Zagreb IP: Experimental nuclear physics inputs for thermonuclear runaway - NuPITheR Neven Soić, Ru đ er Bošković Institute, Zagreb, Croatia EuroGENESIS workshop Reactions of Astrophysical Interest Madrid Apr 2011 Carbon - Carbon Burning and Other Research Topics of Zagreb IP

Objective use of our expertise from structure and reaction studies to study nuclear reactions important for stellar explosive phenomena: novae, SnIa, X-ray bursts and super-bursts not direct low energy measurements of the reactions, focus on reactions which in astrophysically relevant energy range are likely to proceed through resonances which dramatically increase cross section of the reaction our main goal and objective is to obtain new results on the properties of these resonances and their full characterization full characterization of the resonances => obtained data will be important ingredients for calculations of improved reaction rates these indirect measurements complement direct measurements and provide useful input for setup of future direct experiments

Carbon – carbon burning Objective: search for 12 C+ 12 C resonances at 24 Mg excitations MeV and full characterization of the resonances (excitation energy, width, spin, parity, partial decay widths) Two-fold reason: nuclear structure & astrophysical motivation D. A. Bromley, J. A. Kuehner, E. Almquist, Phys. Rev Lett 4 (1960) 385 Elastic scattering data Resonant phenomena in heavy ion reaction

E. Almquist, D. A. Bromley, J. A. Kuehner, Phys Rev Lett 4 (1960) 515 Reaction data Formation of quasi- molecular states in 24 Mg 50 years later: - number of resonances decaying into various channels - kind of unique nuclear system, very complex structure - governed by cluster structure of 12 C – oblate deformation in gs - not fully understand yet

B. R. Fulton et al, Phys Lett B 267 (1991) 325 M. Freer et al, Phys Rev C 57 (1998) 1277 C. Metelko et al, Phys Rev C 68 (2003)

M. Freer et al, Phys Rev C 57 (1998) 1277 But main focus of these studies has been on higher excitations in 24 Mg No data below 20 MeV !

Low energy data for 12 C+ 12 C fusion reaction crucial for many astrophysical phenomena: quiescent burning of massive starts, super-AGB stars, super-bursts and supernovae type Ia The most relevant quantity: total reaction fusion rate 12 C + 12 C → 24 Mg +  12 C + 12 C → 20 Ne + α 12 C + 12 C → 23 Na + p 12 C + 12 C → 23 Mg + n Existing data show large discrepancies Low energy resonance ? E. F. Aguilera et al, Phys. Rev. C 73 (2006) T. Spillane et al, Phys. Rev. Lett. 98 (2007)

Stellar outbursts Bull’s eye 12 C+ 12 C fusion is differentiating between the evolutionary paths leading to either white dwarf or heavy elements burning stages most powerful events since the Big Bang (energy released in few seconds larger than Sun’s output over its entire lifetime) Gamma Ray Bursts Explosive phenomena in binary systems SNIa: initiates thermonuclear runaway on white dwarf temperature range is x10 9 K E cm = MeV Super-bursts: trigger of 12 C ignition up to 2.5x10 9 K MeV

12 C+ 16 O measurement at LNS Catania Coincident detection of 2 reaction products 12 C + 16 O → 4 He + 12 C + 12 C Q=-7.16 MeV E thr ( 24 Mg)=13.93 MeV → 4 He + 16 O + 8 Be Q=-7.37 MeV E thr ( 24 Mg)= MeV → 4 He + 20 Ne + 4 He Q=-2.54 MeV E thr ( 24 Mg)= 9.31 MeV → 4 He + 23 Na + 1 H Q=-4.92 MeV E thr ( 24 Mg)= MeV Excitation energy range: 0.5 – 6 MeV above the 12 C + 12 C threshold, 14.5 – 20 MeV in 24 Mg excitation Resonance parameters: excitation energy, width, spin, parity and partial decay widths of the resonances

Kinematics of the reaction A(a,bc)B Q = E 1 L + E 2 L + E 3 L - E 0 L

Main goal: identify low spin states with significant 12 C+ 12 C partial width Spin/parity = angular correlations M. Freer, Nucl Instr Meth Phys Res A 383 (1996) 463 All involved particles in the reaction 0 + model independent around Θ*=0

Experimental setup 16 O beam energies: 90 MeV, target: 60 μm/cm 2 carbon target

Detector telescopes: 50 x 50 mm 2 20 μm SD /500 μm PSD Particle identification from p to 12 C Test simulations: Energy resolution keV Q-value 500 keV Excitation energy resolution ( 24 Mg excitations MeV) 50 to 160 keV. Excitation energy error <50 keV

Direct measurement of 20 Ne(α, 12 C) 12 C reaction resonant reaction measurement possible experimental sites: LNS Catania, Argonne National Lab 4 He gas target – scattering chamber filled up with gas at low pressure 20 Ne beam of 60 – 100 MeV Q = MeV beam slows down through gas, at resonance energy enhanced production of 12 C+ 12 C – coincidence detection reaction products identical => particle identification using reaction kinematics measurements of angular distributions – resonance characterization pure beam and target => low background very challenging experiment

Direct measurement of 23 Na(p, 12 C) 12 C reaction resonant reaction measurement possible experimental site: LNS Catania if sodium beam from tandem will be developed beam energy 70 – 130 MeV scanning for resonances target: thick CH 2 coincidence detection, angular distributions Q = MeV possible background from carbon component of the target low energy of reaction products – particle identification problem

Expected results In summary, expected results of the measurements will provide answers to following questions: 1)How many resonances are at 24 Mg excitations 14.5 – 20 MeV ? 2)Do exist 12 C+ 12 C resonance at low excitations 14.5 – 16 MeV ? 3)If yes, what are resonance parameters ? 4)Is there any low spin resonance which may influence carbon- carbon burning ? 5)How much observed resonance affects carbon-carbon burning ? 6)Do observed resonances help in explaining 24 Mg structure ?

Resonances in 18 Ne important for reaction rates of the 14 O(α,p) 17 F and 17 F(p,  ) 18 Ne reactions at relevant energies in stellar explosions the 1 st of these reactions is important in hot CNO cycle, largely influences energy production in X-ray bursts thermonuclear runaway affecting later nucleosynthesis the 2 nd reaction is of importance for novae nucleosynthesis, escape from HCNO objective: study of 18 Ne resonances in relevant excitation energy range ( MeV) by studying decays of 18 Ne* into 14 O+α and 17 F+p measurement of the breakup of radioactive 18 Ne beam on 12 C target into 14 O+α and 17 F+p – SPIRAL GANIL

LEVEL SCHEME OF 18 Ne T 9 ~ 1.5 T 9 ~ F + p O +  T 9 ~ 0.1 main, expected contributions to reaction rate from: resonance at 6.15 MeV J  = 1 - direct contribution with =1 states at ~ 7 T  1.5x10 9 T  1.0x10 9 K Information on 14 O( ,p) 17 F reaction rate from:  level structure of 18 Ne  theoretical calculations  inverse reaction 17 F(p,  ) 14 O  some direct data

Other possible reactions for study of 18 Ne* into 14 O+α and 17 F+p Stable beam experiments, available some inclusive experimental data Proposed coincident measurements 1) 16 O( 3 He,n) 18 Ne* 2) 14 N( 10 B, 6 He) 18 Ne* 3) 20 Ne(p,t) 18 Ne*

The 18 F(p,  ) 15 O reaction Experiment approved at ORNL USA – spokesperson I. Martel Huelva, co-spokesperson N. S. RBI, Zagreb Goal: the energy, widths and spins of the relevant states in 19 Ne in a range of excitation energies between MeV; a detailed determination of the spectroscopic properties of these levels, as well as to investigate the impact in the astrophysical reaction rates Measurement of the 18 F(p,  ) 15 O reaction rate in a range of energies between MeV (CM) Measurement of the level energy, width and spin for the resonances in the region around 1089 keV, 1225 keV, 1347 keV and 1573 keV Detailed exploration the energy range between 750 keV and 1100 keV searching for possible resonances. We will as well obtain information on the 18 F(p,p) 15 O reaction which will complement information on 19 Ne resonances.

Beam 18 F beam at 80 MeV. It should be fully stripped to 9+ to reduce 18 O contamination at the analysis magnet. Estimated intensity is 10 6 pps. Targets A foil of large Z value (eg. Au 9um) will be placed at the entrance of the reaction chamber to reduce energy of the beam down to 40 MeV. Coulomb barrier for Au+F is estimated around 97 MeV, so we would expect small contribution from additional nuclear reactions. A thick target of polyethylene (CH 2 ) n of 35um (reaction target). This thickness is sufficient to stop a beam of 18F at 40 MeV Lab (2.0 MeV at CM). The target will be metalized on the back by a thin gold layer (few ug/cm2), so that data can be normalized using 18 F Au elastic scattering at backward angles. Elastic scattering will also serve as monitor of possible beam contamination. A thin carbon foil will be used during 1 shift for controlling reactions on the C ions of the target and other possible source of background.

Summary and Conclusion Main focus on carbon – carbon burning Experiment on 18 Ne resonances will be proposed at GANIL before the project end We are open for collaboration and look forward for common experiments with other IPs