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Radiation Interaction - Detection

Radiation Interaction - Detection. and shielding!!. Radiation detection requires that radiation interacts with detector material. Energy deposition (not all detectors…!). Charged particles continuously transfer their energy to the medium. http://www.srim.org

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Radiation Interaction - Detection

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  1. Radiation Interaction - Detection and shielding!! • Radiation detection requires that radiation interacts with detector material. • Energy deposition (not all detectors…!). • Charged particles continuously transfer their energy to the medium. • http://www.srim.org • Gammas and X-rays interact (if they do) catastrophically. • http://physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html • Photon interactions produce secondary electrons. • Neutron interactions produce secondary heavy charged particles. Energy Loss: Electronic or nuclear Attenuation: Absorption or scattering I0 I Usually corresponds to net area under the full energy peak. If not, then build-up. Good or bad geometry. Could be secondary gamma, but for shielding. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh). Collimation.

  2. Radiation Interaction - Detection Charged particles. Gamma. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  3. Radiation Interaction - Detection Interaction of gammas Buildup Factor • Partial or complete transfer of photon energy to electrons. • Many types of interactions, but three (or four) are important. • Attenuation coefficient and • mass attenuation coefficient. • Compare to macroscopic cross section  for neutrons. HW 11 What is coherent scattering. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  4. Radiation Interaction - Detection Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  5. Radiation Interaction - Detection Photoelectric Absorption. (with atoms, why??): Spectrum if all energy is captured in detector. Allows identification of gamma energy. • Large Detector. • Photo Peak or Full Energy Peak…? • Doppler. • Cost. • Crystal growth. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  6. Radiation Interaction - Detection • Spectroscopy, energy deposition. • Consider what might escape. • Size and material of detector. • Shield lining. Considerations for shields and detectors? Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  7. Radiation Interaction - Detection HW 12 HPGe Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  8. Radiation Interaction - Detection • “Probability” for photoelectric absorption • Strong Z dependence. • Considerations for shields and detectors. Theoretical Practical Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  9. Radiation Interaction - Detection Efficiency considerations. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  10. Radiation Interaction - Detection NaI or BGO Efficiency vs. Resolution HPGe Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  11. Radiation Interaction - Detection Considerations for shields and detectors? Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  12. Radiation Interaction - Detection Compton Scattering. • In the figure: • Photoelectric suppressed. • Single Compton (effect of crystal dimensions). • Below 1.022 MeV. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  13. Radiation Interaction - Detection Reproduce the graph. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  14. Radiation Interaction - Detection • Compton scattering is predominant for energies typical of radioisotope sources. • “Probability” per atom increases linearly with Z (Why). • Electron density. • Effect of binding energy. • Effect of polarized photons. • Compton fraction. HW 13 Let the recoil electron be emitted at an angle , calculate cot() as a function of tan(/2). Klein-Nishina formula Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  15. Radiation Interaction - Detection HW 14 What is Thomson scattering. Note tendency for forward scattering at high energies. Considerations for shields and detectors? Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  16. Radiation Interaction - Detection If you need to measure gamma ray yield from nuclear reactions (using particle accelerators), the photon energies could be as high as 10 MeV. What is the typical Ge detector to be used? Prepared with Monte Carlo simulations. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  17. Radiation Interaction - Detection Pair Production. Single peak if electron and positron “kinetic” energies are captured by the detector. Rest mass of electron and positron. Gamma must have 1.022 MeV minimum energy for PP to occur. Two annihilation photons are then created when positron recombines with an electron. This photon may or may not be captured, causing single and double escape peaks in the spectrum (effect of crystal dimensions). Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  18. Radiation Interaction - Detection High-energy gamma. Low-energy gamma. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  19. Radiation Interaction - Detection Probability of pair production. Recoil nucleus, Why? Effect of screening? HW 15 Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  20. Radiation Interaction - Detection Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  21. Radiation Interaction - Detection Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  22. Radiation Interaction - Detection HPGe Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  23. Radiation Interaction - Detection Very large detector. All secondary radiation, including Compton scattered gamma rays, Bremsstrahlung, x-rays and annihilation photons, are captured in detector volume Large photofraction (fraction of full energy events) is desired in any detector Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  24. Radiation Interaction - Detection Very small detectors. All secondary radiation, including Compton scattered gamma rays and annihilation photons, are not captured in detector volume (escaping). Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  25. Radiation Interaction - Detection A typical detector. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  26. Radiation Interaction - Detection Effect of surrounding material. Detectors are normally shielded to minimize as much as possible the counting of ambient background radiation. X-rays and lining. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  27. Radiation Interaction - Detection • Peak area determination. • Peak-to-total ratio. • Peak-to-Compton ratio. • Relative efficiency. • Absolute efficiency. • Total efficiency. • Solid angle. • Energy Resolution (effect of number of charge carriers). • Dead time. • Resolving time. • Anti-coincidences. • Coincidences. • Summation effects. • True coincidences. • Random coincidences. • Attenuation coefficient. • Mass attenuation coefficient. • Mean-free path. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  28. Radiation Interaction - Detection Select events. Compton suppression. “Anti-coincidences”. What if cascades are present? Coincidences. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  29. Radiation Interaction - Detection Cascade selection Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  30. Radiation Interaction - Detection Compton spectrometer Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  31. Radiation Interaction - Detection THINKING QUIZ Probability of interaction or of no-interaction? Mass thickness Linear attenuation coefficient  = t (photoelectric) + s(Compton) + k (pair production) Mass attenuation coefficient is independent of density and physical state. HW 16 Mean free path Compounds and mixtures?? Give examples. Refer to XCOM. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  32. Radiation Interaction - Detection Photon Attenuation Build-up Solutions to buildup problem? Not realistic…!! Valid for parallel photon paths or far geometries. Self-Absorption HW 17 Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  33. Radiation Interaction - Detection Solutions to self absorption at close geometries? MC Isotropic Photon Emission Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  34. Radiation Interaction - Detection Geometric correction factor THINKING QUIZ Detector Point Source Detector Extended Source Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

  35. Radiation Interaction - Detection Neutron Interaction • Secondary radiation is different from that for gammas, it is mainly heavy charged particles (or gammas). • Utilize them for neutron detection (Chapters 14 and 15). • Slow neutrons: Thermalized through scattering then detected through reactions. • Fast neutrons: Recoil nuclei (elastic) and probable gammas (inelastic). • (Shielding vs. detection). Cd cutoff energy. Macroscopic cross section Nuclei per unit volume Mean free path? Neutron flux? • Later in this course We will discuss neutron detection. Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).

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