A technique for measuring the efficiency of a Ge(Li) spectrometer for gamma-ray sources in “gas bomb” geometries has been developed. The compounds of (CH3)2Se, CH3CH2Br, and CH3I are labeled with 75Se, 82Br, and 131I, respectively. These compounds readily vaporize at reduced pressure. The labeled compounds are flame sealed in small ampoules and the gamma-ray emission rates are measured. The contents of each ampoule are then released into the evacuated gas bomb and the efficiency of the detector for the gas bomb geometry is determined from the emitted gamma rays. The radionuclides of 75Se, 82Br, and 131I emit gamma rays that cover the energy range from 66 to ∼1900 keV without any large gaps. A method is suggested for measuring the efficiency for gas bomb geometries at small detector distances, which minimizes the effect of coincidence summing.