Abstract
Purpose: The feasibility of FWT-70-40(M) dosimeter was studied for gamma dose measurement in a neutron and gamma mixed field. Furthermore, it was adopted as another dosimeter to determine the gamma dose in an epithermal neutron beam for Boron Neutron Capture Therapy (BNCT). Material and Methods: The dosimeter used in this article was FWT-70 series of type FWT-70-40 (M). Using the Co-60 source of 29190 curies, which located in the Nuclear Science and Technology Development Center of National Tsing Hua University, performed calibration of the gamma dose sensitivity. The radiation sensitivity and the range of the linear response were obtained by irradiating the dosimeter with various dose rates and different total dose. Besides, this dosimeter was also irradiated with high neutron flux in the reactor core of the Tsing Hua Open pool Reactor (THOR) to investigate the neutron influence and activation. And then it was adopted as another dosimeter to measure the gamma dose in the BNCT facility at THOR. Results: Experimental data show that: (1) the threshold of linear response is 2 Gy, while the up limitation is 7 kGy for average gamma energy of 1.25 MeV; (2) the major product of the neutron activation is Na-24. The accumulated self-exciting dose for Na-24 is only 1.12 mGy during its average life-time for irradiation of total thermal neutron fluence of 3.6E12 nth/cm^2. Conclusions: Because of the self-exciting dose reduced from neutron activation can be neglected for gamma dose measurement in neutron and gamma mixed field, and the threshold of linear response is 2 Gy, the FWT-70-40 (M) dosimeter not only can be used for high dose rate Co-60 irradiation field and the high energy electron beam for medical purpose, but also can be used for gamma dose measurement in an epithermal neutron beam for boron neutron capture therapy.
Published Version
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