Gamma and Alpha decay from the 2.1-msec isomer213mRa

The isomer^213mRa was produced by the reaction²⁰⁹Bi(¹⁰B, 6n), as well as by bombardments of¹²C on Pb isotopes,¹⁴N on Bi, and¹⁶O on natural Hg, with projectile energies in the range 60–100 MeV. The isomer decays with a halflife of 2.1 ms both via gamma internal transitions and via alpha branching to levels in²⁰⁹Rn. A level scheme is proposed in which the isomeric state is assigned as either 17/2^– or 13/2⁺ with shell-model configurations either of theh_9/2 protons coupled to ap_1/2 neutron hole, or of an uncoupledi_13/2 neutron hole. On the basis of alpha decay rate predictions from the new Fliessbach theory, the 17/2^– isomeric assignment is to be preferred.Phys. Abstracts classifications 4.200–4.375