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Reaction Rate of 15 O( α , γ ) 19 Ne via Indirect Measurements

15 O( ,) 19 Ne as t he trigger of X-ray bursts The present uncertainties in 15 O( ,) 19 Ne The experiment & new results for 15 O( ,) 19 Ne Interpretation & Implication. Reaction Rate of 15 O( α , γ ) 19 Ne via Indirect Measurements. Wanpeng Tan University of Notre Dame.

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Reaction Rate of 15 O( α , γ ) 19 Ne via Indirect Measurements

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  1. 15O(,)19Ne as the trigger of X-ray bursts • The present uncertainties in 15O(,)19Ne • The experiment & new results for 15O(,)19Ne • Interpretation & Implication Reaction Rate of 15O(α,γ)19Ne via Indirect Measurements Wanpeng Tan University of Notre Dame

  2. Nuclear energy release: 5 MeV/u Gravitational energy release: 200 MeV/u Luminosity [rel. units] Time [s] X-Ray Bursts as Nuclear Laboratory Fisker et al., astro-ph/0410561 (2005) Woosley et al. ApJ (2005)

  3. With breakout Without breakout The Trigger of the Bursts Wiescher & Schatz, Nucl. Phys. A 694, 269 (2001) Burst is triggered by 15O(,)19Ne and by generating additional CNO fuel via the triple α process!

  4. KVI MSU Louvain-la-Neuve ANL Yale TRIUMF RIKEN ORNL ND Many proposals and attempts to study 15O(α,γ)19Ne by direct & indirect approach • Direct measurement is difficult! • An intense (1011 /s) radioactive 15O beam gives a count rate of <1/hr (estimated at ISAC, TRIUMF, 109/s achieved at Louvain la Neuve) $ 35,000,000 • Indirect method has been approached many times! • Populate α-unbound states in 19Ne • Measure lifetimes or gamma widths17O(3He,n-γ)19Ne • Measure α-decay branching ratios Bα19F(3He,t-α)19Ne

  5. Reaction Rate of 15O(α,γ)19Ne • Reaction Rate determined by resonance energy ER and strength  • Three measurable quantities characterize the resonance strength: Jπ, Γγ, and Bα=Γα/Γtot Single resonance contribution!

  6. Bα Exp 19F(3He,t-α)19Ne Lifetime Exp 17O(3He,n-γ)19Ne Lab Layout at Notre Dame

  7. γ 19Ne target HPGe 13 fs 4 fs 29 fs 50 fs Best fit 2 limits Upper limit Previous DSAM result 3He 3MeV 28.5o 17O/Ta 90o n detector Measured lifetime τ= 13±96 fs or =51±4321 meV Lifetime measurement using the Doppler-Shift Attenuation Method • Measure lifetime to obtain decay width • Full line shape analysis

  8. Davids et al, 2003 at KVI 1H(21Ne,3H)19Ne* < 4.3x10-4 < 6x10-4 Alpha-decay branching ratios • Pursued at many places such as Yale, ANL, ORNL, Louvain-la-Neuve, KVI, TRIUMF and RIKEN • Dominant resonance of 4.03 MeV state in 19Ne • Itsbranching ratio Γα/Γ~ 10-4 Rehm et al, 2003 at ANL 3He(20Ne,)19Ne* 19Ne- coincidence • Challenges for our experiment 19F(3He,t-α)19Ne: • High statistics for coincidences • Detect low energy alpha’s about 200-500keV 15O- coincidence

  9. Experimental Setup 10% of 4π (30o) • Populate excited states in 19Ne • 3H-alpha coincidences  alpha-decay branching ratios

  10. one million of 3H populating 4.03 MeV State E 5.35 6.01 4.38 5.42 4.60 4.55 4.03 5.09 4.14 4.20 dE 4.71 Triton Energy [keV] … to reach the sensitivity of 10-4 in Bα … after two weeks

  11. 4.55 4.60 α Recoil nuclei e- p 4.03 4.71 5.09 4.14 4.20 Alpha Energy [keV] 4.55 4.60 4.38 Time Energy 4.71 5.09 Alpha Time Alpha spectra from 19Ne* decay <10-3 B= 2.9±2.1·10-4 (<4.3·10-4, Davids et al 2003) =51±4321 meV  =30±4415μeV

  12. Results of α-decay Branching Ratios • Magnus90: Magnus et al, Nucl. Phys. A 506, 332 (1990) • RIKEN: private communication from T. Motobayashi • Laird02: Phys. Rev. C 66, 048801 (2002) • Rehm03: Phys. Rev. C 67, 065809 (2003) • Davids03: Phys. Rev. C 67, 012801R (2003) • Visser04: Phys. Rev. C 69, 048801 (2004) Preliminary

  13. This Work 4.03 4.60 4.14 4.71 Rate% Langanke et al, 1986 4.55 4.38 T (GK) Reaction Rate of 15O(α,γ)19Ne Differences in detail 4.03 MeV NA<σv> (cm3/mol/s) 4.14 MeV T (GK) • More work needed for the near-threshold states

  14. Competition between breakout & β-decay 15O(α,γ)19Ne Breakout 15O β-decay t1/2=122s Xα=0.27 The 15O(,) breakout reaction rate plays a critical role in the ignition phase of the X-ray burst! XRB Density (g/cm3) Novae 15O β-decay 0.2 0.3 0.5 0.7 1 2 T (GK)

  15. Accretion Rate Dependence for XRB Steady state surface burning predicted for low accretion rates! Maccret=1017g/s=0.1·Medd

  16. 15O(α,γ) Rate & Burst Structure Low reaction rate quenches bursts Fisker et al., astro-ph/0410561 (2005) High rate  break-out  H-burning by rp-process Low rate  He-depletion & HCNO  H-burning by 3 fueled HCNO cycle New lower (1) limits  defines accretion rate limit for bursts! Maccret=1017g/s=0.1·Medd New limit of sensitivity for nuclear signatures has been reached!

  17. Present Speculation Fisker et al. in preparation

  18. Conclusion • The reaction rate of 15O(α,γ)19Ne has been determined by determining the lifetimes and branching ratios of α-unbound states in 19Ne • The results seem to provide more stringent limits on the burst behavior of accreting neutron stars. • The results will be used to constrain other X-ray burst model parameters such as accretion rate, ignition conditions ... • Future steps towards improvement requires • Precise measurement for the near threshold states (4.03, 4.14, & 4.20) in 19Ne • Direct measurement with intense radioactive beams?

  19. Acknowledgements Collaborators: W. Tan, J. Görres, J. Daly, H.Y. Lee, University of Notre Dame M. Couder A. Couture, J.L. Fisker, E. Stech

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