LOW-LYING DIPOLE EXCITATIONS IN THE HEAVY, ODD-MASS NUCLEUS TA-181

The strength distribution of low-lying dipole excitations in the heavy odd-mass nucleus Ta-181 was studied in nuclear resonance fluorescence experiments performed at the bremsstrahlung beam of the Stuttgart 4.3 MV Dynamitron accelerator. To increase the detection sensitivity in t he whole range of excitation energies between 1.8 and 4 MeV two measur ements were carried out at different bremsstrahlung end-point energies of 2.7 and 4.1 MeV using two large-volume HPGe detectors of a relativ e efficiency of 100%. Detailed information on excitation energies, dec ay widths, transition probabilities, and branching ratios of 37 new lo w-lying states in the energy range 1.8-3.5 MeV have been obtained. The observed dipole strength is rather fragmented, apart from a strong ex citation at 2.297 MeV. The total strength in the investigated range of excitation energies (1.8-4 MeV) is reduced by a factor of approximate to 3.5 as compared to the neighboring even-even nucleus Hf-180.