1 / 36

Nuclear astrophysics

Introduction Big Bang Stellar structure & solar neutrinos. I. Stellar evolution & s process Supernovae & r process. II. III. Binary systems: Type Ia, novae, x-ray bursts. Nuclear astrophysics. A survey in 3 acts. Jeff Blackmon, Physics Division, ORNL.

marlo
Télécharger la présentation

Nuclear astrophysics

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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction Big Bang Stellar structure & solar neutrinos I Stellar evolution & s process Supernovae & r process II III Binary systems: Type Ia, novae, x-ray bursts Nuclear astrophysics A survey in 3 acts Jeff Blackmon, Physics Division, ORNL • Nuclear physics plays an important role in astrophysics: • Energy generation • Synthesis of elements astronomical observables

  2. Interdisciplinary research A variety of new tools in many areas are driving progress Laboratory measurements Nuclear theory and data Improved shell model, reaction theory, rates, libraries & dissemination via the web New beams & experimental techniques Observations Astrophysics New orbiting instruments, increased optical power, presolar grains Advancing computing power more realistic simulations

  3. Solar system abundances One of the most fundamental and important observables log (abundance) This year marks the 50th anniversary of “B2FH” Mass

  4. reactions/s ions/s atoms/cm2 Nuclear reactions in the lab & in space What you are used to in the lab: cross section reaction rate In astrophysical events:

  5. MeV·fm The Coulomb barrier Energy of particles in astrophysical environments is much lower than the Coulomb barrier

  6. The Gamow window

  7. Why the S-factor is useful Example: 3He(,)7Be • Important for: • The sun ( production) • Big Bang (Li production) Rolfs&Rodney, p. 157. Data from Kräwinkel et al., ZPA 304 (1982) 307. Limit of experiments Need  here for sun But be careful…

  8. Gp>>Gg Gg>>Gp Identifying resonances is crucial Lecture 3 Keiser, Azuma & Jackson, NPA331 (1979) 155. If resonance is narrow “resonance strength”

  9. 14O 15O 16O 1 m 2 m 13N 14N 15N 10 m 12C 13C Solving a reaction rate network Network of many coupled equations The CN cycle: hydrogen burning Identify important reactions Nuclear physics  reaction rates Astrophysical model to define the equations of state: , T Numerically solve for Nx(t)

  10. The Early Universe Space, time, matter, & energy began with the Big Bang Independent observations tell us about different epochs Nucleosynthesis CMB -The afterglow Stellar observations Light Elements Formed

  11. New Cosmological Paradigm WMAP: CMB Observations (Lecture 3) Type 1a supernova redshift vs. distance indicates the expansion rate of the universe is accelerating DARK ENERGY (e.g. cosmological constant) exerts a “negative pressure” causing the acceleration Only 4% of matter is baryonic  test with nucleosynthesis

  12. proton proton neutron neutron 2H 2H 3He 3He 4He 7Be 7Li p ~75% 4He ~25% 2H,3He ~ 10-5 7Li ~ 10-10 The Homogeneous BBN Model Assume adiabatic expansion ( flavors) n/p ratio set by weak strength (n half-life) Only free parameter is baryon/photon ratio ~All free neutrons into 4He Mass 5 & 8 gaps inhibit formation of heavy elements

  13. A Typical Big Bang Network

  14. p 4He d 3He 7Li final abun- dances Solve the reaction rate network Time (sec) 1 100 300 start finish

  15. proton neutron 2H 3He 4He d / H abundance ratio 7Be 7Li  = baryon / photon Abundance Observations can be used to constrain the “normal” matter density - the free parameter in the theory - independent of WMAP Theoretical Abundance Prediction

  16. Quasi-Stellar Object (QSO) (absorbs light) d / H abundance ratio hydrogen Deuterium abundance observations deuterium range of densities consistent with observations & theory Keck Telescopes  = baryon / photon “Primordial” Interstellar Gas Cloud D / H = 2.78 ± 0.4 • 10-5 Abundance Observations can be used to constrain the “normal” matter density - the free parameter in the theory - independent of WMAP Theoretical Abundance Prediction 10-10

  17. 7Li: good constraint on baryonic matter density 4He: relatively weak constraint but good observations? Yp = 0.242 ± 0.002 7Li / H = 1. 0 – 1.6 • 10-10 7Li/ H abundance ratio 4He mass fraction  

  18. WMAP using 7Li using 4He Disagrees with WMAP Disagrees with WMAP using 2H Agrees with WMAP Precision needs improvement Comparing Matter Density Constraints “Gold Standard” Highest precision Independent of how light Elements formed in Big Bang 1 2 3 4 5 6 7 8 • 1010 ~ normal matter density Is our understanding of dark energy / dark matter is wrong? Are our observations / interpretations wrong? Are there problems with our nuclear reaction network?

  19. Enables users to run and visualize BBN calculations with choice of reaction rateschoice of primordial abundance observationschoice of standard BBN or some non-standard variants New online suite of cosmology codes under development at bigbangonline.org

  20. Hydrogen burning in stars DP G Hydrostatic equilibrium Energy conservation The sun M=2x1030 kg (0)=150 g/cm3 T(0)=1.5x107 K T(surf)=5800 K L=3.8x1026 W Pressure For sun (non-degenerate) Large T,P gradient Opacity: photons absorbed and emitted at shorter  5x104 yr for energy produced in sun’s core to be radiated at surface LM4 Luminosity/opacity/T relationship

  21. Thanks to substantial efforts in experiment, theory & evaluation 5% 5% 7% 7% 13% 5-10% Solar power:

  22. Super-K 1967 1996 6x109ne/cm2/s only direct probe of solar core Homestake Homestake Super-K 2002 Nobel Prize Davis & Koshiba Radiochemical Real-time counting Homestake Homestake Gold Mine 600kt perchloroethylene 100 events/yr 37Cl+ne 37Ar+e ~30% expectations Mozumi Mine 50,000 kt water 5,000 events/yr ne+ e- scattering ~40% expectations

  23. SNO 1998 SNO NC = (5.21  0.27stat 0.38sys) x 106 /(cm2s) metallicity reaction rates  ~15% SNO & SuperK measure only neutrinos from the decay of 8B Flux measurements determine neutrino properties n 7Be(p,g)8B A accurate value for the predicted 8B neutrino flux is need for comparison to the current generation of measurements SuperK CC = (2.39  0.03stat 0.06sys) x 106 /(cm2s) Creighton Nickel Mine 1 kt heavy water nx + d  p + n SSM = 5.7 x 106 /(cm2s)

  24. Flavor oscillation P(nenm) • Neutrino mass eigenstates not the same as flavor eigenstates In vacuum • Strong evidence from observations of atmospheric neutrinos ( ) • Observed in reactor experiments: KamLAND & Chooz • Oscillations of solar (8B) neutrinos are enhanced by interactions with the high density of electrons in the solar core MSW: Mikheyev & Smirnow, SJNP 42 (85). Wolfenstein, PRD 17 (78). • 7Be = Focus of current experiments • KamLAND • Borexino • pp = Next-generation • CLEAN • LENS 7Be pp KamLAND

  25. October 2004 One of the 3 major recommendations “Thereareraremomentsinsciencewhenaclearroadtodiscoveryliesaheadand there is broad consensusaboutthestepstotakealongthatpath This is one such moment.” • The pp neutrino flux is accurately predicted by the solar luminosity. • pp neutrinos oscillate (primarily) by vacuum oscillations not MSW oscillations. • Would provide a clear test of solar physics, hydrostatic equilibrium, etc. • Is the sun’s energy output now the same as 50,000 years ago?

  26. McKinsey & Coakley, Astroparticle Physics 22 (2005) 355. Measuring the pp flux: CLEAN Very high purity liquid Ne or Ar Thin film of shifting flour in front of PMTs Good recoil/electron discrimination Very low threshold (few 10’s keV) 130 ton device proposed (either SNO-Lab or DUSEL) MiniCLEAN now operating 65 liters

  27. Now: 8% In-loaded scintillator Background 2x 115In decays 1 mimics prompt e 1 mimics g cascade  high segmentation air In-loaded scintillator LENS: e from pp fusion #1 prompt electron  e energy (-like) signal #1 signal #2 Buffer up to 10s Shower Time/space correlation discrimination 3D array of transparent cells (~6 m)3 fiducial volume = ~15 tons In ~ 500 pp events/yr

  28. Nuclear Physics Laboratory Measurements beam detectors target small accelerator ion source Directly measure cross sections in the lab at the lowest possible energies Bombarding energy range ~ 10 keV to 3 MeV • High currents (~ mA) • Long run times • Efficient detectors to obtain high statistics • Pure, stable targets • Absolute cross section measurements • Good normalization & careful control of systematic uncertainties • Background suppression crucial

  29. LNGS ROME Laboratory space adjacent to highway tunnel 1400 m rock coverage cosmic µ reduction= 10–6 µ rate ~ 1 (/m2 h)

  30. Low-energy accelerators at LNGS 50 keV accelerator First  measurements in solar Gamow widow 3He()7Be with 400 keV accelerator 3He(3He,2p) R. Bonetti et al., PRL 82 (1999) 5205.

  31. PRL 48 (1982) PRC 27 (1983) ZPA 310 (1983) PRL 93 (2004) Gy. Gyürky, PRC 75 (2007) 035805. 3He()7Be @ LUNA

  32. 7Be Target Rotating target arm 450mm2,Ep=305 keV Faraday Cup 22.3 ± 0.7 eV barn 150mm2,Ep=305 keV 22.1 ± 0.6 eV barn Proton beam going through LN2 trap Junghans et al., PRC 68 (2003) 065803. 7Be(p,)8B at Seattle Si detectors Extraordinary control over systematic uncertainties.

  33. New Coulomb dissociation result Schumann et al., PRC 73 (2006) 015806. Small E2 Change in S17(E) 20.60.81.2 eV b

  34. Schumann (CD 2006) Trache (Glauber 2004) Schumann (CD 2003) Davids & Typel (CD 2003) Azhari (ANC 2001) Evaluated S17 (eV b) Junghans PRC 68 (2003) 065803. 21.40.50.6 Davids & Typel PRC 68 (2003) 045802. 18.60.41.1 Cyburt et al., PRC 70 (2004) 045801. 19.3  21.4 with ~ 6-7%  Recent 7Be(p,)8B results Junghans et al. • Precision has been significantly improved. • Some questions remain. • Additional high-precision measurement(s) are desired.

  35. Thanks to substantial efforts in experiment, theory & evaluation 5% 5% 7% 7% 13% 5-10% Solar power:

  36. Act II: Stars and their catastrophic deaths Act I log (abundance) Mass

More Related