CN116106346A - Seawater in-situ gamma energy spectrum efficiency calibration method - Google Patents

Seawater in-situ gamma energy spectrum efficiency calibration method Download PDF

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CN116106346A
CN116106346A CN202310338758.5A CN202310338758A CN116106346A CN 116106346 A CN116106346 A CN 116106346A CN 202310338758 A CN202310338758 A CN 202310338758A CN 116106346 A CN116106346 A CN 116106346A
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neutron
seawater
gamma
energy spectrum
water
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杨翊方
王海军
王震涛
张凯
桑文娟
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Chinese Peoples Liberation Army Naval Characteristic Medical Center
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Chinese Peoples Liberation Army Naval Characteristic Medical Center
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/221—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material by activation analysis
    • G01N23/222—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material by activation analysis using neutron activation analysis [NAA]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/36—Measuring spectral distribution of X-rays or of nuclear radiation spectrometry
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

Abstract

A seawater on-site gamma energy spectrum efficiency calibration method belongs to the technical field of fissile nuclide measurement methods. The method is characterized in that the testing process comprises the following steps: 1) Loading a neutron activator NaBr into 24 pvc pipes with phi of 30mm, compacting, and inserting the pvc pipes into 24 activation pore channels of a neutron activation device; 2) The neutron activation device is arranged at the irradiation position of the Cf-252 neutron source, the neutron source is lifted to the center of the neutron activation device, and NaBr is taken out after continuous irradiation for 1-10 d; 3) And after weighing, the obtained product is dissolved into a water radiation simulation device to obtain an efficiency scale curve of 554-2754 keV energy range, so that the efficiency scale of the water lanthanum bromide gamma spectrometer is realized. The efficiency scale method of the underwater gamma energy spectrum is convenient to obtain materials and low in cost; the half-life period of the selected radionuclide is short; the energy coverage of the characteristic gamma rays is wide; and the wastewater is nontoxic.

Description

Seawater in-situ gamma energy spectrum efficiency calibration method
Technical Field
A seawater on-site gamma energy spectrum efficiency calibration method belongs to the technical field of fissile nuclide measurement methods.
Background
Gamma spectral efficiency scale is the basis for quantitative measurement, with standard radioactive sources (point sources or bulk sources) being the most common method. The efficiency calibration method is recommended in the standards of GB/T11713, GB/T16140, GB/T11743, GB/T16145, WS/T184, and the like, respectively, for the analysis of low specific activity gamma radioactive samples by a semiconductor gamma spectrometer. And (3) using a plurality of point sources or body sources of radionuclides emitting gamma rays with different energy characteristics to carry out efficiency calibration on a gamma spectrometer under a fixed geometric condition, and establishing an efficiency calibration curve to provide conditions for quantitative measurement of unknown nuclides. The method has the advantages that the method is high in accuracy through a large number of experiments, the structure and the model establishment of the detector are not required to be known, but obvious defects exist, including the need of purchasing a plurality of expensive radioactive sources, including the radioactive sources with short half-life period, short service period and the like.
The prior research establishes the utilization of natural soil samples 232 Th、 226 Ra decay daughter determines HPGe measurement efficiency method. In soil radioactivity measurement studies, the naturally occurring samples are used 232 Th decay system 226 Relative relation of each gamma photon emissivity when Ra and its subvolumes decay balance, establishing relative efficiency scale curve for gamma photons with different energies, then using each gram of KCl 40 The absolute photon emissivity of K determines absolute efficiency, realizes the full-energy peak efficiency scale of HPGe gamma spectrums, and has very good consistency by comparing the full-energy peak efficiency scale with the analysis result of the same sample carried out by the national defense department, industrial and scientific commission metering primary station. The method has the advantages of avoiding using radioactive sources, saving expenses, being beneficial to environmental protection, and flexibly changing the shape and the size of the sample according to actual needs. The defects are that: due to nature in the soil 232 Th、 226 Ra decay daughter is difficult to dissolve in water and even if the specific activity in the dissolved water is low, it cannot be used for efficiency calibration, so the method is only suitable for the efficiency calibration of the HPGe gamma spectrometer for detecting soil samples.
The Monte Carlo method adopts a particle transport calculation mode (including MCNP and the like), establishes a geometric model of a detected sample and a detector, utilizes continuous tracking of various actions of particle running tracks and substances with large sample size, and counts the energy deposition probability of rays in a detection crystal, thereby realizing calculation of the gamma ray full-energy peak detection efficiency by the detector, further increasing the sample size of the tracked particles for controlling statistical errors, and reducing the statistical errors. The method has the advantages of no use of any radioactive substance, no experiment, high efficiency and any adjustment, but has the following disadvantages: it is necessary to precisely grasp the internal bonding and materials of the probes, and as a user has difficulty in precisely grasping, it is difficult for even the manufacturer of the probes to ensure the consistency of the internal structure and materials of each probe, so that a certain error is introduced at the low energy end due to uncertainty of the model, and it is difficult to avoid.
No current national standard and industry standard exists for the scale of the underwater gamma spectrometer. In summary, the conventional various gamma spectrum detection efficiency calibration methods have respective characteristics. Since the natural radioactive decay system in water has very little content, it is difficult to scale the efficiency of an underwater gamma spectrometer using the natural radioactive decay system. And a large multi-radionuclide standard solution pool is built by using a standard radioactive substance scale underwater gamma spectrometer, wherein part of radionuclides have long half-life periods, and a large amount of radioactive solutions stored for a long time can be generated. Two units are built in China and comprise a national ocean technical center of the natural resource department and a third ocean research institute of the natural resource department, wherein the national ocean technical center of the natural resource department is a cylindrical custom barrel with the diameter of 2.5m and the height of 3m, and is made of PE plastic; the top is provided with a track and a bracket, and the outside is provided with a water pump; the mixed solution of Ba-133, cs-137 and Co-60 is filled in the reactor, and the total activity is below the exemption value. The device of the third ocean research institute of the natural resource department is a cylindrical chemical industry standard barrel, the diameter is 3m, the height is 3.3m, and the material is PE plastic; the Cs-137 solution is filled in the reactor, and the activity is less than 10000Bq. Although the existing 2 devices can obtain accurate detection efficiency factors through experiments, the detection efficiency scales of the full spectrum cannot be realized due to few nuclides, the detection efficiency scales of the nuclides are only suitable for the detection efficiency scales of the nuclides, and the measurement of a large number of fissile nuclides in offshore nuclear emergency cannot be obviously realized.
Disclosure of Invention
The invention aims to solve the technical problems that: overcomes the defects of the prior art and provides a seawater on-site gamma energy spectrum efficiency calibration method with convenient material acquisition, low price and wide energy coverage.
The technical scheme adopted for solving the technical problems is as follows: the seawater in-situ gamma energy spectrum efficiency calibration method is characterized in that the testing process comprises the following steps:
1) Loading a neutron activator NaBr into 24 pvc pipes with phi of 30mm, compacting, and inserting the pvc pipes into 24 activation pore channels of a neutron activation device;
2) The neutron activation device is arranged at the irradiation position of the Cf-252 neutron source, the neutron source is lifted to the center of the neutron activation device, and NaBr is taken out after continuous irradiation for 1-10 d;
3) After weighing, dissolving the materials into a water radiation simulation device, fully stirring, sampling, and analyzing by a laboratory low background gamma spectrometer to obtain specific activities of Na-24 and Br-82 in water; meanwhile, immersing a detector of the lanthanum bromide gamma spectrometer in water into the center of the radiation simulation device in water, and collecting the etching spectrum; so as to obtain an efficiency scale curve of 554keV-2754keV energy range and realize the efficiency scale of the lanthanum bromide gamma spectrometer in water.
The method for calibrating the efficiency of the underwater gamma energy spectrum has the following advantages:
1. the materials are convenient to obtain and the price is low;
2. the radionuclide has short half-life;
3. the energy coverage of the characteristic gamma rays is wide;
4. the wastewater is nontoxic.
In the preferred seawater on-site gamma energy spectrum efficiency calibration method, the thermal neutron capture cross section of the neutron activator NaBr is respectively 0.528 target and 2.364 target, and the half lives of the captured thermal neutrons to generate Na-24 and Br-82 are respectively 14.997h and 35.282h. The neutron activator NaBr selected by the invention has low price, no toxicity and high solubility (80.2 g at 0 ℃ and 90.8g at 20 ℃) and consists of an 11-element Na natural nuclide Na-23 (the abundance is 100%) and a 35-element Br natural nuclide Br-81 (the abundance is 49.31%), the thermal neutron capture sections are respectively a 0.528 target and a 2.364 target, the half lives of the thermal neutron capture produced Na-24 and Br-82 are 14.997h and 35.282h respectively, and the efficiency scale can be carried out on the 221keV-2754keV energy range.
Preferably, the yield of the Cf-252 neutron source is 2.34E+06 n/mu g.s, and the average energy is 2.158MeV. The Cf-252 isotope neutron source has high yield of 2.34E+06 n/. Mu.g.s and average energy of 2.158MeV, the neutron energy is further reduced through neutron moderation, and the target is activated specifically: and (3) utilizing paraffin to slow neutrons, placing the target substance into a paraffin layer, and after the neutrons pass through the paraffin layer, reducing the energy to the vicinity of thermal neutrons to react with the target substance to generate activation.
Preferably, the neutron activation device is a hollow columnar body. The activation device is designed into a hollow columnar body, so that the neutron source can be lifted conveniently.
Specifically, the neutron activation device is cylindrical, the radius is 25cm, and the height is 60cm; a cylindrical channel with the radius of 7.5cm is arranged at the center; 24 activation pore channels are arranged on a cylindrical surface with the radius of 12.5cm by taking the axial direction of the neutron activation device as an axis, the radius of the activation pore channel is 1.5cm, and the height is 40cm. The neutron activation device is integrally cylindrical; the radius of the device is 25cm, so that the reflection can be increased, and the gravity center of the device is ensured to be stable; in order to facilitate the lifting of the neutron source, the mass of the target material is large enough after the paraffin slowing layer is considered, and the radius of the central cylindrical channel is designed to be 7.5cm; to increase the solid angle of illumination, the height of the device was 60cm. The paraffin layer reaches the peak value of thermal neutrons at the position of 4.5cm, and neutrons in the neutron incidence direction are lower than neutrons in the reflection direction, so that 24 points are uniformly selected as circle centers on a cylindrical surface with the radius of 12.5cm by taking the axial direction of the activation device as an axis, and 24 activation pore channels of target substances with the radius of 1.5cm and the height of 40cm are arranged for loading the target substances during irradiation.
Specifically, the filling mass density of the neutron activator NaBr in the activated pore canal is 1.74g/cm 3 ～1.90g/cm 3 . The solid NaBr particles are filled into the activated pore canal by a physical extrusion method, and the mass density of the solid NaBr particles is 1.74g/cm 3 ～1.90g/cm 3 The NaBr loading in 24 activated tunnels with the length of 40cm is 6786cm 3 About 12kg. The preferred packing density is capable of producing as many activated atoms as possible in the neutron activation device。
Preferably, the seawater on-site gamma energy spectrum efficiency calibration method is characterized in that the structure of the underwater radiation simulation device is cylindrical, and the dimension is phi 2500mm multiplied by 3000mm. The underwater radiation simulation device can meet the measurement and scale test of underwater radiation detection equipment.
The relation between the detection efficiency epsilon and the energy of the detector of the lanthanum bromide gamma spectrometer in water is (R= 0.99722, the error is less than 1.3 percent):
ε＝0.32113-0.06442lnE+0.01713(lnE) 2 +0.00171(lnE) 3 -0.01212(lnE) 4 -0.00265(lnE) 5 。
the efficiency is as follows: under the water body immersed state, when 1 ray occurs per second per liter in water, the counting rate of the detector of the lanthanum bromide gamma spectrometer in the water corresponds to the channel address. Under the offshore nuclear emergency condition, the activity concentration is calculated by adopting a plurality of gamma-ray full-energy peak counts with different characteristics.
Compared with the prior art, the seawater on-site gamma energy spectrum efficiency calibration method has the following beneficial effects: the efficiency calibration method establishes an in-water radiation simulation device and a neutron activation device. The neutron activation device can generate as many activated atoms as possible under the same neutron source irradiation condition. The efficiency scale method of the underwater gamma energy spectrum is convenient to obtain materials and low in cost; the half-life period of the selected radionuclide is short; the energy coverage of the characteristic gamma rays is wide; and the wastewater is nontoxic.
Detailed Description
The invention will be further illustrated with reference to specific examples.
Examples
1) The thermal neutron capture sections of the neutron activator NaBr are respectively 0.528 target and 2.364 target, and the half lives of the captured thermal neutrons are 14.997h and 35.282h respectively. The neutron activation device is a hollow cylinder, the radius is 25cm, and the height is 60cm; a cylindrical channel with the radius of 7.5cm is arranged at the center; 24 activation pore channels are arranged on a cylindrical surface with the radius of 12.5cm by taking the axial direction of the neutron activation device as an axis, the radius of the activation pore channel is 1.5cm, and the height is 40cm. The neutron activator NaBr is put into 24 pvc pipes with the diameter of 30mm,the packing mass density is 1.74g/cm 3 ～1.90g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Pvc tubes were inserted into 24 activation tunnels of a neutron activation device.
2) The yield of Cf-252 neutron source was 2.34E+06 n/. Mu.g.s and the average energy was 2.158MeV. The neutron activation device is arranged at the irradiation position of the Cf-252 neutron source, the neutron source is lifted to the center of the neutron activation device, and NaBr is taken out after continuous irradiation for 1-10 d.
3) NaBr is weighed and then is dissolved into an underwater radiation simulation device, and the underwater radiation simulation device is cylindrical in structure and has the dimensions of phi 2500mm multiplied by 3000mm. After fully stirring, sampling and analyzing by a laboratory low background gamma spectrometer to obtain specific activities of Na-24 and Br-82 in water; meanwhile, immersing a detector (3 inches) of a lanthanum bromide gamma spectrometer in water into the center of a radiation simulation device in water, and collecting an etching spectrum; so as to obtain an efficiency scale curve of 554keV-2754keV energy range and realize the efficiency scale of the lanthanum bromide gamma spectrometer in water.
The relation between the detection efficiency epsilon and the energy of the detector of the lanthanum bromide gamma spectrometer in water is (R= 0.99722, the error is less than 1.3%):
ε＝0.32113-0.06442lnE+0.01713(lnE) 2 +0.00171(lnE) 3 -0.01212(lnE) 4 -0.00265(lnE) 5 。
na-24 and Br-82 characteristic gamma rays and 3 inch lanthanum bromide monoenergetic peak detection limit
Figure BDA0004157397010000061
The above description is only a preferred embodiment of the present invention, and is not intended to limit the invention in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims (8)

1. A seawater in-situ gamma energy spectrum efficiency calibration method is characterized in that the testing process comprises the following steps:
1) Loading a neutron activator NaBr into 24 pvc pipes with phi of 30mm, compacting, and inserting the pvc pipes into 24 activation pore channels of a neutron activation device;
2) The neutron activation device is arranged at the irradiation position of the Cf-252 neutron source, the neutron source is lifted to the center of the neutron activation device, and NaBr is taken out after continuous irradiation for 1-10 d;
3) After weighing, dissolving the materials into a water radiation simulation device, fully stirring, sampling, and analyzing by a laboratory low background gamma spectrometer to obtain specific activities of Na-24 and Br-82 in water; meanwhile, immersing a detector of the lanthanum bromide gamma spectrometer in water into the center of the radiation simulation device in water, and collecting the etching spectrum; so as to obtain an efficiency scale curve of 554keV-2754keV energy range and realize the efficiency scale of the lanthanum bromide gamma spectrometer in water.
2. A seawater in situ gamma energy spectrum efficiency scaling method as claimed in claim 1, wherein: the thermal neutron capture sections of the neutron activator NaBr are respectively 0.528 target and 2.364 target, and half lives of Na-24 and Br-82 generated by capturing thermal neutrons are 14.997h and 35.282h respectively.
3. A seawater in situ gamma energy spectrum efficiency scaling method as claimed in claim 1, wherein: the yield of the Cf-252 neutron source is 2.34E+06 n/mu g.s, and the average energy is 2.158MeV.
4. A seawater in situ gamma energy spectrum efficiency scaling method as claimed in claim 1, wherein: the neutron activation device is a hollow columnar body.
5. A seawater in situ gamma energy spectrum efficiency scaling method as claimed in claim 1, wherein: the neutron activation device is cylindrical, the radius is 25cm, and the height is 60cm; a cylindrical channel with the radius of 7.5cm is arranged at the center;
24 activation pore channels are arranged on a cylindrical surface with the radius of 12.5cm by taking the axial direction of the neutron activation device as an axis, the radius of the activation pore channel is 1.5cm, and the height is 40cm.
6. A seawater in situ gamma energy spectrum efficiency scaling method as claimed in claim 1, wherein: the filling mass density of the neutron activator NaBr in the activated pore canal is 1.74g/cm 3 ～1.90g/cm 3 。
7. A seawater in situ gamma energy spectrum efficiency scaling method as claimed in claim 1, wherein: the structure of the underwater radiation simulation device is cylindrical, and the dimension is phi 2500mm multiplied by 3000mm.
8. A seawater in situ gamma energy spectrum efficiency scaling method as claimed in claim 1, wherein: the relation between the detection efficiency epsilon and the energy of the detector of the lanthanum bromide gamma spectrometer in water is (R= 0.99722, the error is less than 1.3 percent):
ε＝0.32113-0.06442lnE+0.01713(lnE) 2 +0.00171(lnE) 3 -0.01212(lnE)w-0.00265(lnE) 5 。
CN202310338758.5A 2023-03-31 2023-03-31 Seawater in-situ gamma energy spectrum efficiency calibration method Pending CN116106346A (en)

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