Hyperfine Enhancement of r.f. Pulses

A significant technical challenge in ENDOR is to produce a strong r.f B2 field at the location of the sample. The effective r.f field that induces transitions 

Equation (29) shows that for low-frequency transitions, where As 2 ai, one of the E values is close to zero so that it becomes exceedingly difficult to excite these nuclear transitions. In this case ESEEM methods are required. 

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