Antiprotonic atoms as a tool to study the nuclear periphery

Two different methods were employed by the collaboration PS209 at LEAR (CER N) to investigate the nucleon density at the outer nuclear periphery. The f irst one was the comparison of the yield of (N - 1) nuclei and (Z - 1) nucl ei produced by antiproton annihilation on a nucleus with mass number A (her e 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 obser vable transitions in antiprotonic atoms. Earlier studies of (A - 1) product ion were extended by measurements of short-lived isotopes (lifetimes down t o a few seconds). More than thirty widths and twenty shifts were extracted from the antiprotonic x-ray data. The results fit nicely into the systemati cs established recently by C.J. Batty, E. Friedman, and A. Gal [Nucl. Phys. A592, 487 (1995)]. Pronounced isotope effects were found for some of the i nvestigated elements.