No abstract

An isomeric state of Hf 177 with T_~_=(1,12_0,10)s was found by a fast chemical separation of the hafnium daughter from the 155 d Lu 177m activity. We measured the sanae half-life by observing the delayed fl-y-coincidences. A systematic investigation of the whole region 5s> T 89 10 -7 s by the technique of delayed coincidences gave no further isomerism. We assign the observed half-life to the ~ three particle state of Hf 177 at 1315 keV and assume that the second hypothetical three particle state at 1337 keV does not exist. The ~1 rotational state of the K=-~ band is populated by a strongly converted 14,16keV y-transition from the isomeric state at 1315 keV. The 14,16 keV M I and N I conversion lines were observed by use of a double focusing magnetic fl-spectrometer. The isomerism is caused by the K-selection rule. The retardation of the following three y-transitions by different degrees of K-forbiddeness is discussed. The pulse height spectrum, measured by means of a Li-drifted Ge-detector, does not show the 36,52 keV-y-transition which was previously assumed topopulate the 1301keVstate. In addition to the known y-transitions we found a 40,9 keV-line. This is probably the transition between the 1301,1 keV and the 1260,3 keV-states.

The technique of differential ~-7 angular correlation measurements has been applied to an investigation of the hyperfine interactions in the 482 keV level of 181Ta. The activity was embedded in the lattice of a hafnium single crystal. The investigation of the quadrupole interaction gave for the electric interaction frequency ~o0= (313 +_ 4) MHz.The electric field gradient was found to be axially symmetric, the asymmetry parameter being ~/<0.1.Furthermore the combined collinear magnetic dipole and electric quadrupole interaction was studied. The angular correlation was investigated as a function of the strength of the external magnetic field by integral as well as time differential measurements. The integral anisotropy as function of the magnetic field has the shape of a resonance curve. The maximum was observed at a magnetic field of Bres = (24.2 + 0,5) kG.