Magnitude and position dependence of Gammacell 220 drawer transit doses

A common use for Gammacell 220 (Atomic Energy of Canada, Ltd.) drawer-type 60Co irradiators is to deliver doses of hundreds or thousands of rads to a variety of biological specimens ranging from mammalian cell suspensions to whole animals such as mice or hamsters. With high 60Co loading such exposures may require only a few seconds even with attenuators present. Since absorbed dose typically is calculated on the basis of time spent in the center of the radiation field, and automatic timers typically begin timing only when the specimen reaches the center of the radiation field, radiation absorbed during transit can significantly modify the dose expected from standard calculations when the irradiation time is short. We measured the magnitude and position dependence of Gamma-cell 220 drawer transit doses with film dosimetry, and obtained data permitting calculation of actual samples dose for different 60Co loadings and for off-center sample positioning. (author)