Cylindrical ionizing radiation

DNA compaction decreases the surface area per molecule exposed to bulk OH by 14%. Based on the cylindrical model (Mark et al. 1989), it has been calculated that competitive scavenging leads to a protection factor of 2, while a factor of 50 appears as a consequence of compaction (Newton et al. 1996). There is also a -20% contribution by the direct effect of ionizing radiation on DNA in this special system. 

Particle Tracks. Thus, irrespective of the particulate or photon nature of the primary radiation, the net effect is the formation of tracks consisting of ionized and excited molecules. These tracks, and their detailed structure can be revealed by the Cloud Chamber invented by Wilson in 1911(11). For fast electrons (low LET) the tracks mainly consist of spherical regions called spurs which contain from one to four ion-pairs which are separated in condensed phases by about 10 A. For more highly ionizing particles such as a-particles the tracks are essentially cylindrical columns of ionized and excited molecules. 

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