Absolute electromagnetic transition rates in semi-magic N = 50 and 126 isotones as a test for (π9/2)ⁿ single particle calculations

Assuming a seniority-conserving interaction, single- j calculations for (j) n configurations with n = 1,..,2j+1 can be performed using a semi-empirical approach, provided that the energies and absolute electromagnetic transition rates are known for the two-particle (hole) nucleus. Using those and the coefficients of fractional parentage, all needed matrix elements for the (j) n configurations can be predicted. At the Cologne Tandem Accelerator of the Institute for Nuclear Physics these relations were tested by measuring lifetimes of excited states in (π9/2) n isotones with N = 50 and N = 126 over the last years. The studies started in the two-proton nucleus 210 Po where the abnormal B(E2:2 1 + → 0 1 + ) value was remeasured, providing important input for the other N = 126 configurations. Then lifetimes of excited states in 211 At were measured using the electronic γ-γ fast timing technique, the Recoil Distance Doppler Shift (RDDS) method, and the Doppler Shift Attenuation (DSA) method. Very good agreement with the analytical single -j calculation is obtained. For N = 50 isotones, we recently started by measuring the previously unknown B(E2:4 1 + → 2 1 + ) value in 92 Mo needed for the prediction of other N = 50 isotones. We also report on experiments on 93 Tc and 94 Ru.