From GSI Helmholtz Association of German Research Centres [Helmholtz-Gemeinschaft Deutscher Forschungszentren GmbH] (DE): “Helium nuclei at the surface of heavy nuclei discovered”

From GSI Helmholtz Association of German Research Centres [Helmholtz-Gemeinschaft Deutscher Forschungszentren GmbH] (DE)


The experiments took place at the Research Center for Nuclear Physics (RCNP) Grand Raiden spectrometer in Osaka in Japan.

Scientists are able to selectively knockout nucleons and preformed nuclear clusters from atomic nuclei using high-energy proton beams. In an experiment performed at the Research Center for Nuclear Physics (RCNP) in Osaka, Japan, the existence of preformed helium nuclei at the surface of several tin isotopes could be identified in a reaction. The results confirm a theory, which predicts the formation of helium clusters in low-density nuclear matter and at the surface of heavy nuclei. A research team, lead by scientists from TU Darmstadt and the GSI Helmholtz Center for Heavy-Ion Research, and from the RIKEN Nishina Center for Accelerator-Based Science, discuss the new findings in a contribution to the latest issue of the journal Science.

The strong interaction binds neutrons and protons together to atomic nuclei. The knowledge of properties of nuclei and their theoretical description is basis for our understanding of nuclear matter and the development of the universe. Laboratory-based studies of reactions between atomic nuclei provide means to explore nuclear properties. These experiments allow the testing and verification of theories that describe properties of extended nuclear matter at different conditions, as present, for instance, in neutron stars in the universe.

Several theories predict the formation of nuclear clusters like helium nuclei in dilute nuclear matter. This effect is expected to occur at densities significantly lower than saturation density of nuclear matter, as present in the inner part of heavy nuclei. A theory developed in Darmstadt by Dr. Stefan Typel predicts that such a condensation of helium nuclei should also occur at the surface of heavy nuclei. The goal of the experiment, which is presented in the latest issue of Science, was the verification of this prediction.

Prediction confirmed

The present experiment bombarded tin isotopes with high-energy protons and detected and identified the scattered protons as well as knocked-out helium nuclei. Dr. Junki Tanaka and Dr. Yang Zaihong could demonstrate that the reaction occurs as a direct “quasi-elastic” scattering of the protons off preformed helium nuclei in the surface of tin nuclei. The extracted cross sections for different tin isotopes reveal a decrease of the formation probability with the neutron excess of the nuclei, which impressively confirms the theoretical prediction.

This new finding, which has far-reaching consequences for our understanding of nuclei and nuclear matter, will now be studied in more detail in experimental programs planned at RCNP, and in inverse kinematics at RIKEN and the new FAIR facility at GSI, where also unstable heavy neutron-rich nuclei are accessible.

See the full article here.


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Helmholtz Zentrum München (DE) by numbers.

The Helmholtz Association of German Research Centres [Helmholtz-Gemeinschaft Deutscher Forschungszentren GmbH] is the largest scientific organization in Germany. It is a union of 18 scientific-technical and biological-medical research centers. The official mission of the Association is “solving the grand challenges of science, society and industry”. Scientists at Helmholtz therefore focus research on complex systems which affect human life and the environment. The namesake of the association is the German physiologist and physicist Hermann von Helmholtz.
The annual budget of the Helmholtz Association amounts to €4.56 billion, of which about 72% is raised from public funds. The remaining 28% of the budget is acquired by the 19 individual Helmholtz Centres in the form of contract funding. The public funds are provided by the federal government (90%) and the rest by the States of Germany (10%).
The Helmholtz Association was ranked #8 in 2015 and #7 in 2017 by the Nature Index, which measures the largest contributors to papers published in 82 leading journals.

The laboratory performs basic and applied research in physics and related natural science disciplines. Main fields of study include plasma physics, atomic physics, nuclear structure and reactions research, biophysics and medical research. The lab is a member of the Helmholtz Association of German Research Centres.