1. Radioactivity and ionizing radiation Ivan 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, m
nucleus m
protons and neutrons
electrons

4. excite state of atoms and molecules
EXCITATION
excite state of atoms and molecules
absorption of energy by atomic or 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 electron gets (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 eV = 1,602 x 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 eV = 1,602 x J

9. Electromagnetic spectrum
 Type of Radiation
Effects
Source
Wavelength
(m)

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 → Th alpha

14. 4019K → 4020Ca + beta + antineutrino

15. 6028Ni → 6028Ni + gamma

16. Number of disintegrations per second
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)
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 OF IONIZING RAYS
alpha and other nuclei of atoms (heavy and electrically charged particles)
beta (light electrically charged particles)
gamma and X rays (electromagnetic field)
neutrons (heavy particles without any electric charge)

22. WITHIN THE ENVIRONMENT - low penetration
2 protons and 2 neutrons
Electric charge +2
mass 4 (atomic mass units, each proton or neutron = 1)
relatively „slow“ and „heavy“
WITHIN THE ENVIRONMENT
- low penetration
- high level of ionization and excitation of atoms and molecules
danger Q = 20
(20 fold more compared to photon)

23. ELECTRON (or positron)
electric charge minus 1
mass about 1/2000 (of atomic unit)
fast (near the light sped) and light
WITHIN THE ENVIRONMENT
- medium penetration
ionization and excitation of atoms and molecules, but less than alpha rays
production of braking X rays (bremsstrahlung)
danger Q = 1-2

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

25. WITHIN THE ENVIRONMENT high penetration
PHOTON
no quiet mass and no electric charge
WITHIN THE ENVIRONMENT
high penetration
„individual ionizations“ by processes of
PHOTOEFEKT
COMPTON SCATTER
PRODUCTION of pairs
electron-positron
danger Q = 1
Photons interact particularly with electrons – for their absorption dense material with many electrons is needed (heavy metals)

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 biological molecules - 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 structures of cell - genetic information (NA) and control of NA function (related enyzmes)
Sensitive tissues – bone marrow, mucosae, reproductive organs (genetic and hereditary / inherited diseases)
proliferative activity of the tissues (so also cancer cells are sensitive to irradiation),
because complete genome is necessary to „copy“ compared to the mature cells that are using only limited number of genes
reparative mechanisms of the cells are not efficient during replication, 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. LIMITS maximum permissive (acceptable) doses
- gonads, bone marrow (the whole body) mSv / year
- skin, thyroid gland, bone
- 30 mSv / year
- hand, forearm, leg, ankle mSv / year
- rest of tissues - 15 mSv / year

40. Real irradiation (exposure)
natural
Rn in the air, terestrial, internal and cosmic - approximately 2.5 mSv / year
artificial
medical expose, fallout and waste (army), nuclear power plants –
approximately 0.5 mSv / year