Single-Neutron States in ¹⁰¹Sn

The first data on the relative single-particle energies outside the doubly magic ¹⁰⁰Sn nucleus were obtained. A prompt 171.7(6)  keV γ-ray transition was correlated with protons emitted following the β decay of ¹⁰¹Sn and is interpreted as the transition between the single-neutron g_7/2 and d_5/2 orbitals in ¹⁰¹Sn. This observation provides a stringent test of current nuclear structure models. The measured νg_7/2-νd_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 ¹⁰⁰Sn.