A comparison between Engin and Engin-X, a new diffractometer optimized for stress measurement

Engineering diffractometers are used extensively by both engineers and materials scientists for the measurement of strain within polycrystalline materials, both metallic and ceramic. In the past neutron diffractometers have generally been built as 'all-purpose' instruments, with designs that are compromises, balancing competing requirements to measure the intensities, positions and widths of diffraction peaks simultaneously. In contrast the newly constructed diffractometer ENGIN-X was designed with the single aim of making engineering strain measurements; essentially the accurate measurement of polycrystalline lattice parameters, at a precisely determined position. Under this design philosophy, considerable performance improvements have been obtained compared to the existing instrument. This paper details the design philosophy of this instrument, including tuneable incident resolution, together with the approaches used to realise the performance required. The improved instrument performance is demonstrated here, with results obtained during the commissioning of ENGIN-X. These results include strain mapping experiments, and demonstrate the influence of resolution on required count times, and provide a direct comparison with measurements from the existing ENGIN instrument at ISIS. (C) 2004 Published by Elsevier B.V.