Low Energy Solar Neutrino Detection by using Liquid Xenon
  Possibility to use ultra pure liquid Xenon as a low energy solar neutrino detector by means of $\nu$+e scatterings is evaluated. A possible detector with 10 tons of fiducial volume will give $\sim$14 events for pp-neutrinos and $\sim$6 events for $^{7}$Be neutrinos with the energy threshold at 50 keV. The detector can be built with known and established technologies. High density of the liquid- Xe would provide self-shields against the incoming backgrounds originating from the container and outer environments. Internal backgrounds can be reduced by distillation and other techniques. Purification of the liquid Xe can be done continuously throughout the experiment. The spallation backgrounds are estimated to be small though an experimental determination is neccessary. The liquid-Xe detector can also provide a significantly better sensitivity for the double beta decay and a dark matter search. However the 2$\nu$ double beta decay of $^{136}$Xe would be most background. It could be overcome if the 2$\nu$ lifetime is longer than 10$^{22}$yr. However, an isotope separation of $^{136}$Xe is inevitable for a shorter lifetime.   The isotope separations would, intoroduce a new opportunity to definitively identify dark matter. The interesting feature in addition to the solar neutrino measurements will also be discussed. 
Y. Suzuki