Focused Neutrons: A Point to be Made

Just over two years ago, the guide hall of the newly created Cold Neutron Research Facility (CNRF) at the NIST reactor was inaugurated. This is currently the only cold source at a U.S. research reactor which serves a large number of scientific instruments.1 While most of the instruments installed in the facility are spectrometers for neutron scattering studies covering a wide range of scientific endeavors, two of the new instruments have been designed specifically for chemical quantitative analysis. For a long time, there have been facilities for prompt gamma activation analysis (PGAA) and neutron depth profiling (NDP) at the NIST reactor. These instruments use a white beam from the thermal neutron source. Completely new instruments have been designed which use the long wavelength neutrons available from the cold source. The advantage, of course, is that the absorption cross section increases linearly with wavelength of the neutron. Therefore, the availability of cold neutrons enables measurements of greater precision, and improves the detection limits for those elements which can be analyzed by each technique.