An international research group observed bubble-like proton distribution in the isotope 34Si with neutron excess. The proton density in the center is almost half of that in the outer part of this nucleus while the neutron density is uniform. Researchers of MTA Atomki were involved in the data evaluation of the radioactive ion beam experiments.
According to the classical model of nucleus – the liquid drop model – such a low central density cannot occur. Since only the direct neighbouring protons and neutrons interact with each other, the density of matter in the nucleus is constant. This idea had been proven by very precise electron scattering experiments made on stable isotopes.
According to the other basic model of nucleus – the shell model –, nucleons in the nucleus are arranged in nuclear shells of different sizes similarly to the electrons in the atomic shells. Long time ago, theoretical physicists had the idea that if the spherical nuclear shells in the center of a nucleus are not filled but the outer shells are then a bubble-like system is formed. Although correlations between nucleons can mask this phenomenon.
Due to the complexity of the facilities used, radioactive ion beam experiments are performed in international collaborations of 20-50 experts. Physicists of Institute for Nuclear Research, Hungarian Academy of Sciences are involved in this nuclear structure research since 2000.
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Nature Physics (2016) – Published online: 24 October 2016