Speaker
Description
Neutron-rich nuclei in the vicinity of doubly-magic nucleus $^{78}$Ni ($Z=28, N=50$) is important for both nuclear physics and astrophysics. To explore these very neutron-rich isotopes, the question of how to produce them effectively in a laboratory arises. So far, two methods are widely used for production of neutron-rich nuclei: fragmentation of relevant stable nuclei and induced fission of $^{238}$U. However, for the production of most neutron-rich nuclei in the $^{78}$Ni region, both projectile fragmentation and the fission of $^{238}$U encounter difficulties. For projectile fragmentation, no suitable relevant stable nuclei are available as projectiles. In the case of in-flight fission, the production cross sections dramatically decrease towards the very neutron-rich side.
Recently, a new method of the two-step scheme by combing ISOL and in-flight fragmentation has been proposed to produce very neutron-rich nuclei in “next-generation” facilities, such as EURISOL, BISOL and RAON. In order to evaluate the potential of the two-step scheme in producing exotic isotopes in the vicinity of $^{78}$Ni, the fragmentation reactions of unstable nuclei $^{81}$Ga ($Z=31, N=50$) and $^{82}$Ge ($Z=32, N=50$) at 250 MeV/nucleon have been measured at RIKEN RIBF. The $^{81}$Ga and $^{82}$Ge beams were produced by in-flight fission of $^{238}$U primary beam in BigRIPS separator. A 1.89-g/cm$^2$ $^{9}$Be target was used to induce the fragmentation reactions. The reaction products were analyzed by the ZeroDegree spectrometer. For the first time, the fragmentation cross sections for very neutron-rich nuclei around $^{78}$Ni were obtained. The newly measured cross sections were compared with various calculations. These data enable to make a comparison between the two-step and one-step methods for the production of extremely neutron-rich nuclei in the $N = 50$ region. In the presentation, the cross section results as well as the potential of two-step scheme in the production of very neutron-rich nuclei near $^{78}$Ni will be discussed.
