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NEEP 541 – Neutron Damage

This outline covers the fundamentals of neutron damage, including definitions, modeling, inelastic collisions, and empirical data. Learn how neutron-target collisions lead to damage and the unique behavior of neutrons. Explore the impact of thermal and fast neutrons, inelastic collisions, and example calculations. Discover typical fusion dose rates, spectra, accelerator sources, and recoil spectra. Gain insights into damage cross sections, thresholds, and neutron absorption processes.

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NEEP 541 – Neutron Damage

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  1. NEEP 541 – Neutron Damage Fall 2002 Jake Blanchard

  2. Outline • Neutron Damage • Definitions • Modeling • Inelastic Collisions • Empirical Data

  3. Introduction • Neutron damage results from the production of PKAs by neutron-target collisions • Neutrons, because they aren’t charged, behave differently from other particles we’ve discussed • The mean free path of fast neutrons in most solids is on the order of 15 cm

  4. Definitions

  5. Thermal Neutrons • Thermal Neutrons produce damage through (n,) reactions, eg. • 27Al+n -> 28Al+Q • For this reaction, Q=7.73 MeV, T=1.1 keV

  6. Fast Neutrons • At low neutron energy (<1 MeV), angular distributions of elastically scattered neutrons is isotropic • As E increases, scattering is more forward • Above a few MeV, scattering becomes inelastic (nucleus is excited, and later emits a photon

  7. Inelastic Collisions • Nucleus recoils in excited state • Kinetic energy not conserved • Excitation energy is Q • Threshold energy exists • Neutron is absorbed, then emitted (fairly isotropic)

  8. Inelastic Collisions

  9. Inelastic Collisions

  10. Inelastic Collisions

  11. Inelastic Collisions

  12. Inelastic Collisions

  13. Example • N=0.0805 /cubic angstrom • el=3 barns • Flux=1015 n/cm2/s • Displacement rate=8.5 1016 disp/cm3/s • Rd/N=33 dpa/year

  14. Plot of d vs E for elastic and inelastic

  15. Typical Fusion Dose Rates 14 MeV neutrons, 1 MW/m2 wall loading

  16. Sample Dose Rates (dpa/s) • Magnetic fusion=3 10-7 • Inertial fusion=3 • Fission= 10-6 • Ion beams= 10-4-10-2 • Electron beams= 10-3

  17. Spectra Fission Lethargy=E

  18. Accelerator Sources • D-T interactions • Spallation uses proton beams (hundreds of MeV) aimed at large targets

  19. Recoil Spectra

  20. Damage Cross Sections

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