A region of oblate nuclides centred at Z = 114 and of spherical nuclides centred at the magic nucleus - A possible scenario to understand the production of superheavy elements beyond copernicium

Abstract

Abstract.The recent experiments at FLNR, Dubna, demonstrated that cross sections to produce SHEs by 48 Ca induced reactions on actinide targets increase beyond Z = 111, reach a maximum of 5 pb at Z = 114/115, and fall below the 1 pb-level at Z = 118. A scenario is proposed to understand the findings within the frame of former experimental results of heavy element production and theoretical predictions on the stability of the nuclides concerned. New ingredients introduced are 1) to shift the next proton shell beyond Pb from Z = 114 to Z = 122, 2) the isotopes of elements Z = 112 to Z = 118 are deformed and their nuclei have oblate shapes, and 3) the fission barriers around the next magic nucleus 306 122 184 are larger than the neutron separation energies and reach values in the range of 10 MeV. The ascent of the flat top at 306 122 184 is described by the proposed scenario, which likewise excludes to reach the doubly closed shell region at the top by today ′ s experimental methods in complete fusion reactions. Closed proton shell shifts away from Z = 11448 Ca-induced fusion reactions on heavy actinide targets have been investigated at the FLNR-Dubna. The discovery of many isotopes and evidence for new superheavy elements (SHEs) Z = 114 to 118 were reported since 2004 and presented in a review [1,2]. For more than 40 years the protonshell of SHEs has been positioned at Z = 114 [3,4]. The next neutron-shell stayed fixed at N = 184, as predicted by the early shell model [5], whereas recent calculations position the proton shell at Z = 120 or Z = 122 [6,7]. In 2008 [8] I presented an analysis of α-decay chains for pairs of even-even nuclei measured in the FLNR-experiments. These chains give access to Q α -values between the groundstates of the isotopes involved. The isospin-values (N − Z)/2 characterising the chains were 29 and 30 and cover the even elements between Z = 118 and Z = 112. They cross the proposed proton-shell Z = 114 at N = 172 and N = 174 away from the next neutron-shell at N = 184 by 12 and 10 neutrons. Q α -values in decay-chains decrease steadily descending the chain to smaller Z-values. Passing a shell a jump from higher Q α -values above the shell to lower values below the shell is well documented in nuclear data tables [9] for the main shells Z = 82, 50. The size of the jump crossing the magic proton-shell becomes smaller going away from the nearest doubly magic nucleus. We will examine by a comparison to the well-established Pbshell at equivalent distances in the neutron numbers, whether for a shell at Z = 114 a jump should still be observed at a distance of 12 or 10 neutrons. The point of comparison for the Pb-shell is N = 118. The Pb-shell crossed at N = 119 − 116 by the chains passing from Po via Pb to Hg manifests a jump of (1.21±0.02) MeV at the shell-crossing. a e-mail: Peter.Armbruster@gsi.deThe analysis presented in Fig. 1 demonstrates that the Pbshell is still clearly visible at 200 Pb, and a shell closure at Z = 114 should be manifested in the α-chains presented by FLNR. An analysis ...