Development of a Silicon Tracker for the All-sky Medium Energy Gamma-ray Observatory Prototype

Abstract

The gamma-ray sky from several hundred keV to ∼ a hundred MeV has remained largely unexplored due to the challenging nature of detecting gamma rays in this regime. At lower energies, Compton scattering is the dominant interaction process whereas at higher energies pair production dominates, with a crossover at a few MeV. Thus, an instrument designed to work in this energy range must be optimized for both Compton and pair-production events. AMEGO, the All-sky Medium Energy Gamma-ray Observatory, a Probe-class mission in consideration for the 2020 decadal survey, is designed to operate at energies from ∼ 200 keV to > 10 GeV with over an order of magnitude increase in sensitivity and with superior angular and energy resolution compared to previous instruments. AMEGO comprises four major subsystems: a plastic anticoincidence detector for rejecting cosmic-ray events, a silicon tracker for tracking pair-production products and tracking and measuring the energies of Compton-scattered electrons, a cadmium-zinc-telluride (CZT) calorimeter for measuring the energy and location of Compton scattered photons, and a CsI calorimeter for measuring the energy of the pair-production products at high energies. A prototype instrument, known as ComPair, is under development at NASA's Goddard Space Flight Center and the US Naval Research Laboratory. In this contribution, we provide details on the development of the silicon tracker subsystem.

Development of the ComPair gamma-ray telescope prototype

“…Fabricated by Micron Semiconductor Ltd, the silicon wafers are 500 µm thick with strips on each side that are orthogonal to each other to reconstruct the X and Y positions of interaction. 13 The strips are 60 µm wide with a pitch of ∼ 510 µm. This results in 192 AC-coupled strips per side.…”

“…This work presents the development of a thallium-doped cesium iodide (CsI:Tl) based calorimeter in support of the ComPair balloon-based telescope [8], which serves as a prototype to AMEGO and will be flown in the summer of 2023. The AMEGO concept consists of four subsystems: the double-sided Silicon strip detectors (DSSD) [9], virtual Frisch-grid CdZnTe calorimeter [10], CsI calorimeter, and a plastic-based anti-coincidence detector (ACD) [8]. The main concept behind this 'hybrid' telescope design is to maintain high detection sensitivity and good imaging performance through a large energy range that includes the Compton and pair-creation region.…”

Developing the Future of Gamma-ray Astrophysics with Monolithic Silicon Pixels

“…Because particle tracking in three dimensions is necessary to reconstruct Compton events, the Si for a combined pair/Compton tracker has to record position information in three dimensions as well as convey the energy associated with interactions in the material. This constrains a joint pair/Compton telescope to two types of Si technologies: double-sided silicon strip detectors (DSSDs) [11] or Si pixels.…”

Subsystem Development for the All-Sky Medium Energy Gamma-ray Observatory (AMEGO) prototype

“…The DSSDs are read out using custom front-end electronics (FEE) based on the IDEAS VATA460.3 ASIC; the device is in the process of being qualified [6]. The ASIC is a combined charge-sensitive preamplifier combined with a 10-bit ADC and supports both positive and negative signals.…”