Single-neutron states in 101Sn

The first data on the relative single-particle energies outside the doubly magic Sn-100 nucleus were obtained. A prompt 171.7(6) keV gamma-ray transition was correlated with protons emitted following the beta decay of Sn-101 and is interpreted as the transition between the single-neutron g(7/2) and d(5/2) orbitals in Sn-101. This observation provides a stringent test of current nuclear structure models. The measured nu g(7/2)-nu d(5/2) energy splitting is compared with values calculated using mean-field nuclear potentials and is used to calculate low-energy excited states in light Sn isotopes in the framework of the shell model. The correlation technique used in this work offers possibilities for future, more extensive spectroscopy near Sn-100.