Raman Spectroscopy as a Nonintrusive Partial Pressure Monitor for Tritium Systems

The strength of selected Raman shift lines for H2, HD, and D2 responds linearly with pressure over the range of 15 torr to 1000 torr using the MarqMetrix spectrometer. Indications are that the linear response will continue up to the design pressure of the detection cell. The detection limit for H2, HD, and D2 is 2.6 ± 1.3 torr, 6.3 ± 3.1 torr, and 6.5 ± 3.2 torr, respectively, using a laser power of 450 mW and an integration time of 10 s. Each unique isotopologue of hydrogen has a correlation among laser power, integration time, pressure, and the counts that are output. This correlation, the K value, is 4.38, 1.76, and 0.85 (countstorr∗W∗s) for H2, D2, and HD, respectively. The shift in the equilibrium spin distribution between ortho and para states of H2 and D2 should be considered when operating at temperatures other than 303°C when calculating the partial pressure of these species.