JPH03185386A - Method for measuring radiation quantity using radiation detector - Google Patents

Abstract

PURPOSE:To measure a dose with high accuracy by flattening the energy characteristic of radiation and stabilizing the sensitivity of a detector constant by missing the pulse signal corresponding to the specific energy level of radiation in counting. CONSTITUTION:The radiation incident to a radiation detector 12 is detected as a pulse height signal. This pulse height signal is inputted to respective height discriminators 20, 22, 24 of low, medium and high energies through amplifiers 14, 16 and height values are compared on the basis of the respective cut energies (a), (b), (c) of respectively preset different low, medium and high levels. In this case, an energy characteristic loses buildup at 100 keV or less and a flattened characteristic can be obtained. By this constitution, the sensitivity of a detector can be kept constant in an entire energy region and desired radiation quantity can be measured with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a radiation dose measurement method, for example, Si (silicon)
, Ge (germanium) semiconductor (solid state) detector, proportional counter, GM counter, ionization chamber, etc. are used to detect the energy of the incident radiation particle, obtain a pulse signal corresponding to the energy, and calculate the number of pulses. The present invention relates to a radiation dose measurement method using a radiation detector that counts and measures the dose of radiation such as X-rays and gamma rays.

[Prior art] Measuring devices using semiconductor detectors are widely used in the JIIJ determination of radiation doses, and in particular, 5tSG
The radiation ray aIIj determination device that uses an e-semiconductor detector has features such as high energy resolution, good proportionality between energy and pulse height, and a small detection unit. Since the rise time of the current pulse is very short, it has the advantage of allowing rapid counting and locating the time of particle incidence, and is widely used for radiation dose measurement.

FIG. 5 shows a conventional radiation measurement device using such a Si semiconductor detector, and FIG. 6 shows energy characteristics related to sensitivity (response) and photon energy of the Si semiconductor detector. It is shown.

Hereinafter, the configuration and operation of a measuring device to which a conventional radiation dose measuring method is applied will be explained using FIGS. 5 and 6.

In the figure (the conventional measuring device includes a filter 10, a Si semiconductor detector 12, an amplifier 14, 16, and a pulse height discriminator 1).
8, a counter 20.

That is, the filter 10 first attenuates the low-frequency energy of the irradiated radiation, the radiation transmitted through the filter 10 is received by the Si semiconductor detector 12, and the S
The i-semiconductor detector 12 outputs a peak value signal having a peak value level corresponding to the radiation energy. Of course, as is well known, the count number of the peak value signal corresponds to the radiation dose.

In this way, radiation energy is detected by the detector 12, and the weak peak value signal output according to the energy level is raised to a predetermined level necessary for later signal processing by the amplifier 14.16. The amplitude is amplified. The amplified wave height value signal is then manually inputted to a wave height discriminator 18 which performs wave height discrimination at a wave height level corresponding to the low energy level (cut energy a) of the radiation.

As shown in the figure, for example, a comparator is used in this pulse height discriminator 18, and the pulse height value signal is inputted from one non-inverting input terminal (+) of the comparator, and the other inverting input terminal (-) The reference voltage Vs is manually applied from the variable resistor 18a through the variable resistor 18a.

By adjusting the variable resistor 18a, the wave height level at which the wave height is discriminated for noise cutting, that is, the position of the cut energy a in the low energy region shown in the figure is determined.

In this way, the wave height discriminator 18 for low energy
Then, due to the cut energy a, only the pulse signal corresponding to the wave height signal having the wave height level or higher is outputted. Therefore, the pulse signal is output according to the noise-cut low energy level that is higher than the wave height level, and the pulse signal is further counted by the counter 20 and the counting result is output and displayed. I can do it.

Next, the specific operation will be explained in detail using FIG. 6 below.

In the Si semiconductor detector 12, the filter 1
By injecting the desired radiation through 0, an interaction occurs inside the detector and part or all of the radiation particle energy is dissipated.

Here, the energy is converted into an amount of charge inside the detector, and is converted into a pulse height pulse, that is, the peak value signal, which uniquely corresponds to the energy of the particle, which is proportional to the amount of charge. As a result, a peak value signal corresponding to the energy of the radiation is output as a number of pulses corresponding to the dose.

By the way, the above-mentioned Si semiconductor detector 12 has a sixth
The radiation sensitivity (response) is as shown in the figure, and its energy characteristics include the above-mentioned interaction inside the detector.
Below 0 keV, the photoelectric effect shown by the dashed-dotted curve is
At 1QQkeV or more, the Compton effect shown by the dashed curve appears.

Therefore, in general, the energy characteristics are IQ Q
At lc e V or more, a relatively flat sensitivity characteristic is obtained as shown in the figure, but at 100 keV or less, the characteristic becomes sloped upward to the left as shown by a dashed-dotted line, and the sensitivity becomes excessively high.

For this purpose, in the past, as shown in FIG. 5, the intensity of the radiation entering 1 is limited by the filter 10, or the cut energy level a set by the wave height discriminator 18 is increased and adjusted. By doing this, the sensitivity is lowered from the dashed-dot line curve to the solid line curve shown in FIG.

As described above, in the conventional radiation dose 1lllJ determination device, the desired line Q fill can be determined using the circuit configuration shown in FIG.
A J-decision was being conducted.

[Problems to be Solved by the Invention] However, in the radiation dose measurement method using such a conventional semiconductor detector, as shown in FIG. A mountain-like swell inevitably remained in the response near the center of 75 keV, and for this reason the sensitivity was still high. As a result, the radiation dose in this energy region is measured to be higher than the actual dose.
There was a problem that highly accurate dose measurement was not possible.

That is, as mentioned above, this swelling occurs due to the influence of the photoelectric effect within the detector, but conventionally, the thickness of the filter 10 and the cut energy a in the low energy region by the wave height discriminator 18 are The swelling was attenuated simply by adjusting the position of.

However, with this method alone, the sensitivity may be reduced too much for a response of 1.0, or as shown in Figure 6, the sensitivity may not be reduced sufficiently and a peak may remain, or the energy characteristic may be flattened. It was difficult to do so.

In addition, with conventional measuring devices, it is difficult to flatten the energy characteristics as described above, so generally the line mAp1
For radiation management purposes, it was necessary to set the sensitivity so that the fixed value was measured to be higher than the actual dose, rather than being measured to be lower than the actual dose.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to flatten the energy characteristics of radiation by counting down pulse signals corresponding to the specific energy level in a specific energy range of radiation. The object of the present invention is to provide a method for measuring radiation dose using a radiation detector, which stabilizes the sensitivity of the detector to a constant value and thereby enables highly accurate dose measurement.

[Means for Solving the Problems] In order to achieve the above object, according to a radiation dose measuring method using a radiation detector according to the present invention, the energy of the radiation emitted is detected and the energy level is determined. a first radiation detection step that outputs a predetermined peak value signal corresponding to the low energy level of the radiation;
The wave height is discriminated based on the wave height level and corresponds to the wave height value signal that is higher than the first wave height level. t'l J - A second wave height value discrimination step of performing wave height discrimination on the wave height value signal at a second wave height level corresponding to the intermediate energy level of the radiation and outputting a pulse signal corresponding to the wave height value signal that is equal to or higher than the second wave height level. a third wave height value discrimination step of discriminating the wave height of the wave height signal at a third wave height level corresponding to the high energy level of the radiation and outputting a pulse signal corresponding to the wave height value signal equal to or higher than the third wave height level; Except for pulse signals corresponding to wave height signals between the second wave height level and the third wave height level, waves that are higher than the first wave height level, lower than the second wave height level, and higher than the third wave height level The method is characterized by comprising a pulse signal selection step of selecting only pulse signals corresponding to high value signals.

[Function] With the above configuration, the features 1 of the present invention are achieved. According to the radiation dose measurement method using a radiation detector, among the detected pulse signals, the second wave height level corresponding to the medium energy level of the radiation and the second wave height level corresponding to the high energy level are determined by the pulse signal selection step. No.') &t 1. Aa+l-L
Speak M nrlm-d-1%EL I-'r) rr
-J-71%# II It is possible to flatten the energy characteristics of the radiation in the radiation detection step except for the signal.

As a result, by counting the pulse signals selected in the pulse signal selection step, it is possible to measure the radiation dose with high precision based on the counting results.

[Example] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 is a circuit configuration diagram of a measuring device to which the radiation dose measuring method according to the present invention is applied.

Note that the same members as in FIGS. 5 and 6 are designated by the same reference numerals, and descriptions of the structure and operation will be omitted below.

A characteristic feature of the present invention is that the pulse signals corresponding to the wave height signals between the second wave height level and the third wave height level are counted down, and the pulse signals corresponding to the wave height values below the second wave height level and those above the third wave height level are counted down. The purpose of this method is to obtain flattened energy characteristics that keep the sensitivity of the radiation detector constant by counting only the pulse signals corresponding to the peak value signals.

Hereinafter, the circuit configuration of this embodiment will be explained in detail using FIG.

In the figure, "a measuring device to which the dose measuring method according to the present invention is applied has a pulse height discriminator 18 for medium energy levels in addition to a pulse height discriminator 18 for low energy levels, compared to the conventional measuring device shown in FIG. 5 described above. 22 and a pulse height discriminator 24 for high energy level are connected in parallel, and the pulse signals output from each of the pulse height discriminators 20, 22, and 24 are inputted to correspond to a peak value signal at a predetermined pulse height level. The pulse signal selection circuit 26 selects only the pulse signals to be used.

That is, in FIG. 1, the radiation incident on the radiation detector 12 is detected as a peak value signal as described above.

Then, this peak value signal is passed through the amplifier 14.16 to each of the low, medium, and high energy pulse height discriminators 20.2.
2.24, and the peak values are compared for each cut energy a, b, and c at different preset low, middle, and high levels. Then, it is converted into pulse signals ASB and C corresponding to the peak value signals having respective energy levels or higher.

Here, the converted pulse signals A, B, and C each correspond to the amount of energy consumed within the detector, and the pulse signals are output according to the low, middle, and high wave height discrimination level. .

Then, each of the discriminated pulse signals is inputted to the pulse signal selection circuit 26, where the pulse signals having a low level or higher, except for the pulse signal corresponding to a peak value signal between the high level and the medium level, are input to the pulse signal selection circuit 26. Then, only the pulse signal corresponding to the wave +Q+ (n signal) between the high level and above and the middle level and below is selected.

That is, if the energy level consumed in the detector due to the interaction is greater than the medium level and less than the high level, the pulse signal is not output; otherwise, e.g. One pulse signal is selectively output for each.

This will later result in not counting only the pulse signals corresponding to peak value signals between the high level and the medium level.

As shown in FIG. 3, this selection circuit 26 is composed of two delay circuits 130, 1132, a one-shot circuit 34, and an AND circuit 36. Pulse signals A and BSC, which are differentiated by level, are input.

Here, the signal A is input to the delay circuit 130, delayed for a predetermined time, and synchronized so that the signal A is within the pulse width of the signal output from the one-shot circuit 34.

On the other hand, the signal B is manually input to the one-shot circuit 34 via the delay circuit 1132 after being delayed for a predetermined time.
A signal C is input as a reset signal to this one-shot circuit 34, and here, the falling edge of the signal B is input to the signal C.
The timing is synchronized to the timing within the pulse width of .

iW , 7 1i 8 r M thick X nl
= 1- 1+ nsef:) ``1'ノX
The i-L circuit 34 is reset and does not operate (however,
A one-shot signal is output by Q), thereby,
Signal A will pass through AND circuit 36 and be output.

Furthermore, when there is no signal C, the one-shot circuit 34 is not reset and operates; however, the one-shot signal is not output due to Q), and the AND circuit 36 is inhibited for a certain period of time, so that the signal A is not output. become.

Next, the mechanism by which the energy characteristics of the detector are flattened by the pulse signal selection circuit 26 will be explained in detail using the characteristics shown in FIG.

FIG. 4(a) is an energy characteristic diagram of 100 keV or less, and FIG. 4(b) is a radiation energy spectral distribution in the energy region of 100 keV or less.

As shown in the figure, the cut energy levels corresponding to each low, medium and high wave height discrimination level are represented by a, b, and c, and the spectral distributions d, e, and f are the spectral wave heights corresponding to specific radiation energy, respectively. distribution.

The combined characteristics of the distributions d, e, and f correspond to the mountain-like curve shown by the broken line in FIG. 4(b), which is the same as the characteristic shown by the solid line in FIG. 4(a). It is understood that

This wave height distribution is dominated by the photoelectric effect in the energy region below 100 keV, and is originally a line spectrum, but it is recognized that the distribution width is broadened due to noise in the circuit system such as the detector and amplifier. .

In other words, in the present invention, this broadening of the distribution width is utilized, and pulse signals corresponding to the cut energy levels b and C shown in FIG. 4(b) are not counted. The energy distribution of radiation e
This made it possible to reduce the sensitivity of the detector to

In other words, this results in a flattened energy characteristic shown by the dashed line in Figure 4(a), but not counting the signal between energy levels b and C means that the shaded area is cut in terms of area. spectral distribution e
For spectral distribution d, a small portion of the right end of the distribution width is cut, and for spectral distribution f, a very small portion of the distribution width and end is cut off.

Therefore, the cut portions of the distributions d, e, and f are the fourth
Arrows d-, e-, f-1 in figure (a). : This corresponds to a decrease in sensitivity by the amount shown, and as a result, the energy characteristics are flattened (characteristics shown by the - dotted chain line).

Note that the degree of sensitivity reduction is determined by b-c of the energy distribution.
This is possible by varying the width between b and c, and the energy distribution e of radiation close to the width between b and c becomes remarkable, and the energy distribution of radiation η・1 line far from the width between b and c The energy distribution dSf becomes gentler as the spectrum broadens.

For example, the energy level b is 70 keV,
The energy level C is set to 80 keV as the optimum level, and therefore the width between b and c is set to 101 ceV.

As described above, the pulse signal B is not selected, whereas the pulse signal A is selected.

C is manually counted by the counter 20, but in order not to count only the signals below the pulse signal C and above the pulse signal B, the energy characteristic is 100 as shown in FIG. Below k e V, the bulge disappears and flattened characteristics are obtained.

Furthermore, in FIG. 4(C), 100keV to 300keV
The energy spectral distribution in the V range is shown, and in FIG. 4(d) the energy spectral distribution above 300 keV is shown.

That is, this high energy, region shown in the figure −
In this case, the Compton effect is the main interaction, and the photoelectric peak characteristic of the photoelectric effect below 100 keV as shown in Figure 4 (b) does not occur, and the radiation spectrum is distributed over a very wide range. I understand that. Therefore, as can be seen from the energy characteristics shown in FIG. 2, relatively flat characteristics are obtained above 30 QkeV.

Therefore, it is understood that in this high energy region, even if the pulse signals between the cut energy levels b and c are not counted, the dependence ratio is extremely small and there is no influence at all.

As described above, according to the method for measuring Group 14 doses according to the present invention, as shown by the dashed line in FIG. It is understood that it has been improved and leveled out. This makes it possible to maintain the sensitivity of the detector constant in the entire energy range, and it is possible to determine all the desired radiation levels at once.

[Effects of the Invention] As described above, according to the radiation dose measurement method using the radiation detector according to the present invention, it is possible to obtain flatter energy characteristics over the entire energy range than the conventional radiation energy characteristics. This enables highly accurate dose measurement.

As a result, the radiation of the present invention! ! According to the j1m measurement method, the measurer can take appropriate measures based on the dose measurement data.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram to which a radiation dose measurement method using a radiation detector according to the present invention is applied, and FIG. 2 is a characteristic showing sensitivity-energy characteristics of the radiation detector according to the present invention. 3 is an explanatory diagram showing the circuit configuration of an example of the pulse signal selection circuit according to the present invention, and FIG. 5 is a circuit configuration diagram to which a conventional radiation dose measurement method using a radiation detector is applied. FIG. 6 is a characteristic diagram showing the sensitivity-energy characteristics of a conventional radiation detector. It is. 12 ... Si semiconductor detector 18 ... Wave height discriminator 22 ... Wave height discriminator 24 ... Wave height discriminator 26 ... Pulse signal selection circuit 30 ... Delay circuit 32 ... Delay circuit 34 ... One-shot circuit 36 ... AND circuit a ... U (level cut energy b ...
Medium level cut energy C... High level cut energy d... Low level wave height needle -/li e... Medium level wave height distribution f... High level wave height needle/Ii A, B, C... Pulse signal.

Claims (1)

[Claims] (1) Radiation detection that obtains a predetermined peak value signal according to the energy of the radiation to be detected, discriminates the peak value signal based on a specific level of radiation energy, and measures the dose by counting the discriminated signals. A radiation dose measurement method using a radiation detector includes a radiation detection step of detecting the energy of irradiated radiation and outputting a predetermined peak value signal according to the energy level, and converting the peak value signal into a low energy level of the radiation. a first wave height value discrimination step of discriminating the wave height at a first wave height level corresponding to the first wave height level and outputting a pulse signal corresponding to the wave height value signal that is equal to or higher than the first wave height level; a second wave height value discrimination step of discriminating the wave height at a second wave height level and outputting a pulse signal corresponding to the wave height value signal equal to or higher than the second wave height level; a third wave height value discrimination step of discriminating wave heights at three wave height levels and outputting a pulse signal corresponding to a wave height value signal equal to or higher than the third wave height level; and a wave height value between the second wave height level and the third wave height level. A pulse signal selection step of selecting only pulse signals corresponding to peak value signals that are higher than the first wave height level, lower than the second wave height level, and higher than the third wave height level, excluding pulse signals corresponding to high value signals. A radiation dose measurement method using a radiation detector, comprising: counting the pulse signals selected in the pulse signal selection step to perform highly accurate dose measurement.