Interaction of electrons with matter Interaction of photons with matter

1. Part B. Radiation sources • Interaction of electrons with matter • Interaction of photons with matter • Interaction of neutrons with matter • Interaction of protons with matter

2. 1. Interaction of electrons with matter The physical processes: 1. Ionization losses inelastic collisions with orbital electrons 2. Bremsstrahlung losses inelastic collisions with atomic nuclei 3. Rutherford scattering elastic collisions with atomic nuclei Positrons at nearly rest energy: annihilation emission of two 511 keV photons

3. 1. Interaction of electrons with matter Graphite – Z = 6 Electrons – stopping power Copper – Z = 29 Lead – Z = 82

4. 1. Interaction of electrons with matter Continuous Slowing Down Approximation range: Radiation yield: Fraction of the initial kinetic energy that is converted to Bremsstrahlung energy as the electron slows down to rest.

5. 1. Interaction of electrons with matter Differential Bremsstrahlung cross section: mbarn mbarn lead – Z = 82 k/T k: photon energy T: electron kinetic energy carbon – Z = 6 k/T

6. 1. Interaction of electrons with matter Multiple scattering mean scattering angle mass scattering power Ssc Es = 21.2 MeV X0: radiation length β: v/c p: momentum

7. 2. Interaction of photons with matter The physical processes: 1. Photo-electric effect removal of an orbital electron of the inner shells (K,L,M) 2.Compton scattering inelastic scattering on loosely bound electrons 3.Pair production production of e-/e+ pair essentially with nuclei 4.Rayleigh (coherent) scattering elastic scattering not important for radiation physics

8. 2. Interaction of photons with matter Photon cross sections Graphite - Z = 6

9. 2. Interaction of photons with matter Photon cross sections Lead - Z = 82

10. 2. Interaction of photons with matter Photo-electric effect: photo-electron ΔE = E0 – E1 = Ka ΔE = E – E0 ΔE = E0 – E2 = Kb E2 E0 E1 E0 E K L M N K L M N incoming X-ray The K lines ΔE = E1 – E2 = La Auger-electron E1 E1 ΔE = E1 – E2 – E3 E2 E2 ΔE = E1 – E3 = Lb K L M N K L M N E3 E3 The L lines Auger electron

11. 2. Interaction of photons with matter Compton scattering: scattered photon energy Ec θ Compton electron energy = E0 - Ec primary photon energy E0 dσ/dW (re2 x cm2 / electron) Ec (MeV)

12. 2. Interaction of photons with matter Pair production: σnucleus Z2 threshold: 1.022 MeV σelectron Z threshold: 2.044 MeV

13. 2. Interaction of photons with matter Interaction of photons with matter Macroscopic description - Attenuation factors The mass attenuation coefficient μ/ρ: units: cm2.g-1 The linear attenuation coefficient μ: units: cm-1 The conversion factor from σ (barns.atom-1) to μ/r (cm2.g-1): N d (cm) d (g.cm-2)

14. Particles involved: Electrons / Positrons Photons Neutrons 2. Interaction of photons with matter

15. 2. Interaction of photons with matter Electromagnetic cascade cm one 500 MeV electron interacting with lead target

16. 2. Interaction of photons with matter Electromagnetic cascade cm one 6 GeV electron interacting with lead target

17. 2. Interaction of photons with matter photonuclear reactions Photonuclear reactions: Neutron production Photo-pion γ(d,p)n Quasi-deuteron Giant resonance m e-60/E sγ(d,p)n 55Mn(γ, n)54Mn

18. 2. Interaction of photons with matter Photonuclear reactions: Neutron production Giant resonance Quasi-deuteron Photo-pion Example: neutron spectrum produced by 600 MeV electrons on Cu target

19. 3. Interaction of neutrons with matter The physical processes: • 1. Elastic scattering • compound elastic scattering • potential scattering • 2. Inelastic scattering (n,n’) • 3. Other inelastic reactions: (n,p), (n,a), … • 4. Absorption reactions • radioactive capture • charged particle reactions • 5. Direct reactions: spallation

20. 3. Interaction of neutrons with matter Compound nucleus formation target nucleus ZA neutron energy = EC

21. 3. Interaction of neutrons with matter Neutron cross sections Example 1: iron

22. 3. Interaction of neutrons with matter Neutron cross sections Example 2: cadmium

23. 3. Interaction of neutrons with matter Neutron cross sections Example 3: hydrogen

24. 3. Interaction of neutrons with matter Neutron cross sections Example 4: boron

25. 3. Interaction of neutrons with matter Neutron cross sections inelastic cross section (barn) Example: iron neutron energy (GeV)

26. 3. Interaction of neutrons with matter scattered neutron energy = E1 Elastic scattering target nucleus initial neutron energy = E0 recoiling nucleus Minimum energy of scattered neutron: Average energy loss per collision:

27. 4. Interaction of protons with matter The physical processes: • ionization • inelastic proton-nucleus scattering • spallation

28. 4. Interaction of protons with matter Proton ionization loss – Stopping power stopping power (MeV.g-1.cm2) minimum ionizing particle proton energy (MeV)

29. 4. Interaction of protons with matter Comparison CSDA range of protons and electrons in iron

30. 4. Interaction of protons with matter Inelastic proton – nucleus scattering: Spallation reaction n n p π Δ π incident proton (GeV range) n p intra-nuclear cascade α d n evaporation γ

31. 4. Interaction of protons with matter Inelastic proton – nucleus scattering Spallation reaction Inelastic cross section E > 1 GeV

32. 4. Interaction of protons with matter Inelastic proton – nucleus scattering Comparison ionization energy loss and inelastic scattering  E > 1 GeV: 100 % probability for spallation reaction

33. 4. Interaction of protons with matter n inter-nuclear cascades Spallation n p π Δ π incident proton (GeV range) n p intra-nuclear cascade Neutron transport below 20 MeV evaporation α d α spallation product α, β, γ decay n fast induced fission γ p γ n n n fission n n n fission products fission products (n,n’), (n,xn), (n, γ) ,… reactions γ γ

34. 4. Interaction of protons with matter Spallation