Cryogenic source of atomic tritium for precision spectroscopy and neutrino-mass measurements

We propose a concept for a cryogenic source of atomic tritium at sub-kelvin temperatures and energies suitable for magnetic trapping. The source is based on the dissociation of solid molecular tritium films below 1 K by electrons from a pulsed RF discharge, a technique recently demonstrated for atomic hydrogen, combined with buffer-gas cooling and magnetic confinement. We analyze the key processes limiting the source performance, adsorption, spin exchange and recombination, and show that atomic tritium fluxes exceeding 1e15 per second at kinetic energies of 100 mK can be achieved at the entrance of a magnetic trap. Such a source would enable Doppler-free two-photon 1S-2S spectroscopy in atomic tritium for high-precision measurements of the triton charge radius, providing a crucial benchmark for bound-state QED and improving the comparison between electronic, muonic, and scattering determinations of nuclear sizes in light systems. Beyond spectroscopy, an atomic tritium source avoids molecular final-state broadening in beta-decay and is therefore necessary for next-generation neutrino-mass measurements; combined with detector technologies such as sub-eV resolution quantum sensors or cyclotron radiation emission spectroscopy, it enables order-of-magnitude improvement compared to the current KATRIN sensitivity, reaching sensitivities below the inverted ordering regime. Additionally, the source can be used to generate a beam of low-field-seeking deuterium atoms for loading magnetic traps, an important benchmark before trapping tritium atoms and useful for precision spectroscopy.