Radioactivityand

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 10-10 m

basic structure

• nucleus - 10-15 m - protons and neutrons• electrons - electron shell (electron cloud)

Scheme of the water molecule

EXCITATIONexcited state of atoms and molecules

• absorption of energy by atomic or molecular system

ENERGY dW = |Wu-Wl |ABSORBED EMITTED

Excitation of the atom

PHOTONW (photon energy)

= dW = |Wu - Wl|

 Type of Radiation

  Effects

Source

Wavelength(m)

Electromagnetic spectrum

IONIZATION - formation of ions

IONIZATION - formation of ionsthe 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

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 10-19 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)

23592U → 231

90Th + alpha

4019K → 40

20Ca + beta + antineutrino

scheme of radioactivity

ACTIVITYnumber of disintegrations per second

Units:Becquerel (Bq) = 1 dps (disintegration per second)

(Curie (Ci) = 3,7 x 1010 Bq)

HALF-LIFEThe time during which one half of the nuclei (atoms) undergo disintegration (decay)

Units:time units – second, hour, day, year

HALF-LIFE

Disintegration formula

N = N0 e-λt

N – a number of nuclei at the time tN0 – a number of nuclei at the time 0

λ – disintegration constantt – 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 +2mass 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 1mass 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

PHOTONno 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 processesCancer 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 coefficientx – 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 1010 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, 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

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 change 0.5 Sv

vomiting (threshold) 1 Sv

mortality (threshold) 1.5 Sv

LD50 3.2 to 5.4 Sv

100 % mortality 8 to 10 Sv

late 0.8% lifetime risk of death from cancer following an acute all body 0.1 Sv

5 % lifetime risk of cancer 1 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