Characterization of 49Ca as a γ-ray intensity standard

49Ca can be used to extend the efficiency calibration and rough energy calibration of a Ge γ-ray detector to almost 5 MeV. Spectra with good statistics can be obtained by multiple neutron irradiations of natural calcium. For calibration purposes the most useful γ-rays are 3084, 4072, and 4738 keV, for which we have obtained intensities of 90.72(4)%, 8.12(3)%, and 0.281(6)%, respectively. There is little coincidence summing of γ-rays in the decay. The absence of summing and the pattern of energies and intensities make 49Ca particularly useful in measuring full energy and annihilation escape efficiencies for small source-to-detector distances. We have acquired over 50 spectra with a large, well-characterized Ge detector and have determined the intensities of all observable γ-rays, six of which have not been reported previously.