SYSTEMATICS OF THE ALPHA-SPECTROSCOPIC FACTORS OF THE NEW ISOTOPE RN-196 AND EVEN-EVEN NUCLEI WITH Z=78-SIMILAR-TO-90

We examined for the first time the spectroscopic factor (S-alpha = Gam ma(exp)/Gamma(sp)) for the newly produced alpha-decaying neutron-defic ient nucleus Rn-196 at the E1 room of the Ring Cyclotron Laboratory of RIKEN. In the Er-166(Ar-36,6n) Rn-196 reaction at E(lab) = 208 MeV, t he alpha-energy and the half-life of this new isotope have been determ ined to be 7492 +/- 30 (keV) and 3(-2)(+4) (ms), respectively. Includi ng these new isotope data, we calculated the alpha-spectroscopic facto rs for the ground states of the even-even nuclei with Z = 78 similar t o 90. We found, from the systematics of S-alpha-values and the largest value of the new isotope, that Rn-196 is more developed in a-clusteri ng than other even-even nuclei. Moreover, the Rn isotopes were quite d ifferent from the Po isotopes in the deeply neutron-deficient region. The Rn values showed a steep increase where the node number changes fr om 11 to 10, presenting a contrast with the Po values. This increase m ag be due to the fact that the configuration of the Rn isotopes is dif ferent from that of the Po isotopes on the neutron-deficient side. Som e possible explanations are discussed.