Abstract
High resolution neutron transmission measurements have been performed on $^{204}\mathrm{Pb}$ in the energy interval $E=0.4\ensuremath{-}105$ keV. The transmission data were analyzed using a multilevel $R$-matrix code to deduce resonance parameters. Previously obtained neutron capture data were reanalyzed in the interval 2.6-86 keV. Values of $\frac{G{\ensuremath{\Gamma}}_{\mathrm{n}}{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}}{\ensuremath{\Gamma}}$ were determined from the capture data. For those resonances where ${\ensuremath{\Gamma}}_{\mathrm{n}}$ could be determined from the transmission data, the capture data were analyzed to extract ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$. Our results yield an average capture for a stellar temperature $kT=30$ keV of 89.5\ifmmode\pm\else\textpm\fi{}4.5 mb. The $s$-wave level density for $^{205}\mathrm{Pb}$ corresponding to the neutron energy range investigated (i.e., $E\ensuremath{\sim}105$ keV) relative to that for $^{207}\mathrm{Pb}$ (which has about the same neutron separation energy) is greater by about a factor of 10. The average $s$-wave strength function in this energy region is determined as ${S}_{0}=0.93\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. This is an order of magnitude greater than that for a similar energy region in $^{206}\mathrm{Pb}$ + n where a doorway is observed at $E\ensuremath{\sim}500$ keV. However, the strength function in the initial $E=0\ensuremath{-}100$ keV in $^{204}\mathrm{Pb}$ + n is almost identical to the average value of that for $^{206}\mathrm{Pb}$ + n when the averaging interval for the latter is taken as ${E}_{\mathrm{n}}\ensuremath{\approx}0\ensuremath{-}1000$ keV (i.e., over the doorway state). This suggests that the $s$-wave doorway state observed in the higher mass lead isotopes is completely mixed with "background" states in $^{205}\mathrm{Pb}$, and most likely no intermediate structure will be observed in the $s$-wave strength function for the $^{204}\mathrm{Pb}$ + n reaction.
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