Does the 12C+12C 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 heatingcrust conductivity

Picture by E. Brown

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Key problem: the standard rate (CF88) is too low to explain observation!

Disk Companion

Neutron star

1.E+15

1.E+16

1.E+17

1.E+18

1.E+19

1.E+20

1 2 3 4 5 6 7

Ec.m. (MeV)

S*

(Me

V*b

)

CF88

Becker

Patterson

Aguilera

)46.0/21.87()(* EEEeES

3x1016 MeV*b

Astrophysical energy range

1.E+15

1.E+16

1.E+17

1.E+18

1.E+19

1.E+20

1 2 3 4 5 6 7

Ec.m. (MeV)

S*

(Me

V*b

)Fowler Cooper 1 Cooper 2

Becker Patterson Aguilera

Spillane

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

Strong resonances at deep sub-barrier energies

24Mg(a,a’) inelasticSearc

h the p

ossib

le

reso

nances

Direct measurement

The exact cross section

12C+13C13C+13C

Provide potential

to model the

smooth behavior

12C+13C13C+13C

Provide potential

to model the

smooth behavior

12C+13C13C+13C 12C+12C

12C(12C,n)23Mg

12C(12C,p)23Na

12C(12C,a)20Ne

12C(12C,8Be)16O

12C(12C,a)20Ne

NPA5 April 7, 2011

10 MV FN Tandem @ ND

20 eA 13C-

2 eA 13C2+

Thick graphite disk

Carbon stripping (100 enA)Gas stripping

The 12C+13C experiment

---- Full (Un-gated)---- Gated1.37MeV

2.74MeV

Ec.m.=2.83 MeV, 1puA*28hr,379 countsVery compact

beta counter

12C(13C,24Na)p

/2

22

)(

21

2

E

ZZ

EeES

E

21.872

Eg. for 12C+12C,

(E in MeV)

Caltech 1983

Not good for comparing xsec among the three systems

12C+13C

12C+12C

13C+13C

)46.0/21.87()(* EEEeES

Use the same conversion formula for all the three carbon systems.

Good for the comparison of xsecs among the three systems!

•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 negligible when Ecm>2.6 MeV.

Two carbon isotope systems: 12C+13C and 13C+13C

1 b20 nb 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!)

Three carbon isotope systems: 12C+13C, 13C+13C and 12C+12C

xsec(12C+13C) or xsec(13C+13C) : Upper limit for 12C+12C13C+13C(Trentalange)

12C+12C

12C+13C

13C+13C

Above the Coulomb barrier

Extrapolation with the 12C+12C 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 12C+12C resonant cross sections!

13C+13C(Trentalange)

•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

IsotopeSystematics

Systematics vs. Spillane’s Experiment

13C+13C(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 rateBest estimated upper limit: ~ Fowler rate* Dr. Zickefoose, U. Connecticut thesis, 2011

Systematics wins!

IsotopeSystematics

Strong resonance At 2.14 MeV

13C+13C(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!

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Notre Dame-ANL-IU fusion experiment

A 5 MV Pelletron with ECR source in terminal. Will be installed at the end of 2011.

Simulation @ 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: 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(,’) 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!

24Mg