RIKEN

University of Tsukuba

Saitama University

The University of Tokyo, Graduate School of Science

Summary

The international collaboration between RIKEN and the University of Tsukuba has been established by Dr. Sarah Naimi, Member of the Spin and Isospin Laboratory, Nishina Center for Accelerator Science, RIKEN, Dr. Hong-Fu Lee, International Program Associate, Dr. Tomohiro Uesaka, Director, Dr. Yoshitaka Yamaguchi, Engineer, Short-Lived Nuclear Mass Measurement Team, Prof. Ken Ozawa, Department of Mathematics and Physics, University of Tsukuba, Prof. Akira Ozawa, Saitama University, Dr. Shin-ichiro Michimasa, Assistant Professor, Graduate School of Science and Engineering, Saitama University. An international research group led by Associate Professor Takayuki Yamaguchi of the Graduate School of Science and Engineering, University of Tsukuba, and Assistant Professor Shinichiro Michimasa of the Graduate School of Science, The University of Tokyo, has developed a newly established ultrafast mass measurement method using the Rare RI Ring in the RI Beam Factory to measure the neutron-rich Pd-123 ( ^123Pd: atomic number 46, neutron number 77) nucleus, which is one of the extremely short-lived isotopes (RIs), has been successfully determined precisely for the first time.

This achievement paves the way for the precise determination of the masses of many rare RIs involved in the fast neutron capture process (r-process) to elucidate the origin of elements heavier than iron.

In this research, the international research group has achieved the world's fastest and most precise mass determination by combining the rare RI ring, which has the property of isochronous orbit time, and the individual injection method, in which RIs are injected into the ring one at a time while identifying each RI. This method has realized the world's fastest and most precise mass determination. This method has demonstrated that the masses of the ^123Pd nucleus and its surrounding nuclei can be measured in a time shorter than their lifetimes. The results show that it can well explain the elemental ratios of mass numbers 122 and 123 observed in the solar system.

The study was published online April 15 in the scientific journal Physical Review Letters.

Figure: Schematic of the ultrafast mass measurement method with rare RI rings.
The reaction between the heavy ion beam from the SRC (upper left) and the production target randomly produces a large number of isotopes, including r-process nuclei. From that particle population, only the peripheral isotopes of the particle under study are separated and selected by the BigRIPS system. A detector placed downstream of the production target then identifies whether the particles that arrive are the ones to be studied. Furthermore, the particles fly at 55% of the speed of light and reach the particle injection system (kicker system) of the rare RI ring after about 1 μs (green arrow). Meanwhile, the detector's identification signal is transmitted to the rare RI ring in 0.5 μs by a coaxial tube (blue line), which can transmit at 95% of the speed of light. As a result, the kicker system can operate in less than 0.5 μs.

Assistant Professor Shinichiro Michimasa of Center for Nuclear Study participated in this research result.

For more information, please visit the RIKEN website.