Radiation-tolerant polarized solid target

TL;DR

This paper presents a novel radiation-tolerant polarized solid target operating at room temperature, demonstrating stable proton polarization under high-intensity irradiation, enabling advanced experiments in accelerator science.

Contribution

The study introduces a radiation-tolerant polarized solid target using Triplet-DNP at room temperature, with effective annealing for damage repair, advancing the practicality of high-intensity beam experiments.

Findings

Proton polarization of 3.0% achieved under irradiation.

Target maintained polarization up to 10^9 cps.

Radiation damage was visually observed and characterized.

Abstract

Polarized targets evolved into indispensable tools in particle and nuclear physics. However, the polarized solid target is degraded by high-intense beam irradiation, known as radiation damage due to target heating and radical generation. We demonstrated a radiation-tolerant polarized solid target operating at room temperature. An annealing allows the spontaneous repair of the damage by reducing unwanted radicals. Using a single crystal of $\it p$-terphenyl doped with 0.01 mol\% pentacene-$\it d$$_{14}$, Dynamic Nuclear Polarization using photoexcited triplet electrons (Triplet-DNP) was applied to proton spins at room temperature and in 0.39 T. For the proof of concept, a deuteron beam with an energy of 135 MeV/u and the intensities of 10$^7$-10$^9$ counts per second (cps) was irradiated. The proton polarization was determined to be 3.0\% $\pm$0.2\%$\rm{{(stat.)}}$ $\pm$0.1\%$\rm {{(sys.)}}$ from a scattering asymmetry. The polarization was almost not attenuated up to 10$^9$ cps, but the target crystal was yellowed. The visible-light absorption spectroscopy suggested irreversible radiation damage due to missing protons by the knock-out reaction. The room-temperature polarized solid target allows impractical experiments with the conventional target system, leading to a next-generation spin-dependent accelerator science.