Determination of transmission factors in tissue using a standard extrapolation chamber

• Böhm extrapolation chamber was tested to be used as a primary standard system.
• The chamber was exposed to the three 90Sr+90Y secondary standard sources.
• Transmission factors were obtained.
• Absorbed dose rates were determined using the sources at certificate conditions.
• The results showed the good performance of the extrapolation chamber.

A commercial ionization chamber, Böhm extrapolation chamber, PTW, model 23392, recommended for measurements in low energy X-rays and beta radiation fields, was tested in three different 90Sr+90Y beams to verify its performance as a primary standard system for the calibration and dosimetry of beta radiation sources and detectors. Characterization tests were performed, as determination of the chamber null depth using two methods (the results presented a difference of only 0.9%), transmission factors in tissue, in comparison with those of the certificate (the maximum difference was 2.1%), and absorbed dose rates of the 90Sr+90Y sources, in comparison with the values provided by the calibration certificates (the maximum difference was 4.90%). The results obtained confirmed that this extrapolation chamber presents a very good behavior in beta radiation fields as a primary standard system.