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

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-U-238 and Th-232-with sensitivities at the 10(-15) g/g level. Our method combines neutron activation analysis with radiochemical techniques, fol lowed by beta/gamma coincidence spectroscopy to minimize interference backgrounds. This approach achieves sensitivities of 0.65 & centerdot;10(-15) g/g for U-238 and 1.9 & centerdot;10(-15 )g/g for Th-232, among the best reported worldwide. Potential pathways for further sensitivity improvements are outlined in the conclusions.