AbstractsPhysics

The velocity variation of the target areas of nuclei for neutrons has been investigated for neutrons obtained by bombardment of Be, B, and F with Po-alpha-particles. The target area of hydrogen was found to increase rapidly with a decrease in the velocity of the neutrons. The target area of carbon and nitrogen also increased with a decrease in the velocity of the neutrons, but not so rapidly as did that of hydrogen. The absorption of neutrons by lead was found to increase with the velocity. This anomalous absorption of lead can be explained by assuming that faster neutrons make relatively more inelastic collisions with the nuclei. Cosmic-ray bursts can be explained on the basis of this assumption. The neutrons from fluorine were found to be slower than those from boron, and the average range of the recoil protons produced by them was estimated to be about 2 cm in air. These slower neutrons were found to be more penetrating in lead than those from either beryllium or boron.