Abstract: Crucial questions about solar neutrinos remain unanswered. Our knowledge of stellar fusion processes and neutrinos themselves is incomplete. Neutrino detectors such as Super-Kamiokande have the exposure needed, but backgrounds are limiting. A leading background is the beta decays of isotopes produced by cosmic-ray muons and their secondary particles, which initiate nuclear spallation reactions. I will discuss my comprehensive studies of the spallation backgrounds, from calculating their production rates, to understanding their production mechanisms, to how to implement better background rejection methods. I will also discuss the applications of our MeV work in detecting PeV astrophysical neutrinos in IceCube.