A study of X‐ray emission from laboratory sparks in air at atmospheric pressure

Abstract

[1] We present a detailed investigation of X-ray emission from long laboratory sparks in air at atmospheric pressure. We studied 231 sparks of both polarities using a 1-MV Marx generator with gap lengths ranging from 10 to 140 cm. The X rays generated by the discharges were measured using five NaI/PMT detectors plus one plastic scintillator/PMT detector, all enclosed in 0.32-cm-thick aluminum boxes. X-ray emission was observed to accompany about 70% of negative polarity sparks and about 10% of positive polarity sparks. For the negative sparks, X-ray emission was observed to occur at two distinct times during the discharge: (1) near the peak voltage, specifically, about 1 ms before the voltage across the gap collapsed, and (2) near the time of the peak current through the gap, during the gap voltage collapse. Using collimators we determined that the former emission emanated from the gap, while the latter appeared to originate from above the gap in the space over the high-voltage components. During individual sparks, the total energy of the X rays that was deposited in a single detector sometimes exceeded 50 MeV, and the maximum energy of individual photons in some cases exceeded 300 keV. X-ray emission near the peak voltage was observed for a wide range of electrode geometries, including 12-cm-diameter spherical electrodes, a result suggesting that the X-ray emission was the result of processes occurring within the air gap and not just due to high electric fields at the electrode.

On the possible origin of X-rays in long laboratory sparks

“…The latter study confirmed the production of X-rays from long laboratory sparks in air at atmospheric pressure obtained by Dwyer et al (2005a) as opposed to mmcm-long discharges mentioned above. Recently, another study (Dwyer et al, 2008) was conducted by combining the X-ray detector system used in Dwyer et al (2005b) study and the high voltage facilities used in the study of Rahman et al (2008). The results of this study too confirmed the results obtained previously by Dwyer et al (2005b) and Rahman et al (2008).…”

Energy Distribution of X-rays Produced by Meter-Long Negative Discharges in Air

“…The two types of distributions considered produce similar results for the mean energy and for the total number of photons. Despite being slightly different from previous estimates reported in [7,[13][14][15][16], the values derived in this study are of the same order of magnitude as these previous estimates.…”

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.…”

“…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.…”