We have used a 100-MeV electron linac and neutron time-of-flight facility to measure the neutron total cross section of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and the cross section difference of ${}_{}{}^{44}{}_{}{}^{}$Ca${\mathrm{-}\mathrm{}}^{40}$Ca for incident neutron energies of 6–60 MeV. Optical model calculations of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ ${\sigma }_T$ have been made and compared to the data. Modifications of a global set of optical model parameters necessary to fit the ${}_{}{}^{44}{}_{}{}^{}$Ca${\mathrm{-}\mathrm{}}^{40}$Ca difference data are discussed. Using these parameters we calculated Δ=〈$r^2$${〉}_{44}^{1/2}$-〈$r^2$〉 ${}_{40}{}^{1/2}{}_{}{}^{}$ for the real part of the potential and found a value of 0.16±0.05 fm. The value of Δ is sensitive to the difference in the matter distribution of the ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ nuclei and our result is consistent with the same quantity determined from low energy alpha particle scattering.

• Received 16 September 1985

DOI:https://doi.org/10.1103/PhysRevC.34.810