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

arXiv:2512.08988v1 Announce Type: new
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.