  The effects induced on the magnetization by coherent fluctuating Cooper pairs
in the normal state have been measured in Pb_{1-x}In_x alloys up to high
magnetic fields, of amplitudes above Hc2(0), the upper critical field
extrapolated to T=0K. Our results show that in dirty alloys these
superconducting fluctuation effects are, in the entire H-T phase diagram above
Hc2(T), independent of the amount of impurities and that they vanish when
H~1.1Hc2(0). These striking results are consistent with a phenomenological
estimate that takes into account the limits imposed by the uncertainty
principle to the shrinkage, when H increases, of the superconducting wave
function.
