Electron Spin Resonance in the Study of Radiation Damage 



245 



jij = 0.40 nm). Carbon, oxygen, and sulfur are of course also prominent 

 constituents of biochemical matter, but their most abundant isotopes have zero 

 nuclear spins and hence cannot interact with the electron spin. In strong 

 resonances one might detect effects caused by C^^ (spin \ and natural abundance 

 1.12 per cent) or S'^^ (spin 3/2 and natural abundance 0.74 per cent). For some 



(o) 

 ACTUAL LINE SHAPE 



(c) 



SECOND DERIVATIVE 



Fig. 1 . Appearance of resonance signals as detected in various ways : (a) High 

 fidelity, (b) First derivative curve obtained by small modulation of the resonance 

 with a phase-sensitive receiver tuned to the modulating frequency, (c) Second 

 derivative curve obtained by small modulation of the resonance with phase- 

 sensitive receiver tuned to twice the modulation frequency. 



substances one can obtain samples concentrated with C^^, S^ or O^'^. Hyperfine 

 structure of their miclei thus obtained will greatly augment the information 

 obtained from proton hyperfine structure, but it is fortunate for these studies 

 that C^^ is not the more abundant isotope of carbon. If hyperfine structure from 

 all the nuclei were present at one time, the resulting pattern would often be 

 unresolvable and its decoding thus more uncertain. As it is, there is seldom 



17 



