Radiative Capture Experiments at ISAC

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Radiative Capture Experimentsat ISAC

• Christof Vockenhuber
• for the DRAGON collaboration

Vancouver, Canada
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ISAC LINACS Energy 0.15 1.8 A MeV Pulse
Separation 86 ns Masses m/q lt 30 amu/e
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Experiments at DRAGON
27Si
25Al
27Al
26Al
22Mg
23Mg
24Mg
25Mg
20Na
21Na
21Na
22Na
23Na
18Ne
19Ne
20Ne
21Ne
22Ne
17F
18F
16O
15O
14O
15N
14N
13N
12C
13C
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Astrophysical Reaction Rate
Reaction rate Resonance strength Measured
Yield (recoil/beam)
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Experiments at DRAGON
R 1.0 m Angle 50 Gap 100 mm B 0.6 T
Inverse Kinematics
R 2.0 m Angle 20 Gap 100 mm V 200 kV
R 0.813 m Angle 75 Gap 120 mm B 0.8 T
Energy spread a few percent -gt achromatic
system Cone angle a few 10 mrad -gt large
gaps, large detectors
R 2.5 m Angle 35 Gap 100 mm V 160 kV
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Beam Suppression
S. Engel et al., NIM A 553 (2005) 491
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DRAGON Gamma Array
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22Na formation NeNaMg cycle
22Na(p,g)23Mg E1023 (J.Caggiano) DRAGON
U.o.Wash.
INTEGRAL
21Na(p,g)22Mg E824 (J.DAuria) DRAGON
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23
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Mg
Mg
Mg
11.3s
3.8s
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22
23
Na
Na
Na
22.5s
2.6yr
20
21
22
Ne
Ne
Ne
1.275 MeV
22Na not observed by COMPTEL or INTEGRAL
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Measurement of 21Na(p,g)22Mg

• 21Na beam on hydrogen target
• Scanned over each resonance in small energy steps
• Detected recoils in singles or in coincidence
  with prompt gammas

22Mg recoils in DSSSD (singles) ER738 keV
Excitation function for ER821 keV
22Mg
21Na
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Results resonance strengths 21Na(p,?)22Mg
PRC 69 (2004) 065803

• Received 21Na beam (? 2 x 109600 epA)
• Determined resonance strengths for seven states
  in 22Mg between 200 and 1103 keV
• DRAGON operations
• - used DSSSD as focal plane detector
• - used beta activity, FC and elastics for flux
• - used BGO gamma despite high ? bgd.

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Estimated reaction rate for 21Na(p,g)22Mg based
on new DRAGON data

• The lowest measured state at 5.714 MeV (Ecm 206
  keV) dominates for all novae temperatures and up
  to about 1.1 GK
• Updated nova models showed that 22Na production
  occurs earlier than previously thought while the
  envelope is still hot and dense enough for the
  22Na to be destroyed
• This results in lower final abundance of 22Na
• Reaction not significant for X-ray burst

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• t½ 7.2 x 105 yr
• Eg 1809 keV
• COMPTEL ? 2 Msolar
• RHESSI, INTEGRAL
• ? 2.80.8Msolar
• Concentration in star forming regions young
  massive progenitors
• CCSN (O-Ne shell and H-shell)
• Wolf-Rayet phases
• AGB, Novae (O-Ne)?

26Al in the Galaxy
RHESSI
SPI
60Fe/26Al ratio measured (RHESSI and
SPI) 60Fe/26Al 0.11 0.03
Harris, M.J. Astronomy Astrophysics 433 (2005)
(SPI result)
Smith, D.M. ApJ 589, L55 (2003)
Knodlseder, J. New Astronomy Reviews 48 (2004)
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MgAl cycle
26gAl(p,g)27Si, 26mAl(p,g)27Si E989,E990 (C.
Ruiz and A. Murphy) DRAGON and
TUDA
25Al(p,g)26Si E922 (A.Chen) DRAGON
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Si
Si
Si
4.16s
2.21s
25
27
26
Al
Al
Al
7.18s
0.717Myr
6.35s
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25
26
Mg
Mg
Mg
1.809 MeV
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Analysis - Yield
leaky beam

• Primary cut on 21 m separator time-of-flight
• 200 ns TOF window
• Background subtraction from large ( 5 ms) cut
  checked with fit to leaky energy distribution
• Modest energy cuts
• 201 keV/u ? 119 14
• 197 keV/u ? 28 6
• 225 keV/u ? lt 3.72(90)

27Si
201 keV/u data
197 keV/u data
200ns t.o.f cut
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Analysis resonance energy
27Si t.o.f cut
Background cut

• Centroid of z-distribution
• of primary gamma hits gives resonance position to
  1cm accuracy
• Translates to error of 1 keV
• Distribution modeled with GEANT, compared with
  other strong, narrow resonance reactions
• 4s deviation from previous measurement leads
  to 15 change in exponential

Z-distribution (along beam-axis) of BGO hits
ER1841 keV
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Results and Implications

• Resonance strength 35 5 sys 4 stat meV - (c.f
  Vogelaar 55 9 meV)
• Combined with new resonance energy, up to 20
  reduction of reaction rate over Gamow window for
  typical O-Ne nova
• Representative case 1.25 Msolar accreting O-Ne
  white-dwarf onset to explosion ejection,
  spherically symmetric, implicit, Lagrangian
  hydro- code (J. José, UPC-IEEC)
• Net reduction of 26gAl(p,g)27Si rate favours 26Al
  synthesis mean ejecta yield 0.07 by mass
• Supports paradigm of secondary nova contribution
  to Galactic 26Al distribution
• Exact contribution uncertain because (mostly) of
  25Al(p,g)26Si rate

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COMPTEL
CGRO
Cas A
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Role of 44Ti in Astrophysics

• laboratory half-life of 60.0 /- 1.0 years
• decay through electron capture
• if ionized half-life becomes longer
• produced in supernovae
• indication of relatively recent supernovae
• alpha-rich freeze-out just above the collapsing
  core
• observed quantity of 44Ti depends critically on
  mass-cut
• understanding of production requires reliable
  reaction rates
• dominated by 4 reactions
• 3a process 44Ti(a,p)47V
• 45V(p,g)46Cr 40Ca(a,g)44Ti

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44Ti identification Ionization chamber
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44Ti identificationIonization chamber g ray
coinc.
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Excitation function 40Ca(a,g)44Ti
1.0 T9
temperature regime
2.8 T9
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Summary

• 21Na(p,g)22Mg completed, seven resonances
  measured, uncertainty of 22Na calculation largely
  reduced
• 26gAl(p,g)27Si completed, lower reaction rate
  gt 20 increase of 26gAl yield in novae
• 40Ca(a,g)44Ti measurement completed, analysis
  under way, higher yield compared to prompt g ray
  data but lower than integral measurement
• 12C(a,g)16O cascade transition via the 6.049
  MeV state found to be nonnegligible, S6.0(300
  keV) about 10 of total S(300 keV)

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DRAGON Collaboration (over the years)
Graduate Students Present Chris Ouellet
(McMaster) Anuj Parikh (Yale) Chris
Wrede (Yale) Catherine Deibel (Yale)
Luke Ericsson (Mines) Bing Guo
(Beijing)
Postdocs Chris Ruiz Mike Trinczek
Christof Vockenhuber Jonty Pearson (McMaster)
Götz Ruprecht Cybele Jewett (Mines)
Non-Canadian Faculty Major
Collaborators Peter Parker (Yale) Uwe Greife
(Mines) Alison Laird (York)
Visitors Walter Kutschera (Vienna) Anton
Wallner (Vienna) Michael Paul (Israel) Mark
Huyse (Leuven) Brian Fulton (York) David
Jenkins (York) Weiping Liu (Beijing) Alex
Murphy (Edinburgh) Jordi Jose (Barcelona) Dieter
Frekers (Münster)
TRIUMF Research Scientists Dave Hutcheon
Jac Caggiano Lothar Buchmann Art
Olin Joel Rogers Marcello Pavan
Barry Davids
Canadian Faculty Alan Chen (McMaster)
John DAuria (SFU) Ahmed Hussein (UNBC)