JPH02157680A - Radiation measuring instrument - Google Patents

Abstract

PURPOSE:To discriminate the energy of each pulse by resetting an integrating means which integrates a pulse signal outputted by a sensor with the output signal of a gate control means. CONSTITUTION:The pulse signal outputted by the sensor 1 is inputted to a charge type preamplifier 2 and the amplifier 20 of a pulse detection part 15. The charge type preamplifier 2 integrates and outputs the pulse signal from the sensor 1. In this case, the pulse detection part 15 and a gate control circuit 14 for discharging are provided and then the integral signal outputted by the charge type preamplifier 2 is reset forcibly a constant time tauD1 after the falling signal of the signal outputted by the pulse detection part 15, so that integrated charges are discharged without resetting in the middle of the integration. Consequently, a pulse with a crest value corresponding to the energy of incident radiation is obtained. Energy discrimination is therefore performed continuously, radiation by radiation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a radiation measurement device used for medical and nuclear radiation measurement and diagnostic equipment that requires measurement of dose rates over a wide range, and non-destructive inspection in industrial measurement. It is something.

In conventional technology radiation measurement devices, the signal output from the radiation-sensitive sensor is a very weak signal, which needs to be amplified by a preamplifier. These preamplifiers include voltage type preamplifiers and charge type preamplifiers.

A voltage preamplifier generates an output voltage proportional to the voltage wave height of the pulse signal output from the sensor, so if the pulse width of the pulse signal output from the sensor and the input capacitance are constant, the input capacitance is constant. It produces an output proportional to the charge Q due to the radiation.

However, if the pulse width or input capacitance changes, this proportional relationship no longer holds, which is not very preferable.

In addition, charge type preamplifiers are not affected much by input capacitance and output by integrating the pulse signal output from the sensor, so the output voltage is equal to the total integrated charge of the pulse signal applied to the input terminal. It will be proportional.

FIG. 7 shows a conventional radiation measuring device using a charge type preamplifier, and FIG. 8 shows output signals of its main parts.

FIG. 7(a) shows a method called the integral method, and 1 is a sensor, which is a semiconductor detector made of a radiation-sensitive semiconductor such as St or Ge. Outputs a pulse signal like this. Reference numeral 2 denotes a charge type preamplifier, which produces an output voltage proportional to the total integrated charge of the pulse signal from the sensor 1, as shown in FIG. 8(b). 3 is a sample hold, which holds the peak value of the integrated output voltage. 4 is an A/D converter.

In the conventional radiation measurement device configured as described above using the integral method, the pulse signal output from the sensor is integrated and output, and the peak value of the output voltage is converted into a digital signal by an A/D converter. and output.

On the other hand, FIG. 7(b) shows a method called the counting method, in which l is a sensor, 2 is a charge-type preamplifier, and 5 is a differentiating circuit, which differentiates the output signal of the charge-type preamplifier and calculates the 8
As shown in Figure (c), each pulse signal is output as a pulse with a wave height corresponding to its energy. however,
In this case, the pulse width of the pulse signal output from the sensor must be constant. 6 is an amplifier, which is a buffer for driving the next stage circuit. 7 is a pulse stretcher, which is a circuit that holds the peak value of the output signal of the amplifier 6 for a certain period of time. 4 is an A/D converter.

In the radiation measuring device using the conventional counting method configured as described above, the pulse signal output from the sensor 1 is integrated and output, and this output signal is differentiated to obtain the pulse signal output from the sensor 1. When the pulse width is constant, it is separated as a pulse with a wave height corresponding to the energy, the peak value of the pulse is held, A/D converted, and output as a digital signal.

Problems to be Solved by the Invention However, in the configuration of the integral method described above, since the sensor output is integrated and output, it is not possible to obtain information about the total dose of radiation incident within a certain period of time. Therefore, it is not possible to obtain information about the energy of each photon incident as radiation.

Next, in the counting method, since the integrated output value of the charge type preamplifier is differentiated, outputs with different pulse heights may occur even if the amount of charge is the same.

This process is shown in FIG. 9. FIG. 9(a) shows the waveform output from the sensor 1 as a rectangular wave.

At this time, consider a case where pulses having the same amount of charge Q but different sizes occur. FIG. 9(b) shows waveforms obtained by integrating the respective waveforms in FIG. 9(a).Since the amount of charge Q of the two waveforms is equal, the integral values are equal. However, when we then differentiate this, the rate of increase in the integral value is output,
The waveform shown in FIG. 9(c) is the same as the amplified waveform of FIG. 9(a), and pulses with different wave heights are output even though the amount of charge is the same.

Therefore, with the integral method, it is not possible to obtain information on the energy of each photon incident as radiation, and with the counting method, even if pulses with the same amount of charge are generated, pulses with different wave heights are output. The problem was that it was not possible to discriminate the energy of each pulse.

In view of this, an object of the present invention is to provide a radiation measuring device that can discriminate the energy of each photon energy incident as radiation.

Means for Solving the Problems The present invention provides a sensor sensitive to radiation, an integrating means for integrating a pulsed output signal from the sensor, and a pulse detection means for detecting the pulsed output signal from the sensor. detection means for detecting the falling or rising edge of the pulse; gate control means for outputting a signal for resetting the integrating means after a certain period of time from the falling edge or rising edge of the pulse; and a pulse height discriminator for discriminating the pulse height of the output of the integrating means. A radiation measuring device is provided with a counting means for counting the output from the wave height discriminating means, and a clocking means for controlling the time width of the counting means.

According to the above-described configuration, the present invention detects the pulse signal output from the sensor by the pulse detection means, and detects the pulse signal output from the sensor by the output signal from the gate control means output after a certain period of time from the fall or rise of the pulse. By resetting the integrating means that integrates the pulse signal, the energy of each pulse can be discriminated.

Embodiment FIG. 1 shows a block diagram of a radiation measuring apparatus which is an embodiment of the present invention. In FIG. 1, numeral 1 denotes a sensor, such as a semiconductor detector, which outputs a pulse signal with a charge Q proportional to the energy of photons of incident radiation.

2 is a circuit that integrates and outputs the pulse signal from the sensor, and is a charge-type preamplifier that can be reset from the outside to forcibly discharge the integrated charge. 10 is a circuit that discriminates the integrated output value by pulse height. A comparator 11 is a counter for counting waveforms subjected to wave height discrimination, and 12 is a display section for displaying the digital signal in the counter as an image or the like. 13 is a timer for determining the period during which the counter takes in data. 14 is a discharge gate control section for applying a reset signal to the charge type preamplifier 2 to discharge the charge. 15 is a pulse detection unit that detects the presence or absence of a pulse output from the sensor 1.

The operation of the radiation measuring device of this embodiment configured as described above will be described below. The discharge time constant of the back-type preamplifier must generally be very large, several μs.
ec or more is required, but by providing a reset signal for this, a pulse with a narrow pulse width of 100 nsec or less can be extracted. At this time, the output signal from sensor 1 is shown in Figure 2 (a), and the output signal from the charge type preamplifier is shown in Figure 2 (b). There are two types of discharge gate control circuit 14 and pulse detection circuit 15 shown in FIGS. 3 and 5, and timing charts of their operations are shown in FIGS. 4 and 6, respectively.

First, in FIG. 1, the portion indicated by the broken line will be described for type 1 operation in which signal processing is performed by detecting a falling edge as shown in FIG. The pulse signal output from the sensor 1 is input to the charge type preamplifier 2 and the amplifier 20 of the pulse detection section 15. The charge type preamplifier 2 integrates and outputs the pulse signal output from the sensor 1.

The pulse detection section 15 is composed of an amplifier 20 and a comparator 21.
Detects the pulse signal output from the The output signal of the comparator 21 at this time is shown in FIG. 4(b), and this signal is then input to the discharge gate control section 14. The discharge gate control section 14 includes a delay circuit 22, a falling detection circuit 23, and a monomulti 24. The output signal from the comparator 21 of the pulse detector 15 is sent to the delay circuit 2.
2 and is output with a delay of time τD1.

The output signal of this delay circuit 22 is shown in FIG. It is input to the multi 24. mono multi 2
The pulse width of the pulse signal outputted by the charge type preamplifier 2 needs at least enough time to discharge all the integrated charge when the charge type preamplifier 2 is reset. However, since the discharge time is instantaneous by reducing the on-resistance of the transistor serving as the discharge path, there is no problem. Figure 4(d) shows the output signal of the monomulti 24. The output signal is input to the charge type preamplifier 2 as a reset signal. The output signal of the charge type preamplifier 2 at this time is shown in FIG. The energy of the radiation can be discriminated by discriminating the wave height using the comparator 10 in the next stage, and only the radiation whose energy exceeds the comparison potential of the comparator 10 is output as a pulse signal. This pulse signal is sent to the counter 11
, and calculate the number of radiation whose energy exceeds the comparison potential. At this time, the time width in which the grain counter 11 performs counting is determined to be a constant time by the timer 13. Finally, the value counted by the counter 11 is output on the display section 12.

As described above, according to this embodiment, since the integrated amount of the signal output from the sensor 1, that is, the amount of charge is measured, the sensor 1 is charged with the amount of charge Q, which is proportional to the energy of the incident radiation.
In addition, by providing the pulse detection section 15 and the discharge gate control section 14, the integrated signal output from the charge type preamplifier 2 can be output from the pulse detection section 15. Since the signal is forcibly reset to τD1r& for a certain period of time from the falling edge of the signal, the integrated charge can be discharged without being reset in the middle of integration. Therefore, it is possible to obtain a pulse with a wave height corresponding to the energy of each incident radiation. Therefore, it is possible to construct a charge amplification type radiation measuring device that can continuously perform energy discrimination of each radiation.

Next, FIG. 6 shows a timing chart for explaining type 2 operation in which signal processing is performed by detecting a rise in the portion indicated by a broken line in FIG. 1 as shown in FIG. 5. The output signal from the amplifier 20 in the pulse detection section 15 is shown in FIG. 6(b).Subsequently, this signal is input to the discharge gate control section 14. The discharge gate control section 14 includes a delay circuit 22, a rise detection circuit 23, and a monomulti 24. Delay circuit 2
The output waveform of the comparator 21 is shown in FIG. 6(c), where the output signal from the comparator 21 is output with a delay of τ02.

Subsequently, the rising edge detection circuit 30 detects the rising edge of the output signal of the delay circuit 22 shown in FIG. 6(c), and in synchronization with this, the monomulti 24 outputs a constant pulse. The pulse signal output from the monomulti 24, whose waveform is shown in FIG. 6(d), is input to the charge type preamplifier 2 as a reset signal for the charge type preamplifier 2.

FIG. 6(e) shows the output waveform of the charge type preamplifier 2.
The subsequent signal processing is the same as that described above, and will therefore be omitted.

As described above, according to this embodiment, since the integral amount of the signal output from the sensor 1, that is, the amount of electric charge is measured, the sensor 1 has an amount of electric charge Q that is proportional to the energy of the incident radiation.
In addition, by providing the discharge gate control section 14 and the pulse detection section 15, the integrated signal output from the charge type preamplifier 2 can be converted into a signal output from the pulse detection section 15. In order to force a reset after a certain period of time τD2 from the rising signal of , it is possible to cut the subsequent radiation when a pile-up occurs. Furthermore, since the pulse width of the output pulse is constant, stable pulses can be obtained. Therefore, it is possible to construct a radiation measuring device that is of a charge amplification type and can continuously perform energy discrimination for each radiation.

As described in detail, according to the present invention, as long as the sensor generates an amount of charge proportional to the energy of incident radiation, it is possible to discriminate energy even if the output pulse width changes. It is possible to construct a radiation measuring device with a high degree of practicality, and its practical effects are great.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a radiation measuring device according to an embodiment of the present invention, Fig. 2 is an operation waveform diagram of the same embodiment, and Fig. 3 is a block diagram of a pulse detection unit that detects a falling edge and a discharge gate control unit. Figure 4 is an operating waveform diagram when detecting a falling edge, Figure 5 is a block diagram of the pulse detector and discharge gate control unit that detects a rising edge, and Figure 6 is an operating waveform diagram when detecting a rising edge. 7 is a block diagram of a conventional radiation measuring device, FIG. 8 is an operational waveform diagram of the conventional radiation measuring device, and FIG. 9 is an explanatory operational waveform diagram. l...Sensor 2...Charge type preamplifier, 20...Amplifier, 10.21...
・Comparator, 11...Counter, 12...
... Display section, 13 ... Timer 14 ...
...Discharge gate control section, 15...Pulse detection section, 22...Delay circuit, 23...
Falling detection circuit, 24... Mono multi, 3
0...Rise detection circuit. Name of agent Patent attorney Shigetaka Awabi and one other person τp □ Seset Figure 9 Figure 9

Claims (2)

[Claims] (1) a sensor sensitive to radiation, an integrating means for integrating a pulsed output signal from the sensor, and a pulse detection means for detecting the pulsed output signal from the sensor;
detection means for detecting a falling edge of a pulse; gate control means for outputting a signal for resetting the integrating means after a predetermined period of time after the falling edge of the pulse; pulse height discriminating means for discriminating a pulse height of the output of the integrating means; A radiation measuring device comprising: a counting means for counting the output from the discriminating means; and a time measuring means for controlling the time width of the counting means. (2) a sensor sensitive to radiation, an integrating means for integrating a pulsed output signal from the sensor, and a pulse detection means for detecting the pulsed output signal from the sensor;
detection means for detecting the rising edge of a pulse; gate control means for outputting a signal for resetting the integrating means after a predetermined period of time after the rising edge of the pulse; pulse height discriminating means for discriminating the pulse height of the output of the integrating means; and the pulse height discriminating means. 1. A radiation measuring device comprising: a counting means for counting the output from the counting means; and a clock means for controlling the time width of the counting means.