The special distribution of X-rays scattered within a water phantom
Griffith, Thomas J.
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The biological effects produced by an X-ray beam are dependent on the spectral distribution of the rays. Untortunately a straight-forward determination of this spectral distribution at a point within a biological medium is complicated by scattering processes which significantly alter the spectral distribution at the point from that of the primary radiation. Prior to the advent of the sodium iodide scintillation counter, direct measurements of the spectrum of the radiation inside a scattering medium were impossible although some information was obtained (1,2) using dual isolation chambers. The application of a scintillation spectrometer to the measurement of the spectral distribution of scattered X-rays within a water phantom has, however, made it possible to obtain more detailed and more extensive information about the radiation. In particular, coupled with a prior investigation of the primary spectral distribution (3) the investigation of the scattered radiation here reported provides the total spectral distribation of the X-rays at central axis points within a phantom, the manner in which the biological effectiveness of the rays as expressed by linear energy transfer changes with depth and field size, and the differetial absorption of the rays in bone and soft tissue for 400 KVP X-rays, HVL 3.8 mm of Cu.