Precision measurement of the neutron-3He spin-dependent scattering length using neutron interferometry

There is strong theoretical interest in the study of few-body nucleon systems. Experimental measurements of neutron scattering lengths are able to perform precise tests of nucleon–nucleon models. Neutron interferometry provides some of the most precise values of spin-independent neutron scattering lengths, bcbc, including measurements for n-H, n-D, and n-3He to better than a percent relative uncertainty. The spin-dependent neutron scattering length, bibi, of n-3He has been measured once before by Zimmer et al. using a polarized 3He target inside a spin echo apparatus. Their result along with measurements of the spin-independent scattering length of n-3He disagree with current theoretical models. An experiment to measure bibi in n-3He to less than 1% relative uncertainty has been conducted at the Neutron Interferometer and Optics Facility at the National Institute of Standards and Technology using small, flat-windowed 3He cells. This experiment has different systematics than that of the spin echo measurement, and is the first use of a polarized gas target in a neutron interferometer.