A further study of the problem of nuclear isomerism: the application of the method of coincidence counting to the investigation of the γ -rays emitted by uranium Z and the radioactive silver Ag 106

Abstract

The application of the method of coincidence conuting by electrical means to the study of essentially nuclear phenomena was made first by Bothe and v. Baeyer in 1935. Since that time, and chiefly as the result of further experiments carried out in Heidelberg, much important information has been obtained by the use of this method. It is the object of the present paper to describe the application of the method to the elucidation of certain features of the problem of isomerism in redioactive nuclei. As pointed out in a discussion of this problem by Feather and Bretscher (1938), if such isomerism is to be explained in terms of close nuclear states differing considerably in nuclear spin, it is frequently to be expected that the disintegration is to be explained in terms of close unclear states differing considerably in unclear spin, it is frequently to be expected that the disintegration of one or other isomeric uncleus will be followed by the emission of two or more quanta of γ -radiation in succession. The aim of the coincidence experiments, therefore, was to explore this possibility in a number of cases—and particularly to look for evidence of paired γ -rays following the β -disintegration of uranium Z, as suggested in Paper I. Clear evidence of the latter effect has been found, and the case of isomerism in radioactive silver (Ag 106 ) has also been studied with positive results. Since the information provided by the coincidence method cannot profitably be discussed without data concerning the particel radiations emitted by the isomeric nuclei as well, full details of absorption measurements on the β - and γ -radiations from the radioactive silver are also given in this paper. During the investigation one of us (N. F) has been responsible chiefly for the absorption measurements, using a single counter, the other (J. V. D.) for the coincidence experiments with two counter. The artificially redioactive sources were prepared for us in the High Voltage Laboratory and we are greatly indebted to the workers in that Laboratory, and particularly to Dr W. E. Burcham, for their efficient and kind co-operation in this under-taking.