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Part 2. IAEA Training Material on Radiation Protection in Nuclear Medicine. Radiation Physics. Objective.

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Part 2

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  1. Part 2 IAEA Training Material on Radiation Protection in Nuclear Medicine Radiation Physics

  2. Objective To become familiar with the basic knowledge in radiation physics, dosimetric quantities and units to perform related calculations, different types of radiation detectors and their characteristics, their operating principles, and limitations. Part 2: Radiation Physics

  3. Content • Atomic structure • Radioactive decay • Production of radionuclides • Interaction of ionizing radiation with matter • Radiation quantities and units • Radiation detectors Note: Radiation units & quantities are in the process of undergoing consensus through ICRU and IAEA. There may be changes necessitating incorporation in this CD. Part 2: Radiation Physics

  4. Part 2. Radiation Physics IAEA Training Material on Radiation Protection in Nuclear Medicine Module 2.1. Atomic structure

  5. THE ATOM • The nucleus structure • protons and neutrons = nucleons • Z protons with a positive electric charge (1.6 10-19 C) • neutrons with no charge (neutral) • number of nucleons = mass number A • The extranucleus structure • Z electrons (light particles with electric charge) • equal to proton charge but negative Particle Symbol Mass Energy Charge (kg) (MeV) ---------------------------------------------------------- Proton p 1.672*10-27 938.2 + Neutron n 1.675*10 -27 939.2 0 Electron e 0.911*10 -30 0.511 - Part 2: Radiation Physics

  6. Identification of an Isotope Part 2: Radiation Physics

  7. Ernest Rutherford (1871-1937) Part 2: Radiation Physics

  8. Electron Binding Energy • Electrons can have only discrete energy levels • To remove an electron from its shell  E  electron binding energy • Discrete shells around the nucleus : K, L, M, … • K shell has maximum energy (i.e. stability) • Binding energy decreasing when Z increases • Maximum number of electrons in each shell : 2 in K,8 in L shell, … Part 2: Radiation Physics

  9. Ionization-Excitation Energy Part 2: Radiation Physics

  10. De-excitation Auger- electron characteristic radiation Part 2: Radiation Physics

  11. The NucleusEnergy Levels ENERGY Excitation Deexcitation Particle emission 0 MeV ~8 MeV Gamma ray Occupied levels The nucleons can occupy different energy levels and the nucleus can be present in a ground state or in an excited state. An excited state can be reached by adding energy to the nucleus. At deexcitation the nucleus will emit the excess of energy by particle emission or by electromagnetic radiation. In this case the electromagnetic radiation is called a gamma ray. The energy of the gamma ray will be the difference in energies between the different energy levels in the nucleus. Part 2: Radiation Physics

  12. Isomeric Transition Normally the excited nucleus will undergo de-excitation within picoseconds. In some cases, however, a mean residence time for the excited level can be measured. The de-excitation of such a level is then called isomeric transition (IT). This property of a nucleus is noted in the label of a nuclide by adding the letter m in the following way: technetium-99m, Tc-99m or 99mTc Part 2: Radiation Physics

  13. Nuclear Excitation • Energy particles photons Part 2: Radiation Physics

  14. Nuclear De-excitation alpha-particle beta-particle Gamma radiation Part 2: Radiation Physics

  15. Internal Conversion characteristic radiation conversion electron Part 2: Radiation Physics

  16. Gamma Ray Spectrum(characteristic of the nucleus) Part 2: Radiation Physics

  17. Photons are part of the electromagnetic spectrum IR: infrared, UV: ultraviolet Part 2: Radiation Physics

  18. Part 2. Radiation Physics IAEA Training Material on Radiation Protection in Nuclear Medicine Module 2.2. Radioactive decay

  19. Stable Nuclides long ranged electrostatic forces p Line of stability p n short ranged nuclear forces Part 2: Radiation Physics

  20. Stable and Unstable Nuclides Too many neutrons for stability Too many protons for stability Part 2: Radiation Physics

  21. RadioactiveDecay Fission The nucleus is divided into two parts, fission fragments. and 3-4 neutrons. Examples: Cf-252 (spontaneous), U-235 (induced) a-decay The nucleus emits an a-particle (He-4). Examples: Ra-226, Rn-222 b-decay Too many neutrons results in b- -decay. n=>p++e-+n. Example:H-3, C-14, I-131. Too many protons results in b+ -decay p+=>n+ e++nExamples: O-16, F-18 or electron capture (EC). p+ + e-=>n+n Examples: I-125, Tl-201 Part 2: Radiation Physics

  22. Radioactive Decay It is impossible to know at what time a certain radioactive nucleus will decay. It is, however possible to determine the probability l of decay in a certain time. In a sample of N nuclei the number of decays per unit time is then: Part 2: Radiation Physics

  23. Activity The number of decaying nuclei per unit of time 1 Bq (becquerel)=1 per second Part 2: Radiation Physics

  24. 1 Bq is a small quantity • 3000 Bq in the body from natural sources • 20 000 000-1000 000 000 Bq in nuclear medicine examinations Part 2: Radiation Physics

  25. Multiple & Prefixes (Activity) Multiple Prefix Abbreviation 1 - Bq 1 000 000 Mega (M) MBq 1 000 000 000 Giga (G) GBq 1 000 000 000 000 Tera (T) TBq Part 2: Radiation Physics

  26. Henri Becquerel 1852-1908 Part 2: Radiation Physics

  27. Maria Curie 1867-1934 Part 2: Radiation Physics

  28. Parent-Daughter Decay A B C λ2 λ1 Part 2: Radiation Physics

  29. Parent-Daughter Decay Secular equilibrium TB<<TA≈ ∞ Transient equilibrium TA≈ 10 TB No equilibrium TA≈ 1/10 TB Part 2: Radiation Physics

  30. 99Mo-99mTc 87.6% 99mTc 99Mo  140 keV T½ = 6.02 h 12.4% ß- 442 keV  739 keV T½ = 2.75 d 99Tc ß- 292 keV T½ = 2*105 y 99Ru stable Part 2: Radiation Physics

  31. Irene Curie (1897-1956)&Frederic Joliot (1900-1958) Part 2: Radiation Physics

  32. Part 2. Radiation Physics IAEA Training Material on Radiation Protection in Nuclear Medicine Module 2.4. Interaction of Ionizing Radiation with Matter

  33. Ionizing Radiation • Charged particles • alpha-particles • beta-particles • protons • Uncharged particles • photons (gamma- and X rays) • neutrons • Each single particle can cause ionization, • directly or indirectly Part 2: Radiation Physics

  34. Charged Particles Interaction with Matter heavy light Macroscopic Microscopic Part 2: Radiation Physics

  35. TransmissionCharged Particles Alpha particles Beta particles Part 2: Radiation Physics

  36. Mean Range of b-particles Radionuclide Max energy Range (cm) in (keV) air water aluminium ------------------------------------------------------------------------------------- H-3 18.6 4.6 0.0005 0.00022 C-14 156 22.4 0.029 0.011 P-32 1700 610 0.79 0.29 Part 2: Radiation Physics

  37. Bremsstrahlung Photon Electron Part 2: Radiation Physics

  38. Bremsstrahlung Production • The higher the atomic number of the X-ray target, the higher the yield • The higher the incident electron energy, the higher the probability of X-ray production • At any electron energy, the probability of generating X-rays decreases with increasing X-ray energy Part 2: Radiation Physics

  39. X-ray Production • High energy electrons hit a (metallic) target where part of their energy is converted into radiation electrons Low to medium energy (10-400keV) High > 1MeV energy target X-rays Part 2: Radiation Physics

  40. X-Ray Tube for low and medium X-ray production Part 2: Radiation Physics

  41. Megavoltage X-ray Linac electrons target X-rays Part 2: Radiation Physics

  42. Issues with X-ray Production • Angular distribution: high energy X-rays are mainly forward directed, while low energy X-rays are primarily emitted perpendicular to the incident electron beam • Efficiency of production: In general, the higher the energy, the more efficient is X-ray production - this means that at low energies most of the energy of the electron (>98%) is converted into heat - target cooling is essential Part 2: Radiation Physics

  43. The Resulting X-Ray Spectrum Characteristic X-rays Bremsstrahlung Spectrum after filtration Maximum electron energy Part 2: Radiation Physics

  44. Photons Interaction with Matter absorption scattering transmission energy deposition Part 2: Radiation Physics

  45. Photoelectric Effect photon electron characteristic radiation Part 2: Radiation Physics

  46. Compton Process scattered photon photon electron Part 2: Radiation Physics

  47. Pair Production positron photon electron Part 2: Radiation Physics

  48. Annihilation (511 keV) (511 keV) + + e- + (1-3 mm) Radionuclide Part 2: Radiation Physics

  49. Photon Interaction Atomic number (Z) Photon energy (MeV) Part 2: Radiation Physics

  50. Transmission-Photons d: absorber thickness m: attenuation coefficient HVL: half value layer TVL: tenth value layer Part 2: Radiation Physics

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