ENERGY LEVELS IN LEAD AND BISMUTH AND NUCLEAR SHELL STRUCTURE

Abstract

A bismuth target and lead targets enriched in Pb 206 , Pb 207 , and Pb 208 have been. bombarded with 14-Mev. deuterons from the M.I.T. cyclotron. Proton and triton spectra were measured with aluminum absorbers and a triple proportional counter. The spectra have been carefully analyzed and resolved into a relatively small number of groups. The proton spectra from all four targets are very similar, except for the long range state groups from the Pb 206 and Pb 207 targets. A striking similarity also occurs among the triton spectra from the four targets. The simplicity in the spectra probably arises because we are dealing with residual nuclei with closed or nearly closed shells of 82 protons and 126 neutrons. The fact that a (d, p) reaction proceeds mainly by means of a stripping process, in which only the neutron enters the nucleus, suggests the possibility that the similarities can be explained by a single particle model of the nucleus. Moreover, the (d, t) reaction is principally a pickup process and thus the single-particle model is suggested again. Observed energy levels are compared with the known levels measured from radiative transitions. Aided by the angular momentum and parity assignments of some of these known levels, tentative assignments of angular momentum and parity are made to many of the new levels from a strong spin-orbit coupling shell model.