| 摘要 |
An x-ray source emits a cone beam to a fixed horizontal slit in an x-ray-blocking sheet. The slit produces a fan beam that is chopped into a pencil beam by a rotating disk with radial slots. The pencil beam sweeps across and strikes a subject, producing backscatter that is read by a backscatter detector. The x-ray source, slit sheet, rotating disk, and detector translate vertically to produce a complete image of the subject. X-ray flux is increased by as much as a factor of 50 over prior art personnel inspection systems using several techniques. The detector uses a plastic scintillator situated very close to and curved around the sides of the subject, which increases the average solid angle subtended by the x-ray backscatter detector at a point on the surface of the subject. Decrease in pencil beam flux intensity farther from the center is compensated for by increasing the area of the pencil beam by increasing the width of the slit toward both ends and by increasing the width of the slots from the inner end to the outer end. The x-ray source is placed as close as possible to the subject, the distance determined as one half of the maximum width of the subject, which reduces the x-ray tube power requirement. A dual-energy x-ray source with a high peak x-ray energy of greater than 50 KeV and a low peak x-ray energy not more than 30 KeV is used. The lower energy is as low as possible to differentiate between the innocent low Z materials and contraband that may also contain only low Z materials.
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