The following report describes the design of a sample cell for observing the neutron inelastic scattering from liquid He a , at high pressures and low temperatures. Because of the high absorption of neutrons by He 3 nuclei, the average mean free path of a neutron in the liquid is very small, (-5 x 10-2mm), therefore, to observe a significant scattered signal we are forced to adopt a plane, reflection geometry for the incident and scattered neutron beams. In these geometries, due to lack of tensile strength, single crystal aluminium and aluminium alloys, which are common materials for neutron windows, cannot be used at high pressures. The material chosen for the pressure window was single crystal sapphire A1203.1 This material is suitably transparent to neutrons while retaining a high modulus of rupture. The sapphire plate was sealed into the body of the sample cell using a special, flexible, metal seal. 2 A schematic cross-section of the sample cell is shown in Fig. 1.
The size of the window is determined by the angle of incidence, 0, and the minimum scattering angle of the neutron beam, Β’, which are limited by the mechanical support of the The author is with the