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 10⁻¹⁶g/g. Samples of 250 ml have been irradiated up to 120 h at a thermal neutron flux of 5–8·10¹²·n·cm⁻²·s⁻¹. Acidic extraction, wet ashing and TBP-extraction are used for radiochemical separations. Finally, coincidence techniques are applied for increased sensitivity.