Heavy-Element Beam-Foil Lifetime Measurements and Related Experimental Problems

Abstract

Atomic-lifetime measurements in heavy elements, especially at low ionic energies, give rise to a number of experimental problems, the solution of which has been discussed for some years. The scope of the present contribution is to review the various approaches to a solution of the problems which have appeared in the literature. Also other aspects of beam-foil spectroscopy with slow, heavy ions will be discussed. Thus, when intense heavy ion beams are penetrating carbon foils mounted in the usual manner, the foils are known to last only a few seconds. The advantages of “sliding foils”, which allow the current to be increased by a factor of ten, will be discussed. When the energy loss in the carbon foil is appreciable compared to the initial ion energy, the evaluation of atomic lifetimes appear to be very complicated. A number of experiments have been performed to study the light-decay curve of spectral lines for which the radiative lifetimes were known. Ionic beams with energies as low as 20 keV were used, and also the thickness of the foil was varied. In order to get a more detailed picture of the stopping processes, the Doppler shift of the foil-excited spectral line was measured with a gas-cell-excited spectral line as reference. In this connection, thickening effects will be discussed.