JP2012058097A - Confirmation and calibration method of radiation dose (rate) measuring instrument, and confirmation and calibration jig - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform confirmation and calibration of a radiation dose (rate) measuring instrument such as a survey meter including γ rays in a measuring target by using a low radiation source, which is not subject to legal regulation and does not require radiation management.SOLUTION: When confirming and calibrating a radiation dose (rate) measuring instrument including γ rays in a measuring target, β-ray sources 32, 33 for confirmation and calibration are disposed at such predetermined positions that a radiation sensing section (an ionization chamber type survey meter body 10, a GM count tube probe 20) of the radiation dose (rate) measuring instrument can measure β rays. The β rays radiated from the β-ray sources 32, 33 are made incident to the radiation sensing sections (10, 20) in place of γ rays, thereby changing an indicated value of the radiation dose (rate) measuring instrument.

Description

  The present invention relates to a confirmation calibration method and a confirmation calibration jig for a radiation dose (rate) measuring instrument, and in particular, an irradiation dose measuring instrument, an air kerma measuring instrument, an air absorbed dose measuring instrument, and a dose equivalent defined in JIS Z4511. Whether or not it is necessary to calibrate a radiation dose (rate) measuring device such as an ionization chamber type survey meter or a GM survey meter suitable for use in a measurement device (hereinafter collectively referred to as a radiation dose (rate) measurement device). The present invention relates to a confirmation calibration method and a confirmation calibration jig for a radiation dose (rate) measuring device that can be easily determined.

  One of the radiation dose (rate) measuring instruments that must be installed in radioisotope (RI) facilities such as laboratories, factories, and university hospitals that handle radioactive materials, as well as nuclear power plants and nuclear fuel cycle facilities. There are an ionization chamber type survey meter exemplified in Fig. 2 and a GM survey meter exemplified in Fig. 2. In FIG. 1, 10 is a main body in which an ionization chamber as a radiation sensing unit is built, 12 is a meter disposed on the rear surface, 13 is an operation switch, 14 is a grip, and 16 is detachable from the main body 10. Possible β-ray shielding cap. In FIG. 2, 20 is a probe with a built-in GM counter tube as a radiation sensing unit, 22 is a β-ray shielding cap removable from the probe 20, and 24 is equipped with a meter 26 and an operation panel 27. The main body 28 is a cable connecting the probe 20 and the main body 24.

  Since such survey meters change in performance due to aging and deterioration, it is necessary to conduct a response invariance test to confirm that there is no change in calibration constants and to continue to check whether the calibration constants can be used. is there. Specifically, during regular inspections, operation should be confirmed using a small beam source for operation inspection (so-called checking radiation source), and as a result, the performance of the measuring instrument, calibration constants and conversion counts can be used continuously. There is a way to prove that. If the calibration constant cannot be used continuously, it is necessary to obtain a new calibration constant.

  Conventionally, in order to determine that the survey meter operates reliably with respect to radiation, a method of confirming that the radiation measurement value rises using a checking radiation source attached 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 attached 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 1995's, the Metrology Law Approved Operator System (JCSS) was established, and a calibration system using standard measuring instruments with clear traceability with national standards was established. Accuracy can be guaranteed.

  The survey meter used for radiation protection is a product that has passed the type test and inspection of Japanese Industrial Standard JIS Z4333. Post-purchase calibration can be calibrated at certified establishments based on the Measurement Act and establishments that possess reference measuring instruments calibrated at certified establishments at the request of the user within the traceability system leading to national standards. It has become.

  A survey meter for measuring external radiation used in establishments regulated by 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 such as using a calibrated product within is given.

  However, the frequency of calibration is not described in related laws and regulations, etc., and at present, it is not calibrated for a long time (for example, several years) after the initial calibration due to the cost of calibration and the number of days required for calibration. Not many survey meters are in use. Therefore, in order to ensure the reliability of measurement by these measuring instruments, the Japanese Industrial Standards relating to calibration have been revised and prescribed as “Appendix 2 Confirmation Calibration of Practical Measuring Instruments” in JIS Z4511 as part of practical calibration. Confirmation calibration was added.

  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. Previously, a Cs-137 braided wire source 3.7 MBq, which was not subject to the Radiation Hazard Prevention Act until 2007, was attached to a holding stand as shown in FIG. Was calibrated by the inverse square method while changing the distance between the source and the probe.

  Since this calibration method is affected by scattered radiation from inside the room, it is necessary to correct the dose due to the scattered radiation, and there is also a problem of exposure during work. In addition, the limits of laws and regulations have decreased, and at present, for example, in Cs-137, a 3.7 MBq radiation source needs to be licensed, and the radioactivity of a radiation source that does not require authorization has decreased to 10 kBq. For this reason, there is also a problem that a sufficient amount of change in the indicated value cannot be obtained with a small radiation source that is not subject to legal regulations. Further, as described above, there is a case where a checking radiation source is attached to the radiation dose (rate) measuring device, but there is a problem of loss, and such a checking radiation source is not attached at present.

  Therefore, survey meter owners may request calibration by a calibration facility such as an accredited establishment, or use a licensed sealed source at their own calibration facility that has received a standard supply from an accredited establishment. It was necessary to calibrate.

  Therefore, the applicant has proposed a verification calibrator in Patent Document 1 that can easily and easily determine whether or not the calibration constant can be continuously used without requiring a special calibration facility. This is made of granite, which is a natural radioactive material, in particular, plate granite obtained by processing into a plate shape granite containing natural radioactive potassium feldspar, and the amount of radiation (in the center of the plate granite on the bottom plate) The perforated granite provided with a hole into which the detector can be inserted is laminated to form a bowl-shaped volume radiation source, and the detector is inserted into the volume radiation source.

JP 2005-265765 A

  However, the technique described in Patent Document 1 requires a volume radiation source having a size capable of inserting a radiation dose (rate) detector, and has a problem such as taking a place for storage. .

  On the other hand, if it is a checking radiation source, it may be small. However, as legal regulations become stricter, it is possible to obtain a checking radiation source that emits gamma rays with a dose rate sufficient to confirm the operation of the survey meter. I can't.

  The present invention has been made to solve the above-mentioned conventional problems, and it is possible to easily and quickly confirm and calibrate a radiation dose (rate) measuring instrument with a low-radiation source that is not subject to legal regulations and does not require radiation management. The first problem is to be able to perform the above.

  It is a second object of the present invention to provide a confirmation calibration jig for a radiation dose (rate) measuring instrument capable of easily performing the calibration according to the present invention.

  As already mentioned, with low-activity γ-ray sources that do not require radiation management, the radiation dose (rate) measuring device hardly operates, and it is difficult to confirm its operation. . On the other hand, ionization chamber survey meters and GM survey meters can measure not only γ-rays but also β-rays by removing β-ray shielding caps, etc. The radiation dose (rate) measuring device can be sufficiently operated by an external low-activity β-ray source.

  The present invention has been made on the basis of such knowledge, and in the method for confirming and calibrating a radiation dose (rate) measuring device including γ rays in a measurement object, the radiation sensing unit of the radiation dose (rate) measuring device is β A β-ray source for confirmation and calibration is arranged at a predetermined position where a line can be measured, and β-rays emitted from the β-ray source are made incident on the radiation sensing unit instead of γ-rays, thereby the radiation. The first problem is solved by changing the indicated value of the quantity (rate) measuring instrument.

  Here, the β-ray source can be a plate-like radiation source having a larger area than the β-ray incident portion.

  Alternatively, the β-ray source can be disposed on a β-ray shielding means that can be attached to and detached from the radiation sensing unit.

  The radiation dose (rate) measuring device can be an ionization chamber type survey meter or a GM survey meter.

  The present invention is also characterized in that a β-ray source for confirmation and calibration is disposed in a detachable β-ray shielding means of a radiation dose (rate) measuring device containing γ-rays as a measurement object. The second problem is solved by a jig for confirmation and calibration of a quantity (rate) measuring instrument.

  Here, the β-ray shielding means can be a β-ray shielding cap.

  In addition, a β-ray source can be disposed in a radiation source holder disposed in an opening provided in the β-ray shielding cap.

  Further, the arrangement position of the β-ray source can be changed between a plurality of predetermined positions having different distances from the radiation sensing unit.

  In addition, a shielding plate can be inserted on the radiation sensing unit side of the β-ray source.

  According to the present invention, radiation is used outside the scope of legal regulation without using a large volume radiation source as described in Patent Document 1 or a high-activity γ-ray source that is subject to legal regulation and requires radiation management. Using a low-activity β-ray source that does not require management, it is possible to confirm and calibrate radiation dose (rate) measuring instruments such as survey meters that include γ-rays as measurement targets. Therefore, it is possible to easily and easily determine whether or not the calibration constant can be continuously used, and the radiation dose (rate) measuring instrument can be accurately calibrated to maintain its performance.

  In particular, when using the confirmation calibration jig according to the present invention, even if a small and inexpensive coin-shaped radiation source is used, only by replacing the β-ray shielding means such as a β-ray shielding cap, The radiation dose (rate) measuring instrument can be easily confirmed and calibrated.

The perspective view which shows the external appearance of an example of the conventional ionization chamber type survey meter The perspective view which shows the external appearance of an example of the conventional GM survey meter 1 is a cross-sectional view of a confirmation calibration jig of an ionization chamber survey meter according to a first embodiment of the present invention. Sectional drawing which shows the state which attached the radiation source to 1st Embodiment The front view which shows the shielding board which can be inserted in 1st Embodiment Sectional drawing which shows the state which inserted the shielding board in 1st Embodiment A cross-sectional view showing a state in which a shielding plate is also inserted and a radiation source is mounted in front of it (A) A cross-sectional view showing a confirmation calibration jig for an ionization chamber type survey meter according to a second embodiment of the present invention, and (B) a grip of the ionization chamber type survey meter to which the second embodiment is mounted is removed. Side view showing condition (A) Sectional view showing a jig for confirmation and calibration of a GM survey meter according to the third embodiment of the present invention, and a side view showing a probe tip of a GM survey meter to which the third embodiment is mounted The side view which shows the state which is confirming and calibrating the ionization chamber type survey meter in 4th Embodiment of this invention

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 3, the cap 16 ′ for calibration of an ionization chamber survey meter according to the first embodiment of the present invention opens an opening 16A in the β-ray shielding cap 16 of the ionization chamber survey meter shown in FIG. As shown in FIG. 4, a coin-like β-ray source 32 can be disposed on the radiation source holder 30 disposed in the opening 16A.

  The radiation source holder 30 is provided with, for example, two shielding plate insertion ports 30A and 30B, and a substantially U-shaped shielding plate 34 as illustrated in FIG. 5 is inserted into the insertion port as illustrated in FIG. It can be inserted into either one or both of 30A and 30B.

  As the shielding plate 34, for example, a plurality of acrylic plates or aluminum (also referred to as aluminum) plates having different thicknesses can be used.

  The β-ray source 32 is disposed at the rear surface position of the radiation source holder 30 as shown in FIG. 4, or the shielding plate 34 inserted into the insertion port 30B of the radiation source holder 30 as shown in FIG. By changing the distance from the radiation sensing unit by disposing it at the front surface position, the amount of change in the indicated value of the meter 12 can be changed. Further, the β-ray source 32 can be arranged at both the rear surface position and the front surface position of the radiation source holder 30. As the β-ray source 32, for example, Cl-36 or Sr-90 (also expressed as Sr-90 / Y-90 including Y-90 as a daughter nuclide) can be used.

  At the time of use, immediately after calibration by the calibration organization, instead of the usual β-ray shielding cap 16, for example, as shown in FIG. A cap 16 'is attached, and the indicated value of the meter 12 at that time is recorded. When the change amount of the indication value of the meter 12 is small, the position of the β-ray source 32 can be set to the front side as shown in FIG. On the contrary, when the change amount of the indicated value of the meter 12 is too large, as shown in FIG. 6, the shielding plate 34 is inserted into one or both of the insertion ports 30A and 30B to reduce the change amount of the indicated value. Can do. Furthermore, by changing the type, thickness, and radiation source position of the shielding plate, a plurality of change amounts can be set to check the linearity of the indicated value. Adjustment of the change amount of the indicated value is easier and cheaper by using the shielding plate than by changing the radiation source position.

  Record the amount of change in the meter indication value immediately after calibration by an accredited establishment, and attach the confirmation calibration cap 16 'instead of the β-ray shielding cap 16 every predetermined period, for example, every year, and then the meter indication at that time By comparing the amount of change in the value with the amount of change in the meter reading immediately after calibration after correcting the half-life of the radiation source according to the elapsed time immediately after calibration, Is within a predetermined range, for example, 1 ± 0.1, it is determined that calibration is not necessary, and when it exceeds the predetermined range, it is determined that calibration is necessary and calibration can be performed by a calibration organization or the like. .

  In this way, it is possible to easily carry out confirmation calibration only by fitting the β-ray shielding cap 16 to the confirmation calibration cap 16 ′ to which the β-ray source 32 is attached, without bringing it into the calibration engine.

  According to this embodiment, since the β-ray source 32 is mounted outside the β-ray shielding cap 16, it is easy to change the position of the β-ray source and to insert / replace the shielding plate.

  FIG. 8A shows an ionization chamber type survey meter according to a second embodiment of the present invention in which a β-ray source 32 is mounted inside the β-ray shielding cap 16 shown in FIG. 8B by, for example, bonding or fitting. The confirmation calibration cap 16 ″ is shown.

  According to the present embodiment, the outer size of the confirmation calibration cap 16 ″ is the same size as the normal β-ray shielding cap 16, and is very compact.

  9A shows a coin-shaped β-ray source 32 mounted on the inside of the β-ray shielding cap 22 of the probe 20 of the GM survey meter shown in FIG. 9B by, for example, adhesion or fitting. The cap 22 'for confirmation calibration of the GM survey meter concerning 3rd embodiment is shown.

  According to the present embodiment, the outer dimension of the confirmation calibration cap 22 ′ is the same size as that of the normal β-ray shielding cap 22, and is very compact.

  Also in the confirmation calibration cap of the GM survey meter, a β-ray source can be disposed outside the β-ray shielding cap 22 as in the first embodiment.

  In each of the above embodiments, since the β-ray source is fixed to the cap, even when a small and inexpensive coin-shaped radiation source is used, the relative positional relationship between the radiation sensing unit and the radiation source is determined. Accurate confirmation calibration can be performed while keeping constant.

  It is also possible to keep the relative positional relationship between the coin-shaped radiation source and the radiation sensing unit constant by using a separate jig other than the cap.

  Alternatively, when a plate-like radiation source having a large area can be used as the radiation source, the tip of the survey meter 10 (probe 20 in the case of a GM survey meter) with the cap removed is used as shown in the fourth embodiment shown in FIG. It is also possible to carry out the confirmation calibration in a state where it is pressed against the plate-like β-ray source 33 having a larger area than the β-ray incident portion.

  In this case, no jig is required. In particular, when a digital survey meter is used, there is no restriction on the measurement posture, so it is extremely easy to perform calibration by placing a plate-like radiation source horizontally and pressing the tip of the survey meter over it. be able to. In addition, when there is a restriction on the measurement posture, for example, a plate-like radiation source may be placed upright.

  As a β-ray source, an Sr-90 10 kBq sealed source that is not subject to legal regulations was used, and an experiment was conducted with a confirmation calibration cap 16 ′ attached to the β-ray shielding cap 16 of an ionization chamber type survey meter. As shown in Fig. 1, it was confirmed that the reproducibility and the amount of change of the meter indication value necessary for the confirmation calibration can be obtained.

  In the above embodiment, since the β-ray source 32 is attached to the refitable β-ray shielding caps 16, 22, even if a small and inexpensive coin-shaped source is used, the meter indication value at the same source position The reproducibility is good. The jig is also small and does not require a place to calibrate. In addition, the attachment position and attachment object of a beta ray source are not limited to this.

  Moreover, in the said embodiment, although this invention was applied to the ionization chamber type survey meter and GM survey meter, the application object of this invention is not limited to this, Survey meters other than these, survey meters, such as an area monitor and a gas monitor It can be similarly applied to other radiation dose (rate) measuring devices in general.

  In the case of an ionization chamber type survey meter, there is a mode for measuring a (cumulative) dose by measuring a potential difference accumulated in a capacitor. However, according to the present invention, not only a calibration of a dose rate but also a calibration of this cumulative dose. Is also possible. That is, when γ rays are used, shielding is not easy, but when β rays are used according to the present invention, shielding is easy. For example, by using a thick acrylic plate or metal plate as the shielding plate 34 in FIG. It is possible to turn on / off β rays by putting them in and out of the confirmation calibration cap 16 ′ as a shutter, and to confirm and calibrate the accumulated dose by irradiating β rays for a predetermined time. Instead of putting the shield plate 34 in and out, the confirmation calibration caps 16 ′, 16 ″ fitted with the β-ray source 32 can be attached and detached for a predetermined time, or the β-ray source 32 itself can be attached and detached for a predetermined time. Also good.

  The type of the radiation source is not limited to Cl-36 or Sr-90, and any sealed β radiation source having low radioactivity and high energy such as Ra-226 and Am-241 exemplified in JIS Z4511 may be used.

DESCRIPTION OF SYMBOLS 10 ... Ionization chamber type survey meter main body 12, 26 ... Meter 16, 22 ... Beta ray shielding cap 16 ', 16 ", 22' ... Confirmation calibration cap 20 ... GM counter probe 30 ... Radiation source holder 30A, 30B ... Shielding plate Insert 32, 33 ... β-ray source 34 ... Shield plate

Claims (9)

In the confirmation calibration method of the radiation dose (rate) measuring instrument containing γ-rays in the measurement target,
A beta ray source for confirmation calibration is arranged at a predetermined position where the radiation sensing unit of the radiation dose (rate) measuring device can measure beta rays,
By causing the β-rays emitted from the β-ray source to enter the radiation sensing unit instead of γ-rays,
A method for confirming and calibrating a radiation dose (rate) measuring device, wherein an indication value of the radiation dose (rate) measuring device is changed.   2. The method for confirming and calibrating a radiation dose (rate) measuring device according to claim 1, wherein the β-ray source is a plate-like radiation source having an area larger than that of the β-ray incident portion.   2. The method for confirming and calibrating a radiation dose (rate) measuring device according to claim 1, wherein the β-ray source is disposed in a detachable β-ray shielding means of the radiation sensing unit.   The radiation dose (rate) measuring instrument according to any one of claims 1 to 3, wherein the radiation dose (rate) measuring device is an ionization chamber type survey meter or a GM survey meter.   A radiation dose (rate) measuring device characterized in that a β-ray source for confirmation and calibration is disposed on a removable β-ray shielding means of a radiation dose (rate) measuring device containing γ rays as a measurement target. Confirmation calibration jig.   6. The jig for confirming and calibrating a radiation dose (rate) measuring instrument according to claim 5, wherein the β-ray shielding means is a β-ray shielding cap.   7. A radiation correction (rate) measuring apparatus for confirming and correcting a radiation dose (rate) measuring device according to claim 6, wherein a β-ray source is disposed in a radiation source holder disposed in an opening provided in the β-ray shielding cap. Ingredients.   The radiation dose according to any one of claims 5 to 7, wherein the arrangement position of the β-ray source can be changed between a plurality of predetermined positions having different distances from the radiation sensing unit. Rate) Jig for checking and calibrating measuring instruments.   9. The jig for confirming and calibrating a radiation dose (rate) measuring instrument according to claim 5, wherein a shielding plate can be inserted into the radiation sensing unit side of the β-ray source.

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