JP2005300245A - Radiation measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation measuring instrument for flattening the directional characteristics of a detected radiation independently of the angle of incidence. <P>SOLUTION: A plurality of sensors are used. At least one sensor is given uniformed β-ray incident windows. At least one sensor is provided with β-ray incident windows being thinner at its middle part as compared with its periphery so as to enhance its response in the front direction of the incident windows while lowering the response in its wide angle direction. An angle correction coefficient is determined by comparing respective responses with each other in a CPU. A response from a sensor with uniformed β-ray incident windows is multiplied by the correction coefficient, thereby reducing an over response problem. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radiation measurement apparatus such as a personal dose management pocket dosimeter, an environmental measurement survey meter, an area monitor, and the like used in nuclear power plants, radiation utilization facilities, accelerator facilities, and the like.

FIG. 6 shows a configuration diagram of a detection unit for explaining a radiation detection unit of a conventional radiation measurement apparatus. In FIG. 6, β rays, which are an example of radiation, are incident on the radiation detector 13 through a filter 11 that also functions as light shielding and electromagnetic shielding. The filter 11 is made of aluminum having a thickness of about 20 mg / cm ² or a laminated sheet of copper and PET. Lead having a thickness of 0.5 mm is added as a filter 12 to the center of the filter 11. To use. The filter 11 is supported by the filter support portion 14 and attached to the printed board 15. β-rays have a very low permeability in X-rays and γ-rays. For example, 0.5 MeV β-rays stop at 0.6 mm thick aluminum (160 mg / cm ² ). In order to improve the directional characteristics, a filter 12 is provided so as to have sensitivity equivalent to the front direction (0 °) up to the normal 60 ° direction, and the sensitivity in the front direction is reduced by reducing the sensitivity in the front direction. Sensitivity was increased so that the directional characteristics normally have the same sensitivity as the 0 ° (front) direction up to the 60 ° direction (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2003-4852

  In the above-described conventional method, the directional characteristic with respect to β rays has a filter structure in which the central portion of the window is thickened because the response becomes smaller as the angle of the incident window is uniform, and the window becomes thicker. When the filter shape is determined so that a response equivalent to ° can be obtained, an over-response may occur with respect to 0 ° at an intermediate angle. That is, the response to 0 ° up to each angle of 60 ° may deviate from ± 30%, which is a standard for variation.

  In order to solve the above-described problem, the radiation measurement apparatus of the present invention uses a plurality of radiation detection units, uniforms the β-ray incident part of β-rays incident on at least one radiation detection part, and detects at least one radiation. In order to increase the response in the front direction of the β-ray incident part of the β-ray incident on the part and to reduce the response in the wide-angle direction, a β-ray incident part with a thinner central part than the surroundings is provided, and each response is sent to the CPU. A correction coefficient for the response is determined by comparison in a processing unit such as (Central Processing Unit), and the correction is performed by multiplying the response from the radiation detection unit having a uniform β-ray incident part by the correction coefficient. is there.

  According to the radiation measuring apparatus of the present invention, the direction characteristic of the radiation to be detected can be made flat regardless of the incident angle.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram of a detection unit for explaining a radiation detection portion in the radiation measurement apparatus of the present embodiment. 1 and 4 are filters serving as a β-ray incident window having a uniform thickness that also functions as a light shielding and electromagnetic shield, 2 is a filter support for supporting the file 1 and the filter 4, and 3 is passed through the filter 1. A radiation detector for detecting radiation, 5 is a perforated filter provided at a location other than the substantially central portion of the filter 4, and 6 is a radiation detector for detecting radiation that has passed through the filter 4. And 7 is a printed circuit board for mounting the radiation detector 3, the radiation detector 6 and the filter support 2.

In addition, as the filter 1 and the filter 4, the sheet | seat which laminated | stacked aluminum or copper and PET about 20 mg / cm < ² > in thickness is used.

  Moreover, the radiation detector 3 and the radiation detector 6 consist of a silicon semiconductor detector as an example.

  The operation of the radiation detection part configured as described above will be described.

β-rays enter the radiation detector 3 through the filter 1 as a β-ray incident window having a uniform thickness that also functions as a light shield and an electromagnetic shield. An ionizing action occurs in the radiation detector 3 and a current is generated. Next, it is amplified by current-voltage conversion by an amplifier circuit (not shown). This amplified analog signal is sent to a comparator circuit (not shown) to be compared with a threshold value. This comparator circuit cuts a noise signal. Then, a signal exceeding the threshold value is converted into a dose D1 (sievert) or a dose rate DR1 (sievert / hour) which is a unit of radiation in a CPU (not shown) as a processing unit.
On the other hand, as in the radiation detector 3, the β-ray has a thickness of 1 mm in which a filter 4 made of the same material as the filter 1 and a hole having an area about 1/5 of the radiation sensitive area of the radiation detector 6 are provided in the center. The light enters the radiation detector 6 through the perforated filter 5 using the lead. An ionizing action also occurs in the radiation detector 6 to generate a current. Then, current-voltage conversion is performed and amplified by an amplifier circuit (not shown). This analog signal is sent to a comparator circuit (not shown) for comparison with a threshold value. A signal exceeding the threshold value is converted into a dose D2 (sievert) or a dose rate DR2 (sievert / time) which is a unit of radiation by a CPU (not shown) as a processing unit.

  Next, the correction coefficient for correcting the measured dose will be described with reference to FIG.

  FIG. 2 is a diagram showing a correction coefficient for correcting the direction characteristics of incident radiation using two radiation detectors of the radiation detector 3 and the radiation detector 6 in a pocket dosimeter which is an example of a radiation measuring apparatus. It is. As for FIG. 2, D2 / D1 (ratio of dose D2 and dose D1) is acquired in advance at each angle by experiment, and a correction coefficient (K) is calculated. The characteristics shown in FIG. 2 are stored in a storage unit (not shown). Then, based on the measured D1 and D2 and the characteristics shown in FIG. 2, in the processing unit (not shown), K (correction coefficient) × D1 (dose detected by the radiation detector 3) is calculated and corrected. I do. Note that D2 / D1 becomes smaller when the incident direction of radiation becomes wider than the front (0 °). Then, this is corrected by multiplying a correction coefficient K corresponding to the ratio by using D2 / D1 as angle information.

  Next, the doses D1 and D2 are measured by the two radiation detectors of the radiation detector 3 and the radiation detector 6, and measured based on the measurement result and the correction coefficient shown in FIG. 2 stored in the storage unit. An example in which the corrected dose is corrected will be described with reference to FIG.

  FIG. 3 is a diagram showing an example of dose measurement and correction at each angle in the vertical direction (front) of the pocket dosimeter at 0 ° to 60 °. The doses D1 and D2 are measured by the two radiation detectors of the radiation detector 3 and the radiation detector 6, and the processing unit obtains the ratio D2 / D1 using the doses D1 and D2. The processing unit selects the correction coefficient K corresponding to this ratio from the values stored in the storage unit shown in FIG. 2, and performs correction by multiplying the correction coefficient K by D1. In the case of the dose rate, correction can be performed by multiplying the same correction coefficient K as in the case of the dose.

  FIG. 4 is a diagram illustrating the β-ray direction characteristics with and without the above-described correction. As shown in FIG. 4, by performing the above-described correction, the correction can be performed without over or under evaluation without deviating from ± 30%, which is a variation standard, at all angles of 0 ° to 60 °.

  The above is a correction coefficient for correcting the β-ray direction characteristics, but when the response to low energy β rays is lower than the response to high energy β rays, it is also based on the results measured with two radiation detectors. Correction may be performed by specifying a correction coefficient. FIG. 5 is a β-ray energy characteristic diagram with and without correction. In this case, by adjusting the hole area of the perforated filter 5, it is possible to realize a radiation measuring instrument having a constant response regardless of the incident direction of radiation and the energy of energy with respect to both direction characteristics and energy characteristics.

  As described above, according to the radiation measuring apparatus of the present embodiment, a plurality of radiation detectors are used, at least one radiation detector has a uniform β-ray incident window, and at least one other radiation detector has In order to increase the response in the front direction in the β-ray incident window and to reduce the response in the wide-angle direction, a β-ray incident window with a thinner central part than the surroundings is provided, and the transmission characteristics are partially different. Radiation is measured using two radiation detectors, the incident angle of the radiation is estimated from each measurement result, a corresponding correction coefficient is specified, and the measurement result is multiplied by this correction coefficient to perform correction. By doing so, it is possible to measure the radiation with the sensitivity characteristic being flat regardless of the incident angle of the radiation.

  In the present embodiment, the example in which lead is used as the material constituting the perforated filter 5 has been described. However, the present invention is not limited to this, and similar results can be obtained even if tungsten is used instead of lead. Can do.

  In the present embodiment, an example in which the radiation detectors 3 and 6 are silicon detectors has been described. However, the present invention is not limited to this. Instead, a gallium arsenide detector, a cadmium telluride detector, or CsI ( Similar results can be obtained by combining a (cesium iodide) scintillator detector and a silicon photo detector.

  In the present embodiment, the pocket dosimeter has been described as an example, but a similar result can be obtained by a survey meter or an area monitor using a detector similar to the pocket dosimeter.

  Further, the number of radiation detection units is not limited to two and may be two or more. These radiation detectors may be arranged as close as possible.

  According to the radiation measuring apparatus of the present invention, the direction characteristics and energy characteristics of β rays can be corrected with high accuracy, so that personal dose management pocket dosimeters used in nuclear power plants, radiation utilization facilities, accelerator facilities, etc. It is useful as an environmental measurement survey meter, area monitor, etc.

The figure which shows schematic structure of the radiation detection part in embodiment The figure which shows the correction coefficient in embodiment The figure which shows the actual example of correction | amendment of the beta ray direction characteristic in embodiment The figure which shows the actual example of correction | amendment of the beta ray direction characteristic in embodiment The figure which shows the beta ray energy characteristic in embodiment The figure which shows schematic structure of the conventional radiation detection part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Filter 2 Filter support part 3 Radiation detector 4 Filter 5 Perforated filter 6 Radiation detector 7 Printed circuit board 11 Filter 12 Filter 13 Radiation detector 14 Filter support part 15 Printed circuit board

Claims (17)

A first filter having a uniform radiation pass characteristic; a first radiation detecting unit for detecting radiation that has passed through the first filter; a second filter having a partially different pass characteristic of the radiation; A radiation measurement apparatus comprising: a second radiation detection unit that detects radiation that has passed through the second filter. A first filter having a uniform radiation pass characteristic; a first radiation detecting unit for detecting radiation that has passed through the first filter; a second filter having a partially different pass characteristic of the radiation; Corresponding to a calculation result based on a second radiation detection unit that detects radiation that has passed through the second filter, a detection result of the first radiation detection unit, and a detection result of the second radiation detection unit Based on the storage unit that stores the correction coefficient obtained in advance, the detection result of the first radiation detection unit, the detection result of the second radiation detection unit, and the correction coefficient stored in the storage unit A radiation measurement apparatus comprising: a processing unit that corrects a detection result of the first radiation detection unit. A first filter having a uniform radiation pass characteristic; a first radiation detecting unit for detecting radiation that has passed through the first filter; a second filter having a partially different pass characteristic of the radiation; Correction obtained in advance in association with the ratio between the second radiation detection unit that detects the radiation that has passed through the second filter, the detection result of the first radiation detection unit, and the second radiation detection unit The first radiation detection based on a storage unit that stores a coefficient, a detection result of the first radiation detection unit, a detection result of the second radiation detection unit, and a correction coefficient stored in the storage unit A radiation measurement apparatus comprising: a processing unit that corrects a detection result of the unit. The radiation measurement apparatus according to claim 2 or 3, wherein correction of the detection result of the first radiation detection unit is performed on the radiation direction characteristic. The radiation measurement apparatus according to claim 2 or 3, wherein the detection result of the first radiation detection unit is corrected for the energy characteristics of the radiation. The radiation measurement apparatus according to claim 2, wherein correction of the detection result of the first radiation detection unit is performed on the radiation direction characteristic and the radiation energy characteristic. The second filter according to any one of claims 1 to 6, wherein the second filter has a partially different pass characteristic due to a difference in thickness, and the thickness of the substantially central portion is thinner than the thickness of the other portions. The radiation measuring apparatus described. The radiation measuring apparatus according to any one of claims 1 to 6, wherein the second filter has a partially different pass characteristic by attaching metal to a part of a filter having a uniform pass characteristic. The radiation measuring apparatus according to claim 8, wherein the metal is made of lead. 9. The radiation measuring apparatus according to claim 8, wherein the metal is made of tungsten. The radiation measuring apparatus according to any one of claims 1 to 10, wherein the first and / or second radiation detector is a silicon detector. The radiation measuring apparatus according to any one of claims 1 to 10, wherein the first and / or second radiation detector is a cadmium telluride detector. The radiation measuring apparatus according to claim 1, wherein the first and / or second radiation detector is a gallium arsenide detector. The radiation measuring apparatus according to claim 1, wherein the first and / or second radiation detector is a combination of a CsI scintillator detector and a silicon photo detector. The radiation measuring apparatus according to claim 1, wherein the radiation measuring apparatus is a pocket dosimeter. The radiation measuring apparatus according to claim 1, wherein the radiation measuring apparatus is a survey meter. The radiation measuring apparatus according to claim 1, wherein the radiation measuring apparatus is an area monitor.

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