Anisotropy measurements of a high dose rate Ir-192 source in air and in polystyrene

Anisotropy measurements in air and in polystyrene were performed for a Nucletron microSelectron 10 Ci Ir-192 source. TLD rods of similar sensitivity (+/- 3%) were placed on a semicircle around the source center which had been precisely localized by either radiographic means or direct measurement. The anisotropy, expressed as a ratio of TLD reading at a given angle relative to the longitudinal source axis, over the reading at 90 degrees, was measured for distances between 1 and 10 cm from the source center. For both media, a marked anisotropy of the high dose rate source was found. In air, there is no detectable variation in anisotropy with distance up to 10 cm from the source. In polystyrene, however, the anisotropy becomes less pronounced with increasing distance due to scatter. For both media, no difference, within the estimated experimental accuracy of +/- 5%, was found between three consecutive sources installed by the vendor.