IONIZING RADIATION AND VIRUSES 



83 



primary ionization anywhere in some sensitive volume can in- 

 activate the virus. Then the results of electron bombardment and 

 deuteron bombardment can be combined to deduce the shape 

 of the virus. This has been done by Pollard and Dimond (1953) as 

 follows. The experimental deuteron cross section is 19 X 10~^^ 



TMV 



rvv^ 



T-l 



SBMV 



-•••• — • — V 



FiG. 3.7. A schematic representation of the passage of (a) a deuteron losing 

 200 ev per 100 A, and (b) 600 ev per 100 A. through three viruses. In all cases, 

 more than one primary ionization occurs in the virus. This inactivates purified 

 TMV, but more energy is needed for SBMV, and this is supplied in case 

 (b). T-l can survive even this. T-l thus presumably has a more complex 

 morphology. 



cm-. Assuming that the target is randomly oriented, the true 

 cross section is 4 ■ tt times this, or roughly 24 X 10~^- cm-. Elec- 

 tron bombardment gave an inactivation volume of 3.1 X 10~^^ 

 cm^. Suppose the virus is a cylinder of radius r and length /. 

 Then 



2r/ = 27 X 10-12 (,n^2 

 irrH = 3.7 X IQ-^' cm^ 



