The design of the radial collimator for residual stress analysis diffractometer of J-PARC

Abstract

Radial collimators are devices needed to define gauge sizes in neutron diffraction experiments. A design work of collimators needed for an engineering diffractometer that will be built at J-PARC is being progressed. Several collimators for different gauge sizes (1, 3, 5 mm, etc … ) are going to be designed to define a gauge size range from 1 to 10 mm. An equation was established to express a relation between the gauge size and geometrical design parameters of the collimator, by applying a normal distribution curve to the error distribution of measured gauge size. Currently, the geometric calculations for several collimators have been finished. A prototype collimator for a gauge size of 1 mm was made and an FWHM (full width at half maximum) of the normal distribution of 1 mm was obtained from performance tests conducted at the neutron diffractometer for residual stress analysis RESA in JRR-3 (Japan Research Reactor-3) of Japan Atomic Energy Agency (JAEA). In addition, the performance test results are in a good agreement with results from a Monte Carlo simulation with the McStas using the design parameters.