New prospects in synthesis and study of neutron rich heavy nuclei

Abstract

Abstract. The present limits of the upper part of the nuclear map are rather close to the beta stability line while the unexplored area of heavy neutron rich nuclides (also those located along the neutron closed shell N = 126 to the right hand side of the stability line) is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis. For elements with Z > 100 only neutron deficient isotopes (located to the left of the stability line) have been synthesized so far. The "north-east" area of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes widely used nowadays for the production of new nuclei. Multi-nucleon transfer processes in near barrier collisions of heavy ions seem to be the only reaction mechanism allowing us to produce and explore neutron rich heavy nuclei including those located at the superheavy island of stability. Neutron capture process can be also considered as an alternative method for the production of long-lived neutron rich superheavy nuclei. Strong neutron fluxes might be provided by nuclear reactors and nuclear explosions in laboratory frame and by supernova explosions in nature. MotivationDue to the bending of the stability line forward to neutron axis, in fusion reactions of stable nuclei one may produce only proton rich isotopes of heavy elements. For example, in fusion of rather neutron rich 18 O and 186 W isotopes we obtain the neutron deficient excited compound nucleus 204 Pb, which after evaporation of several neutrons shifts even more to the proton rich side. That is the main reason for the impossibility to reach the center of the "island of stability" (Z ∼ 110 ÷ 120 and N ∼ 184) in the superheavy (SH) mass region in fusion reactions with stable projectiles. Note that for elements with Z > 100 only neutron deficient isotopes (located to the left of the stability line) have been synthesized so far. Because of that we also have almost no information about neutron rich isotopes of heavy elements located in the whole "north-east" part of the nuclear map: for example, there are 19 known neutron rich isotopes of cesium (Z = 55) and only 4 of platinum (Z = 78).At the same time this unexplored area of heavy neutron rich nuclei is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis (a sequence of neutron-capture and β-decay processes). The origin of heavy elements from iron to uranium remains one of the great unanswered questions of modern physics and it is likely to remain a hot research topic for the years to come. The r-process path is located (and probably interrupted by fission) just in the region of unknown heavy nuclei with a large neutron excess (see Fig. 1). a e-mail: zagrebaev@jinr.ru The neutron shell N = 126 (and Z ∼ 70) is the last "waiting point" on this path. The half-lives and other characteristics of these nuclei are extremely important for the r...