Recommended standards for γ-ray energy calibration (1999)

A consistent set of γ-ray energies, generally with uncertainties of less than 10 ppm, is recommended for use in the energy calibration of γ-ray spectra. The energy scale used for the previously recommended standards (1979) has been modified to take into account subsequent adjustments in the fundamental constants (−7.71 ppm) and in the γ-ray wavelengths deduced from a revised estimate of the lattice spacing of Si crystals (+1.91 ppm). On this revised energy scale, the strong line from 198Au, the “gold standard”, has an energy of 411 802.05±0.17 eV, which is 2.4 eV (or 5.80 ppm) lower than the 1979 value. A significant improvement has come from the reduction in the uncertainty in the wavelength-to-keV conversion factor from 2.6 to 0.3 ppm. The criteria for the selection of γ rays to include are described. The list of γ-ray energies recommended for calibration, especially for Ge semiconductor detectors, has values for about 260 γ-rays from 50 radionuclides ranging from 24 to 4806 keV. Also, γ-ray energies are also given for about 70 additional lines, including 5 other radionuclides.