Radiation Damage in Polarized Ammonia Solids

TL;DR

This paper analyzes the radiation damage effects on polarized ammonia solids used in high-energy physics experiments, focusing on polarization decay, recovery procedures, and microwave frequency optimization.

Contribution

It provides detailed insights into radiation damage mechanisms and practical methods for maintaining polarization in ammonia targets during experiments.

Findings

Polarization decays with accumulated charge but can be recovered through annealing.

Frequency modulation of microwave polarization improves polarization stability.

Radiation damage alters the optimal microwave frequency for polarization.

Abstract

Solid NH3 and ND3 provide a highly polarizable, radiation resistant source of polarized protons and deuterons and have been used extensively in high luminosity experiments investigating the spin structure of the nucleon. Over the past twenty years, the UVA polarized target group has been instrumental in producing and polarizing much of the material used in these studies, and many practical considerations have been learned in this time. In this discussion, we analyze the polarization performance of the solid ammonia targets used during the recent JLab Eg4 run. Topics include the rate of polarization decay with accumulated charge, the annealing procedure for radiation damaged targets to recover polarization, and the radiation induced change in optimum microwave frequency used to polarize the sample. We also discuss the success we have had in implementing frequency modulation of the polarizing microwave frequency.