Ultra-trace analysis of U and Th in organic liquid scintillators with high sensitivity

TL;DR

This paper introduces a highly sensitive method combining neutron activation, radiochemistry, and coincidence spectroscopy to detect ultra-trace levels of uranium and thorium in liquid scintillators, crucial for low-background physics experiments.

Contribution

It presents a novel screening technique achieving unprecedented sensitivity levels for U and Th in organic scintillators, surpassing previous methods.

Findings

Achieved sensitivities of 0.65E-15 g/g for U and 2.3E-15 g/g for Th.

Method combines neutron activation, radiochemistry, and coincidence spectroscopy.

Potential for further sensitivity improvements outlined.

Abstract

Rare event searches demand extremely low background levels, necessitating ever-advancing screening techniques to enhance sensitivity. Liquid scintillators are highly attractive as detector media due to their inherent radiopurity and scalability in mass. In this work, we present a screening procedure to measure ultra-trace concentrations of natural contaminants -- $^{238}$U and $^{232}$Th -- with sensitivities at the \qty{E-15}{g/g} level. Our method combines neutron activation analysis with radiochemical techniques, followed by \bg\ coincidence spectroscopy to minimize interference backgrounds. This approach achieves sensitivities of \qty{0.65E-15}{g/g} for $^{238}$U and \qty{2.3E-15}{g/g} for $^{232}$Th, among the best reported worldwide. Potential pathways for further sensitivity improvements are outlined in the conclusions.