Neutrino Capture on Tritium: Event Rate per Unit Target Mass as a Function of Neutrino Mass and Clustering

Neutrino capture on tritium, the leading proposed method for detecting the relic background directly, yields 4.00 events per year in a 100 gram target at the cosmic mean density in the light-mass limit, rising to 5.40 events per year at a neutrino mass of 0.15 eV once Milky Way clustering is included, or 54.0 events per kilogram per year. At 0.30 eV the rate reaches 9.60 per 100 grams per year. This paper derives the rate scaling from the capture cross section and the number-density budget, keeps every factor visible, and shows that target mass and running time, not cross-section uncertainty, dominate any realistic detection plan. All values are computed from stated assumptions, not measured.