Pressure Dependent Wall Relaxation in Polarized $^3$He Gaseous Cells

TL;DR

This study investigates the pressure dependence of the longitudinal relaxation time in polarized $^3$He cells, combining experiments and finite element analysis to understand the underlying mechanisms beyond diffusion effects.

Contribution

The paper provides experimental measurements and FEA simulations showing that diffusion effects do not fully explain the pressure-dependent wall relaxation in polarized $^3$He cells.

Findings

Diffusion effect is insufficient to explain pressure dependence of T$_1$.

Experimental results show linear pressure dependence of T$_1$.

Finite element analysis supports experimental observations.

Abstract

Pressure dependence of longitudinal relaxation time (T$_1$) due to the cell wall was observed previously at both room temperature and low temperature in valved Rb-coated refillable $^3$He gaseous cells in \cite{Zheng2}. The diffusion of $^3$He from measurement cell through a capillary tube to the valve and the subsequent depolarization on the surface of the valve was proposed to possibly explain such a pressure dependence at room temperature \cite{Saam}. In this paper, we investigate this diffusion effect through measurements of T$_1$ with newly designed Rb-coated Pyrex glass cells at 295 K as well as finite element analysis (FEA) studies. Both the experimental results and FEA studies show that the diffusion effect is insufficient to explain the observed linear pressure-dependent behavior of T$_1$.