Heavy ion production of single- and double-strand breaks in plasmid DNA in aqueous solution

Preliminary measurements on the production of single- and double-strand breaks in SV40 and phi X174 plasmid DNA by various heavy ions in radioprotective Tris buffer are presented. The dependence of the recorded yields on the LET of the incoming ions is discussed and shown to be comprehensible within the framework of a model based on the X-ray sensitivity of the exposed DNA and the local dose distribution inside the heavy ion track. The question of the influence of the chemical environment is addressed by comparing the measured cross sections to data recorded previously in more radiosensitive TE buffer. The results indicate that also for systems with high scavenging capacity RBE values larger than unity can be achieved with maximum values in the LET range 100-1000 keV micrometers-1.