Precise measurement of energies in ${}^{115}\mathrm{Sn}$ following the $(n,\gamma )$ reaction

The first measurement of $\gamma$ rays from the ${}^{114}\mathrm{Sn}\left(n,\gamma \right)$ reaction using cold neutrons, performed with an array of Ge detectors at the PF1B facility of the Institute Laue-Langevin in Grenoble, has provided the most accurate energy, $Q_{\beta }=173\left(12\right)$ eV, of ${\beta }^{-}$ decay of the ${}^{115}\mathrm{In}$ ground state to the first excited state in ${}^{115}\mathrm{Sn}$. This is the lowest of all such energies in the known nuclear landscape. The accuracy of the neutron binding energy of ${}^{115}\mathrm{Sn}$ and the mass of ${}^{114}\mathrm{Sn}$ have been improved.

Figure 1

A scheme of ${\beta }^{-}$ decay of ${}^{115}\mathrm{In}$ into ${}^{115}\mathrm{Sn}$. The data shown in the figure are taken from Refs. [3, 4, 5, 6]. See text for further explanation.

Figure 2

A $\gamma$-ray spectrum from the $(n,\gamma )$ reaction on the ${}^{114}\mathrm{Sn}$ target with admixture of other Sn isotopes. Panel (a) shows a fragment of the total projection of a $\gamma \gamma$ matrix and panel (b) shows fragment of a spectrum gated on the 489-keV line.

Figure 3

(a) A $\gamma$ spectrum from the ${}^{114}\mathrm{Sn}(n_{th},\gamma ){}^{115}\mathrm{Sn}$ reaction, obtained in the present work, containing pairs of $\gamma$ lines summing to 7545 keV. Panel (b) shows an enlarged fragment of the spectrum shown in panel (a).

Figure 4

Partial excitation scheme of ${}^{115}\mathrm{Sn}$, populated in the ${}^{114}\text{Sn}{(n,\gamma )}^{115}\text{Sn}$ reaction, using cold neutrons. Energies of transitions shown in the figure are corrected for the recoil of the nucleus. Energies of levels are calculated based on energies of transitions depopulating them.