  Various large-scale experiments for double beta decay or dark matter are
based on xenon. Current experiments are on the tonne scale but there are also
ideas to aim for even larger sizes in the future. Here we study the potential
of the isotope $^{131}$Xe to allow to make real-time measurements of solar $pp$
neutrinos, besides classical neutrino-electron scattering. Improved nuclear
models are used to determine the cross-section of neutrinos on $^{131}$Xe. The
present calculations deviate significantly from the previous ones due to
updated estimates for the excited-state contributions. The updated capture-rate
estimate for $pp$ neutrinos is $(4.47\pm 0.09)\ \rm SNU$ and for all solar
neutrinos $(80\pm 21)\ \rm SNU$, with neutrino survival probabilities taken
into account. Depending on the amount of Xe, solar $pp$ neutrinos might be
measured with rates of 100 per day, thus allowing to monitor them in real time
for a long period.
