Observation of new isotopes and determination of the neutron dripline at RIKEN RIBF

First I will briefly talk about the BigRIPS in-flight separator [1,2] at RIKEN RIBF [3]. Then I will outline the rare isotope (RI) beam production using the BigRIPS separator, including the search for new isotopes that were conducted several times since 2007. We have produced a total of 629 different RI beams and delivered to 250 experiments so far, and discovered more than 150 new isotopes.

Then I will focus on highlights from the recent new isotope search conducted using an intense 48Ca beam, in which we determined the neutron dripline at fluorine and neon to be 31F and 34Ne, respectively [4] and discovered an extremely neutron-rich isotope 39Na with neutron number N = 28 [5]. These findings provided us with a key to understanding the nuclear structure under such extremely neutron-rich conditions. The location of neutron dripline and the nuclear binding near the limit of existence are determined reflecting details of underlying nuclear structure, such as the evolution of the nuclear shell property and associated nuclear deformation. The nuclear deformation, caused by the magicity loss at N = 20 and 28, plays a key role in the nuclear binding in this region and thus in determining the particle stability of 39Na as well as the location of the neutron dripline at 31F and 34Ne. I will not only overview the experiments, but also outline the discussions of such intriguing nuclear structure.

[1] T. Kubo, Nucl. Instrum. Methods Phys. Res., Sect. B 204, 97 (2003).

[2] T. Kubo, D. Kameda, H. Suzuki, N. Fukuda, H. Takeda, Y. Yanagisawa, M. Ohtake, K. Kusaka, K. Yoshida, N. Inabe, T. Ohnishi, A. Yoshida, K. Tanaka, Y. Mizoi, Prog. Theor. Exp. Phys. 2012, 03C003 (2012).

[3] Y. Yano, Nucl. Instrum. Methods Phys. Res., Sect. B 261, 1009 (2007).

[4] D. S. Ahn, N. Fukuda, H. Geissel, N. Inabe, N. Iwasa, T. Kubo, K. Kusaka, D. J. Morrissey, D. Murai, T. Nakamura, M. Ohtake, H. Otsu, H. Sato, B. M. Sherrill, Y. Shimizu, H. Suzuki, H. Takeda, O. B. Tarasov, H. Ueno, Y. Yanagisawa, K. Yoshida, Phys. Rev. Lett. 123, 212501 (2019).

[5] D. S. Ahn, J. Amano, H. Baba, N. Fukuda, H. Geissel, N. Inabe, S. Ishikawa, N. Iwasa, T. Komatsubara, T. Kubo, K. Kusaka, D. J. Morrissey, T. Nakamura, M. Ohtake, H. Otsu, T. Sakakibara, H. Sato, B. M. Sherrill, Y. Shimizu, T. Sumikama, H. Suzuki, H. Takeda, O. B. Tarasov, H. Ueno, Y. Yanagisawa, K. Yoshida, Phys. Rev. Lett. 129, 212502 (2022).