Radioactivity and ionizing radiation Ivan Poliaček

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

ATOM the size – about m basic structure nucleus m - protons and neutrons electrons - electron shell (electron cloud)

Scheme of the water molecule

EXCITATION excited state of atoms and molecules absorption of energy by atomic or molecular system ENERGY dW = |W u -W l | ABSORBED EMITTED

Excitation of the atom

PHOTON W (photon energy) = dW = |W u - W l |

Type of Radiation Effects Source Wavelength (m) Electromagnetic spectrum

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 miliard MeV = 1 J 1 eV = 1,602 x J

ionization

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 6,200 billion MeV = 1 joule 1 eV = 1,602 x J

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)

U → Th + alpha

40 19 K → Ca + beta + antineutrino

scheme of radioactivity

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

HALF-LIFE

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

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

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

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) in a material- ionization - excitation

scheme of ionizing radiation

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 - very dangeousr Q = 20 (20 fold more compared to photon)

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) - dangerous Q = 1-2

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

PHOTON no quiet mass and no electric charge WITHIN THE ENVIRONMENT - high penetration - „individual ionizations“ PHOTOEFEKT COMPTON SCATTER PRODUCTION OF PAIRS ELECTRON-POSITRON - dangerous Q = 1 Photons interact particularly with electrons – for their absorption dense material with many electrons is needed (heavy metals)

Photo-effect

Compton-effect

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

Electron and positron annihilation

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)

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

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

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.)

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

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

units conversion 1 Ci = 3.7 x Bq = 37 Gigabecquerels (GBq) 1 Bq = 27 picocurie (pCi) 1 rad = 0.01 Gy 1 rem = 0.01 Sv 1 rem = 10 mSv Gonads 0.20 Bone marrow, lungs, stomach, collon 0.12 Thyroid gland, esophagus, breast, liver, bladder 0.05 Skin, bone surfaces 0.01 The whole body 1.00 Tissue factors

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, H 2 O 2, 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

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

LIMITS - maximum 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

Risk of irradiation (exposure) immediate blood count change0.5 Sv vomiting (threshold)1 Sv mortality (threshold)1.5 Sv LD503.2 to 5.4 Sv 100 % mortality8 to 10 Sv late 0.8% lifetime risk of death from cancer following an acute all body0.1 Sv 5 % lifetime risk of cancer1 Sv cataract (exposure of eye)2 to 3 Sv

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

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