1. The Role of 12 C( 12 C,n) in the Astrophysical S-Process Brian Bucher University of Notre Dame

2. Why study 12 C( 12 C,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

3. Effect on Abundances Pignatari, Priv. Comm. Results are model dependent----- 12 C( 12 C,n) rate varied by factors 2, 5, 10

4. Measuring 12 C( 12 C,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

5. Experiment Beam  Counter Ge Detector Catcher Wheel

6. 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, 13 C) PRELIMINARY

7. Mirror Symmetry: A New Way to Extrapolate Extrapolation based on mirror system 12 C( 12 C,p) – Lower energy measurements (Q=+2.2MeV) – Structure effects should be same for both Use statistical model to calculate ratio  n i )/  p i )

8. 12 C( 12 C,p i ) 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

9. 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

10. 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

11. Summary 12 C( 12 C,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

12. 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