Photoneutron Cross Sections for Aluminum and Silicon to 62 MeV

Abstract

Photoneutron cross sections for ${\mathrm{Al}}^{27}$ and ${\mathrm{Si}}^{28}$ have been measured from threshold to 62 MeV using least-structure analysis of the bremsstrahlung activation curves. The aluminum yield was due to the reactions ${\mathrm{Al}}^{27}(\ensuremath{\gamma},n){\mathrm{Al}}^{26*}$ and ${\mathrm{Al}}^{27}(\ensuremath{\gamma},2n){\mathrm{Al}}^{25}$. Secondary maxima in the aluminum cross section, occurring at energies beyond the giant resonance, peak at 49.4\ifmmode\pm\else\textpm\fi{}0.8 and 56.3\ifmmode\pm\else\textpm\fi{}0.9 MeV. The cross section integrated to 62 MeV is 69\ifmmode\pm\else\textpm\fi{}4 MeV mb. The silicon yield was due to the ${\mathrm{Si}}^{28}(\ensuremath{\gamma},n){\mathrm{Si}}^{27}$, ${\mathrm{Si}}^{28}(\ensuremath{\gamma},2n){\mathrm{Si}}^{26}$, and ${\mathrm{Si}}^{28}(\ensuremath{\gamma},pn){\mathrm{Al}}^{26*}$ reactions. Peak energies for secondary maxima are 40.1\ifmmode\pm\else\textpm\fi{}0.9, 46.4\ifmmode\pm\else\textpm\fi{}0.8, 52.5\ifmmode\pm\else\textpm\fi{}0.8, and 58.2\ifmmode\pm\else\textpm\fi{}1.0 MeV. The integrated cross section is 195\ifmmode\pm\else\textpm\fi{}7 MeV mb.