Spectroscopy of high-spin states of ²⁰⁶Po

The yrast and near-yrast energy levels of ²⁰⁶Po have been investigated to over 9 MeV excitation and up to spins of 24. The measurements consisted of γγ-coincidence data, internal-conversion-electron spectra, time spectra of γ-rays relative to a pulsed beam, excitation functions and γ-ray angular distributions. Two new isomers, with lifetimes in the 1 ns range, were found. The observed level structure is compared with the predictions of empirical shell-model calculations in which ²⁰⁶Po is regarded as a ²⁰⁸Pb core with two valence protons and four valence neutron holes. The agreement is generally satisfactory for the observed odd-parity levels and for even parity levels with J > 12; those with J = 6-12 are better accounted for by weak coupling of two valence protons to a ²⁰⁴Pb core in its 0⁺ ₁ and 4⁺ ₁ states.