Recoil charge state distributions in 12C(a,g)16O at DRAGON

1
Recoil charge state distributions in 12C(a,g)16O
at DRAGON

• Joel Zylberberg
  Simon Fraser University
• TRIUMF Student Symposium
• Aug. 2, 2006

2
Outline

• Astrophysical importance of 12C(a,g)16O

• The DRAGON to study nuclear astrophysics
• Yield determination at DRAGON
• Charge state distributions (CSDs)
• Measurements
• Simulations
• Conclusions

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
4
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

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 CSDs!
6
Measuring CSDs

• 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

7
Charge-state distributions

• Collisions in gas
• Electron gain/loss
• Equilibrium eventually reached

CSD of C3 beam in He at 12.8 MeV
8
CSD evolution

• Coupled differential equations ? solve
  numerically
• s charge-changing cross-section

• Equilibrium condition ?

That was (fairly) simple.
What about the recoils?
9
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
10
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)

11
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
12
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

13
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)
14
DRAGON data analysis

• In this particular reaction ? PU0e behavior seen
  (can be modeled)

• May not always be PU0e
• To improve data analysis
• Continue studying CSDs 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

15
Changing fusion cross-section

• Resonance phenomenon
• As beam loses energy in target, fusion
  cross-section changes