Dosimetry in krypton-85 gas irradiation vessel.

概要

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Dose rates obtained in a cylindrical vessel filled with gaseous 85Kr source were measured using blue cellophane dosimeter. Besides obtaining the dose rate distribution within the vessel, the dose rate at vessel center was correlated to the 85Kr pressure, to the shape and size of the vessel, and to the material forming the inner wall surface. The 85Kr source used in the experiment amounted to 300 Ci (11. 1 TBq), with a radioactive concentration of 35.9 mCi/ml NTP (1.33 GBq/m/ NTP). The dose rate in the vessel was found to rise in direct proportion to the 85Kr pressure, and also to increase in keeping with the size of the irradiation vessel and with the atomic number of the material lining the inner wall. Fairly good uniformity of the dose rate was noted, a ratio of only 1. 33 being registered between the values obtained at the locations of maximum and minimum dose rate. The observed relationship between the dose rate and 85Kr pressure agreed fairly well with a theoretical expression derived for spherical β source. A dose rate of 4.8 X 107 rad/h (480 kGy/h) can be expected to be realized with a 85Kr source charged to 760 Torr (1. 01 X 105 Pa) in a vessel measuring 1, 710 mm X 570 mm diameter, lined with Pb.