Antiprotonic atoms as a tool to study the nuclear periphery

Two different methods were employed by the collaboration PS209 at LEAR (CERN) to investigate the nucleon density at the outer nuclear periphery. The first one was the comparison of the yield of (N-1) nuclei and (Z-1) nuclei produced by antiproton annihilation on a nucleus with mass number A (here N and Z denote the neutron and proton number of the nucleus, respectively); the second one is the measurement of widths and shifts of the last observable transitions in antiprotonic atoms. Earlier studies of (A-1) production were extended by measurements of short-lived isotopes (lifetimes down to a few seconds). More than thirty widths and twenty shifts were extracted from the antiprotonic X-ray data. The results fit nicely into the systematics established recently by C.J. Batty, E. Friedman, and A. Gal (1995). Pronounced isotope effects were found for some of the investigated elements. (11 refs).