Speaker
Description
The study of the origins of heavy elements has been a critical issue for nuclear physics since short-lived nuclides far from the stability line are involved in synthesizing them. Notably, the rapid neutron capture process (r-process), which is considered to contribute to half of the nuclides heavier than iron, requires more knowledge of the nuclear properties of very neutron-rich nuclides.
The pathway of the r-process is determined by the neutron separation energies, which are directly derived from the differences in the atomic masses of neighbor isotopes. Furthermore, the “waiting points” of the process, which lead to the so-called r-process peak, are on the neutron magic numbers. A good indicator of the magic number is the shell gap energies derived from the double difference of the atomic masses.
A comprehensive mass measurements campaign is in progress at Riken RIBF, where three RI-beam facilities (BigRIPS, GARIS, and KISS) provide the widest variety of nuclides using different reactions: projectile fragmentation, in-flight fission, fusion, and multi-nucleon transfer. Their beam energies are multi-orders of magnitude different, and the beam emittances are also very different. Different gas catchers with rf-carpets are used to accumulate the ions from these RI-beam facilities to ion traps. The multi-reflection time-of-flight mass spectrographs (MRTOF) measure the masses of these trapped ions. The MRTOF allows precise measurements of multiple ion species at once. We achieved a 1,000,000 mass resolving power via ~10 ms of short flight time.
This campaign has measured the atomic masses of more than 400 nuclides, from titanium isotopes to superheavy elements, dubnium. We continue measurements for more exotic and essential nuclides for r-process studies.
