CN114755708A - Wide-range gamma dosimeter with double GM counting tubes and monitoring method - Google Patents

Wide-range gamma dosimeter with double GM counting tubes and monitoring method Download PDF

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Publication number
CN114755708A
CN114755708A CN202210423297.7A CN202210423297A CN114755708A CN 114755708 A CN114755708 A CN 114755708A CN 202210423297 A CN202210423297 A CN 202210423297A CN 114755708 A CN114755708 A CN 114755708A
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range
counting
counting tube
low
tube
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刘书焕
张君
马勇
宋辞
李忠良
孟凡钧
吴磊
高飞
张国和
曹煜
李浩迪
贺朝会
李永宏
褚俊
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Xian Jiaotong University
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Xian Jiaotong University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/18—Measuring radiation intensity with counting-tube arrangements, e.g. with Geiger counters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/02—Dosimeters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T7/00—Details of radiation-measuring instruments

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
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  • High Energy & Nuclear Physics (AREA)
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  • Spectroscopy & Molecular Physics (AREA)
  • Measurement Of Radiation (AREA)

Abstract

The invention provides a double-GM counting tube wide-range gamma dosimeter and a monitoring method. The signal conditioning circuit converts a current pulse signal generated by the GM counting tube into a regular voltage pulse signal; the range switching circuit is used for controlling the on and off of the GM counting tube; the singlechip working system is used for pulse counting acquisition, dose rate conversion and automatic control range switching. The invention realizes the high-efficiency processing of the output signals of the GM counting tube, simply and reliably controls the on-off of the GM counting tube by adopting a mode of connecting the triode in series with the cathode of the GM counting tube, and realizes the automatic and stable switching of the double GM counting tubes by adopting the logic of range hysteresis judgment, thereby effectively widening the linear detection range of the gamma dosimeter and improving the performance of the instrument.

Description

Wide-range gamma dosimeter with double GM counting tubes and monitoring method
Technical Field
The invention belongs to the technical field of nuclear radiation detection, and particularly relates to a double-GM counting tube wide-range gamma dosimeter.
Background
The GM counting tube is widely applied to nuclear radiation detecting instruments due to the advantages of large output pulse amplitude, high stability, low cost, simple structure of a front-end circuit and the like. The GM counter tube has significant advantages especially in situations where continuous multi-point monitoring of gamma dose rates is required. However, generally, the linear range of a single GM counting tube is only 3 to 4 orders of magnitude, and the dose rate range in various applications can reach 7 to 8 orders of magnitude, and the gamma dosimeter designed by the traditional single GM counting tube cannot meet the requirements.
The gamma dosimeter is designed by adopting the double-GM counting tubes with different measuring range ranges, the linear measuring range of the gamma dosimeter can be effectively expanded, and the key technology for realizing the work of the double-GM counting tubes is a measuring range switching technology. In the existing working mode of the double-GM counting tube, two GM counting tubes work simultaneously or one GM counting tube works continuously while the other GM counting tube is controlled to be switched on or switched off, so that the service life of the GM counting tubes can be shortened, and particularly, when the low-range GM counting tubes are not switched off under high dose rate, the low-range GM counting tubes can be damaged more greatly; the technology of simultaneously controlling two GM counting tubes to enable only one GM counting tube to work at any time is also proposed one after another, wherein the mode of serially connecting a switch on the high-voltage side easily causes circuit damage, and the reliability of the instrument is reduced; the relay is used as a switch on the low-voltage side, so that the circuit structure is complex and large, and electromagnetic radiation exists.
Due to the influence of the inherent dead time of the GM counting tube and the pulse stacking phenomenon under high dose rate, the linear range of the GM counting tube in the working mode of the pulse counting method is extremely limited. The intrinsic dead time of the GM counting tube under the pulse counting method can be reduced by adjusting circuit parameters, such as reducing the resistance value of an anode, selecting proper working voltage and the like, but the method can only reduce the intrinsic dead time of the GM counting tube to a certain extent and cannot thoroughly eliminate the influence of the intrinsic dead time. In addition, the phenomenon of pulse stacking at high dose rate can also cause a large amount of missing counts, so that the range of the GM counting tube is limited, and pulse stacking can be reduced by improving the signal conditioning circuit, but the analysis of the pulse stacking phenomenon improvement circuit in the prior art is very few, and although the output pulse amplitude of the GM counting tube is large and easy to detect, the performance of the dosimeter instrument can also be greatly reduced if the signal conditioning circuit cannot be improved.
Disclosure of Invention
In order to overcome the defects of a GM counting tube used for monitoring dosage rate in the background technology, the invention aims to provide a double-GM counting tube wide-range gamma dosimeter and a monitoring method.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a double-GM counting tube wide-range gamma dosimeter comprises a low-voltage power supply, a high-range GM counting tube, a low-range GM counting tube, an anode load, a cathode load, a signal conditioning circuit, a range switching circuit, a single chip microcomputer working system, a communication module and an upper computer. The low-voltage power supply is used for providing working voltage for the gamma dosimeter and is connected to a chip and a module which need to be powered in the gamma dosimeter; the high-voltage power supply is used for providing working voltage for the high-range GM counting tube and the low-range GM counting tube; the high-range GM counting tube and the low-range GM counting tube are used for detecting gamma rays in the environment, anodes of the two GM counting tubes are connected to a high-voltage power supply through anode loads, and cathodes of the two GM counting tubes are connected to cathode loads; the signal conditioning circuit comprises a high-range GM counting tube signal conditioning circuit and a low-range GM counting tube signal conditioning circuit, the two signal conditioning circuits respectively convert current pulse signals generated by respective GM counting tubes into regular voltage pulse signals, the input ends of the two signal conditioning circuits are respectively connected to the cathodes of the respective GM counting tubes, and the output ends of the two signal conditioning circuits are connected to a single-chip microcomputer working system; the range switching circuit comprises a high-range GM counting tube range switching circuit and a low-range GM counting tube range switching circuit, which are respectively used for controlling the on and off of respective GM counting tubes, the control end of the range switching circuit is connected to the singlechip working system, and the other end of the range switching circuit is connected to the cathode load; the single chip microcomputer working system is used for collecting pulse signals generated by the high-range GM counting tube and the low-range GM counting tube, converting the pulse signals into dosage rates, and controlling the high-range GM counting tube and the low-range GM counting tube to automatically complete range switching; the single chip microcomputer working system transmits the dose rate to an upper computer through a communication module, and displays the current dose rate in real time.
The high-range GM counting tube signal conditioning circuit and the low-range GM counting tube signal conditioning circuit are identical in structure and respectively comprise a GM counting tube cathode load circuit, a CR differential circuit, a bidirectional amplitude limiting circuit and an amplitude discriminator. The LGM signal conditioning circuit for a low range GM-counter is described as follows: the cathode load circuit is formed by connecting a first capacitor C1 and a first resistor R1 in parallel, the input end of the cathode load circuit is connected to the cathode of the low-range GM counting tube LGM, the output end of the cathode load circuit is connected to the collector electrode of a first switching triode Q1, and a current pulse signal generated by the low-range GM counting tube LGM is converted into a voltage pulse signal; the CR differential circuit is formed by connecting a second capacitor C2 and a second resistor R2 in series, the connection point of the second capacitor C2 and the second resistor R2 serves as the output end of the CR differential circuit, the other end of the second capacitor C2 is connected to the cathode of the low-range GM counting tube LGM, the other end of the second resistor R2 is grounded, the CR differential circuit further converts the voltage pulse signal of the cathode of the low-range GM counting tube LGM into a voltage pulse signal with preset amplitude and pulse width, the pulse signals stacked at the front stage are separated from each other to a certain extent, and the leakage count under the high dose rate is reduced; the bidirectional amplitude limiting circuit consists of a fifth resistor R5, a first switch diode D1 and a second switch diode D2, the input end of the fifth resistor R5 is connected to the output end of the CR differential circuit, the cathode of the first switch diode D1 is connected to +5V, the anode of the first switch diode D1 is connected to the cathode of the second switch diode D2, the anode of the second switch diode D2 is grounded, the connection point of the first switch diode D1 and the second switch diode D2 is connected to the output end of the fifth resistor R5 and the positive input end of a first voltage comparator U1, the bidirectional amplitude limiting circuit limits the amplitude of a voltage pulse between-0.6V and +5.6V, and a rear-stage amplitude discriminator is protected; the amplitude discriminator is composed of a first voltage comparator U1 and a first potentiometer RP1, the two ends of a first potentiometer RP1 are connected to +5V and the ground respectively, the sliding end of the first potentiometer RP1 is connected to the negative input end of a first voltage comparator U1 and used for adjusting the threshold voltage of the amplitude discriminator, and the amplitude discriminator converts a preceding-stage pulse signal into a regular rectangular voltage pulse signal.
The high-range GM counting tube range switching circuit is the same as the low-range GM counting tube range switching circuit, wherein the range switching circuit of the low-range GM counting tube LGM consists of a first switching triode Q1, a third resistor R3 and a fourth resistor R4. The collector of the first switching transistor Q1 is connected to the cathode load circuit, the base of the first switching transistor Q1 is connected to the single chip microcomputer working system through a third resistor R3, the emitter of the first switching transistor Q1 is grounded, and a fourth resistor R4 is bridged between the base and the emitter of the first switching transistor Q1 to ensure the stability of the working state of the single chip microcomputer working system. When the singlechip working system controls the first switching triode Q1 to be switched on, the low-range GM counting tube LGM can generate a current pulse signal under normal working voltage, otherwise, the low-range GM counting tube LGM cannot work. At any moment, only one of the first switching triode Q1 in the range switching circuit of the low-range GM counting tube LGM and the second switching triode Q2 in the range switching circuit of the high-range GM counting tube HGM is conducted, namely only one GM counting tube is in a working state at any moment, so that the range switching control of the double-GM counting tube is realized.
The single chip microcomputer working system is composed of a pulse counting module, a counting rate and dosage rate conversion module and a measuring range automatic switching module. The signal output by the signal conditioning circuit is input to the pulse counting module to obtain the counting rate, and then the counting rate is converted into the dosage rate through the counting rate-to-dosage rate conversion module. The automatic range switching module is connected to a first switching triode Q1 in the range switching circuit of the low-range GM counting tube and a second switching triode Q2 in the range switching circuit of the high-range GM counting tube, a hysteresis judgment logic method is adopted, and when the low-range GM counting tube LGM is in a working state, if the measured dose rate R is greater than Q, the second switching triode Q2 is switched to the high-range GM counting tube HGM to work; when the high-range GM counting tube HGM is in a working state, if the measured dose rate R is less than P, the first switching triode Q1 is switched to the low-range GM counting tube LGM to work. The method for judging the range hysteresis can avoid the phenomenon that two GM counting tubes are repeatedly switched when the dosage rate is in a critical state, and improve the stability of automatic switching. Q is a judgment threshold value for converting the work of a low-range GM counting tube LGM into the work of a high-range GM counting tube HGM in the range switching module, and P is a judgment threshold value for converting the work of a high-range GM counting tube HGM into the work of a low-range GM counting tube LGM in the range switching module.
Communication module designs based on singlechip serial ports communication function, simultaneously for the demand that satisfies different environment, designs RS485 communication and LORA wireless communication two kinds of modes. And transmitting the acquired dose rate to an upper computer to realize real-time monitoring of data.
The monitoring method based on the double-GM counting tube gamma dosimeter comprises the following steps:
step 1, after the gamma dosimeter is powered on, a second switching triode Q2 is initially gated, so that a high-range GM counting tube HGM starts to work under a direct-current high voltage HV.
And 2, when gamma rays hit the wall of the high-range GM counting tube HGM and electron avalanche is induced in a gas sensitive area of the high-range GM counting tube HGM, generating a current pulse signal, and shaping the signal into a regular rectangular voltage pulse with the amplitude of 5V and the pulse width of 3 us-7 us through a signal conditioning circuit.
And 3, inputting the regular rectangular voltage pulse in the step 2 into a single chip microcomputer pin of a single chip microcomputer working system, triggering a pulse counting module by the rising edge of the rectangular voltage pulse, and accumulating the number of pulses detected within 1s to obtain a counting rate. And multiplying the counting rate to the dose rate module by the calibration coefficient of the high-range GM counting tube HGM to obtain the dose rate R.
And 4, transmitting the dose rate R to an upper computer interface by the singlechip working system through the communication module, and displaying the environmental dose rate R in real time.
And 5, judging whether the current dosage rate R is in the linear range of the high-range GM counting tube HGM. If the measurement range is within the range, the high-range GM counting tube HGM is continuously used for measurement, and the step 2 to the step 5 are repeated; if the current is not within the range of the range, the second switching triode Q2 is turned off to stop the work of the high-range GM counting tube HGM, meanwhile, the first switching triode Q1 is turned on to start the work of the low-range GM counting tube LGM, and the steps 2 to 5 are repeated.
Compared with the prior art, the invention has the following advantages and technical effects:
a high-performance signal conditioning circuit is designed, a current pulse signal generated by the GM counting tube is converted into a voltage pulse signal with the amplitude of 5V and the pulse width of about 5us, the response is rapid, pulse accumulation under high dose rate can be reduced, missing counting is reduced, and the linear range of a single GM counting tube in a pulse counting method mode can be effectively improved. In addition, the mode that a triode is switched on and off in series with the cathode of the GM counting tube is adopted, the GM counting tube is conveniently and reliably controlled to be switched on and off, the circuit is simple and easy to control, the logic of range hysteresis judgment is adopted, automatic and stable switching of the double GM counting tubes is achieved, and the linear range of the dosimeter can be effectively expanded. The double-GM counting tube wide-range gamma dosimeter has a simple structure, is easy to realize, and can provide certain reference value for the development of related technologies.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention:
FIG. 1 is a hardware structure diagram of the system of the wide-range gamma dosimeter of the invention with a double GM counting tube;
FIG. 2 is a schematic diagram of a part of key circuits of the dual GM counting tube wide-range gamma dosimeter of the invention, which mainly comprises a signal conditioning circuit and a range switching circuit of the GM counting tube;
FIG. 3 is a schematic diagram of the range hysteresis decision logic of the present invention;
FIG. 4 is a waveform of an experiment of key point output from the low-range GM counting tube of the present invention;
FIG. 5 is a waveform of an experiment of key points output by the high-range GM counting tube of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the detailed description.
As shown in fig. 1, an embodiment of the present invention provides a dual-GM counting tube wide-range gamma dosimeter, which includes a low-voltage power supply, a high-range GM counting tube, a low-range GM counting tube, an anode load, a cathode load, a signal conditioning circuit, a range switching circuit, a single chip microcomputer operating system, a communication module, and an upper computer. The low-voltage power supply is used for providing working voltage for the gamma dosimeter and is connected to a chip and a module which need to be powered in the gamma dosimeter; the high-voltage power supply is used for providing working voltage for the high-range GM counting tube and the low-range GM counting tube; the high-range GM counting tube and the low-range GM counting tube are used for detecting gamma rays in the environment, anodes of the two GM counting tubes are connected to a high-voltage power supply through anode loads, and cathodes of the two GM counting tubes are connected to cathode loads; the signal conditioning circuit comprises a high-range GM counting tube signal conditioning circuit and a low-range GM counting tube signal conditioning circuit, the two signal conditioning circuits respectively convert current pulse signals generated by respective GM counting tubes into regular voltage pulse signals, the input ends of the two signal conditioning circuits are respectively connected to the cathodes of the respective GM counting tubes, and the output ends of the two signal conditioning circuits are connected to a single-chip microcomputer working system; the range switching circuit comprises a high-range GM counting tube range switching circuit and a low-range GM counting tube range switching circuit, which are respectively used for controlling the on and off of respective GM counting tubes, the control end of the range switching circuit is connected to the singlechip working system, and the other end of the range switching circuit is connected to the cathode load; the single chip microcomputer working system is used for collecting pulse signals generated by the high-range GM counting tube and the low-range GM counting tube, converting the pulse signals into dosage rates, and controlling the high-range GM counting tube and the low-range GM counting tube to automatically complete range switching; the single chip microcomputer working system transmits the dose rate to an upper computer through a communication module, and displays the current dose rate in real time.
As shown in fig. 2, the high-range GM count tube signal conditioning circuit and the low-range GM count tube signal conditioning circuit have the same structure, and both include a GM count tube cathode load circuit, a CR differential circuit, a bidirectional limiting circuit, and an amplitude discriminator. The LGM signal conditioning circuit for a low range GM-counter is described as follows: the cathode load circuit is formed by connecting a first capacitor C1 and a first resistor R1 in parallel, the input end of the cathode load circuit is connected to the cathode of the low-range GM counting tube LGM, the output end of the cathode load circuit is connected to the collector electrode of a first switching triode Q1, and a current pulse signal generated by the low-range GM counting tube LGM is converted into a voltage pulse signal; the CR differential circuit is formed by connecting a second capacitor C2 and a second resistor R2 in series, the connection point of the second capacitor C2 and the second resistor R2 serves as the output end of the CR differential circuit, the other end of the second capacitor C2 is connected to the cathode of the low-range GM counting tube LGM, the other end of the second resistor R2 is grounded, the CR differential circuit further converts the voltage pulse signal of the cathode of the low-range GM counting tube LGM into a voltage pulse signal with preset amplitude and pulse width, the pulse signals stacked at the front stage are separated from each other to a certain extent, and the leakage count under the high dose rate is reduced; the bidirectional amplitude limiting circuit consists of a fifth resistor R5, a first switch diode D1 and a second switch diode D2, the input end of the fifth resistor R5 is connected to the output end of the CR differential circuit, the cathode of the first switch diode D1 is connected to +5V, the anode of the first switch diode D1 is connected to the cathode of the second switch diode D2, the anode of the second switch diode D2 is grounded, the connection point of the first switch diode D1 and the second switch diode D2 is connected to the output end of the fifth resistor R5 and the positive input end of a first voltage comparator U1, the bidirectional amplitude limiting circuit limits the amplitude of a voltage pulse between-0.6V and +5.6V, and a rear-stage amplitude discriminator is protected; the amplitude discriminator is composed of a first voltage comparator U1 and a first potentiometer RP1, the two ends of a first potentiometer RP1 are connected to +5V and the ground respectively, the sliding end of the first potentiometer RP1 is connected to the negative input end of a first voltage comparator U1 and used for adjusting the threshold voltage of the amplitude discriminator, and the amplitude discriminator converts a preceding-stage pulse signal into a regular rectangular voltage pulse signal.
As shown in fig. 2, the high-range GM count transistor range switching circuit is the same as the low-range GM count transistor range switching circuit, wherein the low-range GM count transistor range switching circuit is composed of a first switching transistor Q1, a third resistor R3 and a fourth resistor R4. The collector of the first switching triode Q1 is connected to the cathode load circuit, the base of the first switching triode Q1 is connected to the working system of the single chip microcomputer through a third resistor R3, the emitter of the first switching triode Q1 is grounded, and a fourth resistor R4 is bridged between the base and the emitter of the first switching triode Q1 to ensure the stability of the working state of the single chip microcomputer. When the singlechip working system controls the first switching triode Q1 to be switched on, the low-range GM counting tube can generate a current pulse signal under normal working voltage, otherwise, the low-range GM counting tube cannot work. At any moment, only one of the first switching triode Q1 in the low-range GM counting tube LGM range switching circuit and the second switching triode Q2 in the high-range GM counting tube HGM range switching circuit is conducted, namely only one GM counting tube is in a working state at any moment, so that the range switching control of the double-GM counting tube is realized.
The single chip microcomputer working system is composed of a pulse counting module, a counting rate and dosage rate conversion module and a measuring range automatic switching module. The signal output by the signal conditioning circuit is input into the pulse counting module to obtain the counting rate, and then the counting rate is converted into the dosage rate through the counting rate-to-dosage rate module. The automatic range switching module is connected to a first switching triode Q1 in the low-range GM counting tube range switching circuit and a second switching triode Q2 in the high-range GM counting tube range switching circuit, a hysteresis judgment logic method is adopted, and a schematic diagram of range hysteresis judgment logic is shown in FIG. 3. When the low-range GM counting tube LGM is in a working state, if the measured dose rate R is greater than Q, a second switching triode Q2 is switched to work as a high-range GM counting tube HGM; when the high-range GM counting tube HGM is in a working state, if the measured dose rate R is less than P, the first switching triode Q1 is switched to the low-range GM counting tube LGM to work. The method for judging the range hysteresis can avoid the phenomenon that two GM counting tubes are repeatedly switched when the dosage rate is in a critical state, and improve the stability of automatic switching. Q is a judgment threshold value for converting the work of a low-range GM counting tube LGM into the work of a high-range GM counting tube HGM in the range switching module, and P is a judgment threshold value for converting the work of a high-range GM counting tube HGM into the work of a low-range GM counting tube LGM in the range switching module.
Communication module designs based on singlechip serial ports communication function, simultaneously for the demand that satisfies different environment, designs RS485 communication and LORA wireless communication two kinds of modes. And transmitting the acquired dose rate to an upper computer to realize real-time monitoring of data.
The embodiment of the invention also provides a monitoring method based on the gamma dosimeter with the double GM counting tubes, which comprises the following steps:
step 1, after the gamma dosimeter is powered on, a second switching triode Q2 is initially gated, so that the high-range GM counting tube HGM starts to work under the direct-current high-voltage HV.
And step 2, when gamma rays hit the tube wall of the high-range GM counting tube HGM and electron avalanche is induced in a gas sensitive area of the high-range GM counting tube HGM, a current pulse signal is generated and is shaped into a regular rectangular voltage pulse with the amplitude of 5V and the pulse width of 3 us-7 us through a signal conditioning circuit.
And 3, inputting the regular rectangular voltage pulse in the step 2 into a single chip microcomputer pin of a single chip microcomputer working system, triggering a pulse counting module by the rising edge of the rectangular voltage pulse, and accumulating the number of pulses detected within 1s to obtain a counting rate. And then obtaining the dose rate R by multiplying the calibration coefficient of the high-range GM counting tube HGM by a counting rate to dose rate module.
And 4, transmitting the dose rate R to an interface of an upper computer by the singlechip working system through the communication module, and displaying the environmental dose rate R in real time.
And 5, judging whether the current dosage rate R is in the linear range of the high-range GM counting tube HGM. If the measurement range is within the range, the high-range GM counting tube HGM is continuously used for measurement, and the step 2 to the step 5 are repeated; if the current is not within the range of the range, the second switching triode Q2 is turned off to stop the work of the high-range GM counting tube HGM, the first switching triode Q1 is turned on to start the work of the low-range GM counting tube LGM, and the steps 2-5 are repeated.
The specific embodiment is as follows:
the double-GM counting tube wide-range gamma dosimeter uses two 3.7V lithium batteries to supply power in series, and the power supply voltage of the lithium batteries is converted into 5V and 3.3V voltage required by an instrument through a low-voltage power supply; the high-voltage power supply uses a high-voltage module of the east high-voltage DW-P102-0.5AL1 model to generate 550V of direct-current high voltage HV as the power supply voltage HV of the high-range GM counting tube HGM and the low-range GM counting tube LGM.
The HGM of the high-range GM counting tube adopts a ZP1301 model, the working voltage range is 500V-600V, and the range is 1 multiplied by 10-1～1×104mGy/h; the low-range GM counting tube LGM is ZP1321 type, the working voltage range is 500V-650V, and the range of measurement is 3 multiplied by 10 -3～1×102mGy/h. Since there is a large overlap of the two GM-tube plateau voltages, a common supply voltage HV is used. According to the range of the two selected GM counting tubes, the threshold value P in the range switching module of the singlechip working system takes the value of 1mGy/h, and the value Q takes the value of 10 mGy/h. According to the data manuals of the two GM counting tubes, the smaller the resistance value of the anode resistor is, the smaller the dead time of the GM counting tube is, so that in order to reduce the influence of the dead time, the anode resistor should be as low as possible under the condition of meeting the requirement of the minimum resistance value.
The cathode load circuit is formed by connecting a first capacitor C1 and a first resistor R1 in parallel, and converts a current pulse signal generated by the GM counting tube into a voltage pulse signal. Experiments show that the larger the capacitance value of the first capacitor C1 is, the larger the pulse width of the cathode voltage pulse is, the smaller the amplitude is; the larger the resistance of the first resistor R1 is, the larger the pulse width of the cathode voltage pulse is, and the larger the amplitude is. The voltage pulse signal with narrow pulse width and easily detectable amplitude can be obtained by adjusting parameters of two elements of the first capacitor C1 and the first resistor R1 according to requirements.
The CR differential circuit consists of a second capacitor C2 and a second resistor R2, and further converts the cathode voltage pulse signal of the GM counting tube into a voltage signal with proper amplitude and pulse width. Experiments show that the larger the capacitance value of the second capacitor C2 is, the larger the output pulse amplitude is, and the influence on the pulse width is smaller; the larger the resistance of the second resistor R2 is, the wider the pulse width of the output pulse is, and the influence on the amplitude is small. The parameters of the second capacitor C2 and the second resistor R2 are adjusted to obtain a voltage pulse signal with a pulse width of less than 10us and an amplitude of about 5V, and the CR differential circuit can separate the pulse signals stacked at the front stage to a certain extent, thereby reducing the drain count at high dose rate.
For the low-range GM counter LGM, after adjusting the parameters of its signal conditioning circuit, the experimental waveforms shown in fig. 4 can be measured using an oscilloscope, and the three waveforms respectively correspond to the signals at point A, B, C in fig. 2. As can be seen from fig. 4, the amplitude of the waveform at point a is 12.73V, the FWHM is 6.56us, the amplitude of the waveform at point B is 5.34V, and the FWHM is 2.13 us.
For the high-range GM counting tube HGM, after adjusting the parameters of its signal conditioning circuit, the experimental waveforms shown in fig. 5 can be measured using an oscilloscope, and the three waveforms correspond to the signals at three points D, F, E in fig. 2, respectively. As can be seen from fig. 5, the amplitude of the waveform at point D is 9.17V, the FWHM is 17.57us, the amplitude of the waveform at point E is 5.32V, and the FWHM is 3.50 us.
The voltage pulse signals at the point B and the point E are respectively input into two positive input ends of a dual-channel amplitude discriminator, wherein the first voltage comparator U1 and the second voltage comparator U2 are in TLV3502 models, and the response time is in ns level. The first potentiometer RP1 and the second potentiometer RP2 are adjusted so that the threshold voltage of the negative input terminal is 1V. When the amplitude of the input pulse signal is higher than the set threshold voltage, the amplitude discriminator outputs a 5V high level, otherwise, the amplitude discriminator outputs a 0V low level. Thereby converting the preceding-stage pulse signal into a regular rectangular voltage pulse signal having a pulse width of about 5us and an amplitude of 5V, as shown by a waveform at point C in fig. 4 and a waveform at point F in fig. 5, and realizing high-speed pulse shaping.
And the shaped two paths of pulses are respectively input to the pins of the single chip microcomputer to carry out dose rate data acquisition. The single chip microcomputer adopts STM32F103ZET6 model of ST company, and the clock working frequency is 72 MHz.
The above description is only an embodiment of the present invention, and the scope of the present invention is not limited thereto, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A double-GM counting tube wide-range gamma dosimeter is characterized by comprising a low-voltage power supply, a high-range GM counting tube, a low-range GM counting tube, an anode load, a cathode load, a signal conditioning circuit, a range switching circuit, a singlechip working system, a communication module and an upper computer; the low-voltage power supply is used for providing working voltage for the gamma dosimeter and is connected to a chip and a module which need to be powered in the gamma dosimeter; the high-voltage power supply is used for providing working voltage for the high-range GM counting tube and the low-range GM counting tube; the high-range GM counting tube and the low-range GM counting tube are used for detecting gamma rays in the environment, anodes of the two GM counting tubes are connected to a high-voltage power supply through anode loads, and cathodes of the two GM counting tubes are connected to cathode loads; the signal conditioning circuit comprises a high-range GM counting tube signal conditioning circuit and a low-range GM counting tube signal conditioning circuit, the two signal conditioning circuits respectively convert current pulse signals generated by respective GM counting tubes into regular voltage pulse signals, the input ends of the two signal conditioning circuits are respectively connected to the cathodes of the respective GM counting tubes, and the output ends of the two signal conditioning circuits are connected to a single-chip microcomputer working system; the range switching circuit comprises a high-range GM counting tube range switching circuit and a low-range GM counting tube range switching circuit, which are respectively used for controlling the on and off of respective GM counting tubes, the control end of the range switching circuit is connected to the singlechip working system, and the other end of the range switching circuit is connected to the cathode load; the single chip microcomputer working system is used for collecting pulse signals generated by the high-range GM counting tube and the low-range GM counting tube, converting the pulse signals into dosage rates, and controlling the high-range GM counting tube and the low-range GM counting tube to automatically complete range switching; the single chip microcomputer working system transmits the dose rate to an upper computer through a communication module, and displays the current dose rate in real time.
2. The dual-GM-counter wide-range gamma dosimeter of claim 1, wherein the high-range GM-counter signal conditioning circuit and the low-range GM-counter signal conditioning circuit are structurally identical and each comprises a cathodic load circuit, a CR differentiation circuit, a bidirectional amplitude limiting circuit, and an amplitude discriminator; the signal conditioning circuit for the low-range GM counter is described as follows: the cathode load circuit is formed by connecting a first capacitor (C1) and a first resistor (R1) in parallel, the input end of the cathode load circuit is connected to the cathode of the low-range GM counting tube (LGM), the output end of the cathode load circuit is connected to the collector electrode of a first switching triode (Q1), and a current pulse signal generated by the low-range GM counting tube (LGM) is converted into a voltage pulse signal; the CR differential circuit is formed by connecting a second capacitor (C2) and a second resistor (R2) in series, the connection point of the second capacitor (C2) and the second resistor (R2) serves as the output end of the CR differential circuit, the other end of the second capacitor (C2) is connected to the cathode of the low-range GM counting tube (LGM), the other end of the second resistor (R2) is grounded, and the CR differential circuit further converts the voltage pulse signal of the cathode of the low-range GM counting tube (LGM) into a voltage pulse signal with a preset amplitude and a preset pulse width, so that pulse signals stacked at the front stage are separated from each other to a certain extent, and the leakage count at the high dose rate is reduced; the bidirectional amplitude limiting circuit is composed of a fifth resistor (R5), a first switch diode (D1) and a second switch diode (D2), the input end of the fifth resistor (R5) is connected to the output end of the CR differential circuit, the cathode of the first switch diode (D1) is connected to +5V, the anode of the first switch diode (D1) is connected to the cathode of the second switch diode (D2), the anode of the second switch diode (D2) is grounded, the connection point of the first switch diode (D1) and the second switch diode (D2) is connected to the output end of the fifth resistor (R5) and the positive input end of a first voltage comparator (U1), the bidirectional amplitude limiting circuit limits the amplitude of a voltage pulse to-0.6V- +5.6V, and protects a rear-stage amplitude discriminator; the amplitude discriminator is composed of a first voltage comparator (U1) and a first potentiometer (RP1), two ends of the first potentiometer (RP1) are connected to +5V and the ground respectively, a sliding end of the first potentiometer (RP1) is connected to a negative input end of the first voltage comparator (U1) and used for adjusting threshold voltage of the amplitude discriminator, and the amplitude discriminator converts a preceding-stage pulse signal into a regular rectangular voltage pulse signal.
3. The dual-GM-counter wide-range gamma dosimeter of claim 1, wherein the high-range GM-counter range switching circuit is the same as the low-range GM-counter range switching circuit, wherein the range switching circuit of the low-range GM-counter (LGM) is comprised of a first switching transistor (Q1), a third resistor (R3), and a fourth resistor (R4); the collector of the first switching triode (Q1) is connected to the cathode load circuit, the base of the first switching triode (Q1) is connected to the working system of the single chip microcomputer through a third resistor (R3), the emitter of the first switching triode (Q1) is grounded, and a fourth resistor (R4) is bridged between the base and the emitter of the first switching triode (Q1) to ensure the stability of the working state of the first switching triode; when the singlechip working system controls the first switching triode (Q1) to be switched on, the low-range GM counting tube (LGM) can generate a current pulse signal under normal working voltage, otherwise the low-range GM counting tube (LGM) cannot work; at any moment, the first switching triode (Q1) in the range switching circuit of the low-range GM counting tube (LGM) and the second switching triode (Q2) in the range switching circuit of the high-range GM counting tube (HGM) are conducted, namely, only one GM counting tube is in a working state at any moment, so that the range switching control of the double-GM counting tube is realized.
4. The dual-GM counter tube wide-range gamma dosimeter of claim 1, wherein the singlechip operating system is composed of a pulse counting module, a count rate to dose rate module and a range automatic switching module; the signal output by the signal conditioning circuit is input into the pulse counting module to obtain the counting rate, and then the counting rate is converted into the dosage rate through the counting rate-to-dosage rate module; the automatic range switching module is connected to a first switching triode (Q1) in the range switching circuit of the low-range GM counting tube and a second switching triode (Q2) in the range switching circuit of the high-range GM counting tube, a hysteresis judgment logic method is adopted, when the low-range GM counting tube (LGM) is in a working state, if the measured dose rate R is greater than Q, the second switching triode (Q2) is switched to be a high-range GM counting tube (HGM) to work; when a high-range GM counting tube (HGM) is in a working state, if the measured dose rate R is less than P, a first switching triode (Q1) is switched to a low-range GM counting tube (LGM) to work; the method for judging the hysteresis of the measuring range can avoid the phenomenon that two GM counting tubes are repeatedly switched when the dose rate is in a critical state, and improve the stability of automatic switching; wherein, Q is a judgment threshold value for converting the work of a low-range GM counting tube (LGM) into the work of a high-range GM counting tube (HGM) in the range switching module, and P is a judgment threshold value for converting the work of the high-range GM counting tube (HGM) into the work of the low-range GM counting tube (LGM) in the range switching module.
5. The dual-GM counting tube wide-range gamma dosimeter of claim 1, wherein the communication module is designed based on serial port communication function of a single chip microcomputer, and simultaneously, in order to meet requirements of different environments, two modes of RS485 communication and LORA wireless communication are designed, and the acquired dose rate is transmitted to an upper computer, so that real-time monitoring of data is realized.
6. The monitoring method of the dual GM counter tube wide range gamma dosimeter according to any one of claims 1-5, comprising the steps of:
step 1, after a gamma dosimeter is electrified, a second switching triode (Q2) is initially gated, so that a high-range GM counting tube (HGM) starts to work under direct current High Voltage (HV);
step 2, when gamma rays hit the tube wall of a high-range GM counting tube (HGM) and electron avalanche is induced in a gas sensitive area of the HGM, a current pulse signal is generated and shaped into a regular rectangular voltage pulse with the amplitude of 5V and the pulse width of 3 us-7 us through a signal conditioning circuit;
step 3, inputting the regular rectangular voltage pulse in the step 2 into a single chip microcomputer pin of a single chip microcomputer working system, triggering a pulse counting module by the rising edge of the rectangular voltage pulse, and accumulating the number of pulses detected within 1s to obtain a counting rate; then multiplying the counting rate to the dose rate module by a calibration coefficient of a high-range GM counting tube (HGM) to obtain a dose rate R;
Step 4, the singlechip working system transmits the dose rate R to an interface of an upper computer through a communication module, and displays the environmental dose rate R in real time;
step 5, judging whether the current dosage rate R is in the linear range of the high-range GM counting tube (HGM), if so, continuing to use the high-range GM counting tube (HGM) to measure, and repeating the steps 2-5; if the current is not in the range of the range, the second switching triode (Q2) is turned off to stop the work of the high-range GM counting tube (HGM), and the first switching triode (Q1) is turned on to start the work of the low-range GM counting tube (LGM), and the steps 2 to 5 are repeated.
CN202210423297.7A 2022-04-21 2022-04-21 Wide-range gamma dosimeter with double GM counting tubes and monitoring method Pending CN114755708A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115327606A (en) * 2022-08-08 2022-11-11 上海核工程研究设计院有限公司 Working gas circulating type source range neutron detector
CN116338761A (en) * 2023-03-29 2023-06-27 西安中核核仪器股份有限公司 Wide-range neutron dose rate instrument
CN116338761B (en) * 2023-03-29 2024-06-07 西安中核核仪器股份有限公司 Wide-range neutron dose rate instrument

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115327606A (en) * 2022-08-08 2022-11-11 上海核工程研究设计院有限公司 Working gas circulating type source range neutron detector
CN115327606B (en) * 2022-08-08 2024-05-10 上海核工程研究设计院股份有限公司 Working gas circulating source range neutron detector
CN116338761A (en) * 2023-03-29 2023-06-27 西安中核核仪器股份有限公司 Wide-range neutron dose rate instrument
CN116338761B (en) * 2023-03-29 2024-06-07 西安中核核仪器股份有限公司 Wide-range neutron dose rate instrument

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