The use of sources emitting coincident gamma-rays for the determination of photopeak and total efficiencies in non-point-source counting geometries

The validity of a previously published method for determination of full-energy peak as well as total efficiency curves and source activity from a Br-82 spectrum is experimentally tested for the case of a thin slab counted on the end cap of a 20% relative efficiency HpGe detector, as well as for a Marinelli beaker geometry. It is concluded that, even though a full-energy and total efficiency curve can be found that reproduce the measured Br-82 spectrum, the corresponding source activity is an underestimation of the true value, apparently depending on the degree of variation of the efficiencies over the source volume. The applicability of the curves found to other radionuclides is as yet unclear.