DEPOPULATION OF TA-180(M) BY COULOMB-EXCITATION AND POSSIBLE ASTROPHYSICAL CONSEQUENCES

The depopulation of Ta-180m by Colomb excitation was investigated in a thick-target experiment using beams of S-32 and S-36 with energies of 70-130 MeV on disks of natural tantalum. The resulting Ta-180 ground-state population was measured by detecting its eight-hour decay. At the higher incident energies the observed Ta-180 yield is dominated by sub-Coulomb neutron pickup transfer reactions on the 10(4) times more abundant Ta-181. At the lower incident energies the Ta-180 ground-state yield is found to be compatible with Coulomb excitation of the isomer to an intermediate level with energies E(x) < 1 MeV and a reduced transition probability B(E2) congruent-to 0.02-0.25 Weisskopf units. Consequences for the astrophysical production mechanism of Ta-180 are discussed.