Nuclear Astrophysics with NIF:Studying Stars in the Laboratory

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344LLNL-PRES-402644

Richard N. Boyd

Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology

July 11, 2008

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NIF has 3 Missions

National Ignition Facility

Peer-reviewed Basic Science is a fundamental part of NIF’s plan

Stockpile Stewardship

BasicScience

FusionEnergy

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We have already fielded ~ half of all the types of diagnostic systems needed for NIF science

Full ApertureBackscatter

Diagnostic Instrument Manipulator (DIM)

Diagnostic Instrument Manipulator (DIM)

X-ray imager

Streaked x-ray detector

VISAR

Velocity Measurements

Static x-rayimager

FFLEX

Hard x-ray spectrometer

Near Backscatter Imager

DANTE

Soft x-ray temperature

Diagnostic Alignment System

Cross Timing System

We have 30 types of diagnosticsystems planned for NIC

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NIF’s Unprecedented Scientific Environments:

• T >108 K matter temperature • >103 g/cc density

Those are both 7x what the Sun does! Helium burning, stage 2 in stellar evolution, occurs at 2x108 K!

• n = 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!

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Reaction Studies for Nuclear Astrophysics

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• Thermonuclear Reaction Rates between charged particles are of the form:

Rate ~ < v> = (8/)1/2 (kBT)-3/2 0 E (E) exp[-E/kBT] dE.

Define (E) = [S(E)/E] exp[- bE-1/2],

where penetrability = exp[- 2 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

Stellar Astrophysics at NIF: Measurements of Basic Thermonuclear Reactions

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NIF and Neutrino Mixing

The Sun emits electron-neutrinos e, but some of them change to some other “flavor” of neutrino x by the time they get to Earth:

Oscillation probability = sin22 sin2(m2L/4E),

where = the mixing angle, m2 = m22 – m1

2, 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.

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Nuclear Reactions and Solar Neutrinos

1H

1H

1H

8B

e-3He

1H

7Li

7Be

4He

3He

2H; LE-’s

1H

4He+1H+1H

4He+4He

8Be*; HE-’s

4He+4He

pp-I

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.

The pp-chains of H-burning

3He+4He→7Be+ is crucial for predicting the neutrino spectrum. But it has proved to be a difficult reaction for which to measure the cross section.

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Comparison of 3He(4He,)7Be Measured at an Accelerator Lab and Using NIF

NIF-Based Experiments

Gamow window

Resonance

Accelerator-Based Experiments

Mono-energetic

Low event rate (few events/month)

Inconsistency between two techniques

High Count rate (~105 atoms per shot)

Integral experiment

Should resolve inconsistency

Detect 7Be with RadChem diagnostic system

Be Ablator

3He(4He,)7Be

XX

1018 3He + 4He atoms

√

√

√

√

√

NIF Point?

3He(4He,) provides important definition of neutrino parameters!

Gyurky et al.

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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

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

MS

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NIF’s Contribution: 14N(p,) Reaction Rate

Astrophysical S-factor for 14N(p,) 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.

The 14N(p,)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.

12C

13N

13C 14N

15O

15N

(p,)

(p,)

(p,)

(p,)

-decay

-decay 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.

Primary CNO-cycle

This is a difficult reaction to study with an accelerator beam; it’s less complicated (!) with NIF.

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Measuring s-process rates in a hot plasma

Er

Tm

Yb

Lu

Hf

168

169

170 171 172 173 174 4.2d 176

9.4d 170

129d 1.9y 64h

1753.7h 176 6.7d

178177176

7.5h

1.9h

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 -decay rate and the effective cross section, possibly by large factors.

NIF will be able to measure that effect for the neutron captures.

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How to do an s-process experiment on NIF?

N172 = collection ∫∫∫ n(r,t,En) N171 (n,)171(En) (4r2)-1 dr dt dEn

↓

N172/N170 → ∫N171 (n,)171 dEn / ∫N169 (n,)

169 dEn

Co-loading isotopes for which the cross section is known with that on which it is to be measured minimizes systematic uncertainties

n determined from NTOF

Ablator

T Ice

T Gas

Compress pellet by a (radial) factor of 20; get neutrons up to a few MeV from T+T→4He+2n

Insert ~1015-16 171Tm + 169Tm

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A unique NIF opportunity: Study ofa Three-Body Reaction in the r-Process

Abu

ndan

ce a

fter

d

ecay

60 80 100 120 140 160 180 200 220Mass Number (A)

• 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 ++n9Be reaction

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8Be

During its 10-16 s half-life, a 8Be can capture a neutron to make 9Be, in the r-process environment, and even in the NIF target

n

9Be

• If this reaction is strong, 9Be becomes abundant, +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

• 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

+n9Be is the “Gatekeeper” for the r-Process

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How to detect the reaction products from NIF?

Detector

SecCryoCollector (4K)

2. PrimCryo (4K)Collector

Hot He Gas

Hot He Gas

1. PrimCryo (30K)Collector

RGA

Shielding

OuterConcrete Wall

T-Chamber

UHVPumpLine

Detector (4 Ge det.)(event mode)

Dedicated Radchem Gas Collection System at NIF

TurboPump

Main Cryo-Pump

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Core-collapse supernova explosion mechanisms remain uncertain

6 x 109cm

• SN observations suggest rapid core penetration to the “surface”• This observed turbulent core inversion is not yet fully understood

Standard (spherical shock) model

[Kifonidis et al., AA. 408, 621 (2003)]

Densityt = 1800 sec

Jet model

[Khokhlov et al., Ap.J.Lett. 524, L107 (1999)]

• 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

1012cm

9 x

109 c

m

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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

From http://www.msnbc.msn.com/id/11463498/

• 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

• 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

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• HEDP provides crucial experiments to interpreting astrophysical observations• We envision that NIF will play a key role in these measurements

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)

6. How do cosmic accelerators work and what are they accelerating?

— Cosmic rays (strong field physics, nonlinear plasma waves)

4. Did Einstein have the last word on gravity? — Accreting black holes (photoionized

plasmas, spectroscopy)

8. Are there new states of matter at exceedingly high density and temperature?— Neutron star interior (photoionized plasmas,

spectroscopy, EOS)

10. How were the elements from iron to uranium made and ejected?

— Core-collapse SNe (reactions of stellar burning, turbulent hydro, rad flow, neutrinos)

NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES

The NRC committee on the Physics of the Universe highlighted the new frontier of HED Science

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