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Searching for the Low-Energy Resonances in the 12C(12C,n)23Mg
Reaction Cross Section Relevant for S-Process Nucleosynthesis
Brian Bucher
University of Notre Dame
Outline
• 12C(12C,n)23Mg in the weak s-process & rate uncertainty
• Measurement at ND via 23Mg decays
• Prediction based on mirror system 12C(12C,p)23Na
• Measurement at ND via n-detection
• Results & astrophysical implications
Effect on Carbon-Shell Yields
Pignatari, Priv. Comm.
12C(12C,n) rate varied by factors 2, 5, 10
• T9=1.1• Results are model-
dependent
• Becker et al. 1981• Spillane et al. 2007
Typical C-shell burning
19771969
Uncertainty in Reaction Rate
• Resonances form important contribution to excitation function
• Resonance structure continues to lowest energies
• Current rate cannot account for resonances
12C(12C,n)23Mg
12C+12C12C+12C→+20Ne →p+23Na →n+23Mg
?
Q=+4.6 MeVQp=+2.2 MeVQn=-2.6 MeV
Low E resonances measured in total fusion x-section
1st Measurement of 12C(12C,n)23Mg at Notre Dame
Online -rays for p & channel
Our Setup
Detect Detect ++ from from 2323Mg decay Mg decay (t(t1/21/2=11s)=11s)
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
Experimental Results
• Measured finer step size over large energy range
• Consistent with others
Note consistent resonance energies
PRELIMINARY
Difficult to measure lower
• Low cross-section
• Increasing background due to reactions with H/D
Neutron to proton ratio predictions from EMPIRE
0
0.2
0.4
0.6
0.8
2.5 3.5 4.5 5.5 6.5
Ecm
n0/p0
n1/p1
n2/p2
Becker et al. Z. Phys. A303, 305-312 (1981)
• n-channel difficult to measure at low E
• Can p-channel(s) provide useful information for n-channel
24Mg*n2
n1
n0
12C 12C p2
p1
p0
MirrorNuclei
Low-Energy Extrapolation
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
Becker pred.
n-channel prediction using Becker et al. p-channel measurements
1. Gross structure reproduced
2. Energy & strength mismatch
3. Low-E resonance predictedPerform measurement at ND to check these results…..
The backward angleθLab: 113.5° - 163.5°θcm: 122.5° - 166.3°
Solid angle calibrated by mixed alpha source
2.59%
3 MeV<Ecm<5.7 MeV
0.5 pA 12C beamfrom FN tandem
target
YY1 detector
YY1 detector
Focus on: 12C(12C, p)23Na
More details are available in
Thursday, May 31, Session 27: Nuclear Astrophysics-3, Room 3: PECAN5:50-6:10 pm Experimental Investigations Of Stellar 12C+12C Fusion Toward Extremely Low Energies by Direct And Indirect MethodsXiao Fang, University of Notre Dame, Notre Dame, Indiana, USA
Extrapolation Using New Measurement
PRELIMINARY
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n6 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n6 prediction
n4+n5 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n4-n6 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n4-n6 prediction
n3 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n3-n6 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n3-n6 prediction
n2 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n2-n6 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n2-n6 prediction
n1 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n1-n6 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
n1-n6 prediction
n0 prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
Total n prediction
S* (MeV b)
0
5E+14
1E+15
2E+15
2E+15
3E+15
3E+15
4E+15
4E+15
5E+15
5E+15
2.5 3 3.5 4 4.5 5 5.5 6 6.5
Ecm
Patterson et al.
Dayras et al.
ND Decay Meas.
CF-Dayras
Becker pred.
ND Prediction
Assumed isotropic angular distribution
1. Better overall agreement
2. Low-E resonance not as strong
2nd Measurement: Direct detection of neutrons using 3He array
BeamTarget
LN2 reservoir
Turbo Pump3He proportional counter
Polyethylene moderator
Central bore for beam tube
Thick Target Detected Neutron Yield per Incident 12C
1.00E-14
1.00E-13
1.00E-12
1.00E-11
2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40 3.60 3.80 4.00
Ecm
Standard Graphite
2H Background
1. Improved detection efficiency (>40%)
2. Low-E measurements hindered by D(12C,n)
Thick Target Detected Neutron Yield per Incident 12C
1.00E-15
1.00E-14
1.00E-13
1.00E-12
1.00E-11
2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40 3.60 3.80 4.00
Ecm
Standard Graphite
HOPG Graphite
HOPG graphite much cleaner!
Highly Ordered Pyrolytic Graphite (renewable surface)
Thick Target Neutron Yield Curves
Thick Target Detected Neutron Yield per Incident 12C
1.00E-16
1.00E-15
1.00E-14
1.00E-13
1.00E-12
1.00E-11
2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40 3.60 3.80 4.00
Ecm
Standard Graphite
HOPG Graphite
13C Background
Use 13C beam to measure background component 13C(12C,n)
Thick Target Detected Neutron Yield per Incident 12C
1.00E-16
1.00E-15
1.00E-14
1.00E-13
1.00E-12
1.00E-11
2.00 2.50 3.00 3.50 4.00
Ecm
Standard Graphite
HOPG Graphite
13C Background
2H Background
Flat Background
Flat component presumably D(12C,n) (target or beam line)
PRELIMINARY
Astrophysical S* Factor 12C(12C,n)23Mg(MeV b)
0
5E+14
1E+15
1.5E+15
2E+15
2.5E+15
2.5 3 3.5 4 4.5
Ecm
Dayras et al.
ND Decay Meas.
ND Prediction
CF-Dayras
Results
Astrophysical S* Factor 12C(12C,n)23Mg(MeV b)
0
5E+14
1E+15
1.5E+15
2E+15
2.5E+15
2.5 3 3.5 4 4.5
Ecm
Dayras et al.
ND Decay Meas.
ND Prediction
ND n detection
CF-Dayras
Good agreement with prediction!
3.4 MeV resonance confirmed as predicted (p0 & p1)
Detector efficiency from Geant4
PRELIMINARY
Astrophysical Rate Sensitivity to Remaining Excitation Function
Resonance below 3.0 MeV from Zickefoose PhD thesis, UConn 2010
• Measured p0+p1 from HOPG
• Assumed isotropic distribution
• Here we assume full strength to p0 channel
n0 prediction (n1 closed)
Typical shell-carbon burning
Predict a maximum of 2x enhancement for weak s-process due to potential resonances at lower energies
Summary
• 12C(12C,n) can be an important component to the weak s-process
• Reaction measured via 2 different methods at ND• 1st measurement at energies of astrophysical
relevance• Mirror system-based prediction provides good
agreement• Uncertainty in rate is reduced with new
measurements
Thank You!
Collaborators: X. Fang, J. Browne, A. Alongi, C. Cahillane, E. Dahlstrom, A. Moncion, W. Tan, M. Notani, X.D. Tang
Nuclear Science Lab: S. Almaraz-Calderon, A. Ayangeakaa, A. Best, M. Couder, J. DeBoer, W. Lu, D. Patel, N. Paul, A. Roberts, R. Talwar, A. Kontos,
M. Smith, S. Lyons, Q. Li, K. Smith, A. Long, M. Beard, M. Wiescher
