Abstract
The energy deposited from X-rays generated by 1 m long laboratory sparks in air created by 950 kV negative lightning impulses on scintillated detectors was measured. Assuming the X-ray energy detected in such sparks results from the accumulation of multiple photons at the detector having a certain energy distribution, an experiment was designed in such a way to characterize their distribution parameters. The detector was screened by a copper shield, and eight series of fifteen impulses were applied by stepwise increasing the copper shield thickness. The average deposited energy was calculated in each series and compared with the results from a model consisting of the attenuation of photons along their path and probable photon distributions. The results show that the energy distribution of X-ray bursts can be approximated by a bremsstrahlung spectrum of photons, having a maximum energy of 200 keV to 250 keV and a mean photon energy around 52 keV to 55 keV.
Highlights
It is a well observed fact that electrical discharges produce high energetic radiation from very soft X-rays in few kilo electron volts up to X-rays and gamma rays having several mega electron volts (Moore et al [1]; Dwyer et al [2,3]; Rahman et al [4]; Nguyen et al [5]; March and Montanyà, [6]; Kochkin et al [7])
Even though the negative discharge development was simplified in the model, the main idea that the streamer encounters can cause X-ray emissions has been supported by recent experimental observations
Encounters occur between positive streamers originating from the space stem and the negative streamers originating from the high voltage electrodes
Summary
It is a well observed fact that electrical discharges produce high energetic radiation from very soft X-rays in few kilo electron volts up to X-rays and gamma rays having several mega electron volts (Moore et al [1]; Dwyer et al [2,3]; Rahman et al [4]; Nguyen et al [5]; March and Montanyà, [6]; Kochkin et al [7]). Energy distribution of X-ray photons generated by laboratory discharges is of interest in understanding the mechanism of X-ray generation This is the case because it provides information concerning the maximum and average energies to which the electrons are accelerated. In order to quantify X-ray energies from electrical discharges, the scintillation detectors could be shielded using attenuating material like lead This is especially helpful where the X-ray detector produces an output higher than that of individual photon energy due to the accumulation of multiple photons. By assuming certain distributions for X-ray fluence and for photon energy, Carlson et al [15] reported that the experimental results of X-rays from 1 MV electrical discharges can be modelled by an exponential X-ray distribution having a mean around 86 keV. This paper describes an experiment carried out using attenuators and a model for the X-ray energy distribution to match the experimental results
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