Measurement of the damping of nuclear shell effect in the doubly magic ${}^{208}$Pb region

The damping of the nuclear shell effect with excitation energy has been measured through an analysis of the neutron spectra following the triton transfer in the ${}^7$Li induced reaction on ${}^{205}$Tl. The measured neutron spectra demonstrate the expected large shell correction energy for the nuclei in the vicinity of doubly magic ${}^{208}$Pb and a small value for ${}^{184}$W. A quantitative extraction of the allowed values of the damping parameter $\gamma$, along with those for the asymptotic nuclear level density parameter $\tilde{a}$, has been made for the first time.