New methods to measure the cross
sections of 12C+12C fusion reaction
Xiao Fang
Department of Physics
University of Notre Dame
Outline
12C+12C
fusion at low energies
New thick target quick-scan
method
Particle-Gamma coincidence
experiment
Future work
Carbon fusion at low energies
[Costantini et al., Rep. Prog. Phys. 72, 086301 (2009)]
 Astrophysical
important
energy range:
1-3 MeV
s~10-11 b @ 2.1 MeV
12C(12C,p)23Na
12C(12C,)20Ne
12C(12C,n)23Mg
 Measurements
at low energies
suffered from
low yield, low
efficiency and
poor
selectivity.
 New methods
are needed.
Experimental setup for thick target
Focus on: 12C(12C, p)23Na
0.5 pmA 12C beam
from FN tandem
The backward angle
θLab: 113.5° - 163.5°
θcm: 122.5° - 166.3°
YY1 detector
target
Solid angle calibrated
by mixed alpha source
2.59%
YY1 detector
 Only measure proton channel
 Two YY1 silicon detectors at backward angle, covered with Aluminum foil
to stop scattered 12C and produced alpha particles
 Use thick target of thickness 1mm
 Detector resolution for 5.486 MeV alpha particles is 40 keV(FWHM).
Thick target measurement
12C
p
12C(12C,
p)23Na
What’s the real
energy of this
reaction?
Ereaction ≈ Ebeam
p
12C
Why not thin target?
Thickness change with carbon build-up
Extremely low yield at low energies
E’reaction = Ebeam – ΔEbeam
Determination of reaction energy
Beam energy
Red: Q(p0)=2.24 MeV
Black: Q(p1)=1.80 MeV
Count
Eproton (MeV)
P0: protons with 23Na at ground state
P1: protons with 23Na at first excited state
P0
P1
Angle (deg)
12C(12C,
p)23Na
Reconstructed reaction energy: Ereaction (MeV)
Q=Qvalue-Eexcited (23Na)
Q, Eproton, θ
With knowing the exact reaction Q value (Q)  Good reaction energy
determination (90 keV for Elab  45 keV for Ecm).
Ereaction
S* factor from a thick target measurement
S* factor extracted from Ebeam=8.2 MeV
Ecm = 4.1 MeV
Ecm=0.5*Ebeam
S* factor (MeV b)
P1
p0
Simulation with a constant S*
Ecm (MeV)
New thick target quick-scan method
Scan resonances in a wide range of 3 MeV<Ecm<5.3 MeV
S* factor (MeV)
p0
−Thick target
−Thin target
p1
Ecm (MeV)
Combined S* factor from a series of
thick target measurements
40 nb
p0
S* factor (MeV b)
0.4 mb
Covers 4 orders of magnitude !
60 nb
p1
0.4 mb
Ecm (MeV)
Particle-γ coincidence experiment at ANL
‘CD’ Silicon strip detector
Beam intensity:
5 – 100 pnA
Thin target:
40 μg/cm2
Gamma sphere
Solid angle:
7%
Particle-γ coincidence experiment at ANL
ND-ANL-IU-CIAE carbon fusion project
Solenoid Spectrometer for
Nuclear AstroPhysics (SSNAP)
Silicon Array at Notre
Dame (SAND)
Simulation @ Ecm=1.5 MeV
A 5 MV Pelletron with ECR
source in terminal is being
built. It is expected to
deliver the first beam in Feb.
2012.
By comparing with the Naples experiment, our setup will increase yield by two orders of magnitude!
Summary
Thick target method
A efficient thick target method has been
developed at ND to map the 12C(12C,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
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