Philip SalterPhilip SalterSchool of Physics &

AstronomyT

HE

U N I V E RS

I TY

OF

ED I N B U

RG

H

Time-reversed measurement of the 18Ne(,p)21Na cross section relevant to breakout from the Hot-

CNO cycle in X-ray bursts

Outline

• Overview of X-ray bursts

• Outline of relevant nuclear processes

• Experimental investigation

• Preliminary results

• Summary

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)

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

What processes are responsible?

http://hubblesite.org/newscenter/newsdesk/archive/releases/2000/24/video/a

X-ray bursts: Hot-CNO breakout

unstable

stable(,)(p,)

(+)(p,)

(,p)

22Mg

17F

18Ne

21Na

breakoutfrom HCNO

12C

13N 14N

15O14O

15N

13C

16O

HCNO

18F

onset of rp-process

• T9 ~ 0.8: breakout through 18Ne(α,p)21Na

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

1.890 MeV

Q = 2.6373 MeV

18Ne + α

21Na + p

22Mg

5.5018 MeV

8.1390 MeV

• 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

)1J2)(1J2(

)1J2)(1J2(

E

E

mm

mm

21

43

12

34

21

43

34

12

Ecm = 1.3 – 2.6 MeVT = 0.9 – 2.7 GK

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

Experimental Approach

• Inverse kinematics

forward focussed, high coincidence detection efficiency

• Detect 4He + 18Ne coincidences

• Select events

PI (Z=10, Z=2), dt, d, Q-value

330 g/cm2 (CH2)n target

S2-S2∆E-E Telescopeθlab = 6o-20o

4He

18Ne

~ 4.1 – 5.5 MeV/u21Na5+

CD-PAD ∆E-E Telescopeθlab = 1.5o-6o

I ~ 5x106 /s

4He Kinematic Loci

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

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

• Lowest energy measurement to date in astrophysical window (900-1700 keV)• Agreement with Hauser Feshbach (HF)

Summary

• Measure 18Ne(,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 targetHF valid? Resonances and interference?

• Extend technique to other (,p) reactionseg. 34Ar(,p)37K (stage 1 approved at ISAC II, M. Aliotta)

Collaboration

M. Aliotta, T. Davinson, G. Lotay, A. Murphy, P. Salter, P. Woods University of Edinburgh

B. Fulton, M. TaggartUniversity of York

B. Davids, N. Galinski, D. Howell, P. Machule, C. Ruiz, S. Sjue, P. WaldenTRIUMF

Previous Studies of the 18Ne(α,p)21Na reaction

Argonne National Laboratory Report 2005

• First direct measurement by LEDA collaboration at UCLBradfield-Smith et al., Phys. Rev. C59 (1999) 3402Groombridge 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 collaborationSinha et al., ANL Annual Report 2003, pp. 8 – 10

4He in S2-S2 dE/E Telescope

S2 vs CD

TUDA: ISAC I ↔ ISAC II

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