JPH0921880A - Radiation measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately compute dose equivalent of βrays in a mixed field of β, γ rays by subtracting mixed γ counting value from the total counting values of βsensor, and computing only the β counting value of only βrays. SOLUTION: Both β rays and γ rays are detected with a βsensor, and only γrays are detected with γ sensors 14, 16, 18. A preamplifier 30, a discriminator 32, a counter 34 are arranged between each of sensors 12, 14, 16, 18, and a computing part 28. A count value of each sensor is inputted into the computing part 28, and a γ sensitivity table 36 for the β sensor, a βsensitivity memory 38 for the β sensor, a γ sensitivity table 40 for the γ sensor, a γ energy estimation table 42, a dose equivalent conversion factor table 44, a display 46, and a printer 48 are connected to the computing part 28. The counting value of mixed γ rays in the total counting values of the βsensor is estimated by multiplying the amount of γ rays by the γ sensitivity of the β sensor. The mixed γcounting value estimated is subtracted from the total counting values of the βsensor, and true β counting value is found. The dose amount or dose equivalent is computed with the computing part 28 from the true β counting value obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation measuring apparatus used in a radiation handling facility such as a nuclear power plant, a nuclear fuel facility, a hospital, etc., and particularly to β-rays and γ-rays (used as photons including X-rays). Β in a mixed state
The present invention relates to a device for calculating a dose or dose equivalent of a line.

[0002]

2. Description of the Related Art Various dosimeters (dosage equivalent meters) have been put into practical use due to the requirements of workers involved in radiation handling facilities for radiation exposure management. In a β-ray measuring device for measuring the dose of β-rays, the detection surface of a β-sensor composed of a semiconductor detector or the like is covered with, for example, a thin aluminized mylar. It functions as a member for electrostatic shield and light shield.

Japanese Patent Publication No. 7-305 and Japanese Patent Laid-Open No. 7-12939 are equipped with a plurality of γ sensors having different energy sensitivity characteristics, and the incident γ-ray (X-ray) is calculated based on each count value. ) Is estimated, and a radiation measurement apparatus that performs sensitivity correction based on the estimated energy is disclosed.

[0004]

By the way, in a measurement environment in which β rays and γ rays coexist, when attempting to measure β rays by the β sensor as described above, γ rays are also measured at the same time. Will end up. That is, since γ-rays (X-rays) generally have a stronger penetrating power than β-rays, the thin aluminum-nulled mylar or the like is easily transmitted, and γ-rays are detected together with β-rays. Therefore, in a place where β rays and γ rays are mixed, there is a problem that it is difficult to calculate the dose or dose equivalent of only β rays.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to eliminate the influence of γ-rays in a mixed field of β-rays and γ-rays and to obtain the dose or dose equivalent of only β-rays. It is an object of the present invention to provide a radiation measuring instrument capable of accurately calculating.

[0006]

In order to achieve the above object, the present invention provides a detection section comprising a β sensor and a plurality of γ sensors having different energy sensitivity characteristics, and the plurality of detection units. On the basis of the mutual ratio of the γ count values of the γ sensor, based on at least one of the γ energy estimation means for estimating the γ energy of the γ rays incident on the detection unit, and the γ count values of the plurality of γ sensors, Γ-dose calculating means for calculating the γ-ray dose of γ-rays incident on the detection unit, and γ for estimating the γ-sensitivity of the β-sensor to the γ-ray energy
A sensitivity estimating means; a mixed γ count value estimating means for estimating a mixed γ count value due to mixed γ rays incident on the β sensor based on the γ dose and the γ sensitivity of the β sensor;
Mixed γ for subtracting the mixed γ count value from the total count value of the sensor to calculate the β count value of only β rays in the β sensor
And a count value removing means for calculating the dose or dose equivalent of the β ray from the β count value of only the β ray.

According to the above configuration, the energy estimating means estimates the energy of the incident γ-ray based on the plurality of γ count values (count number) by the plurality of γ sensors. Here, the γ sensors have different energy sensitivity characteristics, and the ratio of the count value to the energy of γ rays is different. Therefore, based on the ratio of such count values, γ
Estimate the energy of the line. This energy estimation method is described in Japanese Patent Publication No. 7-1305 and Japanese Patent Laid-Open No. 7-305.
The method is basically similar to the method described in Japanese Patent No. 12939.

The gamma dose calculating means specifies the sensitivity of the gamma sensor at the energy based on the estimated gamma ray energy, and obtains the gamma dose from the sensitivity and the count value of the gamma sensor. Here, the sensitivity (absolute sensitivity) is defined as the number of counts per unit dose, and the response (relative sensitivity)
If is known, the sensitivity is obtained by multiplying the response by a predetermined coefficient (sensitivity in response 1).

In the calculation of the gamma dose, one or more of the count values of the plurality of gamma sensors are used. Therefore, γ
The sensitivity table needs to be prepared for the γ sensor corresponding to the count value used in the calculation of the γ dose.
In any case, the gamma dose is calculated using the count value of at least one gamma sensor.

When the energy and dose of the γ-rays incident on the detector are specified as described above, the γ-sensitivity estimating means then estimates the γ-sensitivity of the β sensor at the γ-energy. Then, the mixed γ count value estimating means multiplies the γ dose by the γ sensitivity of the β sensor to estimate the count value of the γ rays (mixed γ rays) detected by the β sensor, and calculates the total of the β sensors. Estimate the count value of the mixed γ-rays included in the numerical value.

Therefore, the mixed γ count value removing means subtracts the estimated mixed γ count value from the total count value of the β sensor to obtain the true β count value. A dose or dose equivalent is calculated from the obtained β count value.

In a preferred aspect of the present invention, the gamma energy estimating means has a gamma energy estimation table for estimating gamma ray energy from a mutual ratio of count values of the gamma sensors. That is, the energy of γ rays is specified using the table. Note that such a table
It can be created by conducting experiments beforehand.

In a preferred aspect of the present invention, the gamma dose calculation means has a gamma sensitivity table of the gamma sensor,
The γ sensitivity estimating means has a γ sensitivity table of β sensor. Further, in a preferred aspect of the present invention, the detection unit includes one β sensor and three γ sensors having filters different from each other.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment of the radiation measuring apparatus according to the present invention, and FIG. 1 is a block diagram showing the overall structure. This radiation measuring apparatus constitutes a dosimeter (dose equivalent meter) used by being attached to a worker who is engaged in a radiation handling facility or the like. of course,
This radiation measuring device can also be applied to other devices such as an area survey meter.

In FIG. 1, the detection unit 10 is one β sensor 12 and three γ sensors 1 in this embodiment.
4, 16, 18, and the like. Each sensor 12, 1
Reference numerals 4, 16 and 18 are semiconductor detectors.
The radiation detection surface of the β sensor 12 is covered with an aluminized mylar film 20, which serves as an electrostatic shield and a light shield.

The three γ sensors 14, 16 and 18 have different energy sensitivity characteristics. Therefore, the radiation detection surface of each γ sensor 14, 16, 18 has
Filters 22, 24, and 26 different from each other are arranged. Here, the filter 22 is made of, for example, 0.5 mm of lead (Pb), and the filter 24 has, for example, a thickness of 0.4.
The filter 26 is made of, for example, a 1 mm thick epoxy resin layer. These filters 22, 24 and 26 have a blocking effect on β rays and allow γ rays to pass through. On the other hand, the β sensor 1 described above
The aluminized mylar film 20 provided on the radiation detection surface 2 of FIG. 2 transmits both β rays and γ rays. That is, the β sensor 12 detects both β rays and γ rays, and the three γ sensors 14, 16 and 18 detect only γ rays.

A preamplifier 30, a discriminator 32, and a counter 34 are provided between the sensors 12, 14, 16, 18 and the arithmetic unit 28 from the sensor side. Here, the preamplifier 30 amplifies the signal output from the sensor, the discriminator 32 removes noise having a predetermined peak value or less from the amplified signal, and the counter 34 detects the discriminated signal (pulse). ) Is counted.

The calculation unit 28 is composed of, for example, a microcomputer, and the calculation unit 28 has a count value (count value) C1 of the β sensor 12, a count value C2 of the γ sensor 14, and a count value of the γ sensor 16. The value C3 and the count value C4 of the γ sensor 18 are input.

In addition, the calculation unit 28 includes a γ for the β sensor.
A sensitivity table 36, a β sensor β sensitivity memory 38, a γ sensor γ sensitivity table 40, a γ energy estimation table 42, a dose equivalent conversion coefficient table 44, a display 46, and a printer 48 are connected to each other.

FIG. 2 shows the γ sensitivity table 36 for β sensor.
The sensitivity characteristics possessed by are shown. The horizontal axis of the graph shown in FIG. 2 represents the γ-ray energy E _γ , and the vertical axis represents the response (relative sensitivity). In this way, the β sensor 12
_Have different sensitivities to the γ-ray energy E _γ .
Note that FIG. 2 shows the response of the β sensor to γ-rays, and the sensitivity (absolute sensitivity) is obtained by multiplying this response by the sensitivity in response 1.

The β sensitivity memory 38 for β sensor shown in FIG.
Stores the sensitivity of the β sensor 12 to β rays, and in order to directly obtain the dose from the β count value as described later, the β sensitivity for converting into the dose equivalent is stored. On the other hand, when the β dose is obtained from the β count value and the dose equivalent of β rays is obtained from the β dose, the sensitivity for dose calculation and the coefficient for obtaining the dose equivalent from the obtained dose are stored. To be done.

In this embodiment, the gamma sensor gamma sensitivity table 40 stores the energy sensitivity characteristics of the gamma sensors 14, 16 and 18 with respect to gamma rays. As will be described later, this γ sensitivity table needs to be stored at least for the γ sensor used in calculating the γ dose.

The γ energy estimation table 42 is shown in FIG.
The function as shown in is stored. The horizontal axis of the graph shown in FIG. 3 represents the γ-ray energy E _γ , and the vertical axis thereof represents the count value ratio. Reference numeral 200 in FIG. 3 denotes a ratio between the count value C3 and the count value C2, and reference numeral 202 denotes a ratio between the count value C4 and the count value C2. A specific method for estimating the γ-ray energy will be described later. .

The dose equivalent conversion coefficient table 44 of FIG.
The dose equivalent conversion coefficient for γ-ray energy is stored, and the dose equivalent conversion coefficient is taken into consideration when determining the dose equivalent for γ-rays, and in this embodiment, the dose equivalent conversion coefficient table 44 is 1 cm dose equivalent. 3 mm
The dose equivalent conversion factors of the dose equivalent and 70 μm dose equivalent are stored. Note that the 70 μm dose equivalent by β-ray and the 70 μm dose equivalent by γ-ray are added, and
It is displayed on the display 46 as a 0 μm dose equivalent. In addition, the display unit 46 displays a 1 cm dose equivalent of γ rays, a 3 mm dose equivalent of γ rays, and the like.

Next, the operation of the arithmetic unit 28 will be described with reference to FIG.

In step S101, the detector 10 detects radiation. As a result, C1 is obtained as the count value of the β sensor 12, and similarly, C2, C3, C4 is obtained as the count values of the γ sensors 14, 16, and 18. These C
1 to C4 are taken into the arithmetic unit 28 as outputs of the counter 34. Although the three γ sensors are used in the embodiment shown in FIG. 1, the γ ray energy can be specified by using two or more γ sensors having different energy sensitivity characteristics.

In S102 of FIG. 4, the count value C of γ rays
The energy (γ energy) E _{γ of} the incident γ-ray is estimated based on the mutual ratio of 2, C3 and C4. This S10
2, the γ energy estimation table 42 of FIG. 1 is referred to, that is, the γ ray energy E _γ is specified based on the characteristics shown in FIG. Specifically, for example, now C3 /
When the count value ratio 0.5 is seen on the characteristic curve 200 when C2 is 0.5 (see 204), the count value ratio 0.5 has a γ-ray energy E _γ of 30 (keV). Since it can be seen that this corresponds to (see 206), the γ-ray energy E _γ is specified based on such a count value ratio. In this case, the characteristic 200 is used when the γ-ray energy E _γ is relatively small, while the characteristic 202 is used when the γ-ray energy E _γ is relatively large. When a plurality of γ-rays having different energies are incident, the γ-ray energy E _γ is specified as the average value of them.

In S103 of FIG. 4, the γ sensor γ sensitivity table 40 is referred to, and _γ at the γ ray energy E _γ is obtained.
The sensitivity S2 is specified. That is, in this embodiment, the count value C2 of the γ sensor 14 is used when obtaining the γ dose D _γ, and the γ sensitivity S2 of the γ sensor 14 is specified in S103. When the response is stored as the γ sensitivity in the γ sensor γ sensitivity table 40 as described above, the sensitivity is specified by multiplying the response by a predetermined coefficient.

Then, in S104, the count value C2 of the γ sensor 14 is divided by the γ sensitivity S2 of the γ sensor 14, that is, C2 / S2 is executed to calculate the γ dose D _γ . That is, in the S104, the dose D _gamma of gamma rays incident on the detector 10 is calculated using at least one of gamma count.

Of course, as shown by the broken line S109 in FIG. 4, the γ-dose D _γ can be calculated using all the count values C2, C3, C4 of the three γ sensors 14, 16, 18. In this case, the weighting coefficients are set to a2, a3, and a4, respectively, and the dose obtained from the count value and the sensitivity of each sensor is weighted and added to obtain the γ dose D.
_{Find γ} .

In S105 of FIG. 4, the β sensor 12 is calculated based on the energy E _γ of the incident γ-ray obtained in S102.
The γ sensitivity S1 at the γ energy E _γ is specified. Specifically, the γ sensitivity table 36 for β sensor in FIG.
Is referred to, that is, the sensitivity characteristic shown in FIG. 2 is referred to, and the γ sensitivity S1 is specified. When the γ sensitivity of the β sensor is expressed as a response as described above, the sensitivity (absolute sensitivity) is calculated by multiplying the response by a predetermined coefficient.

It should be noted that this S105 is performed in S103 and S10.
4 can be performed in parallel and are shown as a series of steps in FIG. 4 for convenience.

In S106 of FIG. 4, the count value C _γ of γ rays (mixed γ rays) incident on the β sensor 12 is estimated. Specifically, the dose D _γ of the incident γ-ray obtained in S104 is S1
The count value C _γ of the mixed γ rays is estimated by multiplying the γ sensitivity S1 of the β sensor 12 obtained in 05.

At S107, the contribution amount of the mixed γ-rays is obtained as C _γ as described above. Therefore, from the count value C1 actually obtained by the β sensor 12, the estimated count value C of the mixed γ-rays is calculated. _γ is subtracted to estimate the count value C _{β of} only β rays. That is, since the energy and dose of γ-rays are calculated as described above, the count value of γ-rays in the β sensor 12 is estimated from the energy and dose of γ-rays, and the estimated value of the β sensor 12 is calculated. By subtracting from the total count value, the count value C _{β of} only β rays is obtained.

Since the count value C _{β of} β rays has been obtained in this way, the 70 μm dose equivalent H _β of β rays is calculated in S108. Specifically, the coefficient value C _{β of} only β rays is set to β
The dose equivalent H _β is obtained by dividing by the sensitivity A of the sensor 12. The sensitivity A is the sensitivity corresponding to the dose equivalent.

As shown by the broken line in S110, after the count value C _{β of} only β rays is obtained, the dose D _{β of} β rays is once obtained, and the dose equivalent H _β of β rays can be obtained from the dose D _β. it can.

The operation unit 10 shown in FIG. 1 has the β value shown in FIG.
In addition to calculating the dose equivalent for rays, it also calculates the dose equivalent for γ rays. That is, the γ-ray dose equivalent is calculated from the γ-dose D _γ specified in S104 of FIG. 4 and the dose-equivalent conversion coefficient at the γ-ray energy E _γ . As the dose equivalent, 1 cm dose equivalent, 3 mm dose equivalent and 70 μm dose equivalent are calculated. In calculating the dose equivalent, the conversion factor of each energy stored in the dose equivalent conversion factor table 44 is used. Then, the calculation unit 28 determines that the dose equivalent H _β of 70 μm of β ray and 70 μm of γ ray.
m dose equivalent H _γ is added to obtain a dose equivalent H _70μ for β rays and γ rays, which is output to the display 46 and the printer 48.

[0039]

As described above, according to the present invention,
In the situation where β rays and γ rays are mixed, the influence of γ rays can be eliminated and the dose equivalent of β rays can be accurately calculated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a radiation measuring apparatus according to the present invention.

FIG. 2 is a characteristic diagram showing a γ sensitivity of a β sensor.

FIG. 3 is a characteristic diagram showing a count value ratio of each γ sensor in relation to γ ray energy.

FIG. 4 is a flowchart showing an operation of a calculation unit.

[Explanation of symbols]

10 detector, 12 β sensor, 14, 16, 18 γ
Sensor, 28 arithmetic unit, 36 β sensor γ sensitivity table, 38 β sensor β sensitivity memory, 40 γ sensor γ sensitivity table, 42 γ energy estimation table.

Front page continuation (72) Inventor Toshinori Oshima 6-22-1, Mure, Mitaka City, Tokyo Aloka Co., Ltd.

Claims (5)

[Claims] 1. A detection unit including a β sensor and a plurality of γ sensors having different energy sensitivity characteristics, and the detection unit based on a mutual ratio of γ count values of the plurality of γ sensors. Γ energy estimating means for estimating γ energy of γ rays incident on the γ-ray, and γ-ray dose of γ-rays incident on the detection unit based on at least one of the γ count values of the plurality of γ sensors.
The dose calculation means, the γ sensitivity estimation means for estimating the γ sensitivity of the β sensor with respect to the γ ray energy, and the γ sensitivity of the γ ray of the γ ray incident on the β sensor from the γ dose and the γ sensitivity of the β sensor. A mixed γ count value estimating means for estimating a count value, a mixed γ count value removing means for subtracting the mixed γ count value from the total count value of the β sensor, and calculating a β count value of only β rays in the β sensor, And a radiation measuring apparatus for calculating a dose or a dose equivalent from the β count value of only the β ray. 2. The apparatus according to claim 1, wherein the γ energy estimation means has a γ energy estimation table for estimating γ ray energy from a mutual ratio of count values of the γ sensors. Radiation measuring device. 3. The radiation measuring apparatus according to claim 1, wherein the gamma dose calculation means has a gamma sensitivity table of a gamma sensor. 4. The radiation measuring apparatus according to claim 1, wherein the γ sensitivity estimating means has a γ sensitivity table of a β sensor. 5. The radiation measuring apparatus according to claim 1, wherein the detection unit includes one β sensor and three γ sensors having different filters from each other.