analysis, after a waste barrel is longitudinally layered, the transmission measurement results in the linear attenuation coefficient of each fault instead of the density, and a common source efficiency function mainly relates to the relation between detection efficiency and sample density and gamma ray energy and cannot meet the requirement of efficiency calibration in SGS analysis.
Disclosure of Invention
The invention aims to provide an SGS efficiency scale function model and a construction method thereof, wherein the SGS efficiency scale function model is applied to SGS efficiency scales, so that the accuracy of the scales can be improved, and the activity of a kernel element in a barrel can be accurately reconstructed; the method solves the problems that the existing SGS calibration method is time lag, limited by experimental sources, and can not be effectively combined with SGS software.
The invention is realized by the following technical scheme:
the SGS efficiency scale function model construction method comprises the following steps:
s1, establishing an MCNP model according to detection system parameters of the SGS system and a waste barrel medium sample;
s2, calculating fault discrete efficiency values under the conditions of different line attenuation coefficient values, characteristic energy and spacing layer numbers based on the MCNP model constructed in the step S1;
s3, utilizing the universal source efficiency function model to perform multiple nonlinear regression fitting on the fault discrete efficiency value obtained in the step S2 by Matlab, and determining a function parameter a in the universal source efficiency function modeli(i＝1,2,…,8)；
S4, converting the function parameter aiAnd (i is 1,2, … and 8) substituting the general source efficiency function model to obtain the SGS efficiency calibration function model.
In step S2 of the present invention, the line attenuation coefficient, the characteristic energy, and the number of layers of space are all known conditions; an efficiency calculation program is written through an MCNP model constructed in S1, an efficiency value can be calculated under each condition that a line attenuation coefficient value, a characteristic energy value and the number of spacing layers are determined, then a plurality of efficiency values under the conditions of different line attenuation coefficient values, characteristic energy values and the number of spacing layers can be realized by modifying the line attenuation coefficient value, the characteristic energy value and the number of spacing layers of a detector and a sample layer in the program, and the calculated efficiency values are fault discrete efficiency values under different spacing layers because the line attenuation coefficient and the characteristic energy are taken discrete points. That is, the fault discrete efficiency values in step S2 are efficiency values calculated in advance by the MCNP model of the known SGS system, similarly to the database established in advance; the universal source efficiency function model is an empirical formula, discrete efficiency values in the databases are utilized, a calculation program is compiled through Matlab, and function parameters are calculated in the program by utilizing a multivariate nonlinear regression fitting method; once the SGS system has determined the function parameters, an SGS system corresponds to a set of intrinsic function parameters at each number of layers.
The SGS efficiency scale function model constructed by the method is used for segmenting gamma scanning efficiency scales, and the efficiency scales of an SGS system can be quickly realized; the method can avoid the problem of time lag caused by the traditional Monte Carlo method and overcome the problem of inaccurate scales caused by the limitation of experimental sources.
Further, in step S1, the detection system parameters include the crystal size and the cold finger size of the HPGe detector, the thickness and the collimation space of the collimator, the thickness of the shield, the distance from the front end of the collimator of the detector to the center of the trash can, and the materials of the collimator and the shield.
Further, in step S1, the height of the sample in the waste barrel is 80cm, the height of the fault in the barrel is 10cm, and the medium and the nuclide are uniformly distributed in the fault in the barrel.
Further, in step S1, the medium in the trash can includes fiber, rubber, metal, soil, plastic, and concrete.
Further, in step S4, the SGS efficiency scaling function model is as follows:
in the formula: e is gamma ray energy, and mu is a linear attenuation coefficient; wherein, ai(i ═ 1,2, …,8) are the function parameters determined by step S3.
The invention relates to a general source efficiency function model expression and SGS efficiency scale function model, which is characterized in that a function parameter a when the general source efficiency function model is used for an SGS system is determined based on discrete efficiency data calculated by an MCNP modeli(i ═ 1,2, …,8), which facilitates the actual radioactive waste drum SGS measurement during which the function parameter a is measuredi(i-1, 2, …,8) it is known that gamma ray attenuation systems can be directly measured in the actual radioactive waste drum by measuring the gamma ray attenuation coefficientSeveral muj(E) Substituting the energy E of the emitted gamma rays into an SGS efficiency scale function model, and calculating to obtain an efficiency matrix epsilon of different faults of the mediumij(E)
The invention relates to a segmented gamma scanning efficiency calibration method constructed based on an SGS efficiency calibration function model, in particular to an SGS efficiency calibration function model constructed by the construction method.
The method for calibrating the segmented gamma scanning efficiency based on the SGS efficiency calibration function model comprises the following steps:
step one, adopting a transmission source to carry out direct transmission measurement on a waste barrel sample, and calculating the gamma ray attenuation coefficient mu of each fault medium under different energiesj(E)；
Secondly, acquiring the energy E of gamma rays emitted from the barrel through emission measurement of a detector;
step three, the gamma ray attenuation coefficient mu obtained in the step onej(E) Substituting the energy E of the gamma rays emitted from the barrel obtained in the step two into an SGS efficiency scale function model to calculate to obtain an efficiency matrix epsilon of different faults of the mediumij(E)。
Further, in the step one, the attenuation coefficient mu of the gamma rayj(E) The calculation model of (2) is as follows:
in the formula I0(E) Intensity of incident gamma rays of energy E, Ij(E) Intensity of gamma ray after penetration of fault, muj(E) The gamma ray attenuation coefficient of the j layer medium of the waste barrel, and d is the diameter of the nuclear waste barrel; according to the calculated linear attenuation coefficient mu of different energies Ej(E) Establishing muj(E) Relation f with gamma ray energy Ej(E)：
μj(E)＝fj(E)＝a1exp(-E/a2)+a3exp(-E/a4)+a5
In the formula, ai(i-1, 2, …,5) is a function parameter.
During SGS measurement of the waste bin, use is made ofTransmission source152Eu (mainly emitting 6 energies of 0.122, 0.344, 0.779, 0.964, 1.112, 1.408 MeV) to perform transmission measurement on the waste bin, the line attenuation coefficients of 6 energies of 0.122, 0.344, 0.779, 0.964, 1.112, 1.408MeV can be obtained, but the energy emitted by the radionuclide in the waste bin is many, such as 0.662, 1.173, 1.332MeV, etc., so that the relation f needs to be establishedj(E)。
The invention can utilize the line attenuation coefficients of 6 energies, namely 0.122, 0.344, 0.779, 0.964, 1.112 and 1.408MeV, to be established in a single waste bucket, the transmission line attenuation coefficients are related to different energies, namely, the line attenuation coefficients are calculated by transmission measurement, not only the line attenuation coefficients of the 6 energies are calculated, but also a relation curve of the line attenuation coefficients and gamma energy is further established, so that any gamma energy emitted in the single bucket can obtain the transmission line attenuation coefficients by the curve, and one waste bucket corresponds to one relation curve.
Further, in the second step, the detector adopts an HPGe detector.
And the SGS efficiency calibration function model is used for the SGS system efficiency calibration.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. according to the invention, through the established SGS efficiency scale function model, the efficiency scale of the SGS system can be quickly realized.
2. The invention is a passive efficiency calibration method, determines function parameters based on a Monte Carlo method, meets the range of waste barrel samples to be tested applicable to the calibration function, and saves the cost for manufacturing a large-volume standard source.
3. The efficiency scale function provided by the invention can be integrated into the developed SGS analysis software.
4. The invention has the advantages of simplicity, convenience, rapidness and strong universality, and has very high practical use value and wide application prospect.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a schematic diagram of a radioactive waste bin SGS test;
FIG. 2 is a graph of the distribution of nuclear elements in a radioactive waste drum;
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1:
the method for constructing the source efficiency function model comprises the following steps:
and S1, establishing an MCNP model based on a 200L standard steel drum according to detection system parameters of the SGS system. The crystal size of the HPGe detector is phi 70mm multiplied by 82.6mm, and the cold finger size is phi 9mm multiplied by 69 mm. The thickness of the collimator is 50mm, the collimation space is 200mm multiplied by 100mm multiplied by 150mm, the thickness of the shielding device is 50mm, and the collimator and the shielding device are made of lead materials. The distance from the front end of the detector collimator to the center of the waste bucket is 485 mm. Usually, the medium in the barrel includes fiber, rubber, metal, soil, plastic, concrete, etc., and the filled medium elements in the barrel adopted by the MCNP model in this embodiment are: h (10%), C (10%), O (20%), N (5%), S (5%), Si (5%), Na (5%), Mg (5%), Al (5%), K (5%), Ca (5%), Fe (10%), Cu (5%), Pb (5%). The linear attenuation coefficient values are selected from 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.21, 0.24cm-1. The calibration nuclide is152Eu, selecting characteristic energy: 0.122, 0.344, 0.779, 0.964, 1.112, 1.408 MeV. The height of the whole barrel of samples is 80cm, the height of the fault layer in the barrel is 10cm, and the medium and the nuclide are uniformly distributed in the fault layer in the barrel;
s2, calculating fault discrete efficiency values under the conditions of different line attenuation coefficient values, characteristic energy and spacing layer numbers based on the MCNP model constructed in the step S1;
the number of interval layers between the detector and the fault position is respectively 0, 1 and 2 (the number of the faults in the embodiment is 8, wherein the detector corresponds to the lowest layer, the number of the interval layers of the radioactive layer at the lowest layer is 0, the number of the interval layers of the radioactive layer at the second layer is 1, the number of the interval layers of the radioactive layer at the third layer is 2, and when the number of the interval layers is more than 2, the radioactive sample layer is not in the detection range, so the detection efficiency is 0, and the calculation is not needed), the fault detection efficiency distribution under different linear attenuation coefficient and gamma ray energy conditions is obtained through the calculation of an MCNP model:
writing an efficiency calculation program through an MCNP model constructed by S1, calculating to obtain an efficiency value under each condition of determining a line attenuation coefficient value, a characteristic energy value and the number of spacing layers, and then realizing a plurality of efficiency values under the conditions of different line attenuation coefficient values, characteristic energy values and spacing layers by modifying the line attenuation coefficient value, the characteristic energy value and the number of spacing layers in the program;
s3, utilizing the universal source efficiency function model to perform multiple nonlinear regression fitting on the fault discrete efficiency value obtained in the step S2 by Matlab, and determining a function parameter a in the universal source efficiency function modeli(i＝1,2,…,8)：
Carrying out multiple nonlinear regression fitting by utilizing Matlab to obtain function parameter ai(i ═ 1,2, …, 8). When the number of spacer layers is 0, a1＝-0.61265,a2＝-0.13140,a3＝0.13347,a4＝-14.18816,a5＝5.76917,a6＝-2.03592，a7＝2.50586,a8＝-1.39255,R20.99710; when the number of spacer layers is 1, a1＝-0.45543,a2＝-0.14752,a3＝0.13524,a4＝-14.31974,a5＝2.99772,a6＝-1.41061，a7＝4.80552,a8＝-1.61936,R20.99785; when the number of spacer layers is 2, a1＝-0.40652,a2＝-1.01215,a3＝0.27050,a4＝-28.80021,a5＝3.84716,a6＝-0.96104，a7＝8.349×107,a8＝-8.19547,R2＝0.99738。Fitting correlation coefficient R when the layer number interval is 0, 1 and 2 layers respectively2All are close to 1, and the function parameters are accurate;
function parameter a in this exampleiThe calculation procedure for (i ═ 1,2, …,8) is:
the fault discrete efficiency values in step S2 are a plurality of efficiency values calculated in advance by using the MCNP model of the known SGS system, and similar to the database established in advance, according to the body source efficiency function model provided by the present invention, the model is an empirical formula, and a calculation program is compiled by using the discrete efficiency values in the databases, and in the program, a function parameter is calculated by using a multivariate nonlinear regression fitting method;
s4, converting the function parameter aiSubstituting (i ═ 1,2, …,8) into the universal source efficiency function model to obtain the SGS efficiency scale function model:
in the formula: e is gamma ray energy, and mu is a linear attenuation coefficient; wherein, ai(i ═ 1,2, …,8) are the function parameters determined by step S3.
Example 2:
the source efficiency function model constructed in example 1 was used for a segmented gamma scan efficiency scale:
radioactive waste barrel SGS detection and analysis are developed by using laboratory SGS system, and transmission source152Eu activity of 2.568X 108And Bq. The medium in the barrel is selected from an aluminum silicate plate, a wood plate and a polyvinyl chloride plate, the total height is 80cm, and the height of each layer is 10cm in sectional measurement. The nuclide in the barrel is a point source137Cs (Activity 3.110X 10)5Bq) and60co (activity 1.371X 10)5Bq). The point sources were located in the middle layer with eccentricities of 0, 6.5, 11.5, 17.5, 22, 25cm, respectively, and the measured projection data were averaged together to simulate the presence of multi-point species in a single layer sample, as shown in fig. 2. In the transmission measurement and the emission measurement, the single tomographic scanning time is 180s and 300s, respectively.
Through152Eu transmission measurement and calculation, the calculation process is as follows:
in the SGS measurement process of the waste bin, an external transmission source is utilized152Eu (mainly emitting 6 energies of 0.122, 0.344, 0.779, 0.964, 1.112, 1.408 MeV) to the trash can, the line attenuation coefficients of the 6 energies of 0.122, 0.344, 0.779, 0.964, 1.112, 1.408MeV can be obtained, and the formula is calculated as follows:
in the formula I0(E) Intensity of incident gamma rays of energy E, Ij(E) Intensity of gamma ray after penetration of fault, muj(E) The gamma ray attenuation coefficient of the j-th layer medium of the waste barrel, and d is the diameter of the nuclear waste barrel.
Thus, the line attenuation coefficients of 6 energies, 0.122, 0.344, 0.779, 0.964, 1.112, 1.408MeV, can be established in a single waste bin, with the transmission line attenuation coefficient μj(E) The relationship with different energies E is as follows:
μj(E)＝fj(E)＝a1exp(-E/a2)+a3exp(-E/a4)+a5
in the formula, each bucket is truncated to correspond to a set of function parameters ai(i＝1,2,…,5)。
The linear attenuation coefficient is calculated through transmission measurement, not only the linear attenuation coefficient of the 6 energies is calculated, but also a relation curve of the linear attenuation coefficient and gamma energy is further established, so that any gamma energy emitted in a single barrel can obtain the transmission linear attenuation coefficient through the curve, and a waste barrel corresponds to the relation curve.
Then the energy of 0.662, 1.173 and 1.332MeV is substituted into the relation, and the linear attenuation coefficient of 0.662, 1.173 and 1.332MeV in a waste bucket is calculated.
The linear attenuation coefficients of 0.662, 1.173 and 1.332MeV in the aluminum silicate plate samples were 0.025153, 0.019066 and 0.017500cm, respectively-1(ii) a In the woodThe linear attenuation coefficients of 0.662, 1.173, 1.332MeV in the plate samples were 0.053672, 0.040917, 0.037931cm, respectively-1(ii) a The linear attenuation coefficients of 0.662, 1.173, and 1.332MeV in the PVC sheet samples were 0.139045, 0.104067, and 0.095657cm, respectively-1。
Attenuation coefficient mu of emitted gamma raysj(E) Substituting the energy E of the emitted gamma rays into an SGS efficiency scale function model epsilon (E, mu, a)i) And calculating to obtain the efficiency matrix epsilon of different faults of the mediumij[8×8]：
Attenuation coefficient mu of emitted gamma raysj(E) Substituting the energy E of the emitted gamma rays into an SGS efficiency scale function model epsilon (E, mu, a)i) And when the number of the spacing layers between the detector and the fault position is 0, 1 and 2 respectively, the fault efficiency is shown in table 1:
TABLE 1
Efficiency matrix ε of 0.662MeV, as an example for the aluminum silicate sampleij[8×8]As shown in table 2:
TABLE 2
1.63E-04
1.39E-04
3.51E-05
0
0
0
0
0
1.39E-04
1.63E-04
1.39E-04
3.51E-05
0
0
0
0
3.51E-05
1.39E-04
1.63E-04
1.39E-04
3.51E-05
0
0
0
0
3.51E-05
1.39E-04
1.63E-04
1.39E-04
3.51E-05
0
0
0
0
3.51E-05
1.39E-04
1.63E-04
1.39E-04
3.51E-05
0
0
0
0
3.51E-05
1.39E-04
1.63E-04
1.39E-04
3.51E-05
0
0
0
0
3.51E-05
1.39E-04
1.63E-04
1.39E-04
0
0
0
0
0
3.51E-05
1.39E-04
1.63E-04
Efficiency matrix ε of 1.173MeV, for example in the case of aluminum silicate samplesij[8×8]As shown in table 3:
TABLE 3
1.13E-04
9.86E-05
2.43E-05
0
0
0
0
0
9.86E-05
1.13E-04
9.86E-05
2.43E-05
0
0
0
0
2.43E-05
9.86E-05
1.13E-04
9.86E-05
2.43E-05
0
0
0
0
2.43E-05
9.86E-05
1.13E-04
9.86E-05
2.43E-05
0
0
0
0
2.43E-05
9.86E-05
1.13E-04
9.86E-05
2.43E-05
0
0
0
0
2.43E-05
9.86E-05
1.13E-04
9.86E-05
2.43E-05
0
0
0
0
2.43E-05
9.86E-05
1.13E-04
9.86E-05
0
0
0
0
0
2.43E-05
9.86E-05
1.13E-04
Efficiency matrix ε of 1.332MeV, as exemplified for the aluminum silicate sampleij[8×8]As shown in table 4:
TABLE 4
1.07E-04
9.22E-05
2.21E-05
0
0
0
0
0
9.22E-05
1.07E-04
9.22E-05
2.21E-05
0
0
0
0
2.21E-05
9.22E-05
1.07E-04
9.22E-05
2.21E-05
0
0
0
0
2.21E-05
9.22E-05
1.07E-04
9.22E-05
2.21E-05
0
0
0
0
2.21E-05
9.22E-05
1.07E-04
9.22E-05
2.21E-05
0
0
0
0
2.21E-05
9.22E-05
1.07E-04
9.22E-05
2.21E-05
0
0
0
0
2.21E-05
9.22E-05
1.07E-04
9.22E-05
0
0
0
0
0
2.21E-05
9.22E-05
1.07E-04
Matrix p of projection values obtained in conjunction with emission measurementsi[8×1]：
pi(E) Projection values, p, obtained for the detector at the i-layer positioni(E)＝ni(E)/[f(E).t]，ni(E) The net count of the detector full energy peak at the ith layer position, f (E) is the gamma ray emissivity branch ratio, f (E) of 0.662, 1.173 and 1.332MeV is 0.85, 0.9987 and 0.99982 respectively, and t is the scanning time of a single fault, which is 300s in the embodiment. Projection value matrix pi[8×1]For each column as in table 5:
TABLE 5
Based on the above matrix pi[8×1]And establishing a nuclide activity reconstruction equation set. Iteratively analyzing the nuclide activity reconstruction equation set by using an MLEM algorithm, wherein the iterative format of the MLEM algorithm is as follows:
in the formula: k is the number of iterations,for fault activity values after k iterations, piFor scanning projection values, ∈ijFor fault efficiency, i is the serial number of the detector position (i is more than or equal to 1 and less than or equal to N), and j is the serial number of the sample layer position (j is more than or equal to 1 and less than or equal to N). Solving by adopting an MLEM algorithm to obtain that the activities of 0.662, 1.173 and 1.332MeV in the aluminum silicate plate sample are 3.296 multiplied by 10 respectively5Bq (error 5.98%), 1.852 × 105Bq (error 35.09%), 1.786X 105Bq (error 30.26%), 0.662, 1.173, 1.332MeV activity in the sample wooden plates 3.316X 105Bq (error 6.63%), 1.756X 105Bq (error 28.1%), 1.644X 105Bq (error 19.95%), 0.662, 1.173, 1.332MeV activity 2.605X 10 respectively in the PVC sheet sample5Bq (error-16.25%), 1.392X 105Bq (error 1.5%), 1.294X 105Bq (error-5.64%). The error range of the activity of the reconstructed nuclide is-16.25% -35.09%, the requirement of the accuracy of the activity measurement of the nuclide in the radioactive waste bucket is met, and the feasibility and the effectiveness of the efficiency scale applied to SGS detection are proved.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
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