Abstract: Flash I machine is a 6MV REB accelerator. A hollow conical cathode is used to produce beam focusing in the diode and hence an intense bremsstrahlung radiation of 250R at 1 meter with a focus diameter of 6mm has been obtained. Using this accelerator, radiography of high density material under jet perforation was performed. Detonation experiments were carried out in a blast chamber. Results indicated that radiographic capability of this accelerator was more than 5cm tungsten. Details of the radiography technique are described.