Extended Data Fig. 1: Illustration of the measurement of column density in the tritium source.
From: Direct neutrino-mass measurement with sub-electronvolt sensitivity
(Top) Relative electron-gun rate measured at four surplus energies (orange circles), defined as the kinetic energy above the retardation potential. Note the change from linear to log-scale at 9.5 eV, indicated by the energy-axis break. The relative uncertainties of the electron-gun rate are at the σRate < 5 × 10−3 level, hence not visible in the plot. A fit of the response function to the data (blue line) infers a column density of ρd = 4.2 × 1017 cm−2 for this specific measurement (the response function description is found in paragraph Spectrum calculation of the Methods section). The green-dashed line illustrates the calculated response function of the β-decay electrons which map the source density profile and show an isotropic starting pitch-angle distribution up to the maximum acceptance angle. (Bottom) Energy-loss function for a single scattering process (red-dotted line) and multiple scatterings (blue line) as they occur for the measured ρd value (For details see Ref. 37).
