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Determination of the exposure rate constant for 125 I using a scintillation detector
Author(s) -
Schulz R. J.,
Chandra Premala,
Nath Ravinder
Publication year - 1980
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.594691
Subject(s) - detector , scintillation , physics , scintillation counter , constant (computer programming) , nuclear physics , nuclear medicine , optics , medicine , computer science , programming language
A scintillation spectrometer was employed to determine the exposure rate constant for an 125 I seed of the type used in therapeutic radiology. The method consisted of converting counting rate to photon fluence incident upon the detector, and then calculating the exposure rate from the photon fluence. Corrections are required for absorption of the 125 I photons in the air path, in the aluminum window of the NaI crystal, and in the aluminum–oxide reflector. Corrections are also required for the escape of iodine K –characteristic radiation, and the intrinsic peak efficiency of the crystal. The experimentally determined exposure rate constant in a direction perpendicular to the long axis of the seed is 1.309 R cm 2 mCi −1 h −1 ±5.8%, and this compares favorably with a calculated value of 1.284 R cm 2 mCi −1 h −1 . The photon fluence as a function of angle of rotation about an axis perpendicular to the seed's long axis was also measured. These data were used to estimate an average exposure rate constant for 125 I seeds of 1.089 R cm 2 mCi −1 h −1 .