1. New methods to measure the cross sections of 12 C+ 12 C fusion reaction Xiao Fang Department of Physics University of Notre Dame

2. Outline 12 C+ 12 C fusion at low energies New thick target quick-scan method Particle-Gamma coincidence experiment Future work

3. [Costantini et al., Rep. Prog. Phys. 72, 086301 (2009)] Astrophysical important energy range: 1-3 MeV Measurements at low energies suffered from low yield, low efficiency and poor selectivity. New methods are needed. Carbon fusion at low energies 12 C( 12 C,p) 23 Na 12 C( 12 C,  ) 20 Ne 12 C( 12 C,n) 23 Mg  ~10 -11 b @ 2.1 MeV

4. Experimental setup for thick target  Only measure proton channel  Two YY1 silicon detectors at backward angle, covered with Aluminum foil to stop scattered 12 C and produced alpha particles  Use thick target of thickness 1mm  Detector resolution for 5.486 MeV alpha particles is 40 keV(FWHM). 0.5 p  A 12 C beam from FN tandem target YY1 detector The backward angle θ Lab : 113.5° - 163.5° θ cm : 122.5° - 166.3° Solid angle calibrated by mixed alpha source 2.59% Focus on: 12 C( 12 C, p) 23 Na

5. Thick target measurement 12 C p E’ reaction = E beam – ΔE beam 12 C p E reaction ≈ E beam 12 C( 12 C, p) 23 Na What’s the real energy of this reaction? Why not thin target? Thickness change with carbon build-up Extremely low yield at low energies

6. Beam energy Reconstructed reaction energy: E reaction (MeV) Count Red: Q(p 0 )=2.24 MeV Black: Q(p 1 )=1.80 MeV With knowing the exact reaction Q value (Q)  Good reaction energy determination (90 keV for Elab  45 keV for Ecm). Determination of reaction energy 12 C( 12 C, p) 23 Na E reaction Q, E proton, θ E proton (MeV) Angle (deg) Q=Qvalue-E excited ( 23 Na) P 0 : protons with 23 Na at ground state P 1 : protons with 23 Na at first excited state P0P0 P1P1

7. S* factor extracted from E beam =8.2 MeV p0 P1P1 Simulation with a constant S* Ecm (MeV) S* factor (MeV b) E cm =0.5*E beam S* factor from a thick target measurement Ecm = 4.1 MeV

8. Scan resonances in a wide range of 3 MeV<E cm <5.3 MeV −Thick target −Thin target p0 p1 S* factor (MeV) Ecm (MeV) New thick target quick-scan method

9. Ecm (MeV) S* factor (MeV b) 60 nb 40 nb 0.4 mb Covers 4 orders of magnitude ! p0 p1 Combined S* factor from a series of thick target measurements

10. Particle- γ coincidence experiment at ANL Gamma sphere ‘CD’ Silicon strip detector Solid angle: 7% Beam intensity: 5 – 100 pnA Thin target: 40 μg/cm 2

11. Particle- γ coincidence experiment at ANL

12. ND-ANL-IU-CIAE carbon fusion project A 5 MV Pelletron with ECR source in terminal is being built. It is expected to deliver the first beam in Feb. 2012. 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!

13. Summary  Thick target method  A efficient thick target method has been developed at ND to map the 12 C( 12 C,p) cross section in a wide range.  It has great potential to search the potential resonances at lower energies which are crucial for astrophysics.  Particle-gamma coincident technique  Suppress background to a reasonable low level

14. Collaborators Thick target measurements B. Bucher, S. Almaraz-Calderon, A. Alongi, D. Ayangeakaa, A. Best, C. Cahillane, E. Dahlstrom, R.DeBoer, N. Paul, Q. Li, S. Lyons, M. Smith, R. Talwar, W.P. Tan and X.D. Tang Particle-Gamma measurement at ANL C.L. Jiang(PI), M. Alcorta, B.B. Back, C.M. Deibel, B. Digiovine, J.P. Greene, D.J. Henderson, R.V.F. Janssens, C.J. Lister, S.T. Marley, R.C. Pardo, K.E. Rehm, D. Seweryniak, C. Ugalde, S. Zhu, B. Bucher and X.D. Tang ND-ANL-IU-CIAE carbon fusion project X.X. Bai, H. Esbensen, B.Guo, C.L. Jiang, W.P. Liu, K.E. Rehm and R.de Souza