Photoneutron Cross Sections forBa138andN14

Abstract

Photoneutron cross sections, including $\ensuremath{\sigma}[(\ensuremath{\gamma}, n)+(\ensuremath{\gamma}, pn)]$, $\ensuremath{\sigma}(\ensuremath{\gamma}, 2n)$, and $\ensuremath{\sigma}(\ensuremath{\gamma}, 3n)$ for ${\mathrm{Ba}}^{138}$ and $\ensuremath{\sigma}[(\ensuremath{\gamma}, n)+(\ensuremath{\gamma}, pn)]$ for ${\mathrm{N}}^{14}$, were measured with monoenergetic photons from threshold to 29 MeV. The partial cross sections were determined by neutron multiplicity counting, and the average neutron energies for both single- and double-photoneutron events were determined simultaneously with the cross-section data by the ring-ratio technique. The ${\mathrm{N}}^{14}$ data, when combined with data from other laboratories, appears to show that the ($\ensuremath{\gamma}, \mathrm{pn}$) process dominates the decay of the giant resonance in this nucleus. The giant-resonance parameters for ${\mathrm{Ba}}^{138}$ are nearly the same as those for ${\mathrm{Pr}}^{141}$, which has the same (magic) neutron number.