Determination of depth-dose curves in beta dosimetry

In beta dosimetry, the absorbed dose rate changes rapidly with the depth in a given medium. Its knowledge is essential for the full characterisation of the beta reference fields and the evaluation of the response of beta detectors. This work presents a general formalism for the precise determination of beta depth-dose curves by means of ionisation chamber measurements. An extrapolation chamber is not required. The formalism is appropriate for the determination of the full range depth-dose curve of up to 10 mm depth and more, when all electrons are stopped. Particular care was taken for the determination of the correction factors for the ISO 6980 reference fields, which are the most common beta reference fields. The formalism is proved experimentally: The depth-dose curves of all beta sources available at the Physikalisch-Technische Bundesanstalt (PTB) were determined and compared with the curves published in ISO 6980, yielding an excellent agreement. The presented formalism reflects the state-of-the-art of depth-dose measurements at the PTB.