Lack of calculating

Another contribution due to nuclear properties is the so-called recoil contribution. It takes into account the finite mass of the nucleus even beyond the non-relativistic reduced mass approximation. Up to now there is a lack of calculations non-perturbatively in (Za) which exist only for the QED corrections of order (a/n) up to now but would definitely be required for heavy systems. 

Effects of a fluctuation occurring in a sphere with radius smaller than 0.05 /xm are not examined numerically here, as the total number of particles involved is too small to warrant a deterministic description [21]. However, since the experiments of Foerster et al. and of Showalter et al. indicate that a region on the order of several microns needs to be perturbed in order for a wave to propagate, the lack of calculations regarding fluctuations in spheres with radius less than 0.05 fim is justified. 

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