K-pi=0(+) 2.29 s isomer in neutron-rich Tm-174

Gamma-ray and conversion-electron spectroscopy have established the existence of a 2.29(1) s, K-pi=0(+), isomeric state in neutron-rich Tm-174. The isomer deexcites via 100- and 152-keV electromagnetic transitions. First results from a newly commissioned Si(Li) detector array have established their M1 and E3 multipolarities, respectively. The single-particle configurations of the excited states suggest that the E3 transition originates from a pi h(11/2)(-1)->pi d(3/2) configuration change, whereas the M1 transition occurs between members of a Gallaghar-Moszkowski doublet. From the measured half-life, the deduced B(E3) value of 0.024(2) W.u. is highly hindered. The reported measurements resolve ambiguities in the previously proposed beta decay scheme of Er-174 to Tm-174.