LJ absorption edges of rare earths. R , in RCu& (except for R = La. Ce, Eu. Er and Lu) and in RCu2Ge2 (except for R = La. Ce, Er and Lu) intermetallic compounds are recorded. Shifts in energy of the L? edge in these systems with respect to corresponding rare-earth metal edge position are measured. It is found that the rare-earth ions exist in a trivalent state except for Eu and Yb. The divalent state of Eu in EuCu2GeZ and that of Yb in YbCuzGe2 are established. Shifts in energy of the K absorption edge of Cu in RCuZSi2 and RCu2Ge2 (except for Ho and Lu) are also measured. The present results on the Kedge shifts of Cu in RCu2GeZ and RCu2Si2 are. in general, consistent with the available NMR measurements on the same systems.

The lifetimes of rubidium atoms in a dark magneto-optical trap are measured at different populations of the`bright' and`dark' hyperéne states of captured atoms. It is found that the lifetime of atoms in the trap decreases if they spend more time in the bright state. A simple explanation of this effect is proposed which is based on the increase in the transport cross section for collisions of thermal rubidium atoms surrounding the trap with cold rubidium atoms upon their electronic excitation.

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We report direct quantitative measurements of the light-induced drift velocity in Na-noble-gas mixtures under well-defined conditions. Results are in excellent agreement with predictions from a realistic numerical model incorporating the multilevel structure of the Na atom. The effect of optical hyperfine pumping on light-induced drift is investigated. Limiting values for the drift velocity are predicted. PACS numbers: 42.65.Jx, 32.90.-l-a, 34.90.+qIn 1979 Germukhanov and Shalagin' predicted a new mechanical effect of light acting upon optically absorbing atoms or molecules immersed in a buffer gas. This effect, light-induced drift (LID), occurs when two conditions are met: (i) the excitation of the absorbing species is velocity selective (Doppler effect); (ii) the rate of collisions with the buffer gas is state dependent. The velocity-selective excitation creates antiparallel fluxes of ground-and excited-state particles which, when condition (ii) is fulfilled, experience different diffusion resistances. As a result the optically absorbing particles acquire a net drift velocity. See Gel'mukhanov and co-