1. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory The 12 C+ 12 C fusion reaction at stellar energies Xiaodong Tang (Aggie since Aug. 1997) Joint Institute for Nuclear Astrophysics, UND International Workshop on Nuclear Dynamics and Thermodynamics Texas A&M University, College Station, Texas

2. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory That is indeed a pretty interesting paper ! Michael Wiescher Director of Joint Institute for Nuclear Astrophysics

3. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Carbon burning processes in the Universe Carbon burning in the laboratory Experimental efforts at Notre Dame a) Upper limit for the 12 C+ 12 C fusion cross sections b) the 12 C( 12 C,n) 23 Mg at stellar energies c) direct measurement towards astrophysical relevant energies Summary

4. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory 20 Ne+  Light particle: p, n,  Gamma: 440 keV (p channel) 1634 keV (  channel) Fusion residue: 20 Ne, 23 Na … no success under barrier 23 Mg: decay spectroscopy

5. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory The world's first tandem accelerator installed at Chalk River in 1959. Molecular resonances in the 12 C+ 12 C fusion reaction measured by Almqvist et al., in 1960

6. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory 10 -22 b 10 -7 b 12 C( 12 C,p) 23 Na (Q=2.24 MeV) 12 C( 12 C,  ) 20 Ne (Q=4.62 MeV) 12 C( 12 C,n) 23 Mg (Q=-2.62MeV)

7. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Ignition conditions in type Ia supernovae Nucleosynthesis in massive stars Candidate for Superburst ignition Carbon burning in the universe t~10 s 10 hr E(erg)~10 39 10 41

8. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Superburst: ignited by Carbon burning Ashes from rp process (He burning) deposit in the outer crust. Crust processes (EC, pycnonuclear fusion)  crust heating  crust conductivity Picture by E. Brown (MSU) ashes Key problem: With the standard rate (CF88), the crust temperature is too low to ignite the carbon fuel!   Add artificial resonance

9. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory 24 Mg(a,a’) inelastic Search the possible Resonances at RCNP Direct measurement The exact cross section Provide potential to model the gross structure 12 C+ 13 C 13 C+ 13 C 12 C+ 12 C 12 C( 12 C,n) 23 Mg 12 C( 12 C,p) 23 Na 12 C( 12 C,a) 20 Ne 12 C( 12 C, 8 Be) 16 O 12 C( 12 C,a) 20 Ne Cross section within Gamow window (1 ~ 3MeV) 10 -22 b ~10 -7 b Cross section within Gamow window (1 ~ 3MeV) 10 -22 b ~10 -7 b

10. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 10 MV FN Tandem @ ND 20 e  A 13 C - 2 e  A 13 C 2+ Thick graphite disk Gas stripping The 12 C+ 13 C experiment at ND: model the gross structure of 12 C+ 12 C ---- Full (Un- gated) ---- Gated 1.37MeV 2.74MeV Ec.m.=2.83 MeV, 1puA*28hr,379 counts Very compact beta counter 12 C( 13 C, 24 Na)p

11. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory The new 12 C+ 13 C data follows the trend of the old data. The smallest cross section has been pushed down by a factor of 50. 1b1b 20nb

12. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory 13 C+ 13 C agrees with 12 C+ 13 C! (systematic error: ~30% not included in the graph) The isotope effect (difference in radius, mass) is negligible within the observed energy range! Where will the 12 C+ 12 C data show up?

13. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory For most energies, the 12 C+ 12 C cross sections are suppressed! Only at resonant energies, the 12 C+ 12 C cross sections matches with those of 12 C+ 13 C and 13 C+ 13 C!

14. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Below the barrier Above the barrier A simple pattern for complicated resonances For most energies, the 12 C+ 12 C cross sections are suppressed! Only at resonant energies, the 12 C+ 12 C cross sections matches with those of 12 C+ 13 C and 13 C+ 13 C! Why? 12C+12C has lowest level density in the entrance channel!

15. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Predict 12 C+ 12 C cross sections with a constrained potential 13 C+ 13 C 12 C+ 13 C 12 C+ 12 C Spillane (2007) CF88 Predicted cross section ? ? Cooper resonance (2009) Coupled channels calculation with IWBC (Esbensen)

16. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Useful Upper limit for lower energies Zickefoose [ 12 C( 12 C,p), 2010] ?? Spillane (2007) Cooper resonance (2009) H. Esbensen et al., Phys. Rev. C 84, 064613 (2011) M. Notani et al., Phys. Rev. C 85, 014607 (2012) Coupled channels calculation with IWBC (Esbensen)

17. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory If the rate can not be that high, there must be some physics missing in the superburst model. Unknown process to heat up the crust to higher temperature. Carbon burning is not the one triggering superbursts! ashes Private communication with E. Brown

18. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Measurement of 12 C( 12 C,n) 23 Mg with 3 He neutron detector array Beam Target LN 2 reservoir Turbo Pump 3 He proportional counter Polyethylene moderator Central bore for beam tube

19. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory E c.m. (MeV) ND new extrapolation based on Zickefoose’s p0+p1 measurement Dayras measurement The impact of our measurement New resonances measured by ND ND measurement covers more than half of the range E th =2.6 MeV T 9 =1.1 PRELIMINARY

20. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Carbon shell burning Carbon core burning Explosive carbon burning T9T9 Comparisons of CCN rates Preliminary

21. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Installation of the tank for the new single end 5 MV Vdg accelerator, Aug. 2011 Measurement of 12C(12C,p)23Na and 12C(12C,a)20Ne towards low energy Expect 40 p  A 12 C beam

22. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Carbon Fusion Project Approach with particle-gamma coincidence E γ (keV) E excited (MeV) 0.3 p  A*30 hr 1 evt for  1 -  0 evt for p 1 -  Using ASIC readout system provided by UW E c.m. (MeV) 0.3p  A*30hr 40p  A*30hr Thick target yield (evt/incident 12 C) Thick target yield for 12 C( 12 C,  ) 2.1 MeV Resonance

23. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Nuclear Astrophysics at Chinese JingPin Laboratory (CJPL) 12 C( ,  ) 16 O 12 C+ 12 C 14 N(p,  ) 17,18 O(p,  ) 22 Ne(p,  ) 22,23 Na(p,  ) 26 Al(p,  ) 33 S(p,  ) …. 14 C(a,  ) 14,15 N( ,  ) 18 O( ,  ) 22 Ne(a,  ) 40 Ca( ,  ) …. 22 Ne( ,n) 13 C( ,n) 12 C( 12 C,n) …… 12 C+ 16 O 16 O+ 16 O Low energy reactions provide the key for disseminating the chemical evolution of the universe from Big Bang to us! Good luck, Joe! Good luck, cyclotron!

24. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Summary “The extrapolation to low energy is VERY uncertain … and more experimental and theoretical studies are urgently needed.” W. Fowler, Nobel lecture (1983) Using Isotope fusion, the upper limit is defined. 12 C( 12 C,n) measured at stellar energies Direct measurement: particle-gamma array coupling with the forthcoming new accelerator at ND Indirect approach: 24 Mg(a,a’) 24 Mg

25. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory Collaborators ND-IU-ANL-CIAE carbon fusion project (SAND,SSNAP) University of Notre Dame: X. Fang, B. Bucher, A. Howard, J. Kolata, A. Roberts, W.P. Tan, X.D. Tang China Institute of Atomic Energy: Y.J. Li Argonne National Laboratory: H. Esbensen, C.L. Jiang, K.E. Rehm Indiana University Bloomington: R.de Souza, S. Hudan The 12 C( 12 C,n) 23 Mg project B. Bucher, X. Fang, J. Browne, A. Alongi, C. Cahillane, E. Dahlstrom, A. Moncion, W. Tan, M. Notani, X.D. Tang, 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. Wiescher, M. Beard, M. Pignatari

26. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory 24 Mg 24 Mg(α, α’) measurement at RCNP University of Notre Dame: X. Fang, B. Bucher, G.Berg, R. DeBoer, U. Garg, J. Goerres, A. Long, R. Talwar, X.D. Tang, M. Wiescher Kyoto University: T. Kawabata, N. Yokota, K. Tomosuke, Y. Matsuda, T. Kadoya Osaka University: A. Tamii, H. Fujita, Y. Fujita, K. Hatanaka, B. Liu, K. Miki Niigata University: T. Itoh Texas A&M University: Y.-W. Lui University of Birmingham: M. Freer