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Contenu archivé le 2022-12-23

Synthesis of spherical superheavy nuclei in the reactions with (48)Ca ions

Objectif

SUMMARY To check the hypothetic existence of nuclear shell closures at Z = 114 and N = 178 - 184, one of the fundamental predictions of modern nuclear theory, an experiments will be performed, aiming at the production of super heavy nuclides with Z = 110, 112, 114, 115 and 116 (N = 166-167, 170-171, 172-175, 172-173 and 176-177 respectively) via the complete fusion reactions of (232)Th, (238)U, (242,244)Pu, (243)Am and (248)Cm targets nuclei and (48)Ca projectiles delivered by the FLNR JINR U400 cyclotron. To separate complete fusion reaction products it is planned to use fast (1 - 2 hours) chemistry using (232)Th target, gaseous chemistry using (238)U target and separators VASSILISSA and the Dubna gas-filled recoil separator. These experimental set-ups provide a fast (> 1 microsecond) and efficient (40 - 60 %) separation of evaporation residues and study of the decay properties of new isotopes of superheavy elements. For the (48)Ca + (243)Am, (248)Cm reactions, this facilities, together with the possibility to use projectile beams with intensities of up to 10(13) pps, provide experimental sensitivity of 1 pb during 10 - 20 days of irradiation and unambiguous identification of new isotopes of superheavy elements on the basis of genetic correlation method.
In 1997-1999 with the use of the recoil separators the new isotopes (283)112, (287,288)114 were synthesised and identified at the formation cross section level about 2 pb.

The calculations predict a steep rise of the half-lives with increasing neutron number. This is a result from the decreasing negative shell-correction energy and a transition of the nuclear shape from well-deformed quadrupole to spherical, which both increase the stability and the fission barrier and thus the partial alpha and SF half-lives. The result of the work, performed under the INTAS support, contract N 96-662, together with the results obtained earlier show good agreement with theoretical predictions and could be interpreted as an experimental check of the shore of the "island of the stability". The obtained data for new heaviest isotope of element 112 - (283)112 and isotopes of element 114 - (287)114 and (289)114 allow to compare of the radioactive properties of these nuclides and known isotope (277)112. It allow to make the conclusion about the existence of the new region of nuclear stability and the strength of spherical shell closures at Z=114 and N=178-184.

It is planned to continue the experiments aimed to the synthesis and study of the decay properties of the neutron rich superheavy nuclei in the complete fusion reactions of (48)Ca with transactinide targets. The first experiment will be the the investigation of the chemical properties of the 112 element using the reaction (48)Ca + (238)U. The chemical procedure will allow to establish the properties of the 112 element. With the use of recoil separators the reactions (48)Ca + (243)Am --> (288)115 + 3n, (48)Ca + (239)Pu --> (284)114 + 3n and (48)Ca + (248)Cm --> (296)116(-) will be studied. The new heaviest isotopes of elements 104-110 can be identified as descendant nuclides, as well. The reactions (243)Am+(48)Ca and (248)Cm+(48)Ca will be used for the synthesis and study of the new elements 115 and 116. The identification of isotopes (287,288)115 and (292,293)116 will be critical and decisive test of the modern macro-microscopic nuclear theory and can means the discovery of the new region of spherical superheavy elements.

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Coordinateur

Gesellschaft für Schwerionenforschung mbH (GSI)
Contribution de l’UE
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Adresse
PlankStrasse 1
64291 Darmstadt
Allemagne

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