Determination of the Upper Limits of the Fission Cross-sections of Lead and Bismuth for Li-D Neutrons by a Track Count Method

Abstract

FOLLOWING the unsuccessful search for fission of lead and bismuth by a chemical method¹, an attempt was made using track counts in irradiated ‘loaded’ plates. It is possible through desensitization (bathing for 5 min. in 1 per cent chromic acid, rinsing with water and drying) before irradiation to suppress fogging by γ-rays and the proton recoil tracks due to the fast neutrons². Therefore the plates can be exposed to very high doses of fast neutrons. α-Ray tracks from uranium are weakened in the desensitized plates, but fission tracks from uranium still stand out boldly, and are easily identified and counted under a microscope (× 1,500).