Experimental evidence of the ${}^6$He level at $E^{\ast }$ = 18.3 MeV by the ${}^4$He+${}^3$H three-body reaction

Measurements of the t-t and p-t coincidence events in the ${}^3$H ($\alpha$, ttp) reaction have been obtained at $E_{\alpha }$ incident energy of 67.2 MeV. Various appropriate angular configurations of detectors were chosen in order to observe the population of the ${}^6$He${}^{\ast }$ state at around 18 MeV. Its contribution appears at the $E_{\mathrm{t}\mathrm{t}}$ relative energy of 6.0 MeV by the analysis of bidimensional spectra. We found the formation of the ${}^6$He excited state at $E^{\ast }=18.3\pm 0.2$ MeV (with a $\mathrm{\Gamma }$ width of 1.1 $\pm$ 0.3 MeV) by the decay into the t+t binary channel, since the threshold energy of the t+t channel is 12.31 MeV. In each analyzed bidimensional energy spectrum of ($E_{\mathrm{t}}$, $E_{\mathrm{t}}$) and ($E_{\mathrm{p}}$, $E_{\mathrm{t}}$) coincidence events resonance structures are present due to the formation of both ${}^6$He${}^{\ast }$ and ${}^4$He${}^{\ast }$ excited states. Our results on the $E^{\ast }$ and $\mathrm{\Gamma }$ values regarding the ${}^6$He${}^{\ast }$ level of about 18 MeV are compared with the results obtained by other reactions. Moreover, we also found new $\mathrm{\Gamma }$ width values of 0.7 $\pm$ 0.3 and 0.8 $\pm$ 0.4 MeV for the 14.0 $\pm$ 0.4 and 16.1 $\pm$ 0.4 MeV ${}^6$He levels, respectively.