Epithermal neutron activation analysis and detection limit calculation for trace amounts of thorium at nanogram level,in Israeli geological samples

Trace amounts of thorium in Israeli geological samples were determined by epithermal neutron activation analysis followed by high resolution gamma-ray spectrometry. Epithermal neutron irradiation has the advantage of enhancing the production of²³³Th via the²³²Th _→ ^{n,γ 233}Th reaction over that of interfering nuclides which have a lower I_o/σ_o ratio. The delay time between the end of irradiation and the start of measurements was shortened to 1–2 days. Under the experimental conditions described, the detection limit of Th was 3.3±0.7 ng. The method is nondestructive, accurate and highly sensitive.