Use of a semi-opaque beamstop for monitoring sample transmissions at GLAD [Glass, Liquid, and Amorphous Materials Diffractometer]

Accurate corrections for many types of measurements made on time-of-flight neutron diffractometers require data on the macroscopic transmission cross-section of the sample used, and this data must span the entire wavelength range covered by the instrument. This report describes a transmission monitor consisting of a semi-opaque beamstop in from of a portion of the array of position-sensitive detectors used for diffraction measurements on the GLAD prototype. The semi-opaque beamstop was made of a molded B4C-epoxy plate pierced by several small-diameter holes which transmitted a small fraction of the beam, and the segments of the position-sensitive- detectors directly behind these holes served as several independent beam monitors. This arrangement was used on the GLAD prototype flightpath to measure the transmissions of a number of samples, and results of these tests are reported and discussed. Based on these results, a similar transmission monitor has been incorporated in the final GLAD instrument. 6 refs., 9 figs