The neutron radius of 208Pb and neutron star structure.

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The neutron radius of 208Pb and neutron star
structure.

• http//www.astro.cornell.edu/shami/guitar/
  guitar nebula, neutron star bow wave

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Outline

• The big picture
• Neutrons in nuclei
• Neutron stars and nuclear matter
• Conclusion

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Phase diagram of waterThe state of matter
depends on pressure, temperature, and density.
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New phases of matter

• We see in the case of water that new phases of
  matter appear at pressures far from our normal
  experience, for example, Ice XI at 1 million
  atmospheres.
• What would happen to matter if we could continue
  to crush it under high pressure?
• What is the phase diagram of matter under extreme
  conditions?

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World map in 1532 Typus Cosmographicus
Universalis, S. Grynaeus/H. Hoblein/S. Münster,
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Danger in new territories!What we dont know for
a fact we can compensate for by imagination.
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Physical properties of systems containing nuclear
matter
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Phase diagram of nuclear matter
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Nuclei and Neutron Stars

• Nuclei are the central cores of atoms. Almost all
  the visible mass in the universe is in protons
  and nuclei.
• Neutron stars are the collapsed iron cores of
  massive stars ( stars with masses greater than 8
  solar masses). These stars no longer generate
  energy internally by nuclear fusion, although
  they can be the sites of huge bursts of energy.

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Equation of state (eos) connects nuclear physics
and neutron stars
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Interactions affect the EOS
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Measuring matter in small boxes

• We measure the angle of scatter, a, of high
  energy electrons ( E 1 GeV) from nuclei.
• R 5.5 x 10-13 cm, dR 0.2 F/ Pg. ,1F 10-13 cm
• Pg. photon momentum in GeV

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Electron Scattering gives very precise
information on charge distributions in the nucleus
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The neutron distribution is not so well known as
the proton .

• Photons couple poorly to neutral neutrons
  compared to the charged protons.
• However, electrons interact with nucleons via the
  weak interaction too.
• The Z0 boson of the weak interaction interacts
  several times more strongly with neutrons than
  with protons.
• Weak interaction scattering is a tough
  experimental challenge.

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Rn Rp for two different theories of the nuclear
mean field
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Look for helicity asymmetry in electron scattering
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Helicity dependent Scattering Asymmetry for
Polarized Electrons
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Aerial View of JLab Accelerator
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Hall A Spectrometers
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High Power Cryogenic Lead Target Built and tested
at CSLA
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High rate integrating detector
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What keeps a star stable?
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Formation of Neutron stars
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Quantum Ideal Gas
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Final state of a massive neutron star
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A 12 km radius neutron star in Los Angeles
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Complementary Laboratories
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Nuclear parameter dependence of N-star radius
calculations
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Neutron Star Structure
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Some statistics of n-stars

• More than 1100 n-stars have been detected,
  primarily as pulsars
• The masses tend to center about 1.4 solar masses
  and the limits expected are 0.2but the creation mechanism may fix the mass at
  1.4 Msun
• Radius determinations are difficult and
  controversial in the 7 to 15 km range
• Reliable measurements of M and R would place
  severe restraints on the EOS
• Pulsars have high velocities, avg 450 km/s
  indicating an asymmetrical core collapse

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Are there areas of the phase diagram that have
never been populated in the history of the
Universe?