national committee for the certification of radiation protection officer fundamentals of ionizing...
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National Committee for the Certification of Radiation Protection Officer
FUNDAMENTALS OF IONIZING RADIATION
National Committee for the Certification of Radiation Protection Officer
• Introduction• Atomic Structure• Radioactivity• Types of Ionizing Radiation• Quantity and Radiation Units• Uses of Ionizing Radiations• Radiation Sources• Summary
ContentsContents
National Committee for the Certification of Radiation Protection Officer
• Radiation is a general term use to describe emission and transmission of energy through space in the form of waves, including charged and uncharged particles as well as electromagnetic radiation.
• Radiation consists of two types: ionizing and non-ionizing radiation.
• Ionizing radiation causes ionization whereas non-ionizing radiation does not cause ionization when it interacts with matter.
IntroductionIntroduction
National Committee for the Certification of Radiation Protection Officer
Elements arranged
according to their
atomic weight
Central positive nucleus with
surrounding in the orbits negatively
charged electrons
1870 - Mendeleef 1913 - Danish physicist - Niels Bohr
Atomic StructureAtomic Structure
National Committee for the Certification of Radiation Protection Officer
• In Nucleus Neutrons
(neutral) and Protons (+)
• Elementary Electrons (-)
Atomic Structure (cont.)Atomic Structure (cont.)
National Committee for the Certification of Radiation Protection Officer
Atomic Number (Z)
• Neutral atom: number of electrons is equal to protons
where:
X - chemical symbol of element A - mass number (= number of protons + number of neutrons) Z - atomic number (= number of protons)
XAZ
Atomic Structure (cont.)Atomic Structure (cont.)
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Isotopes and Nuclides
• Isotopes
Atoms of the same atomic number but different mass number.
Equal number of protons but different number of neutrons.
E.g. 1H, 2H, 3H.o Isotopes refer to the same element. o Isotopes of any element may also be called
nuclides.
Atomic Structure (cont.)Atomic Structure (cont.)
National Committee for the Certification of Radiation Protection Officer
Stable
• Nuclear stability - neutron-proton ratio (N/P) is crucial.
• Stable nuclide - correct balance in the number of neutrons and protons in the nucleus.
• Ratio too low or too high: Nucleus unstable. Rearrange itself into a more stable configuration through transformation
or spontaneous decays and the emission of radiation. Nucleus radioactive.
• Stable elements in the low atomic number range have an almost equal number of neutrons, N and protons, Z.
RadioactivityRadioactivity
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Stability Curve
Radioactivity (cont.)Radioactivity (cont.)
n
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Unstable Nuclides
• As Z increases beyond about 20: N/P ratio becomes greater than 1. Keeps on increasing with Z.
• Beta radiation: Emission of energetic electrons. Results when an N/P ratio is too high for stability.
• Positron emission or electron capture occurs when it is too low for stability.
Radioactivity (cont.)Radioactivity (cont.)
National Committee for the Certification of Radiation Protection Officer
Line of Stability
• Close to line Return by beta
decay
• Far from line Alpha decay Fission Neutron decay
Neutron
Fission
Radioactivity (cont.)Radioactivity (cont.)
n
National Committee for the Certification of Radiation Protection Officer
Definition and Unit of Radioactivity
• Unstable nucleus: Transforms or decays spontaneously into nuclides of other elements. Emits radiation. Radioactive.
• This property is called radioactivity.
• Transformation is termed radioactive decay.
• Nuclide called radionuclide or radioisotope for the same element.
• Radionuclide activity - a measure of the number of nuclear transformations taking place every second.
• Unit - Becquerel (Bq) = one nuclear transformation per second.
Radioactivity (cont.)Radioactivity (cont.)
National Committee for the Certification of Radiation Protection Officer
Half-Life and Decay Law
• Half-life (T1/2) - time required for nuclei to decay one half its original value.
• Activity (A) or transformation rate of a radionuclide is proportional to the number of unstable nuclei and an exponent function of time as follows:
A = Ao e -t
where A is activity at time t, Ao is the initial activity and is the decay constant
λ = 0.693/ T1/2
Radioactivity (cont.)Radioactivity (cont.)
National Committee for the Certification of Radiation Protection Officer
What is radiation?
• Energy that moves from the source to another object where it is finally absorbed.
• Comprise ionizing and non-ionizing.
Radioactivity (cont.)Radioactivity (cont.)
National Committee for the Certification of Radiation Protection Officer
Radioactivity (cont.)Radioactivity (cont.)
National Committee for the Certification of Radiation Protection Officer
neutron
-(negatron)
+(positron)
2
4He
cosmic
-rays
X-rays
Electron
Types of Ionizing RadiationTypes of Ionizing Radiation
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Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Alpha Particle
• Helium nucleus: 2 protons and 2 neutrons tightly bound together.
• Emitted from naturally occurring radio nuclides such as uranium and thorium.
• Lose energy by collisions with atomic electrons - cause ionizations to occur.
• Directly ionizing particles - cause ionization of an atom without any intermediate interaction taking place.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Alpha Particle
• Cause large specific ionization (number of ion pairs formed per unit energy) because of their double positive charge and large mass.
• Lose their energy in short distance hence range in media is short (less of external hazard but present an internal hazard).
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Beta Particles
• High speed electrons emitted by a radionuclide.
• Either be positive (positron) or negative (electrons).
• Not emitted with discrete energies but show a continuous energy spectrum (unlike alphas).
• Lose energy more frequently through ionization and excitation.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Beta Particles
• Directly ionizing particles - cause ionization of an atom without any intermediate interaction taking place.
• For high speed electron (more than 1 MeV) more energy may be lost in the form of X-rays due to interaction with the nuclear field in dense material (bremsstrahlung).
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Beta Particles
• Produce less ionization per unit length than alpha particles because of its smaller mass and charge.
• Have greater range than alpha hence, depending on its energy constitute an external hazard.
• Not as great an internal hazard as alpha particles.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
X- and Gamma-Rays
• Electromagnetic waves or photons.
• Ionization produced is almost all secondary.
• Most concern as potential external hazards.
• Great range in air and other media.
• High Z shielding material is needed to prevent or minimize the intensity of radiation hazard.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Interactions of X- and Gamma-rays With
Matter
• Photoelectric effect• Compton scattering• Pair production
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Photoelectric Effect
• Interaction of photon has a particle-particle collision with an atomic electron.
• Photon transfers all of its energy to the electron.
• If the energy is sufficient to release the electron from its atomic orbit, the atom is ionized.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation Cont.)Types of Ionizing Radiation Cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Compton Scatter
Happens when a photon collides with an atomic electron and transfers only part of its energy to the electron.
Rest of the original photon’s energy is radiated as a lower energy photon.
Secondary photon travels in a different direction from the one creating it.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Pair Production
• Happens when photon, in the presence of a nuclear field, disappears, changing all its energy into matter in the form of an electron and a positive electron (positron).
• Incoming photon must have energy greater than 1.02 MeV.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Pair Production
• Positron loses its extra energy, if any, by ionization.
• Positron has lost all of its energy, it unites with an electron and the two particles disappear, or annihilate giving rise to two characteristic annihilation gamma photons.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Neutrons
• Produced by nuclear reactions
Thermal (when their energies <0.025 eV). Intermediate (when their energies are between 0.5
eV to keV). Fast (when their energies are between 10 keV to
MeV). Relativistic (when their energies are > 10 MeV).
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
Neutrons
• Interaction with matter is totally secondary in nature. It gives up energy to recoil nucleus which causes ionization in the medium.
• Most concern as external hazard.
• No charge and could therefore travel great distances in air and other media.
• Fast neutron being more hazardous than neutrons of lower energy.
• Capture of thermal neutron in some materials will produce gamma ray.
Types of Ionizing Radiation (cont.)Types of Ionizing Radiation (cont.)
National Committee for the Certification of Radiation Protection Officer
• ICRU - International Commission on Radiological Units and Measurements.
• There are five physical quantities and 8 types of units (SI and non-SI):
1. Activity 2. Exposure3. Absorbed dose4. Dose equivalent5. Effective dose
Quantity and Radiation UnitsQuantity and Radiation Units
National Committee for the Certification of Radiation Protection Officer
Activity
• Unit – Becquerel (Bq)• 1 Bq is one nuclear disintegration per second• Old unit – Curie (Ci)
Exposure
• Unit – Coulomb per kilogram (C kg-1)• Old unit – Roentgen (R)
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Dose
• Defined as the absorbed energy per unit of mass.• Measured in Gray.• Always equal to or less than the KERMA.
1 J/kg Incident EnergyScattered Energy
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Absorbed Dose
• Unit – Gray (Gy) – after a British Scientist.
• Quantity of energy absorbed per unit mass of the medium.
• 1 Gy is defined as the absorption of 1 joule of energy in one kilogram of material.
• Old unit – rad (radiation absorbed dose).
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
• Because cells have a great ability to repair DNA damage it generally requires more than one event to cause permanent damage to the DNA.
• High LET radiation has a much greater chance to create the multiple points of damage that are required.
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Radiation Weighting Factor (WR)
• Correct for damage
• Values are 1 for X-rays, gamma-rays and electrons
• Higher for particles (~10)
• All routine medical radiations have a value of one
Equivalent Dose = Absorbed Dose For all practical purposes
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Equivalent Dose
• Dose corrected for biological effects.
• Unit - Sievert (Sv) after Swedish Scientist.
• Different radiation causes different effects.
• Equivalent dose is equal to the absorbed dose multiplied by the quality factor (or radiation weighting factor) and other modifying factors.
• Old unit - rem (radiation equivalent man).
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Radiation Weighting FactorsRadiation WR X and Gamma-rays, electrons, positrons 1 Neutrons < 10 keV 5 Neutrons 10 to 100 keV 10 Neutrons 100 keV to 2 MeV 20 Neutron 2 to 20 MeV 10 Protons > 2 MeV 5 Alpha partic les, fission & heavy nucleus 20
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
The Sievert is the units of biological effect or equivalent dose.
• Equivalent Dose = Absorbed Dose x Radiation Weighting Factor (WR)
• Sievert = Gy x WR
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Effective Dose
• Unit –Sievert (Sv)
• A measure of harm (or health detriment) rather than true dose.
• Different tissues show different sensitivities to radiation.
• Effective dose is the product of Equivalent Dose and Tissue Weighting Factor.
• Old unit – rem.
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Deff = Dorgan x WR x WTorgan
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Tissue Weighting Factors
0.01 0.05 0.12 0.20 Bone Surface Skin
Bladder Breast Esophagus Liver Thyroid Remainder
Bone Marrow Colon Lung Stomach
Gonads
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
Absorbed Dose
Energy/Mass
Equivalent Dose Effective Dose
Corrects for Biological
Effectiveness of Differing
Radiations
Corrects for Organ Sensitivity and Partial Body
Exposures
WR WT
Quantity and Radiation Units (cont.)Quantity and Radiation Units (cont.)
National Committee for the Certification of Radiation Protection Officer
• Industries Non-destructive testing Gauging Sterilization
• Agriculture Extending the use of product Expanding production
• Power Nuclear reactors
• Archeology Carbon-dating
• Food Technology Extending the life span of foodstuff Genetic modified food
• Medicine Diagnosis, therapy, sterilization
• Research
Uses of Ionizing RadiationsUses of Ionizing Radiations
National Committee for the Certification of Radiation Protection Officer
Natural Radiation Sources
1. Cosmic Rays
• Extraterrestrial radiation.
• Originates in outer space as primary cosmic rays (such as from stars and the sun) and reaches the atmosphere, with which the incoming energy and particles interact, giving rise to secondary cosmic rays.
Radiation SourcesRadiation Sources
National Committee for the Certification of Radiation Protection Officer
2. Terrestrial Radiation
• Emitted from the radioactive nuclides present in varying amounts in soils and rocks, the atmosphere and hydrosphere, and from those radionuclides that are transferred to man through the food chains or by inhalation.
• Leads to both external and internal exposures.
Radiation Sources (cont.)Radiation Sources (cont.)
National Committee for the Certification of Radiation Protection Officer
Man-Made Radiation Sources
1. Medicine
• X-rays and gamma rays from both diagnostic and therapeutic uses.
2. Radioactive Fallout
• Man-made artificial radioactivity produced as a consequence of nuclear weapon tests and nuclear accidents.
• Radionuclides produced in the atmosphere and carried by winds eventually spread and fall throughout the world.
Radiation Sources (cont.)Radiation Sources (cont.)
National Committee for the Certification of Radiation Protection Officer
Radiation Sources
Man-Made Radiation Sources
3. Consumer Goods
• Examples of consumer goods containing man-made radionuclide are: electronic tubes emitting X-rays;self-luminous wrist watches;gas lantern mantle; and color television sets
4.Occupational Exposure
• Individuals may be exposed to radiation in the course of their occupation involving radiation sources.
• Radiation of artificial origin is widely used in the manufacturing industry and quality control, as research tools in universities, research institutions and nuclear industry.
Radiation Sources (cont.)Radiation Sources (cont.)
National Committee for the Certification of Radiation Protection Officer
Other Sources
Large scale production of electric power by nuclear fission presupposes a cycle of complex operations, most of which involve some discharges of radioactive material top the environment and corresponding exposure of the population at large.
Radiation Sources (cont.)Radiation Sources (cont.)
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Summary
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Thank YouThank Youfor your attention
National Committee for the Certification of Radiation Protection Officer
Any Questions?