The Disintegration of the Nuclei of Light Atoms by Neutrons. II. Neon, Fluorine and Carbon

Neon and fluorine. Quantitative information is presented on the disintegration, by capture of a neutron, of 11 nuclei of neon and 13 of fluorine. The reactions are considered to be: ${₁₀²⁰Ne₀+₀¹n₁,{→}₈¹⁷O₁+₂⁴He₀}{₉¹⁹F₁+₀¹n₁,{→}₇¹⁶N₂+₂⁴He₀}$ in which nitrogen 16 is a new isotope of nitrogen. As in the earlier work on nitrogen, it is found that: (1) Neutrons effective in disintegration appear both to come directly from the source and to be scattered by nuclear impact prior to the disintegration. (2) Kinetic energy disappears in the process, or is (rarely) conserved. This kinetic energy decrement may be transformed into mass, if mass increases in the reaction, or into γ-rays; it may also excite the heavier product nucleus and later give rise to an artificial radioactivity. (3) The maximum, minimum and average kinetic energy for the neutrons which in our experiments have been found to disintegrate fluorine, neon and nitrogen are listed below in the table.Carbon. Mass values obtained in positive ray work give 6.9 m.e.v. as the mass increase in the reaction: ₆¹²C₀+₀¹n₁→₄⁹Be₁+₂⁴He₀. If the mass values are extremely accurate only neutrons with kinetic energy greater than about 6.9 m.e.v. can therefore disintegrate carbon. Of 6 disintegrations found among 6400 pairs of photographs with ethylene, only 1 involves a neutron which approximates this energy. The other disintegrations may be those of oxygen or nitrogen from the water vapor and trace of air in the chamber. Carbon has therefore not yet been disintegrated with certainty by neutrons. It is of interest that about 20 percent of the neutrons found in this work have extremely high velocities, so that their kinetic energy is from 13.6 to 15.1 m.e.v., and that the energy transformed into γ-rays rises as high as 10 m.e.v.