A DESIGN FOR IMPROVED NEUTRON COLLIMATORS

Seller slit collimators are widely used to define beams of thermal neu trons for scattering experiments and hence to tailor the instrumental resolution. The possibility of using neutron guide principles to incre ase the overall transmission of a collimator for a given overall instr umental resolution has long been recognised. Advances over the last de cades in the semiconductor industry now provide the technology to make such collimators. A feasible design is to use blades of flat silicon wafers on which non-polarising neutron supermirrors are vacuum deposit ed. In its simplest form the coating would consist of two thin layers of a material with a large scattering length, such as nickel, sandwich ing a neutron absorbing layer such as gadolinium. Calculations show th at such devices could increase the counting rate at the detector by up to 47% per collimator for a given instrumental resolution. A simpler design where the silicon wafers support a thin absorbing layer alone i s also described and can be used to build very short, high transmissio n conventional neutron collimators. (C) 1998 Elsevier Science B.V. All rights reserved.