"This U.S. Bureau of Mines report describes a method for determining parts per million (ppm) of helium-4 (he-4) in helium-3 (he-3) to an accuracy of +/-5 pct by mass spectrometry. Gravimetrically prepared primary standards were used for the calibration of a dempster 180 deg magnetic sector mass spectrometer. A comparison between a 2.49 pct he-4 in hydrogen mixture and a 2.49 pct he-4 in he-3 mixture shows that he-3 can be replaced with hydrogen as a diluent for standards with comparable mass spectrometry sensitivities for he-4. Using hydrogen as a diluent allows analysis of he-3 samples for he-4 when he-3 for preparation of standards is not available and also conserves the rare he-3 isotope. Standards of he-4 in h2 were prepared for calibration of the mass spectrometer for quantitative determinations of he-4 in the 2- to 100-ppm range. A minimum detectable limit of 2 ppm he-4 is obtained by this method." - NIOSHTIC-2 NIOSHTIC no. 10006969

National Institute for Occupational Safety and Health