A model balancing diffusive field-line curvature (FLC) scattering loss with other local source, loss, and transport processes is used to compute the L-shell location of the proton radiation belt outer boundary, where intensity falls below observable levels. The FLC scattering rate increases with increasing L and proton energy, decreasing equatorial pitch angle, and increasing geomagnetic activity, as determined with the K-p-dependent T89 external magnetic field combined with a dipole internal field. Simulated proton intensity near the outer boundary is compared to measurements from both the low-altitude SAMPEX satellite and the high-altitude Van Allen Probes satellites, with correction for instrumental biases caused by field-of-view, energy range, and the east-west effect. Good agreement between observations and simulations is obtained for average boundary locations, time-dependent variations caused by magnetic storms, and average equatorial pitch-angle distributions.
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