Solar Neutrino Interactions with 18O in SuperKamiokande
  The ratio of 18O nuclei to electrons in SuperKamiokande is quite small, about 1:5000. However this nucleus provides two unpaired neutrons and a low threshold for solar neutrino absorption, resulting in an unusually large cross section. The 18O nuclei, together with 17O and deuterium, will produce in excess of 460 scattered electrons per year with energies above the initial SuperKamiokande threshold of 6.5 MeV, or about 6.7% of the total solar neutrino signal, for an electron neutrino flux scaled to the current SuperKamiokande counting rate. We explore whether this might complicate efforts to extract the neutrino spectrum from elastic scattering events and whether there might be any prospect of combining 18O and elastic scattering events to separate charged and neutral current interactions. Under current operating conditions the answers are no, as the Fermi, Gamow Teller, and forbidden contributions to the 18O cross section conspire to produce a nearly isotropic cross section. Thus most of the events are indistinguishable from background. This result is relevant to SuperKamiokande detection of solar antineutrinos, which arise in certain oscillation scenarios. 
W. C. Haxton and R. G. H. Robertson