Radioactivity and ionizing radiation Ivan Polia ček

1. Radioactivity and ionizing radiationIvan Poliaček Radioactivityandionizing radiationIvan Poliaček

2. The aims of the lecture • atomic structure • ionization • 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 Basic structure of atoms and molecules - nucleus, electron shell (electron cloud) • size – typically, 10-10 m • nucleus - 10-15 m • protons and neutrons • electrons

4. EXCITATION excite state of atoms and molecules • absorptionof energy by atomicor molecular system ENERGY dW = |Wu-Wl | ABSORBED EMITTED

5. Excitation by absorption of light and de-excitation by emission of light

6. PHOTON W(photon) = dW = |Wu - Wl| • energy of photon

7. IONIZATION The electrongets(receives) an energy that is sufficient to release it from the atom (molecule) ionization energy (in the order of 10 eV) + kinetic energy 6 240 miliard MeV = 1 J 1 eV = 1,602 x 10-19 J

8. Ionizing radiation • Rays (radiation) – that excite but also to ionize atoms and molecules (sufficient energy is necessary) • - electromagnetic wave – wavelength under 100 nm - UV (<100 nm), X rays, gamma • - corpuscular - alpha, beta, neutrons, other particules 6,200 billion MeV = 1 joule 1 eV = 1,602 x 10-19 J

9. Electromagnetic spectrum

10. 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 strikes) • production of continuous(using X-ray lamp) and characteristic X rays • accelerators (electromagnetic field used to speed up the particles to high velocities and energies)

12. 23592U →23190Th + alpha

14. 4019K →4020Ca + beta + antineutrino

15. 6028Ni →6028Ni + gamma

16. 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 (duration) during which one half of the nuclei (atoms) undergo disintegration (decay) Units: time units – second, hour, day, year

17. HALF-LIFE

18. 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

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

21. 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)

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

26. PHOTO-EFFECT

27. Photo-effect

29. Compton-effect

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

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

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

33. neutrons • no direct ionization (practically no interaction of neutrons and electrons) • nuclear interactions - scatter and nuclear reactions (interaction with nuclei leads to their excitation and then gamma radiation, or the capture of neutron by the nucleus produces radioactive nucleus within the material) • very high penetration • danger Q=5-20 neutrons interact with nuclei – they are better absorbed by materials with many atoms (water, carbohydrates, etc.)

34. BASIC QUANTITIES • Absorbed energy - Dose (D) • (basic unit : Gray = J / kg) • Ionization –Irradiation (Exposure) (E) • (basic unit : C / kg) • Biological effects – Dose equivalent = =D x G x Q • (the unit : Sievert = J / kg) Q – coefficient of the danger of radiation G – coefficient of irradiation „geometry“ (particularly which tissues are affected)

35. Biological effects of ionizing radiation • stochastic (random, probabilistic) and deterministic (regular, necessary) • direct damage of molecules - nucleic acids and proteins • undirect damage – due to products of water decomposition (radicals and ions - H, H2O2, H+, OH-) and chemical reactions with them • Deactivation of biologicalmolecules - depolymerization, damage of chemical bonds • Inhibition of metabolic reactions • Abnormal products • Damage of mitochondria • Inhibition of proliferation • Radiation desease • Carcinogenesis

36. Basic mechanism of the impact • Sensitive structuresof cell - genetic information (NA) and control of NA function (related enyzmes) • Sensitive tissues – bone marrow, mucosae, reproductive organs (genetic andhereditary / inherited diseases) • proliferative activity of thetissues (so also cancer cells are sensitive to irradiation), • because complete genomeis necessary to „copy“ compared to the mature cells that are using only limited number of genes • reparative mechanisms of the cells are not efficient duringreplication, similarly as elimination of impaired cells by imunity system

37. THERE IS NO DIRECT POSITIVE EFFECT OF IONIZING RADIATION However, there is significant use of it : • X rays diagnostic methods • Computer tomography • emission tomography • radioimunodetection • rádionuclide diagnostic methods • anti-inflammatory and analgetic therapy

39. LIMITSmaximum permissive (acceptable) doses - gonads, bone marrow (the whole body)- 5 mSv/ year - skin, thyroid gland, bone - 30 mSv/ year - hand, forearm, leg, ankle - 75 mSv/ year - rest of tissues - 15 mSv/ year

40. Realirradiation (exposure) • natural • Rn in the air, terestrial, internal andcosmic - approximately 2.5 mSv/ year • artificial • medical expose, fallout andwaste (army), nuclear power plants – approximately 0.5 mSv/ year