Frequency shifts in the EPR spectrum of $^{39}$K due to spin-exchange collisions with polarized $^3$He and precise $^3$He polarimetry

TL;DR

This paper precisely measures the atomic parameter $0$ for the $^{39}$K-$^3$He system, significantly improving accuracy in $^3$He polarimetry and providing the first direct measurement for this pair, with implications for various applications.

Contribution

It provides the first direct measurement of $0$ for the $^{39}$K-$^3$He system with better than 1% accuracy, enhancing the precision of $^3$He polarimetry.

Findings

Measured $0$ for $^{39}$K-$^3$He with <1% uncertainty.

More than doubled the accuracy of $0$ for this system.

First direct measurement of $0$ for $^{39}$K-$^3$He.

Abstract

The Zeeman splittings and EPR frequencies of alkali-metal atoms are shifted in the presence of a polarized noble gas. For a spherical geometry, the shift is enhanced over what is expected classically by a dimensionless atomic parameter $\kappa_0$ that is unique to each alkali-metal atom - noble-gas pair. We present a precise measurement of $\kappa_0$ for the $^{39}$K-$^3$He system with a relative accuracy of better than 1\%. A critical component of achieving sub-percent accuracy involved characterizing the shape of our samples using both MRI and CT medical-imaging techniques. The parameter $\kappa_0$ plays an important role in establishing the absolute polarization of $^3$He in a variety of contexts, including polarized targets for electron scattering experiments and MRI of the gas space of the lungs. Our measurement more than doubles the accuracy possible when using $\kappa_0$ for polarimetry purposes. Just as important, the work presented here represents the first {\it direct} measurement of $\kappa_0$ for the $^{39}$K-$^3$He system; previous values for $\kappa_0$ in the $^{39}$K-$^3$He system relied on a chain of measurements that were benchmarked by previous measurements of $\kappa_0$ in the Rb-$^3$He system.