Philip Salter School of Physics & Astronomy

1. Philip Salter School of Physics & Astronomy Time-reversed measurement of the 18Ne(a,p)21Na cross section relevant to breakout from the Hot-CNO cycle in X-ray bursts

2. Outline • Overview of X-ray bursts • Outline of relevant nuclear processes • Experimental investigation • Preliminary results • Summary

3. X-ray Bursts • Satellite observations • Beppo-SAX, RXTE, CHANDRA • Sudden, intense emissions of X-rays • Fast rise time (1-10 s) • Duration (~10-100 s) • Some show double peak at max • J. L. Fisker et al,: ApJ 608 (2004) L61-L64 • Recurrence intervals (several hours - days)

4. X-ray bursts: mechanism • Neutron star + less evolved star • H-rich matter transfer from companion to surface of Neutron star • H-burning ignition at base of accreted layer • No cooling on degenerate matter • Leading to thermonuclear runaway • and cataclysmic outburst of energy http://hubblesite.org/newscenter/newsdesk/archive/releases /2000/24/video/a What processes are responsible?

5. (p,) (,) (,p) (p,) (b+) X-ray bursts: Hot-CNO breakout • T9 ~ 0.8: breakout through 18Ne(α,p)21Na onset of rp-process 22Mg 21Na breakout from HCNO 18Ne 17F 18F stable unstable 14O 15O 16O HCNO 13N 14N 15N 13C 12C

6. 18Ne(α,p)21Na ↔21Na(p,α)18Ne • 18Ne(α,p)21Na studies hampered by low RIB intensities Bradfield-Smith et al., Phys. Rev. C59 (1999) 3402 Groombridge et al., Phys. Rev. C66 (2002) 055802 • Alternative approach: study time-reversed 21Na(p,α)18Ne process Ecm = 1.3 – 2.6 MeV T = 0.9 – 2.7 GK • Detailed balance theorem • gs to gs only • High beam energy • Ecm(α,p) 2.63 MeV ↔ Ecm(p,α) 5.27 MeV • Elab = 5.476 MeV/u 1.890 MeV 18Ne + α Q = 2.6373 MeV 21Na + p 8.1390 MeV 5.5018 MeV 22Mg

7. TRIUMF UK DETECTOR ARRAY (TUDA) • Configurable (and mobile!) charged particle detector array geometry optimised per experiment • Nuclear Astrophysics reactions with charged particle channels eg. (p,p), (p,α), (α,p), (d,p) see C.Beer et al. Phys. Rev. C(R) accepted for publication • Operating at ISAC I since 2000 beam energies ~ 0.15-1.5 MeV/u • Operating at ISAC II since 2009 beam energies to ~ 6 MeV/u time reversal studies now possible

8. Experimental Approach • Inverse kinematics forward focussed, high coincidence detection efficiency • Detect 4He + 18Ne coincidences • Select events PI (Z=10, Z=2), dt, df, Q-value S2-S2 ∆E-E Telescope θlab = 6o-20o CD-PAD ∆E-E Telescope θlab = 1.5o-6o 4He ~ 4.1 – 5.5 MeV/u 21Na5+ I ~ 5x106 /s 330 g/cm2 (CH2)ntarget 18Ne

9. 4He Kinematic Loci

10. E[18Ne] vs E[4He] Locus

11. Preliminary 18Ne(α,p)21Na Cross Section PRELIMINARY • Lowest energy measurement to date in astrophysical window (900-1700 keV) • Agreement with Hauser Feshbach (HF)

12. Summary • Measure 18Ne(a,p)21Na via time reversed reaction • Measurements at lowest Ecm to date • Results consistent with HF gs to gs • Further measurements at lower Ecm with H2 target • HF valid? Resonances and interference? • Extend technique to other (a,p) reactions • eg. 34Ar(a,p)37K (stage 1 approved at ISAC II, M. Aliotta)

13. Collaboration M. Aliotta, T. Davinson, G. Lotay, A. Murphy, P. Salter, P. Woods University of Edinburgh B. Fulton, M. Taggart University of York B. Davids, N. Galinski, D. Howell, P. Machule, C. Ruiz, S. Sjue, P. Walden TRIUMF

15. Argonne National Laboratory Report 2005 Previous Studies of the 18Ne(α,p)21Na reaction • First direct measurement by LEDA collaboration at UCL • Bradfield-Smith et al., Phys. Rev. C59 (1999) 3402 • Groombridge et al., Phys. Rev. C66 (2002) 055802 • Comparison with theoretical calculations based on level structure of 22Mg and Hauser Feshbach calculations • Gorres et al,. Phys. Rev. C51 (1995) 392 • Argonne National Laboratory collaboration • Sinha et al., ANL Annual Report 2003, pp. 8 – 10

16. 4He in S2-S2 dE/E Telescope

17. S2 f vs CD f

18. TUDA: ISAC I ↔ ISAC II

19. Preliminary 21Na(p,α)18Ne Cross Section PRELIMINARY