Blocking of Octupole Correlations Deduced from the Decay of a Multiparticle Isomer in ²¹²At

A high spin isomer with spin 25^- and mean lifetime of 220 μs has been observed at an excitation energy of 4772 keV in ²¹²At. The measured E3 decay rate for the 224 keV transition deexciting this level is enhanced but significantly lower than those observed in the neighboring isotopes or predicted using a multiparticle octupole coupling model. The relatively simple configurations involved in this decay and the close relationship to neighboring states allow a clear association to be made between the occupation of a specific single particle orbital and a blocking of the octupole vibrational correlation.