  In previous work, we constructed a statistical framework for estimating the
rate of clustered ionization from charged particle radiation in DNA. This model
is extended to include contributions from secondary electrons. Using a simple
assumption of a uniform strand-breaking probability, analytic forms for the
rates of single- and double-strand break formation are derived. The forms
depend on only three parameters, to which rudimentary values are assigned. The
resulting curves are compared to results from GEANT-DNA and experimental
measurements in dry DNA and found to be in moderate agreement. This approach is
readily refined and extended to more complex DNA systems and may ultimately
contribute to an improved understanding of the physical origins of biological
radiation effects.
