Simulated Performance of CZT-Based Focal Plane Detectors for Gamma-Ray Lenses

The Gamma-Ray Imager (GRI) is a Laue-lens space telescope mission concept utilizing Bragg diffraction to focus gamma rays from roughly 150 keV up to around 1 MeV onto a distant focal plane detector. The novel ability to concentrate gamma rays and the resulting improvements in sensitivity require a focal plane system well matched to the lens (at least a few mm position resolution and a few keV energy resolution). Several layers of CZT detectors constitute one option for the focal plane detector. Above the CZT, several layers of Si-strip detectors might be placed to increase the fraction of Compton scattered events at low energies. Such a setup enables (1) utilizing Compton scattering for background reduction, (2) selecting only events with the initial interaction in the lens´ focal spot, and (3) measuring the photons´ polarization. Simulations of the expected space radiation environment at L2 and the resulting detector activation are performed to determine the achievable narrow and broad line, continuum, and polarization sensitivity of the CZT focal plane detectors and compare them to focal plane configurations based on Germanium.