On the high multipole alpha-decays of the 18+ state in 212Po and the 1- and 9- states in 212 At

The alpha-spectra of the decays of sup(212m,g)At and sup(212m)Po have been studied using isotope separator on-line techniques. These nuclei were produced in the reactions 209Bi(α,n)sup(212m,g)At and 209Bi(α,p)sup(212m)Po, respectively, using 43 MeV alpha-particles from the external beam of the 225-cm cyclotron in Stockholm. The short half-lives of the 1- and 9- states in 212At required a molten bismuth droplet to be placed inside an integrated target ion source of the isotope separator. The intensities and energies of twenty alpha-branches in the decay of sup(212m,g)At, as well as those of three branches in the decay of sup(212m)Po, were carefully measured. The half-lives of the 1- ground state and 9- isomeric state of 212At were found to be 314+-3 and 115+-2 ms, respectively. The Q-value of the alpha-decay from the ground state of 212At was found to be 7817+-3 keV. Calculations of relative alpha-decay widths for sup(212m,g)At have been performed with the approximation made, that the initial and final states consist of pure configurations. The agreement is good for the decay of the (9-) isomeric state in 212At but not so good for the (1-) ground state, which probably indicates that configuration admixtures in the (1-) initial state should be accounted for. (Auth.)