ISSN 1063-7850, Technical Physics Letters, 2009, Vol. 35, No. 6, pp. 508–510. © Pleiades Publishing, Ltd., 2009. Original Russian Text © I.D. Kostyrya, V.F. Tarasenko, 2009, published in Pis’ma v Zhurnal Tekhnicheskoі Fiziki, 2009, Vol. 35, No. 11, pp. 54–60. 508 1. It is well known that nanosecond breakdown in various gases at elevated pressures is accompanied by the generation of X-ray and runaway electron beams (see, e.g., [1–10] and references therein). Maximum doses of X-ray exposure on nanosecond discharge in gases at elevated pressures were observed in inhomoge- neous electric fields of cathodes possessing small radii of curvature. The exposure dose usually decreases with increasing pressure in a gas-filled diode and is small in diodes filled with heavy gases. Recently, the maximum X-ray exposure dose of ~1.5 mR was observed [9, 10] behind the output win- dow of a diode filled with air at atmospheric pressure and powered by nanosecond pulses of high voltage in the regime of generation of a supershort avalanche electron beam with maximum current amplitude. The high-voltage pulses of negative polarity were applied to the gap from a RADAN-220 pulser [11]. The X-ray emission was detected behind a 20-μm-thick copper foil anode, which was connected to the gas diode case. The exposure dose was measured by a Model 138 dose meter (Arrow-Tech Inc.) arranged at a distance of 1 2 mm from the output window. The X-ray pulse full width at half maximum (FWHM) did not exceed 2 ns and was determined by the temporal resolution of a semiconductor detector (SPPD11-04). The X-ray quantum energy outside the gas diode was relatively high. The main contribution to the exposure dose was due to two groups of X-ray quanta with an effective energy of ~30 and 80 keV. A disadvantage of the source of short X-ray pulses described in [9, 10] was that the electron beam propagated in the same direction as the X-ray flux and was also detected behind the 20-μm- thick copper foil. It was found [9, 10] that the sensitiv- ity of both semiconductor detectors (SPPD11-04) and photographic films (RF-3) with respect to electrons was several times greater than that with respect to X-ray quanta. This circumstance complicates the use of X-rays generated in gas-filed diodes and hinders correct detection of the output radiation. Previously, it was experimentally demonstrated [12] that, using a potential anode in gas diodes (as well as in vacuum diodes), it is possible to obtain X-ray radiation fluxes free of electrons. However, the effi- ciency of that radiation source was low and the X-ray exposure dose behind the output window did not exceed 0.1 mR. The present study was aimed at creat- ing a pulsed X-ray source with FWHM below 1 ns and an effective energy of X-ray quanta < 10 keV, which would be capable of providing soft X-ray exposure doses above 1 mR in the absence of an electron beam behind the output window. 2. The experiments were performed using three types of discharge gaps filled with air at atmospheric pressure. Figure 1 shows schematic diagrams of the electrode arrangement in two diodes, whereas the third configuration was described elsewhere [5, 7, 9, 10]. The gas diodes were powered by high-voltage pulses from a SLEP-150 pulser via a line with a ~30 Ω wave impedance. The maximum voltage pulse ampli- tude on a high-ohmic load was ~140 kV, a pulse FWHM on a matched load was ~1 ns, and the leading front width was ~0.3 ns. It should be noted that the energy stored in the high-voltage line of SLEP-150 was about ten times smaller than that in RADAN-220, while the maximum voltage pulse amplitude in the former pulser was smaller by a factor of about 1.5. The experiments were performed with high-voltage pulses of both positive and negative polarity. In the former case, positive pulses were applied to either a flat anode Subnanosecond Pulsed X-ray Source Based on Nanosecond Discharge in Air at Atmospheric Pressure I. D. Kostyrya and V. F. Tarasenko* Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia *e-mail: VFT@loi.hcei.tsc.ru Received December 24, 2008 Abstract—We have studied the characteristics of an X-ray source based on a gas diode filled with air at atmo- spheric pressure. Driven by a SLEP-150 pulser with a maximum voltage amplitude of ~140 kV, a pulse full width at half maximum (FWHM) of ~1 ns, and a leading front width of ~0.3 ns, a soft X-ray source produces subnanosecond pulses with an FWHM not exceeding 600 ps and an exposure dose of ~3 mR per pulse. It is shown that the main contribution to the measured exposure dose is due to X-ray quanta with an effective energy of ~7.5 keV. PACS numbers: 52.80.Mg DOI: 10.1134/S106378500906008X