* Astronomy

French physicists believe they can solve the mystery behind dozens of nuclear experiments conducted years ago. The experiments, conducted with a variety of detectors, energies, and colliding nuclear species, left puzzling results, so puzzling and hard to interpret that many of the experimenters turned their attention to the study of highly spinning nuclei, a quite fashionable subject at the time.

Now, Jerzy Dudek of the Université Louis Pasteur in Strasbourg, France, and his colleagues at Warsaw University and the Universidad Autonoma de Madrid claim that the old results can be explained by arguing that some nuclei, made in the tempestuous conditions of a sufficiently high-energy collision, can exist in the form of a tetrahedron or a octahedron.
Like a pyramid-shaped methane (CH4) molecule held together by the electromagnetic force, a pyramidal nucleus would consist of protons and neutrons held together by the strong nuclear force. Such a nuclear molecule -- in effect the smallest pyramid in the universe -- would be only a few femtometres (10^-15 metre) on a side and millions of times smaller in volume than methane molecules.
Just as there are so-called "magic" nuclei with just the right number of neutrons and protons that readily form stable spherical nuclei, so there are expected to be such magic numbers for forming pyramid nuclei too. Stable, in this case, means that the state persists for 10^12 to 10^14 times longer than the typical timescale for nuclear reactions, namely 10^-21 seconds.
Dudek says that gadolinium-156 and ytterbium-160 are nuclei very conducive to residing in a stable pyramid configuration. Nuclei might exist also in stable octahedral (diamond) forms also. These nuclei would all possess a quantum property not seen before in nuclei: in the process of filling out an energy-level diagram for the nucleus, four nucleons of the same kind (neutrons or protons) could share a single energy level instead of the customary one or two permitted nucleons.

This rule-of-four would inhibit the normally observed decay patterns by which non-spherical nuclei throw off energy, usually by emitting gamma rays. In fact, in the case of nuclear pyramids it is expected to result in new and unprecedented decay rules. This inhibition would explain the puzzling results of earlier experiments.
Dudek and his colleagues plan to test these ideas in upcoming experiments.

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