NEUTRON-RICH HEAVY RESIDUES AND EXOTIC MULTINUCLEON TRANSFER

A thick natural lead target has been bombarded with a 600 MeV O-18 bea m. With the use of an online gas-thermochromatographic device the merc ury isotopes produced as target residues were rapidly separated and co llected. A. special coincident measurement technique increased the sen sitivity to detecting beta(-)-delayed gamma rays, resulting in the obs ervation of six neutron-rich mercury isotopes Hg-203,Hg-205-209. Here Hg-209 was created through an exotic -2p+3n multinucleon transfer proc ess and was identified for the first time. The half-life of 209Hg has been determined to be 35(-6)(+9) s, and four gamma rays following its beta(-) decays have been assigned. The measured thick-target average p roduction cross sections of Hg-203,Hg-205-209 were analyzed together w ith the known cross section data related to the -2p +/-xn exit channel s. It has been found that the independent cross sections from various reactions induced by lighter heavy-ion projectiles below Ar-40, displa y a regular Q(gg) dependence, suggesting that the heavy neutron-rich t arget residues were produced mainly in quasielastic and deep inelastic multinucleon transfer processes. The half-life of Hg-208 has been det ermined to be 41(-4)(+5) min.