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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

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


Nif has 3 missions
NIF has 3 Missions

National Ignition Facility


Stockpile Stewardship


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

R. Boyd 04/18/07

We have 30 types of diagnostic systems planned for nic
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


Hard x-ray spectrometer

Diagnostic Instrument Manipulator (DIM)


Soft x-ray temperature

Static x-ray



Velocity Measurements

Full Aperture


Cross Timing System

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

R. Boyd 04/18/07

Nif s unprecedented scientific environments
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

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

Nif and neutrino mixing
NIF and Neutrino Mixing Thermonuclear Reactions

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

Nuclear reactions and solar neutrinos
Nuclear Reactions and Solar Neutrinos Thermonuclear Reactions


The pp-chains of H-burning

2H; LE-n’s












8Be*; HE-n’s







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

Comparison of 3 he 4 he 7 be measured at an accelerator lab and using nif
Comparison of Thermonuclear Reactions3He(4He,)7Be Measured at an Accelerator Lab and Using NIF

Accelerator-Based Experiments

NIF-Based Experiments


Be Ablator

NIF Point?

1018 3He + 4He atoms


Gamow window

High Count rate (~105 atoms per shot)

Integral experiment

Should resolve inconsistency

Detect 7Be with RadChem diagnostic system

Gyurky et al.


Low event rate (few events/month)

Inconsistency between two techniques



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

R. Boyd 04/18/07

Measuring The Age of the Universe Thermonuclear Reactions

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

R. Boyd 04/18/07

Nif s contribution 14 n p g reaction rate
NIF’s Contribution: Thermonuclear Reactions14N(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.




Primary CNO-cycle


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.




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.






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

R. Boyd 04/18/07

Measuring s process rates in a hot plasma

176 Thermonuclear Reactions




3.7h 176























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

How to do an s process experiment on nif
How to do an s-process experiment on NIF? Thermonuclear Reactions


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

A unique nif opportunity study of a three body reaction in the r process

Abundance after Thermonuclear Reactions 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

A a n 9 be is the gatekeeper for the r process
a+a Thermonuclear Reactions+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



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




  • 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

How to detect the reaction products from nif
How to detect the reaction products from NIF? Thermonuclear Reactions

R. Boyd 04/18/07

R. Boyd 04/18/07 Thermonuclear Reactions

Core collapse supernova explosion mechanisms remain uncertain
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


t = 1800 sec

9 x 109cm


[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

Core collapse supernova explosion mechanisms remain uncertain1
Core-collapse supernova explosion uncertainmechanisms 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


  • 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

The nrc committee on the physics of the universe highlighted the new frontier of hed science
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)



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

R. Boyd 04/18/07 the new frontier of HED Science