James Chadwick’s Secrets Revealed on Neutron Discovery 75th Anniversary

Nuclear secrets revealed on 75th anniversary of neutron discovery. ‘Instructions on how to make plutonium and build a nuclear reactor have been revealed in sealed, World War II research papers which were opened at the Royal Society on Thursday 31 May 2007 to coincide with the 75th anniversary of the neutron discovery.
Between 1940 and 1941 James Chadwick sent five sealed envelopes to the Royal Society for safe keeping as he felt their contents detailing experiments on nuclear fission were too sensitive to publish. The sealed envelopes contained the work of two French scientists, Hans Von Halban and Lew Kowarski who worked at the Cavendish laboratory in Cambridge.
Chadwick’s discovery of the neutron confirmed in his 1932 paper The Existence of a Neutron’ published in Proceedings of the Royal Society A kickstarted the field of nuclear physics.
Keith Moore, Head of Library and Archives at the Royal Society, said “The papers have only recently been discovered, as part of our on-going programme to catalogue the Society’s archives. The documents have been sealed for so long it only seemed right to wait for an occasion to open them. The anniversary of Chadwick’s discovery which made the research outlined in these papers possible seemed fitting”.’

Possible Existence of a Neutron (PDF), James Chadwick, Nature, p. 312 (Feb. 27, 1932).

The Existence of a Neutron, J. Chadwick, F.R.S., Proc. Roy. Soc., A, 136, p. 692-708 (Received May 10, 1932). ‘It was shown by Bothe and Becker that some light elements when bombarded by a-particles of polonium emit radiations which appear to be of the g-ray type. The element beryllium gave a particularly marked effect of this kind, and later observations by Bothe, by Mme. Curie-Joliot and by Webster showed that the radiation excited in beryllium possessed a penetrating power distinctly greater than that of any g-radiation yet found from the radioactive elements. In Webster’s experiments the intensity of the radiation was measured both by means of the Geiger-Muller tube counter and in a high pressure ionisation chamber. He found that the beryllium radiation had an absorption coefficient in lead of about 0.22 cm-1. as measured under his experimental conditions. Making the necessary corrections for these conditions, and using the results of Gary and Tarrant to estimate the relative contributions of scattering, photoelectric absorption, and nuclear absorption in the absorption of such penetrating radiation, Webster concluded that the radiation had a quantum energy of about 7 x 106 electron volts. Similarly he found that the radiation from boron bombarded by a-particles of polonium consisted in part of radiation rather more penetrating that that from beryllium, and he estimated the quantum energy of this component as about 10 x 106 electron volts. These conclusions agree quite well with the supposition that the radiations arise by the capture of the a-particle into the beryllium (or boron) nucleus and the emission of the surplus energy as a quantum of radiation.’ [continue reading]

Cambridge Physics: Discovery of the Neutron

PhysicsLAB – Famous Experiments: The Discovery of the Neutron

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