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Does the 12 C+ 12 C fusion reaction ignite superbursts?

Does the 12 C+ 12 C fusion reaction ignite superbursts?. Disk. Companion. Crust processes (EC, pycnonuclear fusion) crust heating crust conductivity. Neutron star. Superburst: ignited by Carbon burning. ashes. Ashes from rp process (He burning) deposit in the outer crust.

keane-byers
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Does the 12 C+ 12 C fusion reaction ignite superbursts?

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  1. Does the 12C+12C fusion reaction ignite superbursts?

  2. Disk Companion • Crust processes(EC, pycnonuclear fusion) • crust heating • crust conductivity Neutron star Superburst: ignited by Carbon burning ashes Ashes from rp process (He burning) deposit in the outer crust. Key problem: the standard rate (CF88) is too low to explain observation!  Picture by E. Brown

  3. 3x1016 MeV*b Astrophysical energy range

  4. Strong resonances at deep sub-barrier energies CF88 T. Spillane et al., Strong resonance at 2.14 MeV with width <12keV; No confirmation yet. PRL98 (2007) 122501; R. Cooper et al., APJ (2009) 702, 660

  5. 12C+13C 13C+13C 12C+13C 13C+13C 12C+13C 13C+13C Provide potential to model the smooth behavior Provide potential to model the smooth behavior 12C(12C,a)20Ne 12C(12C,a)20Ne 12C(12C,p)23Na Direct measurement The exact cross section 12C(12C,n)23Mg Search the possible resonances 24Mg(a,a’) inelastic 12C(12C,8Be)16O 12C+12C

  6. ---- Full (Un-gated) ---- Gated The 12C+13C experiment Carbon stripping (100 enA) Gas stripping 2 emA 13C2+ 1.37MeV 20 emA 13C- 2.74MeV Thick graphite disk 12C(13C,24Na)p Ec.m.=2.83 MeV, 1puA*28hr,379 counts Very compact beta counter 10 MV FN Tandem @ ND NPA5 April 7, 2011

  7. Caltech 1983 13C+13C Eg. for 12C+12C, 12C+13C (E in MeV) 12C+12C Not good for comparing xsec among the three systems

  8. Use the same conversion formula for all the three carbon systems. Good for the comparison of xsecs among the three systems!

  9. 1 mb 20 nb Two carbon isotope systems: 12C+13C and 13C+13C 13C+13C(Trentalange) • Ah ha, 12C+13C matches with 13C+13C very well! • Each data set (except our data) has additional 15%-30% systematic uncertainty arising from statistical model. • The isotope difference (mass, radius) is negligiblewhen Ecm>2.6 MeV.

  10. xsec(12C+13C) or xsec(13C+13C) : Upper limit for 12C+12C Three carbon isotope systems: 12C+13C, 13C+13C and 12C+12C 13C+13C(Trentalange) • Surprise! The 12C+12C is not enhanced but suppressed! • The 12C+12C resonant xsecs of major resonances matches the xsec of the other two systems: 12C+13C and 13C+13C! • Why ???? (Good question for the question session!)

  11. 12C+13C 12C+12C 13C+13C Above the Coulomb barrier

  12. Extrapolation with the 12C+12C resonant cross sections 13C+13C(Trentalange) • Fit resonant cross sections with ESW (Best upper limit) • CC-AW calculation (always over-predict xsecs at low Es, Safe upper limit ) • The first quantitative description of the 12C+12C resonant cross sections!

  13. Systematics vs. Spillane’s Experiment 13C+13C(Trentalange) Isotope Systematics • Our theory claims: 12C+13C (or 13C+13C)> 12C+12C • The strong resonance at 2.14 MeV: • the failure of our empirical relationship ? • No confirmation of the 2.14 MeV yet: • it may be a mistake in …..? Strong resonance At 2.14 MeV

  14. Systematics wins! 13C+13C(Trentalange) Isotope Systematics • The preliminary data from the recent experiment at Naples*SUPPORT our finding! • No evidence for strange strong resonance! • For the Ecm=1.5 MeV resonance: • Safe upper limit: 6 x Fowler rate • Best estimated upper limit: ~ Fowler rate • * Dr. Zickefoose, U. Connecticut thesis, 2011 Strong resonance At 2.14 MeV

  15. ashes • 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!

  16. Notre Dame-ANL-IU fusion experiment Silicon Array at Notre Dame (SAND)  Solenoid Spectrometer for Nuclear AstroPhysics (SSNAP)  A 5 MV Pelletron with ECR source in terminal. Will be installed at the end of 2011. Simulation @ Ecm=1.5 MeV By comparing with the Naples experiment, our setup will increase yield by two orders of magnitude!

  17. Summary • A strong and interesting empirical correlation found among three system: 12C+12C,12C+13C and 13C+13C. • First empirical upper limit rules out the possibility of strong resonances at 1.5 MeV and 2.14 MeV. Impose new constrain on superburst model. • With new detector + new accelerator building at ND and 24Mg(a,a’) experiment at RCNP, better data will be available soon. • There are still many puzzles on the 12C+12C resonances even this topic is more than 50 years old. • Hope we may solve the carbon fusion problem before the next Rutherford conference!

  18. 24Mg

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