Radioactivity of 178Ta, 179Ta and 180Ta

The neutron deficient isotopes, 178Ta, 179Ta and radioactive 180Ta have been produced by photodisintegration of 181Ta and studied with scintillation spectrometers used singly and in coincidence. The identification of each isotope is based on a knowledge of the (γ, n) threshold and an appropriate choice of bremsstrahlung energies. Radioactive 178Ta is shown to comprise an isometric doublet with half-lives 9.5±0.1 min and 150±10 min. The 9.5 min activity populates levels in 178Hf at 0, 91 and possibly 1480 kev, the first two by both electron capture and β+ emission and the last by electron capture, while the 150 min activity decays by electron capture to a level of 178Hf at 1046 kev. A decay scheme is proposed based on the experimental results and the strong coupling collective model of Bohr and Mottelson. Evidence is presented to support the recent contention that 179Ta decays by electron capture to the ground state of 179Hf. The observed γ radiation from 8.15 hour 180Ta is in general agreement with the decay scheme of Brown et al. except that there is no evidence for gamma radiation in the energy range 175-450 kev.