Multiple x-ray bursts from long discharges in air

Abstract

A lightning surge generator generates a high voltage surge with 1.2 μs 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 μs 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 ns 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.PACS 52.70, La 52.80.Mg, 92.60.Pw

High-Energy Atmospheric Physics: Terrestrial Gamma-Ray Flashes and Related Phenomena

“…These x-rays were usually produced when either the voltage was near its peak value or the voltage in the gap was in the process of collapsing. This work has since been confirmed and expanded upon by several groups in different high voltage laboratories (Dwyer et al 2008a;Rahman et al 2008;Nguyen et al 2008Nguyen et al , 2010Montanyà 2010, 2011;Gurevich et al 2011b). Like lightning, the energy spectra of x-rays from laboratory sparks is too soft to be produced by RREA, which, as we discussed in Sect.…”

Experimental study of hard x-rays emitted from metre-scale positive discharges in air

“…Several reports on the observation of x-rays with lightning impulse generators have been published [12][13][14]. Up to a few metre distance between detector and discharge is usually maintained because of safety.…”

“…The generator is connected to a spark gap with cone-shaped electrodes. The setup is similar to the one described in [13], with five changes worth mentioning here. First, the discharge channel is vertical rather than horizontal.…”

“…The horizontal dimension of the cloud formed collectively by the numerous streamers is much larger than was expected before and equals approximately 1.4 m. This means that all equipment placed at shorter distances will emit or receive streamers at certain times and will affect the measurements [13]. This is why we changed the setup and applied the Velostat foil, as mentioned in section 2.…”

“…X-rays can also occur during the initiation of sparks in the laboratory on a scale of millimetres up to metres, even with standard atmospheric conditions of approximately 1 bar and 20 • C. Unrolling adhesive tapes generates x-rays [9], as do helium-filled spark chambers [10], the formation of corona discharges [11] on a centimetre scale, or metre long discharges [12][13][14][15]. X-rays are a common feature of a high-voltage (HV) discharge, regardless of size.…”