Presentation on theme: "Does the 12 C+ 12 C fusion reaction ignite superbursts?"— Presentation transcript:
Does the 12 C+ 12 C fusion reaction ignite superbursts?
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 ashes Key problem: the standard rate (CF88) is too low to explain observation! Disk Companion Neutron star
3x10 16 MeV*b Astrophysical energy range
CF88 T. Spillane et al., Strong resonance at 2.14 MeV with width <12keV; No confirmation yet. PRL98 (2007) ; R. Cooper et al., APJ (2009) 702, 660 Strong resonances at deep sub-barrier energies
24 Mg(a,a’) inelastic Search the possible resonances Direct measurement The exact cross section 12 C+ 13 C 13 C+ 13 C Provide potential to model the smooth behavior 12 C+ 13 C 13 C+ 13 C Provide potential to model the smooth behavior 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
NPA5 April 7, MV FN ND 20 e A 13 C - 2 e A 13 C 2+ Thick graphite disk Carbon stripping (100 enA) Gas stripping The 12 C+ 13 C experiment ---- 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
Eg. for 12 C+ 12 C, (E in MeV) Caltech 1983 Not good for comparing xsec among the three systems 12 C+ 13 C 12 C+ 12 C 13 C+ 13 C
Use the same conversion formula for all the three carbon systems. Good for the comparison of xsecs among the three systems!
Ah ha, 12 C+ 13 C matches with 13 C+ 13 C very well! Each data set (except our data) has additional 15%-30% systematic uncertainty arising from statistical model. The isotope difference (mass, radius) is negligible when Ecm>2.6 MeV. Two carbon isotope systems: 12 C+ 13 C and 13 C+ 13 C 1 b 20 nb 13 C+ 13 C(Trentalange)
Surprise! The 12 C+ 12 C is not enhanced but suppressed! The 12 C+ 12 C resonant xsecs of major resonances matches the xsec of the other two systems: 12 C+ 13 C and 13 C+ 13 C! Why ???? (Good question for the question session!) Three carbon isotope systems: 12 C+ 13 C, 13 C+ 13 C and 12 C+ 12 C xsec(12C+13C) or xsec(13C+13C) : Upper limit for 12C+12C 13 C+ 13 C(Trentalange)
12C+12C 12C+13C 13C+13C Above the Coulomb barrier
Extrapolation with the 12 C+ 12 C resonant cross sections 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 12 C+ 12 C resonant cross sections! 13 C+ 13 C(Trentalange)
Our theory claims: 12 C+ 13 C (or 13 C+ 13 C)> 12 C+ 12 C 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 Isotope Systematics Systematics vs. Spillane’s Experiment 13 C+ 13 C(Trentalange)
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 Systematics wins! Isotope Systematics Strong resonance At 2.14 MeV 13 C+ 13 C(Trentalange)
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
Notre Dame-ANL-IU fusion experiment A 5 MV Pelletron with ECR source in terminal. Will be installed at the end of Ecm=1.5 MeV Solenoid Spectrometer for Nuclear AstroPhysics (SSNAP) Silicon Array at Notre Dame (SAND) By comparing with the Naples experiment, our setup will increase yield by two orders of magnitude!
Summary A strong and interesting empirical correlation found among three system: 12 C+ 12 C, 12 C+ 13 C and 13 C+ 13 C. 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 24 Mg( , ’) experiment at RCNP, better data will be available soon. There are still many puzzles on the 12 C+ 12 C resonances even this topic is more than 50 years old. Hope we may solve the carbon fusion problem before the next Rutherford conference!