A method for estimating the age of spontaneous fission sources

Abstract

The embodiment of the present application provides a method for estimating the age of a spontaneous fission source, which relates to the field of nuclear technology and is used to improve the accuracy of estimating the age of a spontaneous fission source. The method for estimating the age of a spontaneous fission source provided in the embodiment of the present application includes: obtaining the radioactivity A of the sum of the first nuclides in the spontaneous fission source; 11 ; According to the sum of the radioactivity A of the first nuclide produced by spontaneous fission of multiple nuclides in the spontaneous fission source 21 and the age t of the spontaneous fission source, and let A 21 =A 11 , calculate t; wherein the multiple nuclides include one or more of the decay products of the main nuclides of the spontaneous fission source and the decay products of the impurity nuclides of the spontaneous fission source and the main nuclides. The method for estimating the age of a spontaneous fission source provided in an embodiment of the present application is used to estimate the age of a spontaneous fission source.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on the Chinese patent application "A method for estimating the age of a spontaneous fission source" with application number 202210724309.X and application date June 23, 2022, and the Chinese patent application "A method for estimating the age of a spontaneous fission source" with application number 202210723635.9 and application date June 23, 2022, and claims the priority of the two patent applications. The entire contents of the two patent applications are hereby incorporated into this application by introduction. Technical Field

[0003] The present application relates to the field of nuclear technology, and in particular to a method for estimating the age of a spontaneous fission source. Background Art

[0004] Spontaneous fission sources have many applications in medicine, scientific research, industry and nuclear science education, such as: human nuclide analysis, instrument calibration, neutron imaging, nuclear reactor start-up source, nuclear fuel and explosives, etc. Estimating the age of spontaneous fission sources is of great significance and practical application value, for example: spontaneous fission sources can be traced, their origin and production date can be tracked, etc.; the neutron intensity of spontaneous fission sources can also be accurately determined, so that related instruments can obtain higher accuracy when using spontaneous fission sources for calibration.

[0005] The main nuclides in spontaneous fission sources often do not emit gamma rays, or the gamma rays they emit are difficult to measure. In this case, it is difficult to estimate the age of the spontaneous fission source by measuring the amount of the main nuclides using the gamma spectrum. The main nuclides of spontaneous fission sources will undergo spontaneous fission, and within a certain period of time, the amount of spontaneous fission products of the main elements will change with the age of the spontaneous fission source. Therefore, the age of the spontaneous fission source can be estimated by the amount of spontaneous fission products of the main nuclides. However, in the related art, the age of the spontaneous fission source estimated in this way is not accurate. Summary of the invention

[0006] In view of this, an embodiment of the present application provides a method for estimating the age of a spontaneous fission source, so as to improve the accuracy of estimating the age of a spontaneous fission source.

[0007] The method for estimating the age of a spontaneous fission source provided in the embodiment of the present application includes: obtaining the radioactivity A of the sum of the first nuclides in the spontaneous fission source 11 ; According to the sum of the radioactivity A of the first nuclide produced by spontaneous fission of multiple nuclides in the spontaneous fission source 21 and the age t of the spontaneous fission source, and let A 21 =A 11, calculate t; wherein the multiple nuclides include one or more of the decay products of the main nuclides of the spontaneous fission source and the decay products of the impurity nuclides of the spontaneous fission source and the main nuclides.

[0008] In some optional embodiments of the present application, the relationship between the radioactivity of the sum of the first nuclides produced by spontaneous fission of the main nuclides and t is:

[0009]

[0010] In the formula, is the sum of the radioactivity of the first nuclides produced by spontaneous fission of the main nuclides, is the decay constant of the first nuclide, is the decay constant of the main nuclide, is the total radioactivity of the main nuclides at the initial moment, is the spontaneous fission branching ratio of the main nuclide, It is the cumulative yield of the first nuclide produced by the spontaneous fission of the main nuclide.

[0011] In some optional embodiments of the present application, the relationship between the radioactivity of the sum of the first nuclides produced by spontaneous fission of a decay daughter of a nuclide of a spontaneous fission source and t is:

[0012]

[0013] In the formula, is the number of nuclei of the (n-1)th decay daughter of a nuclide at time t, is the number of nuclei of this nuclide at time t, is the decay constant of the (n-1)th decay daughter of this nuclide, is the decay constant of the nuclide, is the spontaneous fission branching ratio of the (n-1)th decay daughter of this nuclide, is the spontaneous fission branching ratio of the nuclide, is the number of nuclei of the first nuclide produced by the spontaneous fission of the (n-1)th decay daughter of this nuclide, is the cumulative yield of the first nuclide produced by the spontaneous fission of the (n-1)th decay daughter of this nuclide, is the number of decay daughter nuclei of the (n-1)th level of this nuclide at the initial moment, It is the total radioactive activity of the first nuclides produced by the spontaneous fission of the (n-1)th decay daughters of this nuclide.

[0014] In some optional embodiments of the present application, the method further includes: obtaining the radioactivity A of the sum of the second nuclides in the spontaneous fission source12 ; Calculate A 11 With A 12 The ratio between them is R1; according to A 21 The relationship between and t, and let A 21 =A 11 , calculate t as: According to A 21 The total radioactivity A of the second nuclide produced by spontaneous fission of multiple nuclides 22 The relationship between the ratio R2 and t, and let R2=R1, calculate t.

[0015] In some optional embodiments of the present application, any one of the multiple nuclides has a long-lived fission product of the same type as the first nuclide, and any one of the multiple nuclides has a short-lived fission product of the same type as the second nuclide.

[0016] In some optional embodiments of the present application, the relationship between the radioactivity of the sum of the second nuclides produced by spontaneous fission of the main nuclides and t is:

[0017]

[0018] In the formula, is the sum of the radioactivity of the secondary nuclides produced by the spontaneous fission of the main nuclide, is the total radioactivity of the main nuclides at the initial moment, is the spontaneous fission branching ratio of the main nuclide, is the cumulative yield of the second nuclide produced by spontaneous fission of the main nuclide, is the decay constant of the main nuclide.

[0019] In some optional embodiments of the present application, the main nuclides are 252 Cf, multiple nuclides including 252 Cf decay produces 248 Cm and / or 246 Pu.

[0020] In some optional embodiments of the present application, the main nuclides are 252 Impurity nuclides of Cf, spontaneous fission source include 250 Cf, multiple nuclides including 250 Cf decay produces 246 Cm.

[0021] In some optional embodiments of the present application, the plurality of nuclides further includes at least one impurity nuclide of a spontaneous fission source.

[0022] In some optional embodiments of the present application, the main nuclides are 252 Cf, multiple nuclides including250 Cf and / or 254 Cf.

[0023] The method for estimating the age of a spontaneous fission source provided in the embodiment of the present application not only considers the first nuclide produced by the fission of the main nuclide, but also considers the first nuclide produced by the fission of the decay products of the main nuclide and the impurity nuclide. The radioactivity of the sum of the first nuclides in the obtained spontaneous fission source is used as the radioactivity of the sum of the first nuclides produced by the spontaneous fission of multiple nuclides, so as to estimate the age of the spontaneous fission source. In the spontaneous fission source, the decay products of the main nuclide and the decay products of the impurity nuclide will fission to form a relatively large number of first nuclides. Considering the influence of the decay products of the main nuclide and the decay products of the impurity nuclide on the calculation results, the accuracy of the spontaneous fission source age estimation result can be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the method for estimating the age of the spontaneous fission source in the comparative example;

[0025] Figure 2 A method for estimating the age of spontaneous fission sources in some embodiments of the present application;

[0026] Figure 3 A method for estimating the age of a spontaneous fission source in other embodiments of the present application;

[0027] Figure 4 for 252 Decay chain of Cf;

[0028] Figure 5 In some embodiments of this application 252 Method for estimating Cf source age. DETAILED DESCRIPTION

[0029] It should be noted that, in the absence of conflict, the embodiments and technical features in the embodiments of the present application can be combined with each other, and the detailed description in the specific implementation method should be understood as an explanation of the purpose of the present application and should not be regarded as an improper limitation on the present application.

[0030] In the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, unless otherwise specified, "multiple" means two or more.

[0031] In the embodiments of the present application, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0032] In the embodiments of the present application, words such as "exemplarily" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "exemplarily" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplarily" or "for example" is intended to present related concepts in a specific way.

[0033] The present application provides a method for estimating the age of a spontaneous fission source, wherein the type of the spontaneous fission source is not limited, as long as the main nuclide of the spontaneous fission source is a heavy nuclide that can undergo spontaneous fission. For example, a spontaneous fission source can be 252 Cf source, 250 Cf source, 244 Pu source or 248 Cm source, etc. The age of the spontaneous fission source, that is, the time since the spontaneous fission source was separated and purified for the last time.

[0034] The main nuclides of spontaneous fission sources will undergo spontaneous fission, and within a certain period of time, the amount of spontaneous fission products of the main elements will change with the age of the spontaneous fission source, so the age of the spontaneous fission source can be estimated by the amount of spontaneous fission products of the main nuclides. However, in the related art, the age of the spontaneous fission source estimated in this way is not accurate.

[0035] As part of the inventiveness of this application, the reasons for the inaccurate estimation of the age of spontaneous fission sources are analyzed below. Figure 1 In the related art, the method for estimating the age of a spontaneous fission source generally includes the following steps:

[0036] Step S101, obtaining the total radioactivity A of the first nuclide in the spontaneous fission source 11 ;

[0037] Step S102, based on the total radioactivity A of the first nuclides produced by the spontaneous fission of the main nuclides of the spontaneous fission source 01 and the age t of the spontaneous fission source, and let A 01 =A 11 , calculate t.

[0038] In the related art, let A 01 =A 11 That is, the sum of the radioactive activities of the first nuclides in the spontaneous fission source is taken as the sum of the radioactive activities of the first nuclides produced by the spontaneous fission of the main nuclides. However, the first nuclides in the spontaneous fission source may not be completely produced by the fission of the main nuclides. Other nuclides in the spontaneous fission source except the main nuclides may also fission to produce the first nuclides. Therefore, A 11 may actually be greater than A 01 , directly let A 01 =A 11 The calculation of t is not accurate.

[0039] In view of this, the present application embodiment provides a method for estimating the age of a spontaneous fission source, please refer to Figure 2 , the estimation method of the spontaneous fission source age includes:

[0040] S201, obtaining the total radioactivity A of the first nuclide in the spontaneous fission source 11 ;

[0041] S202, based on the total radioactivity A of the first nuclides produced by spontaneous fission of multiple nuclides in the spontaneous fission source 21 and the age t of the spontaneous fission source, and let A 21 =A 11 , calculate t.

[0042] The multiple nuclides include one or more of the decay products of the main nuclides of the spontaneous fission source and the decay products of the impurity nuclides of the spontaneous fission source and the main nuclides.

[0043] The method for estimating the age of a spontaneous fission source provided in the embodiment of the present application not only considers the first nuclide produced by the fission of the main nuclide, but also considers the first nuclide produced by the fission of the decay products of the main nuclide and the impurity nuclide. The radioactivity of the sum of the first nuclides in the obtained spontaneous fission source is used as the radioactivity of the sum of the first nuclides produced by the spontaneous fission of multiple nuclides, so as to estimate the age of the spontaneous fission source. In the spontaneous fission source, the decay products of the main nuclide and the decay products of the impurity nuclide will fission to form a relatively large number of first nuclides. Considering the influence of the decay products of the main nuclide and the decay products of the impurity nuclide on the calculation results, the accuracy of the spontaneous fission source age estimation result can be greatly improved.

[0044] It needs to be explained that the first nuclide refers to a certain nuclide in the spontaneous fission source and cannot include multiple nuclides.

[0045] It should be explained that the total radioactivity A of the first nuclide in the spontaneous fission source is obtained.11 It refers to obtaining the radioactivity of the sum of the first nuclides existing in the spontaneous fission source at the current moment, and the same applies to the second nuclide. In addition, the sum of the first nuclides produced by the spontaneous fission of multiple nuclides in the spontaneous fission source refers to the sum of all the first nuclides produced by the fission of multiple nuclides from the initial moment to the current moment, which are still present in the spontaneous fission source at the current moment. Each nuclide in the multiple nuclides will spontaneously fission to produce the first nuclide, and the same applies to the second nuclide.

[0046] It should be explained that the main nuclide refers to the nuclide with the highest content in the spontaneous fission source at the initial moment, that is, when the age of the spontaneous fission source is zero, such as 252 The main nuclides of Cf sources are 252 Cf.

[0047] Optionally, in some embodiments of the present application, the first nuclide may be a long-lived fission product of the main nuclide. Long-lived fission products accumulate over time, and using long-lived fission products to estimate the lifetime is more accurate.

[0048] It should be explained that the long-lived fission product of a certain nuclide refers to the fission product of the nuclide with a longer half-life, which is not easy to decay into other nuclides and will accumulate as the parent nuclide continues to spontaneously fission. The short-lived fission product of a certain nuclide refers to the fission product of the nuclide with a shorter half-life, which is easy to decay into other nuclides. In the embodiment of the present application, the short-lived fission product can be defined as follows: in the process of spontaneous fission of the parent nuclide, a short-lived fission product of the parent nuclide and the parent nuclide will gradually reach a radioactive equilibrium state and last until the end. The long-lived fission product can be defined as follows: all other spontaneous fission products of the parent nuclide except the short-lived fission product can be used as long-lived fission products.

[0049] It should be explained that the decay of the nuclides in the embodiments of the present application can be either single decay or continuous decay. In the embodiments of the present application, a decay product of a nuclide can refer to any decay daughter in the decay chain of the nuclide, and a decay product refers to including one nuclide and cannot include multiple nuclides.

[0050] In addition, obtain A 11 There are many methods, for example, it can be an absolute measurement method of radioactivity or a relative measurement method of radioactivity. In some optional embodiments of the present application, the peak net count rate of the characteristic γ energy peak of the nuclide to be measured with the energy E is obtained by using the gamma energy spectrum to obtain A 11 Specifically, after determining the peak net count rate of the characteristic γ energy peak of the nuclide to be measured with the energy E, the radioactivity of the nuclide to be measured can be calculated using the following formula:

[0051] I(E)=A×Br(E)×η(E) (1)

[0052] Where A is the radioactivity of the nuclide to be measured; I(E) is the peak net count rate of the characteristic γ energy peak of the nuclide to be measured with energy E; η(E) is the detection efficiency of the total energy peak of the nuclide to be measured with energy E; Br(E) is the branching ratio of the characteristic γ energy peak of the nuclide to be measured with energy E.

[0053] Specifically, in the case of a spontaneous fission source 252 Based on the Cf source, the first nuclide can be 137 Cs. On this basis, in some optional embodiments of the present application, by measuring 137 The energy of Cs is 661.66keV, which is the peak net count rate of the characteristic γ energy peak. 137 The activity of Cs.

[0054] The peak net count rate of the characteristic gamma energy peak of the nuclide to be measured can be measured using a high-energy germanium detector. Specifically, the high-energy germanium detector can be set according to the selected parameters to be measured, and the energy calibration, efficiency calibration and background measurement of the set high-energy germanium detector can be performed, and then the spontaneous fission source can be placed at a suitable distance between the center line of the high-energy germanium detector and the end face for measurement. The spontaneous fission source is 252 Based on the Cf source, in some optional implementations of the present application, an energy range of 0 to 2.6 MeV can be selected for gamma spectrum measurement.

[0055] Further, in some optional embodiments of the present application, the relationship between the radioactivity of the sum of the first nuclides produced by spontaneous fission of the main nuclides and t is:

[0056]

[0057] In the formula, is the sum of the radioactivity of the first nuclides produced by spontaneous fission of the main nuclides, is the decay constant of the first nuclide, is the decay constant of the main nuclide, is the total radioactivity of the main nuclides at the initial moment, is the spontaneous fission branching ratio of the main nuclide, It is the cumulative yield of the first nuclide produced by the spontaneous fission of the main nuclide.

[0058] In this way, Add the radioactivity of the first nuclide produced by spontaneous fission of other nuclides except the main nuclide to get A. 21 The relationship between t.

[0059] It should be explained that e in the embodiments of the present application refers to a natural constant.

[0060] In some optional embodiments of the present application, the relationship between the radioactivity of the sum of the first nuclides produced by the spontaneous fission of a decay daughter of a nuclide of a spontaneous fission source and t is:

[0061]

[0062] In the formula, is the number of nuclei of the (n-1)th decay daughter of a nuclide at time t, is the number of nuclei of this nuclide at time t, is the decay constant of the (n-1)th decay daughter of this nuclide, is the decay constant of the nuclide, is the spontaneous fission branching ratio of the (n-1)th decay daughter of this nuclide, is the spontaneous fission branching ratio of the nuclide, is the number of nuclei of the first nuclide produced by the spontaneous fission of the (n-1)th decay daughter of this nuclide, is the cumulative yield of the first nuclide produced by the spontaneous fission of the (n-1)th decay daughter of this nuclide, is the number of decay daughter nuclei of the (n-1)th level of this nuclide at the initial moment, It is the total radioactive activity of the first nuclides produced by the spontaneous fission of the (n-1)th decay daughters of this nuclide.

[0063] In this way, and By adding them together, we can obtain the relationship between the sum of the radioactive activities of the first nuclides produced by the spontaneous fission of the main nuclides and the sum of the radioactive activities of the first nuclides produced by the fission of the decay daughters of a certain nuclide in the spontaneous fission source and t, and then obtain A 21 The relationship between t.

[0064] In addition, it is necessary to explain:

[0065]

[0066] In the formula, The number of nuclei of the main nuclides at the initial moment.

[0067] Furthermore, in some optional embodiments of the present application, the method for estimating the age of the spontaneous fission source further comprises: obtaining the radioactivity A of the sum of the second nuclides in the spontaneous fission source. 12 ; Calculate A 11 With A 12The ratio between them is R1; according to A 21 The relationship between and t, and let A 21 =A 11 , calculate t as: According to A 21 The total radioactivity A of the second nuclide produced by spontaneous fission of multiple nuclides 22 The relationship between the ratio R2 and t, and let R2 = R1, calculate t. That is, please refer to Figure 3 In this embodiment, the method for estimating the age of the spontaneous fission source comprises the following steps:

[0068] S301, obtaining the total radioactivity A of the first nuclide in the spontaneous fission neutron source 11 , and the sum of the radioactivity of the second nuclide A 12 ;

[0069] S302, calculate A 11 With A 12 The ratio between them is R1;

[0070] S303, according to A 21 The total radioactivity A of the second nuclide produced by spontaneous fission of multiple nuclides 22 The relationship between the ratio R2 and t, and let R2=R1, calculate t.

[0071] In formula 2 and formula 3, it is usually necessary to use To calculate, is the total radioactivity of the main nuclides at the initial moment. It is very likely to be an unknown quantity in the process of estimating the radioactivity of spontaneous fission sources. 21 It is difficult to obtain the relationship between A and t. In view of this, we can use the calculation A 21 With A 22 The ratio R2 between them, and t is calculated by setting R2 = R1. R2 does not contain This item does not need to be obtained The age of the spontaneous fission source can be estimated.

[0072] In some optional embodiments of the present application, any one of the multiple nuclides has a short-lived fission product of the same type as the second nuclide, and the relationship between the sum of the radioactivity of the second nuclides produced by the spontaneous fission of the main nuclide and t is:

[0073]

[0074] In the formula, is the sum of the radioactivity of the secondary nuclides produced by the spontaneous fission of the main nuclide, is the total radioactivity of the main nuclides at the initial moment, is the spontaneous fission branching ratio of the main nuclide, is the cumulative yield of the second nuclide produced by spontaneous fission of the main nuclide, is the decay constant of the main nuclide.

[0075] In this way, Add the total radioactivity of the second nuclides produced by spontaneous fission of other nuclides except the main nuclide to get A 22 The relationship between A and t is used to calculate 21 With A 22 The ratio R2 between them can be used to calculate t.

[0076] The radioactivity of the sum of the second nuclides in the second nuclide spontaneous fission neutron source is obtained, specifically, when the spontaneous fission source is 252 Based on the Cf source, the second isotope can be 132 I. On this basis, in some optional embodiments of the present application, by measuring 132 The energy of I is calculated by the peak net count rate of the characteristic γ energy peak of 667.72keV 132 The activity of I. 137 The characteristic γ energy peak energy measured by Cs is 661.66keV. 132 The characteristic γ energy peak energy measured by I is 667.72keV, with a difference of only 6keV. It can be considered that their detection efficiencies are approximately the same, that is, for formula 1, η(667.72) can be considered to be the same as η(661.66), which helps to simplify the calculation of R1 and improve the calculation efficiency.

[0077] Further, in some optional embodiments of the present application, the main nuclides are 252 Cf, multiple nuclides including 252 Cf decay produces 248 Cm and / or 244 Pu. 252 Cf has the characteristics of high spontaneous fission branching ratio and high neutron emission rate. The spontaneous fission branching ratio is 3.09% and the neutron emission rate is 2.31×106·s-1·μg-1. Please refer to Figure 4 , 248 Cm is 252 The first decay daughter of Cf, 244 Pu 252 The second decay daughter of Cf. 248 The spontaneous fission branching ratio of Cm is 8.39% and the specific activity is 1.57×10 8 Bq·g -1 . 240 Pu and 236U spontaneous fission branching ratio is less than 0.001%. 252 Among the multi-level decay daughters of Cf, the main considerations are 248 Cm and / or 244 The spontaneous fission products of Pu to A 21 and A 22 The influence of other nuclides can be ignored, that is, calculate A 21 and A 22 In the process of adding the activities of the corresponding spontaneous fission products of the multiple nuclides, the corresponding spontaneous fission products refer to the first nuclide or the second nuclide. In this process, the multiple nuclides may not include 248 Cm and / or 244 The decay products of major nuclides other than Pu can be obtained through experiments, which will not have a significant impact on the results.

[0078] Through experiments, it can be found that 252 The age of the Cf source is greater than 40 years. 21 and A 22 In the process, no consideration is given 248 The radioactivity of Cm fission products will have a significant impact on the estimation of the age of spontaneous fission sources.

[0079] Further, in some optional embodiments of the present application, the main nuclides are 252 Impurity nuclides of Cf, spontaneous fission source include 250 Cf, multiple nuclides including 250 Cf decay produces 246 Cm. 250 In the Cf decay chain 242 Pu, 238 U Spontaneous fission branching ratio is less than 10 -5 %.exist 252 Among the decay products of various impurity nuclides in the Cf source, the main considerations are 250 Cf decay produces 246 Spontaneous fission products of Cm to A 21 and A 22 The influence of other impurity nuclides can be ignored. It can be obtained through experiments that this will not have a significant impact on the estimation results of the age of spontaneous fission sources.

[0080] Furthermore, in some optional embodiments of the present application, the plurality of nuclides also include at least one impurity nuclide of a spontaneous fission source. In addition to the main nuclide, other impurity nuclides may also exist in the spontaneous fission source. For example, 252 In the Cf source, due to 250 It is difficult for nuclides such as Cf to 252 Cf is completely separated, 252 In addition to Cf252 Cf often exists 250 Cf and other nuclides. The impurity nuclides and decay products of the impurity nuclides in the spontaneous fission source can also fission to produce the first nuclide or the second nuclide. If A is calculated 21 and A 22 Failure to consider the influence of these nuclides in the process may also lead to inaccurate estimation of the age of spontaneous fission sources. Therefore, in order to further improve the accuracy of spontaneous fission source age estimation, in some optional embodiments of the present application, the calculation of A 21 and A 22 When calculating the atomic nuclide, not only the influence of the main nuclides and their decay products are taken into account, but also the influence of the impurity nuclides and their decay products of the spontaneous fission source are taken into account.

[0081] It needs to be explained that the impurity nuclides in the spontaneous fission source refer to the nuclides other than the main nuclides in the spontaneous fission source at the initial moment, that is, when the age of the spontaneous fission source is zero, and do not include the decay products of various nuclides in the spontaneous fission source during the process of the spontaneous fission source's age increasing.

[0082] In the spontaneous fission source 252 Based on the Cf source, in some optional embodiments of the present application, the multiple nuclides include 250 Cf and / or 254 Cf.

[0083] 252 Cf neutron source also contains 249-254 Cf has many isotopes, among which 249 Cf 251 Cf can be observed in the γ energy spectrum with obvious characteristic rays, which can be determined by direct measurement 249 Cf 251 The activity of Cf, at the same time, 249 Cf 251 The spontaneous fission branching ratio of Cf is very small, and its spontaneous fission products can be ignored. Accordingly, 253 Cf, due to its short half-life, its spontaneous fission products can be ignored. 252 Among the various impurity nuclides in the Cf source, the main considerations are 250 Cf and / or 254 The spontaneous fission products of Cf are 21 and A 22 The influence of other impurity nuclides can be ignored. It can be obtained through experiments that this will not have a significant impact on the estimation results of the age of spontaneous fission sources.

[0084] along with 252 As the age of the Cf neutron source increases, 252 The energy peak of Cf fission products generally shows a downward trend. This downward trend follows252 The decay curve of Cf, after decaying to about 25 years, 250 Cf begins to have an impact and then begins to follow 250 The decay curve of Cf decreases slowly. 248 The relative neutron yield of Cm accounts for only 10% of the total neutron yield. Therefore, until the age of the californium source exceeds 40 years, 248 Cm begins to significantly affect the neutron emission rate.

[0085] 254 The spontaneous fission branching ratio of Cf is 0.31%, but its half-life is 60.5 days. The contribution of the nuclides produced by spontaneous fission of 252Cf sources with a long age can be ignored, while the contribution of nuclides produced by spontaneous fission of 252Cf sources with a short age can be considered. 252 The age of the Cf source is more than 20 months, 254 The spontaneous fission products of Cf are 21 and A 22 The effect of is very small and can be ignored. 252 Cf is older than 20 months, and at least one of the multiple nuclides may include 250 Cf, not included 254 Cf. In addition, through experiments, it can be found that when 252 Cf sources older than 25 years are not considered 250 The Cf fission products will 252 This has a significant impact on the estimation of the age of Cf sources.

[0086] Generally, there is usually a relative ratio between the impurity nuclides and the main nuclides in the spontaneous fission source, for example, 252 In the Cf source, at the initial moment, 250 The sum of Cf and 252 The ratio between the sum of Cf is generally about 0.02 to 0.03. The relationship between the activity of the corresponding spontaneous fission product of the impurity nuclide and t can be calculated by combining this ratio with Formula 2, Formula 3, Formula 4, Formula 5, and Formula 6.

[0087] The following is an elaboration of the method for estimating the age of a spontaneous fission source provided by the present application in conjunction with a specific embodiment. The spontaneous fission source is 252 Cf source, 252 Impurity nuclides in Cf source include 250 Cf, please refer to Figure 5 The method for estimating the age of the spontaneous fission source mainly includes the following steps:

[0088] Select 137 The peak net count rate of the characteristic γ energy peak of Cs at 661.66 keV is 132The peak net count rate of the characteristic γ energy peak with energy of 667.72keV is taken as the parameter to be measured;

[0089] Setting a high energy germanium detector according to the selected parameters to be measured;

[0090] Energy calibration, efficiency calibration and background measurement of high energy germanium detectors;

[0091] Will 252 The Cf source is placed at a preset position on the center line of the high-energy germanium detector, and then gamma spectrum measurement in the range of 0 to 2.6 MeV is performed;

[0092] The obtained parameters to be measured are calculated in the mathematical model 252 The age of the Cf source, the mathematical model is as follows:

[0093]

[0094] Where R is the measured 137 The peak net count rate of the characteristic γ energy peak of Cs with an energy of 661.66keV is similar to the measured 132 The energy of I is the ratio of the peak net count rate of the characteristic γ energy peak of 667.72 keV, I Cf252 (y1), I Cf250 (y1), I Cm248 (y1), I Cm246 (y1) and I Pu244 (y1) Produced by spontaneous fission of various nuclides 137 The time expression of the peak net count rate of the characteristic gamma energy peak of Cs with an energy of 661.66keV, multiple nuclides including 252 Cf 250 Cf 252 Cf decay produces 248 Cm, 250 Cf decay produces 246 Cm and 252 Cf decay produces 244 Pu. I Cf252 (y2), I Cf250 (y2), I Cm248 (y2), I Cm246 (y2) and I Pu244 (y2) produced by spontaneous fission of various nuclides 132 The time expression of the peak net count rate of the characteristic gamma energy peak of I with an energy of 667.72keV, multiple nuclides including 252 Cf 250 Cf 252 Cf decay produces 248 Cm, 250 Cf decay produces 246Cm and 252 Cf decay produces 244 Pu.

[0095] The final estimated 252 The age of the Cf source is 25.7 years, and the certified age of the neutron source is 26.2 years, and the estimated results are relatively accurate.

[0096] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for estimating the age of a spontaneous fission source, characterized in that: include: Obtaining the total radioactivity A of the first nuclide in the spontaneous fission source 11 ; According to the radioactivity A of the sum of the first nuclides produced by the spontaneous fission of multiple nuclides in the spontaneous fission source 21 and the age t of the spontaneous fission source, and let A 21 =A 11 , calculate t; Wherein, the plurality of nuclides include one or more of the decay products of the main nuclide of the spontaneous fission source and the decay products of the impurity nuclides of the spontaneous fission source and the main nuclide; Obtaining the total radioactivity A of the second nuclide in the spontaneous fission source 12 ; Calculate A 11 With A 12 The ratio between them is R1; According to A 21 The relationship between and t, and let A 21 =A 11 , calculate t as: According to A 21 The radioactivity A of the sum of the second nuclides produced by spontaneous fission of the plurality of nuclides 22 The relationship between the ratio R2 and t, and let R2 = R1, calculate t; Any one of the plurality of nuclides has a long-lived fission product of the same type as the first nuclide, and any one of the plurality of nuclides has a short-lived fission product of the same type as the second nuclide; The relationship between the radioactivity of the sum of the second nuclides produced by the spontaneous fission of the main nuclides and t is: In the formula, is the radioactivity of the sum of the second nuclides produced by the spontaneous fission of the main nuclide, is the sum of the radioactivity of the main nuclides at the initial moment, is the spontaneous fission branching ratio of the main nuclide, is the cumulative yield of the second nuclide produced by the spontaneous fission of the main nuclide, is the decay constant of the main nuclide.

2. The method for estimating the age of a spontaneous fission source according to claim 1, characterized in that: The relationship between the radioactivity of the sum of the first nuclides produced by the spontaneous fission of the main nuclides and t is: In the formula, is the radioactivity of the sum of the first nuclides produced by the spontaneous fission of the main nuclides, is the decay constant of the first nuclide, is the decay constant of the main nuclide, is the sum of the radioactivity of the main nuclides at the initial moment, is the spontaneous fission branching ratio of the main nuclide, is the cumulative yield of the first nuclide produced by the spontaneous fission of the main nuclide.

3. The method for estimating the age of a spontaneous fission source according to claim 1, characterized in that: The relationship between the radioactivity of the sum of the first nuclides produced by the spontaneous fission of a decay daughter of the nuclide of the spontaneous fission source and t is: In the formula, is the number of nuclei of the (n-1)th decay daughter of a nuclide at time t, is the number of nuclei of this nuclide at time t, is the decay constant of the (n-1)th decay daughter of this nuclide, is the decay constant of the nuclide, is the spontaneous fission branching ratio of the (n-1)th decay daughter of this nuclide, is the spontaneous fission branching ratio of the nuclide, is the number of nuclei of the first nuclide produced by the spontaneous fission of the (n-1)th decay daughter of the nuclide, is the cumulative yield of the first nuclide produced by the spontaneous fission of the (n-1)th decay daughter of the nuclide, is the number of decay daughter nuclei of the (n-1)th level of this nuclide at the initial moment, It is the total radioactive activity of the first nuclides produced by the spontaneous fission of the (n-1)th decay daughters of this nuclide.

4. The method for estimating the age of a spontaneous fission source according to claim 1, characterized in that: The main nuclides are 252 Cf, the plurality of nuclides include 252 Cf decay produces 248 Cm and / or 246 Pu.

5. The method for estimating the age of a spontaneous fission source according to claim 1, characterized in that: The main nuclides are 252 Cf, the impurity nuclides of the spontaneous fission source include 250 Cf, the plurality of nuclides include 250 Cf decay produces 246 Cm.

6. The method for estimating the age of a spontaneous fission source according to any one of claims 1 to 5, characterized in that: The plurality of nuclides also includes at least one impurity nuclide of the spontaneous fission source.

7. The method for estimating the age of a spontaneous fission source according to claim 6, characterized in that: The main nuclides are 252 Cf, the plurality of nuclides include 250 Cf and / or 254 Cf.

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