CN114646998A - High-flux fast neutron energy spectrum measuring system and method based on gas activation - Google Patents
High-flux fast neutron energy spectrum measuring system and method based on gas activation Download PDFInfo
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Abstract
The invention provides a high-flux fast neutron energy spectrum measuring system and method based on gas activation, and mainly aims to solve the problems that the fast neutron energy spectrum measured by the conventional solid activation detector is difficult to sample at the deep part of an irradiation experiment pore channel, a strong radioactive sample cannot be taken and placed in time, neutron energy spectrum measurement and energy spectrum measurement in a neutron source variable power process are difficult to carry out, the influence of a neutron source power boosting stage on a measurement result and the like. The method takes the flowing activated gas as an activating medium, and only needs to place a gas irradiation device and two gas pipelines at a point to be tested, so that the activated gas is introduced into the gas irradiation device for irradiation and is led out to an activated gas measuring chamber for measurement. The activated gas can be put in when the neutron source does not operate in a radiation-free dose, and the activated gas can be led out through the gas conduit, so that the short-life radioactive gas can be conveniently measured. When the neutron source is operated with variable power, the gas collection and measurement can be carried out after the power is stable, and the measurement of the variable power energy spectrum of the neutron source can be completed by one-time operation.
Description
Technical Field
The invention belongs to the field of fast neutron spectrum measurement, and particularly relates to a high-flux fast neutron spectrum measurement system and method based on gas activation.
Background
The neutron energy spectrum refers to the situation that neutron flux is distributed along with energy, and the neutron energy spectrum of different neutron sources has larger difference, for example, a neutron field of a reactor generally has more low-energy components and is continuously distributed, while a neutron field of an accelerator has more high-energy components and can form single-energy neutrons. Neutrons and atomic nuclei can be elastically scattered and inelastically scattered to change energy, so that neutron energy spectrums can be greatly different at different positions of the same neutron field or different medium material positions.
The neutron and atomic nucleus reaction probability (namely neutron reaction section) is closely related to neutron energy, and generally the capture reaction has a larger reaction section in a low energy region and a smaller reaction section in a high energy region; while some thresholded reactions can only occur when the neutron energy is above a certain threshold. Therefore, accurate measurement of neutron field energy spectrum parameters is a precondition for developing scientific research and irradiation production of neutron sources, and neutron field energy spectrum parameter measurement must be carried out before application.
Currently, various detector measurement methods such as nuclear recoil, nuclear reaction, coincidence measurement, and the like have been developed for low-flux neutron fields, for example, pinus sylvestris. Atomic energy Press, 1998: 77-121.
A solid activation detector measuring method is generally adopted for a high-flux neutron field, for example, Athyrea, Zhang wen shou, Wang Wu Shang and the like, and the parameter test of an experimental device of the Siegan pulse reactor [ J ] nuclear power engineering, 2002.12,23 and 6. However, the neutron spectrum measurement method of the solid activation detector has the following disadvantages:
1) in the deep and small space positions of an irradiation pore channel, the taking and placing of an activation detector are difficult, and particularly, the neutron sources such as a reactor and the like have strong radioactivity after long-time operation, so that the difficulty in taking and placing samples is increased. In order to ensure the safety of operators, sometimes the sampling must be carried out after cooling for several days, so that part of the short half-life sample cannot be measured;
2) in order to measure the energy spectrums of different power levels of neutron sources such as a reactor and the like, the neutron sources can only be operated at one power level each time, the activated dose is reduced to a safe range after the reactor is stopped, sampling measurement and lofting are carried out again, the measurement of the neutron energy spectrums at three to five power levels takes weeks, the measurement period is long, and the radiation dose of personnel is large;
3) the solid sample is generally placed under the zero power level of a reactor, the activated sample is also irradiated in the power increasing stage of the reactor, the power increase in the power increasing stage is generally nonlinear increase and is greatly influenced by human factors of operators, so that the activation of the sample in the stage before the preset power level is reached is difficult to accurately quantify.
Disclosure of Invention
The method aims to solve the problems that the deep sampling of an irradiation experiment pore channel is difficult, a strong radioactive sample cannot be taken and placed in time, the measurement of a neutron source variable power process energy spectrum is difficult, the influence of a neutron source power boosting stage on a measurement result is difficult and the like in the conventional solid activation detector for measuring a fast neutron energy spectrum. The invention provides a high-flux fast neutron energy spectrum measuring system and method based on gas activation.
The method takes the flowing activated gas as an activating medium, and only needs to place a gas irradiation device and two gas pipelines with the inner diameter of 1-2 mm at a point to be measured, so that the activated gas is introduced into the gas irradiation device for irradiation and is led out to an activated gas measuring chamber for measurement. The activated gas can be put in when the neutron source does not operate the non-radiation dose, and the activated gas can be led out through the gas conduit, so that the short-life radioactive gas can be conveniently measured. When the neutron source is operated with variable power, the gas collection and measurement can be carried out after the power is stable, and the measurement of the variable power energy spectrum of the neutron source can be completed by one-time operation.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
a high-flux fast neutron energy spectrum measuring system based on gas activation comprises a gas source, a gas flow and flow rate control device, a gas irradiation device, a short-life activated gas measuring device, a long-life activated gas measuring device, a vacuumizing device and a data processing device; the gas source and the gas flow and flow rate control devices are N, the N gas sources are correspondingly connected with inlets of the N gas flow and flow rate control devices through pipelines one by one, and outlets of the N gas flow and flow rate control devices are connected with an inlet of the gas irradiation device through a pipeline; the short-life activated gas measuring device comprises a short-life activated gas measuring tank and a first detector, wherein a first spiral flow channel is arranged in the short-life activated gas measuring tank, an inlet of the first spiral flow channel is connected with an outlet of the gas irradiation device, and the first detector is arranged in the short-life activated gas measuring tank, is positioned in a central hole of the first spiral flow channel and is used for acquiring a gamma energy spectrum of the short-life activated gas; the outlet of the first spiral flow channel is connected with the external atmosphere through a bypass pipeline, and a bypass valve is arranged on the bypass pipeline; the long-life activated gas measuring device comprises a long-life activated gas measuring tank and a second detector; the long-life activated gas measuring tank is a closed tank body with one end sunken inwards, an inlet of the long-life activated gas measuring tank is connected with an outlet of the first spiral flow channel through an inlet pipeline, an outlet of the long-life activated gas measuring tank is connected with a vacuumizing device through an outlet pipeline, meanwhile, an inlet pipeline of the long-life activated gas measuring tank is provided with an air inlet valve, an outlet pipeline of the long-life activated gas measuring tank is provided with an air outlet valve, and the second detector is arranged in a sunken structure of the long-life activated gas measuring tank and used for acquiring a gamma energy spectrum of the long-life activated gas; the data processing device is connected with the first detector and the second detector, and performs spectrum analysis on the gamma energy spectrums acquired by the first detector and the second detector to obtain gamma energy spectrum data for solving the neutron energy spectrum.
Furthermore, a second spiral flow channel is arranged in the gas irradiation device, an inlet of the second spiral flow channel is connected with the N gas flow and flow rate control devices, and an outlet of the second spiral flow channel is connected with an inlet of the first spiral flow channel.
Furthermore, a gas booster pump is arranged on an inlet pipeline of the long-life activated gas measuring tank and used for improving the pressure in the long-life activated gas measuring tank.
Furthermore, a shielding body is arranged on the outer side of the long-service-life activated gas measuring tank.
Further, the gas flow and flow rate control device is a gas mass flowmeter which automatically stabilizes flow and collects flow data in real time according to a set flow rate, and the first detector and the second detector are high-purity germanium detectors.
Meanwhile, the high-flux fast neutron energy spectrum measuring method based on gas activation provided by the invention comprises the following steps:
acquiring neutron reaction cross section data and selecting activated gas, wherein the activated gas comprises multiple long-life activated gases and multiple short-life activated gases; (ii) a
Determining the irradiation flow rates of the long-life activated gas and the short-life activated gas;
placing a gas irradiation device at an irradiation position to be measured;
step four, opening a bypass valve, irradiating the gas irradiation device, discharging any short-life activated gas selected in the step one through the bypass valve after the short-life activated gas sequentially passes through the gas flow and flow rate control device, the gas irradiation device and the short-life activated gas measuring device according to the irradiation flow rate determined in the step two, and obtaining a gamma energy spectrum of the short-life activated gas through a first detector after the activity of the short-life activated gas is stable; repeating the process to obtain gamma spectra of all the short-lived activated gases;
closing the air inlet valve, opening the air outlet valve, opening the vacuumizing device, vacuumizing the long-life activated gas measuring tank, the inlet pipeline and the outlet pipeline, purifying the activated gas measuring tank, and then closing the vacuumizing device and the air outlet valve to keep the long-life activated gas measuring tank in a vacuum state;
step six, irradiating the gas irradiation device, discharging any selected long-life activated gas in the step one through a bypass valve after the selected long-life activated gas sequentially passes through a gas flow and flow rate control device, the gas irradiation device and a short-life activated gas measurement device according to the irradiation flow rate determined in the step two, closing the bypass valve and opening an air inlet valve after the activity of the long-life activated gas is stable, collecting the long-life activated gas in a long-life activated gas measurement tank after the long-life activated gas sequentially passes through the gas flow and flow rate control device, the gas irradiation device and the short-life activated gas measurement device, closing the air inlet valve after the collection is finished, taking down the long-life activated gas measurement tank, and moving the long-life activated gas measurement tank to a second detector to obtain a gamma energy spectrum of the long-life activated gas;
step seven, replacing the long-life activated gas measuring tank and the gas source, and repeatedly executing the step five and the step six to obtain the gamma energy spectrums of all the long-life activated gases;
and step eight, performing spectrum resolution analysis on the gamma energy spectrum of the short-life activated gas obtained in the step five and the gamma energy spectrum of the long-life activated gas obtained in the step six, so as to obtain a high-flux fast neutron energy spectrum.
Further, in the second step, the irradiation flow rate of the short-life activated gas is 0.2-0.5L/min, and the irradiation flow rate of the long-life activated gas is 0.1-0.3L/mi.
And further, in the third step, after the gas irradiation device is placed at the position to be measured by irradiation, the process of purifying the high-flux fast neutron energy spectrum measurement system is also included, nitrogen is introduced into a pipeline of the high-flux fast neutron energy spectrum measurement system, and the high-flux fast neutron energy spectrum measurement system is purified.
Further, in the sixth step and the seventh step, if the pressure on the inlet pipeline of the long-life activated gas measuring tank is equal to or greater than the outlet pressure of the gas source, the gas booster pump is started for boosting.
Further, in the first step, the specific process of obtaining neutron reaction cross section data is as follows: neutron reaction cross section data are extracted from a G4NDL4.2 database of the Geant4 software, and meanwhile, the neutron reaction cross section data in a G4NDL4.2 database are supplemented by a linear interpolation method.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1. the method has the advantages that samples are very difficult to take and place in the strong radioactivity environment in the deep irradiation pore canal, the activated medium is activated gas, irradiation can be conducted through the air pipe, and timely derivation is achieved, so that measurement is convenient to carry out, and the problems that sampling in the deep irradiation pore canal is difficult and the strong radioactivity samples cannot be taken and placed in time in an irradiation experiment are solved.
2. Compared with a solid detector, the system and the method can measure the gas activity or collect the gas after the power is stable, thereby being more convenient for measuring the variable power of the neutron source and being easier to deduct the influence of the power boosting stage, and avoiding the problems of the influence of the power boosting stage of the neutron source on the measurement result and the like.
3. The invention adopts flowing gas as an activating medium to carry out measurement of fast neutron energy spectrum, and because the gas density is relatively low, the self-absorption is small, the neutron energy spectrum distortion is less in a resonance area, the energy spectrum is smoother in the resonance area, and the uncertainty of the resolution spectrum is smaller.
Drawings
FIG. 1 is a schematic diagram of a high-flux fast neutron spectrum measurement system based on gas activation according to the present invention;
FIG. 2 is a schematic view of a short-lived activated gas measurement device according to the present invention;
FIG. 3 is a schematic view of a long life activated gas measurement device in accordance with the present invention;
FIG. 4 is a schematic representation of a neutron spectrum analysis process in accordance with the present invention;
FIG. 5 is a schematic diagram of cross-sectional data prepared by the method of the present invention in comparison with other data sources;
FIG. 6 is a schematic view of a gas flow rate control device according to the present invention;
FIG. 7 is a schematic view of a gas coincidence measurement system of the present invention;
FIG. 8a is a diagram illustrating the energy spectrum solution result when the smoothing factor is 5 according to the present invention;
FIG. 8b is a diagram illustrating the energy spectrum solution result when the smoothing factor is 25 according to the present invention.
Reference numerals: the system comprises a gas source 1, a gas flow and flow rate control device 2, a gas irradiation device 3, an activated gas measuring device with a short service life 4, an activated gas measuring device with a long service life 5, a vacuumizing device 6, a data processing device 7, a gas booster pump 8, a bypass pipeline 9, a bypass valve 10, an air inlet valve 11, an air outlet valve 12, an activated gas measuring tank with a short service life 41, a first detector 42, a long-service life activated gas measuring tank 51, a second detector 52, an air filling proportional detector 61, a sodium iodide detector 62 and a digital multi-channel instrument 63.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention and are not intended to limit the scope of the present invention.
The invention provides a measuring method and a measuring system for developing fast neutron energy spectrum by adopting flowing gas as an activating medium. The method solves the key problems of preparation of a nuclear reaction section of the gas nuclide and the neutron, gas selection, gas flow and flow rate control, accurate measurement of gas activity, neutron energy spectrum solution and the like, and ensures that the gas activation-based neutron energy spectrum measurement method is realized.
As shown in fig. 1 to 3, the high-flux fast neutron spectrum measuring system based on gas activation of the invention comprises a gas source 1, a gas flow rate and flow rate control device 2, a gas irradiation device 3, a short-life activated gas measuring device 4, a long-life activated gas measuring device 5, a vacuum pumping device 6 and a data processing device 7 (which can adopt a computer); the gas source 1 and the gas flow and flow rate control device 2 are N, N is more than or equal to 4, the N gas sources 1 (high-pressure gas cylinders can be adopted) are correspondingly connected with the inlets of the N gas flow and flow rate control devices 2 one by one through pipelines, and the outlets of the N gas flow and flow rate control devices 2 are connected with the inlet of the gas irradiation device 3 through a pipeline; the short-life activated gas measuring device 4 comprises a short-life activated gas measuring tank 41 and a first detector 42, wherein a first spiral flow passage is arranged in the short-life activated gas measuring tank 41, the first spiral flow passage can be a spiral structure formed by winding a circular tube, or a spiral passage arranged on the side wall of the short-life activated gas measuring tank 41, the inlet of the first spiral flow passage is connected with the outlet of the gas irradiation device 3, and the first detector 42 is arranged in the short-life activated gas measuring tank 41 and is positioned in the central hole of the first spiral flow passage and used for acquiring the gamma energy spectrum of the short-life activated gas; the outlet of the first spiral flow channel is connected with the external atmosphere through a bypass pipeline 9, and a bypass valve 10 is arranged on the bypass pipeline 9; the long-life activated gas measuring device 5 includes a long-life activated gas measuring tank 51 and a second detector 52; the long-life activated gas measuring tank 51 is a closed tank body with one end sunken inwards, the inlet of the closed tank body is connected with the outlet of the first spiral flow channel through an inlet pipeline, the outlet of the closed tank body is connected with the vacuumizing device 6 through an outlet pipeline, meanwhile, an inlet pipeline of the long-life activated gas measuring tank 51 is provided with an air inlet valve 11, an outlet pipeline of the long-life activated gas measuring tank 51 is provided with an air outlet valve 12, and a second detector 52 is arranged in a sunken structure of the long-life activated gas measuring tank 51 and used for acquiring a gamma energy spectrum of the long-life activated gas; the data processing device 7 is connected to the first detector 42 and the second detector 52, and performs spectrum analysis on the gamma energy spectrum acquired by the first detector 42 and the second detector 52 to obtain a neutron spectrum.
The activated gas is sent from the gas source 1 to the gas irradiation device 3 for irradiation through the gas flow and flow rate control device 2. The gas flow and flow rate control device 2 is specifically a gas mass flowmeter which automatically stabilizes flow according to a set flow rate and acquires flow data in real time. The gas irradiation device 3 is a spiral structure inside for ensuring the uniform flow of gas, specifically, a second spiral flow channel is arranged in the gas irradiation device 3, the second spiral flow channel can be a spiral structure formed by winding a round pipe, and can also be a spiral channel arranged on the gas irradiation device 3, the inlet of the second spiral flow channel is connected with the N gas flow and flow rate control devices 2, and the outlet of the second spiral flow channel is connected with the inlet of the first spiral flow channel. The activated gas flows through the gas irradiation device 3 and then first flows into the short-life activated gas measuring device 4, and the middle of the short-life activated gas measuring tank 41 is provided with a hole with the diameter of 10cm and used for placing a high-purity germanium detector. The activated gas flows through the first spiral flow channel of the short-life activated gas measurement tank 41 and then enters the long-life activated gas measurement tank 51, the long-life activated gas measurement tank 51 is a cylinder with a concave end, and the concave part is used for placing a high-purity germanium detector. One gas booster pump 8 is provided in front of the long-life activated gas measurement tank 51 to increase the pressure in the long-life activated gas measurement tank 51. A vacuum-pumping device 6 is provided at the rear end of the long-life activated gas measurement tank 51 for purifying the entire gas circuit. Meanwhile, a lead shield is arranged on the outer side of the long-life activated gas measuring tank 51, and the lead shield can be a lead shield to reduce the influence of the environmental background on the measuring result.
The stable gas flow velocity and the real-time flow data monitoring are necessary equipment for carrying out gas activation neutron energy spectrum measurement. The invention provides a gas flow and flow rate control device 2 taking a GMFC-CXB gas mass flowmeter as a core, and a schematic diagram of a gas flow control system is shown in figure 6. The mass flowmeter can automatically stabilize the flow and collect real-time flow data according to the set flow speed, and a plurality of mass flowmeters can communicate with a computer through 485 interfaces to complete the work of flow value setting, data collection and the like.
The gas activity measurement in the system and method of the present invention is measured using a high purity germanium detector. The short-life activated product and the long-life activated product are respectively measured in a flowing online mode, a gas accumulation mode and a two-mode, wherein the flowing online gas measuring device is internally provided with a spiral slow flow structure.
Based on the device, the high-flux fast neutron energy spectrum measuring method based on gas activation comprises the following steps:
acquiring neutron reaction section data and selecting activated gas;
1.1) acquiring neutron reaction section data;
because the reaction of gas and neutrons is used as an indicator at present, the internationally universal NJOY equal section preparation software does not carry the nuclide neutron reaction section data. The built-in database (based on ENDF-BVII) of the program of the Geant4 is comprehensive in data and has most of neutron reaction cross section data of gas nuclides. Therefore, relevant data can be extracted from G4NDL4.2 database carried by the Geant4 software. Since G4NDL4.2 data are generally grouped into more than ten thousand groups, neutron spectrum solution is generally divided into 640 groups. The raw data is converted to 640 group format. FIG. 5 shows NJOY software, ENDF-BVII database and the prepared58The three kinds of source data basically accord with the same data of the Nin-p reaction section;
extracting neutron reaction section data from a G4NDL4.2 database of the software of Geant4, directly using the data if the database of G4NDL4.2 has the required energy point, and obtaining the neutron reaction section data by adopting a dotted linear interpolation method of two adjacent energy points if the energy point data does not exist;
1.2) selecting activated gas;
selecting an activated gas according to the chemical property, the neutron reaction section data and the activated product, wherein the activated gas comprises a plurality of long-life activated gases and a plurality of short-life activated gases; when selecting the activated gas, firstly selecting the gas which has stable chemical property, is non-toxic, non-flammable and non-explosive; secondly, selecting gas with larger neutron reaction cross section data, and thirdly selecting gas with easy measurement of an activation product;
7 available nuclear reaction types are selected according to conditions such as nuclide neutron reaction coverage energy area, reaction cross section, physical and chemical properties of reaction products and the like, the interval from thermal neutrons to 14MeV can be covered well basically, and the selected gas and neutron types are shown in table 1.
TABLE 1 types of reactions that can be used for neutron spectral measurements
Determining the irradiation flow rates of the long-life activated gas and the short-life activated gas;
the volume of the short-life activated gas measurement tank 41 is generally 300ml, the retention time of the short-life activated gas in the short-life activated gas measurement tank 41 is generally not more than 2 half-lives, and for the gas with the half-life of 30s, the irradiation flow rate is generally selected to be 0.2-0.5L/min;
for the long-life activated gas, the gas collection amount is generally 4-8L and is completed within about 30min, so the irradiation flow rate is generally 0.1-0.3L/min;
placing the gas irradiation device 3 at an irradiation position to be measured, connecting the high-flux fast neutron spectrum measurement system, and then purifying the high-flux fast neutron spectrum measurement system;
the specific process of the purification treatment comprises the following steps: introducing nitrogen with the flow rate of 1-2L/min, continuously flowing for 10min, and purifying a system pipeline;
step four, opening the bypass valve 10, irradiating the gas irradiation device 3, discharging any short-life activated gas selected in the step one after sequentially passing through the gas flow and flow rate control device 2, the gas irradiation device 3 and the short-life activated gas measurement device 4 according to the irradiation flow rate determined in the step two, specifically discharging the short-life activated gas to a waste gas treatment device, and obtaining a gamma energy spectrum of the short-life activated gas through the first detector 42 after the activity of the short-life activated gas is stable; repeating the process to obtain gamma spectra of all the short-lived activated gases;
in this step, for example, the CF is turned on4Obtaining a short-life activated product by gas irradiation, setting the flow rate to be 0.2L/min, waiting for 3-5 minutes until the irradiation is stable, measuring the gas activity in a short-life activated gas measuring tank 41 by using a high-purity germanium detector, continuously measuring for 20-30 minutes, and obtaining19F activated product19Gamma energy spectrum of O;
step five, closing the air inlet valve 11, opening the air outlet valve 12, opening the vacuumizing device 6, vacuumizing the long-life activated gas measuring tank 51, the inlet pipeline and the outlet pipeline for 10 minutes to further purify the pipeline, and then closing the vacuumizing device 6 and the air outlet valve 12 to keep the inside of the long-life activated gas measuring tank 51 in a vacuum state;
step six, irradiating the gas irradiation device 3, discharging any selected long-life activated gas in the step one through the bypass valve 10 after sequentially passing through the gas flow and flow rate control device 2, the gas irradiation device 3 and the short-life activated gas measurement device 4 according to the irradiation flow rate determined in the step two, closing the bypass valve 10 after the activity of the long-life activated gas is stable, opening the air inlet valve 11, collecting the long-life activated gas in the long-life activated gas measurement tank 51 after sequentially passing through the gas flow and flow rate control device 2, the gas irradiation device 3 and the short-life activated gas measurement device 4, closing the air inlet valve 11 after the collection is finished, taking down the long-life activated gas measurement tank 51, and moving the long-life activated gas measurement tank to the second detector 52 to obtain a gamma energy spectrum of the long-life activated gas;
in the step, for example, gas irradiation such as Ar is conducted to obtain a long-life activated product, the flow rate is set to 0.1 to 0.3L/min, the bypass valve 10 is opened first, 3 to 5 minutes are waited, after the irradiated gas is stabilized, the bypass valve 10 is closed, the gas inlet valve 11 is opened, the gas is collected to 0.2MPa, the gas inlet valve 11 is closed, and if the pressure on the inlet pipeline of the long-life activated gas measurement tank 51 is greater than or equal to the outlet pressure of the gas source 1, the gas booster pump is opened to boost the pressure;
step seven, replacing the long-life activated gas measuring tank 51 and the gas source 1, and repeatedly executing the step five and the step six to obtain gamma energy spectrums of all the long-life activated gases;
and step eight, after the needed gamma energy spectrum is obtained, performing spectrum resolution analysis by adopting an SAND-II spectrum resolution method to obtain a neutron spectrum, wherein the spectrum resolution analysis flow is shown in figure 4.
The method firstly selects activated gas according to factors such as reaction section of gas and neutrons, chemical property of the gas and the like; meanwhile, the gas irradiation device 3 and the gas flow and flow rate control device 2 solve the problems of gas irradiation, measurement and accurate quantification. And finally, MCNP simulation is adopted to calculate the gas detection efficiency, and a 4 pi beta-gamma coincidence measurement method is adopted to verify the efficiency calculation reliability. The fast neutron energy spectrum of an irradiation cavity of a certain reactor is actually measured, the measurement result is better in accordance with the solid multi-foil measurement method, and the reliability of the gas activation neutron energy spectrum based measurement method is verified.
In order to verify the detection efficiency simulation calculation reliability, a 4 pi beta-gamma coincidence measurement system is established, which comprises an internal inflation proportional detector 61, a sodium iodide detector 62 and a multi-channel digitizer 63. A gas sampling and balance gas filling interface is reserved on the long-life activated gas measuring tank 51 and is used for filling the working gas and the balance gas of the internal inflation proportional detector 61. After the proportional detector gas is filled with the activated gas, the proportional detector gas and the sodium iodide detector 62 form a 4 pi beta-gamma coincidence measurement system, as shown in fig. 7. Actually test40Ar(n,γ)41Produced by Ar reaction41And (4) the Ar activity is consistent with the activity measured by a high-purity germanium detector, and the reliability of gamma-ray efficiency simulation calculation is verified (the conformity measurement method is the standard method for measuring the radioactivity).
The condition experiment and the energy spectrum measurement are carried out by utilizing the reactor neutron source, the condition experiment mainly verifies a gas control system and a gas measurement system, and the energy spectrum measurement monitors the reliability of gas irradiation and gas activity measurement. The irradiation tank is placed on a simple support of an irradiation cavity of a certain reactor, the distance from the simple support to the front edge is 50cm, and the outer side of the irradiation tank is covered by a boron-aluminum composite material with the thickness of 8mm so as to absorb thermal neutrons. The length of the gas irradiation tube is 12.5m, and the diameter of the inner section is 4 mm. The experimental practical irradiation measures the argon, krypton, xenon and CF4Information on the specific mass flow rates of the four gases is shown in tables 2 and 3.
TABLE 2 gas measurement of irradiation quality
TABLE 3 measurement of sample masses
By using an international SAND-II spectrum resolving method, smooth factors are respectively set to be 5 and 25, the maximum difference of Q values of convergence factors is set to be 0.005, iteration is carried out for 5 times of convergence under the two conditions, and the maximum difference of Q values is 0.00357 and 0.00341 respectively. FIG. 8a and FIG. 8b are the results of the spectrum decomposition with smoothing factors of 5 and 25, respectively, and Table 4 shows the results of neutron flux calculations with 0.1-14 MeV per iteration. The initial spectrum has no influence on the measurement result basically, the initial spectrum 2 is the result of reducing the flux of each energy group of the initial spectrum by 2 times, and the actual output result has no change.
TABLE 4 neutron flux (n cm) of 0.1-14 MeV obtained by spectrum-solving calculation-2·s-1)
Result verification
The nickel foil with longer half-life period of the reaction product is attached to the front end of the irradiator, and the neutron flux of 0.1 MeV-14 MeV is measured through activation of the nickel foil.58NiThe average cross section of the reaction with neutrons relative to the actually measured spectrum, the initial spectrum and the initial spectrum 2 is 0.0379cm2、0.0351cm2、0.0351cm2. By adopting the three initial spectra, the neutron flux of 0.1 MeV-14 MeV actually measured by the nickel foil is respectively 2.82 multiplied by 1010n·cm2·s-1、3.04×1010n·cm2·s-1、3.04×1010n·cm2·s-1The neutron flux of 0.1 MeV-14 MeV calculated by nickel foil is slightly larger than the gas resolution value, and the relative difference is less than 20%. Considering that the nickel foil is positioned at the front end of the gas irradiator, the flux is slightly higher than the normal phenomenon, and the gas spectrum decomposition reliability can be verified.
Claims (10)
1. A high-flux fast neutron energy spectrum measuring system based on gas activation is characterized in that: the device comprises a gas source (1), a gas flow and flow rate control device (2), a gas irradiation device (3), a short-life activated gas measuring device (4), a long-life activated gas measuring device (5), a vacuumizing device (6) and a data processing device (7);
the gas source (1) and the gas flow and flow rate control devices (2) are N, the N gas sources (1) are correspondingly connected with inlets of the N gas flow and flow rate control devices (2) through pipelines one by one, and outlets of the N gas flow and flow rate control devices (2) are connected with inlets of the gas irradiation device (3) through pipelines;
the short-life activated gas measuring device (4) comprises a short-life activated gas measuring tank (41) and a first detector (42), a first spiral flow channel is arranged in the short-life activated gas measuring tank (41), an inlet of the first spiral flow channel is connected with an outlet of the gas irradiation device (3), and the first detector (42) is arranged in the short-life activated gas measuring tank (41), is positioned in a central hole of the first spiral flow channel and is used for acquiring a gamma energy spectrum of the short-life activated gas; the outlet of the first spiral flow channel is connected with the external atmosphere through a bypass pipeline (9), and a bypass valve (10) is arranged on the bypass pipeline (9);
the long-life activated gas measuring device (5) comprises a long-life activated gas measuring tank (51) and a second detector (52); the long-life activated gas measuring tank (51) is a closed tank body with one end sunken inwards, an inlet of the long-life activated gas measuring tank is connected with an outlet of the first spiral flow channel through an inlet pipeline, an outlet of the long-life activated gas measuring tank is connected with the vacuumizing device (6) through an outlet pipeline, meanwhile, an inlet pipeline of the long-life activated gas measuring tank (51) is provided with an air inlet valve (11), an outlet pipeline of the long-life activated gas measuring tank is provided with an air outlet valve (12), and the second detector (52) is arranged in a sunken structure of the long-life activated gas measuring tank (51) and used for obtaining a gamma energy spectrum of the long-life activated gas;
the data processing device (7) is connected with the first detector (42) and the second detector (52), performs spectrum decomposition analysis on the gamma energy spectrums acquired by the first detector (42) and the second detector (52), and obtains neutron spectrums through spectrum decomposition.
2. The gas activation-based high-throughput fast neutron spectroscopy measurement system of claim 1, wherein: and a second spiral flow channel is arranged in the gas irradiation device (3), the inlet of the second spiral flow channel is connected with the N gas flow and flow rate control devices, and the outlet of the second spiral flow channel is connected with the inlet of the first spiral flow channel.
3. The gas activation-based high-throughput fast neutron spectroscopy measurement system of claim 1, wherein: and a gas booster pump (8) is arranged on an inlet pipeline of the long-life activated gas measuring tank (51) and used for increasing the pressure in the long-life activated gas measuring tank (51).
4. The gas activation-based high-throughput fast neutron spectroscopy measurement system of claim 1, wherein: and a shielding body is arranged on the outer side of the long-life activated gas measuring tank (51).
5. The gas activation-based high-throughput fast neutron spectroscopy measurement system of claim 1, wherein: the gas flow and flow rate control device (2) is a gas mass flowmeter which automatically stabilizes flow and collects flow data in real time according to a set flow rate, and the first detector (42) and the second detector (52) are high-purity germanium detectors.
6. A high-flux fast neutron energy spectrum measuring method based on gas activation is characterized by comprising the following steps:
acquiring neutron reaction cross section data and selecting activated gas, wherein the activated gas comprises multiple long-life activated gases and multiple short-life activated gases;
determining the irradiation flow rates of the long-life activated gas and the short-life activated gas;
placing the gas irradiation device (3) at a position to be irradiated;
step four, opening a bypass valve (10), irradiating the gas irradiation device (3), discharging any short-life activated gas selected in the step one through the bypass valve (10) after sequentially passing through the gas flow and flow rate control device (2), the gas irradiation device (3) and the short-life activated gas measurement device (4) according to the irradiation flow rate determined in the step two, and acquiring a gamma energy spectrum of the short-life activated gas through a first detector (42) after the activity of the short-life activated gas is stable; repeating the process to obtain gamma spectra of all the short-lived activated gases;
closing the air inlet valve (11), opening the air outlet valve (12), opening the vacuumizing device (6), vacuumizing the long-life activated gas measuring tank (51) and the inlet pipeline and the outlet pipeline, purifying the activated gas measuring tank, and then closing the vacuumizing device (6) and the air outlet valve (12) to keep the inside of the long-life activated gas measuring tank (51) in a vacuum state;
step six, irradiating the gas irradiation device (3), discharging any long-life activated gas selected in the step one through a bypass valve (10) after sequentially passing through the gas flow rate and flow rate control device (2), the gas irradiation device (3) and the short-life activated gas measuring device (4) according to the irradiation flow rate determined in the step two, and after the activity of the long-life activated gas is stable, the bypass valve (10) is closed, the air inlet valve (11) is opened, the long-life activated gas passes through the gas flow and flow rate control device (2), the gas irradiation device (3) and the short-life activated gas measuring device (4) in sequence and then is collected in the long-life activated gas measuring tank (51), closing the air inlet valve (11) after the collection is finished, taking down the long-life activated gas measuring tank (51), and moving to a second detector (52) to acquire a gamma energy spectrum of the long-life activated gas;
step seven, replacing the long-life activated gas measuring tank (51) and the gas source (1), and repeatedly executing the step five and the step six to obtain gamma energy spectrums of all the long-life activated gases;
and step eight, performing spectrum resolution analysis on the gamma energy spectrum of the short-life activated gas obtained in the step five and the gamma energy spectrum of the long-life activated gas obtained in the step six, so as to obtain a high-flux fast neutron energy spectrum.
7. The gas activation-based high-throughput fast neutron spectrum measurement method according to claim 6, wherein: in the second step, the irradiation flow rate of the short-life activated gas is 0.2-0.5L/min, and the irradiation flow rate of the long-life activated gas is 0.1-0.3L/min.
8. The gas activation-based high-throughput fast neutron spectrum measurement method according to claim 6, wherein: and in the third step, after the gas irradiation device (3) is placed at the position to be measured by irradiation, the process of purifying the high-flux fast neutron energy spectrum measurement system is also included, nitrogen is introduced into a pipeline of the high-flux fast neutron energy spectrum measurement system, and the high-flux fast neutron energy spectrum measurement system is purified.
9. The gas activation-based high-throughput fast neutron spectrum measurement method according to claim 6, wherein: in the sixth step and the seventh step, if the pressure on the inlet pipeline of the long-life activated gas measurement tank (51) is equal to or greater than the outlet pressure of the gas source (1), the gas booster pump (8) is started for boosting.
10. The gas-activation-based high-throughput fast neutron spectrum measurement method according to claim 6, wherein in the first step, the specific process of obtaining neutron reaction cross-section data is as follows: neutron reaction cross section data are extracted from a G4NDL4.2 database of the Geant4 software, and meanwhile, the neutron reaction cross section data in a G4NDL4.2 database are supplemented by a linear interpolation method.
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