Datasets for determination of the resolution function of the Wombat High Intensity Neutron Diffraction instrument: Pyrolitic Graphite monochromator

Wombat is a high-intensity neutron diffraction instrument located at the OPAL reactor, Sydney, Australia. This dataset is one of a series collected to characterise the resolution of the instrument in different configurations.

For this dataset, data were collected from a Na2Ca3Al2F14 (NAC) sample at varying takeoff angles with a pyrolitic graphite focussing monochromator and cooled Be filter installed. The three raw data files correspond to takeoff angles of 90 degrees/4.78A (74999), 75 degrees/5.35A (74004), and 105 degrees/4.11A (74008) using the 002 reflection.

The files ending in .nx.hdf are raw data files conforming to the NeXus standard (see nexusformat.org). The files ending in .xye are three-column ASCII reduced data derived from the corresponding raw data NeXus file, with the columns being angle, intensity and standard uncertainty of that intensity. In order to obtain the reduced data from the raw data, Monitor 1 counts were used to scale the data to 1000 monitor counts. Following this each pixel was multiplied by the corresponding value in the efficiency map contained in file eff_2020_03_03.gumtree.hdf, after which all pixels at each angle were summed vertically and the final values output.

The detector/x_pixel_angular_offset raw data file entry gives the angular boundaries of each detector pixel. These values were used to derive pixel centres, which were then added to sample/azimuthal_angle to give the final angular values found in the reduced data file.