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ORIGIN OF IONIZING RADIATION AND RADIONUCLIDS

ORIGIN OF IONIZING RADIATION AND RADIONUCLIDS. Historical b ackground. H umans have evolved in an environment of ionizing radiation. Discovery of X r ays (1895). Wilhelm Conrad Roentgen. Discovery of u ranium ’s n atural r adioactivity (1896). Antoine Henri Becquerel.

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ORIGIN OF IONIZING RADIATION AND RADIONUCLIDS

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  1. ORIGIN OFIONIZING RADIATIONAND RADIONUCLIDS

  2. Historical background

  3. Humans have evolved in an environment of ionizing radiation

  4. Discovery of X rays (1895) Wilhelm Conrad Roentgen

  5. Discovery of uranium’snatural radioactivity (1896) Antoine Henri Becquerel

  6. Discovery of polonium and radium (1898) Marie Curie

  7. Discovery ofharmful effects of ionizing radiation • First report about local radiation injuries (1896) and radiation-induced skin cancer (1902) • First report about radiation-induced sterility (1903) and radiation-induced leukemia (1911) • 1920s:bone cancer among radium dial painters • 1930s:liver cancer and leukemia due to Throtrast administration • 1940s: excess leukemiaamong first radiologists

  8. Discovery of A-bomb’s effect in Japan (1945) Hiroshima, 6.08.1945 Nagasaki, 9.08.1945

  9. Discovery of radiation accidents consequences Coiania, Brazil (1987) Chernobyl, USSR (1986)

  10. Terrorist can use of radioactive material After September 11th, growing apprehension that by shrouding a core of conventional explosives around a radioactive source….

  11. …..contamination could be spread over a wide area… + = …and terror created!!

  12. What is radiation?

  13. Origin of ionizing radiation

  14. Ionizing radiation

  15. Origin of radiation is from atom anatomy Proton Neutron Electron Nucleons

  16. Atomic symbols MASS NUMBER (the number of protons and neutrons) A XN SYMBOL OF ELEMENT Z The number of neutrons ATOMIC NUMBER (the number of protons) Example: 131 53I78 131I or I-131

  17. Isotopes

  18. Why are some nuclides radioactive? The stable isotopes of elements have very definite ratios of neutrons to protons in their nuclei. As the atomic mass number increases, the ratio of neutrons to protons increases according to a definite pattern. If isotopes vary from this pattern, they are relatively unstable. The most stable state of a nucleus is called the ‘ground’ state. In an unstable nucleus the nucleons are in an ‘exited’ state and must release energy to reach the ground state. In the transformation of an unstable nucleus to a more stable nucleus, energy is emitted in the form of particles such as alpha and beta particles, and in some cases photons (gamma rays). This is the process of radioactive decay.

  19. Alpha (α++) decay AZX A-4Z-2Y + 42He e.g. 23892U 23490Th + 42He

  20. Beta (-) decay n p + e- + υ AZXAZ+1 Y +e- + e.g. 13153I13154Xe+e-+

  21. Positron(+) decay p n + e+ + υ AZXAZ-1 Y+e++ e.g. 189F188O+e++

  22. Electron capture p+ + e-n +  AZXAZ-1 Y + 12553 I 12552 Te+

  23. Gamma () emission

  24. Nuclear energy levels:gamma radiation SIMPLIFIED NUCLEAR MODEL Gammaray

  25. Activity • Radioactivity is the number of decaying nuclei per unit of time • The System International (SI) unit of radioactivity is theBecquerel (Bq) • 1 Bq = one disintegration per second • Non-SI unit of radioactivity is theCurie (Ci) • 1 Ci = 3,7 x 1010 radioactive disintegration per second • 1 Bq = 2.7 x 10-11 Ci • 1 Ci = 3.7x1010 Bq

  26. Time of half-life

  27. Electric generators of ionizing radiation Ionizing radiation can also be obtained by subjecting matter to a sufficient amount of energy. This is the principle of X-ray generators and particle accelerators X-rays can have two sources: • electron rearrangement: their energy is then specific to the element considered but not to the isotope • the phenomenon of incident electron retardation (Bremsstrahlung effect): their energy is non specific and varies between zero and the maximum energy as a direct function of the initial energy of the electron.

  28. Comparison of the risks from radioactive sources and electric generators • The emission of ionizing radiation by a radioactive source behaves a law of decay governing the time in which work can be done • Electric generators obey an “On/Off” effect which is tied to the presence or absence of the electricity supply

  29. Forms of ionizing radiation and its abilities

  30. Excitation ofatom or molecules by ionizing radiation

  31. Ionization ofatom or moleculesby ionizing radiation

  32. Forms of ionizing radiation Particulate radiation Directly ionizing • consisting of atomic or subatomic particles (electrons, protons, etc.) which carry energy in the form ofkinetic energy of mass in motion Indirectly ionizing Electromagnetic radiation • in which energy is carried by • oscillating electrical and magneticfields traveling through space atspeed of light

  33. Specific ionization andlinear energy transfer (LET)

  34. Penetrating power of radiation

  35. Alpha particle interaction

  36. Interaction of alpha radiation with living matter: external deposition • Alpha radiation is not external hazard • The maximum range in tissue is < 0.1 mm • All alpha radiation is absorbed in stratum corneum

  37. Interaction of alpha radiation with living matter: internal deposition Prime danger is inhalation and ingestion of alpha emitter

  38. Beta interaction with matter

  39. Interaction of beta radiation with living matter Cell nucleus Cell diameter 100 cell diameter alpha 1.7 MeV beta 0.15 MeV beta beta 5.3 MeV alpha Auger I I I I I ı 0.001 0.01 0.1 1 10 100 mm

  40. Interaction of beta radiation with living matter: external and internal deposition • Beta radiation damages epithelial basal stratum. High energy ß-radiation may affect vascular layer of derma, with lesion like thermal burn • Danger is inhalation and ingestion of beta emitter • Danger is external ß-irradiation whole body

  41. Neutron interaction

  42. Interaction of neutron radiation with living matter Neutron radiation is only external hazard: high danger of external irradiation whole body

  43. Interaction of gamma radiation with matter • In terms of ionization, gamma radiation interacts with matter in three main ways: • 1. Photoelectric effect • 2. Compton scattering • 3. Pair production

  44. Gamma interaction by photoelectric effect

  45. Gamma interaction by Compton scattering

  46. Pair production

  47. DifferencebetweenX-rays and gamma rays

  48. Interaction of gamma radiation with living matter: external and internal deposition • Gamma radiation is very external hazard: - high danger of external irradiation whole body; - danger of external irradiation of skin • Danger is inhalation and ingestion of gamma emitter

  49. Risk due to radiation exposure

  50. Summary of lecture • Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from their orbits, causing the atom to become excitated or ionized. • Ionizing radiation occurs in two forms – particles or waves. • Alpha particles is not external hazard and can bee shielded against by clothing. Internal deposition of alpha particles is of importance on a long-term basis in terms of causing radiation injury. • Beta irradiation causes damage to the epithelial basal stratum. The lesion is similar to a superficial thermal burn. Beta particles shielding requires solid materials, like a wall. • Gamma and neutron radiation are the most biologically active, and required lead equivalent shielding for protection. • Fission products are the major radiation hazard, because a large number emit penetrating gamma radiation. This can result in whole body injuries, even at great distance.

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