Development of a CdZnTe Imaging Calorimeter for Gamma-ray Astronomy

Building on our previous APRA work, we propose to advance the capabilities of CdZnTe bar detectors for use in future medium-energy -ray missions. The largely unexplored MeV energy range offers great potential for astrophysics discovery, including aspects of nucleosynthesis, multimessenger/gravitational waves, jets, and compact objects. This field has been constrained by low cross sections, high backgrounds, and limitations in technology. With current APRA funding that ends this year, our team in collaboration with Brookhaven National Laboratory has been working on the development of a CdZnTe bar detector that can be used in next-generation -ray telescopes to explore the MeV gap. Initial measurements of the detector performance are encouraging and have exceeded the predicted response. At the same time, based on the results obtained, we identified several opportunities for further improvements of the calorimeter performance and increased potential utilization in space instruments. With its impressive energy and position resolution and good efficiency, the proposed CdZnTe Imaging Calorimeter will be a mission-enabling technology in the next generation of -ray telescopes, for example the Probe-class concept AMEGO being submitted to the Astro2020 Astronomy and Astrophysics Decadal Survey. In this APRA, we are proposing to continue development of the promising CdZnTe bar detector with the following objectives: • Design, optimize and develop a prototype of a modular CdZnTe calorimeter (Sec 4.1) o Confirm detector parameters of energy resolution and position resolution. o Investigate the improvement of the calorimeter performance by using a wave-front-sampling ASIC which offers the digitized waveform processing. • Perform bench and beam tests of the complete CdZnTe calorimeter (Sec 4.2) o Investigate and optimize the imaging calorimeter operation with high-energy photons (above 2 MeV) where multi-interaction events dominate and the Compton and Pair regime compete. o Perform activation tests of the CdZnTe at a proton beam facility to understand the dominating background component at MeV energies: activation. o Develop the event reconstruction, calibration and data analysis algorithms for the proposed calorimeter, based on the MEGAlib toolkit. • Validate higher-level instrument requirements (Sec 4.3) o Confirm the operation of the CdZnTe Imaging Calorimeter as a standalone Compton detector, with capability of measuring polarization of -rays. o Simulate a coded aperture mask instrument with the proposed Imaging Calorimeter as the focal plane. Such a system could achieve high angular resolution, on the order of arcminutes, which is not possible with any other high TRL method. This work will elevate overall TRL of the CdZnTe calorimeter from the current level of 2-3 to 4-5 allowing the proposed imaging calorimeter to enable future -ray missions.

The Astrophysics Research and Analysis program (APRA) supports suborbital and suborbital-class investigations, development of detectors and supporting technology, laboratory astrophysics, and limited ground based observing. Basic research proposals in these areas are solicited for investigations that are relevant to NASA's programs in astronomy and astrophysics, including the entire range of photons, gravitational waves, and particle astrophysics. The emphasis of this solicitation is on technologies and investigations that advance NASA astrophysics missions and goals.

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