Development of 3He neutron spin filter cells at the HMI

The spin-dependent cross section for thermal and epithermal neutrons gives 3He a high importance in neutron scattering. Because of the wide range of experimental possibilities, the construction of a 3He neutron-spin filter is a central point of instrument development at the HMI. In addition to a high transmission, the reduction of relaxation losses due to wall collisions and magnetic field gradients is crucial. Refillable cylindrical quartz cells were evacuated, heated and coated with Cs. They were then filled with compressed polarised 3He (p≈1 bar) at the University of Mainz. Scattering experiments with polarised and unpolarised neutrons (λ=0.24 nm) revealed time constants between 33 h and 50 h. NMR measurements at low-pressure cells (p=3.5 mbar) verified these results. The transmission of the empty cells was around 80%.