Identification of 45 New Neutron-Rich Isotopes Produced by In-Flight Fission of a ²³⁸U Beam at 345 MeV/nucleon

Abstract

A search for new isotopes using in-flight fission of a 345 MeV/nucleon 238 U beam has been carried out at the RI Beam Factory at the RIKEN Nishina Center. Fission fragments were analyzed and identified by using the superconducting in-flight separator BigRIPS. We observed 45 new neutron-rich isotopes: Since the pioneering production of radioactive isotope (RI) beams in the 1980s, 1) studies of exotic nuclei far from stability have been attracting much attention. Neutron-rich exotic nuclei are of particular interest, because new phenomena such as neutron halos, neutron skins, and modifications of shell structure have been discovered.2-5) Furthermore these neutron-rich nuclei are important in relation to astrophysical interests, 6) because many of them play a role in the astrophysical r-process. 7) To make further advances in nuclear science and nuclear astrophysics, it is essential to expand the region of accessible exotic nuclei towards the neutron dripline. In-flight fission of a uranium beam is known to be an excellent mechanism for this purpose, having large production cross sections for neutron-rich exotic nuclei. became operational, in which the superconducting in-flight separator BigRIPS 10,11) has been used for the production of RI beams. The BigRIPS separator is designed as a two-stage separator with large acceptance, so that excellent features of in-flight fission can be exploited. In May 2007, right after the commissioning of the BigRIPS separator, we performed an experiment to search for new isotopes using in-flight fission of a 345 MeV/nucleon 238 U beam, aiming to expand the LETTERS Ã

Shell Evolution towards Ni78 : Low-Lying States in Cu77Şahin1, Garrote2, Tsunoda3 et al. 2017Phys. Rev. Lett.347220View full textAdd to dashboardCite

“…In this Letter, we report on the first measurement of excited states in neutronrich 77 Cu by means of β-delayed γ-ray spectroscopy. An experimental campaign to study neutron-rich nuclei took place at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center [28,29]. The present data were collected during two separate beam times in which radioactive isotopes were produced via in-flight fission of 238 U projectiles with an incident energy of 345 A MeV on thick 9 Be targets.…”

New Isotopes and Proton Emitters–Crossing the Drip Line in the Vicinity ofSn100

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“…Since the discovery of these isotopes at the RI Beam Factory (RIBF) facility at RIKEN [12,13], steady improvements in the intensity of uranium beams, in combination with a highly efficient -ray detection system, enable us to conduct detailed spectroscopic studies.…”