Spectra of scattered diagnostic x-rays from an Alderson phantom

The spectra of scattered diagnostic X-rays, at 90° and a distance of 1 m from the central ray of the primary beam, was measured at the side of an Alderson, average man, phantom for a 14 × 17 in. field size. A NaI(T1) spectrometer system was used to make the spectral measurements. A digital computer was utilized to correct the observed spectrum, Nk(E), for distortions introduced by the spectrometer system. The average photon energy, E, derived from the spectrum measurements, and the effective photon energy, Ee, derived from HVL measurements, are compared for the different spectra. Scattered X-ray spectra, normalized to an exposure of one R, are presented in both graphic and tabular form. The shape and average energy of the primary and scattered spectra were found to be very similar. The ratio of the scattered to primary intensity was found to be larger than that commonly used in shielding calculations. Scattered X-ray spectra were measured from 40 to 110 kVp for 0–3 mm A1 added filter in the primary beam for a typical diagnostic unit. Scattered and primary X-ray spectra are compared in the range 40–110 kVp.