Proton Radiation Damage and Annealing of COSI p-type Cross-strip HPGe Detectors

TL;DR

This study examines how high-energy proton radiation degrades COSI germanium detectors and demonstrates that high-temperature annealing can significantly repair spectral resolution loss caused by space radiation damage.

Contribution

It provides the first detailed analysis of proton radiation effects on COSI detectors and evaluates annealing as a method for long-term spectral resolution maintenance.

Findings

Proton irradiation increased detector FWHM from 2.98 keV to 4.08 keV.

High-temperature annealing reduced FWHM close to pre-radiation levels.

Charge traps were effectively repaired through annealing, restoring detector performance.

Abstract

In order to understand the effects of a space radiation environment on cross-strip germanium detectors, we investigated the effects of high-energy proton damage on a COSI detector and the capabilities of high-temperature annealing in repairing detector spectral resolution. We irradiated a COSI-balloon cross-strip high-purity germanium (HPGe) detector with 150 MeV protons resulting in a net fluence of $4.95\times10^8$ p$^+$/cm$^2$ and corresponding to ~10 years in COSI's space radiation environment. We repaired the resulting degradation in spectral resolution through a series of high-temperature anneals to obtain a final FWHM of 4.08 keV, within 37% of its preradiation value (2.98 keV FWHM). We characterized the repair of charge traps with time spent under high-temperature anneal to inform an annealing procedure for long-term maintenance of COSI's spectral resolution.