Design and fabrication of a ring-shaped ionization chamber with graphite guard rings

The development of a graphite ionization chamber in Iran is reported for first time, using graphite coatings collecting electrodes and guard rings. Its sensitive volume is about 200cm³, with a shape of a ring which is different from its older equivalents and a 7cm central hole that allows the passage of the direct radiation beam without attenuation. This kind of ionization chamber has already been designed with aluminum electrodes in IPEN (institute de pesquisas energetic as e nucleares, Brazil), however in the present model, the whole of the inside part of the ionization chamber is coated with graphite instead of aluminum. By changing the electrode material from aluminum to a graphite coating, an improvement in action of ionization chamber response in pre-operational tests such as stability, saturation curve, repeatability, polarity effect, linearity response and calibration is expected, which is in accordance with the international recommendations.