Technical note: the measurement of mammographic room protection

Owing to the inherent design of mammographic X-ray tubes, transmission measurements through the surrounding protective barriers are difficult to obtain using the primary beam. An alternative method has been developed which employs an iodine-125 source. Transmission measurements were obtained through common building materials using both the iodine-125 source and a mammographic X-ray beam generated at 35 kVp. Measurements were converted into an aluminium equivalence, from which correction factors were calculated to convert the aluminium equivalence determined using iodine-125 to the true aluminium equivalence. Average correction factors for samples of glass, chipboard and plasterboard were 1.10, 0.75, and 0.85, respectively.