The Role of 12C(12C,n) in the Astrophysical S-Process

Brian BucherUniversity of Notre Dame

Why study 12C(12C,n)?• Possible important contribution to weak s-process

– Occurs in massive stars– Not well understood– Responsible for 60<A<90

• Reaction not well-studied; uncertain astrophysical reaction rate

Typical C-shell burning

Effect on AbundancesPignatari, Priv. Comm.

Results are model dependent-----12C(12C,n) rate varied by factors 2, 5, 10

Measuring 12C(12C,n)• Patterson et al. 1969: thin target, count +• Dayras et al. 1977: thin target, count 440 &

511 keV• Notre Dame 2011: thin & thick targets, count

+

Online -rays for p & channel

Experiment

Beam

Beam

CounterGe Detector

Catcher Wheel

Results

• Largest range and finest step size ever measured• Used thin and thick targets with consistent results

Low E measurments hindered by low yield, high background…. (H contamination, cosmic rays, 13C)

PRELIMINARY

Mirror Symmetry: A New Way to Extrapolate

• Extrapolation based on mirror system 12C(12C,p)– Lower energy measurements

(Q=+2.2MeV)– Structure effects should be

same for both

• Use statistical model to calculate ratio ni)/pi)

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

12C(12C,pi) Measurements!

• Use Becker et al. 1981 measurements for extrapolation• Experiment at ND (2 weeks ago) to provide check for Becker

et al. measurements

Becker et al. 1981

YY1 Si strip detectors

Detector chamber at ND

New Extrapolation

• Number of resonances reproduced, but strength & position needs improvement

• Preliminary ND results indicate better agreement

Target effect!Thick target for low E measurement

Low E resonance!

PRELIMINARY

New Reaction Rate

• Renormalize and align Becker prediction with experimental data

• Rate sensitive to low energy resonance– Position and strength need to be precisely determined

• Factor 5 increase in rate at shell carbon burning temperatures

Typical C-shell temp

Best rate prediction

PRELIMINARY

Summary

• 12C(12C,n) likely has a significant impact in the weak s-process and synthesis of light-heavy elements

• Presence of low energy resonance(s) could have dramatic effect on reaction rate

• Improved extrapolation can provide important constraints for stellar models

• Additional measurements and nucleosynthesis calculations coming soon

Thank You!

Collaborators: X.D. Tang, X. Fang, J. Browne, A. Alongi, C. Cahillane, E. Dahlstrom, A. Moncion, W. Tan, M. Notani

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