Design and performance of the high-resolution stress and texture neutron diffractometer HETU

The high-resolution stress and texture neutron diffractometer HETU at the China Mianyang Research Reactor is dedicated to measuring and analysing the residual stress and texture of engineering materials. The instrument can provide a high instrument resolution and a high neutron flux at the sample position. This article presents the HETU neutron optics design based on Monte Carlo simulation and the first assessment of its experimental performance. The technical parameters of the monochromators, slit system, radial collimators and detector were determined. A double-focusing silicon monochromator with (311) and (400) planes and a highly oriented pyrolytic graphite (HOPG) monochromator with (002) and (004) planes were selected to provide either high instrument resolution or high neutron flux modes. The highest instrument resolution of Delta d/d = 1.65 x 10(-3) is obtained when using Si(400), while the highest neutron flux at the sample position is 3.0 x 10(7) n s(-1) cm(-2) at the wavelength of 2.37 angstrom reflected by HOPG(004). The HETU diffractometer started operation in early 2022.