Selective Absorption of Neutrons by Gold

Abstract

Six small gold disks, 15 mm. in diameter and 0.5 mm. thick, were placed in a hole in a cadmium plate and irradiated by slow neutrons, by putting the whole arrangement in a cavity in a large block of paraffin wax, near a radon-beryllium source. On measuring the activities of the successive disks, it was discovered that the bottom of the lowest disk (which lay directly on the cadmium) was very much more active than the top of the same disk, and was indeed comparable in activity with the uppermost disk. All the disks decayed with the normal gold period (2½ days).