On low-level tritium measurements with LSC Quantulus

Low-level measurements of 3H have been made with the "Quantulus" liquid scintillation counter (LSC) using different scintillation cocktails together with selected types of counting vials. Comparisons were made between counters at the underground laboratory "Felsenkeller" (110 m water equivalent) and in an above ground laboratory (0 m water equivalent) of the TU Freiberg. In the underground laboratory, the background is strongly influenced by the beta-decay of the 220Rn-daughter 212Pb (T(1/2) = 10.6 h) from the laboratory air, stimulating luminescence irradiation in the vial. The effective background count rate in the 3H-window (having subtracted the "luminescence effect") in the underground laboratory is two times lower than that in the above ground laboratory due to the better shielding of cosmic rays.