Detection of radiation in the energy range 0.1 to 10MeV by use of a nuclear gamma-ray spectrometer

An 86 cm(^3), actively shielded Ge(Hp), Nuclear Gamma-ray Spectro-meter was flown from Palestine, Texas, U.S.A., in August 1979, to a residual atmospheric pressure of 4.3 g cm(^-2); by means of a high altitude balloon. The design, construction and response characteristics of the instrument, which has: (a) an energy resolution of 2.5 keV at 1.33 MeV, (b) an opening angle of 5.2 (FWHM) and (c) a measured efficiency of 23% relative to a 3" x 3" NaI(T&) crystal, is described herein. Also presented are measurements of the gamma-ray lines which were detected at various atmospheric depths during the ascent phase of the flight. These features originate from secondary gamma production in the shield and Ge(Hp) crystal from atmospheric radiation 'leaking’ through it. The results are in accord with those obtained from independent experiments of other workers. The minimum sensitivity of the spectrometer to cosmic, point, line sources is shown to be 3 x 10(^3) and 1 x I0(^2) photons cm(^-2)s(^-1) for active and passive shielding respectively, for an observation time of one hour on both source and background.