Progress of³He spin-exchange for neutron polarization in Jülich

Nuclear spin-polarized ³He efficiently polarizes neutrons over a wide energy range including cold, thermal and hot neutron spectra by means of its strongly spin-dependent absorption of neutrons. At Forschungszentrum Jülich we are studying the optical polarization of ³He by two methods, metastable exchange and spin-exchange, in order to optimize the neutron polarization at various spectrometers of the FRJ-2 reactor. For the spin-exchange method we designed an open, refillable cell system. In contrast to the conventional sealed cells adopted at many other laboratories, we will be able to vary many crucial parameters in the ³He cell, such as gas ratios of ³He and N₂, total gas pressure, and temperature while always working in the same experimental environment of a single cell. Laser polarized Rb vapor is used to polarize ³He through the spin-exchange interaction, and NMR is employed to determine the polarization of the ³He after calibration with a proton (water) NMR signal. In this paper we will report the ³He polarization and relaxation rate, T ₁, observed for various gas conditions.