Zeeman relaxation of cold iron and nickel in collisions with ³He

Abstract

This thesis describes a measurement of the ratio of elastic to Zeeman-projection changing collision cross sections ([gamma]) in the Fe-3He and Ni-3He systems. This ratio is a probe of the anisotropy of the interaction between the colliding species. Theory and experiment confirm that Zeeman-projection collisions are suppressed in transition metals due to the presence of a spherically symmetric, full 4s shell, making them good candidates for loading a magnetic trap with the buffer gas cooling method. Nickel and iron atoms are introduced via laser ablation into an experimental cell containing a background 3He buffer gas. Elastic collisions with the buffer gas thermalize the atoms to less than 1K. The highest energy mJ = J Zeeman state decays via diffusion through the buffer gas and collisional Zeeman relaxation. Therefore the mJ = J lifetime depends on the buffer gas density of the cell. By measuring the mJ = J lifetime as a function of buffer gas density we determine [gamma]. We find [gamma] for Ni [3F4, mJ = 4] is between 2 x 103 and 1:1 x 104 at 0.75 K in a 0.8 T magnetic field. Zeeman relaxation in Fe [5D4, mJ = 4] occurs on time scales too rapid for us to measure accurately, and we are only able to set an upper bound of [gamma] < 3 x 103. The nickel result confirms that Zeeman relaxation is highly suppressed in submerged shell transition metal atoms.