CAPILLARY NEUTRON OPTICS FOR PROMPT-GAMMA ACTIVATION-ANALYSIS

A neutron lens has been constructed to focus cold neutrons from the ex it of a Ni-58 neutron guide, which delivers a beam to the Prompt-Gamma Activation Analysis (PGAA) station at the MST Cold Neutron Research F acility. The lens compresses a neutron beam of cross section 50 mm x 4 5 mm onto a focal spot of diameter 0.53 mm (fwhm) with an average gain of 80 in neutron current density. PGAA measurements have been perform ed to demonstrate the enhanced sensitivity and detection limits for va rious elements and the spatial resolution in one transverse dimension. For the two test particles (a gadolinium glass bead and cadmium metal of sizes less than 0.5 mm), the gain in the gamma-count rate with the lens is a factor of 60, and the detection limit is improved by a fact or of 20. The system can be used for two-dimensional mapping of sample s on a sub-millimeter scale to complement other analytical techniques such as neutron depth profiling (NDP).