We discuss the precession of spin-polarized Ultra Cold Neutrons (UCN) and $^{ 3}$He atoms in uniform and static magnetic and electric fields and calculate the spin relaxation effects from motional $v\times E$ magnetic fields. Particle motion in an electric field creates a motional $v\times E$ magnetic field, which when combined with collisions, produces variations of the total magnetic field and results in spin relaxation of neutron and $^{ 3}$He samples. The spin relaxation times $T_{ 1}$ (longitudinal) and $T_{ 2}$ (transverse) of spin-polarized UCN and $^{ 3}$He atoms are important considerations in a new search for the neutron Electric Dipole Moment at the SNS \emph{ nEDM} experiment. We use a Monte Carlo approach to simulate the relaxation of spins due to the motional $v\times E$ field for UCN and for $^{ 3}$He atoms at temperatures below $600,\mathrm{ mK}$. We find the relaxation times for the neutron due to the $v\times E$ effect to be long compared to the neutron lifetime, while the $^{ 3}$He relaxation times may be important for the \emph{ nEDM} experiment.
Categories: nucl-ex