The optimisation of absorber thickness for neutron Soller slit collimators

When constructing neutron Soller slit collimators an absorbing layer is applied to the blades. Choice of an optimum absorber thickness becomes more important as the collimator is made shorter or the neutron absorption becomes poorer as occurs for short wavelength neutrons. A quality factor for the performance of Soller slit collimators is proposed and used to determine the optimum thickness of the absorbing layer. The solution to this problem is non analytic but easily coded as a computer program. Sample calculations of optimum thickness are described. A simple formula for the approximate optimum thickness is given.