Download
slide1 n.
Skip this Video
Loading SlideShow in 5 Seconds..
Alex Murphy PowerPoint Presentation
Download Presentation
Alex Murphy

Alex Murphy

140 Views Download Presentation
Download Presentation

Alex Murphy

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Experimental Nuclear Astrophysics Relevant to Supernovae Alex Murphy http://www.ph.ed.ac.uk/nuclear/ 1/2 Day IOP meeting on Supernovae http://hepwww.rl.ac.uk/ukdmc/ukdmc.html/

  2. Nuclear Astrophysics Interstellar gas nucleosynthesis Gravitational collapse Explosive nucleosynthesis Triple a HCNO Breakout rp-process p-process r-process Rise in T and r Formation of stars pp-chains Nuclear Reactions  Stellar stability Thermonuclear runaway pp-chains CNO cycles s-process 1/2 Day IOP meeting on Supernovae

  3. Nuclear Physics in Stars The rate at which reactions occur is determined by the overlap of the thermal energy distribution and nuclear cross sections Thermal energy distribution • For ions – use MB statistics • Novae: up to 2-3 x108 K • X-ray bursts: up to 2-3 x109 K • Supernovae: up to 1010 K Relevant energies 10keV - 10 MeV Cross sections • Typically below Coulomb barrier • Low cross sections • Resonant processes dominate • Low density of states • Indirect methods can be useful Need to know energies, spins, widths 1/2 Day IOP meeting on Supernovae

  4. What we do and how we do it Coulomb barrier Ecoul  E, J, ℓtr, G direct measurements E, J, ℓtr, G non-resonant resonance E, J, ℓtr, G E, J, ℓtr, G Astrophysical region EG (E) LOG SCALE 1/2 Day IOP meeting on Supernovae

  5. Focus of recent research… • Explosive astrophysical environments • Novae, X-ray bursters, exotic scenarios • Typically we have been concentrating on proton rich side, A<30 • This is largely for technical reasons • (H)CNO cycles • Breakout from CNO processing • rp-processing… 1/2 Day IOP meeting on Supernovae

  6. Example of what we do… Novae • Masssive star (e.g. Red Giant) • More massive star expands… • Outer layers transferred to compact object • movie • Layer of H builds up on top of evolved material (e.g. C/O/…) • Slow accretion rate leads to degeneracy • Conditions for a thermonuclear runaway • High temperatures and short timescales • Ejecta • Elemental composition • Gamma ray emission…? 1/2 Day IOP meeting on Supernovae

  7. Gamma-ray production in Novae • Clayton & Hoyle Ap. J. 494 (1974) – direct observation of g-rays in novae ejecta • Intensity of an observed g-ray flux would provide a strong constraint on novae modelling. • Need to know the relevant reaction rates!  21Na(p,g)22Mg INTEGRAL: launched Oct ’02 1/2 Day IOP meeting on Supernovae

  8. 22Na Example: Novae Why is this reaction important? 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 24Si 25Si 26Si 27Si 28Si rp – process 23Al 24Al 25Al 26Al 27Al 22Mg 23Mg 24Mg 25Mg 26Mg MgAl Cycle 20Na 21Na 22Na 23Na NeNa Cycle Need to know (p,g) rate compared to b-decay rate 18Ne 19Ne 20Ne 21Ne 22Ne 17F 18F 19F 1/2 Day IOP meeting on Supernovae

  9. Experimental method Radiative capture and elastic scattering studies (p,g) (p,p) We use radioactive beam facilities such as those at TRIUMF and Louvain-la-Neuve DRAGON TUDA 1/2 Day IOP meeting on Supernovae

  10. Resonant elastic scattering TUDA Radioactive Beam 5x107 pps Target:795 mg/cm2 CH2 foil LEDA surface ion source SiC primary target 192 strips, energy, angle and time of flight from each Primary beam:20 mA, 500 MeV, protons 1/2 Day IOP meeting on Supernovae

  11. Particle Identification Elastically scattered protons 1H(20Na,1H) 20Na beam is radioactive!  alpha decays Time of Flight Energy 12C(20Na,12C) 20Na @ 32 MeV on 795 mg/cm2 CH2, with 12.65 mm Mylar 1/2 Day IOP meeting on Supernovae

  12. Data… Three resonances observed • Ex(21Mg) = 4.005MeV Primary aim of the experiment. Tentative Jp = (1/2+)  3/2+ • Ex(21Mg) = 4.26 MeV Previously only Ex known (no width, spin information) 5/2+ • Ex(21Mg) = 4.44 MeV Previously unknown Jp = 3/2+ 1/2 Day IOP meeting on Supernovae

  13. Radiative Capture • (p,g) or (a,g) • Use a Recoil mass separator + a gamma-ray array • E.g. DRAGON: Detector of Recoils And Gammas of Nuclear Reactions • Windowless gas target • End detectors – silicon strip detector or ion chamber 1/2 Day IOP meeting on Supernovae

  14. Measurement of 21Na(p,g)22Mg • 21Na beam on hydrogen target • Varied 21Na beam energy in small steps so as to scan resonances • Detected recoils in coincidence with prompt gammas • Determined resonance strengths for seven states in 22Mg between 200 and 1103 keV 1/2 Day IOP meeting on Supernovae

  15. Results – resonance strengths 22Mg 21Na 22Mg recoils in DSSSD ER=740 keV Yield curves for state at 206 keV (above) and at 821 keV (left) 1/2 Day IOP meeting on Supernovae

  16. Results: Reaction rate Results: • The lowest measured state at 5.714 MeV (Ecm = 206 keV) dominates for all novae temperatures and up to about 1.1 GK • Updated nova models showed that 22Na production occurs earlier than previously thought while the envelope is still hot and dense enough for the 22Na to be destroyed • Results explain the low abundance of 22Na 1/2 Day IOP meeting on Supernovae

  17. Nova Her 1991 What about observations…? g-ray emission from several close novae has been search for… • CGRO/COMPTEL – So far no detection; upper limits only. • But… consistent with current theory incorporating new reaction rate data. • Expectation… • INTEGRAL should see signal from nova < 1.1 kpc away • (~1 ONe nova per 5 yrs) 1/2 Day IOP meeting on Supernovae

  18. Future directions: • Around the world, facilities are advancing… • ISAC-II (Canada), RIA (US), RIPS (Japan), Eurisol, REX-Isolde, SPIRAL-II, FAIR (Europe), • More intense beams, more exotic beams, heavier beams • Opportunities for detector development • Now is the time to go after new physics! SUPENOVAE 1/2 Day IOP meeting on Supernovae

  19. Future Directions An example relevant to type Ia supernovae 1/2 Day IOP meeting on Supernovae

  20. SN Ia • Scatter in brightness <0.3 mags, even without extinction correction (which is usually quite small). Over 90% have very reproducible light curves. • Thus very useful as a standard candle • Especially important in light of LCDM • Non-standard SN Ia’s • Effects that can change luminosity (e.g. metalicity) SN1991 D 1/2 Day IOP meeting on Supernovae

  21. Recent ‘atypical’ observations: • Recently, several atypical SNIa’s have been observed: • SN 1987G - fast decline from maximum • SN 1986G - anomalies in optical spectra • SN 1990N - anomalies in optical spectra • SN 1991T - 'largely deviated' from standard • SN1991bg - dimmer than usual, some H detected. • SN1999by - very similar to SN1991bg • These differences suggest that maybe there really are two progenitor types...  He rich accretion on to sub-Chandrasekhar mass CO WDs may be responsible for the <10% of SNIa’s that have ‘peculiar’ light curves. 1/2 Day IOP meeting on Supernovae

  22. Sub-Chandrasekhar mass models • The existence of sub-luminous SN Ia’s interpreted as less than 1.4 M56Ni powering the light curve The Sub-Chandrasekhar mechanism: • A 0.6 – 0.8 M CO WD accretes He rich matter. • 98% 4He, 1% 12C, 0.5% 14N, 0.5% 16O • Existence (but not the exact quantity) of 14N critical – a product of pop-I burning • Moderate accretion rate (~10-8 M yr-1)  He ignition at the CO/He interface. • Competition between 14N(e–,n)14C(a,g)18O (‘NCO’) & Triple-a • Ignition of He may strongly depend on rate of14C(a,g)18O 1/2 Day IOP meeting on Supernovae

  23. Alex Murphy LOI XXXV An indirect study of the 14C(a,g)18O reaction Alison Laird Jordi Jose EEC Meeting, TRIUMF

  24. Future Directions An example relevant to Core Collapse supernovae 1/2 Day IOP meeting on Supernovae

  25. Core Collapse Supernovae • There is consensus on the basic mechanism • And yet even the best simulations still don’t explode! • Extremely complex • Need a good diagnostic • Produced in vicinity of mass cut • Sensitive diagnostic of models • Gamma-ray observable nuclide SN1987A 44Ti! M1 – The Crab 1/2 Day IOP meeting on Supernovae

  26. Core Collapse Massive star (>10–12 M) • Stellar evolution  onion-skin-like structure • At maximum of BE/A, thermal support lost  Core collapses • After core-bounce, shock wave passes through Si layer above core • Dissociation back to n, p, and a • …Nuclear statistical equilibrium… • …Alpha-rich freeze out • Dominant site for 44Ti production • Key reactions to be studied* • 40Ca(a,g) • 44Ti(a,g) • 44Ti(a,p) • 45V(p,g) • Triple a EPSRC Grant * (The et al ApJ 504 (1998) 500) 1/2 Day IOP meeting on Supernovae

  27. 44Ti production as a diagnostic Amount ejected sensitively depends on location of the ‘mass cut’ • Material that ‘falls back’ is not available for detection • 44Ti yield a sensitive diagnostic of the explosion mechanism • Thus, VERY useful for models to make comparisons against • What’s more, it’s (relatively) easily observed • Gamma-Ray observation • 1.157 MeV • INTEGRAL & other missions • Meteoritic data • Enrichment of 44Ca in type X presolar grains Wilson. (1985) Timmes et al. (1996) 1/2 Day IOP meeting on Supernovae

  28. Integral A grain from the Murchison Meteorite GLAST Pretty pictures… 1/2 Day IOP meeting on Supernovae

  29. Summary • Nuclear reactions are the power behind most astrophysical phenomena • Astrophysical models require accurate nuclear physics inputs • New facilities (and upgrades) mean we can now start looking at reactions important in new environments • Nuclear Astrophysicists need good guidance! 1/2 Day IOP meeting on Supernovae

  30. The End Thank you 1/2 Day IOP meeting on Supernovae

  31. Spare slides 1/2 Day IOP meeting on Supernovae

  32. Latest development… • Proposed research requires: • Low energy 44Ti and 45V beams • Refractory elements are hard to extract from ‘standard’ ion sources • A new approach… ExoticRadionuclides fromIrradiatedMAterialsforScienceandTechnology • PSI is looking at reducing the amount of radioactive waste it has produced • Potential users: • Nuclear Medicine • Geophysics • Astrophysics • … • Could bleed these ions into a non-RNB ion source and re-accelerate them • LLN? Triumf? Other? • Proposal in to EU FP7 programme 1/2 Day IOP meeting on Supernovae

  33. Typical set-up (from 20Na(p,p) expt) 9.55 or 12.40 mm Mylar High sensitivity Faraday cup 5.65 or 9.65 mm Mylar Recoil proton LEDA 795mg/cm2 CH2 20Na LEDA • 1.25 MeV/u • 1.60 MeV/u 4.6o < qlab <31.2o 60.5 cm 19.5 cm 3.50 < Ex (21Mg) < 4.64 MeV 1/2 Day IOP meeting on Supernovae

  34. Astrophysical significance: NeMg 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 21Ne NeNa cycle 1/2 Day IOP meeting on Supernovae

  35. Observations Nuclear Astrophysics An understanding of the cosmos Modelling … 1/2 Day IOP meeting on Supernovae

  36. Novae and X-ray Bursters… Binary systems! • Compact, evolved star (white dwarf or neutron star) orbiting a massive star (e.g. Red Giant) • More massive star expands… • Outer layers transferred to compact object • Layer of H builds up on top of evolved material (e.g. C/O/…) • Slow accretion rate leads to degeneracy • Conditions for a thermonuclear runaway • High temperatures and short timescales • Radioactive nuclei important 1/2 Day IOP meeting on Supernovae

  37. Novae • White dwarf with companion star • Temperatures of up to 3 x 108K • Time: 100-1000s to eject layer • Light curve increases to max in hours but can take decades to decline • Absolute magnitude can increase by up to 11 magnitudes • Can be recurrent • Ejecta • Elemental composition • Gamma ray emission…? Nova Herculis 1934: AAT 1/2 Day IOP meeting on Supernovae

  38. Some recent measurements… p(20Na,p)Indirect study of 20Na(p,g)21Mg reaction X-ray bursters: a crucial link in the rp-process Novae: affects NeNa cycle. p( 21Na,p)Indirect study of 21Na(p,g)22Mg reaction Novae: Potential for satellite gamma ray observations p( 11C,p) Indirect study of 11C(p,g)12N reaction High mass stars/Novae: 18Ne(a,p) Direct study. Breakout from HCNO cycle: Catalyst for rp-process? 1/2 Day IOP meeting on Supernovae

  39. 20Na(p,p)20NaMotivation Better knowledge of the level structure of 21Mg is needed… • Astrophysics • Nucleosynthesis and energy generation • X-ray bursts • Novae • Reaction rates dominated by resonant contributions • Nuclear Physics • Proton-rich nuclei far from stability, Large level shifts, Comparison of reaction mechanisms, Shell model studies The Experiment Resonant elastic scattering: 20Na(p,p)20Na(inverse kinematics, using TUDA at TRIUMF) 1/2 Day IOP meeting on Supernovae

  40. T  6 x 108K • (a,p) and (p,g) rates overtake b+ decays • Reaction flow dominated by 15O(a,g)19Ne(p,g)20Na(p,g)21Na… • ‘Breakout’ into rp-process begins • Triggers subsequent explosion 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 • T ~ 4 x 108K • Energy generation by HCNO cycles • Waiting points at 14O, 15O and 18Ne isotopes 18Ne 17F 18F 14O 15O 16O 17O 13N 14N 15N 12C 13C 1/2 Day IOP meeting on Supernovae

  41. The run: Successful experiment ran at TRIUMF • 5 days of stable 20Ne calibration beams • 7 days of radioactive 20Na beams: up to 5x107 pps. • Thick target method: Scan through region of excitation in 21Mg to look for resonances • Detect proton recoils • Expect Rutherford + resonances (+ interference). • Resonance depends on Ex, Gp,J, and ltr • Two–body kinematics • For a selected angle  energy of detected protons reflect the energy the reaction occurred at. • Hence, proton energy spectrum is just an excitation function. 1/2 Day IOP meeting on Supernovae

  42. Calibrations etc Pulser walk-through… Standard triple alpha source 1/2 Day IOP meeting on Supernovae

  43. Analysis of proton data • Gate on protons… • Project out energy spectrum… • Subtract alpha background… • R-matrix analysis… General formalism – Lane & Thomas • Inverse level matrix approach • Based on earlier coding separately developed by Lothar Buchman and by Dick Azuma • Present version courtesy of C. Ruiz. • ½ integer spin, multi-channel, non-zero ltr, … 1/2 Day IOP meeting on Supernovae

  44. X-ray Bursters… • Similar environment to novae, but replace white dwarf with a neutron star. • Much deeper gravitational potential • Hotter, denser, faster • Less accreted material/smaller surface area  lower luminosity than novae • Temperatures up to ~2-3 x 109K • Time: 1-10s to lift degeneracy and eject layer • Ejecta? • little net ejecta due to gravitational field X-ray burster in NGC 6624: HST HEAO light curve of X-ray burst MXB 1728-34 1/2 Day IOP meeting on Supernovae

  45. Simulations • Helium burning at base of He layer • Occurs around r=106g/cc • Competition between 14N(e–,n)14C(a,g)18O (‘NCO’) & Triple-a • Nucleosynthesis (extended network codes : Goriely et al. A & A 388 2002) • Possible site for generating p-process nuclides. • Expanding outward shock wave  T9=2 – 3 • Material ejected  • Mo and Ru isotopes produced  • Such explosions produce 44Ti (contrary to standard SN1a) • Ignition of He may strongly depend on rate of 14C(a,g)18O See also: Hoflich, Khokhlov & Wheeler [1995], Goriely, Jose, Hernanz, Rayet and Arnould [2002] 1/2 Day IOP meeting on Supernovae

  46. The 14C(a,g) reaction rate: Effect This reaction rate is undetermined, with an uncertainty factor 100 • Model ‘A’ – Standard reaction rate • Model ‘B’ – Standard reaction rate x 100 • Model ‘C’ – Standard reaction rate 100 • Model B • Shorter accretion duration • Less mass accreted • Less 56Ni in explosion • Ignition density r=1.77x106g/cc • Less violent explosion • Peak (at base of He layer) T9 = 2.77 • Model c • Longer accretion duration • More mass accreted • More 56Ni in explosion • Ignition density r=3.92x106 g/cc • More violent explosion • Peak T9 (at base of He layer) = 3.22 1/2 Day IOP meeting on Supernovae

  47. 1/2 Day IOP meeting on Supernovae

  48. Direct capture 3– state at 177 keV Current knowledge of reaction rate • Reaction rate • See Buchmann, D’Auria & McCorquodale (1998), Funck & Langanke (1989), Görres et al. (1992) • Direct capture component (T<3x107 K) • 177 keV resonant component remains undetermined. • Dominates rate 0.03 < T9 < 0.2 • State of interest: • Er=177 keV (6.404 MeV in 18O), Jp=3– • No direct measurements • No spectroscopic factor • Not calculated in theoretical studies (e.g. Descouvemont & Baye 1985) • Proximity to a-threshold • Resonance strength determined by Ga • small branching ratio (~10-10) • Indirect methods must be used • 6Li(14C,d)18O,12C(14C,8Be)18O, 7Li(14C,t)18O… Funck & Langanke (1989) 1/2 Day IOP meeting on Supernovae

  49. 14C(a,g)18O Experimental details Experimental issues • Can 14C be separated from 14N? • 5x107 pps for 1 week not likely to be a radiological safety hazard • Rate of FC <1000 Bq: b range ~3 cm (in air) • 6Li(14C,d)18O – kinematics drive 2H from different states very close together. • Would require very thin (10mg/cm2) targets • Target contamination (C/O/F) • 12C(14C,8Be)18O • Identify 8Be from 2 alphas Erel=92 keV • Coulomb Barrier… 1/2 Day IOP meeting on Supernovae

  50. Spectroscopic factor Compare angular distribution to reaction model to get spectroscopic factor. • Alpha transfer below Coulomb barrier • Need spectroscopic factor measured in transfer reaction Ga • Must be careful of model uncertainties • FRESCO, ZAFRA • Calibration reaction? • Compound nucleus contribution • HF & Angular distribution… 1/2 Day IOP meeting on Supernovae