Photoneutron Cross Sections of ${\mathrm{Pb}}^{206}$, ${\mathrm{Pb}}^{207}$, ${\mathrm{Pb}}^{208}$, and ${\mathrm{Bi}}^{209}$

Cross sections for ($\gamma , n$) and ($\gamma , 2n$) reactions on ${\mathrm{Pb}}^{206}$, ${\mathrm{Pb}}^{207}$, ${\mathrm{Pb}}^{208}$, and ${\mathrm{Bi}}^{209}$ have been measured using monochromatic gamma rays having an energy resolution of 3%. The peak cross sections for $\sigma \left[\right(\gamma , n)+(\gamma , np\left)\right]$ are 515, 475, 495, and 515 mb, respectively, and for $\sigma (\gamma , 2n)$ are 76, 80, 117, and 105 mb, respectively. Integrated cross sections for $\sigma (\gamma , n)$ up to 28 MeV are 2.22, 2.05, 1.96, and 2.17 MeV-b, while for $\sigma (\gamma , 2n)$ are 0.56, 0.60, 0.95, and 0.76 MeV-b, respectively. Level-density parameters for the residual nuclei ${\mathrm{Pb}}^{205}$, ${\mathrm{Pb}}^{206}$, ${\mathrm{Pb}}^{207}$, and ${\mathrm{Bi}}^{208}$ were found to be 6.6, 13.5, 9.6, and 10.2 Me${\mathrm{V}}^{-1\mathrm{}}$, respectively, each determined to ± 11%. Values obtained for ${\sigma }_{-2\mathrm{}}$ are 15.6, 14.5, 14.1, and 16.6 mb/MeV, respectively.