High‐Speed Video Observation of a Dart Leader Producing X‐rays

Abstract

This work presents the first simultaneous X-ray measurement and high-speed video observation of the propagation of a lightning leader producing X-rays. As a result, the three-dimensional leader distance from the X-ray measurement and, for the first time, the conditions of the preexisting channel during the leader propagation were observed. Although four leaders in this seven-stroke flash followed the same path to ground, X-rays were only observed during the leader before the return stroke with the highest peak current. The fact that the other three leaders following the same path to ground did not produce detectable X-rays confirms the hypothesis that leader line charge density is an important factor that determines X-ray production. The fact that X-rays was recorded only when the leader tip was at a certain portion of the lightning channel confirms that the orientation of the leader plays an important role in the detection of X-rays. Plain Language SummaryIt was known that lightning can produce X-rays. However, in this study, thanks to the use of a high-speed video camera it was possible to determine when lightning produces X-rays, how far it was, how it was oriented when the detection of X-rays, and what the conditions of the preexisting channel were during the leader propagation. The observations of the present work allow for new insights, confirmation of some hypotheses, and comparison with past studies. The results presented help to understand why X-rays are sometimes detected and sometimes not. It is shown that the amount of charge transferred by the discharge plays a crucial role. This study also confirms that the orientation of the descending leader plays an important role in the detection of X-rays.

High‐Energy Radiation From Natural Lightning Observed in Coincidence With a VHF Broadband Interferometer

“…This observation is consistent with Saba et al. (2019) measurements, which confirm the important role of the leader orientation in the X‐ray detection.…”

“…(2014) and Saba et al. (2019). The first observation is related to the LB7 in Figure 12.…”

“…Recently, Saba et al. (2019) measured X‐ray emissions in coincidence with a dart leader using high‐speed video and pointing out the role of the leader orientation in the X‐ray detection.…”

Synchrotron mechanism of X-ray and gamma-ray emissions in lightning and spark discharges

“…It was shown recently, that TGFs are produced during strong initial breakdown pulses (IBPs) in the beginning stages of negative-polarity breakdown [38,39]. Similar effect was shown in [40], where X-rays were only observed during the leader before the return stroke with the highest peak current.…”

“…This will cause the strong dependence of the detected radiation power on the direction of the detector. It was shown in [40] that the orientation of the descending leader plays an important role in the detection of X-rays. It was also pointed out in [7], that the x-ray bursts in a laboratory spark discharge have a finite opening cone.…”