[A polarization effect-free graphite double extrapolation chamber for the absolute dosimtery of high energy...

Theoretical principles, constructional features and operation of an improved extrapolation-chamber intended for absolute ionization dosimetry of high-energy electrons are described. The construction allows a precise variation of the cylindrical measuring volume by varying thickness and diameter (exactly from 0 to 30 or 3 to 30 mm resp.), whereat measurements can be taken either using cylindrical graphitic walls or "no walls". The improvements consist in a combination of the following characteristics: high electric and mechanical stability; avoidance of disturbances due to electrostatic charges; elimination of the polarity error; practically homogeneous graphitic construction without foreign materials; graphite as a preferential reference material; measurements by chemical dosimetry following within the same apparatus. Results of measurements are reported concerning the verification of the complete or partial equilibrium of electrons, the deviations from the ideal cavity conditions of Bragg and Gray, and the comparison with ferrous sulfate dosimetry. Absolute measurements of the ion dose being accurate to about 0.5% can be obtained with the chamber. Thus, the chamber seems qualified to be used as a primary standard.