Construction of Gamma-ray and Neutron Irradiation Field

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  • γ線及び中性子線照射場の構築
  • ガンマセン オヨビ チュウセイシセン ショウシャジョウ ノ コウチク

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Abstract

Gamma-ray and neutron irradiation field was constructed in National Institute of Radiological Sciences, primarily for calibration of survey meters and test of dosimeters that are to be supplied for radiation emergency medicine. This facility has nine irradiation sources:137Cs(7.4MBq, 74MBq, 740MBq, 7.4GBq, 74GBq), 60Co(74MBq), 241Am(3.7GBq), 241Am-Be(185GBq), and a dummy. Experimental investigations about dose rates on the irradiation table, dose rate changes with angle and their dependence on distance have been performed so far. It is found that 1-cm dose equivalent rates at 1m from the sources were in the range from 0.7×10−6 to 6.9×10−3 Sv h−1 in gamma-ray irradiation, and 1.3×10−4 Sv h−1 in neutron irradiation. The distribution of the dose rate from the gamma-ray(neutron) source changed at less than 3%(4%) from isotropic distribution. The dose rate dependence on distance between the gamma-ray source center and the geometrical center of the spherical ionization chamber differed slightly from inverse square law due to gamma-ray scattering by concrete walls and an irradiation table. As a result, it is considered that the constructed irradiation field has satisfying performance for the primary purpose. The future task is to advance the evaluation and maintenance of the irradiation field for more precise experiment.

Journal

  • RADIOISOTOPES

    RADIOISOTOPES 57 (3), 167-174, 2008

    Japan Radioisotope Association

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