Correlated ionisations in two spatially separated nanometric volumes in the track structure of 241Am alpha particles: Measurements with the PTB ion counter

Abstract

The simultaneous occurrence of two double-strand breaks in spatially separated locations on the DNA molecule can cause the loss of a whole DNA loop. The length of the lost DNA loop depends on the geometrical position of the two damaged sites and on the degree of damage in sites of several nanometres in size. As they are more prone to produce complex ionisation clusters in such sites, densely ionising charged particles are expected to produce more spatially correlated ionisation clusters than electrons and photons. In this work, correlations in the production of ionisation clusters in two spatially separated sites were investigated for the first time in detail by nanodosimetric measurements in 1.2 mbar H2O, 1.2 mbar C3H8 and 1.2 mbar C4H8O using alpha particles from a 241Am source. The results show that there are irradiation geometries where only weak correlation exists between the probabilities for ionisation clusters in the two spatially separated sites, e. g. when the primary beam passes one site centrally. In general, however, the two probability distributions are not statistically independent, for instance if both sites are irradiated in a broad beam.