An optically polarised dense 3He target as a spin filter for slow-neutron beams

The possibility of polarising ³He and preserving the polarisation in an external magnetic field of 0.05 Oe is demonstrated experimentally. A neutron filter with an extremely weak guiding field is fabricated for obtaining polarised neutron beams. The degree of polarisation equal to 25% was obtained for 0.025-eV neutrons. Some fields of application of other polarised noble gases are considered. The cross section for cross-relaxation of nuclear polarisation in the ¹²⁹Xe – ¹³¹Xe mixture is estimated.