L. H. GRAY 



Shorter pulses could probably be delivered without difficulty at the same 

 dose rate, i.e. at a proportionate sacrifice of the upper limit of total dose. 

 The spectrometer under construction for this work in our laboratory will have 

 an air-core magnet, since it would be very difficult with conventional spec- 

 trometer design, to expose the specimen in the waveguide in the electron 

 beam which had to traverse the gap between the poles across the transverse 

 magnetic field. The tolerance in radial variation in magnetic field is so tight 

 that it is doubtful whether the electron beam could be made to enter down 

 the axis of the poles. 



The irradiation of specimens in situ in the waveguide, and the recording 

 of transient electron spin resonance signals, will no doubt pose many prob- 

 lems, both in instrumentation and interpretation, but we are of opinion 

 that a determined attempt should be made to explore this unknown territory. 



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