JP3153434B2 - Radiation dosimeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation dosimeter used for radiation exposure control of workers such as radiation handling facilities, and more particularly to a radiation dosimeter.
The present invention relates to a portable radiation dosimeter for measuring the dose of radiation.

[0002]

2. Description of the Related Art In radiation handling facilities such as nuclear power plants, it is important to control personal exposure. A so-called pocket dosimeter is known as an apparatus for managing such individual exposure. The worker wears the pocket dosimeter on clothes or the like when entering the radiation control area. Thereby, the worker can know the dose (dose equivalent: Sv) exposed during the work.

As such a pocket dosimeter, in addition to a conventional type using an ionization chamber, in recent years, a device using a semiconductor detector having high sensitivity and easy to miniaturize has been widely used.

[0004] The dose equivalent is a quantity indicating the effect of radiation on a living body. According to laws and ordinances, a dose equivalent to 1 cm dose equivalent, 3 mm dose equivalent and 70 mm
Three dose equivalents of μm dose equivalent have been introduced. The dose equivalent is obtained by multiplying the absorbed dose by a quality factor and other correction factors depending on the type and energy of the radiation. The 1 cm dose equivalent is a dose equivalent at a depth of 1 cm of an ICRU sphere simulating the body, and 3 mm and 70 μm dose equivalents are similarly defined.

[0005] Among various radiations, β-rays are mainly related to the exposure of the skin, and 70 μm
Dose equivalents are used.

FIG. 4 is a block diagram showing the structure of a conventional β-ray dosimeter using a semiconductor.

In FIG. 1, a detector 10 comprises a semiconductor detector 10a and a thin aluminized mylar film (hereinafter abbreviated as a mylar film) 10b which covers the semiconductor detector 10a. The detection unit 10 is housed in a resin case 19. An entrance window is provided in the resin case 19, and the detection unit 10
Are arranged with the sensitive surface side facing the entrance window. The mylar film 10b is a light-shielding conductive film formed by evaporating aluminum on mylar,
0a is provided for light shielding and electrostatic shielding. The resin case 19 is provided to protect the detection unit 10 and a circuit for signal processing described later.

An amplifier 12 for amplifying an output signal is connected to the semiconductor detector 10a, and a wave height discriminator 14 is connected to the amplifier 12. This wave height discriminator 14 is for removing noise on the low energy side, and discriminates only pulses having a predetermined cut energy value or more called a discrete level from output pulses of the amplifier 12 and outputs the pulses to a counter 16 at a subsequent stage. Output. Then, the counter 16 counts the output pulses of the wave height discriminator 14, and the counting result is digitally displayed on the display 18.

FIG. 5 shows the energy characteristics of such a β-ray dosimeter of FIG. In FIG. 5, the horizontal axis is β
Maximum energy MeV line (effective energy) and the vertical axis response - shows the ^{90 Sr-Y sensitivity ratio 70μm dose equivalent when the sensitivity to β-rays (1.4 MeV) of (strontium yttrium) was 1} I have.
That is, the response is the ratio of the indicated value of the β-ray dosimeter in FIG. 4 to the true value of the 70 μm dose equivalent,
It depends on the energy of the line. As shown in FIG.
In a conventional β-ray dosimeter, the response for β-rays of 0.2 MeV or more is in the range of 0.8 to 1.2, and although the sensitivity of low energy is slightly low, the 70 μm dose of β-rays is fairly accurate. The equivalent could be determined.

[0010]

In this conventional β-ray dosimeter, the sensitive surface side of the detection unit 10 is exposed from the entrance window of the resin case 19 to the outside, so that this detection device There is a possibility that the semiconductor detector 10a may be damaged when the object is hit against a peripheral object. Further, even if the semiconductor detector 10a is not directly damaged by such an impact, the dose may be erroneously evaluated due to erroneous counting due to light leakage only by damage or damage to the mylar film 10b. was there.

As a method of solving this problem, a method of covering the entrance window (that is, the sensitive surface side of the detection unit 10) with a resin case without exposing the detection unit 10 can be considered. However, since β-rays have a low penetrating power, if the entrance window is covered with a resin case for protection, a part of the β-rays that should enter the detection unit 10 is blocked by the resin case. Therefore, the dosimeter in which the sensitive surface side of the detection unit is covered with the resin case has the same β
Even if a line is received, the count value becomes smaller than that of a dosimeter in which the sensitive surface side of the detection unit is not covered, and the sensitivity (response) is reduced. In this case, the incident β-ray is more likely to be blocked as the energy is lower, so that the lower the energy β-ray, the lower the response of the dosimeter is, and the indicated value of the dosimeter is a small value far from the true 70 μm dose equivalent. I will. As described above, if the detection unit is covered with the resin case, the energy characteristics of the β-ray dosimeter deteriorate, and
There is a problem that the μm dose equivalent cannot be obtained.

The present invention has been made in order to solve such a problem, and it is intended to prevent a detector from being damaged and to compensate for a decrease in sensitivity to low energy β-rays to obtain any energy. It is an object of the present invention to provide a radiation dosimeter capable of obtaining an accurate 70 μm dose equivalent even for β-rays.

[0013]

In order to achieve the above-mentioned object, a radiation dosimeter according to the present invention comprises two detectors having different energy characteristics and each of the detectors,
A case having a protective plate for preventing damage that covers the sensitive surface side of each of the detection units, and a counting unit that separately counts output signals of each of the detection units and obtains a count value for each of the detection units, Incident β based on the ratio between the count values of the respective detection units
Find the energy of the wire and based on the energy found
An arithmetic processing unit for calculating the dose equivalent by compensating for the sensitivity drop caused by the protection plate .

In the radiation dosimeter according to the present invention, the arithmetic processing unit may include an energy characteristic table indicating the energy characteristics of each of the detection units covered with the protection plate, and a count value for each of the detection units. From the ratio of the energy characteristic table, an energy calculation unit that calculates the energy of the incident β-ray based on the energy characteristic table, a sensitivity calculation unit that calculates the sensitivity of the detection unit at the calculated energy based on the energy characteristic table, A dose equivalent calculation unit for correcting the count value of the detection unit according to the obtained sensitivity and obtaining a dose equivalent.

[0015]

In the radiation dosimeter according to the present invention, the detection surface is covered with a protective plate to prevent the damage of the detection unit, and at the same time, the low energy β-ray due to the detection unit being covered with the protective plate. The sensitivity drop is corrected by using two detectors having different energy characteristics.

That is, even if the sensitivity is lowered, if the value of the lowered sensitivity can be obtained, the measured value at that time is corrected using the sensitivity to obtain the true value (that is, the value when the sensitivity is 1). Dose equivalent value). In addition, since the sensitivity of the detection unit itself depends on the energy of the incident β-ray, if the energy of the incident β-ray can be obtained, the sensitivity of the detection unit can be obtained from this energy. Therefore, in the present invention, two detectors are provided, the energy of the incident β-ray is obtained from the ratio of the count values of the detectors, and one of the two detectors (or both may be used) according to the energy value.
Is obtained, and the count value is corrected using this sensitivity to obtain a correct dose equivalent.

Since the two detectors have different energy characteristics from each other, if the two detectors simultaneously perform detection, their respective count values will differ. Since the count value of each detection unit is proportional to the sensitivity and the sensitivity of each detection unit is proportional to the energy, the energy of the incident β-ray can be obtained from the mutual ratio of the count values of each detection unit.

As described above, according to the present invention, two detectors having different energy characteristics are provided, the energy of the incident β-ray is specified from the ratio of the count values of these two detectors, and the energy of the detector is determined from the obtained energy. The sensitivity is obtained, and the count value is corrected based on the sensitivity to obtain a correct dose equivalent.

In the present invention, the relationship between the energy of the incident β-ray and the sensitivity of the detection unit is obtained in advance by experiments or the like, and this is stored as an energy characteristic table. Then, the energy calculating unit calculates the energy of the incident β-ray by comparing the ratio between the count values of the two detecting units with this table. Then, the sensitivity calculation unit obtains a sensitivity corresponding to the obtained energy from the energy characteristic table. This sensitivity is sufficient if it is determined for one of the two detectors. Then, the dose equivalent calculation unit,
The dose equivalent is calculated by correcting the count value of the detection unit for which the sensitivity was determined based on the sensitivity determined in this manner.

The difference between the energy characteristics of the two detectors can be set depending on the presence or absence of a filter.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the radiation dosimeter according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a radiation dosimeter according to the present invention.

The radiation dosimeter shown in FIG.
And 30. The detection section 20 is composed of a semiconductor detector 20a and a thin aluminized mylar film 20b covering the same, similarly to the detection section of the conventional device of FIG.
On the other hand, the detection unit 30 includes a semiconductor detector 30a and an aluminized mylar film 30b.
The thin filter 30c (for example, having a thickness of 0.3 mm) made of a light metal such as aluminum, mylar, or the like provided on the sensitive surface side of FIG.
1 mm). In this embodiment, the sensitive surfaces of the semiconductor detectors 20a and 30a have a size of about 3 mm × 3 mm.

As described above, the two detection units 20 and 30
The energy characteristics for β-rays differ depending on the presence or absence of the filter.

The β-rays transmitted through the entrance window protection plate 70a of the resin case 70 and having a low energy region attenuated are detected by the semiconductor detector 20a and converted into pulse signals.
An amplifier 22 is connected to the semiconductor detector 20a,
The detection signal of the semiconductor detector 20a amplified by the amplifier 22 is input to a wave height discriminator 24 connected to the subsequent stage of the amplifier 22. The wave height discriminator 24 is for removing noise on the low energy side. The wave height discriminator 24 discriminates only pulses having a predetermined level or more from the output pulses of the amplifier 22 and outputs the pulses to the counter 26 at the subsequent stage. The counter 26 counts the detection signal from which the peak has been discriminated.

The entrance window protection plate 70 of the resin case 70
The β-rays that have passed through a and have been attenuated in the low energy region are further attenuated by the filter 30c,
a and is converted into a pulse signal. Semiconductor detector 3
0a is connected to an amplifier 32. The output signal of the semiconductor detector 30a amplified by the amplifier 32 is supplied to the amplifier 3a.
The signal is input to a wave height discriminator 34 connected to the second stage. The wave height discriminator 34 is for removing noise on the low energy side, and discriminates only pulses having a predetermined level or more from the output pulses of the amplifier 32 and outputs the pulses to the counter 36 at the subsequent stage. The counter 36 counts the detection signal from which the peak has been discriminated.

Based on the count values (integrated values) of the counters 26 and 36, the counters 26 and 36 store
An arithmetic processing unit 40 for calculating in 0 μm dose equivalent unit is connected. The arithmetic processing unit 40 includes an arithmetic circuit 42 that performs a calculation process, and a memory 44 that stores a table indicating the energy characteristics and the like of each of the detection units 20 and 30. The arithmetic circuit 42 calculates a value of 7 based on the count value given from the counters 26 and 36 and the table stored in the memory 44.
Calculate the 0 μm dose equivalent. The table stored in the memory 44 will be described later in detail when describing the arithmetic processing in the present embodiment. Further, a display 50 for displaying a calculation result and a data output circuit 60 are connected to the calculation processing unit 40.

The whole of these devices is housed in a resin case 70. The resin case 70 is formed of, for example, ABS resin, and differs from the resin case 19 of the conventional device in that the resin case 70 also covers portions on the sensitive surface side of the detection units 20 and 30. The portion on the sensitive surface side of the resin case 70 of the present embodiment, that is, the entrance window protection plate 70a is higher than the other portions so as not to completely block the β-rays incident toward the detection units 20 and 30. It is getting thinner. For example, the thickness of the incident window protection plate 70a made of ABS resin is 0.2 mm or less, and if the thickness is about this, low energy (for example, 0.2 mm) can be obtained.
(MeV) is not completely blocked.
The entrance window protection plate 70a is, for example, 5 mm × 10 mm.
The size is about 0.2m
Even with a thickness of about m, it has sufficient strength to protect the detection units 20 and 30.

The configuration of the radiation dosimeter of the present embodiment has been described above. In the above configuration, the processes from the detection of β-rays by the detection units 20 and 30 to the counting by the counters 26 and 36 are the same as those in the related art, and thus the description is omitted, and the dose equivalent is calculated from the count values of the two detection units. The following describes the arithmetic processing for performing the calculation.

Since the detectors 20 and 30 have different energy characteristics depending on the presence or absence of the filter, the sensitivities differ depending on the energy of the incident β-ray. In the present embodiment, the energy characteristics of each of the detection units 20 and 30 are obtained in advance by experiments or the like, and stored in the memory 44 of the arithmetic processing unit 40. FIG. 2 shows an example of such energy characteristics. Each energy characteristic in FIG. 2 indicates the maximum energy of β-rays on the horizontal axis, and the sensitivity (response) of 70 μm dose equivalent unit on the vertical axis, and indicates that each detector 20a,
The change in sensitivity to the change in the energy of the incident β-ray at 30a is shown. The unit of the sensitivity on the vertical axis in FIG. 2 is, for example, [count / μSv]. Therefore, FIG.
Values of 1 μSv at 70 μm dose equivalent
This shows how many counters 26 and 36 each show when receiving a line. Therefore, if the sensitivity of the detection unit to the incident β-ray is obtained from the energy characteristic in FIG. 2, an accurate 70 μm dose equivalent can be obtained by multiplying the reciprocal of this sensitivity by the count value of the detection unit. In FIG. 2, the sensitivity value for each energy is the β value of ⁹⁰ Sr-Y (strontium-yttrium).
It is shown as a relative value when the sensitivity to the line (1.4 MeV) is set to 1.

In addition to the energy characteristic table, the memory 44 stores a sensitivity ratio table indicating the energy dependence of the sensitivity ratio of each of the detection units 20 and 30. FIG. 3 is a diagram showing such energy dependence of the sensitivity ratio (hereinafter, referred to as a sensitivity ratio characteristic), and shows the ratio of each energy characteristic shown in FIG. That is, FIG. 3 shows the relative ratio of the sensitivity when there is a filter (that is, the detection unit 30) when the sensitivity when there is no filter (that is, the detection unit 20) is set to 1. As can be seen from FIG. 3, the sensitivity ratio of each detection unit depends on the maximum energy of the incident β-ray in the range of about 0.2 to 10 MeV. Therefore, if the sensitivity ratio of each detection unit is known, the energy of the incident β ray can be specified from the sensitivity ratio characteristics shown in FIG.

Here, it is considered that the count values of the detection units 20 and 30 are proportional to the respective sensitivities. Therefore, the ratio of the count values of the respective detection units indicates the sensitivity ratio of the respective detection units. Conceivable. Therefore, in this embodiment, the ratio of the count values of the counters 26 and 36 is obtained, and the energy of the incident β-ray is obtained by comparing this count value ratio with the sensitivity ratio characteristic of FIG.

That is, the arithmetic circuit 42 of the arithmetic processing unit 40
Receives the count values N1 and N2 from the counters 26 and 36, and calculates the ratio N2 / N1 of the count values N1 and N2.
Then, from the sensitivity ratio table (FIG. 3) stored in the memory 44, the arithmetic circuit 42 obtains β-ray energy corresponding to this ratio.

Then, the arithmetic circuit 42 obtains the sensitivity corresponding to the obtained energy from the energy characteristic table (FIG. 2), and further multiplies the reciprocal of this sensitivity by the count value output from the counter to obtain an accurate dose. Find the equivalent.
It is sufficient that the sensitivity is obtained for one of the two detectors 20 and 30, and a correct 70 μm dose equivalent can be obtained by multiplying the reciprocal of the obtained sensitivity by the count value of the corresponding detector.

As described above, according to this embodiment,
It is possible to prevent the damage of the detection unit by completely covering the case with a robust case, and at the same time, to correct the decrease in sensitivity for low energy due to covering with the case by arithmetic processing using the count values of the two detectors. By doing
An accurate 70 μm dose equivalent can be determined. Therefore, a compact and robust radiation dosimeter suitable for carrying can be obtained.

If two detectors having different energy characteristics are used, the effect of the present embodiment can be obtained in principle. Therefore, even if more detectors are provided, the effect of the present embodiment can be obtained. Can be obtained.

In the above example, the counter 26 or 36
Processing unit 4 from the count value (integrated value) obtained by
Although the dose equivalent is calculated at 0, the present invention is not limited to this, and the counters 26 and 36 may calculate the count rate, and the arithmetic processing unit 40 may calculate the dose equivalent rate from the count rate.

[0038]

As described above, according to the present invention,
Accurate 70 for incident β-rays of any energy
It is possible to obtain a radiation dosimeter that can determine the μm dose equivalent and that does not easily damage the detector. The radiation dosimeter according to the present invention is suitable for portable use since the detector is hardly damaged as described above.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a radiation dosimeter according to the present invention.

FIG. 2 is a diagram illustrating energy characteristics of each detection unit in the example.

FIG. 3 is a diagram illustrating the energy dependence of the sensitivity ratio of each detection unit in the example.

FIG. 4 is a diagram showing a configuration of a conventional radiation dosimeter.

FIG. 5 is a diagram showing energy characteristics of a conventional radiation dosimeter.

[Explanation of symbols]

10, 20, 30 detection unit, 10a, 20a, 30a
Semiconductor detector, 10b, 20b, 30b Aluminized mylar film, 30c filter, 12, 22, 32 amplifier, 14, 24, 34 Wave height discriminator, 16, 26, 3
6 counter, 18, 50 display, 19, 70 resin case, 40 arithmetic processing unit, 42 arithmetic circuit, 44 memory, 60 data output circuit, 70a entrance window protection plate.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshinori Oshima 6-22-1, Mure, Mitaka-shi, Tokyo Aloka Co., Ltd. (56) References JP-A-3-65686 (JP, A) JP-A-5 -232234 (JP, A) JP-A-7-20246 (JP, A) JP-A-4-152288 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01T 1/24 G01T 1/02 G01T 7/00

Claims (3)

(57) [Claims] 1. A case, comprising: two detection units having different energy characteristics from each other; a case accommodating each of the detection units; and a protection plate for preventing damage, which covers a sensitive surface side of each of the detection units; and each of the detection units. Counting the output signals separately, a counting unit for calculating the count value for each of the detection units, and the energy of the incident β-ray based on the mutual ratio of the count values of the detection units, based on the obtained energy Said protection
A radiation dosimeter, comprising: an arithmetic processing unit that calculates a dose equivalent by compensating for a decrease in sensitivity due to a plate . 2. The radiation dosimeter according to claim 1, wherein the arithmetic processing unit comprises: an energy characteristic table indicating an energy characteristic of each of the detection units covered with the protection plate; From a ratio of numerical values, an energy calculation unit that calculates the energy of the incident β-ray based on the energy characteristic table, and a sensitivity calculation unit that calculates the sensitivity of the detection unit at the determined energy based on the energy characteristic table, A radiation dosimeter comprising: a dose equivalent calculation unit that corrects a count value of the detection unit based on the obtained sensitivity and obtains a dose equivalent. 3. The radiation dosimeter according to claim 1, wherein one of the two detectors is a semiconductor detector with a filter, and the other is a semiconductor detector without a filter. Radiation dosimeter.