The nucleosynthesis of 180Ta
Abstract
It has been proposed by Beer and Ward that the abundance of nature's rarest isotope, ^ {180}Ta, could be quantitatively accounted for in the standard stellar slow (s) and/or rapid (r) neutron -capture processes through the existence of small, previously unmeasured beta-branches which drain and feed the population of the t_{1/2 } = 5.5 hour isomer of ^{180 }Hf (BE81). We have conducted a series of experiments designed to measure these small beta -branches. We have: (1) measured the direct (isomer -to-isomer) 214-keV-endpoint beta branch from ^{180}Hf ^{rm m} to ^ {180}Ta^{rm m} to be f_beta = 0.30 +/- 0.07 +/- 0.07% (KE87), (2) observed a new gamma ray in the decay of ^{180}Hf ^{rm m} which indicated a small beta-branch of 0.023% to an excited state in ^{180}Ta (KE85), (3) established a stringent limit of 0.023% on the fraction f_{rm m} of ^{180}Lu decays which populate ^{180}Hf ^{rm m} (KE86), (4) sought to identify a possible high-spin, short-lived isomer of ^{180}Lu, and established upper limits on its possible half-life (LE86), (5) established limits on the ^{180}Ta ^{rm m} photodeexcitation cross-section via resonant and nonresonant processes (NO84a), and (6) calculated upper-limits on the life-time of ^{180}Ta^{ rm m} in a stellar environment. Taken together, this body of work makes it unlikely that the Beer and Ward model can account for the observed solar-system abundance of ^{180} Ta. Other possible production schemes are reviewed and directions for further research are suggested.
- Publication:
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Ph.D. Thesis
- Pub Date:
- September 1987
- Bibcode:
- 1987PhDT.......120K
- Keywords:
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- Physics: Nuclear