Measurements of 6 MV X rays. II. Characteristics of secondary radiation

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Abstract
The measurements reported are for secondary radiation scattered from either a Presdwood phantom or a concrete barrier. The magnitude, angular distribution and attenuation characteristics of these secondary radiations are discussed. The relative dose from radiation scattered by a Presdwood phantom was evaluated at 1 m from the phantom. Expressed as a percentage of the dose at the center of the phantom it varied from 0.04% at 135[degree] to 0.8% at 15[degree]. Expressed as a 10th-value thickness the attenuation thickness for this scattered radiation in concrete varied from 14.7 cm at 135[degree] to 33.3 cm at 15[degree] The attenuation of 90[degree] scatter was also investigated for Presdwood, steel and lead. The 90[degree] scatter has a monochromatic equivalent energy of slightly less than 500 keV [Kilo electron volts]. The intensity and angular distribution of scatter from a concrete barrier was examined for both 90[degree] and 60[degree] incidence of the primary beam. For these measurements the scattered dose at 1 m did not exceed 0.25% of the dose maximum just below the barrier surface for a 48 x 48 cm field.