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Nuclear Astrophysics with NIF: Studying Stars in the Laboratory

Nuclear Astrophysics with NIF: Studying Stars in the Laboratory. Richard N. Boyd Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology July 11, 2008.

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Nuclear Astrophysics with NIF: Studying Stars in the Laboratory

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  1. Nuclear Astrophysics with NIF: Studying Stars in the Laboratory Richard N. Boyd Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology July 11, 2008 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 LLNL-PRES-402644

  2. NIF has 3 Missions National Ignition Facility BasicScience Stockpile Stewardship FusionEnergy Peer-reviewed Basic Science is a fundamental part of NIF’s plan R. Boyd 04/18/07

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  5. We have 30 types of diagnosticsystems planned for NIC Diagnostic Alignment System Near Backscatter Imager Diagnostic Instrument Manipulator (DIM) X-ray imager Streaked x-ray detector FFLEX Hard x-ray spectrometer Diagnostic Instrument Manipulator (DIM) DANTE Soft x-ray temperature Static x-ray imager VISAR Velocity Measurements Full Aperture Backscatter Cross Timing System We have already fielded ~ half of all the types of diagnostic systems needed for NIF science R. Boyd 04/18/07

  6. NIF’s Unprecedented Scientific Environments: •T >108 K matter temperature • r >103 g/cc density Those are both 7x what the Sun does! Helium burning, stage 2 in stellar evolution, occurs at 2x108 K! • rn = 1024 neutrons/cc Core-collapse Supernovae, colliding neutron stars, operate at ~1022! • Electron Degenerate conditions, Rayleigh-Taylor instabilities for (continued) laboratory study. These apply to Type Ia Supernovae! • Pressure > 1011 bar Only need ~Mbar in shocked hydrogen to study the EOS in Jupiter & Saturn These certainly qualify as “unprecedented.” And Extreme! R. Boyd 04/18/07

  7. Reaction Studies for Nuclear Astrophysics R. Boyd 04/18/07

  8. Stellar Astrophysics at NIF: Measurements of Basic Thermonuclear Reactions • Thermonuclear Reaction Rates between charged particles are of the form: Rate ~ <s v> = (8/pm)1/2 (kBT)-3/20 E s(E) exp[-E/kBT] dE. Define s(E) = [S(E)/E] exp[- bE-1/2], where penetrability = exp[- 2 p z1 Z1 e2/ v] = exp[- bE-1/2] • S factors are extrapolated to the relevant stellar energies, in the Gamow window, from higher energy experimental data • Screening • Laboratory atomic electron screening effects are significant • Stellar electron screening effects are also significant, but quite different • NIF screening is due to degenerate electrons; that’s different still R. Boyd 04/18/07

  9. NIF and Neutrino Mixing The Sun emits electron-neutrinos ne, but some of them change to some other “flavor” of neutrino nx by the time they get to Earth: Oscillation probability = sin22 sin2(Dm2L/4E), where  = the mixing angle, Dm2 = m22 – m12, where the m’s are the masses of the two neutrino species, and L = the distance they have travel from Sun to Earth. The KamLAND neutrino oscillation result, showing the ratio of detected neutrinos from reactors to the no-oscillation result (for which the data points would be at 1.0), versus L/E. From Abe et al. 2008. Two types of neutrino oscillations have been observed, solar and atmospheric: their solutions are indicated. The lower mass solution is the result from solar neutrino oscillations. From Bahcall et al. R. Boyd 04/18/07

  10. Nuclear Reactions and Solar Neutrinos 1H The pp-chains of H-burning 2H; LE-n’s 4He 1H 3He 7Be 8B 1H 1H 3He 4He+1H+1H e- 7Li 8Be*; HE-n’s pp-I 4He+4He 4He+4He 1H pp-II pp-III The pp-chains describe how 4 1H →4He + energy in the Sun. Blue indicates where neutrinos are emitted. pp-III emits the highest energy, and therefore most detectable, neutrinos, but that branch is very weak. 3He+4He→7Be+g is crucial for predicting the neutrino spectrum. But it has proved to be a difficult reaction for which to measure the cross section. R. Boyd 04/18/07

  11. Comparison of 3He(4He,)7Be Measured at an Accelerator Lab and Using NIF Accelerator-Based Experiments NIF-Based Experiments 3He(4He,)7Be Be Ablator NIF Point? 1018 3He + 4He atoms Resonance Gamow window √ High Count rate (~105 atoms per shot) Integral experiment Should resolve inconsistency Detect 7Be with RadChem diagnostic system Gyurky et al. Mono-energetic Low event rate (few events/month) Inconsistency between two techniques √ √ X √ X √ 3He(4He,g) provides important definition of neutrino parameters! R. Boyd 04/18/07

  12. Measuring The Age of the Universe Globular clusters are clusters of ~1 million stars that formed at about the same time, early in the history of our Universe. Stars on the main sequence (MS; red curve) of the H-R diagram burn H until it is gone; then they leave the main sequence. Knowing the age of the stars that have just turned off the MS gives a lower limit on the age of the Universe. Globular cluster NGC 104. From South African Large Telescope MS H-R diagram for the globular cluster M3. Note the characteristic "knee" in the curve at magnitude 19 where stars begin entering the giant stage of their evolutionary path. From Wikipedia R. Boyd 04/18/07

  13. NIF’s Contribution: 14N(p,g) Reaction Rate The 14N(p,g)15O reaction is the slowest one in the primary CNO cycle; thus it determines (with a stellar evolution code) how long stars exist in their H- burning, or main sequence, phase. (p,g) 14N 13C Primary CNO-cycle b-decay Astrophysical S-factor for 14N(p,g) from the LUNA (underground) facility (filled squares). The new reaction rate is 60% of the older rate at stellar temperatures. From Lemut et al., 2006. (p,g) 13N 15O This reaction is so crucial to determining the ages of the globular clusters that it needs to be studied again, preferably with a different technique. NIF will provide that. b-decay (p,g) 12C (p,a) 15N This is a difficult reaction to study with an accelerator beam; it’s less complicated (!) with NIF. R. Boyd 04/18/07

  14. 176 177 178 Hf 3.7h 176 175 6.7d Lu Yb 170 171 172 173 174 4.2d 176 1.9h Tm 169 129d 1.9y 64h Er 168 9.4d 170 7.5h Measuring s-process rates in a hot plasma The s-process occurs at kT ~ 8 keV or ~25 keV; NIF will achieve kT ~ 10 keV. 171Tm has an excited state at 12 keV; that will be populated in the s-process environment, and in the NIF capsule. An excited state will affect both the effective b-decay rate and the effective cross section, possibly by large factors. NIF will be able to measure that effect for the neutron captures. R. Boyd 04/18/07

  15. How to do an s-process experiment on NIF? Ablator Compress pellet by a (radial) factor of 20; get neutrons up to a few MeV from T+T→4He+2n T Ice Insert ~1015-16171Tm + 169Tm T Gas fn determined from NTOF N172 = ecollection∫∫∫fn(r,t,En) N171s(n,g)171(En) (4pr2)-1 dr dt dEn ↓ N172/N170→ ∫N171s(n,g)171 dEn / ∫N169s(n,g)169 dEn Co-loading isotopes for which the cross section is known with that on which it is to be measured minimizes systematic uncertainties R. Boyd 04/18/07

  16. Abundance after  decay 80 100 120 140 160 180 200 220 Mass Number (A) A unique NIF opportunity: Study ofa Three-Body Reaction in the r-Process • Currently believed to take place in supernovae, but we don’t know for sure • r-process abundances depend on: • Weak decay rates far from stability • Nuclear Masses far from stability • The cross section for the a+a+n9Be reaction R. Boyd 04/18/07

  17. a+a+n9Be is the “Gatekeeper” for the r-Process • If this reaction is strong, 9Be becomes abundant, a+9Be 12C+n is frequent, and the light nuclei will all have all been captured into the seeds by the time the r-process seeds get to ~Fe • If it’s weak, less 12C is made, and the seeds go up to mass 100 u or so; this seems to be what a successful r-process (at the supernova site) requires 9Be a During its 10-16 s half-life, a 8Be can capture a neutron to make 9Be, in the r-process environment, andeven in the NIF target 8Be a n • The NIF target would be a mixture of 2H and 3H, to make the neutrons (not at the right energy—but it might be modified), with some 4He (and more 4He will be made during ignition). This type of experiment can’t be done with any other facility that has ever existed R. Boyd 04/18/07

  18. How to detect the reaction products from NIF? R. Boyd 04/18/07

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  20. Core-collapse supernova explosion mechanisms remain uncertain • SN observations suggest rapid core penetration to the “surface” • This observed turbulent core inversion is not yet fully understood Jet model Standard (spherical shock) model Density t = 1800 sec 9 x 109cm 1012cm [Kifonidis et al., AA. 408, 621 (2003)] • Pre-supernova structure is multilayered • Supernova explodes by a strong shock • Turbulent hydrodynamic mixing results • Core ejection depends on this turbulent hydro. • Accurate 3D modeling is required, but difficult • Scaled 3D testbed experiments are possible 6 x 109cm [Khokhlov et al., Ap.J.Lett. 524, L107 (1999)] R. Boyd 04/18/07

  21. Core-collapse supernova explosionmechanisms remain uncertain • A new model of Supernova explosions: from Adam Burrows et al. • A cutaway view shows the inner regions of a star 25 times more massive than the sun during the last split second before exploding as a SN, as visualized in a computer simulation. Purple represents the star’s inner core; Green (Brown) represents high (low) heat content • In the Burrows model, after about half a second, the collapsing inner core begins to vibrate in “g-mode” oscillations. These grow, and after about 700 ms, create sound waves with frequencies of 200 to 400 hertz. This acoustic power couples to the outer regions of the star with high efficiency, causing the SN to explode From http://www.msnbc.msn.com/id/11463498/ • Burrows’ solution hasn’t been accepted by everyone; it’s very different from • any previously proposed. But others (Blondin/Mezzacappa) are also looking at • instabilities as the source of the explosion mechanism R. Boyd 04/18/07

  22. The NRC committee on the Physics of the Universe highlighted the new frontier of HED Science Eleven science questions for the new century: 2. What is the nature of dark energy? — Type 1A SNe (burn, hydro, rad flow, opacities, EOS, age of universe) 4. Did Einstein have the last word on gravity? — Accreting black holes (photoionized plasmas, spectroscopy) 6. How do cosmic accelerators work and what are they accelerating? —Cosmic rays (strong field physics, nonlinear plasma waves) 8. Are there new states of matter at exceedingly high density and temperature? —Neutron star interior (photoionized plasmas, spectroscopy, EOS) NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES 10. How were the elements from iron to uranium made and ejected? —Core-collapse SNe (reactions of stellar burning, turbulent hydro, rad flow, neutrinos) • HEDP provides crucial experiments to interpreting astrophysical observations • We envision that NIF will play a key role in these measurements R. Boyd 04/18/07

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