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

Simulations and measurements of the background encountered by a high-altitude balloon-borne experiment for hard X-ray astronomy

“…The sources of detected background in balloon-borne hard X-ray detectors are reviewed in detail by Gehrels [5] and Dean et al [6]. We include the effects of atmospheric and cosmic gamma rays, and atmospheric and locally produced neutrons.…”

“…The first part of the code consists of a photon-transport program, phot trans (developed initially at the Massachusetts Institute of Technology and then by us at Harvard), which takes input spectral and spatial distributions of gamma rays and from these generates the spectral and spatial distributions of photons incident on the actual detector. For the input spectrum, we use the one given by Gehrels [5], which is based on data obtained at balloon altitudes (∼ 3.5 g cm −2 residual atmosphere) over Palestine, Texas. The incident photons are assumed to be isotropic, which is a good approximation [5].…”

“…For the input spectrum, we use the one given by Gehrels [5], which is based on data obtained at balloon altitudes (∼ 3.5 g cm −2 residual atmosphere) over Palestine, Texas. The incident photons are assumed to be isotropic, which is a good approximation [5]. A simplified flow diagram of phot trans is shown in Figure 2.…”

Simulation of HEAO 3 Background

“…where i is a stable isotope in volume V, a i is its fractional abundance, i the density, N o is Avogadro's number, A i is the atomic weight, n(j,i) and p(j,i) are the cross-sections for neutron and proton spallation to beta-unstable isotope j from isotope i, and f p and f n are the proton and neutron fluxes [5]. The fractional abundance a i was calculated for the isotopic fraction for each element in each material.…”

“…In this work, the proton and neutron flux inside the shield was estimated according to the scaling method used by Gehrels [4]. This method was based on data from the balloon instrument, Low Energy Gamma-ray Spectrometer (LEGS), and scaled to predict fluxes as a function of altitude and orbit inclination [5].…”