1. Recoil charge state distributions in 12C(a,g)16O at DRAGON
Joel Zylberberg Simon Fraser University
TRIUMF Student Symposium
Aug. 2, 2006

2. TRIUMF Student Symposium 02/08/2006
Outline
Astrophysical importance of 12C(a,g)16O
The DRAGON to study nuclear astrophysics
Yield determination at DRAGON
Charge state distributions (CSD’s)
Measurements
Simulations
Conclusions
TRIUMF Student Symposium 02/08/2006

3. Astrophysical importance of 12C(a,g)16O
Red giant stars
He-Burning
3a  12C
12C(a,g)16O
16O or 12C from He-burning?
HST image of red giant Mira
TRIUMF Student Symposium 02/08/2006

4. TRIUMF Student Symposium 02/08/2006
The DRAGON
At ISAC-TRIUMF
a and p capture reactions: He and H targets
Recoil mass separator
Magnetic dipole: q/m and momentum
Electric dipole: q/m and energy
TRIUMF Student Symposium 02/08/2006

5. Yield calculations at DRAGON
Beam and recoils in several charge states; DRAGON selects one of them
Need to know:
Number of recoils
Number of beam ions
Detector efficiency
Charge state fraction 
Measuring and modeling CSD’s!
TRIUMF Student Symposium 02/08/2006

6. TRIUMF Student Symposium 02/08/2006
Measuring CSD’s
FC4: incident beam current
FC1: after target (all charge states)
FCCH: after dipole (only the selected charge state)
Target thickness ~ pressure  repeat at different pressures
TRIUMF Student Symposium 02/08/2006

7. Charge-state distributions
Collisions in gas
Electron gain/loss
Equilibrium eventually reached
CSD of C3+ beam in He at 12.8 MeV
TRIUMF Student Symposium 02/08/2006

8. TRIUMF Student Symposium 02/08/2006
CSD evolution
Coupled differential equations  solve numerically
s = charge-changing cross-section
Equilibrium condition 
That was (fairly) simple.
What about the recoils?
TRIUMF Student Symposium 02/08/2006

9. TRIUMF Student Symposium 02/08/2006
CSDsim code
Want to predict recoil CSD
Perform fit to CSD data to get cross-sections for C and O in He
Calculate beam CSD numerically
In each step:
Add recoils
Evolve CSD of recoils
CSD of 9.6 MeV O3+ beam in He target as a function
of target thickness. Data from ERNA (DRAGON-like
facility in Germany) [Shurmann et al. NIMA 531 (2004) 428]
TRIUMF Student Symposium 02/08/2006

10. TRIUMF Student Symposium 02/08/2006
CSDsim
What happens during fusion?
2 main scenarios
PU0e: Recoil Picks Up No Electrons (qrecoil = qbeam +2)
PU2e: Recoil Same Charge as Beam ion (qrecoil = qbeam)
TRIUMF Student Symposium 02/08/2006

11. TRIUMF Student Symposium 02/08/2006
CSDsim
Model agrees with data
Labels:
PU0e - no e- capture during fusion
PU2e – recoil picks up both e- during fusion
Predictions converge for thick target
F6/F5 in recoils: data from DRAGON compared to CSDsim predictions
TRIUMF Student Symposium 02/08/2006

12. TRIUMF Student Symposium 02/08/2006
Summary
12C(a,g)16O important in astrophysics
DRAGON detects 1 charge state of recoils
CSDsim predicts charge state fractions: first successful modeling of recoil CSD
No electrons captured during fusion, in this reaction (at this energy)
12C(a,g)16O data analysis improved
TRIUMF Student Symposium 02/08/2006

13. TRIUMF Student Symposium 02/08/2006
Acknowledgements
Thanks to:
D. Hutcheon & the DRAGON group
D. Shürmann at ERNA
TRIUMF
You, for your attention
Questions? Comments?
HST image of red supergiant Betelgeuse (Alpha Orionis)
TRIUMF Student Symposium 02/08/2006

14. TRIUMF Student Symposium 02/08/2006
DRAGON data analysis
In this particular reaction  PU0e behavior seen (can be modeled)
May not always be PU0e
To improve data analysis:
Continue studying CSD’s of recoils (see if always PU0e)
Use a post-stripper (gas or foil)
Use a very thick target
Measure recoil CSD each time a new reaction is measured
TRIUMF Student Symposium 02/08/2006

15. Changing fusion cross-section
Resonance phenomenon
As beam loses energy in target, fusion cross-section changes
TRIUMF Student Symposium 02/08/2006