ULTRA-SENSITIVE DETERMINATION OF K, TH, U AND OTHER TRACE IMPURITIES IN LIQUID ORGANIC SCINTILLATORS BY NAA

We present a NAA method to determine ultratraces of K, Th, U and other trace impurities in liquid organic scintillators, which are known as ultrapure detector materials for neutrino or dark matter experiments. A combined optimization of relevant factors for sensitive NAA has been realized, leading to a sensitivity for U down to 10(-16) g/g. Samples of 250 mi have been irradiated up to 120 h at a thermal neutron flux of 5-8.10(12).n.cm(-2)s(-1). Acidic extraction, wet ashing and TBP-ext raction are used for radiochemical separations. Finally, coincidence t echniques are applied for increased sensitivity.