PHOTONEUTRON CROSS SECTIONS WITH MONOENERGETIC NEUTRON-CAPTURE GAMMA RAYS

Monoenergetic gamma rays produced by thermal neutron capture have been used to study photoneutron cross sections of the isotopes ${\mathrm{Ta}}^{181}$, ${\mathrm{Li}}^{7}$, ${\mathrm{Li}}^{6}$, ${\mathrm{C}}^{13}$, and ${B}^{10}$ for $\ensuremath{\gamma}$-ray energies between threshold and 10.8 MeV. Some cross sections were obtained with uncertainties as low as 10%. Wherever possible, these cross sections are compared with those obtained by other methods. The threshold for the ${\mathrm{Ta}}^{181}(\ensuremath{\gamma}, n)$ reaction has been determined to be 7.64\ifmmode\pm\else\textpm\fi{}0.04 MeV. Information about the radiative widths of the 7.47-MeV level in ${\mathrm{Li}}^{7}$ and the 8.89-MeV level in ${\mathrm{B}}^{10}$ is presented.