Indirect tritium determination by an original (3)he ingrowth method using, a standard helium leak detector mass spectrometer

摘要

A traditional helium leak detector m As's spectrometer is applied in analytical chemistry. We report its straightforward use for the precise quantification of He-3 and He-4 concentrations at a sub-ppb level. Repetitive external calibrations with certified gases demonstrate long-term stability, reproducibility of 3% at the ppb range, and linearity versus helium concentration over 5 orders of magnitude. The mass spectrometric determination of He-3 takes into account a H-3(+) contribution and has a He-3 detection limit of 2 ppb. Since He-4 induces an attenuation effect Of the mass 3 signal, this apparatus is only suitable for the measurement of He-3/He-4 ratio greater than 10 R-a (atmospheric ratio R-a = 1.38 x 10(-6)). This mass spectrometric technique has found novel application in the determination of tritium concentrations with an original 3He ingrowth method. Here, samples are first purified cryogenically onto activated charcoal to eliminate tritium interfering during the He-3 mass spectrometric determination step. Helium is also preconcentrated, and He-3 is routinely determined around 0.05 ppb with a 20% relative uncertainty. This He-3 measurement technique has been successfully applied in the field of tritiated waste drums as a nondestructive method. The total amount of tritium present in these 200-L drums can be determined as low as similar to1 GBq. [References: 18]