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

The half-life of the neutron-rich nuclide Fe-60 has been in dispute in recent years. A measurement in 2009 published a value of (2.62 +/- 0.04) x 10(6) years, almost twice that of the previously accepted value from 1984 of (1.49 +/- 0.27) x 10(6) yr. This longer half-life was confirmed in 2015 by a second measurement, resulting in a value of (2.50 +/- 0.12) x 10(6) yr. All three half-life measurements used the grow-in of the.-ray lines in Ni-60 from the decay of the ground state of Co-60 (t(1/2) = 5.27 yr) to determine the activity of a sample with a known number of Fe-60 atoms. In contrast, the work presented here measured the Fe-60 activity directly via the 58.6 keV gamma-ray line from the short-lived isomeric state of Co-60 (t(1/2) = 10.5 min), thus being independent of any possible contamination from long-lived Co-60g. A fraction of the material from the 2015 experiment with a known number of Fe-60 atoms was used for the activity measurement, resulting in a half-life value of (2.72 +/- 0.16) x 10(6) yr, confirming again the longer half-life. In addition, Fe-60/Fe-56 isotopic ratios of samples with two different dilutions of this material were measured with accelerator mass spectrometry to determine the number of Fe-60 atoms. Combining this with our activity measurement resulted in a half-life value of (2.69 +/- 0.28) x 10(6) yr, again agreeing with the longer half-life.

Externe Organisation(en)
University of Notre Dame, Paul Scherrer Institute, Argonne National Laboratory, Hebrew University Jerusalem
Physical Review C
Anzahl der Seiten
ÖFOS 2012
103014 Kernphysik
ASJC Scopus Sachgebiete
Nuclear and High Energy Physics
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