JPS6117307B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation dose rate meter that provides an analog indication or digital display of a dose rate obtained by integrating pulses corresponding to the detection output of a radiation detector over a certain period of time, and particularly relates to a radiation dose rate meter that displays in analog or digital form a dose rate that is obtained by integrating pulses corresponding to the detection output of a radiation detector over a certain period of time. It is possible to expand the range in which dose rates can be specified by correcting errors.

Generally, in this type of dose rate meter, the number of radiation pulses is counted based on the ability of the radiation detector to resolve and discriminate the pulsed radiation and the resolution of the electronic circuit that transmits the detected output pulses. Since the radiation drop increases in a high dose rate region where radiation pulses are continuously emitted, the radiation emission amount, that is, the true radiation dose rate, and the dose rate indication value are no longer proportional, and the indication error increases. For example, the indication scale in analog instructions becomes too dense to be practical. Therefore, in conventional dose rate meters, the scale range of the indicating instrument is determined only for the range where the radiation emission amount and the dose rate indication value are approximately proportional, and the scale range of the indicating instrument is set only for the range where the radiation emission amount and the dose rate indication value are approximately proportional, and the scale range of the indicating instrument is set only in the range where the radiation emission amount and the dose rate indication value are sufficiently indicated. Therefore, there was a strong desire to expand the measurable range.

That is, the conventional dose rate meter is configured as shown in Fig. 1, and the detection output of a detector 1 that detects radiation emitted in a pulsed manner is converted into a pulse signal by a dose rate conversion circuit 2 and counted. On the other hand, the pulse train from the pulse generating circuit 5 is supplied to the frequency dividing circuit 6 to divide the frequency, and every time the number of pulses in the pulse train reaches a certain number, the frequency divided output is set to the latch/reset generating circuit. Supply to 7.

In response to the supply of the frequency-divided output described above, the latch/reset generation circuit 7 supplies the reset start pulse shown in the top row of FIG. With the pulse, as shown in the third stage, for example, the counting of radiation detection pulse signals in the counting period A is started, and the counted value after a certain period of time is sent to the display circuit 4 according to the latch pulse to be stored, and finally As shown in the lower row, the counting result A is displayed as a dose rate, and the same counting table is shown below.
Have students repeat the instructions.

However, as mentioned above, the more frequently the pulsed radiation emission approaches the state of continuous radiation, the more it becomes impossible to distinguish the pulsed radiation, so as shown in Figure 3, the actual amount of radiation emitted is The dose rate indication value gradually becomes less proportional to the increase, and the indication value does not change much even if the emitted amount increases. Therefore, in conventional dose rate meters, only the linear proportional range shown in FIG. 3 has been used as the indicated range.

An object of the present invention is to eliminate the above-mentioned disadvantages of the conventional indication range limitation, correct radiation detection errors that increase in high dose rate areas with a simple circuit configuration, and provide a radiation dose measurement indication range that is sufficiently wide. The goal is to provide a rate meter.

In order to achieve such an objective, the present invention
The radiation dose rate expressed by the number of radiations emitted within a predetermined period is displayed by a count output obtained by counting the number of pulses emitted in response to the detection of radiation, and the counting period is repeated for a predetermined period. In a radiation dose rate meter, which is set according to the length of time that the number of pulses in a periodic pulse train reaches a predetermined number, the number of pulses generated in response to radiation detection is
Multiply by a multiple such that the count output becomes a value that can be directly read as a dose rate, and each time radiation is detected, remove a predetermined number of pulses from the pulse train to determine the length of time it takes for the number of pulses to reach the predetermined number. By changing the counting period, the counting period is changed according to the frequency of radiation detection, and the time for deleting a predetermined number of pulses from a pulse train of a predetermined repetition period is set equal to the radiolysis discrimination time of the radiation detector. Features.

The invention will be explained in detail below with reference to the drawings.

An example of the configuration of the dose rate meter of the present invention is shown in FIG. 4. As is clear from the correspondence with the configuration shown in FIG. 1, the configuration shown in FIG. is supplied to a monostable circuit 8, for example, a one-shot multivibrator, and a square wave signal with a constant time width is generated each time the radiation detection output is supplied in the monostable circuit 8, and the pulse generation circuit 5 and the frequency dividing circuit 6 as a gate signal to the gate circuit 9 inserted between the pulse generating circuit 5 and the pulse generating circuit 5.
The pulse train supplied to the frequency dividing circuit 6 is cut off and deleted during the application period of the gate signal.

That is, in the dose rate meter of the present invention, as in the conventional case, the n pulse signals taken out from the detector 1 per second are multiplied by x by the dose rate conversion circuit 2, and
The counting circuit 3 integrates the xn pulse signals per second for a certain period of time, for example, 1 to 10 seconds, and the display circuit 4 displays the integrated value as a dose rate. The multiple x is appropriately selected so that it can be read directly.

On the other hand, in the dose rate meter of the present invention, the detection output pulse signal from the detector 1 is also supplied to the monostable circuit 8, and each time a radiation pulse is detected, the pulse width as shown in the middle row of FIG. A square wave pulse of W is generated, and the square wave pulse is applied to the gate circuit 9 to gate the pulse train from the pulse generation circuit 5 shown in the upper row. Delete pulses during a period of width W. Therefore, the frequency division period length of the frequency divider circuit 6, which sends a frequency-divided output pulse every time the number of pulses in the input pulse train reaches a predetermined number, is extended in accordance with the number of pulses deleted by the gate circuit 9. be done. Therefore, in response to the supply of the frequency-divided output pulse, the time intervals between the reset start pulse and the latch pulse applied from the latch/reset generation circuit 7 to the counting circuit 3 are similarly extended.

Now, the dose rate n ₀ (counts/second) obtained as a count value obtained by integrating the detected output pulses of radiation with an emitted amount P (mR/hour) for a period T is, when K is a constant, P=Kn ₀ T ( 1) becomes. However, as mentioned at the beginning, in high dose rate regions, the number of radiation pulses that are emitted in pulses becomes close to each other, and the number of radiation pulses that fail to be detected exceeds the resolving power of the detector. Although the dose rate gradually increases, if the true dose rate corrected for the missing count is n _t (counts/second), then the time required for the detector's decomposition discrimination is τ, n _t =n ₀ /1−n ₀ τ (2 ) becomes. In the low dose rate region, n ₀ τ<<1, so n _t ≈n ₀ , and the radiation amount P is proportional to the count value n ₀ without requiring correction. However, in the high dose rate region, as shown in Figure 6, radiation
The detection frequency and the emission amount, that is, the true dose rate, are no longer proportional to each other, but in the above equations (1) and (2), the decomposition discrimination time τ, the count value n ₀ , and the constant K are values specific to the detector. , the counting time T can be changed. Therefore, if the counting period T is set appropriately, it is possible to correct errors caused by the radiation detection frequency and to indicate a dose rate value proportional to the amount of radiation emitted over a wide range. It can be done.

That is, if a pulse for a certain period of time W is deleted from the pulse train from the pulse generation circuit 5 each time radiation is detected, the number of pulses per second m' supplied to the frequency dividing circuit 6 will be equal to the number of pulses generated from the pulse generation circuit 5. Let m (number of pulses/second) be m'=m(1-n ₀ W) (3). Therefore, if the frequency dividing circuit 6 generates frequency divided pulses every fixed number of pulses Y, then the number of pulses Y between the counting period T in the counting circuit 3
= mT, so if the number of input pulses in the frequency divider circuit 6 changes from m to m', the counting period in the counting circuit 3 also changes from T to T', and Y=mT=m'T' (4) Based on the relationship, T'=mT/m'=T/1-n ₀ W (5). If this equation (5) is substituted into equation (1), P=Kn ₀ T/1−n ₀ W (6). Therefore, if the time width W in which the gate circuit 9 deletes a pulse each time radiation is detected is selected to be equal to the radiolysis discrimination time τ of the detector 1, and W=τ, then P=Kn ₀ /1−n ₀ τ・T=K・_nt・T (7) Therefore, the amount of radiation emitted P and the dose rate instruction value _nt corrected for the deletion of pulses by the above-mentioned gate circuit are always proportional.

As is clear from the above description, according to the present invention, when measuring the radiation dose rate using a GM counter, scintillator, etc. as a detector for a digital survey, digital rate meter, etc., radiation detection in the detector is possible. It is possible to skillfully correct instruction errors due to leakage and provide accurate radiation dose rate instructions.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of a conventional dose rate meter, Figure 2 is a waveform diagram showing the signal waveforms of each part, Figure 3 is a characteristic curve diagram showing its dose rate indicating characteristics, and Figure 4. 5 is a block diagram showing a configuration example of the dose rate meter of the present invention, FIG. 5 is a waveform diagram showing signal waveforms of various parts thereof, and FIG. 6 is a characteristic curve diagram showing the dose rate indicating characteristics thereof. 1...Detector, 2...Dose rate conversion circuit, 3...
Counting circuit, 4... Display circuit, 5... Pulse generating circuit, 6... Frequency dividing circuit, 7... Latch/reset generating circuit, 8... Monostable circuit, 9... Gate circuit. 〓〓〓〓〓

Claims (1)

[Claims] 1 The radiation dose rate expressed by the number of radiation emitted within a predetermined period is displayed by the count output obtained by counting the number of pulses generated in response to the detection of radiation, and the period of said counting is In a radiation dose rate meter that is set according to the length of time during which the number of pulses in a pulse train of a predetermined repetition period reaches a predetermined number, the counting output directly reads the number of pulses generated in response to the detection of the radiation as a dose rate. Each time radiation is detected, a predetermined number of pulses are removed from the pulse train and the length of time for the number of pulses to reach a predetermined number is varied, The counting period is changed according to the frequency of radiation detection, and the time for deleting a predetermined number of pulses from the pulse train of the predetermined repetition period is set equal to the radiolysis discrimination time of the radiation detector. Radiation dose rate meter.