A source of 3.85-MeV gamma rays for testing Ge(Li) detectors

Abstract

Mono-energetic 3.85-MeV gamma rays, and lower energy gamma rays, have been produced in a source consisting of an intimate mixture of 10 B and PuO 2 . Levels in 13 C are excited by the 10 B(α,pγ) 13 C reaction and the Doppler broadening of gamma rays from the 3.85-MeV level is attenuated, since its lifetime is long compared with the slowing-down time of 13 C ions in the source material. When observed with a particular 15-cm 3 Ge(Li) detector, the 3.85-MeV full-energy peak had a width of 4.5 keV(FWHM), consistent with no Doppler broadening. The measured energy of the gamma ray from the third excited state of 13 C is 3854 ± 1 keV. The branching ratios I(3854 → 3090)/I(3854 → 0) = 2.5 ± 0.5 × 10 −2 and I(3854 → 3685)/I(3854 → 0) = 0.55 ± 0.03 have been determined using the source.