Measurement of the Half-Life of Fe-60 for Early Solar System and Stellar Models. Presentation given on May 5, 2016 as part of the requirements to earn a Ph.D. degree at the University of Notre Dame.

1. Measurement of the Half-Life of 60
Fe for Early
Solar System and Stellar Models
Karen M. Ostdiek
Nuclear Science Laboratory, University of Notre Dame
Notre Dame, Indiana U.S.A.
May 5, 2016

2. Motivation from Nuclear Astrophysics for 60
Fe
Possible Production Sites for 60Fe
Weak s-process, successive neutron
captures on 58Fe.
Massive AGB stars -
13C(α, n)16O
Core Collapse Supernova -
22Ne(α, n)25Mg.
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Fe 2/ 35

3. Motivation from Nuclear Astrophysics & Evidence of 60
Fe
Evidence of 60Fe
Less of 60Ni granddaughter
product in meteorite inclusions.
γ decay observed in Galaxy.
Increased concentration in
ocean crust samples.
Superimposed 60
Fe decay lines, W. Wang, et al. Astro.
and Astrophys. 469. (2007).
Unequilbrated Ordinary Chondrites, R. K. Mishra, et al.
Astrophys. Journal. Letters. 714. (2010).
K. Knie, et al. Phys. Rev. Letters. 93. (2004).
Fitoussi, et al. Phys. Rev. Letters. 101. (2008)
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Fe 3/ 35

4. Recent Nature Papers
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Fe 4/ 35

5. Previous Half-life Measurements
Roy & Kohman, 1957:
∼ 3 · 105 years
factor of 3 uncertainty
Kutschera, et. al, 1984:
(1.49 ± 0.27) · 106 years
Rugel, et. al, 2009:
(2.62 ± 0.04) · 106 years
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Fe 5/ 35

6. Measuring long half-lives and ‘making’ a Sample
A = dN
dt = λN = ln2
t1/2
N
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Fe 6/ 35

7. Samples for Activity and AMS Experiments
Original material from PSI copper beam stop (bombarded by
protons for 12 years).
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Fe 7/ 35

8. Ascertaining the Activity - Sample Evaporation
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Fe 8/ 35

9. Ascertaining the Activity - Sample Evaporation
VERA “Fe-1” 13 mL sample evaporated to
point source.
Contains ∼ 1.4 · 1014 60
Fe atoms.
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Fe 9/ 35

10. Ascertaining the Activity - Decay Scheme for 60
Fe
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Fe 10/ 35

11. Ascertaining the Activity - Decay Scheme for 60
Fe
Direct Decay: Roy and
Kohman
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Fe 11/ 35

12. Ascertaining the Activity - Decay Scheme for 60
Fe
Direct Decay: Roy and
Kohman
Grow-in Decay:
Kutschera, et al., Rugel,
et al., and Wallner, et al.
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Fe 12/ 35

13. Ascertaining the Activity - Detailed Decay and Sample Prep.
60Fe
0+
2+
60Co
5+
2.62 Myr
10.5 min
1925.28 days
58 keV
Zoomed in on Direct Decay
Isomeric Decay of 60m
Co = Internal Conversion.
2 HPGe Planar detectors with
thin Be windows.
Total Efficiencies of 10% based
on 241Am.
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Fe 13/ 35

14. Ascertaining the Activity - Results
Background line at 63 keV is from 234Th in the 238U decay chain
Increase in continuum is from bremsstralung photons.
Activity Corrected = (9.7926 ± 0.0031) decays/second
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Fe 14/ 35

15. Now on to part two...
Concentration 60/56 × (# of 59Fe atoms added) = # of 60Fe atoms
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Fe 15/ 35

16. Identifying 60
Fe - Facilities
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Fe 16/ 35

17. Identifying 60
Fe - Second Stripper
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Fe 17/ 35

18. Identifying 60
Fe - Wien Filter
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Fe 18/ 35

19. Identifying 60
Fe - AMS Beam Line
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Fe 19/ 35

20. Identifying 60
Fe - Separating by Position
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Fe 20/ 35

21. Identifying 60
Fe - Separating by Position
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Fe 21/ 35

22. Identifying 60
Fe - Separating by Energy
Energy = 112 MeV using 8.5 MV, Second stripper, 9+ to 16+
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Fe 22/ 35

23. Identifying 60
Fe - Finding Concentration
Concentration 60/56 × (# of 59Fe atoms added) = # of 60Fe atoms
Concentration 60/56 = (Count60/time) × (1/Transmission) × (1/I56)
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Fe 23/ 35

24. Identifying 60
Fe - 60
Fe Spectra and Results
Blank (background) concentration
= ∼ 10−12 60Fe/56Fe
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Fe 24/ 35

25. Identifying 60
Fe - 60
Fe Spectra and Results
Fe-4 (unscaled) concentration =
(8.243 ± 0.910) × 10−10 60Fe/56Fe
Fe-4 (scaled) concentration =
(2.095 ± 0.331) × 10−9 60Fe/56Fe
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Fe 25/ 35

26. Identifying 60
Fe - 60
Fe Spectra and Results
Fe-1 (unscaled) concentration =
(8.408 ± 0.211) × 10−7 60Fe/56Fe
Fe-1 (scaled) concentration =
(2.066 ± 0.242) × 10−6 60Fe/56Fe
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Fe 26/ 35

27. Preliminary Result & Conclusion
60
Fe t1/2: (2.29 ± 0.27) · 106
years
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Fe 27/ 35

28. Combined Results with Wallner, et al.
t1/2 =
ln 2 · (1.145 × 1015 atoms)
9.7926 Bq
= (2.57 ± 0.11) × 106
years
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Fe 28/ 35

29. Preliminary Results from May 3-4, 2016
Mass 58
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Fe 29/ 35

30. Preliminary Results from May 3-4, 2016
Fe-1:
Preliminary Scaled Concentration
= (2.218 ± 0.112) × 10−6
Preliminary Half-Life =
(2.46 ± 0.12) × 106 years.
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Fe 30/ 35

31. Summary
Activity
Built low-background counting station
Measured 60m
Co state, combining for the first time with AMS
Results for Fe-1 = 9.7926 Bq
AMS
Development 60
Fe beam and AMS settings
Recommissioned second stripper for higher energy beams
Only lab to have measure Fe-1 sample directly
Results=2.218 × 10−6
Concentration
Results: 60Fe half-life = 2.46 million years
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Fe 31/ 35

32. Thank You!!!
Collaborators:
Tyler Anderson
William Bauder
Matthew Bowers
Adam Clark
Philippe Collon
Wenting Lu
Austin Nelson
Daniel Robertson
Michael Skulski
Rugard Dressler - PSI
John Greene - ANL
Walter Kutschera - VERA
Michael Paul - Racah Inst.
Dorothea Schumann - PSI
Toni Wallner - ANU
Others: NSL Staff:
Bryan Ostdiek Jeff Holdeman
Ed Lamere Jim Kaiser
Mike Moran Jerry Lingle
Mallory Smith Brad Mulder
Matt Sanford
Ed Stech
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Fe 32/ 35

33. Measuring the Activity - Old Lead Castles
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Fe 33/ 35

34. Measuring the Activity - Testing Lead Bricks
Tested almost 100 Lead bricks, including several half-bricks, each
measured for 8 hours.
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Fe 34/ 35

35. Measuring the Activity - Testing Lead Bricks
Tested almost 100 Lead bricks, including several half-bricks.
137Cs - in dirt and dust, 235U - in “modern” Lead bricks, Pb X ray,
and ROI.
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Fe 35/ 35

36. Measuring the Activity - Testing Lead Bricks
Tested almost 100 Lead bricks, including several half-bricks.
137Cs - in dirt and dust, 235U - in “modern” Lead bricks, Pb X ray,
and ROI.
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Fe 36/ 35

37. Measuring the Activity - Lead Castle renovations
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Fe 37/ 35

38. Measuring the Activity - “New” Lead Castle
2 HPGe Planar detectors with
thin Be windows (courtesy of
ANL)
Total Efficiencies of both
Detectors near 58 keV ∼10%
based on the 59.54 keV decay
in 241Am
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Fe 38/ 35

39. Preliminary Results & Conclusions
Small deviations in 60Fe/56Fe concentrations lead to significant
changes in half-life.
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Fe 39/ 35