A search for in-beam \gamma -ray transitions in ¹⁰¹Sn, which contains only one neutron outside the ¹⁰⁰Sn core, using a novel approach was carried out at the Argonne Tandem-Linac System. ¹⁰¹Sn nuclei were produced using the ⁴⁶Ti(⁵⁸Ni, 3n)¹⁰¹Sn fusion–evaporation reaction. Beta-delayed protons with energies and decay times consistent with previous ¹⁰¹Sn decay studies were observed at the focal plane of the Fragment Mass Analyzer. In-beam \gamma rays were detected in the Gammasphere Ge-detector array and were correlated with the ¹⁰¹Sn \beta -delayed protons using the Recoil-Decay Tagging method. As a result, a \gamma -ray transition between the single-neutron \nu g_7/2 and \nu d_5/2 states situated at the Fermi surface was identified. The measured \nu g_7/2–\nu d_5/2 energy splitting was compared with predictions corresponding to various mean-field potentials and was used to calculate multi-neutron configurations in light Sn isotopes. Similar approach can be used to study core excitations in ¹⁰¹Sn and other exotic nuclei near ¹⁰⁰Sn.

PACS numbers: 21.10.Pc, 21.60.Cs, 23.20.Lv, 27.60.+j