JP2637204B2 - Random pulse counter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a random pulse counting device that counts random pulse signals, and more particularly to a device that corrects random pulse count loss.

"Prior art" This type of device is used, for example, in a radiation measurement device.

A general configuration of the radiation measurement device will be briefly described. As shown in FIG. 4, first, the radiation detector 1 detects radiation and outputs a pulse signal 2. This pulse signal 2 is amplified by the amplifier 3. The pulse signal 4 output from the amplifier 3 is discriminated by a pulse height discriminator 5 and converted into a pulse signal 6 having a small width. This pulse signal 6 is counted by a counter 7.

This radiation measuring apparatus records one event (in this case, detection of radiation) as one independent pulse having a finite width. After recording one event, the next event is recorded. It takes a certain minimum amount of time. This time may be determined by one radiation detector, or may be determined by the circuits 3, 5, and 7 attached thereto. This minimum time is called dead time.

Regarding the behavior of the dead time of the counting device, two models of a paralysis type and a non-paralysis type are generally used. Fig. 5 shows the basic concept. The random event 8 entering the radiation detector 1 is shown in FIG. FIG. 5B shows the behavior in the case of the non-parasitic model. Assuming that the dead time is τ, the next event that occurs within this dead time after an event occurs is lost. In this case, five events 8A, 8B, 8C, 8D, 8E
Of the events 8B, 8D will be lost. This loss of true counts is called counting down.

Next, the case of the paralysis model is shown in FIG. 5 (C). In this case, when the next event occurs within the dead time, the dead time is further extended. However, in this case, the event that occurred next is not counted. In this example, five events
Only the count of two events 8A, 8C out of 8A, 8B, 8C, 8D, 8E is obtained, and the countdown of three events 8B, 8D, 8E occurs.

A conventional technique for correcting such counting loss is described in JP-B-56-37512. This technique is applied to the non-parasitic model described above. The following are common symbols used in the following description.

n: true count rate m: measured count rate τ: dead time of the device Here, the count rate indicates the count per unit time.

The percentage of all time the device is insensitive is mτ, and therefore the countdown is nmτ. On the other hand, this is nothing less than the subtraction of the measured count rate from the true count rate, so that the following equation holds.

nm = nmτ When this equation is solved for n, the following equation (1) is obtained.

That is, when this equation (1) is expanded, the following equation is obtained.

n = m + m (mτ) + m (mτ) ² +... + m (mτ) ^N +.
... (2) Rewriting the following correction terms of equation (2) gives the following equation.

In the conventional technique, the N-th order correction is repeated on the circuit based on the equation (3), thereby performing the correction for counting down.

First, a first-order term is calculated by multiplying (m ₀ τ) by a zero-order term m ₀ . Next, a second-order term is calculated by multiplying (m ₀ τ) by a first-order term. By repeating N times in this way, it is possible to calculate up to the N-th term. By adding all these terms, the measured count rate m is corrected to obtain the true count rate n.

"Problem to be Solved by the Invention" However, in the above-mentioned conventional technology, since equation (1) is a correction equation for a non-parasitic model, there is a problem that it is not suitable for a paralyzed model. Further, in order to perform the correction by repeating the Nth-order correction, N stages of calculation circuits are required, and there is a disadvantage that the circuit becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to improve a technique for correcting counting loss when counting random pulse signals. In other words, it is an object of the present invention to provide a random pulse counting device that can perform correction in any of the paralysis-type model and the non-paralysis-type model, requires a small circuit configuration, and can perform correction in real time.

[Means for Solving the Problems] Means taken by the present invention to achieve the above object will be described with reference to the drawings.

The principle configuration of the random pulse counting device according to the present invention comprises the following units as shown in FIG.

(1) Discriminating means 10 for discriminating the random pulse signal 9. Here, the random pulse is a pulse in which at least one of the pulse width and the pulse interval is irregular.

(2) While the random pulse signal 9 is being input, the first
A first detection means 13 for outputting the detection signal 12 of FIG.

(3) Second detection means 15 which outputs the second detection signal 14 while the random pulse signal 9 is not input.

(4) A first clocking means 16 for clocking the output time of the first detection signal per unit time. Here, "measuring the output time of the first detection signal per unit time" includes a mode in which a target value is indirectly obtained by counting pulses indicating a dead time per unit time. Here, counting means measuring the number of pulses generated in a certain cycle. The first detection signal means a signal indicating a dead time, and means an output signal 27 from the threshold detector 23 of the present invention. This threshold detector 23 generates the random pulse signal 21
Is the threshold (two-dot chain line in FIG. 3 (A) shown later)
Is output by exceeding.

(5) Second clocking means 17 for clocking the output time of the second detection signal per unit time. Here, “measuring the output time of the second detection signal per unit time” includes a mode in which a target value is indirectly obtained by counting pulses indicating the live time per unit time. Further, the second detection signal means a signal indicating a live time,
In the present invention, the output signal 30 from the NOT circuit (inverting circuit) 29
Means Although the NOT circuit 29 inverts the signal of the threshold detector 23, the value obtained by subtracting the dead time from the total time is the live time, so the output signal from the NOT circuit 29 is a signal indicating the live time. .

(6) The ratio of the first detection signal output time per unit time to the second detection signal output time per unit time Δτ /
At the rate of [Delta] T _1, the gate means to pass the output pulse signal 11 of the discrimination means 10 18.

(7) The output pulse signal 11 of the discrimination means 10 is added to the gate means 18
Counting means 20 for adding and counting the pulse signals 19 of the above.

When the true count rate of the random signal is low (n << 1 / τ)
It is known that the following approximate expression can be used for both the paralysis model and the non-paralysis model.

m = n (1−nτ) When this is solved by n / m, the following equation (4) is obtained.

n / m = 1 / (1-nτ) (4) Assuming that _Tt is the average time interval of the incident random pulse, n = 1 / _Tt , so the above equation is modified as follows: Is done.

n / m = T _t / (T _t −τ) The time obtained by subtracting the dead time from T _t is generally called a live time because the device is in an operable state. Expressed here in a live time at T _1, since the _{T 1} = T _t -τ,
The above equation is expressed as follows.

_{n / m = T t / T} 1 = (T 1 + τ) / T 1 = 1 + (τ / T 1) Solving this equation for n (5) becomes as expression.

n = m + (τ / T ₁ ) m (5) The pulse indicating the dead time is the clock pulse signal 33 emitted from the oscillator 32, but the output signal 27
Since the gate circuit 28 transmits the clock pulse signal according to the (signal indicating the dead time), the pulse signal 34 passing through the gate circuit 28 becomes a pulse indicating the dead time.
In the equation (5), the pulse indicating the live time is a clock pulse signal generated from the oscillator 32, and is output from the NOT circuit (inverting circuit) 29 by the output signal 30 (signal indicating the live time). Transmits a clock pulse, the pulse signal 38 passing through the gate circuit 31 becomes a signal indicating the live time.

The present invention corrects the undercount based on the equation (5).

First, the random pulse counting device according to the present invention discriminates the random pulse signal 9 by the discriminating means 10.

The random pulse signal 9 is output to the first detecting means 13
And the second detection means 15. Then, the first detection means 13 outputs the first detection signal 12 while the random pulse signal 9 is being input. On the other hand, while the random pulse signal 9 is not input, the second detection means 15
The second detection signal 14 is output.

The first timing means 16 is based on the first detection signal 12,
The first detection signal per unit time, that is, the dead time is measured. This time is called Δτ. On the other hand, the second timing means
17 measures the second detection signal per unit time, that is, the live time, based on the second detection signal 14. This time is referred to as ΔT _l.

On the basis of the timing results of the first and second time measuring means 16 and 17, the gate means 18 determines the second time per unit time.
First per unit with respect to the detection signal output time [Delta] T _l Time
Detection signal output time .DELTA..tau ratio, i.e. a ratio of .DELTA..tau / [Delta] T _l, passing the output pulse signal 11 of the discrimination means 10. Assuming that the number of pulses of the output pulse signal 19 of the gate means 18 per unit time is M 'and the number of pulses of the output pulse signal 11 of the discriminating means 10 per unit time is M, the number of pulses M' is expressed by the following equation. You.

M ′ = (Δτ / ΔT _l ) M (6) Then, the counting means 20 determines the number M of pulses of the output pulse signal 11 per unit time of the discrimination means 10 and the gate means.
Number of pulses per unit time M 'of the output pulse signal 19 of 18
Is added and counted. In other words, the count result M ₀ of the counting means 20 is expressed by the following equation.

_{M 0 = M + (Δτ /} ΔT l) M ...... (7) On the other hand .DELTA..tau, [Delta] T _l is per unit time both tau, since it is T _l, the following equation is established.

(Δτ / ΔT _l ) = τ / T _l Therefore, the expression (7) becomes equivalent to the expression (5), and it is possible to correct the undercount.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

This embodiment shows an example of application to a radiation measuring apparatus. First, the structure of the radiation measuring apparatus according to the present embodiment will be described.

The random pulse signal 21 shown in FIG. 2 is obtained by detecting radiation by a radiation detector (not shown) and amplifying the detected signal by an amplifier (not shown).
This random pulse signal 21 is a pulse signal in which the pulse width, the pulse interval, and the wave height are all irregular.

This random pulse signal 21 is input to a wave height discriminator 22 and a threshold detector 23. The wave height discriminator 22 discriminates the random pulse signal 21 based on the wave height. The pulse signal 24 output from the wave height discriminator 22 is input to the gate circuit 25 and the adder 26.

The threshold detector 23 outputs a detection signal 27 when the wave height of the random pulse signal 21 exceeds a threshold. The detection signal 27 is input to a gate circuit 28 and a NOT (negation) circuit 29.

The NOT circuit 29 outputs an inverted signal of the detection signal 27. The output signal 30 of the NOT circuit 29 is input to the gate circuit 31.

The oscillator 32 outputs a clock pulse signal 33. This clock pulse signal 33 is applied to gate circuits 28 and 31
Is input to

The gate circuit 28 transmits the clock pulse signal 33 while the detection signal 27 is input. This gate circuit
The pulse signal 34 output by 28 is input to the counter down-converter 35.

The counter down-converter 35 down-converts the pulse signal 34 at a down conversion rate N. Here, the step-down rate N is equivalent to a 1 / N frequency divider, and is a function of outputting one pulse by inputting N pulses. The pulse signal 36 output from the counter down-converter 35 is input to the set input terminal of the flip-flop circuit 37.

The gate circuit 31 transmits the clock pulse signal 33 while the output signal 30 of the NOT circuit 29 is input. The pulse signal 38 output from the gate circuit 31 is
Entered in 39.

The gate circuit 39 outputs the output signal of the flip-flop circuit 37.
The pulse signal 38 is transmitted while there are 40 inputs. The pulse signal 41 output from the gate circuit 39 is input to the counter down-converter 42.

The counter down-converter 42 steps down the pulse signal 41 at the same step-down rate N as the counter down-converter 35. The pulse signal 43 output from the frequency multiplier 42 is input to the reset input terminal of the flip-flop circuit 37.

The flip-flop circuit 37 starts outputting when the pulse signal 36 output from the counter down-converter 35 is input, and
When there is an input of the pulse signal 43 output from 42, the output is stopped. Output signal of this flip-flop circuit 37
40 is input to the gate circuits 25 and 39.

The gate circuit 25 outputs the output signal of the flip-flop circuit 37.
Pulse signal output by the wave height discriminator 22 while there are 40 inputs
24 is transmitted. The pulse signal 44 output from the gate circuit 25 is input to the delay circuit 45.

The delay circuit 45 includes a pulse signal 44 output from the gate circuit 25.
Is delayed for a required time. The pulse signal 46 output from the delay circuit 45 is input to the adder 26.

The adder 26 adds the pulse signal 24 output from the pulse height discriminator 22 and the pulse signal 46 output from the delay circuit 45. The pulse signal 47 output from the adder 26 is input to a counter 48.

The counter 48 counts the pulse signal 47.

 Next, the operation of the apparatus of the present embodiment will be described.

When the wave height of the random pulse signal 21 exceeds a threshold (indicated by a dashed line in FIG. 3A), the pulse height discriminator 22 outputs a pulse signal 24 (third pulse) having a smaller pulse width than the random pulse signal 21. Figure B) is output. At this time, a signal that has overlapped with the previous pulse signal, such as the random pulse signal 21A, or a signal whose wave height has not reached the threshold value, such as the random pulse signal 21B, is dropped. That is, pulse signals 24 corresponding to random pulse signals 21A and 21B are not output.

The threshold detector 23 outputs a detection signal 27 (FIG. 3C) while the wave height of the random pulse signal 21 exceeds a threshold (shown by a two-dot chain line in FIG. 3A). This detection signal
Reference numeral 27 denotes a time during which the random pulse signal 21 is input, that is, a dead time τ. The NOT circuit 29 inverts the detection signal 27 and outputs an output signal 30 (FIG. 3D).
The output signal 30 indicates a time during which the random pulse signal 21 is not input, that is, a live time _Tl .

The clock pulse signal 33 (FIG. 3E) generated by the oscillator 32 is masked by the detection signal 27 in the gate circuit 28. The clock pulse signal 33 is masked by the output signal 30 in the gate circuit 31. The pulse signal 34 (FIG. 3F) output by the gate circuit 28
When the number of pulses of the output signal 34 of the gate circuit 28 reaches N, a pulse signal 36 (FIG. 3H) is output.

Here, consider the case where the counter down-converter 35 outputs the pulse signal 36A. Hereinafter, a description will be given assuming that this time is a starting point and time 0.

The counter down-converter 35 counts the pulse signal 34 again, and outputs a pulse signal 36B when the number of pulses reaches N.
When this time and t _1, the scaling unit 35 until a time t ₁
Is input only during the dead time. This time is a decreasing rate N, the period of the clock pulse 33 and t _C, represented by N * t _C. Further, since the ratio of the dead time is τ / _Tt , the following relationship is established.

t ₁ * (τ / T _t ) = N * t _C (8) Therefore, when this equation is solved at time t ₁ , the following equation is obtained.

t ₁ = (T _t / τ) * N * t _C (9) When the pulse signal 36A is input to the set input terminal of the flip-flop circuit 37, the output signal 40 of the flip-flop circuit 37 (the 3 I) goes to the H (high) level. As a result, the gate circuit 39 is opened, and the pulse signal 38 (FIG. 3G) output from the gate circuit 31 is transmitted. The pulse signal 41 (third signal) output from the gate circuit 39
FIG. J) is counted by the count-down converter 42. Counter down converter
42 outputs a pulse signal 43A (FIG. 3K) when the number of pulses reaches N. Pulse input to the scaling unit 42 until a time t ₂ to the time pulse signal 43A is output
41 is only during the live time. This time is a decreasing rate N, the period of the clock pulse 33 and t _C, represented by N * t _C. The live time ratio is T _l / T
_{Since t} , the following equation holds.

t ₂ * (T ₁ / T _t ) = N * t _C (10) Therefore, when this equation is solved at time t ₂ , the following equation is obtained.

t ₂ = (T _t / T _l ) * N * t _C (11) When the pulse signal 43A is input to the reset input terminal of the flip-flop circuit 37, the output signal 40 of the flip-flop circuit 37 becomes L ( Low) level. Gate circuits 25 and 39 are open while output signal 40 is at H level. That is, the gate circuit 25 only in the time interval t _2, it will send a pulse signal 24. Accordingly, the pulse number M 'of the pulse signal 14 (FIG. 3L) output from the gate circuit 25 is as follows.

M ′ = (t ₂ / t ₁ ) M Here, M is the number of pulses of the pulse signal 24 in the time interval t ₁ .

By transforming equation (12) based on equations (9) and (11), equation (6) is obtained.

The pulse signal 44 output from the gate circuit 25 is a pulse height discriminator.
The signal is delayed by a delay circuit 45 so as not to overlap with the pulse signal 24 output by the signal 22. Usually two pulse signals 24, 46
Are input at the same time, the adder does not operate. Then, the pulse signal 24 output from the pulse height discriminator 22 and the pulse signal 46 (FIG. 3M) output from the delay circuit 45 are added by the adder 26.

The pulse number M ₀ of the pulse signal 47 output from the adder 26 is the third
It is represented by equation (7) as shown in FIG. That is, the number of pulses of the random pulse signal 21 eliminated in the wave height discriminator 22 is corrected by adding the number of pulses M '.

The pulse number M ₀ of the pulse signal 47 is counted by the counter 48. This counting result is output to an external device (not shown) as a radiation measurement value.

As described above, the embodiment of the present invention has been described using the example of application to the radiation measuring apparatus. However, the present invention is not limited to the application to the radiation measuring apparatus, but can be generally applied to an apparatus that corrects the count-down of random pulses.

"Effects of the Invention" As described above, according to the present invention, the first detection means measures the first detection signal output time per unit time, and the second time measurement means measures the first detection signal output time per unit time. Is measured for the second detection signal output time. The gate means allows the output pulse signal of the discriminating means to pass at a ratio of the ratio of the first detection signal output time per unit time to the second detection signal output time per unit time. The pulse signal obtained in this way is added to the output pulse signal of the discriminating means by the counting means and counted, whereby the correction based on the equation (7) can be performed.

Therefore, according to the present invention, the following effects can be obtained.

(1) Since a complicated operation (for example, an N-stage approximation calculation based on Expression (3)) is not performed as in the related art, the circuit scale can be reduced, and the reliability and economy are improved.

(2) Appropriate correction can be performed regardless of the paralysis model and the non-paralysis model. Further, the present invention can be generally applied to the counting of pulses in which either the pulse width or the pulse interval is irregular.

(3) The output pulse signal of the discriminating means is masked by the gate means, and the obtained pulse signal is added to the output pulse signal and counted, so that correction can be performed in real time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the present invention, FIG. 2 is a block diagram showing a configuration of a radiation measuring apparatus according to one embodiment of the present invention, and FIGS. 3 (A) to 3 (N) are diagrams of FIG. FIG. 4 is a waveform diagram showing a signal in each section, FIG. 4 is a block diagram showing a configuration of a general radiation measuring apparatus, and FIGS. 5A to 5C are waveform diagrams showing a signal in each section in FIG. 9 random pulse signal, 10 discriminating means, 11 output pulse signal, 12 first detection signal, 13 first detecting means, 14 second detection signal, 15 Second detection means, 16 first time measurement means, 17 second time measurement means, 18 gate means, 19 output pulse signal, 20 count means.

Claims (1)

(57) [Claims] A random pulse signal in which at least one of a pulse width and a pulse interval randomly output from a predetermined detector is irregular is discriminated by a wave height, and the result is converted into a pulse signal. A pulse height discriminator to be output, and a random pulse signal input to the pulse height discriminator are input in parallel, and when this exceeds a predetermined threshold value, one event is recorded and then the next event is recorded. A threshold detector that outputs a detection signal indicating a dead time as a minimum time of the oscillator; an oscillator that outputs a clock pulse signal; and an output of the oscillator while the detection signal is being input from the threshold detector. A first gate circuit for outputting a clock pulse to be output as a pulse signal indicating a dead time; and a detection signal output from the threshold detector and an inverted signal thereof. And an inverting circuit that outputs a signal indicating a live time as a value obtained by subtracting the dead time from the entire time. While the signal is output from the inverting circuit, a clock pulse output from the oscillator indicates a live time. A second gate circuit that outputs a pulse signal; a first counter that inputs a pulse signal output from the first gate circuit and reduces the pulse signal at a predetermined reduction rate N; And a flip-flop circuit which is set by the pulse signal output by the output circuit, and an output signal which is output from the flip-flop circuit while the flip-flop circuit is set, and the supplied pulse signal is output as the pulse signal only during this period. A third gate circuit, and a pulse signal output from the third gate circuit is reduced by the reduction rate N. A second counter which inputs a signal to a reset terminal of the flip-flop circuit; and a pulse signal supplied from the wave height discriminator is output as a pulse signal while an output signal is being output from the flip-flop circuit. A fourth gate circuit, and a pulse signal output from the fourth gate circuit delayed by a predetermined time and a pulse signal supplied from the pulse height discriminator are added to count down by the pulse height discriminator. A random pulse counting device comprising: an adder for correcting the number of pulses of a random pulse signal; and a counter for counting a pulse signal output from the adder.