Study of the Nuclear Periphery with Antiprotons

Abstract

In the experiments of the PS209 collaboration at the Low Energy Antiproton Ring LEAR at CERN two methods were applied to study the nuclear periphery: first the yields of residual nuclei with mass number A — 1 were determined with radiochemical methods, and secondly the widths and shifts of the last observable transitions in antiprotonic atoms were measured with Ge detectors. The ratio of yields after annihilation for nuclei with one neutron missing to those with one proton missing from the target nucleus was found to depend strongly on the binding energy of the most loosely bound neutron of the target nucleus. The values were in astonishingly good agreement with a rather simple model for the proton and neutron density distribution devised by Gambhir et al. Furthermore the normalized yield ratio stays constant up to a relative neutron excess of about 0.15 and afterwards rises steeply. Widths for in total 62 x-ray Unes from antiprotonic atoms were compared with the results of calculations of Batty et al. The agreement is reasonable on a semiquantitative basis, but improvements are desirable. For a number of nuclei the differences between the diffuseness values for the proton and neutron distributions were determined directly from the x-ray-line intensity and width data. The root-mean-square radii for the neutron and proton distributions may be derived from these results. The experimental data for four tin isotopes are in reasonable agreement with the experiments of Krasznahorkay et al., but lower than theory predicts.