A GM tube range extension device and a GM tube range extension method based on hardware dead time compensation

Abstract

The application relates to the technical field of nuclear radiation measurement, in particular to a GM tube range expansion device and a GM tube range expansion method based on hardware dead time compensation. The device comprises a detection module, an electric signal conversion module, a pulse discrimination module, a dead time measurement module, a counting module, an anti-interference module and a data processing unit. The GM tube range expansion device has the advantages of strong anti-interference capability, good linearity, less component consumption and an overload detection function, and can greatly expand the GM tube range.

Description

Technical Field

[0001] This invention relates to the field of nuclear radiation measurement technology, specifically to a GM tube range extension device and a GM tube range extension method based on hardware dead time compensation. Background Technology

[0002] GM tubes (Geiger counters) are widely used in nuclear radiation measurement due to their mature manufacturing technology, simple peripheral circuits, and high reliability. However, when measuring in strong radiation fields, GM tubes are prone to severe pulse accumulation in the output pulses. The subsequent pulse discrimination circuit cannot distinguish the accumulated pulses and outputs them as single pulses, resulting in a significantly lower reading on the instrument, or even zero when saturated.

[0003] In the existing technology, a differentiating circuit is used to extract accumulated pulses, but there are obvious drawbacks: on the one hand, the differentiating circuit will attenuate the amplitude of normal pulses, so the threshold of the discriminator needs to be set lower, which will result in a poorer anti-interference capability of the circuit; on the other hand, the differentiating circuit can only handle mild pulse accumulation, which cannot meet the requirements for accurate measurement under strong radiation fields, thus limiting the measurement range of the GM tube. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies such as poor pulse accumulation processing effect, weak anti-interference ability, and limited range of GM tubes under strong radiation fields, a GM tube range extension device and dead time compensation method with strong anti-interference ability, good linearity, low component quantity, and overload detection function are provided, so as to achieve a significant expansion of the GM tube range.

[0005] The technical solution of the present invention is as follows: A GM tube range extension device includes a core functional module and auxiliary structures. The modules work together to achieve pulse processing, dead time measurement, counting, and anti-interference functions. Specifically, it includes: Detection module: The core detection element is a GM tube, which is used to receive X-ray particles and generate pulsed current; Electrical signal conversion module: connected to the cathode of the GM tube in the detection module, used to convert the pulse current output by the GM tube into a distinguishable pulse voltage; Pulse discrimination module: connected to the output terminal of the electrical signal conversion module, performs threshold discrimination on pulse voltage, and outputs standardized discrimination pulse; Dead time measurement module: connected to the output of the pulse discrimination module, configured in gated mode, used to measure the total width per second of the discrimination pulse to obtain the dead time Tdead of the GM tube; Counting module: connected to the output of the pulse discrimination module, configured in counting mode, used to count the number of discrimination pulses per second to obtain the counting rate CPS; Anti-interference module: Specifically, it is a shielding layer, which is set on the outside of the cathode of the GM tube to shield electromagnetic interference and improve the anti-interference performance of the circuit; Data processing unit: connected to the data output terminals of the dead time measurement module and the counting module, and calculates the true count rate CPS1 of the GM tube according to the dead time calibration formula CPS1=CPS / (1-Tdead).

[0006] Furthermore, the electrical signal conversion module is a mirror constant current source, which includes transistor Q1 and transistor Q2; the collector of transistor Q1 is connected to the cathode of the GM transistor, and the collector of transistor Q2 is connected in series with a conversion resistor R2; the emitter of transistor Q1 and the emitter of transistor Q2 are connected together, and the base of transistor Q1 and the base of transistor Q2 are connected together, which is used to transfer the conversion resistor R2 to the branch of transistor Q2, so as to avoid the shielding layer and the conversion resistor R2 forming a low cutoff frequency filter.

[0007] Furthermore, the anode of the GM tube is connected in series with an anode resistor R1, and the anode resistor R1 satisfies the following constraints: R1*C>>t1, where C is the total capacitance of the anode node of the GM tube to ground, and t1 is the time it takes for positive ions inside the GM tube to move to the cathode. (HV-Vmin) / R1*R2>V1, where HV is the high voltage of the anode of the GM tube, Vmin is the minimum voltage for normal operation of the GM tube, and V1 is the discrimination threshold of the pulse discrimination module.

[0008] Furthermore, the value of R1 is 5.1MΩ, and the value of R2 is 82KΩ; the pulse discrimination module is a voltage comparator U1, and the discrimination threshold of the voltage comparator U1 is V1=500mV.

[0009] Furthermore, the dead time measurement module is a first timer, the counting module is a second timer, and the GM tube is a J304 counting tube.

[0010] A method for extending the range of a GM tube based on hardware dead-time compensation includes the following steps: X-ray detection: The GM tube receives X-ray particles, causing an avalanche effect and forming a pulsed current at the cathode; Electrical signal conversion: The pulse current is converted into a pulse voltage through a current-to-voltage conversion module; Pulse discrimination: The pulse discrimination module discriminates pulse voltages based on preset thresholds and outputs standardized discrimination pulses; Dead time measurement: The dead time measurement module measures the total width per second of the discrimination pulse in gating mode to obtain the dead time Tdead of the GM tube; Pulse Counting: The counting module counts the number of pulses per second in counting mode to obtain the count rate CPS; Dead time compensation: Calculate the true count rate CPS1 of the GM tube based on the calibration formula CPS1=CPS / (1-Tdead) derived from nuclear physics theory; Saturation detection: The GM tube is detected to be in a saturated state by judging whether Tdead is close to 1 second.

[0011] Furthermore, in step 2, the switching resistor R2 is transferred to the transistor Q2 branch by transistors Q1 and Q2 of the mirror constant current source, so as to avoid the shielding layer and R2 forming a low cutoff frequency filter and prevent the pulse voltage amplitude from attenuating.

[0012] Furthermore, in step 7, when Tdead ≥ 900000 μS, the GM tube is determined to be in a saturated state.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Strong anti-interference capability: The shielding layer effectively shields electromagnetic interference. Combined with the design of the transfer conversion resistor R2 in the electrical signal conversion module (mirror constant current source), the shielding layer and R2 are prevented from forming a low cutoff frequency filter, which not only ensures the anti-interference effect but also prevents the pulse voltage amplitude from attenuating. Good measurement linearity: The dead time of the GM tube is directly measured by the dead time measurement module. Combined with the counting results of the counting module, the data processing unit compensates and calculates to solve the counting deviation caused by pulse accumulation. After compensation, the count rate and dose rate maintain a good linear relationship. Significantly expanded range: Extreme tests show that when the detection module uses a J304 counter tube, the maximum range in the uncompensated state is less than 10 mSv / h. After compensation by this device and method, the saturation dose rate reaches 100 mSv / h, and the range is expanded by at least 10 times. The structure is simple and reliable: the device only includes a detection module, an electrical signal conversion module, a pulse discrimination module, a dead time measurement module, a counting module, and an anti-interference module. It uses fewer electronic components, which reduces circuit complexity and failure rate. It has an overload detection function: by measuring the dead time (Tdead) of the dead time module, it can determine whether the GM tube is saturated and realize radiation intensity overload detection. Attached Figure Description

[0014] Figure 1 This is the circuit schematic for the GM tube range extension device. In the diagram: 1-First timer, 2-Second timer, 3-GM tube. Detailed Implementation

[0015] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0016] See Figure 1 The structure of the GM tube range extension device in this invention is as follows: Detection module: GM tube 3 uses a domestic J304 counter tube, with its anode connected in series with an anode resistor R1, and the anode connected to a high voltage HV; Electrical signal conversion module: adopts a mirror constant current source structure, including transistor Q1 and transistor Q2; the collector of transistor Q1 is connected to the cathode of GM transistor 3, and the collector of transistor Q2 is connected in series with a conversion resistor R2; the emitter of transistor Q1 and the emitter of transistor Q2 are connected together, and the base of transistor Q1 and the base of transistor Q2 are connected together, forming a mirror current path, which is used to transfer the conversion resistor R2 to the transistor Q2 branch, avoiding the anti-interference module (shielding layer) and the conversion resistor R2 from forming a low cutoff frequency filter; Pulse discrimination module: It adopts voltage comparator U1, whose discrimination threshold V1 is set to 500mV, to discriminate the pulse voltage after conversion by switching resistor R2 and output valid discrimination pulse; Dead time measurement module: It adopts the first timer, configured in gated mode, and outputs the dead time Tdead of GM tube 3 by recording the total width of the discrimination pulses per second; Counting module: Employs a second timer, configured in counting mode, to record the number of discrimination pulses per second and output the counting rate CPS; Anti-interference module: This is a metal shielding layer covering the outside of the cathode of GM tube 3. The shielding layer is grounded to reduce electromagnetic interference to the cathode and to avoid forming a low cutoff frequency filter with the switching resistor R2. Parameter constraints: The anode resistance R1 satisfies: R1*C>>t1.

[0017] Where C is the total capacitance to ground of the anode node of GM tube 3, and t1 is the time for positive ions inside GM tube 3 to move to the cathode. The effect of t1 on the dead time measurement is ignored. R1 satisfies (HV-Vmin) / R1*conversion resistor R2>V1.

[0018] Where HV is the high voltage at the anode of GM tube 3, Vmin is the minimum voltage at which GM tube 3 operates normally, and V1 is the discrimination threshold of the pulse discrimination module. Optimal parameters: anode resistance R1 = 5.1MΩ, switching resistance R2 = 82KΩ.

[0019] In this embodiment, transistors Q1 and Q2 are model BC846DS, and voltage comparator U1 is model TLV7011DBVR. The shielding layer is made of 0.1mm thick conductive tape or copper foil, which wraps around the GM tube 3 body.

[0020] The mirror constant current source is powered by 3.3V. The high voltage HV of the GM tube's 3 anode is 400V. According to the J304 tube's instruction manual, the operating voltage range is 380V-420V, and the recommended operating voltage is 400V.

[0021] The specific implementation steps of the GM tube range extension method of the present invention are as follows: X-ray detection: The J304 counter tube of the detection module receives X-ray particles from radiation sources such as Cs137. Avalanche discharge occurs between the anode and cathode, forming a pulse current at the cathode. Electrical signal conversion: In the mirror constant current source of the electrical signal conversion module, transistor Q1 receives the pulse current from the cathode of GM transistor 3, and transistor Q2 mirrors the output of the same magnitude of current, which is converted into pulse voltage after flowing through the conversion resistor R2; the mirror structure of transistors Q1 and Q2 avoids the anti-interference module (shielding layer) and the conversion resistor R2 from forming a low cutoff frequency filter, thus preventing the pulse voltage amplitude from attenuating. Pulse discrimination: The voltage comparator U1 of the pulse discrimination module uses 500mV as the discrimination threshold to discriminate the pulse voltage output by the switching resistor R2. Pulses higher than the threshold are judged as valid pulses and output. Dead time measurement: The first timer (gated mode) of the dead time measurement module records the total width of the effective discrimination pulses per second. This total width is the dead time Tdead of GM tube 3 (unit: μS). Pulse counting: The second timer (counting mode) of the counting module counts the number of valid discrimination pulses per second to obtain the counting rate CPS; Dead time compensation: The data processing unit substitutes the formula CPS1=CPS / (1-Tdead) to calculate the true count rate CPS1, thereby achieving pulse accumulation compensation; Saturation detection: When Tdead≥900000μS, GM tube 3 is determined to be in a saturated state, indicating that the radiation field intensity exceeds the uncompensated range and measurement should be performed based on the compensated data.

[0022] Using Cs137 as the radiation source, the device described in the above embodiment was tested at different standard dose rate locations. The test data are shown in Table 1 below:

[0023] The test data shows that: The uncompensated measured count rate has extremely poor linearity after 2770 CPS and cannot reflect the true radiation dose. After compensation by the device and method, the count rate maintains a good linear relationship with the standard dose rate, and can still be accurately measured even at a high dose rate of 18800 uSv / h; When the J304 counter tube of the detection module is not compensated, its maximum range is less than 10 mSv / h. After compensation by the present invention, the saturation dose rate reaches 100 mSv / h, and the range is extended by more than 10 times, which verifies the effectiveness of the device and method of the present invention.

[0024] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A GM tube range extension device, characterized in that, include: Detection module: GM tube, used to receive X-ray particles and generate pulsed current; Electrical signal conversion module: connected to the cathode of the GM tube, used to convert the pulse current into a pulse voltage; Pulse discrimination module: connected to the output of the electrical signal conversion module, used to perform threshold discrimination on the pulse voltage and output a standardized discrimination pulse; Dead time measurement module: connected to the output of the pulse discrimination module, configured in gated mode, used to measure the total width per second of the discrimination pulse to obtain the dead time Tdead of the GM tube; Counting module: connected to the output of the pulse discrimination module, configured in counting mode, used to count the number of discrimination pulses per second to obtain the counting rate CPS; Anti-interference module: Shielding layer, located on the outside of the cathode of the GM tube, used to shield electromagnetic interference; The data output terminals of the dead time measurement module and the counting module are used to connect to the data processing unit, which calculates the true counting rate CPS1 of the GM tube according to the formula CPS1=CPS / (1-Tdead).

2. The GM tube range extension device according to claim 1, characterized in that, The electrical signal conversion module is a mirror constant current source, which includes transistor Q1 and transistor Q2. The collector of transistor Q1 is connected to the cathode of the GM transistor, and the collector of transistor Q2 is connected in series with a conversion resistor R2. The emitters of transistor Q1 and Q2 are connected together, and the bases of transistor Q1 and Q2 are connected together. This is used to transfer the conversion resistor R2 to the branch of transistor Q2, avoiding the shielding layer and the conversion resistor R2 from forming a low cutoff frequency filter.

3. The GM tube range extension device according to claim 2, characterized in that, The anode of the GM tube is connected in series with an anode resistor R1, and the anode resistor R1 satisfies the following constraints: R1*C>>t1, where C is the total capacitance of the anode node of the GM tube to ground, and t1 is the time it takes for positive ions inside the GM tube to move to the cathode. (HV-Vmin) / R1*R2>V1, where HV is the high voltage of the anode of the GM tube, Vmin is the minimum voltage for normal operation of the GM tube, and V1 is the discrimination threshold of the pulse discrimination module.

4. The GM tube range extension device according to claim 3, characterized in that, The value of R1 is 5.1MΩ, and the value of R2 is 82KΩ; the pulse discrimination module is a voltage comparator U1, and the discrimination threshold of the voltage comparator U1 is V1=500mV.

5. A GM tube range extension device according to claim 1, characterized in that, The dead time measurement module is a first timer, the counting module is a second timer, and the GM tube is a J304 counting tube.

6. A method for extending the range of a GM tube based on the device described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: The GM tube receives X-ray particles, causing an avalanche effect and forming a pulsed current at the cathode; Step 2: The electrical signal conversion module converts the pulse current into a pulse voltage; Step 3: The pulse discrimination module discriminates the pulse voltage using a preset discrimination threshold and outputs a standardized discrimination pulse; Step 4: The dead time measurement module measures the total width per second of the discrimination pulse in gating mode to obtain the dead time Tdead of the GM tube; Step 5: The counting module counts the number of discrimination pulses per second in counting mode to obtain the counting rate CPS; Step 6: Calculate the true count rate CPS1 of the GM tube using the formula CPS1=CPS / (1-Tdead) to achieve dead time compensation; Step 7: Determine whether the dead time Tdead is close to 1 second. If it is close, determine that the GM tube is in saturation.

7. The GM tube range extension method according to claim 6, characterized in that, In step 2, the switching resistor R2 is transferred to the transistor Q2 branch by transistors Q1 and Q2 of the mirror constant current source, so as to avoid the shielding layer and R2 forming a low cutoff frequency filter and prevent the pulse voltage amplitude from attenuating.

8. The GM tube range extension method according to claim 6, characterized in that, In step 7, when Tdead ≥ 900000 μS, the GM tube is determined to be in a saturated state.

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