Cosmic Ray Albedo Neutron Decay (CRAND) as a Source of Inner Belt Electrons: Energy Spectrum Study

Cosmic Ray Albedo Neutron Decay (CRAND) has been recently confirmed as a source of energetic electrons at the inner edge of the inner belt by the Colorado Student Space Weather Experiment (CSSWE) mission. Here we use observations from the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) mission, to investigate the CRAND contribution to inner belt electrons quantitatively over a broad energy range (similar to 100-800 keV). Spectral fitting analysis supports the conclusion that CRAND is the most important electron source at the inner edge of the inner belt. For the first time, we show that CRAND is the dominant source of >250-keV quasitrapped electrons throughout the inner belt and slot region during quiet times. We suggest that additional sources for <250-keV electrons exist, perhaps from inward transport. In contrast, dynamics of electrons in the inner belt and slot region is dominated by injections during active times. Plain Language Summary Albedo neutrons are produced when cosmic ray particles (energetic protons and alpha particles) enter the Earth's atmosphere and then decay into protons, electrons, and antineutrinos, which is known as the Cosmic Ray Albedo Neutron Decay (CRAND) process. The produced energetic protons fill up the inner proton radiation belt, but the CRAND-produced electrons were not expected to be an important source of the electron belts until measurements from the Colorado Student Space Weather Experiment (CSSWE) mission recently showed that 500-keV electrons at the inner edge of the inner belt are produced by CRAND. This study uses measurements from the Detection of ElectroMagnetic Emissions Transmitted from Earthquake Regions (DEMETER) mission and analyze the electron energy spectrum over a broad energy range (similar to 100-800 keV), combining the theoretical calculation of the energy spectrum of CRAND-produced electrons, to confirm CRAND is the dominant electron source at the inner edge of the inner belt. Furthermore, we show that CRAND is also an important source of >250-keV quasitrapped electrons (freshly produced ones) in the inner belt and slot region during quiet times. This study discusses the CRAND contribution to the radiation belt electrons and shows that with the knowledge of this new electron source, some other physics processes, such as pitch angle scattering, need to be revisited and quantified.