Activity measurement of Fe 60 through the decay of Co 60m and confirmation of its half-life

Karen M. Ostdiek, Tyler S. Anderson, William K. Bauder, Matthew R. Bowers, Adam M. Clark, Philippe Collon, Wenting Lu, Austin D. Nelson, Daniel Robertson, Michael Skulski, Rugard Dressler, Dorothea Schumann, John P. Greene, Walter Kutschera, Michael Paul

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Abstract

The half-life of the neutron-rich nuclide Fe60 has been in dispute in recent years. A measurement in 2009 published a value of (2.62±0.04)×106 years, almost twice that of the previously accepted value from 1984 of (1.49±0.27)×106 yr. This longer half-life was confirmed in 2015 by a second measurement, resulting in a value of (2.50±0.12)×106 yr. All three half-life measurements used the grow-in of the γ-ray lines in Ni60 from the decay of the ground state of Co60 (t1/2=5.27 yr) to determine the activity of a sample with a known number of Fe60 atoms. In contrast, the work presented here measured the Fe60 activity directly via the 58.6 keV γ-ray line from the short-lived isomeric state of Co60 (t1/2=10.5 min), thus being independent of any possible contamination from long-lived Co60g. A fraction of the material from the 2015 experiment with a known number of Fe60 atoms was used for the activity measurement, resulting in a half-life value of (2.72±0.16)×106 yr, confirming again the longer half-life. In addition, Fe60/Fe56 isotopic ratios of samples with two different dilutions of this material were measured with accelerator mass spectrometry to determine the number of Fe60 atoms. Combining this with our activity measurement resulted in a half-life value of (2.69±0.28)×106 yr, again agreeing with the longer half-life.

Original languageEnglish
Article number055809
JournalPhysical Review C
Volume95
Issue number5
DOIs
StatePublished - 26 May 2017

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© 2017 American Physical Society.

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