Apparatus for Precision Flash Radiography of Shock and Detonation Waves in Gases

Abstract

An apparatus is described which is based on the technique introduced by Kistiakowsky utilizing the absorption of soft x‐rays to measure densities behind gaseous shock and detonation waves. Experimental conditions leading to the smallest absorption statistical uncertainty consistent with maximum sensitivity are defined. These may be approximated at reasonable pressures and tube diameters by adding a strongly absorbing rare gas diluent to the experimental gas mixture. Under such conditions measured densities are accurate to ±1%, as demonstrated by comparison of experimental and calculated densities for shock waves in krypton. At some sacrifice in accuracy, space resolution of 1 mm and time resolution of 1 μsec may be achieved. A continuously pumped, laboratory‐built, demountable, pulsed x‐ray tube with an L‐cathode and tungsten target is used at an accelerating voltage of 20–‐30 kv to obtain currents up to 0.2 amp for durations of the order of 1 msec. Copper and chromium targets were also investigated. For calibration purposes the tube is operated at a steady current of ≈0.2 ma and detector signals are measured potentiometrically to obtain transmission as a function of gas density.