The angular distribution of charged x mesons produced by 300 <x> 30 Mev neutrons on C12 and Be9 have been studied. An analysis of the kinematics for meson production in a nucleon-nucleon collision indicates a fairly well defined center-of-mass system.

This report was prepared at the request of the Subcommittee on Radiochemistry of the Committee on Nuclear Science of the National Research Council as a contribution to a proposed master file on the radiochemistry of all the elements. All known material on the radiochemistry of thorium is included in this report.

This revised version contains material published in the two years since the original report was issued in January 1960. The report covers the history of the discovery of fission, fission theory, and the probability of fission. It discusses the distribution of mass in fission, the distribution of nuclear charge in fission, kinetic energy of fission fragments, and the role of neutrons and gamma rays in fission.