Development of a secondary standard for the absorbed dose to water based on the alanine EPR dosimetry system

The primary measurand in the dosimetry for radiation therapy is the absorbed dose to water, DW. An alanine/EPR based secondary standard for DW for high-energy photon and electron radiation is presently under construction at the Physikalisch-Technische Bundesanstalt. A technique of transfer dosimetry that makes it possible to reduce the reproducibility to a level below 0.5% in the 5-50Gy range is presented. It takes advantage of a reference sample. Results of investigations of some effects, such as environmental humidity, are presented.