Instrumental background in balloon-borne gamma-ray spectrometers and techniques for its reduction

Abstract A study of the instrumental background in balloon-borne gamma-ray spectrometers is presented. The calculations are based on newly available interaction cross sections and new analytic techniques, and are the most detailed and accurate published to date. Results compare well with measurements made in the 20 keV to 10 MeV energy range by the Goddard Low Energy Gamma-ray Spectrometer (LEGS). The principal components of the continuum background in spectrometers with Ge detectors and thick active shields are (1) elastic neutron scattering of atmospheric neutrons on the Ge nuclei, (2) aperture flux of atmospheric and cosmic gamma rays, (3) β − decays of unstable nuclides produced by nuclear interactions of atmospheric protons and neutrons with Ge nuclei, and (4) shield leakage of atmospheric gamma rays. The improved understanding of these components leads to several recommended techniques for reducing the background. These include minimizing the passive material inside the shield and reducing the level of the shield threshold. A new type of coaxial n-type Ge detector with its outer contact segmented into horizontal rings can be used in various modes to reduce background in the 20 keV to 1 MeV energy range. The resulting improvement in instrument sensitivity to spectral lines is a factor of ∼ 2 in this energy range.

[1]  V. Schoenfelder,et al.  The vertical component of 1--20 MeV gamma rays at balloon altitudes , 1980 .

[2]  J. Kurfess,et al.  A balloon observation of the diffuse cosmic X-radiation above 20 keV. , 1978 .

[3]  M. Leventhal,et al.  A search for gamma-ray lines from Nova Cygni 1975, Nova Serpentis 1970, and the Crab Nebula , 1977 .

[4]  J. Corbett.  Electron Radiation Damage in Semiconductors and Metals. , 1966 .

[5]  K. C. Chandler,et al.  Calculations of neutron flux spectra induced in the Earth's atmosphere by galactic cosmic rays , 1973 .

[6]  R. D. Evans,et al.  Atomic Nucleus , 2020, Definitions.

[7]  G. H. Nakano,et al.  High‐Resolution Measurements of Atmospheric Gamma Rays from a Satellite , 1976 .

[8]  J. A. Lezniak,et al.  The comparative spectra of cosmic-ray protons and helium nuclei , 1974 .

[9]  J. Ryan,et al.  atmospheric gamma ray angle and energy distributions from 2 to 25 MeV , 1977 .

[10]  H. Paul.  Shapes of beta spectra , 1966 .

[11]  W. Mahoney,et al.  A balloon-borne Ge(Li) spectrometer for gamma-ray astronomy , 1975 .

[12]  J. Ling.  A semiempirical model for atmospheric γ rays from 0.3 to 10 MeV at λ = 40° , 1975 .

[13]  M. Niel,et al.  Study of diffuse cosmic and atmospheric gamma radiation using a spark chamber in the energy range 4 MeV--100 MeV , 1982 .

[14]  L. Hsieh.  ATMOSPHERIC NEUTRON AND GAMMA RAY FLUXES AND ENERGY SPECTRA AT BALLOON ALTITUDE , 1979 .

[15]  J. Matteson,et al.  Techniques in balloon X-ray astronomy , 1972 .

[16]  U. Graser,et al.  Diffuse cosmic and atmospheric MeV gamma radiation from balloon observations , 1977 .

[17]  Jennifer K. Ryan.  Energy and angle distributions for atmospheric and cosmic diffuse gamma rays from 2 to 25 MeV , 1976 .

[18]  G. Knoll.  Radiation detection and measurement , 1979 .

[19]  W. H. Kelly,et al.  A single crystal Ge(Li) Compton spectrometer , 1967 .

[20]  W. Mahoney,et al.  Measurement of 0.511-MeV Gamma Rays With a Balloon-Borne Ge(Li) , 1977 .

[21]  F. Albernhe.  Recent Measurements with a Balloon-Borne ge (Li) Spectrometer in Gamma-Ray Astronomy (Presented by P. Durouchoux) , 1978 .

[22]  B. Rossi,et al.  High-Energy Particles , 1953 .