Seventy-three new isotopes discovered at RIKEN’s RI Beam Factory

Scientists from an international collaboration led by the RIKEN Nishina Center for Accelerator-Based Science have discovered 73 previously unknown isotopes at the RI Beam Factory, ranging in atomic number from manganese—with an atomic number of 25 to erbium, with a number of 68. The periodic table of the elements—which lists elements in order of the number of protons—is very familiar even to schoolchildren, but fewer people are aware that there is another table—the table of the nuclides—which shows isotopes of elements that have different numbers of neutrons. There are roughly 7,000 isotopes that are believed to exist or to have existed in extreme conditions such as supernova explosions and neutron star mergers, but only a small number of those have been generated in laboratories such as the RI Beam Factory. Generating and analyzing them is important for understanding the structure of atomic nuclei and the chemical and physical properties of unstable atoms that are rare in nature. This process helps to grasp how, through a balance of the rapid neutron capture and beta decay, the so-called r-process nucleosynthesis, enormously energetic events shaped the current ratio of nuclei in the universe. In earlier work, 59 previously unknown isotopes have been generated at the RI Beam Factory starting with its first discovery in 2007. The current work was done following an upgrade of the beam in 2011-2013. Two papers reporting on the work were published in the Journal of the Physical Society of Japan (vol. 87. No. 1, December 22, 2017) and two others were published in Physical Review C (May and September, 2017).