High-energy gamma dose rate valuing method of (alpha, n) isotope source
By using the calibration method of (α, n) isotope source and high-energy gamma radiation monitoring instrument, the response deviation and overestimation problems of gamma radiation monitoring instruments in high-energy gamma radiation measurement are solved, and efficient and low-cost high-energy gamma dose rate fixed value and large-batch calibration are achieved.
Patent Information
- Application Number
- CN202411599421.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-11
- Publication Date
- 2025-04-11
AI Technical Summary
In the prior art, gamma radiation monitoring instruments have large energy response differences when measuring high-energy gamma rays. Some instruments have the problem of overestimating dose rates, and rely on accelerator and reactor high-energy gamma sources, which are costly and are not suitable for large-scale calibration.
Using (α, n) isotope sources, by analyzing their high-energy γ characteristics, selecting suitable high-energy γ ray isotope sources, calibrating the high-energy γ radiation monitoring instruments, obtaining their detection efficiency and net γ energy spectrum, estimating the equivalent high-energy γ radioactive activity, calculating the high-energy γ dose rate, and performing radiation field measurement and uncertainty assessment.
The determination of the magnitude of the high-energy γ component of the (α, n) isotope neutron source is achieved, reducing the deviation of the response of the γ radiation monitoring instrument to the high-energy γ rays, which is low-cost and is suitable for the calibration of large-scale γ radiation monitoring instruments. The method uncertainty is controlled within 20% (k=2).
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of radiation detection, and in particular relates to a method for determining a high-energy gamma dose rate of an (α, n) isotope source. Background Art
[0002] There is E in the radiation protection of nuclear facilities γ ≥2MeV high-energy gamma rays, in the widely used advanced experimental reactors, pressurized water reactors, high-flux experimental reactors, etc., due to neutron proliferation, the moderator uses water, high-energy neutrons and 16 O nuclide reaction produces 16 N nuclide, 16 N decays to 16 O * , 16 O * Deexcitation releases 6.13MeV (67.0%) and 7.115MeV (4.9%) gamma rays. Reactor coolant transports radioactive nuclides outside the core, and high-energy gamma rays increase the risk of accidental exposure to workers. The energy range of gamma radiation monitoring instruments currently used in nuclear facilities is 30keV to 2MeV, and the energy response varies greatly. Some instruments have the problem of overestimation of dose rate, so it is urgent to calibrate the high-energy gamma energy response of gamma radiation instruments. ISO4037 and GB / T12162 stipulate that high-energy gamma radiation is generated by accelerators or reactor filtration, but the accelerator has a complex structure, expensive construction, and high test costs. The platform cannot meet the calibration of large quantities of gamma radiation monitoring instruments. Summary of the invention
[0003] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method suitable for determining the high-energy gamma dose rate of (α, n) isotope sources, which is mainly used for determining the high-energy gamma dose rate in (α, n) isotope neutron sources, realizing the determination of the value of the high-energy gamma component in the n / γ mixed field, and solving the problems that the gamma radiation monitoring instrument has a large response deviation to high-energy gamma radiation and the energy response calibration is overly dependent on the accelerator and reactor high-energy gamma sources.
[0004] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:
[0005] A method for determining a high-energy gamma dose rate of an (α, n) isotope source comprises the following steps:
[0006] Step 1, analyzing the high-energy gamma characteristics of different (α, n) isotope sources and selecting a suitable high-energy gamma ray (α, n) isotope source;
[0007] Step 2, calibrating the high-energy gamma radiation monitoring instrument;
[0008] Step 3, obtaining the detection efficiency e of the high energy gamma radiation monitoring instrument for high energy gamma;
[0009] Step 4: Obtain the net gamma energy spectrum of the (α,n) isotope source from the high-energy gamma radiation monitoring instrument net ;
[0010] Step 5, calculate the equivalent high-energy gamma radioactivity A of the (α,n) isotope source;
[0011] Step 6, calculating the high energy gamma dose rate of (α,n) isotope sources at different positions;
[0012] Step 7, performing radiation field measurement;
[0013] Step 8: Evaluate the uncertainty of the high-energy gamma dose rate.
[0014] Furthermore, in step 1, a (α,n) isotope source containing high-energy gamma rays having a monoenergetic photon radiation energy of 4 to 9 MeV consistent with that recommended by ISO4037 and GB / T 12162 is selected through analysis.
[0015] Furthermore, in step 2, the detection efficiency of the radiation monitoring instrument suitable for measuring in the high-energy gamma energy region for gamma rays of different energies is obtained through the accelerator.
[0016] Furthermore, in step 3, the high-energy gamma radiation monitoring instrument conducts a detection efficiency experiment on (α, n) isotope gamma point sources of different energies, completes the comparison between the experiment and the MCNP simulation, fits the detection efficiency curve, and extrapolates to obtain the high-energy gamma detection efficiency e.
[0017] Furthermore, the (α, n) isotope γ point source includes 22 Na, 241 Am, 137 Cs, 60 Co and 152 Eu, or a series of sources including low-energy, medium-energy and high-energy gamma rays. The gamma point source should be traced and the activity including uncertainty should be given.
[0018] Furthermore, the MCNP simulation, including Monte Carlo modeling of high-energy gamma radiation monitoring instruments, should include the probe structure, PMT, and housing. The simulation should be consistent with the test state, and the influencing factors in the environment should also be considered. The Monte Carlo modeling of the radioactive source should consider the source activity, source size, uniform mixing of the default source material, and isotropic emission. The gamma energy spectrum of probes of different specifications should be obtained, and the full energy peak should be clearly seen.
[0019] Further, in step 4, the ambient background γ spectrum is measured. background ; Use MCNP to simulate the neutron-induced γ spectrum and obtain the γ spectrum Spectrum n-γ; Use high-energy gamma radiation monitoring equipment to measure the gamma energy spectrum of the (α,n) isotope source total , and deduct Spectrum background and Spectrum n-γ , obtain the net gamma energy spectrum of the (α,n) isotope source from the high-energy gamma radiation monitoring instrument net .
[0020] Furthermore, in step 5, for an equivalent γ body source, the Monte Carlo method is used to calculate the air absorption dose rate at a certain point. The calculation formula for the air absorption dose rate of a monoenergetic γ nuclide at a certain point is:
[0021]
[0022] In the formula is the gamma ray fluence rate at a certain point, The energy is E γ The air mass energy absorption coefficient of γ photons, E γ is the energy of the gamma ray.
[0023] Furthermore, the radioactivity A of the equivalent high-energy gamma of the (α,n) isotope source is calculated by combining the detection efficiency and the branching ratio; the calculation method is A=N / (ηε), where N is the total energy peak area obtained, or counts, η is the branching ratio, that is, the probability that the (α,n) source emits the corresponding high-energy gamma, and ε is the extrapolated detection efficiency or the measured detection efficiency.
[0024] Furthermore, in step 6, the high-energy gamma dose rate at different positions is obtained by using the inverse square of the distance for the point source, and the high-energy gamma dose rate at different positions is obtained by using the point kernel integration method for the volume source.
[0025] Furthermore, in step 7, the monoenergetic high-energy gamma generated by the accelerator is used to calibrate another high-energy gamma radiation monitoring instrument, and the two high-energy gamma radiation monitoring instruments are measured at the same position and angle, and the field range is obtained with a 90% confidence interval, and the comparison is completed.
[0026] Furthermore, the probe structures of the two high-energy gamma radiation monitoring instruments should be consistent.
[0027] Furthermore, in step 8, the uncertainty assessment involves the uncertainty of the efficiency calibration u e , the net spectral uncertainty u of the deducted neutron-induced γ spectrum and γ background spectrum s , Distance uncertainty u of dose rate measurement l , uncertainty u of body source simulation D , all belong to Class B uncertainty, and the combined standard uncertainty is calculated according to the root mean square and u, and k = 2 is taken to obtain the relative expanded uncertainty U r .
[0028] The beneficial effects of the present invention are as follows:
[0029] 1. Realize the measurement of high-energy γ components of (α,n) isotope neutron sources, and the method uncertainty is U r ≤20% (k=2), which can be used to calibrate the response of gamma radiation monitoring instruments to high-energy gamma rays, improve the problem of large instrument response, and has low cost. The developed radiation field can be used for calibration of large quantities of gamma radiation monitoring instruments;
[0030] 2. Through the analysis of the characteristics of (α,n) type isotope neutron sources, an isotope neutron source with 4-9 MeV high-energy gamma rays recommended by ISO 4037 and GB / T 12162 was selected. The detector response, energy spectrum and dose contribution to the neutron component and high-energy gamma component in the (α,n) type isotope neutron source were determined respectively. The high-energy gamma dose rate of this type of radiation source was determined, and the uncertainty U r ≤20% (k=2). BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 The figure is a flow chart of a method for determining the high-energy gamma dose rate of a (α,n) isotope source. DETAILED DESCRIPTION
[0032] The present invention is described in detail below with reference to the accompanying drawings and embodiments.
[0033] The present invention is a method for determining the high-energy gamma dose rate of an (α, n) isotope source, which is used for determining the high-energy gamma dose rate in an (α, n) type isotope neutron source, and comprises the following steps:
[0034] Step 1, analyzing the high-energy gamma characteristics of different (α, n) isotope sources and selecting a suitable high-energy gamma ray (α, n) isotope source;
[0035] Step 2, calibrating the high-energy gamma radiation monitoring instrument;
[0036] Step 3, obtaining the detection efficiency e of the high energy gamma radiation monitoring instrument for high energy gamma;
[0037] Step 4: Obtain the net gamma energy spectrum of the (α,n) isotope source from the high-energy gamma radiation monitoring instrument net ;
[0038] Step 5, calculate the equivalent high-energy gamma radioactivity A of the (α,n) isotope source;
[0039] Step 6, calculating the high energy gamma dose rate of (α,n) isotope sources at different positions;
[0040] Step 7, performing radiation field measurement;
[0041] Step 8: Evaluate the uncertainty of the high-energy gamma dose rate.
[0042] The high-energy gamma dose rate determination method of the (α, n) isotope source designed by the present invention involves the steps of efficiency calibration of the high-energy gamma radiation monitoring instrument A, environmental gamma background deduction, neutron-induced gamma influence, high-energy gamma spectrum integration, and gamma dose rate calculation. Figure 1 As shown, a technical solution for a method for determining a high-energy gamma dose rate of an (α, n) isotope source includes:
[0043] a) Analyze the high energy gamma characteristics of different (α, n) isotope sources;
[0044] b) The detector efficiency of the radiation monitoring instrument A for measuring in the high-energy gamma energy region at different energies is obtained through the accelerator. The calibration of the gamma radiation monitoring instrument A is completed in the high-energy gamma radiation field of the accelerator, and the calibrated gamma radiation monitoring instrument A is used as a standard;
[0045] c) Verify the gamma detection efficiency of different energies by using low-energy and medium-energy gamma sources, complete the comparison between the experiment and the MCNP simulation, and extrapolate to obtain the high-energy gamma detection efficiency;
[0046] d) Complete the response measurement of the gamma radiation monitoring instrument A on the accelerator platform and the isotope neutron source respectively, mainly to distinguish the contribution of neutrons to the gamma dose rate indication. As a standard instrument, the gamma radiation monitoring instrument A needs to obtain the response of the instrument to high-energy gamma from the accelerator platform. The response measurement on the isotope neutron source is mainly to exclude the collinearity of the gamma peak of interest caused by neutron induction. The high-energy gamma induced by neutrons needs to be subtracted as background;
[0047] e) Measure the ambient background spectrum background , mainly from cosmic rays, interference from natural radionuclides U, Th, and K;
[0048] f) Use MCNP to simulate the neutron-induced γ spectrum, mainly considering the (n,γ) reaction of the detector material, and obtain the energy spectrum Spectrum n-γ ;
[0049] g) Use gamma radiation monitoring instrument A to measure the gamma energy spectrum of the (α,n) isotope source total , and deduct Spectrum background and Spectrum n-γ , get the net γ spectrum Spectrum net ;
[0050] h) Integrate the energy spectrum within ±1σ according to the energy resolution of the gamma radiation monitoring instrument A to obtain counts. Since the gamma energy spectrum measured by the instrument is continuous and there is a full energy peak at the place of interest, take the half width of the energy spectrum for integration to obtain counts;
[0051] i) The radioactivity A of high-energy gamma is calculated by combining the detector efficiency and branching ratio. The calculation method is A = N / (ηε), where N is the total energy peak area obtained, or counts, η is the branching ratio, that is, the probability that the (α,n) isotope source emits the corresponding high-energy gamma, and ε is the extrapolated detection efficiency or the measured detection efficiency;
[0052] j) For point sources, the inverse square of the distance is used to obtain the high-energy gamma dose rate at different locations, and for volume sources, the point nuclear integral method is used to obtain the high-energy gamma dose rate at different locations;
[0053] k) Use the monoenergetic high-energy gamma generated by the accelerator to calibrate the gamma radiation monitoring instrument B, and measure it at the same position and angle as the gamma radiation monitoring instrument A, and finally measure the equivalent high-energy gamma radioactivity of the (α,n) isotope source, obtain the radiation field range with a 90% confidence interval, and complete the comparison. Both radiation monitoring instrument B and radiation monitoring instrument A set the radiation field of the (α,n) isotope source to ensure that the measurement is accurate and consistent. Conduct uncertainty assessment of the high-energy gamma dose rate setting.
[0054] Example
[0055] A method for determining the high-energy gamma dose rate of (α,n) isotope sources can be used to determine the high-energy gamma dose rate values of Am-Be sources, Pu-C sources, and Pu-Be sources with high-energy gamma rays of 4.43MeV or 6.13MeV by analyzing the characteristics of (α,n) isotope neutron sources. The method deducts factors such as neutron-induced gamma interference, environmental background gamma, and neutron influence of gamma radiation monitoring instruments, and obtains the net high-energy gamma spectrum. Combined with the extrapolated high-energy gamma detection efficiency of the gamma radiation monitoring instrument, the high-energy gamma dose rate values at different distances are determined, and the radiation field measurement and uncertainty evaluation are performed.
[0056] 1. Analysis of (α,n) isotope source characteristics
[0057] The (α,n) isotope source is a fissile nuclide that releases high-energy α particles to bombard the target material to produce neutrons. The emitter of α particles is usually 241 Am, 226 Pa, 210 Po 238 For nuclides such as Pu, the target material is usually beryllium, boron, lithium and other materials. For Am-Be and Pu-Be neutron sources, they are accompanied by three high-energy gamma rays, as shown in formula (1):
[0058]
[0059] Where E γ1 =4.438MeV, E γ2 =3.216MeV, E γ3 =9.641MeV; for Pu-C and Cm-C neutron sources, 13 C(α,n) 16 O generated 16 O * The excited state deexcitation is accompanied by 6.13MeV high-energy gamma rays, with an intensity of about 40%. 16 O * The de-excitation time is 2×10 -11 s, which has significant advantages in obtaining high-energy gamma. The high-energy gamma rays accompanying this type of (α,n) isotope source are consistent with the 4-9 MeV monoenergetic photon radiation energy recommended by ISO4037 and GB / T 12162. The relevant standards recommend that the generation method is an accelerator. 19 F(p,αγ) 16 O Nuclear reaction 16 O De-excitation, 12 C de-excitation, 16 N decay, the difference is that the gamma component using (α,n) isotopes is more complex and has a larger broadening, and it is necessary to consider interference factors such as low-energy gamma and neutrons.
[0060] 2. Efficiency calculation of high energy gamma radiation monitoring instrument A
[0061] The high-energy gamma radiation monitoring instrument A has at least two functions: gamma spectrum measurement and dose rate measurement. The detector specifications are 2-inch to 4-inch NaI, HPGe, LaBr3 detectors, etc. After the high-energy gamma radiation monitoring instrument A is calibrated in the accelerator field, it is used as a mass transfer instrument to calibrate the detection efficiency of isotope gamma point sources. Isotope gamma point sources include 22 Na, 241 Am, 137 Cs, 60 Co and 152Eu, etc., or a series of sources including low-energy, medium-energy, and high-energy gamma rays. Isotope gamma point sources should be traced to the source and the activity including uncertainty should be given. Simulation calibration is divided into two parts. Monte Carlo modeling of radiation monitoring instrument A should be carried out, which should include the probe structure, PMT, shell, etc. The simulation should be consistent with the test state, and the influencing factors in the environment should also be considered. The modeling of the radioactive source should consider the source activity, source size, and the default uniform mixing of source materials and isotropic emission. The gamma energy spectrum of probes of different specifications should be obtained, and the full energy peak should be clearly seen. The simulation and experimental conditions should be consistent, and the gamma energy spectrum and dose rate of probes of different gamma point sources, different distances, and different specifications should be obtained. The dose rate value should be traceable to the source activity. The simulated gamma energy spectrum is energy broadened to complete the energy scale of radiation monitoring instrument A, the full energy peak is integrated, the detection efficiency of radiation monitoring instrument A for different gamma rays is obtained, the detection efficiency curve is fitted, and the detection efficiency e of 4.438MeV and / or 6.13MeV high-energy gamma rays is obtained by extrapolation.
[0062] 3. Neutron-induced gamma interference on instrument A
[0063] (α,n) isotope sources are usually used as neutron sources, and the (n,n ′ ) and (n,γ) nuclear reactions. This part of the energy spectrum cannot be measured experimentally, so the simulated spectrum is used as the background part of the energy spectrum to be deducted in subsequent processing. For the Am-Be source, the induced gamma spectrum contains 2.23MeV of H nucleon neutron capture, excited state 12 C * De-excited to 12 The 4.438MeV of C and the 3.927MeV and 3.416MeV gamma rays of gamma capture. In addition, for different detectors, the interaction between neutrons and detector materials should also be considered. For NaI(Tl) detectors, the interaction between neutrons and 23 Na, 127 For the nuclear reactions related to I, the neutrons and 79 Br, 139 La-related reactions can be induced by obtaining relevant cross sections through databases such as TENDL and JENDL. n-γ simulation.
[0064] 4. Equivalent high-energy gamma activity of (α,n) isotope sources
[0065] High-energy gamma radiation monitoring instrument A measures the gamma energy spectrum of (α,n) isotope sources total , measure the ambient background spectrum background , and the Spectrum obtained by simulation n-γ Subtract them together as background spectrum to obtain Spectrumnet The high-energy γ full-energy peak of 4.438MeV or 6.13MeV is integrated by ±1σ, and the total count is N′. The count N at this point can be calculated by the energy detection efficiency e. The (α,n) isotope source is usually a cylindrical or spherical body source. For an equivalent γ body source, the Monte Carlo method is used to calculate the air absorption dose rate at a certain point, as shown in the following formula (2):
[0066]
[0067] In the above formula is the gamma ray fluence rate at a certain point, in m -2 ·s -1 , The energy is E γ The air mass energy absorption coefficient of γ photons, in m 2 / kg,E γ is the energy of the gamma ray. The dose rate of the equivalent gamma body source is the sum of the gamma dose rates of multiple monoenergetic gamma point sources. After considering the detection efficiency e of the radiation monitoring instrument A at this point, the counts N and N′ are consistent within the error limit of 5%. The equivalent gamma body source activity is the equivalent high-energy gamma radiation source activity A of the (α,n) isotope source.
[0068] 5. Radiation field measurement and uncertainty assessment
[0069] The radiation monitoring instrument B and the radiation monitoring instrument A, which have been calibrated by the accelerator, are used to measure the radiation field of the (α,n) isotope source at the same position and angle. The radiation field range is within the range of ±10% of the maximum dose rate. The probe structures of the selected radiation monitoring instrument B and the radiation monitoring instrument A should be consistent. Both the radiation monitoring instrument B and the radiation monitoring instrument A set the radiation field of the (α,n) isotope source to ensure that the measurement is accurate and consistent. The radiation field measurement includes the 95-100% dose rate field range at different distances, that is, the field area.
[0070] Uncertainty assessment involves the uncertainty u of efficiency calibration e , the net spectral uncertainty u of the deducted neutron-induced γ spectrum and γ background spectrum s , Distance uncertainty u of dose rate measurement l , uncertainty u of body source simulation D , all belong to Class B uncertainty. Calculate the combined standard uncertainty u according to the root mean square sum, and take k = 2 to obtain the relative expanded uncertainty U r .
[0071] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.
Claims
1. A method for determining the high energy gamma dose rate of an (α, n) isotope source, characterized in that: The following steps are involved: Step 1, analyzing the high-energy gamma characteristics of different (α, n) isotope sources and selecting a suitable high-energy gamma ray (α, n) isotope source; Step 2, calibrating the high-energy gamma radiation monitoring instrument; Step 3, obtaining the detection efficiency e of the high-energy gamma radiation monitoring instrument for high-energy gamma; Step 4: Obtain the net gamma energy spectrum of the (α,n) isotope source from the high-energy gamma radiation monitoring instrument net ; Step 5, calculate the equivalent high-energy gamma radioactivity A of the (α,n) isotope source; Step 6, calculating the high energy gamma dose rate of (α,n) isotope sources at different positions; Step 7, performing radiation field measurement; Step 8: Evaluate the uncertainty of the high-energy gamma dose rate.
2. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 1, characterized in that: In step 1, an (α,n) isotope source containing high-energy gamma rays with a monoenergetic photon radiation energy of 4 to 9 MeV consistent with that recommended by ISO4037 and GB / T 12162 is selected through analysis.
3. The method for determining the high energy gamma dose rate of an (α, n) isotope source according to claim 1, characterized in that: In step 2, the detection efficiency of the radiation monitoring instrument suitable for measuring in the high-energy gamma energy region for gamma rays of different energies is obtained through an accelerator.
4. The method for determining the high energy gamma dose rate of an (α, n) isotope source according to claim 1, characterized in that: In step 3, the high-energy gamma radiation monitoring instrument conducts a detection efficiency experiment on (α,n) isotope gamma point sources of different energies, completes the comparison between the experiment and the MCNP simulation, fits the detection efficiency curve, and extrapolates to obtain the high-energy gamma detection efficiency e.
5. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 4, characterized in that: The (α, n) isotope γ point source includes 22 Na, 241 Am, 137 Cs, 60 Co and 152 Eu, or a series of sources including low-energy, medium-energy and high-energy gamma rays. The gamma point source should be traced and the activity including uncertainty should be given.
6. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 4, characterized in that: The MCNP simulation, including Monte Carlo modeling of high-energy gamma radiation monitoring instruments, should include probe structure, PMT, and housing. The simulation should be consistent with the test state, and the influencing factors in the environment should also be considered. The Monte Carlo modeling of the radioactive source should consider the source activity, source size, uniform mixing of the default source material, and isotropic emission. The gamma energy spectra of probes of different specifications should be obtained, and the full energy peak should be clearly seen.
7. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 1, characterized in that: In step 4, measure the ambient background γ spectrum background ; Use MCNP to simulate the neutron-induced γ spectrum and obtain the γ spectrum Spectrum n-γ ; Use high-energy gamma radiation monitoring equipment to measure the gamma energy spectrum of the (α,n) isotope source total , and deduct Spectrum background and Spectrum n-γ , obtain the net gamma energy spectrum of the (α,n) isotope source from the high-energy gamma radiation monitoring instrument net .
8. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 1, characterized in that: In step 5, for the equivalent γ body source, the Monte Carlo method is used to calculate the air absorption dose rate at a certain point. The calculation formula for the air absorption dose rate of a monoenergetic γ nuclide at a certain point is: In the formula is the gamma ray fluence rate at a certain point, The energy is E γ The air mass energy absorption coefficient of γ photons, E γ is the energy of the gamma ray.
9. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 8, characterized in that: The radioactivity A of the equivalent high-energy gamma of the (α,n) isotope source is calculated by combining the detection efficiency and branching ratio; the calculation method is A=N / (ηε), where N is the total energy peak area obtained, or counts, η is the branching ratio, that is, the probability that the (α,n) source emits the corresponding high-energy gamma, and ε is the extrapolated detection efficiency or measured detection efficiency.
10. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 1, characterized in that: In step 6, the high-energy gamma dose rate at different positions is obtained by using the inverse square of the distance for the point source, and the high-energy gamma dose rate at different positions is obtained by using the point kernel integration method for the volume source.
11. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 1, characterized in that: In step 7, the monoenergetic high-energy gamma generated by the accelerator is used to calibrate another high-energy gamma radiation monitoring instrument, and the two high-energy gamma radiation monitoring instruments are measured at the same position and angle to obtain the field range with a 90% confidence interval and complete the comparison.
12. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 11, characterized in that: The probe structures of the two high-energy gamma radiation monitoring instruments should be consistent.
13. A method for determining high energy gamma dose rate of an (α, n) isotope source as claimed in claim 1, characterized in that: In step 8, the uncertainty assessment involves the uncertainty of the efficiency calibration u e , the net spectral uncertainty u of the deducted neutron-induced γ spectrum and γ background spectrum s , Distance uncertainty u of dose rate measurement l , uncertainty u of body source simulation D , all belong to Class B uncertainty, and the combined standard uncertainty is calculated according to the root mean square and u, and k = 2 is taken to obtain the relative expanded uncertainty U r .