JP2005265765A - Survey meter check calibrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a confirmation calibrator capable of easily and easily confirming whether or not a continuous use of a calibration constant attached to a survey meter is possible without requiring a special facility such as a radiation shielding room. This is the issue.
SOLUTION: Granite, which is a natural radioactive material, in particular, plate granite obtained by processing granite containing natural radioactive potassium feldspar into a plate shape is used as a bottom plate, and radiation detection is performed on the bottom plate at the central position of the plate granite. A perforated granite provided with a hole into which a vessel can be inserted was laminated to form a bowl-shaped volume source, and a detector was inserted into the volume source.
[Selection] Figure 1

Description

The present invention relates to a survey calibrator for a survey meter.
More specifically, the present invention relates to a simple survey meter calibrator using a radiation source. In particular, the present invention relates to a confirmation calibrator using a natural radioactive substance and a ¹³⁷ CS or the like as a radiation source and having a uniform dose rate distribution and a small calibration error.

  Incidentally, “confirmation calibration” as used in the present invention refers to determining whether or not the performance of the calibrated practical measuring instrument is continuously maintained and the calibration constant can be used continuously in the calibration system leading to the national standard. This is a simple calibration. The use of the measuring device is performed to verify and confirm that the measuring device is sufficiently accurate for the purpose of measurement, and does not newly define a calibration constant.

  At present, the operation of area monitors, gas monitors, etc. in nuclear facilities is checked using a checking radiation source during periodic inspections. As a result, it is proved that the performance of the measuring instruments, calibration constants and conversion factors can be used continuously. Yes. This calibration method is also applied to survey meters, and is scheduled to be newly defined as "Appendix 2 Confirmation Calibration of Practical Measuring Instruments" in JIS Z 4511 as a verification calibration method that has been expanded to general radiation measuring instruments.

  Radiation cannot be estimated by human senses like “length”, “weight”, “temperature”, “brightness”, and the like. Its existence can be confirmed by a radiation measuring instrument. However, even if an abnormality occurs in the indicated value, the problem cannot be easily found.

  Conventionally, in order to determine whether a survey meter operates reliably with respect to radiation, a method of confirming that a radiation measurement value increases using a checking radiation source added to the survey meter is generally used.

  However, in consideration of the frequent loss of such a checking source, a checking source has not been added to survey meters since the 1975s. For this reason, it is no longer possible to easily check the operation of the survey meter using radiation.

  On the other hand, in the 1995s, the Metrology Law Approved Operator System (JCSS) was established, a calibration system using standard measuring instruments and the like with clear traceability with national standards was established, and radiation measurement was also systematic. The accuracy can be guaranteed.

  The survey meter for measuring external radiation used in establishments subject to the Radiation Hazard Prevention Act is one year on the day of measurement using standard measuring instruments that are clearly traceable to national standards. Guidance has been given, such as using a calibrated product within the period (October 23, 2000, Notification of Director of Radiation Safety Division, Science and Technology Agency).

  However, at present, many survey meters have been used without being calibrated for several years due to costs, the number of days required for calibration, etc. after the initial calibration. Therefore, in order to ensure the reliability of measurement by these measuring instruments, the concept of “confirmation calibration” described above was formulated as part of practical calibration.

  The survey meter used for radiation protection is a product that has passed the type test and inspection of Japanese Industrial Standard (JIS Z 4333). Re-calibration after purchase can be calibrated at certified establishments based on the Measurement Law and establishments that possess reference measuring instruments calibrated at the certified establishments at the request of the user within the traceability system leading to national standards. It has become.

  The frequency of calibration is not described in related laws and regulations, and currently there are not a few survey meters that are used without recalibration for a long time due to the cost of calibration and the number of days.

Under such circumstances, Japanese Industrial Standards related to calibration were revised, and confirmation calibration was added as part of practical calibration. This calibration method is a method for determining whether or not recalibration is appropriate from the ratio between the initial indicated value of the survey meter and the current indicated value for a certain dose rate. Conventionally, a non-legal regulation ¹³⁷ CS hermetically brazed radiation source 3.7 MBq was attached to a holding stand, this was placed on a desk, and the distance between the radiation source and the probe was changed to calibrate by the inverse square method.

  Since this calibration method is affected by scattered radiation from the room, it is necessary to correct the dose due to the scattered radiation, and there is a problem of exposure during work. In addition, as described above, there is a case where a small beam source for operation inspection (checking beam source) is added to the radiation measuring instrument, but there is a problem of loss, and such a radiation source is currently added. Absent.

  A calibration constant is added to a survey meter calibrated at an authorized establishment or an establishment that owns a reference measuring instrument calibrated at an authorized establishment. However, if the survey meter performance is no longer maintained, the calibration constants need to be reviewed. The conditions that require the addition of calibration constants are specified again, and the development of a confirmation calibrator for determining the continuous use of calibration constants is desired by survey meter users at small business establishments.

  Accordingly, the present invention provides a confirmation calibrator that can easily and easily confirm whether or not the calibration constant attached to the survey meter can be continuously used without the need for a special facility such as a radiation shielding room. Is an issue.

A plate-shaped granite obtained by processing granite containing a lot of natural radioactive potassium feldspar into a plate shape is used as a bottom plate, and a hole is provided on the bottom plate so that a radiation detector can be inserted at the center of the plate-shaped granite. Granite was laminated to form a bowl-shaped volume source, and a detector was inserted into the volume source.
A sheet produced by granulating natural radioactive thorium ore was wound around the outside of the detector guide to constitute a cylindrical radiation source, and the detector was inserted into the cylindrical radiation source.
Natural radioactive thorium ore is powdered, the powdered thorium ore is formed into a plate and perforated plate and sintered, and the sintered bodies are stacked to form a bowl-shaped volume source. The detector was inserted into the volume source.
Two or more rod-like radiation sources (welding rods) containing thorium are arranged in a cylindrical shape around the detector guide to constitute a cylindrical radiation source, and the detector is inserted into the cylindrical radiation source.
Two or more ¹³⁷ Cs sealed small radiation sources having the same radioactivity are arranged around the detector guide symmetrically with respect to the axis of the detector to constitute the radiation source, and the detector is located at the center of the radiation source. Was inserted.
In an ionization chamber survey meter calibration calibrator, in order to enable calibration of the low dose rate range, a lead attenuation plate that can be mounted and removed is inserted between the radiation source and detector, and several ranges can be achieved with one radiation source. Enabled calibration.
In the calibrator of the neutron survey meter, ²⁴¹ Am + Be neutron sources that can move toward the detector in the shielding container are arranged symmetrically one by one on the left and right of the detector of the neutron survey meter, and the neutron source is Calibration was carried out by protruding sideways from the shielding container toward the detector.

  Conventionally, the owner of a survey meter has requested calibration to an authorized office or the like, or has calibrated the survey meter using a sealed braid source in a small radiation shielding room. However, the former calibration request is expensive, and in the latter case, it is difficult to evaluate the scattered dose, the work efficiency is poor, and there is a risk of exposure.

In the present invention, except for the ionization chamber and the neutron survey meter, natural granite or the like and a plurality of ¹³⁷ Cs beam sources are devised so that the entire detector is evenly irradiated, so that the calibration corresponding to each measurement range is performed. The detector can be inserted into the detector and the calibration work can be performed quickly regardless of the installation position error, and the exposure dose can be reduced.
In addition, the use of small radiation sources that are not subject to the Radiation Hazard Prevention Act is mainly used, so it is no longer necessary to permit the use of radiation sources or set management areas.

  Further, according to the confirmation calibrator of the present invention, it is possible to give a guarantee for recalibration execution and continuous use of the calibration constant from the ratio of the fluctuation range of the instruction value at the time of confirmation calibration and the initial instruction value .

In summary, the verification calibrator of the present invention is characterized by the following points (1) to (4).
(1) As a calibration radiation source used for the survey meter, granite, which is a natural radioactive material, particularly granite containing a lot of natural radioactive potassium feldspar, thorium ore, and sealed braided sources such as ¹³⁷ CS, ²⁴¹ Am + Be are used.
(2) Confirmation of scintillation survey meter and GM survey meter In the calibrator, a volumetric radiation source (Fig. 1) obtained by processing the granite into a bowl shape, a cylindrical radiation source manufactured using a sheet made by granulating thorium ore ( 2), and a detector is inserted in the center of a cylindrical radiation source produced by arranging two or more thorium rod radiation sources (welding rods) in a cylindrical shape (FIG. 3). In addition, two or more point-shaped ¹³⁷ CS sealed small beam sources are placed symmetrically with respect to the detector axis (Fig. 4), creating a calibration field with a uniform dose rate, reducing calibration errors, and equipment. Downsizing.
(3) Ionization chamber survey meter check Calibrator (Fig. 5) In order to reduce the weight of the shielding body by miniaturization, the distance between the detector and the sealed small wire source is about 30 cm, In order to be able to calibrate several ranges (measurement ranges), a lead attenuation plate (shielding plate) that can be easily attached and detached is inserted between the radiation source and the detector so that the low dose rate range can be calibrated.
(4) Further, the calibrator (Fig. 6) of the neutron survey meter is placed in a shielding container in which a ²⁴¹ Am + Be neutron source can be easily projected, and two of these are arranged symmetrically on the left and right of the neutron detector. The source is projected and calibrated.

(Embodiment 1)
FIG. 1 is a sectional view of a confirmation calibrator using granite. In FIG. 1, reference numeral 1 denotes a plate granite obtained by processing natural radioactive granite into a plate shape. This plate-shaped granite 1 is placed on the bottom of a lead shielding box 8, and a perforated granite 2 provided with a hole 4 into which the radiation detector 3 can be inserted is laminated on the center of the plate-shaped granite 1 (three layers in the figure). ) To form a bowl-shaped volume radiation source.
When the detector 3 is inserted from above into the bowl-shaped volume source along the detector guide 5, the entire detector is irradiated with radiation uniformly. 6 is a detector cable, and 7 is a detector support.

(Embodiment 2)
FIG. 2 is a cross-sectional view of a confirmation construction device using a thorium sheet cylindrical radiation source. In this embodiment, natural radioactive thorium ore and the like are granulated to form a production sheet 9, which is wound around the outside of the detector guide 5 to constitute a cylindrical radiation source.
Thus, when the detector 3 is inserted to the center of the cylindrical radiation source, the detector 3 can be irradiated with radiation evenly.

(Embodiment 3)
Although not shown in the figure, natural radioactive thorium ore is powdered, formed into a plate-like body and a perforated plate-like body having a hole in the center, and sintered to obtain the plate-like granite described in FIG. A plate-like body and a hole-perforated plate-like body similar to the perforated granite can be produced, and these plate-like bodies can be laminated to form a bowl-shaped volume source.

(Embodiment 4)
FIG. 3 shows a rod-like source symmetrically arranged type confirmation calibrator. This is a cylindrical radiation source in which two or more rod-like radiation sources (welding rods) 10 containing thorium are arranged symmetrically in parallel to the outside of the detector guide 5.
Also in this radiation source, when the detector 3 is inserted along the detector guide to the center of the cylindrical radiation source composed of a rod-shaped radiation source, the radiation can be uniformly irradiated on the entire surface of the detector.

(Embodiment 5)
FIG. 4 shows a check calibrator with a point source symmetrical arrangement. In this configuration, two or more, for example, ¹³⁷ Cs hermetically brazed radiation sources having equal radioactivity are arranged symmetrically with respect to the axial center outside the detector guide 5 to constitute a cylindrical radiation source.
^{The 137} Cs sealed small wire source is held by the radiation source holder 11 and can be moved up and down along the detector guide 5 by the radiation source lifting platform 12.
Since it is this structure, since a radiation source can be hold | maintained in the optimal position with respect to the detector 3, the detector 3 can receive irradiation of a radiation equally.

(Embodiment 6)
FIG. 5 is a cross-sectional view showing an example of a confirmation calibrator of an ionization chamber survey meter. In this calibrator, a lead attenuation plate (shielding plate) 15 is detachably installed between the ionization chamber survey meter 13 and the radiation source 14. Then, the distance between the radiation source 14 and the ionization chamber detector 18 is adjusted by attaching the radiation source 14 to the tip of the radiation source moving rod 16 and moving the movable rod 16 in the horizontal direction by the radiation source moving device 17. Can do. In this case, the radiation source moving bar 16 moves on the scale table 19, and the scale provided on the scale table 19 can be adjusted within a configuration distance range of about 30 cm (distance between A and B in the figure) while viewing the scale. ing.

(Embodiment 7)
FIG. 6 is a cross-sectional view of an embodiment of a confirmation calibrator for a neutron survey meter. In FIG. 6, a shielding container 21 is provided symmetrically on both sides of a neutron survey meter 20 installed on a table 25, and a radiation source moving rod 23 fitted with a neutron source 22 at its tip is movable in the horizontal direction. Is provided. Reference numeral 24 denotes a height adjuster provided on the table 25, whereby the shielding container can be moved up and down, and its position can be adjusted with respect to the neutron source 22 and the neutron survey meter 20. With this configuration, the neutron source 22 can be calibrated by protruding sideways from the shielding container 21.

It is embodiment sectional drawing of the confirmation calibrator using granite. It is sectional drawing of the confirmation calibrator using the thorium sheet cylindrical radiation source. It is sectional drawing of a rod-shaped radiation source symmetrical arrangement | positioning confirmation calibrator. It is sectional drawing of a point-like radiation source symmetrical arrangement check calibrator. It is sectional drawing of an ionization chamber type survey meter confirmation calibrator. It is a conceptual diagram of a neutron survey meter confirmation calibrator.

Explanation of symbols

1 Plate granite 2 Hole granite 3 Radiation detector 4 Hole 5 Detector guide 6 Detector cable 7 Detector support 8 Lead shield box 9 Sheet made by granulating thorium ore
10 Rod-like radiation source containing thorium (welding rod)
11 Radiation source holder 12 Radiation source lifting platform
13 Ionization chamber survey meter 14 Radiation source
15 Lead attenuation plate 16 Radiation source moving rod
17 Source moving device 18 Ionization chamber detector
19 Scale stand 20 Neutron survey meter
21 Shielding container 22 Neutron source
23 Radiation source moving rod 24 Height adjuster
25 units

Claims (7)

A plate-shaped granite obtained by processing granite containing a lot of natural radioactive potassium feldspar into a plate shape is used as a bottom plate, and a hole is provided on the bottom plate so that a radiation detector can be inserted at the center of the plate-shaped granite. A survey calibrator for survey meters, characterized in that granite is laminated to form a bowl-shaped volume radiation source, and a detector is inserted into the volume radiation source. Confirmation of a survey meter characterized in that a sheet made by granulating natural radioactive thorium ore is wound around the outside of the detector guide to form a cylindrical radiation source, and the detector is inserted into the cylindrical radiation source Calibrator. Natural radioactive thorium ore is powdered, the powdered thorium ore is formed into a plate and perforated plate and sintered, and the sintered bodies are stacked to form a bowl-shaped volume source. A check calibrator for a survey meter, wherein a detector is inserted into the volume radiation source. A cylindrical radiation source is configured by arranging two or more rod-shaped radiation sources (welding rods) containing thorium in a cylindrical shape around a detector guide, and the detector is inserted into the cylindrical radiation source. Survey meter verification calibrator. Two or more ¹³⁷ Cs hermetically brazed radiation sources having equal radioactivity are arranged around the detector guide in an objective manner with respect to the axis of the detector to constitute the radiation source, and the detector is located at the center of the radiation source. A check calibrator for survey meters, characterized by inserting In order to enable the calibration of the low dose rate range, a lead attenuation plate that can be mounted and removed is inserted between the radiation source and the detector, and several ranges can be calibrated with one radiation source. Ionization chamber survey meter confirmation calibrator. ²⁴¹ Am + Be neutron sources that are movable inside the shielding container and are movable toward the detector are arranged symmetrically one by one on the left and right of the detector of the neutron survey meter, and the neutron source is directed from the shielding container to the detector. A calibration calibrator for a neutron survey meter, characterized in that it is calibrated by protruding sideways.

Images