Natural Magnitudes of Corrections to the Lamb Shift

It is clear now that the scale setting factor which should be used for qualitative estimates of the high order corrections to the Lamb shift is equal to Am Za) /n. Note the characteristic dependence on the principal quantum number 1/n which originates from the square of the wave function at the origin V (0) 1/n . All corrections induced at small distances (or at high 

Bjorken and S. D. Drell, Relativistic Quantum Mechanics, McGraw-Hill Book Co., NY, 1964. 

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