NRL Develops Novel Portable X-ray Unit

A team of scientists working in the Naval Research Laboratory's (NRL's) Space Science Division has developed a portable, lightweight pulsed X-ray unit, which may someday be critical for medical radiographic imaging and triage in the field, as well as for nondestructive testing, threat detection and surveillance in remote locations.

The mobile X-ray unit (MXU) is compact, battery-operated and weighs just 26 pounds. Conventional and older X-ray generators use rack-mounted power supplies and can weigh hundreds of pounds. When combined with an X-ray detector of the type that is used for dental X ray imagery and controlled by a notebook computer, the MXU becomes an instrument that can be used in remote or confined spaces for X-ray inspection, security surveillance and medical applications.

Although the energy of the X-ray pulse is determined by the user who can set the charging voltage on the MXU's Marx generator, the duration of the X-ray pulse lasts about 50 nanoseconds (a nanosecond is one billionth of a second). Since motion blurring of biological subjects and most mechanical objects is not possible in 50 nanoseconds, the X-ray image produced by this device is essentially a stop-action photograph and is ideal for examining rapidly-moving mechanical devices and for small animal imaging.

NRL's Dr. John Seely, Program Manager, along with Glenn Holland of Sachs Freeman Associates, the project's mechanical technician, and Craig N. Boyer of Universities Space Research Association, the project scientist, explain how the X-ray unit works. "The system is constructed like a spark plug. Two metal electrodes face one another and when high voltage is applied, electrons fly. In this case, the electron current is intense enough and energetic enough to create a bright flash of X-rays. All of this happens in a small vacuum tube, which then emits the X-ray pulse through a thin aluminum window."

The MXU comprises (a) the X-ray head assembly, (b) a Marx capacitor bank, (c) a programmable high voltage charging supply, and (d) power management and trigger electronics. The Marx generator pulse-shaping circuit and the Marx triggering source are built into an insulating cylinder, which is pressurized with nitrogen gas. An aluminum tube fits over the pressurized cylinder and serves as the structural and electrical connection between the Marx generator and the X-ray tube. The power management and triggering electronics are housed in an adjoining enclosure shielded from electromagnetic interference and located beneath the MXU.

The mobile X-ray unit was originally conceived and developed for use in testing silicon X-ray detectors, X-ray framing cameras and charge-coupled device X-ray imaging arrays. The unit design was completed in mid-January 1996 and tested for the first time at the beginning of February, 1996. The current, portable version was completed in just 7-1/2 months and the researchers are already convinced that they can fabricate an even smaller, lighter version, possibly reducing the weight to about 13 pounds.

Note: sample X-ray images taken by the MXU include a computer chip and a wisdom tooth.

About the U.S. Naval Research Laboratory

The U.S. Naval Research Laboratory is the Navy's full-spectrum corporate laboratory, conducting a broadly based multidisciplinary program of scientific research and advanced technological development. The Laboratory, with a total complement of nearly 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 85 years and continues to meet the complex technological challenges of today's world. For more information, visit the NRL homepage or join the conversation on Twitter, Facebook, and YouTube.

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