RADIOACTIVITY MEASUREMENTS OF GD-153 PELLET SOURCES BY CALORIMETRIC METHODS

The thermal power generation per 37 MBq (1 mCi) of Gd-153 is 0.839-mu-W. The activity of a sealed Gd-153 source can be determined by absorbing all radiations within a calorimeter to be converted into the thermal power. Sources are sintered pellets (3 mm diameter, 2 mm thickness) of Gd2O3.Al2O3 which are encapsulated in titanium capsules of 7 mm diameter and 10 mm length. A cylindrical radiation absorber made of solid copper having a space in the center for the Gd-153 source is used and the temperature rise of the absorber is measured. Uncertainties are added up to +/- 2.9% for a 3-sigma confidence interval in the final result for the measurement of the activity of an approximately 1.5 GBq (40 mCi) pellet source of Gd-153 in a fully nondestructive way.