Observation of an excited state in $^{101}$Sn via the $\alpha$-decay of $^{105}$Te

The doubly magic nucleus $^{100}$Sn is a key test nucleus for the nuclear shell model. Required information in this region is knowledge of single-particle energies, particularly the energy separation between the $\nu d_{5/2}-\nu g_{7/2}$ orbitals. For the $^{100}$Sn region, the energy separation can be best extracted from the energy of the first excited state in $^{101}$Sn. In experiments performed at the HRIBF using the RMS $\alpha$-decay chains of $^{109}$Xe~$\rightarrow$~$^{105}$Te~$\rightarrow$~$^{101}$Sn~were observed following implants of $^{109}$Xe ions into a DSSD, fully instrumented with Digital Signal Processing, placed within the $\gamma$-array CARDS. Double $\alpha$-decay pulse shapes provide a unique and clean coincidence requirement which resulted in the observation of a $\gamma$-ray, interpreted as being emitted from the first excited state in $^{101}$Sn. These results will be presented and the implications for the single-particle level assignments will be discussed.