Observations on the energy resolution of germanium detectors for 0.1-10 MeV gamma rays

The ratio of variance to yield was studied for γ-rays at energies up to 10.080 MeV in lithium-drifted germanium detectors. With detectors of thickness up to 14 mm this ratio was found to be as low as 0.13 /spl I.plusmn/ 0.02 at 122 and 356 keV. At energies between 1 and 10 MeV the ratio was found to be 0.16 ± 0.01, corresponding to a detector contribution of 4.8 /spl I.plusmn/ 0.1 keV (FWHM) at 10 MeV. Investigation of the dependence of the ratio of variance to yield on electric field intensity resulted in acceptance of F = 0.13 /spl I.plusmn/ 0.02 as the best experimental estimate of the Fano factor, and F = 0.16 is interpreted as an upper limit for γ-rays at energies between 1 and 10 MeV.