Isotope Shift of Nuclear Magnetic Resonances in 129Xe and 131Xe Caused by Spin-Exchange Pumping by Alkali Metal Atoms

Abstract

The effect of isotope shifts of nuclear magnetic resonance (NMR) frequency in xenon isotopes 129Xe and 131Xe polarized by optically-oriented alkali metal atoms is not only of fundamental interest, but also of practical significance, since it is the main factor limiting the accuracy of a whole class of prospective navigation and metrological devices. Our study of the parametric dependences of the isotope shift has shown that this effect is largely due to incomplete averaging of an inhomogeneous local magnetic field by two xenon isotopes, and therefore, its value can be influenced by applying an external magnetic field gradient. A numerical model is derived that qualitatively describes the effect of the isotopic frequency shift, as well as its dependence on the cell temperature and the external magnetic field gradient. The model provides a good quantitative agreement with the experiment – e.g., at a temperature of 85°C, the isotope shift values predicted by the model coincide with experimental data with an accuracy of up to the experimental error, which, in turn, does not exceed 8% of the total change in the isotopic shift in the entire range of applied magnetic field gradients.