No abstract

A 70 ns isomeric state at 2 641 keV has been produced in the 209Bi(α,2n)211 At reaction and interpreted as the 29/2+ state of the h 9/2 2 i 13/2 proton configuration. It decays to the states (h 9/2 2 f 7/2)23/2, (h 9/2 3)21/2, (h 9/2 3)17/2, (h 9/2 3)13/2 and (h 9/2 3)9/2 by a straight cascade of transitions with energies (multipolarities) 713.3 keV (E3), 511.6 keV (M1), 96.0 keV (E2), 253.4 keV (E2), and 1 066.9 keV (E2). There is also indirect evidence for a 24.4 keV (E2) branch to a (h 9/2 2 i 13/2)25/2 state followed by a 688.9 keV (E1) transition to the 21/2- state. The reduced transition rate B(E3, 29/2+ → 23/2-) = 51 000 e 2 fm6 can be reproduced by taking the value 0.9 MeV for the particle-phonon coupling matrix element ⟨i 13/2, 3-; 7/2|H coupl|f 7/2⟩.

Using alpha particles from the Stockholm 225-cm cyclotron, gamma rays from the 208Pb(α, 3n) reaction have been studied. Excitation functions, angular distributions, prompt and delayed gamma rays and gamma-gamma coincidences were measured. The results give strong evidence for a 31/2- isomeric state in 209 84Po125 with a half-life of 118 ± 3 ns, which is interpreted as being mainly due to the core-excited πh 9/2πi 13/2νg 9/2 (ν-2)0+ configuration.

The energies of high-spin states formed by adding a few valence nucleons to 208 Pb can be accurately calculated by using empirical interaction matrix elements. It is shown that the energies of high-spin states with 207 Pb, 206 Pb, and 204 Pb as the core can also be accurately calculated if an additional quadrupole interaction with a strength proportional to the increased polarizability of the core is included. This interaction may contribute to the formation of yrast traps from states with a few valence nucleons with aligned angular momenta.

Using alpha-particles in the energy range 35-51MeV and in-beam gamma ray and conversion electron spectroscopy techniques the reaction 2~ 3n)Z~ was studied. A 15 _+1 ns isomeric 15 + state was found at an excitation energy of 3147keV in 2~ The main configuration of the isomeric state is suggested to be 7"ch9/2 vp~/~i~/2. The isomeric state decays mainly through a stretched cascade of five gamma rays to the previously known 0.88ms 10-state of the 7ch9/2 vi13~2(j-2)o + configuration at an excitation energy of 1045 keV. A shell model calculation of the yrast states has been performed and it is found that the calculation agrees fairly well with the experiments. The average deviation between experimental and calculated energies for the yrast states with angular momenta in the region 6-18 is +4keV and the root mean square deviation is 22keV.