Study of hard ionizing radiation generation regions in an atmospheric discharge

The distributions of time and energy parameters of X-ray radiation of the nanosecond megavolt atmospheric discharge of “reverse-conical cathode with a tip–grid anode” configuration have been measured for the first time on the coordinate along the discharge axis with a resolution of 12 cm. The discharge gap length is 60.5 cm and the maximum applied voltage is 1.2 MV with a front rise time of $\sim$ 220 ns. The photon energy has been evaluated using lead filters of stepped attenuation with thicknesses up to 10 mm. About 1200 axial discharges have been examined. It has been found that radiation pulses are clustered in time and arise together with features of the time derivative of the applied voltage. The most intense and hard X-ray and gamma radiation is observed at the time when the applied voltage reaches its maximum value. The radiation energy from the anode region exceeds the radiation energy from the gas gap by a factor of 5–8. Radiation energy maxima are also observed near the cathode region. The maximum photon energy does not exceed $\sim$ 400 keV. The amplitude spectra of ionizing radiation are studied. Relativistic electrons deceleration in the anode material can be the bremsstrahlung source for the observed radiation.