DECAY OF AN ISOMERIC STATE IN 178HF WITH K ]= 16

A long-lived isomeric activity in 178Hf has been produced by neutron irradiation of hafnium. The isomeric state occurs at an energy of ≈2.5 MeV and has a half-life >10 y. The gamma-ray transitions associated with the decay of the isomer have been studied by means of a Ge(Li) spectrometer and a NaI(Tl) gamma-gamma coincidence system. The resulting decay scheme includes the following known levels of the Kπ=0+ ground-state rotational band: 93.181 (I=2), 306.625 (4), 632.19 (6), and 1058.56 keV (8). This scheme also includes the previously reported Kπ=8- level at 1147.44 keV along with the following members of its rotational band: 1364.11 (I=9), 1601.50 (10), 1859.12 (11), 2136.50 (12), and 2433.32 keV (13). The M1 transition probabilities of these intraband transitions were obtained from the observed gamma-ray intensities assuming the validity of the Alaga rules for the rotational E2 transitions. These probabilities provide an estimate of the amount of mixing between this band and that built on the Kπ=8- state at 1480 keV. Although a configuration assignment for the isomeric state cannot be made with certainty on the basis of the present data, the most plausible interpretation is that it is a four-quasi-particle state with Kπ=16+. © 1968.