Dissertation Defense Presentation

Measurement of the Half-Life of 60Fe for EarlySolar System and Stellar Models

Karen M. Ostdiek

Nuclear Science Laboratory, University of Notre DameNotre Dame, Indiana U.S.A.

May 5, 2016

Motivation from Nuclear Astrophysics for 60Fe

Possible Production Sites for 60Fe

I Weak s-process, successive neutroncaptures on 58Fe.

I Massive AGB stars -13C(α, n)16O

I Core Collapse Supernova -22Ne(α, n)25Mg.

Karen Ostdiek Measuring the Half-life of 60Fe 2/ 35

Motivation from Nuclear Astrophysics & Evidence of 60FeEvidence of 60Fe

I Less of 60Ni granddaughterproduct in meteorite inclusions.

I γ decay observed in Galaxy.I Increased concentration in

ocean crust samples.

Superimposed 60Fe 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)


Recent Nature Papers


Previous Half-life Measurements

Roy & Kohman, 1957:∼ 3 · 105 yearsfactor of 3 uncertainty

Kutschera, et. al, 1984:(1.49± 0.27) · 106 years

Rugel, et. al, 2009:(2.62± 0.04) · 106 years


Measuring long half-lives and ‘making’ a Sample

A = dNdt = λN = ln2

t1/2N


Samples for Activity and AMS Experiments

Original material from PSI copper beam stop (bombarded byprotons for 12 years).


Ascertaining the Activity - Sample Evaporation

I VERA “Fe-1” 13 mL sample evaporated to

point source.

I Contains ∼ 1.4 · 1014 60Fe atoms.


Ascertaining the Activity - Decay Scheme for 60Fe

I Direct Decay: Roy andKohman

I Grow-in Decay:Kutschera, et al., Rugel,et al., and Wallner, et al.


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 60mCo = Internal Conversion.

I 2 HPGe Planar detectors withthin Be windows.

I Total Efficiencies of 10% basedon 241Am.


Ascertaining the Activity - Results

Background line at 63 keV is from 234Th in the 238U decay chainIncrease in continuum is from bremsstralung photons.

Activity Corrected = (9.7926± 0.0031) decays/second


Now on to part two...

Concentration 60/56 × (# of 59Fe atoms added) = # of 60Fe atoms


Identifying 60Fe - Facilities


Identifying 60Fe - Second Stripper


Identifying 60Fe - Wien Filter


Identifying 60Fe - AMS Beam Line


Identifying 60Fe - Separating by Position


Identifying 60Fe - Separating by EnergyEnergy = 112 MeV using 8.5 MV, Second stripper, 9+ to 16+


Identifying 60Fe - Finding Concentration

Concentration 60/56 × (# of 59Fe atoms added) = # of 60Fe atoms

Concentration 60/56 = (Count60/time)× (1/Transmission)× (1/I56)Karen Ostdiek Measuring the Half-life of 60Fe 23/ 35

Identifying 60Fe - 60Fe Spectra and Results

Blank (background) concentration= ∼ 10−12 60Fe/56Fe



Fe-4 (unscaled) concentration =(8.243± 0.910)× 10−10 60Fe/56FeFe-4 (scaled) concentration =

(2.095± 0.331)× 10−9 60Fe/56Fe



Fe-1 (unscaled) concentration =(8.408± 0.211)× 10−7 60Fe/56FeFe-1 (scaled) concentration =

(2.066± 0.242)× 10−6 60Fe/56Fe


Preliminary Result & Conclusion

60Fe t1/2: (2.29± 0.27) · 106 yearsKaren Ostdiek Measuring the Half-life of 60Fe 27/ 35

Combined Results with Wallner, et al.

t1/2 =ln 2 · (1.145× 1015 atoms)

9.7926 Bq= (2.57± 0.11)× 106 years


Preliminary Results from May 3-4, 2016

Mass 58


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.


Summary

I ActivityI Built low-background counting stationI Measured 60mCo state, combining for the first time with AMSI Results for Fe-1 = 9.7926 Bq

I AMSI Development 60Fe beam and AMS settingsI Recommissioned second stripper for higher energy beamsI Only lab to have measure Fe-1 sample directlyI Results=2.218× 10−6 Concentration

I Results: 60Fe half-life = 2.46 million years


Thank You!!!

Collaborators:Tyler AndersonWilliam BauderMatthew BowersAdam ClarkPhilippe CollonWenting LuAustin NelsonDaniel RobertsonMichael SkulskiRugard Dressler - PSIJohn Greene - ANLWalter Kutschera - VERAMichael Paul - Racah Inst.Dorothea Schumann - PSIToni Wallner - ANU

Others: NSL Staff:Bryan Ostdiek Jeff HoldemanEd Lamere Jim KaiserMike Moran Jerry LingleMallory Smith Brad Mulder

Matt SanfordEd Stech


Measuring the Activity - Old Lead Castles


Measuring the Activity - Testing Lead Bricks

Tested almost 100 Lead bricks, including several half-bricks, eachmeasured for 8 hours.


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


Measuring the Activity - Lead Castle renovations


Measuring the Activity - “New” Lead Castle

I 2 HPGe Planar detectors withthin Be windows (courtesy ofANL)

I Total Efficiencies of bothDetectors near 58 keV ∼10%based on the 59.54 keV decayin 241Am


Preliminary Results & Conclusions

Small deviations in 60Fe/56Fe concentrations lead to significantchanges in half-life.


Dissertation Defense Presentation

Science

Transcript of Dissertation Defense Presentation