The Roos electron chamber, developed in cooperation with Dr. Roos, PTB-Braunschweig (National Laboratory of Germany), is used as a reference electron chamber. It is recommended by the IAEA for high precision electron dosimetry in radiation therapy. The chamber has a 4 mm wide guard ring to exclude any perturbation effect even at low electron energies. The polarity effect is negligible (< 0.5 % at 10 MeV).

The energy response is only influenced by the stopping power ratios. The chamber is waterproof for absolute dose and depth dose measurements in a water phantom. The acrylic entrance window has a thickness of 1 mm. The nominal useful energy range is from 2 MeV to 45 MeV. A calibration certificate with a Co-60 calibration factor given in absorbed dose to water is included. Air density correction is required for each measurement. A radioactive check device with adapter is available as an option. The chamber cable length is 1.08 m.