Fe54(n,p), (n,α), (n,2n) Cross Sections

Absolute cross sections for the ${\mathrm{Fe}}^{54}\mathrm{}(n,p)\mathrm{}{\mathrm{Mn}}^{54}$, and ${\mathrm{Fe}}^{54}(n,\alpha ){\mathrm{Cr}}^{51}$ reactions have been measured for the neutron energy intervals 2.2 to 6.2 MeV and 13.1 to 16.8 MeV. The cross section for the ${\mathrm{Fe}}^{54}\mathrm{}(n,2n)\mathrm{}{\mathrm{Fe}}^{53}$ reaction has been measured at 14.0 and 16.8 MeV. Ten samples 1 by 2 by 0.45 cm enriched to 97% in ${\mathrm{Fe}}^{54}$ were irradiated. Neutrons were produced with the $\mathrm{D}\mathrm{}(d,n)\mathrm{}$ and $\mathrm{T}\mathrm{}(d,n)\mathrm{}$ reactions, using gas targets and a Van de Graaff accelerator. Samples were placed 9 cm from the gas cell at angles from 0° to 122°. The absolute neutron flux at 11° was measured with a proton-recoil telescope. Relative neutron angular distributions were obtained from published $\mathrm{D}\mathrm{}(d,n)\mathrm{}$ and $\mathrm{T}\mathrm{}(d,n)\mathrm{}$ cross sections by integrating over source and target dimensions; the effect of scattering in the gas-cell window foil was also included. These angular distributions were normalized to the telescope values. The induced gamma activity following the decay of ${\mathrm{Mn}}^{54}$, ${\mathrm{Cr}}^{51}$, and ${\mathrm{Fe}}^{53}$ was counted with a large calibrated NaI scintillation spectrometer. The ($n,p$), ($n,\alpha$), and ($n,2n$) results at 14 MeV agree with previous experimental work. Previous measurements of the ($n,p$) cross section from 2 to 6 MeV give values somewhat lower than the present work. All experimental results are somewhat higher than cross sections obtained by a statistical-model calculation based on optical-model potentials, while a more empirical calculation gives good agreement with the ($n,2n$) data.