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NEEP 541 – Neutron Damage

NEEP 541 – Neutron Damage. Fall 2002 Jake Blanchard. Outline. Neutron Damage Definitions Modeling Inelastic Collisions Empirical Data. Introduction. Neutron damage results from the production of PKAs by neutron-target collisions

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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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