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          What Is an "Entrance Dose" of X-Rays?

          By John W. Gofman, M.D., Ph.D. and Egan O'Connor,
          Editor of CNR Books
          February 2000
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              An "entrance dose" of x-rays is the dose absorbed at
          the surface of the skin where the x-ray beam enters. An
          x-ray beam enters the body from the direction of the
          x-ray tube. A small share of the beam exits from the
          body on the opposite side, where it exposes the film or
          other image-receiver. The share of the beam which never
          exits from the body is absorbed as extra energy by the
          body's internal organs and bones.