Wilhelm Roentgen, discoverer of X-rays, with 1895 radiograph (inset) of his wife's hand.
Flash radiograph of a bullet passing through a coffee mug. (Courtesy Titan PSD)

Flash Radiography Sources

Abstract: The talk will open with a historical review of radiography over the past 100 years, and give a quick assessment of the state of the art in modern radiography and future trends in industrial and medical applications. Emphasis will then be focused on flash radiography and its application in fast time scale dynamic investigations such as ballistics engineering, detonation or combustion studies, materials science, or hydrodynamics testing. The source "side" of flash radiography systems can also find unique utilization as electron beam sources or as x-ray generators in wide-ranging applications such as semiconductor radiation upset studies.

The range of commercially available units will be described and their strengths and limitations noted. The importance of source spot size on image quality will be emphasized. The tradeoff of size and capability will be obvious. The importance of careful high-voltage design and pulsed power engineering techniques will be illustrated. Several research flash radiation machines will be described based on both diode and accelerator-driven sources.

The relatively recent development of high-current, linear induction accelerator technology will be described and machines such as FXR (Flash X-Ray) at Livermore, and the Dual-Axis Radiographic Hydrodynamics Test (DARHT) at Los Alamos will be presented. These accelerators produce kiloamp electron beams to multi-MeV potentials and deliver high-quality, millimeter-sized beams to Bremstrahlung-based targets. The development of these machines has been accompanied by key breakthroughs in pulsed power, target development, and in the modeling of beam transport and mitigation of beam instabilities. The speaker will describe some of the key issues and technologies involved in fielding these large machines.

Finally, a novel diode source will be described that is under development as a collaboration between LLNL, the Naval Research Laboratory, and Bechtel Nevada. Capable of diagnostic support in many flash x-ray applications, this source utilizes a compact Marx generator driving a rod-pinch diode. Radiographic goals are to produce at least 0.5 rads at 1 m in a pulsewidth of less than 50 ns with a spectral end point above 1 MeV from a spot size less than 1 mm. The source shows promise for a wide range of flash radiographic needs from a device that is table-top sized.

This work was performed under the auspices of the U.S. Dept. of Energy by the University of California, Lawrence Livermore National Laboratory, under Contract No. W-7405-Eng-48.

Bill DeHope

Lawrence Livermore National Laboratory

Bill DeHope has been an electrical engineer within the Defense Sciences Engineering Division at the Lawrence Livermore National Laboratory since 1998. He is presently developing pulsed power and plasma devices for the Lab's National Ignition Facility. He has also made contributions to the Beam Research Program and served as project engineer in developing a compact radiographic source.

Before joining the Lab, the author worked for 19 years in industrial research supporting high power microwave generation or charged particle acceleration. He has held positions at Hughes Aircraft Company, General Atomics, Varian Associates, and Physics International.

His undergraduate education was in physics and mathematics at San Diego State University. He holds an MSEE and Degree of Engineer from Stanford University in Physical Electronics. He has been a member of IEEE for over 20 years and has held memberships in the Nuclear and Plasma Sciences Society, the Electron Device Society, and the Microwave Theory and Techniques Society.

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24-13 map
From highway 24 or 13, take the Berkeley/Tunnel Road/13 exit. Tunnel Road becomes Ashby past the Claremont Hotel. Turn right at the traffic light at College Ave (at the Wells Fargo Bank). Turn right at the traffic light at Durant (one-way street located one block before College Ave ends at the UC campus). At the end of Durant (one block), turn left onto Piedmont, which becomes Gayley Road. Turn right at the traffic light at Hearst at the northeast corner of the campus. Hearst becomes Cyclotron Road. At the LBL guard station the guard can give you instructions to Building 2, Room 100B.

Alternative route from 24-13 (Green line on map; shorter, but through residential neighborhood): On Ashby, turn right at Claremont Ave. (at gas station; second traffic light after main entrance to Claremont Hotel). Immediately bear left around the "island", with the restaurant on it. You will find yourself driving through a wrought iron and brick gateway if you have performed this maneuver properly. Proceed to the end of the street to a forced left turn onto Derby at the UC-Clark Kerr campus. Turn right at Warring at the southwest corner of the campus. After two blocks, follow the road as it bears to the left to join Piedmont Ave at the traffic light (stay in the right lane on Piedmont to avoid a forced left turn at Haste). Continue along Piedmont until it becomes Gayley Road and proceed as described in the previous paragraph.