The Production of Collimated Beams of Monochromatic Neutrons in the Temperature Range 300°-10°K

An electrical velocity selector is described, which allows the production and use of highly collimated beams of pure thermal neutrons. The mean temperature of the neutrons may be varied from 300°K to an undetermined lower limit, probably less than 10°K, without the use of refrigerants. The temperature width of the neutron "line" is also adjustable. Fast neutron effects are completely eliminated. Qualitative verification of the $\frac{1}{v}$ law for Boron has been extended to 30°K. The intensity of neutrons available from the cyclotron allows counting rates of 1000 per minute to be obtained at 30°K, with a source-detector distance of 4 meters, and an angular spread of 1°.