Approaches to element 120 (unbinilium)

Attempts have been made at GSI to make element 120 (unbinilium). Several new elements have been made at GSI in the last few years. However after 120 days no decay chain of element 120 was found. With the total number of 2.6 × 1019 projectiles which impinged upon the target, it deduced that the stability in the region around Z=120, N=184 is not exceptionally high with respect to the neighbouring regions.

Currently it is not clear what proton number defines the location of the "island of stability". Various theoretical models suggest numbers of Z=114, 120 or 126. Workers at GSI investigated the element Z=120 (element 120, containing 120 protons within the nucleus). Three different projectile-target combinations all lead to the same compound nucleus 302120 or 302Ubn

  • 64Ni + 238U
  • 58Fe + 244Pu, and
  • 54Cr + 248Cm

The neutron number of the compound nucleus 302120 is N=182. This is only 2 neutrons below N=184 where the neutron shell closure is expected. Therefore, 302120 or 302Ubn is closer to the N=184 shell than any other so far produced compound nucleus with lower Z.

The largest production rate for Z=120 is predicted for the most mass asymmetric projectile/target combination 54Cr + 248Cm. However, at SHIP this experiment was not possible so the reaction 64Ni + 238U was studied. If the proton shell closure is at Z=120 then an enhanced production rate and half-live of the element 120 would be expected. Depending on the magnitude of the stabilization due to the closed shell, one could expect up to a few events per week for the isotopes 299120 and 298120 produced in 64Ni + 238U reactions. The half-lives are expected to be of the order of some 10 μs, but in the end no luck, this time at least.

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Copyright 1993-2011 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.