Neutron collimator with rectangular beam profile

Several Soller slit-type neutron collimators which give rectangular profiles of transmission as a function of angular divergence have been constructed. The collimators accept a beam of realistic dimensions – greater than 12×22 mm2 in all cases. The blades of the collimators are 280 μm thick wafers of single-crystal silicon each coated with a Ni–Gd–Ni multilayer on one side. Tests at a neutron wavelength of 7.5 Å confirm that the transmission profiles are rectangular. Tests at a wavelength of 4.2 Å show that two such collimators rocked against each other give dramatically enhanced transmission and resolution by comparison with conventional collimators. This is the first such demonstration of increased counting rates in a scan on an instrument from rectangular profile collimators, an effect expected but not produced for over 40 years.