MEASUREMENTS OF IONIZATION DISTRIBUTION AROUND A PARTICLE TRACK AT THE NANOMETER LEVEL

Radiobiological data reveal that radiation action on the living cell i s at the nanometre level. In this paper a new approach is proposed for the measurement of the radial radiation induced ionisation distributi on across the particle track at this level. It is based on coupling a parallel-plate ionisation chamber to a cylindrical proportional electr on multiplier. A detector of this type, filled with propane at pressur es of 227 and 454 Pa, was used for the measurement of the radial ionis ation distribution induced by alpha particles. The displacement of the detector with respect to the alpha particle beam provided a tissue-eq uivalent ionisation distribution at the nanometre level. The data obta ined with this novel technique are presented and the secondary effects due to radiation induced electron emission from the detector walls ar e discussed. Further developments are also discussed.