Scanned-beam x-ray source technology for photon backscatter imaging technique of mine detection: advanced technology research

A very high power, state-of-the-art, scanning x-ray source has been developed for use with an x-ray backscatter system that detects and images buried land mines. This paper describes the distinctive qualities of the x-ray source technology necessary to prove the feasibility of the mine detection technique in the field. The imaging system requires that an x-ray beam, having a nominal illumination area on the ground of two centimeters by two centimeters, sweeps across a width of three meters in a time of 15 milliseconds or less. The source must produce an integrated flux of 106 x-rays (min) at 120 kVp (min) for each pixel. The source technology is based on a plasma-focused electrom beam operating up to 140 kilovolts with a current of 0.7 ampere. The electrom beam is magnetically shaped to form a thin ellipse with dimensions of approximately one millimeter by ten millimeters. The scanner is designed to run continuously with target temperature of 160 degrees F (max). The overall design allows the scanner to run with operational and auxilary power generators in the field. A unique 400 hertz, 440 volt, 3-phase, SCR-controlled, low energy storage DC source, with low ripple and 1% voltage regulation, supplies the scanner with 100 kilowatts of power at up to 160 kilovolts. The uniqueness of the mine detection technique and scanner design limits radiation hazards: 1) focusing and tight collimation minimizes stray x-rays; 2) the x-rays travel directly into the ground and are mostly absorbed; 3) radiation leakage from the source is not permitted; and 4) backscatter radiation is strongly localized around the irradiation area, is directed upward, and has a small angular distribution.