RIKEN

Technical University of Darmstadt

Graduate School of Science, The University of Tokyo

Tokyo Institute of Technology

Summary

Dr. Hideaki Otsu, Team Leader of the Multispecies Instrumentation Team at the RIKEN Nishina Center for Accelerator-Based Science, Dr. Valery Panin, Member of the Spin and Isospin Laboratory (at the time of the research, now Visiting Researcher), Dr. Meitel Duerr and Dr. Stefanos Pashalis of the Technical University of Darmstadt (at the time of the research), Professor Thomas Aumann, Professor Kyou Shimoura (at the time of the research) of the Center for Nuclear Study, Graduate School of Science, The University of Tokyo, Professor Takashi Nakamura and Assistant Professor Yosuke Kondo of the Department of Physics, Graduate School of Science, Tokyo Institute of Technology, and other international research groups have conducted a joint research at RIBF, RIKEN's heavy-ion accelerator facility, using the The research group, led by Professor Takashi Nakamura and Assistant Professor Yosuke Kondo, has successfully observed a tetra-neutron nucleus, a nucleus composed of only four neutrons, using the multi-species particle measuring instrument "SAMURAI Spectrometer" at the RIBF, and obtained new evidence that multiple neutrons without protons can exist as a nucleus.

This research result is expected to lead to a significant change in the model of "nuclear force" that determines the stability of nuclei and, by extension, elements, as well as to a better understanding of neutron stars, which are mysterious, ultra-dense celestial bodies.

In this experiment, the international research group produced a tetra-neutron nucleus ( ⁴ⁿ⁾ by scattering a beam of helium-8 ( ^8He, 2 protons and 6 neutrons) and protons obtained at the RIBF. The idea that led to the success of the experiment was the use of a reaction that instantaneously extracts helium-4 ( ^4He, 2 protons, 2 neutrons) from ^8He without disturbing the four neutrons. This technique can be compared to pulling out four wine glasses (neutrons) on a tablecloth ( ^4He ) without breaking the tablecloth.

This research was published in the online edition of the scientific journal Nature ( June22: June23, Japan time).

Figure: Energy distribution of the four-neutron system obtained in the measurement

For more information, please visit the RIKEN website.