Alex Murphy PROCON 2003 1

Proton unbound states in 21Mg and their astrophysical significance

Alex MurphyAlex Murphy

Nova Herculis 1934: AAT

Nova Persei 1901: Herschel

X-ray burster in NGC 6624: HST

Alex Murphy PROCON 2003 2

Motivation

Better knowledge of the level structure of 21Mg is needed… Astrophysical

Nucleosynthesis and energy generation X-ray bursts Novae Reaction rates dominated by resonant contributions

Nuclear Proton-rich nuclei far from stability Large level shifts Comparison of reaction mechanisms Shell model studies

The Experiment

Resonant scattering reaction: 20Na(p,p)20Na (using TUDA at TRIUMF)

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Astrophysical motivation

Binary systems

Compact, evolved star (WD or neutron star) orbiting less evolved massive star (e.g. RG)

More massive star expands… Material flows through L1 Material is typically hydrogen

Accretion on compact object Layer of H builds up on top of

evolved material (e.g. C/O/…)

Artist’s conception of accretion from a red giant on to a compact object

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Astrophysical motivation…

Subsequent evolution depends on compactobject’s mass and accretion rate.

High rate ‘stable’ H and He burning and mass increase beyond Chandrasekhar: SN 1a

Lower accretion rate cataclysmic variable Neutron star host X-ray burst White dwarf host nova

Nuclear reactions: explosive hydrogen burning HCNO, rp-process (p,), (,p) important

Material ejected to ISMHEAO light curve of X-ray burst MXB 1728-34

20Na(p,)21Mg reaction significance

X-ray bursters: a crucial link in the rp-process

Novae: affects NeNa cycle.

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Astrophysical significance: X-ray Bursters

T9~0.4 Energy generation by HCNO cycles Waiting points at 14O, 15O and 18Ne

isotopes Unable to generate required energy

output

12C 13C

13N 14N

15O 16O

17F 18F

18Ne

15N

17O14O

15O 16O

17F 18F

18Ne

17O14O 15O 16O

17F 18F

18Ne 19Ne

21Na 22Na20Na

23Mg21Mg 22Mg

17O14O

T9 0.6 (,p) and (p,) rates overtake decays Breakout via rp-process begins (required because

of waiting points from). Reaction flow dominated by

15O(,)19Ne(p,)20Na(p,)21Na… Triggers subsequent explosion

Alex Murphy PROCON 2003 6

Reaction path in X-ray burster

12C 13C

13N 14N

15O 16O

17F 18F

18Ne 20Ne19Ne

21Na 22Na20Na

15N

23Mg21Mg 22Mg

17O14O

T9>0.8 Alternative breakout path kicks in Reaction flow dominated by 14O(,p)17F(p,)18Ne(,p)21Na…

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Astrophysical significance: ONeMg Novae

Temperatures achieved are too low for breakout

NeNa and MgAl cycles thought to provide necessary energy production.

NeNa cycle: First stage is 20Ne(p,)21Na.

Where does the 20Ne come from? -decay of 20Na feeds 20Ne. Rate of 20Na(p,) compared to the +

decay of 20Na (448ms) determines abundance of 20Ne

20Ne19Ne

21Na 22Na20Na

23Mg21Mg 22Mg

23Na

NeNa cycleNeNa cycle

Alex Murphy PROCON 2003 8

Nuclear significance

Specific case Unusual level shifts observed in previous measurements

Thomas – Ehrman shift. Breaking of isospin symmetry due to Coulomb induced differences in proton and neutron distributions.

Selectivity of 24Mg(3He,6He)21Mg measurement. could mean there are other states so far unobserved

Wider case Few studies on proton rich nuclei in this mass region Level shift in p-rich nuclei Comparison of reaction models

our (p,p) vs (3He,6He) Shell model…

poor performance near drip lines

(M. Horoi, private comm.).

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Previous knowledge of 21Mg

Above proton threshold, only data are Kubono et al. (NPA 537 (1992) 53) 24Mg(3He,6He)21Mg

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Previous knowledge of 21Mg

Ex uncertain to ~15 keV L from fits to DWBA. J then from comparison with 21F Parity by (–1)L

Widths calculated (from Kubono et al., Alburger et al. PRC 23 (1981) 2217 and Wiescher et al. A&A 160 (1986) 56)

Ex (MeV) Er(MeV) J p (eV)

3.086 -0.130 (3/2+, 5/2+)

3.244 0.028 (3/2+, 5/2+) 3.04x10-19

3.347 0.131 (7/2+) 1.23x10-6

3.643 0.427 (7/2+,9/2+) 1.58x10-4

3.752 0.536 (1/2-,3/2-) 99.4

3.901 0.685 (7/2+) 0.872

4.010 0.794 (1/2+) 4720

4.261 1.045 ? ?

4.824 1.608 ? ?

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20Na(p,p)20Na Experimental details

Primary beam: 20 A, 500 MeV, protons Secondary beam: 20Na from ISAC

intense sodium beam

surface ion source,

SiC primary target Currents up to 5x107 pps achieved

3.50 < Ex (21Mg) < 4.64 MeV 2 energy settings

Target: 795 g/cm2 CH2 foil

Detectors: 1.5 x LEDA (130° < cm< 170°)

TUDA

Thick target method: Scan through region of excitation in 21Mg to look for resonances.

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LEDA

LEDA

800g/cm2 CH2

• 1.25 MeV/u• 1.60 MeV/u

High sensitivity Faraday cup

Recoil proton

9.5 or 13 m Mylar

6 or 9.5 m Mylar

19.5 cm 60.5 cm

4.7o < lab < 33.7o

Experimental set-up

~1 epA 20Na

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The run:

Successful experiment ran in November 2002 5 days of stable 20Ne calibration beams 7 days of radioactive 20Na beams: up to 5x107 pps.

Expect Rutherford + resonances. Resonance depends on Ex, p and Ltr

Interference Two–body kinematics, low energy loss of protons in target For a selected angle energy of detected protons reflect the

energy the reaction occurred at. Hence, proton spectrum is just an excitation function.

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Data…

Three resonances observed Ex(21Mg) = 4.01MeV Primary aim of the experiment Ex(21Mg) = 4.26 MeV Previously only Ex known (no width, spin information) Ex(21Mg) = 4.44 MeV (approx) Previously unknown

R-matrix Analysis

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Other recent data taken with TUDA

21Na(p,p)21Na 22Na observation in novae 21Na(p,)22Mg(+)22Na*(1.275 MeV -ray)

observability in, e.g., INTEGRAL (launched Oct ’02)

Synthesis of 22Na in ONe novae

20Ne(p,)21Na(p,)22Mg(+)22Na

or

20Ne(p,)21Na(+)21Ne(p,)22Na

Ph.D. Thesis (Edinburgh, 2003)

PRC 65 Chris Ruiz et al. (2001) 042801(R)

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Future directions:

Resonant scattering: a powerful technique Requires beam development Limited to states of width > few keV

Other channels (p,), (,p), (d,p)… Many of these are directly of astrophysical significance Maybe used as indirect probes of low cross-section reactions 2 proton unbound states?

Facility development Driven by the physics programme Source development

Crucial to future programme ECR / Laser ion sources

Accelerator development Charge state booster: A < 30 A < 60 ISAC II: up to 6.5 MeV/u, A < 150

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Many thanks to…

M.Aliotta, T.Brown, L.Buchmann, T.Davinson, J.D’Auria, M.Eaton, S.Engel, B.Fulton, D.Groombridge, D.Hunter, D.Hutcheon, A.Laird,

J.Pearson, R.Pitkin, I.Robinson, J.Rogers, F.Sarazin, P.Walden, P.Woods

Edinburgh TRIUMF

YorkSFU

Langara