Collective dipole oscillations in atomic nuclei and small metal particles

The systematics of photon absorption cross sections in nuclei and small metal particles are examined as a function of the number of constituent fermionsA. It is pointed out that the shell-structure-linked oscillations in the full width at half maximum (FWHM) of the photoneutron cross section in nuclei, earlier recognized forA>63, in fact persist down to the lightest nuclei. Averaging over the oscillations or focusing on the lower envelope of the oscillating curve (magic nuclei), the FWHM is seen to generally decrease with increasingA, consistent withA−1/3, a dependence which was earlier known to hold in metal particle systems. If the FWHMs are scaled by the respective Fermi energies and the inverse radii by the Fermi wave vectors, the two data sets become comparable in magnitude. A schematic theoretical description of the systematics is presented.