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Radioactivity and ionizing radiation Ivan Polia ček, Nadezda Visnovcova

Radioactivity and ionizing radiation Ivan Polia ček, Nadezda Visnovcova. The aims of the lecture. atomic structure Ionization vs. excitation (low vs. high energy photon) production of ionizing radiation basic particles and their properties mechanisms of interaction basic units

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Radioactivity and ionizing radiation Ivan Polia ček, Nadezda Visnovcova

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  1. Radioactivityandionizing radiationIvan Poliaček, Nadezda Visnovcova

  2. The aims of the lecture • atomic structure • Ionization vs. excitation (low vs. high energy photon) • production of ionizing radiation • basic particles and their properties • mechanisms of interaction • basic units • basics of the damage of biological material

  3. ATOM the size – about 10-10 m chemically indivisible particle of chemical element basic structure • nucleus - 10-15 m - protons and neutrons • electrons - electron shell (electron cloud)

  4. Scheme of the water molecule

  5. EXCITATION • absorptionof energy (in a form of radiation or by a collision with another particle) by atomicor molecular system ENERGY dW = |Wu-Wl | ABSORBED EMITTED

  6. Excited state of atoms and molecules • Excited state – at higher energy than the base energia ΔW = (Wu-Wl

  7. Excitation of the atom

  8. PHOTON W(photon energy) = dW = |Wu - Wl|

  9. Photon – a quantum of electromagnetic field Electromagnetic spectrum

  10. IONIZATION - formation of ions

  11. IONIZATION - formation of ions the electron gathers more than ionizing energy = in the order of 10 eV (the rest of it turns into kinetic energy 6 240 miliard MeV = 1 J 1 eV = 1,602 x 10-19 J

  12. ionization

  13. Questions 1 • What is atomic structure? • What particles are their components? • What are main properties of particles? • What is excitation? • How does excitation happen? • What is ionization? • How does ionization happen? • What is photon? • Can stream of photon ionize?

  14. Ionizing radiation • rays (radiation = particles) – that excite but also ionize atoms and molecules (sufficient energy is necessary) - electromagnetic – wavelength under 100 nm (UV <100 nm, X rays, gamma rays) - corpuscular - alpha, beta, neutrons, other particules with the energy > 10 eV Cell phones - 900 or 1800 MHz – non-ionizing radiation 6,200 billion MeV = 1 joule 1 eV = 1,602 x 10-19 J

  15. The sources of ionizing radiation • The source of ionizing radiation – radioactive material, device, or equipment that emits ionizing rays or produces radioactive material • Natural - sun, space, environment • Artificial (e.e. used in medicine) X-ray devices,radiotherapeutic devices, accelerators e.g. cyclotron) • Sources used in medicine • Closed – within the solid container, coming out just for exposure (tightness according to the norms,example: Co60in radiotherapy) • Open (other than closed) – administered directly into body(i.v, inhalled, e.g. 99m Tc)

  16. The sources of ionizing radiation • radioactivity-significant transformation of the atomic nucleus – change of the mass, electric charge, energy(disintegration formula, activity) • artificial radioactivity - following the change of stable nucleus e.g. by neutron capture • production of X rays(using X-ray lamp) • accelerators (electromagnetic field used to speed up the particles to high velocities and energies)

  17. 23592U →23190Th + alpha

  18. 4019K →4020Ca + beta + antineutrino

  19. Gamma decay, X rays, photons • Photon energy above 10 keV -   wavelength below 124 pm, • No difference gamma and X ray, they just come from different source nuclear atomic rtg

  20. scheme of radioactivity

  21. Terminology • Radioactive substance – substance with one or more radio-nuclides with activity that cannot be neglected (from the point of view of radiation protection) • Radionuclide– atoms with the same number of protons, neutrona, energy status and they disintegrate Radioactiveemitter - radioactivesubstance with activity above limits in appendix 2, table 1 Statute of SR government (345/2006 Z.z. SR)

  22. Questions 2 • What is radiation? What types of them? • The sources of ionizing radiation? The processes of the production? • Decay? • Types of decay? • What is altered during the decay types? • What is radioactive substance? • What is radionuclide? • What is the difference - gamma and X rays?

  23. ACTIVITY number of disintegrations per second Units: Becquerel (Bq) = 1 dps (disintegration per second) (Curie (Ci) = 3,7 x 1010 Bq) HALF-LIFE The time during which one half of the nuclei (atoms) undergo disintegration (decay) Units: time units – second, hour, day, year

  24. HALF-LIFE

  25. Disintegration formula N = N0 e-λt N – a number of nuclei at the time t N0 – a number of nuclei at the time 0 λ – disintegration constant t – time λ = ln2 / half-life

  26. Bremsstrahlung produced by a high-energy electron deflected in the electric field of an atomic nucleus

  27. Electric and / or magnetic forces (electromagnetic field) accelerate charged particles to high energy

  28. SORTS OFIONIZINGRAYS • alpha and other nuclei of atoms (heavy and electrically charged particles) • beta (light electrically charged particles) • gamma andX rays (electromagnetic field) • neutrons (heavy particles without any electric charge) in a material - ionization - excitation

  29. Questions 3 • What is activity? • What is half-life? • What units are used for activity and half-life? • Explain disintegration formula! • What is braking radiation - bremsstrahlung ? • What are effects of radiation in the substance? • What types of radiation you know?

  30. scheme of ionizing radiation

  31. Scheme of ionization (electrons of atoms and molecules are released) by fast moving electron - beta particle

  32. Photo-effect

  33. Compton-effect

  34. Electron – positron pairs (nucleus is not changed, it only took a momentum of e-e+)

  35. Electron and positron annihilation

  36. Positron emission tomography Biological processes Cancer localization PET tomograph – a set of thousands detectors - 2 photons at the same time (from e+e- annihilation) - PC analysis of milions of recordings • 3D picture of radiolabeled drug distribution in the body (fluorodeoxyglucose [18F]-FDG – maximum 10 hours)

  37. ABSORPTION of photons (whatever elmg field – light, X rays, gamma rays, etc.) µ - linear absorbtion coefficient x – thickness (depth of penetration)

  38. Alpha particles are easy to stop, gamma rays are hard to stop.

  39. neutrons • no direct ionization - no interaction with electrons • nuclear interactions - scatter - excitation of nuclei then deexcitation producing gamma radiation - nuclear reactions - the capture of neutron by the nucleus – artificial radioactivity • very high penetration • very dangerous Q=5-20 neutrons interact with nuclei – they are better absorbed by materials with many atoms (water, carbohydrates, etc.)

  40. Detection of ionizing radiation • high energy particles deliver energy to the medium • EXCITATION – scintilation detector • IONIZATION - ionizing chamber, Geiger-Miller detector

  41. Questions 4 • What are properties of individual types of rays? • What are mechanisms of their interaction with a matter? • How dangerous are they? • What are processes of gamma interaction? • How is gamma absorption quantified? • How direct and indirect ionization differ? • What material absorb what rays?

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