Simulation And Optimization Of Residual Stress Neutron Diffractometer

In this thesis, components of residual stress neutron diffractometer including guide, monochromator, collimators and slit have been simulated and optimized using Monte-Carlo simulation softwares, McStas and Vitess.Influence of guide position, length, cross section and critical angle multiplier on neutron intensity, divergence, spectrum and uniformity at the exit of guide was investigated. Comparison shows neutron flux decreases to 24.3% at thermal channel exit and 6.7% at guide exit.Flux gain of vertically bent Cu(110) monochromator compared to flat one has been estimated. The mosaicity and the number of crystal stripes were optimized under given conditions. Influence of focusing curvature radius on neutron flux was investigated. Neutron fluxes at sample were calculated for Cu(222) , (220) and (002) at different take-off angles. Among general Cu, Ge and HOPG monochromators, PG(004) results in maximal flux while Cu(222) optimal resolution.Influences of primary and secondary collimators on neutron flux and resolution have been studied respectively. For a standardα-Fe poly crystal sample, collimation system's impact on intensity and FWHM of stress free diffraction peak has been investigated. Thus three different settings of collimation system were suggested for best resolution, maximal intensity and optimal balance respectively. Besides, the "pseudo-strain" phenomenon has been exhibited which suggests stress free difraction peak position should be measured accurately beforehand.Simulation of slit before sample shows the vertical dispersion of neutron beam becomes much severer than the horizontal one as the distance increases.Finally a Vitess model was set up for the same residual stress neutron diffractometer and the simulation result was compared with McStas'.In a word, this thesis has provided essential data for residual stress neutron diffractometer design.