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Abstract Determination of the fluxes and spectra of energetic particle precipitation into the Earth's atmosphere is of critical importance for radiation belt dynamics, magnetosphere‐ionosphere coupling, as well as atmospheric chemistry. To improve the assessments of precipitating electrons using X‐ray measurements requires deeper understanding of bremsstrahlung production, transport, and redistribution throughout the atmosphere. Here we use first‐principles Monte Carlo models to explore relativistic electron precipitation events from the perspective of bremsstrahlung X‐rays. The spatial distribution of X‐rays is quantified from the ground level up to satellite altitudes. We then simulate X‐ray images that would be captured using an ideal camera and calculate the energy spectra of X‐rays originating from monoenergetic beams of precipitating electrons. Moreover, we show how these impulse responses to monoenergetic beams can be used to reconstruct the precipitating source using an inversion technique. Modeling results show that space‐borne measurements of backscattered X‐rays provide a promising method to estimate precipitation spatial size, fluxes, and spectra.
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Geant4 simulations of x-ray photon pileup produced by runaway electrons in streamer discharges
Runaway electron acceleration is the keystone process responsible for the production of energetic radiation by lightning and thunderstorms. In the laboratory, it remains undetermined if runaway electrons are merely a consequence of high electric fields produced at the ionization fronts of electrical discharges, or if they impact the discharge formation and propagation. In this work, we simulate photon pileup in a detector next to a spark gap. We compare laboratory measurements to ensembles of monoenergetic electron beam simulations performed with Geant4 (using the Monte Carlo method). First, we describe the x-ray emission properties of monoenergetic beams with initial energies in the 20 to 75 keV range. Second, we introduce a series of techniques to combine monoenergetic beams to produce general-shape electron energy spectra. Third, we proceed to attempt to fit the experimental data collected in the laboratory, and to discuss the ambiguities created by photon pileup and how it constrains the amount of information that can be inferred from the measurements. We show that pileup ambiguities arise from the fact that every single monoenergetic electron beam produces photon deposited energy spectra of similar qualitative shape and that increasing the electron count in any beam has the same qualitative effect of shifting the peak of the deposited energy spectrum toward higher energies. The best agreement between simulations and measurements yields a mean average error of 8.6% and a R-squared value of 0.74.
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- Award ID(s):
- 1917069
- PAR ID:
- 10325111
- Date Published:
- Journal Name:
- Physics of Plasmas
- Volume:
- 29
- Issue:
- 5
- ISSN:
- 1070-664X
- Page Range / eLocation ID:
- 053506
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0086579
