A SUBTHERMAL NEUTRON BEAM COLLIMATED BY TOTAL REFLECTION

摘要

A. method for providing an experimental beam of long wavelength neutrons was investigated. The method involved allowing neutrons to travel from the vicinity of a reactor core to the experimental area by means of a curved hollow tube. The method makes use of the phenomenon of total internal reflection of long wavelength neutrons to selectively transport subthermal neutrons the length of the tube. The tube was slightly curved so that a line-of-sight path through the tube did not exist. The tube was 20 feet long, had an internal diameter of 1.5 inches, and was made of copper. A nickel-plated tube was also investigated. Wavelength spectra taken of the beam of emerging neutrons peaked in the vicinity of 3.75 A. The general shape and position of the spectrum of emerging neutrons was investigated as a function of the tube curvature, the internal finish of the tube, and the reflective material inside the tube. The range over which these parameters could be varied did not produce significant variations in the spectrum. Using nickel as the reflective material instead of copper did, however, increase the. total intensity by a factor of nearly four. Gammas and fast neutrons were not able to negotiate the curvature of the tube and as a result the beam obtained was virtually free from contamination.