Isomeric E1 and M1 transitions in 177Ta and in neighbouring odd-A Lu and Ta isotopes

Delayed γ-ray spectra as well as time distributions have been measured applying the r.f.-γ method and the method of delayed γ-γ coincidences. Using the reaction ¹⁷⁵Lu(α, 2n)¹⁷⁷Ta, the half-lives of the levels at 70.6 and 73.6 keV in ¹⁷⁷Ta have been determined as $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 80±10}\text{ns}$ and $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 370±50}\text{ns}$, respectively. In further experiments, upper limits for the lifetimes of the $\text{9}\text{2}{}^{\mathrm{?}}\text{514]}$ and $\text{5}\text{2}{}^{\mathrm{+}}\text{402]}$ states in ¹⁷¹Lu and ¹⁷³Lu were estimated. Comparisons of the experimental half-lives to Weisskopf and Nilsson model predictions are performed taking into account pairing correlations. For the calculations, a modified Nilsson Hamiltonian has been used. The hindrance factors obtained are summarized together with those deduced for corresponding transitions in neighbouring odd-proton nuclei. From the experimental results in ¹⁷⁷Ta, conclusions have been drawn on the possible value of the constant k₂ occurring in the magnetic dipole operator.