Fig. 4From: Dynamics of the terrestrial radiation belts: a review of recent results during the VarSITI (Variability of the Sun and Its Terrestrial Impact) era, 2014–2018The “impenetrable barrier” for relativistic electrons as observed by the REPT instrument on Van Allen Probes (reproduced from Baker et al. (2014a)). At all energies, inward radially diffusing electrons do not penetrate below L ≈ 2.8Back to article page