Exotic clustering in heavy and superheavy nuclei within the relativistic and non-relativistic mean field formalisms

The clustering phenomenon in heavy and superheavy nuclei is studied within the relativistic mean field ( RMF) approach using axially deformed basis and the non- relativistic Skyrme - Hartree - Fock ( SHF) formalism. The calculated ground and intrinsic excited state properties, and the total matter densities as well as the neutron - proton asymmetry distributions are analysed to look for the cluster configurations and/ or exotic clusters in the known cluster emitting Ra-222, U-232, Pu-236 and Cm-242 nuclei, and the superheavy nuclei with Z = 114, N = 172 - 184. Both the theories predict N approximate to Z, alpha- like matter or clustering in the ground states, and both N approximate to Z matter and N not equal Z clustering in the excited intrinsic states of radioactive actinides, though this result is more apparent and universal for the RMF approach. For superheavy nuclei, the detailed analysis shows a non- clustering, 'bubble'- like structure for Z = 114, N = 184 nucleus in the RMF method and Z = 114, N = 176 or 180 nucleus in the SHF method, as the signatures of doubly closed shell nuclei. Our earlier similar calculations for Z = 120 nuclei predicted the same for Z = 120, N = 172 nucleus in the RMF model. Also, in contrast to radioactive actinides, in superheavy nuclei the two fragments, N not equal Z cluster configurations at the centre of ground superdeformed states in the RMF approach, and the same for at least some of the excited superdeformed states in the SHF method, are some of the interesting results obtained. Thus, new possibilities of exotic clusters at the centre of superheavy nuclei are indicated as ground or excited intrinsic superdeformed state configurations, more so as ground superdeformed states in the RMF theory. The N/ Z ratios of the clusters are also calculated on the basis of the ( average value of) colour code of the contours, which give a reasonable correspondence with the experimental data on cluster decay of radioactive nuclei.