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

Abstract

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 (~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.

On Energetic Electron Dynamics During Geomagnetic Quiet Times in Earth's Inner Radiation Belt due to Atmospheric Collisional Loss and CRAND as a Source

“…where q 0 is 3.7 × 10 −13 cm −3 sec −1 sr −1 from Lenchek et al (), φ ( E ) is the neutron β‐decay spectrum (see equation of Selesnick, ), and v is the electron speed. The intensity of S e in equation has been verified by the spectral shape of quasi‐trapped electrons (Xiang et al, ; Zhang et al, ) and compared with previous independent calculations (Hess et al, ; Li et al, ).…”

“…We used the observed energy spectrum from DEMETER to evaluate the energy loss effect from atmospheric collisions. Previous studies suggest that the flat spectrum of higher energy trapped electrons (Figure j, >200‐keV electrons at L = 1.2) is possibly due to penetrating proton contamination (Zhang et al, ). However, the simulation results with CRAND as a source for 304 and 509 keV at L = 1.2 present comparable values with DEMETER observations (Figures b and b), suggesting that the flat spectrum can actually exist at low L during quiet times.…”

“…In Figures 1j–1l, the lines with higher flux level are energy spectra of trapped electrons measured in SAA region, while the ones with lower flux levels are energy spectra of quasi‐trapped electrons (longitude = [235°, 245°], in the drift loss cone). The gray dashed line is the energy spectrum of CRAND‐produced electrons based on the equation in Zhang et al (). The energy spectrum of CRAND‐produced electrons well fits DEMETER observations of quasi‐trapped electrons, demonstrating that CRAND is the main source of these quasi‐trapped electrons (Li et al, ; Xiang et al, ; Zhang et al, ).…”

“…The gray dashed line is the energy spectrum of CRAND‐produced electrons based on the equation in Zhang et al (). The energy spectrum of CRAND‐produced electrons well fits DEMETER observations of quasi‐trapped electrons, demonstrating that CRAND is the main source of these quasi‐trapped electrons (Li et al, ; Xiang et al, ; Zhang et al, ). The discrepancy at <200 keV between observations and CRAND‐produced spectrum is discussed at the end of section .…”

“…CRAND was identified as an important source of the inner proton radiation belt six decades ago (Kellogg, ; Singer, ), but not for electrons in the inner belt (Lenchek et al, ). Recently, based on energetic electrons measured by the Colorado Student Space Weather Experiment CubeSat (Li et al, , ) near the inner edge of the inner radiation belt (Li et al, ), the analysis of the energy spectrum from CRAND electrons (Zhang et al, ), and numerical simulations based on the drift‐source model (Xiang et al, ), CRAND had been demonstrated to be the main source of hundreds of kiloelectron‐volt quasi‐trapped electrons at L < 2 and L ≈ 3. These new findings suggest that CRAND must also contribute to inner belt trapped electrons, and thus, the overall contribution of CRAND to inner radiation belt electrons needs to be further investigated.…”