Electron contamination of large cobalt 60 photon beams

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Abstract
Experimental results [in humans] are presented of the electron contamination of 60Co .gamma. photon beams from the Mobaltron MS80, over a range of SSD [source to skin distance] from 60 cm to 3.5 m. In the absence of an electron filter, the skin dose can exceed the dose at 4 mm depth by up to 1.6 times due to the high level of electron emission from the depleted U collimators. Four millimeters of perspex effectively removes these electrons, and in the filtered beam, the skin dose cannot exceed the 4 mm dose. The electron contamination of a 6 MV X-ray beam is compared.