Line features in the background γ-ray spectrum in the range 0.05–10 MeV at balloon altitudes

Abstract An actively shielded high resolution γ-ray spectrometer has been flown as a balloon payload on two occasions, and most recently in June 1981, to search for γ-ray features in the spectra of astrophysical sources. A comprehensive table of background lines recorded on the June 1981 flight is given and there is evidence for γ-rays from several members of the natural uranium radioactive series; the origin of which is uncertain. The main nuclide detected in the series is 214 Bi and there is no evidence that this originates in the spectrometer material therefore an atmospheric origin is suggested.