A SPIN REVERSAL SYSTEM FOR POLARIZED EPITHERMAL NEUTRONS

The design and construction of a spin-reversal system for longitudinal ly polarized epithermal neutrons are presented. The design uses a stat ic magnetic field parallel to the momentum of the neutron. The longitu dinal field changes the direction at its midpoint. A transverse magnet ic field is turned off to control the spin direction at the end of the spin flipper. The neutron spin is reversed with respect to both the n eutron momentum and the static longitudinal field at the exit of the s pin flipper. In the transverse field-on state the spin adiabatically f ollows the field direction and the spin direction is reversed. In the transverse field-off state the spin passes rapidly through the region where the solenoidal field reverses the sign and the spin direction is not reversed With this design, the spins of an 8-cm-diameter beam of longitudinally polarized neutrons can be reversed with an efficiency g reater than 88% over a range of neutron energies of more than four ord ers of magnitude.