The Beta Spectra of the Mass 12 Nuclei

Citation

Michel, F. Curtis (1962) The Beta Spectra of the Mass 12 Nuclei. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4BW8-8827. https://resolver.caltech.edu/CaltechTHESIS:08232011-105654839

Abstract

This thesis, "The Beta Spectra of the Mass 12 Nuclei," is mainly concerned with an experimental test of the conserved-vector-current theory. This theory predicts a deviation from the allowed shape of the B¹² and N¹² beta spectra. The ratio of the shape factor of the two spectra is expected to have an energy dependence of 1.10 ± 0.17 percent per Mev. If the CVC hypothesis is not invoked, this ratio is estimated to be an order of magnitude smaller. The two spectra have been measured with a magnetic spectrometer and found to give for this ratio the value 1.30 ± 0.31 percent per Mev. In addition the branching fraction of the N¹² decay to the 7.6-Mev state of C¹² has been determined to be 3.0 ± 0.5 percent. The geometrical mean of the two shape factors was observed to have an unexpected linear energy dependence of 1.18 percent per Mev. Theoretical estimates are made of relevant matrix elements in search of an understanding of this. Baffle penetration by the beta particles gives a systematic effect estimated to account for about one third of the observed mean shape factor. The uncertainty in this estimate precludes a definite conclusion on the actual presence of this term in the spectra. Such penetration is expected, however, to have little influence on the conserved vector current theory test. A preliminary report of this work has been published (1, 2).

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