1 / 29

NEEP 541 Radiation Interactions

NEEP 541 Radiation Interactions. Fall 2003 Jake Blanchard. Outline. Elementary Particles Electrons Ions Neutrons Photons Radiation in Space Photon Interactions Charge Transfer. Elementary Particles. Photons no mass no charge. Elementary Particles. Electrons Light

moral
Download Presentation

NEEP 541 Radiation Interactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. NEEP 541Radiation Interactions Fall 2003 Jake Blanchard

  2. Outline • Elementary Particles • Electrons • Ions • Neutrons • Photons • Radiation in Space • Photon Interactions • Charge Transfer

  3. Elementary Particles • Photons • no mass • no charge

  4. Elementary Particles • Electrons • Light • negatively charged • Rest mass=0.51 MeV • Protons • Mass about 1837 times that of an electron • Positive charge • Neutron • Slightly heavier than proton • No charge

  5. Neutrons • Flux is neutrons/area/time • Equivalent to beam intensity

  6. Fission Energy Spectrum

  7. Neutrons • Collisions are elastic or inelastic • Neutrons can be captured, form compound nucleus; then nucleus emits neutrons, protons, gammas, or fission products • These products are “recoils”

  8. Recoil and PKA spectra recoils PKAs

  9. Gammas • Mean gamma energies are on the order of 100 eV • Negligible effect on displacements

  10. Electrons • Charge implies short range, but low mass implies longer range • Most energy transfer is to other electrons in target • Collisions are coulomb • Must be relativistic to cause displacements (> ~0.2 MeV) • Low temperature irradiation leads to homogeneous vacancy and interstitial distribution over about 1 mm

  11. Positive Ions • Light ions = He, H, D (> 1 MeV) • Heavy ions (<1 MeV) • Fission products (~100 MeV) • Inelastic losses low at low energy • Electrons dominate at high energy • Damage is narrower because range is smaller

  12. Radiation in Space • Energies from keV to TeV • Particles are trapped by Earth’s magnetic field or pass through solar system • Trapped radiation is broad spectrum of charged particles (radiation belts) • Cosmic Rays are low fluxes of heavy ions beyond TeV • Solar Flares produce protons with energies to hundreds of MeV • Space is also pervaded by plasma of electrons and protons with energies around 100 keV

  13. Energies

  14. Belts

  15. Plasma Conditions

  16. More Plasma

  17. Van Allen Belts

  18. Cosmic Rays • 85% protons, 14% alpha particles • 1% nuclides with Z>4 (ions of Z>26 are rare) • energies from 0 to over 10 GeV • Most heavy ions are H, He, C, and O with peak energies around 1 GeV. • Cosmic rays have low flux but higher energy

  19. Solar Flares • heaviest doses at solar maximum (10-12 yrs) • Flares produce heavy ions and protons (90%, remainder is He, heavy ions, electrons) • Heavy ion fluxes from solar flares are generally less than galactic background but can be 4 times greater • Hheavy ion spectrum is less energetic than galactic cosmic ray spectrum • Solar protons are energetic (10 MeV to 1 GeV) • Protons from a single flare produce fluences up to ~2x1010 p/cm2

  20. Radiation Interactions • What happens when energetic particles interact? • Elastic Scattering • Inelastic Scattering • Bremsstrahlung Radiation • Accelerating charged particles emit radiation • Amplitude of radiation is proportional to acceleration

  21. Photon Interactions • Photoelectric Effect – low energy • Photon interacts with target electrons and is absorbed • Electron is ejected • Electron energy is photon energy minus binding energy • Binding energy reappears as x-rays

  22. Photon Interactions • Compton Effect • Elastic scattering between photon and target electron • Electrons emitted in spectrum with average about 2/3 of maximum

  23. Photon Interactions • Pair production • Threshold energy is 1 MeV • Photon disappears and electron-positron pair is formed

  24. Attenuation Coefficients • Measure of absorption of beam impinging on absorbing medium • Units are inverse length • Total attenuation coefficient is sum of contributions from three photon interaction effects

  25. Attenuation of Photons in Air

  26. Attenuation of Photons in Lead

  27. Attenuation of Photons in Al

  28. Charge Transfer • Radiation interactions result in the transfer of charge from one location to another • Electrons from photon interactions tend to be emitted with a forward bias, so there is a net charge transfer in the forward direction • For 1.3 MeV photons on Si, current is on the order of 10-21 C/photon (Compton scattering)

  29. Forward Electron Current

More Related