1. Radiation Physics An Introduction
Presented on 14 Dec 2010 at IAEA Workshop, Maseru Sun, Maseru, Lesotho
By:
Dr. Himanshu Narayan
Department of Physics & Electronics
National University of Lesotho

2. H Narayan, National University of Lesotho
Outline
What is radiation?
Types and source
Ionizing
Non-Ionizing
Units of activity and dose
Radiation damage (on health)
A rough idea about ‘safe’ radiation dose
H Narayan, National University of Lesotho

3. H Narayan, National University of Lesotho
What is Radiation? In physics, radiation describe a process in which energetic particles or waves travel through a medium or space Types: Ionizing and Non-Ionizing
Ionizing radiation
Alpha
Beta (+/-)
Gamma
X-Ray
High energy Neutrons
Non-Ionizing radiation
Low energy Neutron
Electromagnetic radiation
Ultraviolet
Visible Light
Infrared
Microwave
Thermal radiation (heat)
Radio Waves
Very Low Frequency (VLF)
Extremely Low Frequency (ELF)
The word radiation is commonly used in reference to ionizing radiation only (i.e., having sufficient energy to ionize an atom), but it may also refer to non-ionizing radiation (e.g., radio waves or visible light). The energy radiates (i.e., travels outward in straight lines in all directions) from its source. This geometry naturally leads to a system of measurements and physical units that are equally applicable to all types of radiation. Both ionizing and non-ionizing radiation can be harmful to organisms and can result in changes to the natural environment.
H Narayan, National University of Lesotho

4. H Narayan, National University of Lesotho
Ionizing radiation Radiations with sufficiently high energy can ionize atoms!
Alpha (), Beta () and Neutron (n0) radiations  Particles moving with high speed (in general).
 They carry momentum: [ high speed ↔ high momentum]
Gamma () and X-rays  Energetic electromagnetic waves. They can also be treated as moving particles (called ‘photons’) <wave-particle duality>
 They have momentum: [ high energy ↔ high momentum]
With sufficiently high momentum, all these radiations are capable of knocking one or more electrons off the target atoms  Ionization.
Ionization of the atoms present in the living cells and tissues  Radiation induced damage (or, Radiation Damage)!
Radiation with sufficiently high energy can ionize atoms. Most often, this occurs when an electron is stripped (or 'knocked out') from an electron shell, which leaves the atom with a net positive charge. An individual cell is made of trillions of atoms. The probability of ionizing radiation causing cancer is dependent upon the dose rate of the radiation and the sensitivity of the organism being irradiated.
H Narayan, National University of Lesotho

5. Alpha, Beta and Gamma Radiations Associated with radioactivity
Alpha particle  A ‘bunch’ of two neutrons and two protons (identical to a helium nucleus, He2+).
Emitted during the radioactive decay of large nuclei.
 radiation:
Beta particle  Electron!
Emitted during the radioactive decay of large nuclei.
 radiation:
Gamma rays  Electromagnetic wave (Photon energy typically ~106 eV).
Emitted after alpha or beta radiation.
H Narayan, National University of Lesotho

6. H Narayan, National University of Lesotho
The figure shows relative penetration efficiency of the ,  and  radiations. More about these radiations will be discussed in the section: Radioactivity.
An Alpha (α) particle travels relatively slowly and is stopped quickly through ionizing interactions with other atoms. To a human being, material emitting Alpha radiation presents little to no external hazard, since it is unable to penetrate the dead skin layer. However, if ingested, Alpha emitting radioactive material can cause internal ionization. This can lead to cell damage, cell death or the development of cancer. Alpha particles can be stopped with a sheet of paper. It is more ionizing than alpha radiation, but less than gamma. The electrons can often be stopped with a few centimeters of metal. Gamma radiation penetrates much further through matter than either alpha or beta radiation.
Gamma rays, which are highly energetic photons, penetrate deeply and are difficult to stop. They can be stopped by a sufficiently thick layer of material with high atomic number, such as lead or depleted uranium.
H Narayan, National University of Lesotho

7. H Narayan, National University of Lesotho
X-Rays
X-Rays are electromagnetic waves (photons) with a wavelength smaller than about 10 nanometers (photon energy > 124 eV).
X-Rays can knock off electron from an atom and thus ionize it (Depends on atomic number of the target atom and the energy of the X-ray).
Average energy required to produce an ion in air ~ 34 eV.
High Energy Neutrons
Categorized according to speed.
High energy (high speed) neutrons have the ability to ionize atoms and are able to deeply penetrate materials.
Only type of ionizing radiation that can make other objects, or materials, radioactive (Neutron activation).
When an X-ray photon collides with an atom, the atom may absorb the energy of the photon and boost an electron to a higher orbital level. Depending on the structure of the atom and the energy of the X-ray photon, it may knock an electron from the atom altogether, causing the atom to ionize. Generally, a larger atom is more likely to absorb an X-ray photon in this way, since larger atoms have greater energy differences between orbital electrons. Soft tissue in the human body is composed of smaller atoms than the calcium atoms that make up bone. X-ray machines are specifically designed to take advantage of the absorption difference between bone and soft tissue, allowing physicians to examine structure in the human body.
Neutrons are categorized according to their speed. High energy (high speed) neutrons have the ability to ionize atoms and are able to deeply penetrate materials. Neutrons are the only type of ionizing radiation that can make other objects, or material, radioactive. This process, called neutron activation, is the primary method used to produce radioactive sources used in medical, academic, and industrial applications.
H Narayan, National University of Lesotho

8. Non-Ionizing radiation
Low energy neutrons:
Slow neutrons can induce radioactivity even if they cannot ionize atoms
Electromagnetic (EM) radiations:
An electric and a magnetic field oscillating in phase perpendicular to each other and to the direction of energy propagation.
H Narayan, National University of Lesotho

9. H Narayan, National University of Lesotho
Classification:
Y: Gamma rays;
HX: Hard X-rays; SX: Soft X-rays;
EUV: Extreme ultraviolet; NUV: Near ultraviolet
Visible light
NIR: Near infrared; MIR: Moderate infrared; FIR: Far infrared
Radio Waves:
EHF: Extremely high frequency (microwaves)
SHF: Super high frequency (microwaves)
UHF: Ultra high frequency;
VHF: Very high frequency;
HF: High frequency;
MF: Medium frequency; LF: Low frequency;
VLF: Very low frequency
VF: Voice frequency; ULF: Ultra low frequency
SLF: Super low frequency
ELF: Extremely low frequency
H Narayan, National University of Lesotho

10. H Narayan, National University of Lesotho
From:
H Narayan, National University of Lesotho

11. H Narayan, National University of Lesotho
Ultra Violet (UV)
High energy EM radiations
Can break chemical bonds  can damage DNA
Wavelengths longer than ~10 nm and shorter than ~400 nm
Visible Light
Can excite electrons and induce photochemical reactions
Wavelength that is visible to the human eye (about 400–700 nm).
Infra Red (IR)
Generates heat
Wavelength ~0.7 to 300 μm, (frequency ~1 to 430 THz).
H Narayan, National University of Lesotho

12. H Narayan, National University of Lesotho
Sunlight
Bright sunlight provides an irradiance of just over 1 kW.m-2 at sea level.
Sunlight = 527 W of IR W of visible + 32 W of UV
H Narayan, National University of Lesotho

13. H Narayan, National University of Lesotho
Microwave
Wavelength ~1 m to 1 mm, (frequency ~300 MHz (0.3 GHz) to 300 GHz)
Radio astronomy: Most radio astronomy uses microwaves
Heating effect
H Narayan, National University of Lesotho

14. Thermal radiation (heat)
Surface of an object radiates its thermal energy in the form of EM waves.
Examples: IR radiation from a common household radiator or electric heater; heat and light (IR and visible EM waves) emitted by glowing bulbs.
Thermal radiation is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation.
Black-body radiation: The term generally used by physicists to refer to the thermal radiation.
H Narayan, National University of Lesotho

15. H Narayan, National University of Lesotho
Radio Waves
Wavelengths longer than infrared light
Natural  lightning, from astronomical objects.
Artificial  fixed and mobile radio communication, broadcasting, radar and other navigation systems, satellite communication, computer networks and innumerable other applications
Long waves may cover a part of the Earth very consistently.
Shorter waves can reflect off the ionosphere and travel around the world
H Narayan, National University of Lesotho

16. H Narayan, National University of Lesotho
Very Low Frequency (VLF)
VLF refers to radio frequencies (RF) of 3 kHz to 30 kHz.
Not much bandwidth  Used in radio navigation.
Also known as the myriametre band/myriametre wave [wavelengths 10 to one myriametres;
1 myriameter = 10 km (obsolete )]
Extremely Low Frequency (ELF)
ELF describes RF from 3 to 30 Hz.
In atmosphere science, an alternative definition is usually given, from 3 Hz to 3 kHz.
H Narayan, National University of Lesotho

17. H Narayan, National University of Lesotho
Radiation units Absorbed dose & Equivalent dose To avoid any risk of confusion between the absorbed dose (by matter) and the equivalent dose (by biological tissues), we have two different unit systems
Absorbed dose units:
rad: Radiation Absorbed Dose
Conventional units: Absorbed dose of 1 rad = absorption of 100 ergs of radiation energy per gram of absorbing material
SI units: Absorbed dose of 1 gray (Gy) = absorption of 1 joule of radiation energy per kilogram of absorbing material
Conversions:
1 Gy = 100 rad
(Note: Units of radioactivity are different from the units of radiation)
Activity of an isotope or material
Conventional unit:
1 curie = 37 billion disintegrations per second
SI unit:
1 becquerel = 1 disintegration per second
Conversion:
1 curie (Ci) = 37 gigabecquerel (GBq)
H Narayan, National University of Lesotho

18. H Narayan, National University of Lesotho
Equivalent dose A measure of biological effect for whole body irradiation. The dose equivalent = the absorbed dose (rad or Gy) × the Quality Factor (Q).
The Quality Factor (Q) depends on the type of radiation:
X-ray, gamma ray, or beta radiation: Q = 1
alpha particles: Q = 20
neutrons of unknown energy: Q = 10 (If the neutron energy is known, Q values are more specific)
Conventional units:
Eq. dose (rems) = dose (rad) × Q
SI units:
Eq. dose (sieverts) = dose (gray) × Q
Conversion:
1 Sv = 100 rems
1 rem = 0.01 Sv
rem: röntgen (roentgen) equivalent in man/mammal
sievert: named after Rolf Sievert, a Swedish medical physicist
gray: This SI unit is named after Louis Harold Gray
Roentgen equivalent physical (rep)
An obsolete unit of absorbed dose of any ionizing radiation with a magnitude of 93 ergs per gram. It has been superseded by the rad
H Narayan, National University of Lesotho

19. H Narayan, National University of Lesotho
SI Units
In terms of SI base units:
Absorbed Dose: 1 Gy = 1 J/kg = 1 m2/s2 = 1 m2·s–2 [(just the dose; same as 1 Sv for radiations with Q = 1 (X-rays, gamma and beta rays)]
Equivalent Dose: 1 Sv = 1 J/kg = 1 m2/s2 = 1 m2·s–2 [dose × Q; Q is unitless]
1 Sv = 100 rem & 1 mSv = 100 mrem
Frequently used SI multiples are the milli-sievert (1 mSv = 10−3 Sv) and micro-sievert (1 μSv = 10−6 Sv)
Example:
A 100 kg human, exposed to beta rays (or, gamma/X-rays with Q = 1) of energy 100 J will be said to be exposed to 1 Gy of absorbed dose or 1 Sv (or, 100 rem) of equivalent dose of that irradiation.
H Narayan, National University of Lesotho

20. H Narayan, National University of Lesotho
Background radiation Constantly present in the environment and is emitted from a variety of natural and artificial sources
Sources in the earth: In food and water, in building materials and other products that incorporate those radioactive sources
Sources from space: In the form of cosmic rays
Sources in the atmosphere: Radon gas (released from the Earth's crust) decays into radioactive atoms and gets attached to airborne dust and particulates
Radioactive atoms produced in the bombardment of atoms in the upper atmosphere by high-energy cosmic rays
Man made sources:
Self-luminous dials and signs
Global radioactive contamination (nuclear weapons testing)
Nuclear power station or nuclear fuel reprocessing accidents
Normal operation of facilities used for nuclear power and scientific research
Emissions from burning fossil fuels (coal fired power plants)
Emissions from nuclear medicine facilities and patients
H Narayan, National University of Lesotho

21. H Narayan, National University of Lesotho
Exposed! In one year:
Cosmic rays: 25 – 50 mrem
From air (Radon): 200 mrem
Terrestrial radiations: 30 mrem
From food: 20 mrem
Watching TV: 1 mrem
Medical X-ray: 2 mrem
H Narayan, National University of Lesotho

22. Sources of radiation (Some examples) About 80% of the total radiation exposure results from natural sources!
Cosmic radiation  Around 25 mrem a year (at sea level), to around 50 mrem a year (at an altitude of 1 mile)
Terrestrial radiation  An average value is around 30 mrem a year, though this can be much less along the coasts, around half as much
Inhaled Radon  Around 200 mrem a year
Foods  An average dose of around 20 mrem a year
Nuclear weapons fallout  Less than 1 mrem a year
Watching TV  About 1 mrem a year
Porcelain false teeth or crowns  Around 0.1 mrem a year
The total equivalent dose for an average person in one year is about 3.6 mSv
(Summing up the exposures from all possible sources)
H Narayan, National University of Lesotho

23. H Narayan, National University of Lesotho
Radiation Damage All radiations are harmful. Ionizing radiations are more harmful than the non-ionizing radiations.
Exposure to radiation  damage to living tissue, skin burns, radiation sickness and death (at high doses); and cancer, tumors and genetic damage (at low doses)
Radiation induced ionization of atoms in the living cells and tissues can result in cancer
Alpha radiation presents little to no external hazard, since it is unable to penetrate the dead skin layer, but, if ingested, Alpha emitting radioactive material can cause internal ionization, which can lead to cell damage, cell death or the development of cancer
Prolonged exposure to non-ionizing radiations may lead to burn injuries
Over-exposure to UV radiation may result in skin cancer
H Narayan, National University of Lesotho

24. Some facts
Chances of dying from cancer can increase by 10% if a total of around 250 rem (= 2.5 Sv) of equivalent dose gets accumulated in our body!!!
The exposure for an average person is about 3.6 mSv/year
(which is = 360 mrem/year OR 0.36 rem/year)
Fortunately, at this rate it should take nearly 700 years to reach to above mentioned limit of 2.5 Sv [This should make us happy!!!]
A whole-body exposure to 5 Gy or more of high-energy radiation at one time usually leads to death within 14 days
A single dose of around 450 rem (= 4.5 Sv) is usually
considered to produce death in 50% of the cases!!!
H Narayan, National University of Lesotho

25. Resources/Further reading
Wikipedia articles
Thank you!
Questions please…!
H Narayan, National University of Lesotho