The rigid stem chambers are designed as reference chambers for absolute dosimetry to be used in radiation therapy or by secondary standard dosimetry laboratories (SSDL). They have very small variations of response with radiation quality from low X-ray energies up to high-energy photon and electron radiation. The nominal useful energy range is from 30 kV to 50 MV photons and 6 MeV to 50 MeV electrons. Both chambers are shaped cylindrically (thimble chambers). The wall material is graphite with a protective acrylic cover. The electrodes are made of aluminum. The guard rings are designed up to the measuring volume. Both chambers are constructed with a long stem of approx. 25 cm length for easy mounting in the radiation beam.