CN112965097B - Method for deducting interference of same product as target nuclear reaction in nuclear reaction section measurement - Google Patents
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Abstract
The invention relates to the technical field of nuclear data measurement, in particular to an algorithm for deducting interference of a product identical to a target nuclear reaction in nuclear reaction section measurement. Which comprises measuring nuclear reaction cross-sections using a natural sample containing a plurality of isotopes; judging whether other nuclear reactions generating the same product can ignore the interference of the measurement of the cross section of the target nuclear reaction; other nuclear reactions that produce the same product, which cannot be ignored, are subtracted from the cross-sectional measurement interference of the target nuclear reaction. In the present invention, in the case where the interference generated by other nuclear reactions producing the same product on the target nuclear reaction section measurement is not negligible, the interference thereof on the target nuclear reaction section measurement is subtracted by the experimental or evaluation value where the reaction sections of other nuclear reactions producing the same product are reliable, thereby improving the accuracy of nuclear reaction section data obtained when the nuclear reaction section is measured using a natural sample containing a plurality of isotopes.
Description
Technical Field
The invention relates to the technical field of nuclear data measurement, in particular to a method for deducting interference of a product identical to a target nuclear reaction in nuclear reaction section measurement.
Background
The accurate and reliable nuclear reaction section experimental data is basic data required by nuclear reactor design, radiation shielding calculation and other nuclear engineering calculation, and plays an important role in the fields of national defense construction, national economy construction and basic science research.
However, the problem of mutual interference of various nuclear reactions can be generally solved by using isotope separation or different cooling times depending on the half-life of the nuclei to be produced, but in practical experiments, natural samples are generally used, and if the sample element contains a plurality of stable isotopes, the problem of mutual interference of a plurality of nuclear reactions which produce the same nuclei after the natural sample is activated is generally difficult to avoid.
Disclosure of Invention
The present invention is directed to a method for subtracting the interference of the same product as the target nuclear reaction in the nuclear reaction section measurement, so as to solve the above-mentioned problems in the prior art.
In order to achieve the above object, the present invention provides a method for subtracting interference of the same product as the target nuclear reaction from the nuclear reaction section measurement, comprising the following steps:
s1.1, measuring a nuclear reaction section by adopting a natural sample containing a plurality of isotopes;
S1.2, judging whether interference generated by other nuclear reaction products on the target nuclear reaction section measurement can be ignored;
s1.3, deducting gamma-ray interference of target nuclear reaction section measurement by using other nuclear reactions which cannot be ignored and generate the same product.
As a further improvement of the technical scheme, in the process of measuring the nuclear reaction section of the natural sample containing a plurality of isotopes in S1.1, 14MeV neutron irradiation is carried out on the natural sample, and the method comprises the following steps of;
s2.1, sample preparation: preparing a high-purity natural sample into a wafer with the diameter of 20mm, clamping the wafer between two high-purity monitoring pieces (niobium or aluminum) with the same diameter, and wrapping the outer side of the wafer by a cadmium skin with the thickness of about 1 mm;
s2.2, sample irradiation: irradiating the sample with 14MeV generated by a strong current D-T neutron generator;
S2.3, gamma-ray activity measurement: measuring the gamma-ray activity of the reaction product by using a high-purity germanium gamma-spectrometer system;
s2.4, calculating and correcting the section: and calculating and correcting the section of the nuclear reaction to be detected.
As a further improvement of the present technical solution, the calculation formula of the nuclear reaction section in S2.4 is as follows:
Wherein subscripts "x" and "0" represent the values of the sample to be tested and the monitor panel, respectively; epsilon is the total peak efficiency of the measured characteristic gamma rays; i γ is the intensity of the characteristic gamma ray; η is the natural abundance of the measured nuclide; m is the mass of the sample; d is a measurement collection factor; a is the atomic weight of a sample element; c is the measured characteristic gamma ray total peak area of the nuclear reaction product to be measured; lambda is the decay constant; f is the total gamma ray activity correction factor: f=f s×fc×fg, where F s、fc、fg is the self-absorption correction factor, cascade gamma-ray coincidence correction factor, and geometric correction factor, respectively, of gamma-rays in the sample; k is a neutron fluence rate fluctuation correction factor, s=1-e -λT represents a growth factor of the remaining nuclei; σ 0 is the cross-sectional evaluation value of the supervised reaction.
As a further improvement of the present technical solution, the calculation formula of the measurement collection factor is as follows:
where t 1 is a time interval from the end of irradiation to the start of measurement, and t 2 is a time interval from the end of irradiation to the end of measurement.
As a further improvement of the technical scheme, the neutron fluence rate fluctuation correction factor is calculated as follows:
Wherein L is the number of segments into which the irradiation time is divided; Δt i is the time interval of the i-th segment; t i is the time interval between the end of the ith segment and the end of all irradiation; phi i is the average neutron flux incident during Δt i time; phi is the average neutron flux incident on the natural sample over the entire irradiation time.
As a further improvement of the present technical solution, the cross section of the other nuclear reactions that generate the same nuclei in S1.2 is extremely small, and when the interference to the measurement of the cross section of the target nuclear reaction is extremely small, it is negligible.
As a further improvement of the present technical solution, the gamma-ray interference measured by the cross section of the target nuclear reaction is subtracted from the other nuclear reactions which generate the same species and cannot be ignored in S1.3, and the subtraction method is as follows:
S3.1, calculating the gamma-ray total energy peak count to be deducted: calculating the gamma-ray totipotent peak count to be deducted by using the evaluation value or reliable experimental value of other nuclear reaction sections with the same product;
S3.2, calculating gamma-ray total energy peak count after deduction of influence: subtracting the total peak count of the same gamma rays generated by other nuclear reactions from the total peak count of the characteristic gamma rays of the actually measured target nuclear reaction products to obtain the total peak count of the characteristic gamma rays of the actual (i.e. deducted interference of other nuclear reactions) target nuclear reaction products;
S3.3, calculating a target nuclear reaction section after interference deduction: the cross section of the target nuclear reaction after the interference of other nuclear reactions is subtracted is calculated by using the total energy peak count of the characteristic gamma rays of the actual target nuclear reaction product (namely the interference of other nuclear reactions is subtracted) and a nuclear reaction cross section calculation formula.
As a further improvement of the present technical solution, in S3.1, interference of the target nuclear reaction section measurement is subtracted from other nuclear reactions that cannot be ignored and generate the same products, and the calculation formula of the gamma-ray total peak count C' to be subtracted is as follows:
Wherein subscripts '0' and 'y' respectively represent values of a sample to be detected and a monitoring sheet, sigma y is a section evaluation value of interference reaction or a reliable experimental value, sigma 0 is a section evaluation value of monitoring reaction, and C is a characteristic gamma ray total peak area of an actually measured nuclear reaction product to be detected; epsilon is the total peak efficiency of the measured characteristic gamma rays; i γ is the intensity of the characteristic gamma ray; η is the natural abundance of the measured nuclide; m is the mass of the sample; for measuring the collection factor (t 1 is the time interval from the end of irradiation to the start of measurement, t 2 is the time interval from the end of irradiation to the end of measurement); a is the atomic weight of a sample element; lambda is the decay constant; f=f s*Fc*Fg is the total gamma-ray activity correction factor: f s,Fc,Fg is the self-absorption correction factor, cascade gamma ray coincidence effect correction factor and geometric correction factor of gamma ray in the sample respectively; k is neutron fluence rate fluctuation correction factor, and the expression is/> Wherein L is the number of segments into which the irradiation time is divided, Δt i is the time interval of the i-th segment, and T i is the time interval between the end of the i-th segment and the end of all the irradiation; Φ i is the average neutron flux incident on the sample during Δt i time, Φ is the average neutron flux incident on the sample during the entire irradiation time T, s=1-e -λT represents the growth factor of the remaining nuclei.
It should be noted that, in the actual measurement of the nuclear reaction section, in the process of measuring and calculating the target nuclear reaction section by using the general calculation formula of the nuclear reaction section, the total peak area of the gamma ray should be the total peak area of the gamma ray of the actually measured target nuclear reaction product, the total peak area C 'of the same gamma ray generated by other nuclear reactions with the same product is subtracted, and C' can be obtained by the calculation formula of the total peak count of the gamma ray which should be subtracted from the evaluation value of the reaction section or the experimental value sigma y.
Compared with the prior art, the invention has the beneficial effects that: in the case that interference generated by other nuclear reaction products on the target nuclear reaction section measurement cannot be ignored, the interference problem between the multiple nuclear reactions of the same product generated by activating the natural sample is solved by subtracting the influence of the reliable experimental value or evaluation value of the other nuclear reactions of the same product on the target nuclear reaction section measurement.
Drawings
FIG. 1 is a flowchart of the algorithm steps for obtaining a target nuclear reaction cross section by calculating and subtracting interference in the invention;
FIG. 2 is a flow chart showing the steps of the method for measuring nuclear reaction cross section according to the present invention;
FIG. 3 is a general technical scheme for obtaining a target nuclear reaction cross section by subtracting interference according to the invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1-3, the present invention provides a technical solution:
the invention provides a method for deducting interference of the same product as a target nuclear reaction in nuclear reaction section measurement, which comprises the following steps:
the invention provides a method for deducting interference of the same product as a target nuclear reaction in nuclear reaction section measurement, which comprises the following steps:
s1.1, measuring a nuclear reaction section by adopting a natural sample containing a plurality of isotopes;
S1.2, judging whether interference generated by other nuclear reaction products on the target nuclear reaction section measurement can be ignored;
s1.3, deducting gamma-ray interference of target nuclear reaction section measurement by using other nuclear reactions which cannot be ignored and generate the same product.
In addition, in the process of measuring the nuclear reaction section of the natural sample containing various isotopes in S1.1, 14MeV neutron irradiation is carried out on the natural sample, and the method comprises the following steps of;
s2.1, sample preparation: preparing a high-purity natural sample into a wafer with the diameter of 20mm, clamping the wafer between two high-purity monitoring pieces (niobium or aluminum) with the same diameter, and wrapping the outer side of the wafer by a cadmium skin with the thickness of about 1 mm;
s2.2, sample irradiation: irradiating the sample with 14MeV generated by a strong current D-T neutron generator;
S2.3, gamma-ray activity measurement: measuring the gamma-ray activity of the reaction product by using a high-purity germanium gamma-spectrometer system;
s2.4, calculating and correcting the section: and calculating and correcting the section of the nuclear reaction to be detected.
Furthermore, in the measurement of nuclear reaction cross-sections using natural samples containing a plurality of stable isotopes, the activation of the samples tends to create problems of mutual interference of the various nuclear reactions of the same nuclei, for example: a+1X(n,3n)(a-1)mX,aX(n,2n)(a-1)mX,a-1X(n,n')(a-1)m The four nuclear reactions of X and a-2X(n,γ)(a-1)m X produce the same product m X; the three nuclear reactions of aX(n,p)aY,a+1X(n,d*)a Y and a+2X(n,t)a Y also produced the same product a Y. However, in the 14MeV neutron energy region, the a+1X(n,3n)(a-1)m X reaction threshold energy of many nuclides is large, and the reaction does not actually occur; the cadmium coating treatment is carried out on the sample in the irradiation process, so that the section of a-2X(n,γ)(a-1)m X reaction in a 14MeV neutron energy region is of the order of μb, compared with aX(n,2n)(a-1)m X reaction section (hundreds of mb to thousands of mb) and a-1X(n,n')(a-1)m X reaction section (hundreds of mb to hundreds of mb), the influence of a-1X(n,n')(a-1)m X on aX(n,2n)(a-1)m X reaction section measurement is negligible. In the 14MeV neutron energy region, the a+2X(n,t)a Y reaction cross section is on the order of μb, which is negligible compared with aX(n,p)a Y and a+1X(n,d*)a Y reaction cross sections (several to several hundred mb), but the interaction of aX(n,p)a Y and a+1X(n,d*)a Y reactions cannot be ignored.
Specifically, this example measures 182W(n,p)182 Ta reaction cross-sections. In the case of tungsten natural samples, since tungsten has five stable isotopes, their isotopic abundance is 180W-0.13％,182W-26.3％,183W-14.3％,184W-30.67％,186 W-28.6%, respectively. By using a nuclear reaction section calculation formulaThe cross section of the nuclear reaction 182W(n,p)182 Ta was measured and the results were the same for both 183W(n,d*)182 Ta and 184W(n,t)182 Ta reactions.
The cross-sectional value of the nuclear reaction 182W(n,p)182 Ta to be measured in the 14MeV neutron energy region is about 2-7mb, and the cross-sectional evaluation value of the 183W(n,d*)182 Ta reaction in the 14MeV neutron energy region is about 0.5-2mb. In this example, if the 183W(n,d*)182 Ta reaction effect is not subtracted, the 182W(n,p)182 Ta measurement and calculation results are shown in table 1:
Table 1:
Wherein the unit of the section is mb;
The results of 182W(n,p)182 Ta reaction cross-section measurements after 183W(n,d*)182 Ta was subtracted by the algorithm described above to subtract the same product interference as the target nuclear reaction are shown in table 2.
Table 2:
wherein the carrier surface unit is mb;
As can be seen by comparing Table 1 with Table 2, there was a 183W(n,d*)182 Ta effect that was 11.2%,20% and 21% greater than the unaffected effect at the three neutron energy points of 13.5.+ -. 0.2, 14.4.+ -. 0.2, 14.7.+ -. 0.2MeV, respectively. It can be seen that the same 183W(n,d*)182 Ta reaction minus the product was necessary for the 182W(n,p)182 Ta reaction cross-section measurement.
By comparison with the early relevant experimental results, the method has the following advantages that: the 182W(n,p)182 Ta reaction cross-section measurement result after 183W(n,d*)182 Ta influence is subtracted by the method is consistent with the result measured by an isotope separation method. The method is therefore an effective method for subtracting the effect of the same nuclear reaction of the product on the cross-sectional measurement of the target nuclear reaction in the case of using a natural sample containing a plurality of stable isotopes.
Further, the calculation formula of the nuclear reaction section in S2.4 is as follows:
Wherein the subscripts "x" and "0" denote the values of the sample to be tested and the supervisor chip, respectively. Epsilon is the total peak efficiency of the measured characteristic gamma rays; i γ is the intensity of the characteristic gamma ray; η is the natural abundance of the measured nuclide; m is the mass of the sample; d is a measurement collection factor; a is the atomic weight of a sample element; c is the measured characteristic gamma ray total peak area of the nuclear reaction product to be measured; lambda is the decay constant; f is the total gamma ray activity correction factor: f=f s×fc×fg, where F s、fc、fg is the self-absorption correction factor, cascade gamma-ray coincidence correction factor, and geometric correction factor, respectively, of gamma-rays in the sample; k is a neutron fluence rate fluctuation correction factor, and s=1-e -λT represents a growth factor of the remaining nuclei. σ 0 is the cross-sectional evaluation value of the supervised reaction.
Furthermore, the calculation formula of the measurement collection factor is as follows:
Wherein t 1 is the time interval from the end of irradiation to the start of measurement; t 2 is the time interval from the end of irradiation to the end of measurement.
In addition, the neutron fluence rate fluctuation correction factor is calculated as follows:
Wherein L is the number of segments into which the irradiation time is divided; Δt i is the time interval of the i-th segment; t i is the time interval between the end of the ith segment and the end of all irradiation; phi i is the average neutron flux incident during Δt i time; phi is the average neutron flux incident on the natural sample over the entire irradiation time, s=1-e -λT representing the growth factor of the remaining nuclei.
Further, the cross section of other nuclear reactions forming the same nucleus in S1.2 is extremely small, and when the cross section measurement interference to the target nuclear reaction is extremely small, the cross section measurement interference can be ignored.
In addition, the gamma-ray interference of the target nuclear reaction section measurement is subtracted from other nuclear reactions which generate the same species and cannot be ignored in S1.3, and the subtraction method is as follows:
S3.1, calculating the gamma-ray total energy peak count to be deducted: calculating the gamma-ray totipotent peak count to be deducted by using the evaluation value or reliable experimental value of other nuclear reaction sections with the same product;
S3.2, calculating gamma-ray total energy peak count after deduction of influence: subtracting the total peak count of the same gamma rays generated by other nuclear reactions from the total peak count of the characteristic gamma rays of the actually measured target nuclear reaction products to obtain the total peak count of the characteristic gamma rays of the actual (i.e. deducted interference of other nuclear reactions) target nuclear reaction products;
S3.3, calculating a target nuclear reaction section after interference deduction: the cross section of the target nuclear reaction after the interference of other nuclear reactions is subtracted is calculated by using the total energy peak count of the characteristic gamma rays of the actual target nuclear reaction product (namely the interference of other nuclear reactions is subtracted) and a nuclear reaction cross section calculation formula.
In addition, in S3.1, interference of the target nuclear reaction section measurement is subtracted from other nuclear reactions which cannot be ignored and generate the same species of products, and the calculation formula of the gamma-ray totipotent peak count C' to be subtracted is as follows:
Wherein subscripts '0' and 'y' respectively represent values of a sample to be detected and a monitoring sheet, sigma y is a section evaluation value of interference reaction or a reliable experimental value, sigma 0 is a section evaluation value of monitoring reaction, and C is a characteristic gamma ray total peak area of an actually measured nuclear reaction product to be detected; epsilon is the total peak efficiency of the measured characteristic gamma rays; i γ is the intensity of the characteristic gamma ray; η is the natural abundance of the measured nuclide; m is the mass of the sample; for measuring the collection factor (t 1 is the time interval from the end of irradiation to the start of measurement, t 2 is the time interval from the end of irradiation to the end of measurement); a is the atomic weight of a sample element; lambda is the decay constant; f=f s*Fc*Fg is the total gamma-ray activity correction factor: f s,Fc,Fg is the self-absorption correction factor, cascade gamma ray coincidence effect correction factor and geometric correction factor of gamma ray in the sample respectively; k is neutron fluence rate fluctuation correction factor, and the expression is/> Wherein L is the number of segments into which the irradiation time is divided, Δt i is the time interval of the i-th segment, and T i is the time interval between the end of the i-th segment and the end of all the irradiation; Φ i is the average neutron flux incident on the sample during Δt i time, Φ is the average neutron flux incident on the sample during the entire irradiation time T, s=1-e -λT represents the growth factor of the remaining nuclei.
It should be noted that, when calculating the cross section of the target nuclear reaction by using the calculation formula of the cross section of the nuclear reaction, C x is the total peak area of the characteristic gamma rays of the actually measured target nuclear reaction product, the total peak area C 'of the same gamma rays generated by other nuclear reactions with the same product is subtracted, and C' can be calculated by subtracting the cross section evaluation value sigma y of the reaction and the formulaObtained.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and that the above-described embodiments and descriptions are only one specific example of the present invention, and are not intended to limit the invention, and that various changes and modifications may be made therein without departing from the spirit and scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (5)
1. A method for subtracting interference of the same product as a target nuclear reaction from nuclear reaction section measurement, which is characterized by comprising the following method steps:
s1.1, measuring a nuclear reaction section by adopting a natural sample containing a plurality of isotopes;
s1.2, judging whether other nuclear reactions generating the same product can ignore the interference of the cross section measurement of the target nuclear reaction;
s1.3, deducting gamma-ray interference of target nuclear reaction section measurement from other nuclear reactions which cannot be ignored and generate the same product, wherein the method comprises the following steps of: s1.3.1, calculating the gamma ray totipotent peak count to be deducted: calculating the gamma-ray totipotent peak count to be deducted by using the evaluation value or reliable experimental value of other nuclear reaction sections with the same product;
S1.3.2, calculating gamma ray full energy peak count after deduction influence: subtracting the total peak count of the same gamma rays generated by other nuclear reactions from the total peak count of the characteristic gamma rays of the actually measured target nuclear reaction products to obtain the total peak count of the characteristic gamma rays of the target nuclear reaction products deducting the interference of other nuclear reactions;
s1.3.3, calculating a target nuclear reaction section after interference subtraction: the cross section of the target nuclear reaction after the interference of other nuclear reactions is deducted is calculated by using the total energy peak count of the characteristic gamma rays of the target nuclear reaction product deducted from the interference of other nuclear reactions and a nuclear reaction cross section calculation formula;
The calculation formula of the gamma-ray total peak count C' to be deducted is as follows:
Wherein subscripts '0' and 'y' respectively represent values of a sample to be detected and a monitoring sheet, sigma y is a section evaluation value of interference reaction or a reliable experimental value, sigma 0 is a section evaluation value of monitoring reaction, and C is a characteristic gamma ray total peak area of an actually measured nuclear reaction product to be detected; epsilon is the total peak efficiency of the measured characteristic gamma rays; i γ is the intensity of the characteristic gamma ray; η is the natural abundance of the measured nuclide; m is the mass of the sample; d=e -λt1 -e-λt2 is the measurement collection factor; t 1 is a time interval from the end of irradiation to the start of measurement, and t 2 is a time interval from the end of irradiation to the end of measurement; a is the atomic weight of a sample element; lambda is the decay constant; f=f s*Fc*Fg is the total gamma-ray activity correction factor: f s,Fc,Fg is the self-absorption correction factor, cascade gamma ray coincidence effect correction factor and geometric correction factor of gamma ray in the sample respectively; k is neutron fluence rate fluctuation correction factor, and the expression is Wherein L is the number of segments into which the irradiation time is divided, Δt i is the time interval of the i-th segment, and T i is the time interval between the end of the i-th segment and the end of all the irradiation; Φ i is the average neutron flux incident on the sample during Δt i time, Φ is the average neutron flux incident on the sample during the entire irradiation time T, s=1-e -λT represents the growth factor of the remaining nuclei.
2. The method for subtracting interference of the same product as the target nuclear reaction from the nuclear reaction section measurement according to claim 1, wherein: in the process of measuring the nuclear reaction section of the natural sample containing various isotopes in S1.1, 14MeV neutron irradiation is carried out on the natural sample, and the method comprises the following steps of;
s2.1, sample preparation: preparing a high-purity natural sample into a wafer with the diameter of 20mm, clamping the wafer between two high-purity monitoring pieces with the same diameter, and wrapping the outer edge of the wafer by a cadmium skin with the thickness of 1 mm;
s2.2, sample irradiation: irradiating the sample with 14MeV generated by a strong current D-T neutron generator;
S2.3, gamma-ray activity measurement: measuring the gamma-ray activity of the reaction product by using a high-purity germanium gamma-spectrometer system;
s2.4, calculating and correcting the section: and calculating and correcting the section of the nuclear reaction to be detected.
3. The method for subtracting interference of the same product as the target nuclear reaction from the nuclear reaction section measurement according to claim 2, wherein: the calculation formula of the nuclear reaction section in S2.4 is as follows:
Wherein subscripts "x" and "0" represent the values of the sample to be tested and the monitor panel, respectively; epsilon is the total peak efficiency of the measured characteristic gamma rays; i γ is the intensity of the characteristic gamma ray; η is the natural abundance of the measured nuclide; m is the mass of the sample; d is a measurement collection factor; a is the atomic weight of a sample element; c is the measured characteristic gamma ray total peak area of the nuclear reaction product to be measured; lambda is the decay constant; f is the total gamma ray activity correction factor: f=f s×fc×fg, where F s、fc、fg is the self-absorption correction factor, cascade gamma-ray coincidence correction factor, and geometric correction factor, respectively, of gamma-rays in the sample; k is a neutron fluence rate fluctuation correction factor, s=1-e -λT represents a growth factor of the remaining nuclei; σ 0 is the cross-sectional evaluation value of the supervised reaction.
4. The method for subtracting interference of the same product as the target nuclear reaction from the nuclear reaction section measurement according to claim 3, wherein: the calculation formula of the measurement collection factor is as follows:
where t 1 is a time interval from the end of irradiation to the start of measurement, and t 2 is a time interval from the end of irradiation to the end of measurement.
5. The method for subtracting interference of the same product as the target nuclear reaction from the nuclear reaction section measurement according to claim 3, wherein: the neutron fluence rate fluctuation correction factor is calculated as follows:
Wherein L is the number of segments into which the irradiation time is divided; Δt i is the time interval of the i-th segment; t i is the time interval between the end of the ith segment and the end of all irradiation; phi i is the average neutron flux incident during Δt i time; phi is the average neutron flux incident on the natural sample over the entire irradiation time.
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