A method for testing the upper limit of radiation resistance of γ-ray monitor

Abstract

The present invention discloses a method for testing the upper limit of radiation resistance of a gamma monitor, comprising: a) determining a radiation source and its radiation dose rate; b) placing the gamma monitor at a preset radiation dose rate point of the radiation source until the gamma monitor fails; c) determining the cause of the failure of the gamma monitor; d) shielding and protecting a monitoring circuit module by using a shielding structure; e) placing a J405 counter tube of the gamma monitor at different radiation dose rate points of the radiation source to obtain the response credibility of the J405 counter tube; f) calculating the error of the pulse counting rate, and terminating the experiment if the error is within a preset error range; otherwise, repeating step e). The present invention verifies the feasibility of extending the upper limit of radiation resistance of the gamma monitor through sufficient and complete quantitative tests, and provides good technical support and reference for the shielding structure design of the gamma monitor.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear radiation monitoring, and in particular to a method for testing the upper limit of radiation resistance of a gamma monitor. Background Art

[0002] The research field of gamma radiation monitoring technology is mainly used for environmental investigation from environmental background monitoring level to high-dose rate radiation environment, fixed-point monitoring of nuclear power plants, various nuclear facilities, airport customs and border customs, nuclear waste sites, isotope medical enterprises and institutions, law enforcement monitoring of the construction industry and units using radiation sources, nuclear research departments, education departments, nuclear accidents, nuclear terrorist attacks and nuclear explosion sites. The wide-range monitor can continuously monitor the changes of environmental gamma radiation to the level of nuclear terrorist incidents in real time. Once a nuclear terrorist attack, nuclear accident or large-scale migration of radioactive nuclides from abroad occurs, the gamma radiation monitoring technology can provide an early warning and measure the dose rate in real time.

[0003] However, most of the radiation measurement equipment in China currently uses J405 counter tubes, and the calibration range of J405 counter tubes is between 20mGy / h and 10Gy / h, with an overload dose rate of 30Gy / h. The calculation chip of the γ monitor can generally only withstand radiation dose rates below 10Gy / h to work properly. In recent years, the military and nuclear monitoring have increasingly higher requirements for measurement ranges, and there are already requirements for measurement ranges of 30Gy / h, 50Gy / h, and 100Gy / h. Therefore, it is necessary to determine which component is restricted by the upper limit of the range of the existing γ monitor, and at the same time determine whether the J405 counter tube can meet the requirements of use in high-radiation environments, and provide technical support and reference for the shielding structure design of the existing γ monitor, so as to improve the upper limit of the γ monitor's radiation resistance. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is: to provide a method for testing the upper limit of radiation resistance of a gamma monitor, which solves the problems of the prior art gamma monitor having a small measuring range, a low upper limit of radiation resistance, and difficulty in determining the shortcomings of its upper limit.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for testing the upper limit of radiation resistance of a γ monitor comprises a γ monitor and a radioactive source, wherein the γ monitor comprises a J405 counter tube and a monitoring circuit module, and comprises the following steps:

[0007] a) determine the radiation source and its radiation dose rate;

[0008] b) placing the gamma monitor at a preset radiation dose rate point of the radiation source, subjecting the gamma monitor to a radiation dose rate exceeding its measuring range for a preset time until the gamma monitor fails;

[0009] c) Determine the cause of the γ monitor failure. If the cause of the failure is caused by the monitoring circuit module, proceed to the next step;

[0010] d) replacing the monitoring circuit module causing the fault, and shielding the monitoring circuit module with a shielding structure;

[0011] e) placing the J405 counter tube of the gamma monitor at different radiation dose rate point positions of the radiation source, and recording the pulse count rates of the J405 counter tube at different radiation dose rate point positions respectively, to obtain the response credibility of the J405 counter tube; wherein the radiation dose rate point positions include at least one radiation dose rate point position exceeding the calibration range of the J405 counter tube;

[0012] f) calculating the error of the pulse counting rate, and if the error is within a preset error range, terminating the experiment; otherwise, repeating step e).

[0013] As an optimization, the radiation source adopts a 60Co source with an activity of 7205Ci, and the incident dose rate at a distance of 90.43 cm is 100Gy / h.

[0014] As an optimization, in step b), the gamma monitor is placed at the radiation dose rate point of 30 Gy / h of the radiation source.

[0015] As an optimization, in step b), a malfunction of the gamma monitor is detected by a sudden drop of the pulse count rate of the gamma monitor to zero.

[0016] As an optimization, in step d), the shielding structure uses a lead shielding plate or a tungsten shielding plate, and the thickness of the shielding plate is determined by being able to attenuate the radiation dose rate of the radiation source to within the normal operating range of the monitoring circuit module.

[0017] As an optimization, in step e), the J405 counter tube of the γ monitor is placed in sequence at the point positions where the radiation dose rate of the radiation source is 3 Gy / h, 5 Gy / h, 8 Gy / h, 10 Gy / h, 20 Gy / h, 30 Gy / h, 50 Gy / h, 80 Gy / h, and 100 Gy / h, and the response reliability of each point position of the J405 counter tube is obtained.

[0018] As an optimization, in step f), the J405 counter tube of the gamma monitor is placed at a point where the radiation dose rate of the radiation source is 100 Gy / h and irradiated continuously for 11 hours, and the pulse counting rate is recorded once every hour, and the error of the pulse counting rate is calculated.

[0019] As an optimization, the error is calculated by the following formula,

[0020]

[0021] in,

[0022]

[0023] Where N i is the pulse counting rate recorded for the i-th time.

[0024] As an optimization, the preset error range is ±10%.

[0025] Compared with the prior art, this application has the following beneficial effects:

[0026] The present invention preliminarily excludes the J405 counter tube as the cause of equipment damage in the 30Gy / h dose point environment of the γ monitor through experimental design. At the same time, the feasibility of extending the range of the J405 counter tube with an overload dose rate of 30Gy / h to 100Gy / h, which is calibrated in the technical parameters and measures the γ dose rate, is verified through experiments. After the shielding structure is added to the monitoring circuit module, the γ monitor is irradiated for 11 hours in a 100Gy / h high dose rate environment, further verifying and confirming that the J405 counter tube fully meets the 100Gy / h high dose rate test environment, and through error calculation, it is determined that the J405 counter tube can stably work normally in a 100Gy / h high dose rate environment, thereby improving the upper limit of the radiation resistance of the entire γ monitor. The present invention, through sufficient and complete quantitative testing, verification, discussion and elimination of the radiation resistance characteristics of the GM counter tube in a high-dose rate environment, deduces and determines that the short board problem occurs in the monitoring circuit module, so it is necessary to fully discuss and analyze the mainboard shielding solution. The present invention provides good technical support and reference for the shielding structure design of the γ monitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the experiment of the present invention;

[0028] Figure 2 This is a radiation resistance characteristic diagram of the voltage conversion chip TPS78233, the RS485 transceiver chip ISL32601, and the microprocessor STM32L475VGT6 under 30Gy / h dose rate irradiation in the present invention;

[0029] Figure 3 This is a fault analysis diagram of the gamma monitor in the present invention under irradiation at a dose rate of 30 Gy / h;

[0030] Figure 4 The response credibility of the J405 counter tube of the present invention at different dose rate points;

[0031] Figure 5 The pulse count rate curve of the J405 counter tube of the present invention after 11 hours of irradiation in a 100 Gy / h environment. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0033] For specific implementation: see Figure 1-Figure 5 ,

[0034] A method for testing the upper limit of radiation resistance of a γ monitor includes a γ monitor and a radiation source. The γ monitor includes a J405 counter tube and a monitoring circuit module. The monitoring circuit module includes a conventional micro-power circuit, a microprocessor circuit, a storage circuit, an RS485 communication circuit, a voltage conversion circuit, etc., which are used to analyze and process the signal of the J405 counter tube. The hardware involved mainly includes a voltage conversion chip TPS78233, an RS485 transceiver chip ISL32601, and a microprocessor STM32L475VGT6. The following steps are included:

[0035] a) Determine the radiation source and its radiation dose rate; the radiation source is a 60Co source with an activity of 7205Ci, and the incident dose rate at a distance of 90.43 cm is 100Gy / h.

[0036] b) placing the gamma monitor at a radiation dose rate point of 30 Gy / h of the radiation source, and subjecting the gamma monitor to a radiation dose rate exceeding its measuring range for a preset time until the gamma monitor fails.

[0037] c) Determine the cause of the γ monitor failure. If the cause of the failure is caused by the monitoring circuit module, proceed to the next step;

[0038] Specifically, Figure 2 As shown in the figure, Line-1, Line-2, and Line-3 correspond to the pulse count rate values ​​of the J405 counter tube and the voltage conversion chip TPS78233, the RS485 transceiver chip ISL32601, and the microprocessor STM32L475VGT6 exposed to the 30Gy / h dose rate point for 280 minutes. After 180min, 240min, and 200min, the pulse count rate of Line-1, Line-2, and Line-3 dropped suddenly from about 55,000 to 0. The fault phenomenon caused by each condition and the reasons analyzed by power-on test of the equipment are as follows Figure 3 shown.

[0039] The reasons for the above phenomenon are analyzed as follows:

[0040] (1) Single-particle effect: A single-particle upset refers to the change in the potential state of a component due to the influence of radiation, where "0" becomes "1" and "1" becomes "0". It generally does not cause physical damage to the component.

[0041] (2) For chip materials, radiation defects are caused by vacancy defects, which means atoms are kicked out of the lattice or extra atoms are stuck in the lattice. These two types of damage may accumulate and cause product failure. Radiation can cause the SiO2 layer in the chip to accumulate positive charges, reducing chip performance. When the radiation is severely affected, radiation can increase the leakage current of the transistor and prevent the transistor from shutting down normally.

[0042] Solution:

[0043] Replace the voltage conversion chip TPS78233 and conduct tests. The fault "probe not connected" is solved and the equipment works normally.

[0044] Replace the microprocessor STM32L475VGT6 and conduct tests. The fault "no count" problem is solved and the equipment works normally.

[0045] After replacing the RS485 transceiver chip ISL32601 and conducting tests, the fault "probe not connected" was solved and the equipment worked normally.

[0046] In summary, we can determine that, first, different chips have different radiation resistance capabilities under a 30Gy / h dose rate environment. Figure 3 They have been listed one by one;

[0047] Second: Under a 30Gy / h dose rate environment, the radiation resistance of each chip was qualitatively discussed. However, at the same time, the irradiation was continuously performed beyond the effective range of the J405 counter tube. Therefore, it was necessary to quantitatively verify the radiation resistance of the J405 counter tube in the next step to further verify that there was indeed a shortcoming in the chip's radiation resistance.

[0048] d) Replace the monitoring circuit module that causes the fault, and use a shielding structure to shield the monitoring circuit module; the shielding structure uses a lead shielding plate or a tungsten shielding plate, and its thickness is determined by being able to attenuate the radiation dose rate of the radiation source to within the normal working range of the monitoring circuit module.

[0049] e) Place the J405 counter tube of the γ monitor at different radiation dose rate points of the radiation source, and record the pulse count rates of the J405 counter tube at different radiation dose rate points respectively to obtain the response credibility of the J405 counter tube; wherein the radiation dose rate point positions include at least one radiation dose rate point position that exceeds the calibration range of the J405 counter tube. Specifically, place the J405 counter tube of the γ monitor at the point positions of the radiation dose rate of the radiation source of 3Gy / h, 5Gy / h, 8Gy / h, 10Gy / h, 20Gy / h, 30Gy / h, 50Gy / h, 80Gy / h, and 100Gy / h in sequence to obtain the response credibility of each point position of the J405 counter tube.

[0050] Specifically, Figure 4 As shown, in the experiment of the present invention, as the dose rate continues to increase, each dose rate point corresponds to a group of pulse count rate values, and the count rate values ​​are stably counted within 60 minutes, thereby verifying the response credibility of the counter tube in the dose rate range of 3Gy / h, 5Gy / h, 8Gy / h, 10Gy / h, 20Gy / h, 30Gy / h, 50Gy / h, 80Gy / h, and 100Gy / h. This round of experiments verified the feasibility of the range expansion of the J405 model GM counter tube from 3Gy / h to 100Gy / h.

[0051] f) calculating the error of the pulse counting rate, and if the error is within a preset error range, ending the experiment; otherwise, repeating step e). Specifically, Figure 5 As shown, the J405 counter tube of the gamma monitor is placed at a point where the radiation dose rate of the radiation source is 100 Gy / h and irradiated continuously for 11 hours. The pulse counting rate is recorded once every hour, and the error of the pulse counting rate is calculated.

[0052] The error is calculated by the following formula,

[0053]

[0054] in,

[0055]

[0056] Where N i is the pulse counting rate recorded for the i-th time.

[0057] According to formula (1), the relative error of the equipment under 11h irradiation condition is controlled within ±5.94%, which fully meets the requirement of the relative inherent error of the equipment within ±10%.

[0058] After 11 hours of continuous irradiation in a high-dose rate environment of 100Gy / h, the cumulative dose exceeded 1100Gy, meeting and exceeding the requirements of the development task.

[0059] The present invention, firstly, further verifies and confirms that the J405 counter tube fully meets the 100Gy / h high-dose rate test environment by irradiating the device for 11 hours in a 100Gy / h high-dose rate environment;

[0060] Second: Through the sufficient and complete quantitative test, verification, discussion and elimination of the radiation resistance characteristics of the GM counter tube in a high-dose rate environment in the present invention, it is deduced and determined that the short board problem occurs on the probe mainboard chip, so it is necessary to fully discuss and analyze the mainboard shielding solution.

[0061] The present invention preliminarily excludes the J405 counter tube as the cause of equipment damage in the 30Gy / h dose point environment of the γ monitor through experimental design. At the same time, the feasibility of extending the range of the J405 counter tube with an overload dose rate of 30Gy / h to 100Gy / h, which is calibrated in the technical parameters and measures the γ dose rate, is verified through experiments. After the shielding structure is added to the monitoring circuit module, the γ monitor is irradiated for 11 hours in a 100Gy / h high dose rate environment, further verifying and confirming that the J405 counter tube fully meets the 100Gy / h high dose rate test environment, and through error calculation, it is determined that the J405 counter tube can stably work normally in a 100Gy / h high dose rate environment, thereby improving the upper limit of the radiation resistance of the entire γ monitor. The present invention, through sufficient and complete quantitative testing, verification, discussion and elimination of the radiation resistance characteristics of the GM counter tube in a high-dose rate environment, deduces and determines that the short board problem occurs in the monitoring circuit module, so it is necessary to fully discuss and analyze the mainboard shielding solution. The present invention provides good technical support and reference for the shielding structure design of the γ monitor.

[0062] Although the embodiments of the present invention have been shown and described, it is apparent to those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and basis of the present invention. The scope of the present invention is defined by the appended claims and their equivalents. Therefore, the embodiments of the present invention are merely illustrative examples of the present invention. The embodiments of the present invention do not constitute limitations on the present invention from any point of view.

Claims

1. A method for testing the upper limit of radiation resistance of a γ monitor, comprising a γ monitor and a radiation source, wherein the γ monitor comprises a J405 counter tube and a monitoring circuit module, and is characterized in that: The following steps are included: a) determine the radiation source and its radiation dose rate; b) placing the gamma monitor at a preset radiation dose rate point of the radiation source, subjecting the gamma monitor to a radiation dose rate exceeding its measuring range for a preset time until the gamma monitor fails; c) Determine the cause of the γ monitor failure. If the cause of the failure is caused by the monitoring circuit module, proceed to the next step; d) replacing the monitoring circuit module causing the fault, and shielding the monitoring circuit module with a shielding structure; e) placing the J405 counter tube of the gamma monitor at different radiation dose rate point positions of the radiation source, and recording the pulse count rates of the J405 counter tube at different radiation dose rate point positions respectively, to obtain the response credibility of the J405 counter tube; wherein the radiation dose rate point positions include at least one radiation dose rate point position exceeding the calibration range of the J405 counter tube; f) calculating the error of the pulse counting rate, and if the error is within a preset error range, ending the experiment; otherwise, repeating step e).

2. The method for testing the upper limit of radiation resistance of a γ monitor according to claim 1, characterized in that: The radiation source is a 60Co source with an activity of 7205Ci, and the incident dose rate at a distance of 90.43 cm is 100Gy / h.

3. The method for testing the upper limit of radiation resistance of a γ monitor according to claim 1, characterized in that: In step b), the gamma monitor is placed at the radiation dose rate point of 30 Gy / h of the radiation source.

4. The method for testing the upper limit of radiation resistance of a γ monitor according to claim 1, characterized in that: In step b), the γ monitor failure is detected by the pulse count rate of the γ monitor suddenly dropping to zero.

5. The method for testing the upper limit of radiation resistance of a γ monitor according to claim 1, characterized in that: In step d), the shielding structure uses a lead shielding plate or a tungsten shielding plate, and the thickness of the shielding plate is determined by being able to attenuate the radiation dose rate of the radiation source to within the normal working range of the monitoring circuit module.

6. The method for testing the upper limit of radiation resistance of a γ monitor according to claim 1, characterized in that: In step e), the J405 counter tube of the gamma monitor is placed in sequence at the point positions where the radiation dose rate of the radiation source is 3 Gy / h, 5 Gy / h, 8 Gy / h, 10 Gy / h, 20 Gy / h, 30 Gy / h, 50 Gy / h, 80 Gy / h, and 100 Gy / h, and the response reliability of each point position of the J405 counter tube is obtained.

7. The method for testing the upper limit of radiation resistance of a γ monitor according to claim 6, characterized in that: In step f), the J405 counter tube of the gamma monitor is placed at a point where the radiation dose rate of the radiation source is 100 Gy / h and irradiated continuously for 11 hours, and the pulse counting rate is recorded once every hour, and the error of the pulse counting rate is calculated.

8. The method for testing the upper limit of radiation resistance of a γ monitor according to claim 7, characterized in that: The error is calculated by the following formula, in, Where N i is the pulse counting rate recorded for the i-th time.

9. The method for testing the upper limit of radiation resistance of a γ monitor according to claim 8, characterized in that: The preset error range is ±10%.

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