Shell Structure in Nuclei and in Metal Clusters

The conduction electrons in ultrasmall metal drops form ordered quantum states in analogy to the nucleons in the nucleus. This becomes visible in experiments with clusters produced by expansion of sodium vapour. The droplets form an entire periodic system of “giant” nuclei that can be understood by applying Bohr’s quantization rule to electrons moving classically inside the droplets in triangular and square orbits. Drops with 2 to 3000 atoms are ordered in 22 periods divided between two main groups, or supershells.