Accurate assays of radioactive materials by gamma-ray spectroscopy depend on many factors, the most obvious being accurate
gamma-ray intensities. We have used radiochemical methods to prepare pure samples of actinides. One portion of each of these
samples was used to measure disintegration rates (generally by liquid scintillation counting), and the remainder was used
to obtain count rates of specific gamma-rays in a well-characterized HPGe spectrometer. These methods are illustrated by results
from studies of neptunium isotopes 237, 238, and 239.