The neutron-capture cross sections of ${}^{168}\mathrm{Yb}$, ${}^{180}\mathrm{W}$, ${}^{184}\mathrm{Os}$, ${}^{190}\mathrm{Pt}$, and ${}^{196}\mathrm{Hg}$ have been measured by means of the activation technique. The samples were irradiated in a quasistellar neutron spectrum of $\mathit{kT}=25$ keV, which was produced at the Karlsruhe 3.7-MV Van de Graaff accelerator via the ${}^7\mathrm{Li}$($p,n$)${}^7\mathrm{Be}$ reaction. Systematic uncertainties were investigated in repeated activations with different samples and by variation of the experimental parameters, that is, irradiation times, neutron fluxes, and $\gamma$-ray counting conditions. The measured data were converted into Maxwellian-averaged cross sections at $\mathit{kT}=30$ keV, yielding $1214\pm 61$, $624\pm 54$, $590\pm 43$, $511\pm 46$, and $201\pm 11$ mb for ${}^{168}\mathrm{Yb}$, ${}^{180}\mathrm{W}$, ${}^{184}\mathrm{Os}$, ${}^{190}\mathrm{Pt}$, and ${}^{196}\mathrm{Hg}$, respectively. The present results either represent first experimental data (${}^{168}\mathrm{Yb}$, ${}^{184}\mathrm{Os}$, and ${}^{196}\mathrm{Hg}$) or could be determined with significantly reduced uncertainties (${}^{180}\mathrm{W}$ and ${}^{190}\mathrm{Pt}$). These measurements are part of a systematic study of stellar ($n,\gamma$) cross sections of the stable $p$ isotopes.

• Received 24 February 2010

DOI:https://doi.org/10.1103/PhysRevC.82.035806