Multiple X-ray bursts from long discharges in air

TL;DR

This study investigates multiple X-ray bursts generated during high-voltage air discharges, revealing their timing, energy, and dependence on surge polarity, with implications for understanding radiation during lightning-like events.

Contribution

It provides detailed measurements of X-ray bursts during lightning surge simulations, highlighting the timing, energy levels, and polarity effects of radiation emissions in air discharges.

Findings

X-ray bursts occur during the surge between half of maximum voltage and gap breakdown.

Negative surges produce more intense radiation than positive surges.

Some X-ray signals reach energies of several MeV.

Abstract

A lightning surge generator generates a high voltage surge with 1.2 microsec. rise time. The generator fed a spark gap of two pointed electrodes at 0.7 to 1.2 m distances. Gap breakdown occurred between 0.1 and 3 microsec. after the maximum generator voltage of approximately 850 kV. Various scintillator detectors with different response time recorded bursts of hard radiation in nearly all surges. The bursts were detected over the time span between approximately half of the maximum surge voltage and full gap breakdown. The consistent timing of the bursts with the high-voltage surge excluded background radiation as source for the high intensity pulses. In spite of the symmetry of the gap, negative surges produced more intense radiation than positive. This has been attributed to additional positive discharges from the measurement cabinet which occurred for negative surges. Some hard radiation signals were equivalent to several MeV. Pile-up occurs of lesser energy X-ray quanta, but still with a large fraction of these with an energy of the order of 100 keV. The bursts occurred within the 4 nanosec. time resolution of the fastest detector. The relation between the energy of the X-ray quanta and the signal from the scintillation detector is quite complicated, as shown by the measurements.