Proton unbound states in
This presentation is the property of its rightful owner.
Sponsored Links
1 / 17

Proton unbound states in 21 Mg and their astrophysical significance PowerPoint PPT Presentation


  • 80 Views
  • Uploaded on
  • Presentation posted in: General

Proton unbound states in 21 Mg and their astrophysical significance. Nova Herculis 1934: AAT. Nova Persei 1901: Herschel. Alex Murphy. X-ray burster in NGC 6624: HST. Motivation. Better knowledge of the level structure of 21 Mg is needed… Astrophysical

Download Presentation

Proton unbound states in 21 Mg and their astrophysical significance

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Proton unbound states in 21 mg and their astrophysical significance

Proton unbound states in 21Mg and their astrophysical significance

Nova Herculis 1934: AAT

Nova Persei 1901: Herschel

Alex Murphy

PROCON 2003

X-ray burster in NGC 6624: HST


Motivation

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)

PROCON 2003


Astrophysical motivation

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

PROCON 2003


Astrophysical motivation1

Astrophysical motivation…

Subsequent evolution depends on compact

object’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,g), (a,p) important

  • Material ejected to ISM

HEAO light curve of X-ray burst MXB 1728-34

20Na(p,g)21Mg reaction significance

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

Novae: affects NeNa cycle.

PROCON 2003


Astrophysical significance x ray bursters

21Mg

22Mg

23Mg

20Na

21Na

22Na

18Ne

18Ne

19Ne

17F

17F

18F

18F

14O

14O

15O

15O

16O

16O

17O

17O

Astrophysical significance: X-ray Bursters

  • T9 0.6

    • (a,p) and (p,g) rates overtake b+ decays

    • Breakout via rp-process begins (required because of waiting points from).

    • Reaction flow dominated by 15O(a,g)19Ne(p,g)20Na(p,g)21Na…

    • Triggers subsequent explosion

  • T9~0.4

    • Energy generation by HCNO cycles

    • Waiting points at 14O, 15O and 18Ne isotopes

    • Unable to generate required energy output

18Ne

17F

18F

14O

15O

16O

17O

13N

14N

15N

12C

13C

PROCON 2003


Reaction path in x ray burster

21Mg

22Mg

23Mg

20Na

21Na

22Na

18Ne

19Ne

20Ne

17F

18F

14O

15O

16O

17O

13N

14N

15N

12C

13C

Reaction path in X-ray burster

  • T9>0.8

    • Alternative breakout path kicks in

    • Reaction flow dominated by

      14O(a,p)17F(p,g)18Ne(a,p)21Na…

PROCON 2003


Astrophysical significance onemg novae

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,g)21Na.

      • Where does the 20Ne come from?

    • b-decay of 20Na feeds 20Ne.

    • Rate of 20Na(p,g) compared to the b+ decay of 20Na (448ms) determines abundance of 20Ne

21Mg

22Mg

23Mg

20Na

21Na

22Na

23Na

19Ne

20Ne

NeNa cycle

PROCON 2003


Nuclear significance

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.).

PROCON 2003


Previous knowledge of 21 mg

Previous knowledge of 21Mg

  • Above proton threshold, only data are Kubono et al. (NPA 537 (1992) 53)

    • 24Mg(3He,6He)21Mg

PROCON 2003


Previous knowledge of 21 mg1

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., Alburgeret al. PRC 23 (1981) 2217 and Wiescher et al. A&A 160 (1986) 56)

PROCON 2003


20 na p p 20 na experimental details

20Na(p,p)20Na Experimental details

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

  • Primary beam: 20 mA, 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 mg/cm2 CH2 foil

  • Detectors: 1.5 x LEDA (130° < qcm< 170°)

TUDA

PROCON 2003


Proton unbound states in 21 mg and their astrophysical significance

Experimental set-up

9.5 or 13 mm Mylar

High sensitivity

Faraday cup

6 or 9.5 mm Mylar

800mg/cm2 CH2

LEDA

Recoil proton

LEDA

~1 epA 20Na

  • 1.25 MeV/u

  • 1.60 MeV/u

60.5 cm

4.7o < qlab <33.7o

19.5 cm

PROCON 2003


The run

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, Gp 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.

  • PROCON 2003


    Proton unbound states in 21 mg and their astrophysical significance

    Data…

    • Three resonances observed

      • Ex(21Mg) = 4.01MeVPrimary aim of the experiment

      • Ex(21Mg) = 4.26 MeVPreviously only Ex known (no width, spin information)

      • Ex(21Mg) = 4.44 MeV (approx)Previously unknown

         R-matrix Analysis

    PROCON 2003


    Other recent data taken with tuda

    Other recent data taken with TUDA

    21Na(p,p)21Na

    22Na observation in novae

    • 21Na(p,g)22Mg(b+)22Na*(1.275 MeV g-ray)

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

        Synthesis of 22Na in ONe novae

    • 20Ne(p,g)21Na(p,g)22Mg(b+)22Na

      or

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

    Ph.D. Thesis (Edinburgh, 2003)

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

    PROCON 2003


    Future directions

    Future directions:

    • Resonant scattering: a powerful technique

      • Requires beam development

      • Limited to states of width > few keV

    • Other channels

      • (p,a), (a,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

    PROCON 2003


    Many thanks to

    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

    York

    SFU

    Langara

    PROCON 2003


  • Login