Radioactivityand

ionizing radiation

Ivan Poliaček

Radioactivity and ionizing radiation

Ivan Poliaček

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

ATOMBasic structure of atoms and molecules -

nucleus, electron shell (electron cloud)

• size – typically, 10-10 m

• nucleus - 10-15 m– protons and neutrons

• electrons

EXCITATIONexcite state of atoms and molecules

• absorption of energy by atomic or molecular system

ENERGY dW = |Wu-Wl |ABSORBED EMITTED

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

PHOTON

W(photon)

= dW

= |Wu - Wl| energy of photon

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 1 eV = 1,602 x 10-19 J

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

 Type of Radiation

  Effects

Source

Wavelength(m)

Electromagnetic spectrum

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)

235

92U → 23190Th + alpha

4019K → 40

20Ca + beta + antineutrino

6028Ni → 60

28Ni + gamma

ACTIVITYNumber 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

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

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)

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- danger 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)- danger 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“ 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)

  PHOTO-EFFECT

Photo-effect

Compton-effect

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

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 (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.)

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)

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

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

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

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