JPH03214088A - Radiation monitor - Google Patents

Abstract

PURPOSE:To save a space by providing a counting rate calculating element which calculates a counting rate of this time on the basis of a pulse signal count value, a selecting element which compares the counting rates of this time and the last time with each other and selects the one meeting the condition, etc. CONSTITUTION:When radiation enters a pulse-type radiation detector 1, first, an output pulse corresponding to the strength of the radiation is outputted from this detector 1 and it is amplified by an amplifier circuit 2 and then inputted to a counter circuit 3. The circuit 3 conducts level discrimination at a level corresponding to a peak value of the output pulse supplied from the circuit 2 and filters noise, and then it counts the pulse and supplies a count value thereof to an arithmetic circuit 4. The circuit 4 collects the count value every time when it is supplied from the circuit 3, determining a counting rate of this time on the basis of the time passing from the supply of the count value of the last time to the supply of that of this time and the count value supplied this time and comparing it with the counting rate of the last time. Next, the circuit 4 determines a time constant by determining an increase or decrease of the counting rate, executes an operation to determine the counting rate to be outputted this time, and outputs it.

Description

[Detailed description of the invention]

[Object 1-1 of the Invention] (Industrial Application Field) The present invention relates to a radiation monitoring device for monitoring radiation. (Prior Art) As is well known, in a conventional radiation monitoring device, the output of a pulsed radiation detector (signal indicating the 7ti charge of radiation) is supplied to a diode pump circuit, and the CRH constituting this diode pump circuit After converting the output of the pulse type radiation detector into a voltage value while suppressing the variation in the indicated value within a certain range using the time constant of the pulse, the intensity of the radiation is displayed based on this mil value. However, the fluctuation of the indicated value of such a diode pump circuit increases in proportion to the relative standard deviation, which is expressed by There is a problem in that the variation in indicated values becomes large when the counting rate is small. Therefore, as a method to solve this problem, a method has been developed in which multiple diode pump circuits with different time constants are provided and the diode pump circuits are switched depending on the output level to keep the variation in indicated values within a certain range. However, with this method, there is a problem that the number of components increases, which requires extra mounting space, and the time constant is switched in stages.
There is a problem that when the human power changes, the output becomes a polygonal line. Furthermore, there are problems such as data exchange with a computer or the like becoming analogue, and there being a limit to improvement in accuracy. For this reason, recently, as shown in FIG. 5, after the output of the pulse type radiation detector 101 is multiplied by J numbers by the counting circuit 102, this counting result is supplied to the arithmetic circuit 1()3 and the counted value is calculated at the sampling time. A method of calculating the counting rate by dividing is often adopted. In this case, as in the case of the diode pump circuit, the calculation circuit 103 performs a calculation simulating a multi-stage diode pump circuit, for example, calculates the previous counting rate R1-1 of the output as shown in the following equation.
By performing calculations that change the time constant in accordance with However, R++-1: Counting rate (CPS) output last time R7
: Counting rate (CPS) output this time ΔC: Count value (count) Δ collected this time

[ : Sampling time (seconds) T Two time constants (seconds) And the time constant T in this formula (2) is R, -1 σ
2 However, since it can be expressed as σ: relative standard deviation (a value indicating the variation when the output is set to 1), the count value ΔC can be filtered with the characteristic corresponding to m*deviation σ. (Problems to be Solved by the Invention) However, each of the conventional methods described above has the following problems. In other words, when a diode pump circuit with a fixed time constant is used, there is a problem in that when the counting rate changes, the standard deviation (degree of variation in output instruction values) σ changes, causing the counting rate R7 to vary. . Furthermore, when using a circuit in which diode pump circuits with different time constants are arranged in parallel, the time constant T can be changed according to the counting rate R9, so that the standard deviation σ
Although it is possible to keep T approximately constant, since the time constant T changes stepwise, the output change becomes linear, and the large number of parts causes problems such as cost and mounting space. Also, with this method, since the output is an analog value,
There are problems in that it is difficult to exchange data with computers, etc., and it is difficult to ensure the necessary accuracy. In addition, in the method of calculating the counting rate R0 from the #1 value 80 by digital processing using the arithmetic circuit 103, the time constant T can be changed continuously, so the output change can be made smooth. Furthermore, there are advantages in that the number of parts can be reduced, and data can be exchanged with a computer or the like in digital values. However, in this method, since the above-mentioned equation (2) is used, it is necessary to perform the exponential function operation used in this equation (2), so m1 becomes long during calculation, and it is necessary to calculate from the count value ΔC. There is a problem in that the process of calculating the rate R1 cannot be performed at high speed. In addition, in this method, when the time constant T is determined by the above equation (3), when the counting rate R7 suddenly changes from a low state to a high state, the time constant T corresponding to the low counting rate is used. There is a problem in that the increase in the counting rate R is delayed and the response becomes slow. In view of the above circumstances, the present invention enables counting rates to be determined through digital processing, thereby making it possible to improve measurement precision, reduce device costs, save space, etc., and improve output clarity. It is an object of the present invention to provide a radiation monitoring device that can further improve the response speed significantly. [Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a radiation monitoring device according to the present invention counts pulse signals output from a pulse type radiation detector and calculates the counted value. In a radiation monitoring device that calculates a count rate by processing with a first-order lag filter, a 51 count rate calculation unit that calculates a current AI count rate based on the count value of a pulse signal output from the pulse type radiation detector; A selection section that compares the current count rate obtained by the count rate calculation section with the previous count rate and selects the one that satisfies a predetermined condition, and a selection section that selects the one that satisfies predetermined conditions. The present invention is characterized by comprising a filter characteristic changing section that changes the characteristics of the first-order lag filter by determining a time constant. (Function) In the above configuration, if the current count rate corresponding to the count value of the pulse signal output from the pulse radiation detector is calculated by the count rate calculation unit, the selection unit The current counting rate and the previous counting rate are compared, and the one that satisfies a predetermined condition is selected, and a time constant is calculated by the filter characteristic changing unit based on the counting rate selected by the selecting unit. The characteristics of the first-order lag filter are changed, and the counting rate corresponding to the counted value is calculated. (Embodiment) FIG. 1 is a block diagram showing an embodiment of a radiation monitoring device according to the present invention. The radiation monitoring device shown in this figure includes a pulse type radiation detector 1 that detects radiation, converts it into electric pulses, and outputs the electric pulses.
an amplifier circuit 2 that amplifies the output pulses output from the pulse radiation detector 1; a counting circuit 3 that discriminates the levels of the output pulses output from the amplifier circuit 2 and counts the output pulses;
It is provided with an arithmetic circuit 4 that arithmetic processes the count value outputted from the counting circuit 3 to obtain and output a counting rate. Next, the operation of this embodiment will be explained with reference to the flowchart shown in FIG. First, when radiation enters the pulsed radiation detector 1, the pulsed radiation detector 1 outputs an output pulse corresponding to the intensity of the radiation, which is amplified by the amplifier circuit 2 and then sent to the counting circuit 3. Man-powered. The counting circuit 3 performs level discrimination at a level corresponding to the peak value of the output pulse supplied from the amplifier circuit 2 (this peak value is proportional to the energy of the radiation), removes noise, and then counts and calculates the noise. The numerical value ΔC is supplied to the arithmetic circuit 4. The arithmetic circuit 4 collects the count value ΔC every time it is supplied from the counting circuit 3 (step 5T1),
The current count value Δ since the previous count value ΔC was supplied
The current counting rate Δ is based on the time until C is supplied (sampling time Δt) and the currently supplied count value ΔC.
After determining C/Δt, this counting rate ΔC/Δt is compared with the previously output counting rate λ, -1 (step 5T2). When ΔC/Δt≧Ra−1, the arithmetic circuit 4
determines that the counting rate has not increased or changed, and calculates the time constant T by performing the calculation shown in the following equation (step 5T3).
). T...(4)ΔC/
Δt Further, when ΔC/Δj<Rs-1, the arithmetic circuit 4 determines that the counting rate is decreasing and calculates the time constant T by performing the computation shown in the following equation (step 574). T
... (5) R1 After this, the arithmetic circuit 4 performs the calculation shown in the following equation to obtain the count rate R7 to be output this time from the count value ΔC supplied this time (step 5T5), and outputs it (step 5T6).
). T + Δt Thus, in this example, the previous counting rate R1-
1, when the current counting rate ΔC/Δt is the same or increasing, the time constant T is changed according to the current counting rate ΔC/Δt, and the current counting rate ΔC/Δt is changed from the previous counting rate R7.
When is decreasing, the time constant T is changed according to the previous counting rate R, -1, and then the current count value ΔC is subjected to first-order lag filtering processing according to the changed time constant T. Therefore, it is possible to obtain the same integration effect as an analog circuit using a conventionally used diode pump circuit, and when the counting rate R1 is rapidly increased, the time constant T can be immediately changed. . In addition, the relative standard deviation σ of the radiation count rate R7 is expressed as j
It is known that it can be obtained. The time constant T can be treated as approximately equivalent to the measurement time in equation (7), and in this example, the time constant T is calculated using equations (4) and (5). Therefore, by simply determining the time constant T so that the product of the counting rate and the time constant T is constant, the relative standard deviation σ of the counting rate can be made constant, and as a result, the counting rate R7 changes. Also, the relative standard deviation σ can be kept at a constant value, and the variation in indicated values can be made almost constant. FIG. 3 is a block diagram showing another embodiment of the radiation monitoring device according to the present invention. The radiation monitoring device shown in this figure includes a radiation detector 12 composed of a scintillator 10 and a photomultiplier 11, a high-voltage power supply 13 that biases the photomultiplier 11, and a signal output from the radiation detector 12. It includes a capacitor 14 that cuts the DC component and extracts the pulse signal, a preamplifier 15 that amplifies the pulse signal that has passed through the capacitor 14, and an operational amplifier 16. The level of the pulse signal amplified by the preamplifier 15 is discriminated and the noise component is extracted. Comparator 17 that removes
and an arithmetic circuit 18 that counts the pulse signals output from the comparator 17 to calculate the counting rate R0, and digitally processes the pulse signals output from the radiation detector 12 to calculate the counting rate R1. and output this. The arithmetic circuit 18 includes a counter circuit 19 that counts pulse signals output from the comparator 17, a CPU 20 that performs various operations, and a memory circuit 21 that is used as a work area for the CPU 20 and a storage area for constants and programs. Perform the time measurement operation and send the result at 31 o'clock to the CP.
It includes a timer circuit 22 that supplies the U20, an input/output circuit 23 that outputs the calculation result of the CPU 20 to an external device (not shown), and a bus 24 that connects one of these counter circuits or the input/output circuit 23. ing. Next, the operation of this embodiment will be explained with reference to the flowchart shown in FIG. First, when a pulse signal is output from the radiation detector 12, the DC component of the pulse signal is removed by the capacitor 4, and is input to the preamplifier 15, where it is amplified. Thereafter, the signal is input to a comparator 17, where the level is discriminated, and then supplied to a counter circuit 9 for counting. In addition, in parallel with this operation, if the timer fijJ path 22 outputs a signal indicating that a certain period of time has elapsed, the CP
After reading the count value ΔC from the counter circuit 19, U20 resets the counter circuit 19 to restart the counting operation (step ST] 0). After this, the CPU 20 checks whether the count value ΔC that has been imported this time is the first count value or not (Step STI 1)
, if this is the first count value, calculate the count rate R++-1 by performing the calculation shown in the following equation, and store this as the previous count rate (step 5T12). Δ, where Δt: counting time (sampling time) of the counter circuit 19 Next, the CPU 2Q compares the previous counting rate R7-1 and the current counting rate ΔC/Δt (step S713),
If R,,>Δc/Δt, calculate the time constant T by performing the calculation shown in the following equation (step 5T15); Then, the time constant T is obtained (step 5T14). ΔC/Δt After this, the CPU 20 performs filtering processing on the count value ΔC based on the calculation shown in the following formula to obtain the counting rate R7 (
Step 5T16), and supplies this to the input/output circuit 23 to output it to the outside (Step 5T17). After T + Δ, the CPU 20 repeats the above-described operation every time the timer circuit 22 times up to obtain the counting rate R and outputs it to the outside. As described above, in this embodiment, the current counting rate ΔC/Δ[
is the same or increasing, the current 31 numbers ΔC/Δ
[Change the time constant T according to [, and change the previous counting rate R@-
When the current counting rate ΔC/Δt is decreasing from 1, the time constant T is changed according to the previous counting rate R0, so it is similar to the conventional analog circuit using a diode pump circuit. In addition, when the counting rate R7 is rapidly increased, the time constant T can be changed immediately. Furthermore, in this embodiment, the time constant T can be determined by determining the relative standard deviation σ, so T
-10000/R, , the standard deviation σ is approximately 1%
It can be done. Furthermore, in the above embodiment, the range of the time constant T is not restricted, but in a practical radiation monitor device, when the counting rate Rs -1 becomes sufficiently small, the time constant T becomes too large. Therefore, it may be aborted at an appropriate value, for example, 40 seconds. In addition, when the counting rate Ro and ΔC/Δt are sufficiently large, the time constant T becomes small, and when T is less than Δt, there is almost no need for filtering, so the counting rate R You can also ask for . Δ t [Effects of the Invention] As explained above, according to the present invention, the counting rate can be determined by digital processing, thereby achieving higher measurement accuracy, lower cost of the device, and space saving. In addition to this, the output can be made smoother, and the response speed can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the radiation monitoring device according to the present invention, FIG. 2 is a flowchart showing an example of the operation of the embodiment shown in FIG. FIG. 4 is a block diagram showing an example of the embodiment, FIG. 4 is a flowchart showing an example of the operation of the embodiment shown in FIG. 3, and FIG. 5 is a block diagram showing an example of a conventionally known radiation monitoring device. 1... Pulse type radiation detector 3... Counting circuit 4... First-order lag filter, counting rate calculation section, selection section, filter characteristic Mugisara section (arithmetic circuit)

Claims (1)

[Claims] (1) In a radiation monitoring device that counts pulse signals output from a pulse-type radiation detector and processes the counted value with a first-order lag filter to obtain a counting rate, the pulses output from the pulse-type radiation detector A counting rate calculation unit that calculates the current counting rate based on the count value of the signal, and a unit that satisfies a predetermined condition by comparing the current counting rate obtained by this counting rate calculation unit and the previous counting rate. A radiation monitoring device comprising: a selection section that selects a count rate; and a filter characteristic change section that changes the characteristics of the first-order lag filter by determining a time constant based on the counting rate selected by the selection section. .