Neutron-rich heavy residues and exotic multinucleon transfer

A thick natural lead target has been bombarded with a 600 MeV ¹⁸O beam. With the use of an online gas-thermochromatographic device the mercury isotopes produced as target residues were rapidly separated and collected. A special coincident measurement technique increased the sensitivity to detecting β^--delayed γ rays, resulting in the observation of six neutron-rich mercury isotopes ^203,205-209Hg. Here ²⁰⁹Hg was created through an exotic -2p+3n multinucleon transfer process and was identified for the first time. The half-life of ²⁰⁹Hg has been determined to be 35⁺⁹_-6 s, and four γ rays following its β^- decays have been assigned. The measured thick-target average production cross sections of ^203,205-209Hg were analyzed together with the known cross section data related to the -2p+/-xn exit channels. It has been found that the independent cross sections from various reactions induced by lighter heavy-ion projectiles below ⁴⁰Ar, display a regular Q_gg dependence, suggesting that the heavy neutron-rich target residues were produced mainly in quasielastic and deep inelastic multinucleon transfer processes. The half-life of ²⁰⁸Hg has been determined to be 41⁺⁵_-4 min.