Photoneutron Cross Sections of Cobalt and Manganese

The total photoneutron yields of ${\mathrm{Mn}}^{55}$ and ${\mathrm{Co}}^{59}$ have been measured from threshold to approximately 30 Mev. Analysis of these data using the Leiss-Penfold matrix indicates that the cross sections for both elements show a splitting in the giant resonance region in accord with the predictions of the classical hydrodynamic model. The ${\mathrm{Mn}}^{55}$ peaks occur at energies of 16.8±0.25 Mev and 19.75±0.25 Mev corresponding to cross sections of 90 mb and 77 mb, respectively. ${\mathrm{Co}}^{59}$ maxima occur at 16.75±0.25 Mev and 18.75±0.25 Mev with cross sections of 109 mb and 92 mb. The cross sections $\sigma (\gamma , n)+\sigma (\gamma , 2n)+\sigma (\gamma , np)+\cdots$ integrated to 25 Mev are 627 Mev-mb for ${\mathrm{Mn}}^{55}$ and 709 Mev-mb for ${\mathrm{Co}}^{59}$. Breit-Wigner resonance lines were fitted to both cross sections and the intrinsic quadrupole moments determined from these fits are +0.78±0.10 barn for manganese and +0.76±0.11 barn for cobalt.