Measurements of ionisation distribution around a particle track at the nanometre level

Radiobiological data reveal that radiation action on the living cell is at the nonometre level. In this paper a new approach is proposed for the measurement of the radial radiation induced ionisation distribution across the particle track at this level. It is based on coupling a parallel-plate ionisation chamber to a cylindrical proportional electron multiplier. A detector of this type, filled with propane, was used for the measurement of the radial ionisation distribution induced by α particles. The displacement of the detector with respect to the α particle beam provided a tissue-equivalent ionisation distribution at the nonometre level. The data obtained with this novel technique are presented and the secondary effects due to radiation induced electron emission from the detector walls are discussed. (Author)