M22 – the electron accelerator for calibration and research in radiation dosimetry at METAS

This overview aims to present the metrologically relevant aspects as well as applications beyond conventional radiation dosimetry of the irradiation facility installed at the Swiss Federal Institute of Metrology (METAS). The accelerator, based on the microtron principle, can deliver electron beams to three different beamlines. At the treatment head, the properties of the conventional photon and electron radiation field in water have been characterized in terms of quality specifier TPR 20,10 and R 50 respectively. In a second beamline delivering a narrow electron beam, the focus is on the characterization of the beam energy spectrum using a magnetic spectrometer as well as the beam intensity using an absolutely calibrated integrating current transformer. These two components allow the calibration of Fricke solution, a chemical dosimeter to be used as a primary standard for electron beams. In addition to these two long-established beamlines, a recently installed third beamline delivers a narrow electron beam offering great flexibility for exploration. Its use is not limited to ultra-high dose rates but also, for example, to determining the cross sections of photonuclear reactions.