Synthesis of superheavy nuclei in Ca-48+Pu-244 interactions

This article reports the results of experiments aimed at producing hypothet ical long-lived superheavy elements located near the spherical-shell closur es with Z greater than or equal to 114 and N greater than or equal to 172. For the synthesis of superheavy nuclei, we used a combination of neutron-ri ch reaction partners, with a Pu-244 target and a Ca-48 projectile. The sens itivity of the present experiment exceeded by more than two orders of magni tude previous attempts at synthesizing superheavy nuclides in reactions of Ca-48 projectiles with actinide targets. We observed new decay sequences of genetically linked alpha decays terminated by spontaneous fission. The hig h measured alpha-particle energies, together with the long decay times and spontaneous fission terminating the chains, offer evidence for the decay of nuclei with high atomic numbers. The decay properties of the synthesized n uclei are consistent with the consecutive alpha decays originating from the parent nuclides (288,289)114, produced in the 3n- and 4n-evaporation chann els with cross sections of about a picobarn. The present observations can b e considered experimental evidence for the existence of the "island of stab ility" of superheavy elements and are discussed in terms of modern theoreti cal approaches. (C) 2000 MAIK "Nauka/Interperiodica ".