| In this dissertation, we show that the energetic electrons that produce x-rays exhibit a characteristic energy less than 3 MeV for the natural and rocket-triggered leaders investigated. Furthermore, the spectra from 47 leaders were determined using data from NaI detectors to show the variability of the average source energy. Energetic electron luminosity, total energy, and energetic electron per meter from 28 different leaders from 12 triggered flashes were also compared to their return stroke currents. It was found that the electron luminosity increases exponentially with return stroke current up to about 10 kA and was roughly constant for currents greater than 10 kA. The maximum luminosity in this report was measured to be on the order of 1017 electrons/s, which is less than the value found from theoretical calculations.;Additionally, we investigate x-ray emission from individual lightning leader bursts to determine if energetic electrons at the source are emitted isotropically or with some degree of anisotropy. We find that at least 8 out of 18 x-ray bursts show a statistically significant first-order anisotropy, and are inconsistent with isotropic emission. The level of anisotropy of the runaway electrons is important because it provides, in principle, information on the electric field near the lightning leader tip.;Finally, we investigate the structure of x-ray emissions from downward rocket-triggered leaders using a pinhole-type x-ray camera (XCAM). Five out of 12 leaders, from 2011, produced XCAM images showing the leader propagating downward with x-ray emission. Particularly, two of these five leaders displayed unique x-ray emission patterns (compact and diffuse). These two distinct x-ray emission patterns illustrate the variability of the emission pattern of lightning leaders. Using Monte Carlo simulations, we show that the diffuse x-ray source must originate from a diffuse source of energetic electrons and that compact x-ray sources originate from compact electron sources. Furthermore, we show one "chaotic" dart and one dart-stepped leader that displays a narrow electron source. The maximum x-ray source region radius and maximum electric charge contained within the x-ray source region were also found. |
