The separation of isotopes for the investigation of nuclear transmutations

Abstract

The Bombardment of an element with intense beams of protons or deuterons may lead to a variety of processes of nuclear transmission. When, as is normally the case, the bombarded element is composed of two or more isotopes it is often difficult to establish with certainly the nature of the transmission which give rise to the observed disintegration products. The use of separated isotopes as targets for such experiments greatly facilitates the interpretation of the results. The investigation of the radio-activity of 8 Li, for example, was simplified considerably by the use of the separated isotopes of lithium (Rumbaugh and Hafstad 1936; Lewis, Burcham and Chang 1937). Apart from hydrogen, lithium is the only light element which has been separated into its constituent isotopes in quantities sufficient for disintegration experiments. Oliphant, Shire and Crowther (1934) have described two simple mass spectrography by means of which quantities of the lithium isotopes of the order of 10 -7 g. were obtained, while Rumbaugh (1936) has used a mass spectrograph more complicated design to produce several hundred micrograms of the lithium and potassium isotopes. The present paper describes an improves but still comparatively simple mass spectrograph, similar to those described by Oliphant, Shire and Crowther, which has been used for the separation of 30 μ g. of the heavier isotope of lithium and 2 μ g. of each of the isotopes of boron. The apparatus has also been used for the preparation of several micrograms of the isotope of carbon of mass 12 free from the heavier isotope.