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3 a reaction a + a + a 12 C

In detail: a p process. 3 a reaction a + a + a 12 C. a p process: 14 O+ a 17 F+p 17 F+p 18 Ne 18 Ne+ a …. Alternating ( a ,p) and (p, g ) reactions: For each proton capture there is an ( a ,p) reaction releasing a proton. Net effect: pure He burning.

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3 a reaction a + a + a 12 C

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  1. In detail: ap process 3a reactiona+a+a12C ap process:14O+a 17F+p17F+p 18Ne18Ne+a … Alternating (a,p) and (p,g) reactions: For each proton capture there is an (a,p) reaction releasing a proton Net effect: pure He burning

  2. Recent progress in mass measurements ISOLTRAPRodriguez et al. NSCL LebitBollen et al. ANL CPTSavard et al. JYFL Trap NSCL Set of experiments use (p,dg) to determinelevel structure Measure: • decay properties • gs masses • level properties • rates/cross sections Mass known < 10 keV Mass known > 10 keV Only half-life known seen • Reaction rates: • direct measurements difficult • “indirect” methods: • Coulomb breakup • (p,p) • transfer reactions • stable beams and RIBS • Guide direct measurements • Huge reduction in uncertainties • If capture on excited states matters only choice Figure: Schatz&Rehm, Nucl. Phys. A,

  3. Nuclear physics needed for rp-process: (ok) • b-decay half-lives • masses • reaction ratesmainly(p,g), (a,p) (in progress) (just begun) some experimental information available(most rates are still uncertain) Theoretical reaction rate predictions difficult neardrip line as single resonances dominate rate: Hauser-Feshbach: not applicable Shell model: available up to A~63 but large uncertainties (often x1000 - x10000) (Herndl et al. 1995, Fisker et al. 2001)  Need rare isotope beam experiments

  4. H. Schatz Techniques with rare isotope beams 21Na + p  22Mg 1) Direct Measurements Bishop et al. 2003 (TRIUMF) For p-captureonly 2 cases so far !  Need RIA 2) First step: indirect techniques with low intensity rare isotope beams Many developed at a number of facilities: (ANL, GSI, MSU, ORNL, RIKEN, Texas A&M, …) Example: 32Cl + p  33Ar*  33Ar + g Resonant enhancement through states in 33Ar ?

  5. H. Schatz 34Ar 33Arexcited d Plastic with experimental data shell model only x 3 uncertainty x10000 uncertainty NSCL Experiment: Clement et al. PRL 92 (2004) 2502 Doppler corrected g-rays in coincidence with 33Ar in S800 focal plane: g-rays from predicted 3.97 MeV state stellar reaction rate reaction rate (cm3/s/mole) 33Ar level energies measured: 3819(4) keV (150 keV below SM) 3456(6) keV (104 keV below SM) temperature (GK)

  6. H. Schatz Stellar Enhancement Factor stellar capture rate SEF = ground state capture rate MeV 1/2+ 4.190 5/2+ Dominantresonance 3.819 this work 7/2+ 3.456 2+ 90 keV 5/2+ 3.364 1+ 3.343 NON Smoker 32Cl 33Ar • direct measurement of this rate is not possible – need indirect methods • SEF’s should be calculated with shell model if possible

  7. H. Schatz • Wind ejects ashes in radius expansion bursts for wide range of parameters wind Neutron star interior ? depth Initial radiative profile wind surface Mass ejection in X-ray bursts ? Weinberg, Bildsten, Schatz 2005 Winds can eject <1% of accreted massDoes convection zone reach into theouter layers that get blown off ??? Temperature (K) Column density (g/cm2)

  8. H. Schatz 12C(a,g) bypass 16O (a,p) 13N slow (p,g) 12C Need protons as catalysts(~10-9 are enough !) Source: (a,p) reactionsand feedback through bypass Reaction flow during burst rise in pure He flash • Increases risetime • Triggers late reexpansion of convection zone • enhances production of heavy elements vs. carbon

  9. H. Schatz Composition of ejected material 28Si 32S Weak p-captureon initial Fe seed • Observable with current X-ray telescopes • in wind • on NS surface as spectral edges • Explanation for enhanced Ne/O ratio in 4U1543-624, 4U1850-087, … ??? (ratios ~1 – ISM 0.18)

  10. H. Schatz Step 2: Deep ocean burning: Superbursts Neutron star surface H,He superburst gas ashes ocean ~ 20m, r=109 g/cm3 outer crust Innercrust

  11. H. Schatz ~hours Deep burning ? • long duration through longer radiation transport • long time to accumulate means long recurrence timemore material means more total energy by same factor for same MeV/u) The origin of superbursts – Ashes to Ashes Accreting Neutron Star Surface ~ x1000 longer burst duration ~ x1000 longer recurrence time ~ x1000 more energy H,He Radiation transport fuel ~10s Thermonuclear H+He burning(rp process) ~1 m gas ashes ocean ~10 m outer crust ~100 m Innercrust ~1 km 10 km core

  12. Burst peak (~7 GK) Carbon can explodedeep in ocean(Cumming & Bildsten 2001) ~ 55% Energy ~ 45% Energy Ashes to ashes – the origin of superbursts ? Puzzle: The ocean is too cold ignition about every 10 years instead of every year as observed (Schatz, Bildsten, Cumming, ApJ Lett. 583(2003)L87

  13. And nuclear power plantson earth Energy generation in Superbursts(plus C->Ni fusion)only place in cosmos ? • Energy generation everywhere else in comos: • Stars • X-ray bursts, Novae

  14. H. Schatz Step 3: Crust burning Neutron star surface H,He gas ashes ocean outer crust ashes ~ 25 – 70 mr=109-13 g/cm3 Innercrust

  15. Surface of accreting neutron stars Neutron star surface Hydrogen, Helium X-ray bursts gas 1m Ocean (palladium? Zinc?) 10m Crust of rare isotopes Innercrust ashes D. Page

  16. 106Pd rp-ashes 4.8 x 1011 g/cm3 106Ge 56Fe 1.8 x 1012 g/cm3 68Ca 2.5 x 1011 g/cm3 72Ca 4.4 x 1012 g/cm3 56Ar 1.5 x 1012 g/cm3 34Ne Crust processes Known mass superbursts Haensel & Zdunik 1990, 2003 Gupta et al. 2006

  17. Known mass Crust processes Recent massmeasurementsat GSI (Scheidenberger et al.,Matos et al.) Recent massmeasurementsat Jyvaskyla (Hager et. al. 2006) Q-valuemeasurementat ORNL (Thomas et al. 2005) Recent massmeasurementsat ISOLTRAP (Blaum et. al.) Recent TOF massmeasurementsat MSU (Matos et al.) Reach of next generation Rare Isotope Facility FRIB(here MSU’s ISF concept)(mass measurements)

  18. NEW JINA Result: S. Gupta, E. Brown, H. Schatz, K.-L. Kratz, P. Moeller 2007Electron capture into excitedstates increases heatingby up to a factor of ~10 rp-ashes superbursts Excitation energyof main transition Increasedheating

  19. Enhanced crust heating New heatingenhanced by x 5-6 Former estimate  Heats entire crust and increases ocean temperature from 480 Mio K to 500 Mio K

  20. Almost: Without excited states Ignition depth Inferred fromobservations Mass number of crust composition (pure single species crust) Impact of new crust modeling on superbursts Can the additional heating from EC into excited states make the crust hot enough to get the superburst ignition depth in line with observations ?

  21. H. Schatz Observables: transients in quiescence Low crust conductivity, normal core cooling KS 1731-260 (Wijands 2001) Bright X-ray burster for ~12 yr Accretion shut off early 2001 High crust conductivity, enhanced core cooling Is residual luminosity coolingneutron star crust ?  If yes: probe neutron star ! (Ouellette & Brown 2005)(Rutledge 2002)

  22. H. Schatz Comparison with observations during quiescence M. Ouellette Low crust conductivityNormal core cooling High crust conductivity Normal core cooling Low crust conductivityEnhanced core cooling High crust conductivityEnhanced core cooling (data from Wijnands 2004)  but: a superburst has been observed from KS 1731-260 this indicates a hotter crust and low crust conductivity (Brown 2004)

  23. H. Schatz Superbursts as probes for NS cooling Superburst ignition depth (Ed Brown, to be published) (for accretion rate of 3e17 g/s and X(12C)=0.1) Low crust conductivity High crust conductivity Recurrence times(observed ~ 1yr) 1.4 yr 3.1 yr “regular” core cooling 5.2 yr 27 yr “enhanced” core cooling • Recurrence time depends on crust conductivity and core cooling • Observations require LOW conductivity and no enhanced cooling (incl. KS1731-260)

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