Neutron Photoproduction Cross Section of Calcium

The photoneutron cross section of natural calcium has been measured from 15 to 30 MeV using the bremsstrahlung from the University of Virginia electron synchrotron. The neutron yields, measured in 0.5-MeV intervals, were used to unfold the photoneutron cross sections both in 1- and 0.5-MeV intervals. The cross section, which reaches the maximum value of 16.8 mb at 20.25 MeV, exhibits considerable structure. Below 21 MeV, it was possible to fit the data to the superposition of four discrete resonance curves of the Gaussian form, $\sigma ={\sigma }_0\exp \{-{\left[\frac{(E_0-E)}{\Delta }\right]}^2\}$, where ${\sigma }_0$ is the maximum cross section at energy $E_0$, and the parameter, $\Delta$, is related to the full width at half maximum, $\Gamma$, by $\Gamma =2\mathrm{}{\left(\ln 2\right)}^{\frac{1}{2}}\Delta =1.67\mathrm{}\Delta$. The results are compared with the available shell-model calculations.