Measuring the Half Life of 60Fe forStellar and Early Solar System Models

Karen M. Ostdiek

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

August 25, 2014

Motivation from Nuclear Astrophysics & Evidence of 60Fe

Production Sites for 60FeI Weak s - process, successive

neutron captures on 58Fe.I Likely sites include Massive

AGB stars and Core CollapseSupernovae (CCSNe).

Knie, K., et al. Phys. Rev Letters. 93. (2004).

Life Cycle of Massive Star.

Evidence of 60FeI in Galaxy through γ ray decay of

60Fe.I in Ocean Crust samples,

corresponding to 3 Myrs ago.I in Meteorite Inclusions, as an

enrichment of 60Ni.

Motivation from Previous Measurements

I Roy and Kohman (1957)- 3 ·105 years, factor of 3 uncertainity.

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

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

Technique for half lives of long-lived radioisotopes:

Activity, dN/dt → by Gamma Ray SpectroscopyNumber of Atoms of Interest,No → by AMS

dN

dt= −λ · No = − ln2

t1/2· No

Activity Measurement - Decay Scheme for 60Fe

60Fe

0+ 2+

60Co 5+

2.62 Myr 10.5 min

1925.28 days

60Ni

2+

4+

0+

2+ 1173 keV

1332 keV

58 keV G

row

-in D

ecay

Direct Decay

Full Decay Scheme including “Direct” and “Grow-in” Decays.

Activity Measurement - Decay Scheme for 60Fe

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.

Activity Measurement - Decay Scheme for 60Fe

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 VERA “Fe-1” sampleevaporated to point source(13% of original 100 mL).

I Contains ∼ 1.4 · 1014 60Featoms.

I Emits γ ray of 58 keV ∼ 2% ofthe time.

Activity Measurement - HPGe Planar Detector Setup

Two HPGe Planar Detectors (courtesy of ANL)

In Head-to-head geometry.

Total Efficiencies for both Detectors near 58 keV = 9 - 14 %(depending on spacing between, using 241Am source).

Activity Measurement - Results

50 55 60 65 700

50

100

150

200

250

Energy in keV

Counts

1 day Hreal timeL Runs

60Fe Sample, Fe-1

Background

The background peak at 64 keV - from 238U decay chain

→ (decay of 234Th to 234Pa)

AMS @ ND - Facilities

AMS @ ND - Spectra - 95.3 MeV at 9+ Charge State

“Fe-2” Sample, Full Beam,Expected Concentration: 2 · 10−7

“Fe-2” Sample, Shield In.

Background Run on Fe powder, ∼ 10−12,Shield In, Contaminations.

Measured 60Fe/56Fe values:"VERA Fe-4"→ (1.49± 0.04) · 10−9

“VERA Fe-3"→ (1.52± 0.03) · 10−8

"VERA Fe-2"→ (1.31± 0.03) · 10−7

“VERA Fe-1” → not measured yet.

AMS @ ND - Low Energy Injection Upgrade

Proposed Layout for new Low Energy Injection.Re-positions SNICS source, adds 45 degree Electrostatic Analyzer,adds 90 degree Analyzing Magnet, adds off - set Faraday Cups

Activity and AMS Preliminary Results & Outlook

AMSI Have also explored 10 + charge state - too many

contaminants.I Attempted 11 + charge state, 113 MeV - PromisingI Higher Energies using Second Carbon Stripper?I Experiment to double check concentrations this Fall &

measure Fe-1 Sample.

Activity

I Second Sample from VERA.I 58 days of data taking on Fe-1 Sample.I Using assumed # of 60Fe (∼ 1.4 · 1014),

Half Life - (2.33± 0.26) · 106 years - PRELIMINARY.

Thank You!!!

U. of Notre DamePhilippe CollonTyler AndersonWilliam BauderMatthew Bowers

Wenting LuDaniel RobertsonMichael Skulski

Sam Austin - MSUJohn Greene - ANL

Walter Kutschera - VERAMartin Martschini - VERA

Michael Paul - Racah InstitutePeter Steier - VERAToni Wallner - ANU