Neutron radii of the calcium isotopes

We have analyzed pion scattering data to determine the proton and neutron radii of the calcium isotopes 40,42,44,48Ca using model densities in which the neutron matter distributions are considered to have components corresponding to core and valence neutrons. The proton radii determined agree with those obtained by electromagnetic means. The radii of the valence distributions show a monotonic decrease throughout the shell from {~}4.9 fm in ⁴²Ca to {~}4.4 fm in ⁴⁴Ca and {~}4.2 fm in ⁴⁸Ca, although this last case is only indicative. The large valence neutron radius of ⁴²Ca suggests that the ground state of this nucleus may have some characteristics of a bound dineutron orbiting a closed core.