Abnormal distribution of double strand breaks in DNA after direct action of ionizing energy.

Experiments on purified DNA irradiated under circumstances which maximize direct absorption of ionizing energy in the DNA suggest that double strand breaks to the DNA helix are caused when energy depositions in spheres of comparable size to the diameter of the DNA helix exceed a threshold energy of between 70 and 100 eV. Evidence is also presented that shows that these events can lead to non-random patterns of double strand breakage within the molecule which are manifested as an excess of small fragments of DNA.