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Recently, cosmic ray albedo neutron decay (CRAND) has been identified as the main source of relativistic electrons measured at the inner edge of inner radiation belt. Here we introduce a drift-source model that includes azimuthal drift and a CRAND electron source to simulate the quasi-trapped electron distribution measured by the DEMETER satellite during 20-30 April 2010. The simulated longitude distribution of quasi-trapped electron fluxes at the inner edge of inner radiation belt successfully reproduces the DEMETER observations, confirming CRAND as the main source for these electrons. Furthermore, a comparison of the energy spectrum and the L distribution of the quasi-trapped relativistic electrons between simulations and observations further suggests that CRAND is likely the dominant source for 300-700-keV quasi-trapped electrons at L<2 and L approximate to 3.

Plain Language Summary Cosmic rays are mostly high-energy protons origin form supernovae in our galaxy. By interacting with neutral atoms in the Earth's upper atmosphere, cosmic rays can produce albedo neutrons with a mean lifetime of 887s. An albedo neutron decays into a proton, an electron, and an antineutrino. This process is called cosmic ray albedo neutron decay, or CRAND. Li et al. (2017; ) find that quasi-trapped electrons near the inner edge of the inner radiation belt measured by the Colorado Student Space Weather Experiment CubeSat are CRAND-produced. CRAND-produced electrons can accumulate during the drift and electron flux increase with longitude before reaching South Atlantic Anomaly. In return, the quasi-trapped electron fluxes can be used to infer the neutron density in the near-Earth space. Here we report a modeling study to reproduce this drift accumulation process.