Proton irradiation of plastic scintillator bars for POLAR-2

TL;DR

This study evaluates the radiation tolerance of plastic scintillator bars for the POLAR-2 gamma-ray polarimeter, focusing on their performance after proton irradiation to ensure suitability for space-based gamma-ray measurements.

Contribution

It provides the first detailed analysis of plastic scintillator behavior under space-like proton irradiation doses exceeding the mission lifetime.

Findings

EJ-200 and EJ-248M scintillators maintain performance after high-dose irradiation.

Proton activation leads to beta-plus decay with 511 keV gamma-ray emission.

Scintillator properties degrade minimally up to doses beyond expected space mission exposure.

Abstract

POLAR-2, a plastic scintillator based Compton polarimeter, is currently under development and planned for a launch to the China Space Station in 2025. It is intended to shed a new light on our understanding of Gamma-Ray Bursts by performing high precision polarization measurements of their prompt emission. The instrument will be orbiting at an average altitude of 383 km with an inclination of 42{\deg} and will be subject to background radiation from cosmic rays and solar events. In this work, we tested the performance of plastic scintillation bars, EJ-200 and EJ-248M from Eljen Technology, under space-like conditions, that were chosen as possible candidates for POLAR-2. Both scintillator types were irradiated with 58 MeV protons at several doses from 1.89 Gy (corresponding to about 13 years in space for POLAR-2) up to 18.7 Gy, that goes far beyond the expected POLAR-2 life time. Their respective properties, expressed in terms of light yield, emission and absorption spectra, and activation analysis due to proton irradiation are discussed. Scintillators activation analyses showed a dominant contribution of $\beta^+$ decay with a typical for this process gamma-ray energy line of 511 keV.