Seminarium Struktura Jądra Atomowego

Back in 1971 a long-lived superheavy element with Z=112 has been produced via secondary reactions in CERN W targets which were irradiated with 24-GeV protons. For many years it was difficult to understand these results and in particular the long lifetime of several weeks of the new nucleus and its large deduced fusion cross section. In a parallel study, long-lived isomeric states have been found in various actinide nuclei produced in the same W target. It was then claimed that, as in the actinides, long-lived isomeric state has been produced in the superhavy element region. At that time the character of the isomeric states was not known. In more recent studies new kinds of isomeric states have been discovered by us. These are high spin isomers in the second (superdefomed) and third (hyper-deformed) minima of the potential energy surfaces, when plotted as a function of deformation. The existence of such isomeric states and their unusual radioactive decay properties enabled us to consistently interpret the production of the superheavy element with Z=112 and of some previously unexplained radioactivities seen in nature. Based on these results a search has been performed for the existence of long-lived isomeric states in natural materials using high resolution atomic mass measurements. Long-lived isomeric states with T1/2 ≥ 108 years have been found in the neutron-deficient 211,213,217,218Th nuclei, and in the superheavy element region, at atomic mass numbers 261 and 265, most probably at 261Rg and 265Rg (Z = 111), and at mass 292 and Z = 122, 292(Eka-Th).