82 



RADIATION BIOLOGY 



sion of the spatial distribution of the action along the track, but this 

 impression is often distorted by various circumstances. Figure 1-47 

 shows the tracks of a very fast and of several slower electrons. Spots cor- 

 responding to successive clusters are generally distinguishable along the 

 fast-electron track but not along the slow-electron tracks. The separate 



Fig. 1-47. Cloud-chamber picture of the tracks of one fast 

 and several slower electrons. {Gentner et al., 1950.) 



Fig. 1-48. Cloud- 

 chamber picture of a 

 magnified electron 

 track. {Gentner et al., 

 1940.) 



ions in each cluster cannot be resolved in the picture unless time is 

 allowed for the ions to diffuse apart before the chaml)er expands. Figure 

 1-48 is a magnified picture of a track with resolved clusters, but the posi- 

 tions of the individual ions in this picture do not correspond to the actual 

 points of origin of the ions. 



The tracks of a particles or protons of a few million electron volts are 

 marked by collisions so closely spaced (owing to the low velocity of these 

 particles) that the successive clusters merge to form a single compact 

 column (Fig. 1-49). It seems somewhat uncertain how well the cloud- 



