A mercuric iodide detector system for X-ray astronomy: I. Design considerations and predictions of background and sensitivity

Abstract

This is the first of two papers describing an extremely sensitive astronomical hard X-ray telescope design based on a mercuric iodide (HgI 2) detector shielded by a bismuth germanate (Bi 4Ge 3O 12) scintillator. In a version suitable for a Spacelab mission, this shielded detector is located at the focus of a pyrolytic graphite or lithium fluoride concentrator (the Hard X-ray Diffraction Telescope, or HXDT). The background counting rate of the mercuric iodide detector at balloon altitudes is calculated using a Monte Carlo simulation of the detector assembly in the radiation environment at 40 km above sea level. In paper II of this series, these predictions are compared to actual balloon flight measurements of a prototype detector assembly.