Composition of the nuclear periphery from antiproton absorption using short-lived residual nuclei

The neutron-to-proton density ratio at the nuclear periphery was determined for six targets from the yield of nuclei with mass ${(A}_t-1)$ generated by antiproton annihilation on targets with mass number $A_t.$ A new setup allowed us to measure this yield for nuclei with half-lives down to 6 s. The experiment confirmed the negative correlation between the peripheral neutron-to-proton density ratio and the neutron binding energy, which had been previously found. Results of Hartree-Fock-Bogoliubov and relativistic Hartree-Bogoliubov calculations show good agreement for a large number of nuclei. By comparing the measured values with those derived from Hartree-Fock-Bogoliubov calculations, the ratio R of the imaginary parts of the effective scattering lengths of antiprotons on bound neutrons and protons was deduced to be $\mathcal{R}=0.69\mathrm{}\left(4\right).$ For the first time yields of several excited states of some ${(A}_t-1)$ nuclei have been investigated.