Evidence for a 3.6 minute isomeric 12⁻ state of the πh ^2/−1₁₁ vi ^2/−1₁₃ configuration in²⁰⁶Tl and effective two-particle interactions

Abstract

Using the²⁰⁴Hg(α, pn)-reaction andα-particles of energies 39–55 MeV, we have found an isomeric 3.6 min 12⁻ state in²⁰⁶Tl at 2,642.9 keV which has the two-hole configurationπh ^2/−1₁₁ vi ^2/−1₁₃ The 12⁻ state decays mainly by anE5 transition of energy 1,021.4 keV to a 7⁺ state at 1,621.5 keV whose main configuration isπs ^2/−1₁ vi ^2/−1₁₃ There is, in addition, evidence for a weak 565 keVM 4 branch to an 8⁺ state at 2,078 keV whose main configuration should beπh ^2/−1₁₁ vf ^2/−1₅ . The 7⁺ state decays by a stretched cascade ofγ-rays to states of the following values ofJ ^π and excitation energy: 5 ⁺₋ , 1,405.4 keV; 4⁻, 952.1 keV; 2⁻, 265.8 keV and 0⁻, 0 keV. The main configurations of these states areπh ^2/−1₁₁ vp ^2/−1₁ ,πd ^2/−1₃ vf ^2/−1₅ ,πd ^2/−1₃ vp ^2/−1₁ andπs ^2/−1₁ vp ^2/−1₁ respectively. From the nuclear masses of²⁰⁸Pb,²⁰⁷Pb,²⁰⁷Tl, and²⁰⁶Tl and the experimental excitation energies it is possible to obtain the proton hole-neutron hole interaction in²⁰⁶Tl. This interaction is compared with the calculations of Kuo and Herling and the discrepancies are discussed. The 12⁻→8⁺ M4 transition rate is reduced because of destructive interference between the protonh _11/2→d _3/2 and the neutroni _13/2→f _5/2 contributions. The magnitude of the reduction is accurately reproduced by the wave functions of Kuo and Herling. The 12⁻→7⁺ E5 transition rate is about twice as large as the single-holeπh ^2/−1₁₁ πs ^2/−1₁ transition rate. This deviation is fully explained by the configuration admixtures in the 7⁺ state, given by Kuo and Herling.