The first data on the relative single-particle energies outside the doubly magic ${}^{100}\mathrm{Sn}$ nucleus were obtained. A prompt $171.7(6)\mathrm{keV}$ $\gamma$-ray transition was correlated with protons emitted following the $\beta$ decay of ${}^{101}\mathrm{Sn}$ and is interpreted as the transition between the single-neutron $g_{7/2}$ and $d_{5/2}$ orbitals in ${}^{101}\mathrm{Sn}$. This observation provides a stringent test of current nuclear structure models. The measured $\nu g_{7/2}\mathrm{\text{−}}\nu d_{5/2}$ 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 ${}^{100}\mathrm{Sn}$.

• Received 15 April 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.022504