Nuclear Molecule: Nature's Smallest Dumbbell

An oxygen molecule is a small dumbbell less than a nanometer across: two oxygen atoms with two electrons flying between acting as the bonding agent. Now, an international consortium has succeeded in making a dumbbell far smaller: a beryllium-10 nucleus consisting of two alpha particles (nuclear fragments containing two protons and two neutrons) with two neutrons flying between acting as a sort of nuclear bonding agency.

This nuclear dumbbell is only a few fermis (10^-15 m) across (see figure at Physics News Graphics). These tiny oblong nuclei are made by colliding a beam of helium-6 nuclei into a gas of helium-4 atoms. (The helium-6 nuclei, which are themselves a novelty, were made by shooting protons at lithium.)

The berillium-10 nuclei created in this way don't live very long. With a lifetime of about 10^-21 seconds, they fly apart, usually back into helium-4 and helium-6 fragments.

Martin Freer (M.Freer@bham.ac.uk) says that the beryllium results support the idea that nuclei sometimes behave like atomic systems in that they can be thought of as a core of particles with extra "valence" particles (electrons/neutrons) exchanged between cores. Several exotic shapes are thought to be possible among the light nuclei. Carbon-12, for instance, can exist as a triangular arrangement of three alpha particles and oxygen-16 as a tetrahedron of alphas. But these nuclei are tightly bound, so their exotic geometry cannot be discerned. But berillium-10's prolate shape can be seen clearly through the rotational behavior of the decaying system.

Freer is part of a team from the Universities of Birmingham and Surrey (U.K.), Université Catholique de Louvain and University of Leuven (Belgium), Université de Caen (France), and the Rudjer Boskovic Institute (Croatia).

Freer et al., Physical Review Letters, upcoming article