High-sensitivity measurement of ³He−⁴He isotopic ratios for ultracold neutron experiments

Abstract

Research efforts ranging from studies of solid helium to searches for a neutron electric dipole moment require isotopically purified helium with a ratio of ³He to ⁴He at levels below that which can be measured using traditional mass spectroscopy techniques. We demonstrate an approach to such a measurement using accelerator mass spectroscopy, reaching the 10⁻¹⁴ level of sensitivity, several orders of magnitude more sensitive than other techniques. Measurements of ³He/⁴He in samples relevant to the measurement of the neutron lifetime indicate the need for substantial corrections. We also argue that there is a clear path forward to sensitivity increases of at least another order of magnitude.

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