Enhanced sensitivity to trace $^{238}$U impurity of sapphire via coincidence neutron activation analysis

TL;DR

This paper demonstrates that combining gamma-gamma coincidence counting with neutron activation analysis significantly improves the detection sensitivity of trace uranium and thorium impurities in sapphire, reaching parts-per-trillion levels.

Contribution

It introduces an experimental verification of a method that enhances sensitivity for detecting ultra-trace impurities in sapphire using gamma-gamma coincidence counting coupled with neutron activation analysis.

Findings

Achieved detection limits of <0.26 ppt for $ m ^{232}Th$ and <2.3 ppt for $ m ^{238}U$ in sapphire.

Validated the effectiveness of gamma-gamma coincidence counting combined with NAA for ultra-trace impurity analysis.

Provided the best constraints on sapphire radiopurity to date.

Abstract

Sapphire has mechanical and electrical properties that are advantageous for the construction of internal components of radiation detectors such as time projection chambers and bolometers. However, it has proved difficult to assess its $\rm ^{232}Th$ and $\rm ^{238}U$ content down to the picogram per gram level. This work reports an experimental verification of a computational study that demonstrates $\gamma\gamma$ coincidence counting, coupled with neutron activation analysis (NAA), can reach ppt sensitivities. Combining results from $\gamma\gamma$ coincidence counting with those of earlier single-$\gamma$ counting based NAA shows that a sample of Saint Gobain sapphire has $\rm ^{232}Th$ and $\rm ^{238}U$ concentrations of $<0.26$ ppt and $<2.3$ ppt, respectively; the best constraints on the radiopurity of sapphire.