JP7391752B2 - Radiation measurement device - Google Patents

Description

Embodiments of the present invention relate to a sample-hold type radiation measuring device.

A sample-and-hold radiation measurement device measures radiation energy from a pulsed electrical signal (pulse signal) generated when a radiation detector detects radiation. That is, the energy is measured by converting the energy lost by the radiation inside the radiation detector into a pulse signal, processing the wave height so that it is proportional to the energy, and measuring the wave height. When measuring the wave height of a pulse signal, an operation is performed to sample a measurement value at one point.

However, in sample-and-hold radiation energy measurement, the time at which the signal exceeds the discrimination threshold is shifted depending on the wave height, so the timing at which the sample value is obtained is slightly off from the peak value of the signal. This phenomenon is called a time walk, and the constant fraction method and the extrapolation leading edge method are known as trigger generation methods for eliminating this time lag.

Glenn F. Knoll, translated by Ikuo Jinno et al., Radiation Measurement Handbook (4th edition), Ohmsha.

Both the constant fraction method and the extrapolation leading edge method are methods that can suppress time walks. However, this may be disadvantageous when creating a measuring device that requires a wide dynamic range.

For example, in the case of the constant fraction method, the attenuated pulse waveform and the inverted and delayed pulse waveform are synthesized, resulting in a poor signal-to-noise ratio, making it impossible to reduce the minimum measurable value, and making it difficult to achieve a wide dynamic range. There was a problem in that it was disadvantageous when creating a measurement circuit.

Furthermore, since the extrapolation leading edge method requires two comparators with different discrimination thresholds, it is possible to reduce the minimum value of the detectable signal compared to the case where there is only one discrimination threshold. This poses the problem of being disadvantageous when creating a measurement circuit with a wide dynamic range.

Embodiments of the present invention have been made to solve the above-mentioned problems, and even when a wide dynamic range is required, the present invention provides a sample-and-hold type radiation source that can detect pulse signals with reduced influence of time walk. The purpose is to obtain a measuring device.

A radiation measuring device according to an embodiment of the present invention includes: a radiation detector that outputs a pulsed electrical signal by detecting radiation; a preamplifier that integrates and amplifies the output of the radiation detector; a high-speed shaping amplifier which has a time constant and gives a predetermined gain by slowing the rise of the output of the preamplifier and hastening the subsequent return to the base state; a pulse height discriminator that outputs an on signal only when the pulse height discriminator starts outputting the on signal; and a pulse height discriminator that outputs a first trigger signal after a predetermined first delay time from when the pulse height discriminator starts outputting the on signal. a threshold exceedance time measuring device that measures the threshold exceedance time from when the wave height discriminator starts outputting the on signal until the output of the on signal ends; a second trigger signal that is delayed by a second delay time obtained by multiplying the threshold exceeding time by a predetermined additional delay ratio greater than zero and smaller than 1 from the start time of the trigger signal; 2 delay device and a slow time constant longer than the high speed time constant to slow the rise of the output of the preamplifier, hasten the subsequent return to the base state, and provide a predetermined gain. The present invention is characterized by comprising an amplifier and a sample hold device that holds and outputs the output of the low-speed shaping amplifier at the time when the second trigger signal is output.

According to the embodiments of the present invention, even when a wide dynamic range is required in a sample-and-hold type radiation measurement device, it is possible to detect a pulse signal with reduced influence of time walk.

FIG. 1 is a block diagram showing the configuration of a radiation measurement device according to a first embodiment. The figure which shows the example of the time chart of the signal of each part in the radiation measurement apparatus based on 1st Embodiment. 3 is an explanatory diagram showing the relationship between TOT and peak arrival time when the wave heights are different in the time chart of the high-speed shaping amplifier output signal of FIG. 2. FIG. FIG. 2 is a block diagram showing the configuration of a radiation measurement device according to a second embodiment. FIG. 3 is a block diagram showing the configuration of a radiation measurement device according to a third embodiment. FIG. 3 is a block diagram showing the configuration of a radiation measurement device according to a fourth embodiment.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a radiation measurement device according to the present invention will be described with reference to the drawings. Here, common parts are given the same reference numerals and redundant explanations will be omitted.

[First embodiment]
FIG. 1 is a block diagram showing the configuration of a radiation measurement device according to a first embodiment. FIG. 2 is a diagram showing an example of a time chart of signals of each part in the radiation measurement device according to the first embodiment.

The radiation measurement device according to the first embodiment includes a radiation detector 11, a preamplifier 12, a high-speed shaping amplifier 13, a pulse height discriminator 14, a trigger generator (first delay device) 15, and a TOT. A measuring device (threshold excess time measuring device) 16, a TOT delay device (second delay device) 17, a low-speed shaping amplifier 18, a sample and hold device 19, and an analog-to-digital converter (AD converter) 20. has.

The radiation detector 11 converts the energy lost by the radiation within the sensitive region into an amount of charge, and outputs it as a pulsed current signal. The output signal S1 of this radiation detector 11 is sent to a preamplifier 12. The preamplifier 12 is a charge-sensitive amplifier that integrates and amplifies the output of the radiation detector 11, and outputs a pseudo-step signal S2. The peak value of the output signal S2 of the preamplifier 12 is proportional to the total charge amount of the output signal S1 of the pulsed radiation detector 11.

The high-speed shaping amplifier 13 shapes and amplifies the output signal S2 of the preamplifier 12 and outputs a pulse signal S3. The high-speed shaping amplifier 13 performs shaping to slow the rise of the output signal S2 of the preamplifier 12 and to hasten the return to the base state after the peak value is achieved. This shaping makes it possible to detect radiation that will reach the radiation detector 11 next.

The pulse height discriminator 14 outputs a signal S4 as a logical level that changes depending on whether the output signal S3 of the high-speed shaping amplifier 13 exceeds a predetermined threshold (discrimination threshold). This signal S4 becomes an on (H level) signal when the signal S3 exceeds a predetermined threshold value, and becomes an off (L level) signal at other times.

The trigger generator 15 outputs the first trigger signal S5 after a predetermined first delay time Td1 after the output signal S4 of the pulse height discriminator 14 changes from off to on.

The TOT measuring device 16 measures the threshold crossing time (TOT) from when the output signal S4 of the pulse height discriminator 14 changes from off to on to when it returns from on to off, and determines the threshold crossing time. It outputs a signal St1 representing . To measure the time over threshold (TOT), for example, the number of internal clocks is counted in the TOT measuring device 16 from the time when it is detected that the output signal S4 of the pulse height discriminator 14 changes from off to on. It is possible to start the counter, stop the counter when it detects that the output signal S4 of the pulse height discriminator 14 changes from on to off, and output the count value at that time as the time over threshold (TOT). .

The TOT delay device 17 outputs a second trigger signal S7 delayed from the first trigger signal S5 from the trigger generator 15 by a second delay time Td2. Here, the second delay time Td2 is given by the following equation.

(Second delay time Td2) = (TOT) x (additional delay ratio rd) (1)
However, the additional delay ratio rd is a number greater than zero and less than one. This additional delay ratio rd will be described later.

The low-speed shaping amplifier 18 shapes and amplifies the output signal S2 of the preamplifier 12 and outputs a signal S6. The low-speed shaping amplifier 18 has the same function as the high-speed shaping amplifier 13, and performs shaping to slow the rise of the output signal S2 of the preamplifier 12 and hasten the return to the base state after reaching the peak value. However, the slow shaping amplifier 18 has a longer time constant than the fast shaping amplifier 13.

The sample and hold device 19 holds the output signal S6 of the low-speed shaping amplifier 18 at the time of receiving the second trigger signal S7 from the TOT delay device 17 as a sample value Sp1, and outputs it to the analog-to-digital converter 20.

The analog-to-digital converter 20 outputs a digital signal as a measurement value representing the energy of the radiation.

Here, the additional delay ratio rd for determining the second delay time Td2 will be explained using FIG. 3.

FIG. 3 is an explanatory diagram showing the relationship between TOT and peak arrival time when the wave heights are different in the time chart of the output signal S3 of the high-speed shaping amplifier 13 in FIG. Figure 3(a) shows a case where the wave height is relatively low, Figure 3(b) shows a case where the wave height is higher than Figure 3(a), and Figure 3(c) shows a case where the wave height is even higher than Figure 3(b). It shows the case.

Generally, the output signals S3 of the high-speed shaping amplifier 13 are similar to each other when the signal S3 has different wave heights. Therefore, if the second delay time Td2 is adjusted to the time from when the signal S3 exceeds the threshold until it reaches its peak value, the value of the additional delay ratio rd=(second delay time Td2)/(TOT) is a substantially constant value regardless of the wave height of the signal S3. That is, the second delay time Td2 can be determined by the above equation (1).

As shown in FIG. 3, the waveform of the signal S3 is approximately symmetrical in the portion exceeding the threshold (TOT period) around the time when the peak value is taken (left and right in FIG. 3). Therefore, the additional delay ratio rd may be set to 0.5, for example. However, since it is not necessarily completely symmetrical, the additional delay ratio rd may be selected from an actually optimal value in the range of 0.4 to 0.6 or 0.3 to 0.7, for example.

As described above, according to this embodiment, even when a wide dynamic range is required in the radiation measurement apparatus, pulse signals can be detected with reduced influence of time walk.

[Second embodiment]
FIG. 4 is a block diagram showing the configuration of a radiation measurement device according to the second embodiment. The radiation measuring device according to the second embodiment includes, in addition to the components of the radiation measuring device according to the first embodiment, a high-gain high-speed shaping amplifier 113 and a high-gain pulse height discriminator (hereinafter simply referred to as "wave height discriminator"). 114 (also referred to as a "trigger generator"), a high gain trigger generator (first high gain delay device, hereinafter also simply referred to as "trigger generator") 115, and a high gain TOT measuring device (high gain threshold exceedance time measurement device) 115; a high-gain TOT delay device (second high-gain delay device; hereinafter also simply referred to as a "TOT delay device") 116; and a high-gain low-speed shaping amplifier 118. , a high gain sample and hold device (hereinafter also simply referred to as a “sample and hold device”) 119, a high gain analog-to-digital converter (hereinafter also simply referred to as an “analog to digital converter”) 120, and a sample signal selector 30. has.

Like the high-speed shaping amplifier 13, the high-gain high-speed shaping amplifier 113 shapes and amplifies the output signal S2 of the preamplifier 12 and outputs a pulse signal S103. High gain fast shaping amplifier 113 is similar to fast shaping amplifier 13, but with higher gain.

The high gain pulse height discriminator 114 is similar to the pulse height discriminator 14, and has a signal S104 as a logical level that changes depending on whether the output signal S103 of the high gain high speed shaping amplifier 113 exceeds a predetermined threshold. Output.

The high gain trigger generator 115 is similar to the trigger generator 15, and has a predetermined first high gain delay time Td101 after the output signal S104 of the high gain pulse height discriminator 114 changes from off to on. Afterwards, the first high gain trigger signal S105 is output.

The high gain TOT measuring device 116 is similar to the TOT measuring device 16, and has a threshold value from when the output signal S104 of the high gain pulse height discriminator 114 changes from off to on to when it returns from on to off. The overtime time (TOT) is measured and a signal St101 representing the threshold overage time is output.

The high-gain TOT delay device 117 is similar to the TOT delay device 17, and is a second high-gain trigger signal delayed by a second high-gain delay time Td102 from the first high-gain trigger signal S105 from the high-gain trigger generator 115. A high gain trigger signal S107 is output.

High gain low speed shaping amplifier 118 is similar to low speed shaping amplifier 18, and shapes and amplifies the output signal S2 of preamplifier 12 to output signal S106. However, high gain slow shaping amplifier 118 has a greater gain than slow shaping amplifier 18. Also, high gain slow shaping amplifier 118 has a longer time constant than high gain fast shaping amplifier 113.

The high gain sample and hold device 119 is similar to the sample and hold device 19, and includes the output signal S106 of the high gain slow shaping amplifier 118 upon receiving the second high gain trigger signal S107 from the high gain TOT delay device 117. is held as a high gain sample value Sp101 and output to the high gain analog-to-digital converter 120.

High gain analog-to-digital converter 120 outputs a digital signal as a measurement representing the energy of the radiation.

The sample signal selector 30 selects the output signal S4 of the pulse height discriminator 14, the output signal S104 of the high gain pulse height discriminator 114, the output signal S7 of the TOT delay device 17, and the output signal S107 of the high gain TOT delay device 117. Receive input. When the sample signal selector 30 receives the output signal S4 of the pulse height discriminator 14, the sample signal selector 30 outputs the output signal S7 of the TOT delay device 17 as a sampling instruction signal to the sample hold device 19, and outputs the output signal S7 of the TOT delay device 17 as a sampling instruction signal. When the output signal S104 is present, the output signal S107 of the high gain TOT delay device 117 is outputted to the high gain sample and hold device 119 as a sampling instruction signal.

When the sample signal selector 30 receives the ON signal from both the pulse height discriminator 14 and the high gain pulse height discriminator 114, the sample signal selector 30 does not use the output signal S107 of the high gain TOT delay device 117, and selects the output signal of the TOT delay device 17. Preferably, S7 is output to sample and hold device 19. This means that a signal with a large gain has a relatively small discrimination threshold, and the pulse signal is not symmetrical, but the peak value of the signal is midway between the point where it begins to exceed the threshold and the point where it falls below the threshold. This is because it is more accurate to use the signal from the high-speed shaping amplifier 13 side, which has a relatively low gain.

According to this embodiment, when the output S2 of the preamplifier 12 is small, the output value of the high gain slow shaping amplifier 118 is sampled and a measured value is obtained by the analog-to-digital converter 20. On the other hand, when the output S2 of the preamplifier 12 is large, the output value of the slow shaping amplifier 18 is sampled and a measurement value is obtained by the high gain analog-to-digital converter 120. Therefore, it is possible to perform measurements over a wide measurement range.

As described above, according to the second embodiment, not only the same effects as the first embodiment can be obtained, but also measurements over a wider measurement range can be performed.

[Third embodiment]
FIG. 5 is a block diagram showing the configuration of a radiation measurement device according to the third embodiment. The radiation measuring device according to the third embodiment is a modification of the radiation measuring device according to the second embodiment, and the position where the sample signal selector 31 is connected is the same as that of the radiation measuring device according to the second embodiment. The sample signal selector 30 of FIG. That is, in this third embodiment, the output signal of the sample-and-hold device 19 and the output signal of the high-gain sample-and-hold device 119 are input to the sample signal selector 31, and the signals are input to the analog-to-digital converter 20 and the high-gain analog-to-digital converter 20. input to converter 120.

Further, the output signal S7 of the TOT delay device 17 is input to the sample and hold device 19, and the output signal S107 of the high gain TOT delay device 117 is input to the high gain sample and hold device 119. Furthermore, the output signal S4 of the pulse height discriminator 14 and the output signal S104 of the high gain pulse height discriminator 114 are input to the sample signal selector 31.

According to the third embodiment, similarly to the second embodiment, when the output S2 of the preamplifier 12 is small, the output value of the high gain low speed shaping amplifier 118 is sampled, and the analog-to-digital converter 20 converts the measured value. is obtained. On the other hand, when the output S2 of the preamplifier 12 is large, the output value of the slow shaping amplifier 18 is sampled and a measurement value is obtained by the high gain analog-to-digital converter 120. Therefore, it is possible to perform measurements over a wide measurement range.

[Fourth embodiment]
FIG. 6 is a block diagram showing the configuration of a radiation measurement device according to the fourth embodiment. The radiation measuring device according to the fourth embodiment is a modification of the radiation measuring device according to the third embodiment, and the position where the sample signal selector 32 is connected is the same as that of the radiation measuring device according to the third embodiment. The sample signal selector 31 is different from the sample signal selector 31 shown in FIG. That is, in this fourth embodiment, the output signals of the analog-to-digital converter 20 and the high-gain analog-to-digital converter 120 are input to the sample signal selector 32, and the output signal S4 of the pulse height discriminator 14 and the high-gain pulse height are input to the sample signal selector 32. The output signal S104 of the discriminator 114 is input to the sample signal selector 32. The output signal of the sample signal selector 32 is output as a measurement value by this radiation measuring device.

According to this fourth embodiment, similarly to the second and third embodiments, when the output S2 of the preamplifier 12 is small, the output value of the high gain slow shaping amplifier 118 is sampled, and the analog-to-digital converter 20 The measured value is obtained by On the other hand, when the output S2 of the preamplifier 12 is large, the output value of the slow shaping amplifier 18 is sampled and a measurement value is obtained by the high gain analog-to-digital converter 120. Therefore, it is possible to perform measurements over a wide measurement range.

[Other embodiments]
Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

11... Radiation detector, 12... Preamplifier, 13... High speed shaping amplifier, 14... Wave height discriminator, 15... Trigger generator (first delay device), 16... TOT measuring device (Threshold exceedance time measuring device) ), 17... TOT delay device (second delay device), 18... low speed shaping amplifier, 19... sample hold device, 20... analog digital converter, 30, 31, 32... sample signal selector, 113... high gain high speed Shaping amplifier, 114... High gain pulse height discriminator (wave height discriminator), 115... High gain trigger generator (trigger generator, first high gain delay device), 116... High gain TOT measuring instrument (TOT measuring instrument, high gain 117... high gain TOT delay device (TOT delay device, second high gain delay device), 118... high gain low speed shaping amplifier (low speed shaping amplifier), 119... high gain sample hold Device (sample hold device), 120...High gain analog-to-digital converter (analog-to-digital converter)

Claims (10)

a radiation detector that outputs a pulsed electrical signal by detecting radiation;
a preamplifier that integrates and amplifies the output of the radiation detector;
a high-speed shaping amplifier having a predetermined high-speed time constant, slowing the rise of the output of the preamplifier to hasten the subsequent return to the base state, and providing a predetermined gain;
a pulse height discriminator that outputs an on signal only when the output of the high-speed shaping amplifier exceeds a predetermined threshold;
a first delay device that outputs a first trigger signal after a predetermined first delay time after the wave height discriminator starts outputting the on signal;
a threshold exceedance time measuring device that measures the threshold exceedance time from when the wave height discriminator starts outputting an on signal until the output of the on signal ends;
The second trigger signal is delayed from the start time of the first trigger signal by a second delay time obtained by multiplying the threshold excess time by a predetermined additional delay ratio greater than zero and smaller than 1. a second delay device that outputs;
a low-speed shaping amplifier having a low-speed time constant longer than the high-speed time constant, slowing the rise of the output of the preamplifier to hasten the subsequent return to the base state, and providing a predetermined gain;
a sample hold device that holds and outputs the output of the low-speed shaping amplifier at the time when the second trigger signal is output;
A radiation measuring device characterized by having. The radiation measuring device according to claim 1, wherein the predetermined additional delay ratio is 0.3 or more and 0.7 or less. The radiation measuring device according to claim 2, wherein the predetermined additional delay ratio is 0.4 or more and 0.6 or less. The radiation measurement device according to any one of claims 1 to 3, further comprising an analog-to-digital converter that converts the output of the sample and hold device into a digital signal. A high-gain, high-speed device having a predetermined high-gain, high-speed time constant, slowing the rise of the output of the preamplifier to hasten the subsequent return to the base state, and providing a high gain larger than the gain of the high-speed shaping amplifier. a shaping amplifier;
a high gain pulse height discriminator that outputs an on signal only when the output of the high gain high speed shaping amplifier exceeds a predetermined threshold;
a first high gain delay discriminator that outputs a first high gain trigger signal after a predetermined first high gain delay time after the high gain pulse height discriminator starts outputting the on signal;
a high-gain threshold-exceeding time measuring device that measures a high-gain threshold-exceeding time from when the high-gain wave height discriminator starts outputting an on-signal to when outputting the on-signal ends;
Delaying from the start time of the first high gain trigger signal by a second high gain delay time obtained by multiplying the high gain threshold exceeding time by a predetermined high gain additional delay ratio greater than zero and smaller than 1. a second high gain delay separator that outputs a second high gain trigger signal;
It has a high gain slow time constant that is longer than the high gain fast time constant to slow the rise of the output of the preamplifier and hasten the subsequent return to the base state, and has a gain greater than the gain of the slow shaping amplifier. a high gain slow shaping amplifier that provides gain;
a high gain sample hold device that holds and outputs the output of the high gain low speed shaping amplifier at the time when the second high gain trigger signal is output;
The radiation measurement device according to any one of claims 1 to 4, further comprising: The radiation measuring device according to claim 5, further comprising a high gain analog-to-digital converter that converts the output of the high gain sample and hold device into a digital signal. One of the output of the low-speed shaping amplifier at the time when the second trigger signal is output, and the output of the high-gain low-speed shaping amplifier at the time when the second high-gain trigger signal is output. When the output of the low-speed shaping amplifier at the time when the second trigger signal is output is selected, a sampling instruction signal is output to the sample-hold device, and the second high-gain a sample signal selector capable of outputting a sampling instruction signal to the high gain sample and hold device when the output of the high gain low speed shaping amplifier at the time when the trigger signal is output is selected;
The radiation measuring device according to claim 5 or 6, further comprising: The sample signal selector selects the output of the low-speed shaping amplifier at the time when the second trigger signal is output, and the high-gain low-speed shaping amplifier at the time when the second high-gain trigger signal is output. 8. The radiation measuring device according to claim 7, wherein the sampling instruction signal is outputted only to the high gain sample and hold device when there are both outputs from the amplifier. a sample signal selector that selects and outputs only one of the output of the sample and hold device and the output of the high gain sample and hold device;
The radiation measuring device according to claim 5 or 6, further comprising: The sample signal selector selects the output of the low-speed shaping amplifier at the time when the second trigger signal is output, and the high-gain low-speed shaping amplifier at the time when the second high-gain trigger signal is output. 10. The radiation measuring device according to claim 9, wherein when there are both outputs of the amplifier, the output of the sample and hold device is selected and output.

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