To establish a criterion for the local energy required to induce a ssb, numerous values have been used in the literature based mostly on their physical and chemical significance.These include average energy loss, ionisation energy, oscillator strength and average excitation potential ranging from to about eV.To obtain a more realistic value based on experi mental data, experiments were simulated in which the DNA fragment length distributions were measured after decay of incorporated I. By contrast, values obtained from a series of experiments using synchrotron radiation seem to indicate a much lower threshold energy of about eV needed to induce a ssb, but experiments using very low energy electrons indicated a higher threshold of up to about eV. However, a detailed analysis and modelling of the experiments using synchrotron radiation or electrons have yet to be done.The classification of numbers of base damages is described in the above section on the yield of strand breaks.As an initial approach for the estimation of base damage, the same criterion as for the induction of direct strand breaks was adopted, viz. was assumed for induction of base damage from the reaction of OH radicals with DNA to include all OH reactions with nucleobases.In the calculations, transfer of charge to a preferential base was not considered explicitly on the assumption that transfer occurs only over a few base pairs.Figure shows the frequencies of base damage as a function of LET of the particle.Data are presented according to the number of base damages in the hit region of the DNA.Frequency of base damage for protons and alphaparticles as a function of LET.Data are presented according to the number of base damages in the hit region of the DNA segment.Numbers listed under of BD refer to the segments containing, or, and damages.Data for segments containing more than base damages are not explicitly shown age, and the total yield increases with increasing LET, as does the degree of complexity.To obtain a more realistic picture of complex DNA dam age, it is necessary to include base damage, as the above initial approach has shown.It is envisaged that significant refinements to the simulation of base damage will be the focus of future approaches on DNA damage.For instance, for direct energy deposition events in DNA, the ionisation potential of the bases could be used as an energy threshold for ionisation.These may be derived from experimental data on radiationinduced base damage.Therefore, a future approach to simplify the simulation of base damage could be to estimate its contribution from direct and indirect effects for the different radiations from the respective yields of ssb and using the experimental basedamagessb ratios above.Table provides a relative distribution of damage in terms of its complexity.Data are presented for simple and complex strand breaks induced by electrons, protons and alphaparticles of various energies.Complex ssb are defined as those segments of DNA containing a ssb with an associated break. From the database on the frequencies of energy deposition in volumes of biological dimensions, it became possible to seek and correlate the size of energy deposition with particular biological effects.