. The basic aspects of radiation effects on living systems. Radiation -- Physiological effect. 8 PHYSICAL PROCESSES IN LIVING MATTER though they may still excite complex molecules and transfer their kinetic energy in elastic collision into simple heat motion. We are almost at the point of chemistry. Loss by elastic collision would require perhaps 10~^° sec, but much molecular excitation might take place earlier. Now the free electrons will become captured by a molecule of the medium. In water one will most frequently find this capture leading to a free negative hydroxy 1 radical, setting free
. The basic aspects of radiation effects on living systems. Radiation -- Physiological effect. 8 PHYSICAL PROCESSES IN LIVING MATTER though they may still excite complex molecules and transfer their kinetic energy in elastic collision into simple heat motion. We are almost at the point of chemistry. Loss by elastic collision would require perhaps 10~^° sec, but much molecular excitation might take place earlier. Now the free electrons will become captured by a molecule of the medium. In water one will most frequently find this capture leading to a free negative hydroxy 1 radical, setting free a neutral H atom as well Density (arbitrary units) Initial effect. Angstroms from track Lateral distributions Fig. 5. Qualitative representation of the lateral distribution of disturbed atoms and molecules across an ionizing track. To the left is shown the distribution immediately- after passage of a fast electron; to the right, the distribution of diffusing positive and negative ions after an alpha particle has traversed water, about 10"^** sec earlier. Note the charge separation due to the faster motion of the secondary electrons which are captured some distance from the track. [After Lea (6).] in the reaction. What the spatial distribution of these initial products will be is a little obscure. The feathery track will be smeared out by the diffusion processes, but the caging effect of the surrounding medium and the frequently high density of ions along the track itself will combat this free diffusion by making recombination easy, and even by the overall electric field which attracts negative ions toward the generally more concentrated positive-ion core. (Figure 5 suggests the situation.) It is most doubtful that any of the quantitative treatments yet given [see (6), p. 59, and (7)] are adequate for the complex problem involved here. It can be said that the diffusion from a lightly ionizing track may spread the radicals over sizable distances, even a tenth micron or two,
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