How to Set the Flip Angle to Maximize the Sensitivity per Hour: Meaning of Ernst Angle

Summary
Information

NM130017E

A flip angle b smaller than 90 degree is often applied in the single-pulse measurements for long T₁ samples to accumulate the signals with a short recycle delay RD. Signal sensitivity per scan as a function of b shown below indicates maxima with smaller flip angles bopt when T₁becomes longer than RD, or when x=RD/T₁ becomes smaller.
The angle bopt is called Ernst angle and given by cos bopt = exp(RD/1) [1,2].

Some combinations of RD and β_opt to be set in the experiments are summarized below:

As shown left, measurements with an appropriate combination of RD and bopt may maximize the signal sensitivity per hour [3].

References

R. R. Ernst, G. Bodenhausen, and A. Wokaun, “Principles of Nuclear Magnetic Resonance in One and Two Dimensions”, Clarendon Press, 1987, pp124-125.
T. D. W. Claridge, “High-Resolution NMR Techniques in Organic Chemistry”, Second Ed., Elsevier, 2009, pp99-102.
T. Nakai, New Glass, 28(2), 17-28 (2013).