Evidence for a $^{\mathrm{7}}$Li state at E* $=$ 10.2 MeV from inelastic neutron scattering at 14 MeV

A bright neutron source generating 10$^{\mathrm{11}}$ incident particles, produced in inertial confinement implosions\footnote{ T. R. Boehly \textit{et al.}, Opt. Commun. \textbf{133}, 495 (1997).} by the OMEGA laser, were used to irradiate an isotopically enriched $^{\mathrm{7}}$Li target. Absolute yields and energy spectra were measured for neutrons emitted from interactions of 14-MeV neutrons with $^{\mathrm{7}}$Li in a forward-angle geometry ($\theta $~$=$~0\textdegree ~to 7.4\textdegree ) with a neutron time-of-flight spectrometer. The data were analyzed with an R-matrix calculation using a single-level, single-channel approximation to interpret the level structure of $^{\mathrm{7}}$Li. The inferred differential neutron cross section reveals several $^{\mathrm{7}}$Li resonances in the range 4~MeV $\le $ E* $\le $ 12~MeV, attributed to inelastic $^{\mathrm{7}}$Li$\left( {\mbox{n,{n}'}} \right)^{\mathrm{7}}$Li scattering. In addition, a neutron line with significant cross section is observed at E$_{\mathrm{n}}$~$=$~3.5~MeV and a width of E$_{\mathrm{\Gamma }}\le $~0.9~MeV, which may correspond to excitation of a $^{\mathrm{7}}$Li state at E* $=$ 10.2 MeV. It is tempting to identify this state with a narrow resonance at E* $=$ 10.2 MeV, predicted\footnote{ M. Vorabbi \textit{et al.}, Phys. Rev. C \textbf{100}, 024304 (2019).} by a no-core shell model with continuum (NCSMC) to exist just above the threshold for the mass partition of p $+$ $^{\mathrm{6}}$He reaction. However, the measured linewidth is larger than that (E$_{\mathrm{\Gamma }}$~$=$~0.13 MeV) predicted by the NCSMC model. This material is based upon work supported by the DOE NNSA under Award Number DE-NA0003856.