On the detection of ultrahigh-energy neutrinos

Cross sections for the interactions of ultrahigh-energy neutrinos with nucleons are evaluated using contemporary information about nucleon structure functions. For ${10}^{19}$-eV neutrinos, the cross section is an order of magnitude larger than the values traditionally used in astrophysical calculations. Some consequences for interaction rates in the Earth and for event rates in large-scale acoustic and electronic detectors from generic astrophysical neutrino sources are noted.