Gamma decay from the quasicontinuum of 197,198Au

The average electromagnetic dipole response of levels in the quasicontinuum of $^{197,198}\mathrm{Au}$ has been measured using $(^{3}\mathrm{He},{}^{3}{\mathrm{He}}^{\ensuremath{'}})$ and $(d,p)$ reactions. The extracted $\ensuremath{\gamma}$-ray strength functions have been normalized according to three model assumptions for the nuclear spin distribution. An enhancement in the energy region ${E}_{\ensuremath{\gamma}}=3.0\text{--}6.5$ MeV is observed for both isotopes. The $E1$ component of such excess of strength is studied in detail for $^{198}\mathrm{Au}$ and is interpreted as the pygmy dipole resonance with an energy centroid of $5.9(1)$ MeV and exhausts about $1%$ of the total integrated strength. The pygmy dipole resonance is shown to have a significant impact on the calculated ${}^{197}\mathrm{Au}{(n,\ensuremath{\gamma})}^{198}\mathrm{Au}$ cross section.