JP5509002B2 - Ionization chamber type radiation measuring instrument confirmation calibration method and ionization chamber type radiation measuring instrument - Google Patents

Description

The present invention relates to check the calibration method and ionization chamber radiation measuring instrument ionization chamber radiation meter, in particular, whether it is necessary to perform calibration of the ionization chamber Sabeime data of which ionization chamber radiation counters capable of determining easily, confirmed on calibration method and ionization chamber radiation measuring instrument ionization chamber radiation counter.

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 is ionization chamber Sabeime data illustrated in. 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. Ru possible β-ray shielding cap der.

  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 measuring instrument , and has a problem of 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, wherein those so has been made to solve the conventional problems, in the source of the low activity outside radiological management is not required legally relevant, easily and quickly check the calibration of the ionization chamber radiation counters The first problem is to be able to perform the above.

It is a second object of the present invention to provide an ionization chamber type radiation measuring instrument capable of easily performing confirmation calibration according to the present invention.

As already mentioned, in the γ-ray source of the following low radioactivity radiological management is unnecessary regulatory lower limit quantity, the survey meter does not throat operation N殆, the operation check is difficult. On the other hand, in etc. ionization chamber Sabeime data, by removing the like β-ray shield cap, has a can operate in β-rays not only γ rays, by removing and β-ray shield cap, regulatory limit The survey meter can be operated sufficiently with a low-activity β-ray source of less quantity .

The present invention has been made on the basis of such knowledge. By removing the β-ray shielding means detachably disposed on the β-ray incident window, the ionization can be operated not only with γ-rays but also with β-rays. In the method of confirming and calibrating a box-type radiation measuring instrument, a sealed β-ray source whose radioactivity is less than or equal to the regulated lower limit quantity determined based on the Radiation Hazard Prevention Act is disposed on the β-ray shielding means, and the sealed β-ray By making the β-rays radiated from the radiation source enter the β-ray incident window instead of the γ-rays, the indication value of the ionization chamber radiation measuring device is changed, and the operation is confirmed. This is a solution to the first problem.

  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 shielding means can be a β-ray shielding cap .

Further, the ionization chamber radiation meter can be an ionization chamber survey meter.

The present invention also is detachably attached to the β-ray incident window, it can run on β rays not only by Ri γ rays by removing the β-ray shield means that will be mounted at the time of measurement and has been ionization chamber An ionization chamber comprising a calibration β-ray shielding means in which a sealed β-ray source having a radioactivity equal to or lower than a lower limit quantity subject to regulation determined based on the Radiation Hazard Prevention Law is provided in a radiation measuring instrument . The above-mentioned second problem is solved by the type radiation measuring instrument .

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

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

Moreover, the arrangement position of the sealed β-ray source can be changed between a plurality of predetermined positions having different distances from the β-ray incident window.

In addition, a shielding plate can be inserted into the β-ray incident window side of the sealed β-ray source.

According to the present invention, large and volume-ray source as described in Patent Document 1, without using a γ-ray source of highly radioactive requiring radiological management, the radiation control in the following regulatory limit quantity Using an unnecessary low-activity sealed β-ray source, it is possible to confirm and calibrate an ionization chamber type radiation measuring device for measuring γ-rays. Therefore, it can be determined easily and easily whether or not the calibration constant can be continuously used, and the ionization chamber radiation measuring instrument can be accurately calibrated to maintain its performance.

In particular, when the ionization chamber radiation measuring instrument according to the present invention is used, even if a small and inexpensive coin-shaped radiation source is used, it is only necessary to replace a β-ray shielding means such as a β-ray shielding cap. By removing the β-ray shielding means that is detachably disposed on the β-ray incident window, it is possible to easily confirm and calibrate the ionization chamber radiation measuring instrument that can operate not only with γ-rays but also with β-rays .

The perspective view which shows the external appearance of an example of the conventional ionization chamber type 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

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

As shown in FIG. 2 , the cap 16 ′ for confirming and calibrating the 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. 3 , a coin-like β-ray source 32 can be disposed in the radiation source holder 30 disposed in the opening 16A.

The radiation source holder 30, for example two shielding plates outlet 30A, 30B are provided, the shield plate 34 of a substantially U-shape as illustrated in FIG. 4, as illustrated in FIG. 5, the insertion port 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, or disposed on a surface position after the source holder 30 as shown in FIG. 3, or, as shown in FIG. 6, the source holder 30 for example of the shield plate 34 inserted into the insertion port 30B By changing the distance from the β-ray incident window by disposing it at the front surface position, the amount of change in the indication 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.

In use, immediately after the calibration by the calibration engine, instead of the normal β-ray shield cap 16, for example as shown in FIG. 3, for checking the calibration of mounting the β-ray source 32 to the surface position after the source holder 30 A cap 16 'is attached, and the indicated value of the meter 12 at that time is recorded. When the amount of change in the indicated value of the meter 12 is small, as shown in FIG. 6, the position of the β-ray radiation source 32 may be a front side. On the contrary, when the change amount of the indicated value of the meter 12 is too large, as shown in FIG. 5 , 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. 7 (A) is a β-ray source 32, FIG. 7 inside the β-ray shield cap 16 (B), the ionization chamber according to a second embodiment of the present invention mounted, for example, by bonding or fitting surveymeter 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.

In the above embodiments, since the β-ray source is fixed to the cap, the relative positional relationship between the β-ray incident window and the radiation source can be obtained even when a small and inexpensive coin-shaped radiation source is used. It is possible to carry out accurate confirmation calibration while maintaining a constant value.

It is also possible to keep the relative positional relationship between the coin-shaped radiation source and the β-ray incident window constant by using β-ray shielding means other than the cap.

  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.

Further, in the above embodiment, although the present invention has been applied to the ionization chamber Sabeime data, application of the present invention is not limited thereto, the ionization chamber radiation measurement apparatus generally non survey meter, such as area monitor Can be applied similarly.

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, by not easy shielding case of using γ-rays, when using a β-ray according to the present invention is to shield since it is easy, for example, thick acrylic plate shielding plate 34 in FIG. 5 and the metal plate, 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 1 2 ... Meter 1 6 ... Beta ray shielding cap 16 ', 16 "... Confirmation calibration cap 30 ... Radiation source holder 30A, 30B ... Shield plate insertion port 32 ... Beta ray source 34 ... Shield

Claims (8)

In a method for confirming and calibrating an ionization chamber radiation measuring instrument that can operate not only with γ rays but also with β rays by removing the β ray shielding means detachably disposed on the β ray incident window,
In the β-ray shielding means, a sealed β-ray source whose radioactivity is less than or equal to the lower limit quantity regulated based on the Radiation Hazard Prevention Act is disposed,
By making β rays emitted from the sealed β ray source enter the β ray incident window instead of γ rays,
The method of confirming calibration ionization chamber radiation counter, characterized in that to check the operation by changing the instruction value of the ionization chamber radiation counter.   The method for confirming and calibrating an ionization chamber radiation measuring instrument according to claim 1, wherein the β-ray shielding means is a β-ray shielding cap. The method for confirming and calibrating an ionization chamber radiation meter according to claim 1 or 2, wherein the ionization chamber radiation meter is an ionization chamber survey meter. In an ionization chamber type radiation measuring instrument that is detachably disposed on the β-ray incident window and is operable not only with γ-rays but also with β-rays by removing the β-ray shielding means attached at the time of measurement.
An ionization chamber type radiation measuring instrument comprising calibration β-ray shielding means in which a sealed β-ray source having a radioactivity equal to or less than a lower limit quantity to be regulated determined based on the Radiation Hazard Prevention Law is provided.   The ionization chamber radiation measuring instrument according to claim 4, wherein the calibration β-ray shielding means is a β-ray shielding cap. 6. The ionization chamber radiation measuring instrument according to claim 5, wherein the sealed β-ray source is disposed in a radiation source holder disposed in an opening provided in the β-ray shielding cap. The ionization according to any one of claims 4 to 6, wherein an arrangement position of the sealed β-ray source is changeable between a plurality of predetermined positions having different distances from the β-ray incident window. Box-type radiation measuring instrument. The ionization chamber type radiation measuring instrument according to any one of claims 4 to 7, wherein a shielding plate can be inserted into a beta ray incident window side of the sealed beta ray source.

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