First-excited state g factor of Te 136 by the recoil in vacuum method

The g factor of the first 2+ state of radioactive Te136 with two valence protons and two valence neutrons beyond double-magic Sn132 has been measured by the recoil in vacuum (RIV) method. The lifetime of this state is an order of magnitude longer than the lifetimes of excited states recently measured by the RIV method in Sn and Te isotopes, requiring a new evaluation of the free-ion hyperfine interactions and methodology used to determine the g factor. The calibration data are reported and the analysis procedures are described in detail. The resultant g factor has a similar magnitude to the g factors of other nuclei with an equal number of valence protons and neutrons in the major shell. However, an unexpected trend is found in the g factors of the N=84 isotones, which decrease from Te136 to Nd144. Shell model calculations with interactions derived from the CD Bonn potential show good agreement with the g factors and E2 transition rates of 2+ states around Sn132, confirming earlier indications that Sn132 is a good doubly magic core.