Gamma-ray astronomy in the MeV range suffers from weak fluxes from sources and high background in the nuclear energy range. The background comes primarily from neutron-induced gamma rays, with the neutrons being produced by cosmic-ray interactions in the Earth's atmosphere, the spacecraft, and the instrument. Compton telescope designs often suppress this background by requiring coincidences in multiple detectors and a narrow time-of-flight (ToF) acceptance window. The COMPTEL experience on the Compton Gamma Ray Observatory shows that a 1.9-ns ToF resolution is insufficiently narrow to achieve the required low background count rate. Furthermore, neutron interactions in the detectors themselves generate an irreducible background. By employing LaBr3 scintillators for the calorimeter, one can take advantage of the unique speed and resolving power of the material to improve the instrument sensitivity and simultaneously enhance its spectroscopic performance and thus its imaging performance. We present a concept for a balloon- or space-borne Compton telescope that employs deuterated liquid in the scattering detector and LaBr3 as a calorimeter and estimate the improvement in sensitivity over past realizations of Compton telescopes. We show initial laboratory test results from a small prototype, including energy and timing resolution. Finally, we describe our plan to fly this prototype on a test balloon flight to directly validate our background predictions and guide the development of a full-scale instrument.
Space Science Center, Physics
Digital Object Identifier (DOI)
Peter F. Bloser ; James M. Ryan ; Jason S. Legere ; Manuel Julien ; Christopher M. Bancroft ; Mark L. McConnell ; Mark Wallace ; R. Marc Kippen and Shawn Tornga "A new low-background Compton telescope using LaBr3 scintillator", Proc. SPIE 7435, UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XVI, 74350H (August 20, 2009); doi:10.1117/12.826191; http://dx.doi.org/10.1117/12.826191
© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering.