New methods to measure the cross New methods to measure the cross sections of sections of 1212C+C+1212C fusion reactionC fusion reaction

New methods to measure the cross New methods to measure the cross sections of sections of 1212C+C+1212C fusion reactionC fusion reaction

Xiao Fang

Department of PhysicsUniversity of Notre Dame

Outline

[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

12C(12C,p)23Na12C(12C,)20Ne 12C(12C,n)23Mg

~10-11 b @ 2.1 MeV

Experimental setup for thick target

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).

0.5 pA 12C beamfrom FN tandem

target

YY1 detector

YY1 detector

The backward angleθLab: 113.5° - 163.5°θcm: 122.5° - 166.3°

Solid angle calibrated by mixed alpha source

2.59%

Focus on: 12C(12C, p)23Na

Thick target measurement

12C

p

E’reaction = Ebeam – ΔEbeam

12C p

Ereaction ≈ Ebeam

12C(12C, p)23Na

What’s the real energy of this reaction?

Why not thin target?Thickness change with carbon build-upExtremely low yield at low energies

Beam energy

Reconstructed reaction energy: Ereaction (MeV)C

ount

Red: Q(p0)=2.24 MeVBlack: Q(p1)=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

12C(12C, p)23Na

Ereaction

Q, Eproton, θ

Epr

oton

(M

eV)

Angle (deg)

Q=Qvalue-Eexcited (23Na)

P0: protons with 23Na at ground stateP1: protons with 23Na at first excited state

P0

P1

S* factor extracted from Ebeam=8.2 MeV

p0P1

Simulation with a constant S*

Ecm (MeV)

S*

fact

or (

MeV

b)

Ecm=0.5*Ebeam

S* factor from a thick target measurement

Ecm = 4.1 MeV

Scan resonances in a wide range of 3 MeV<Ecm<5.3 MeV

−Thick target−Thin target

p0

p1

S*

fact

or (

MeV

)

Ecm (MeV)

New thick target quick-scan method

Ecm (MeV)

S*

fact

or (

MeV

b)

60 nb

40 nb

0.4 mb

0.4 mb

Covers 4 orders of magnitude !

p0

p1

Combined S* factor from a series of thick target measurements

Particle-γ coincidence experiment at ANL

Gamma sphere

‘CD’ Silicon strip detector

Solid angle:7%

Beam intensity: 5 – 100 pnA

Thin target: 40 μg/cm2

Particle-γ coincidence experiment at ANL

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!

Summary

Thick target methodA 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 techniqueSuppress background to a reasonable low level

Collaborators

Thick target measurementsB. 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 ANLC.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 projectX.X. Bai, H. Esbensen, B.Guo, C.L. Jiang, W.P. Liu, K.E. Rehm and R.de Souza