Basics of Radiation

1. BASICS OF RADIATION
M.Vharshini
4th year BMS(Human Genetics)
CHAPTER 1

2. TERMINOLOGIES
Frequency:
• The frequency of a wave is the number of waves per second.
Denoted as ( ) Nu.
Wavelength:
• The wavelength is the distance from the peak of one wave to the
next one. Denoted as ( )Lambda.
Wave:
• A disturbance causing energy transfer from one location to
another location is called a Wave.
• The highest point on a wave is called the crest..
• The lowest point is called the trough.

3. ELECTROMAGNETIC SPECTRUM
• The electromagnetic waves are the waves which are
generated by coupling of magnetic field with electric field.
• These waves are in perpendicular direction to both the
electric and magnetic and also perpendicular to each other.

4. ELECTROMAGNETIC SPECTRUM

5. Relationship between
wavelength and frequency
• All parts of the electromagnetic spectrum travel at
the same speed of 3 x 10 8 m/s in a vacuum.
• Therefore, wavelength and frequency are inversely
proportional (i.e.) as wavelength increases,
frequency decreases and vice versa.
• Short wavelengths have a high frequency.
– E.g. X-rays
• Long wavelengths have a low frequency.
– E.g. Radio waves

6. Relationship between Energy
Wavelength and Frequency
ENERGY:
• Wavelength and energy are inversely proportional.
• Frequency and energy are directly proportional.
Therefore,
• High frequency waves have high energy.
– E.g. Gamma rays
• Low frequency waves have low energy.
– E.g. Radio waves

7. STRUCTURE OF ATOM
• Atoms are the basic units of matter
and defining structure of elements.
• Atoms are made up of three
particles: Protons, Neutrons and
Electrons.
• Protons and neutrons reside inside
the nucleus of the atom.
• Atomic No. (A) = No. of Protons (or)
No. of Electron
• Mass No. (Z) = No. of Protons + No.
of Neutrons

8. ISOTOPES
• The number of neutrons in a
nucleus determines the
isotope of that element.
• For example, hydrogen has
three known isotopes:
protium, deuterium, tritium.
• They have same chemical
properties but differ in
physical and nuclear
properties.
• Tritium is radioactive.

9. RADIATION
• Radiation, as defined as the emission and
propagation of energy through space or a substance
in the form of waves or particles.
• Atom is unstable if it as more electron or neutron, so
it becomes stable by releasing the excess particle.
• The radiation may be α, β, γ radiation.
Radiation

10. PARTICULATE RADIATION
• Particulate radiation is the radiation of energy by
means of fast-moving subatomic particles that has
finite mass and may or may not carry a charge.
• Particulate radiation is primarily produced by
disintegration of an unstable atom.
• Particulate radiation is of four forms:
• Positively Charged alpha particle (α ⁺).
• Positively charged (Positrons) or negatively
charged (Electron) beta particles (β+ or β−).
• neutrons, subatomic particles which have no charge.
• photons (called a gamma ray, γ, and acting in some ways
like a particle.)

11. ALPHA PARTICLE
• Certain radionuclides of high atomic mass (U-238,
Ra-226, Pu-239) decay by emission of α particles.
• Alpha particle is positively charged and consists of 2
protons & 2 neutron.
• Alpha particle is identical to the nucleus of the
helium atom.

12. ALPHA PARTICLE
• Has very high mass, highly charged.
• They produce intense ionization in the gas through which
they pass.
• Has very low penetration power and can be stopped by a
thin sheet of paper. Alpha particles are unable to
penetrate the outer layer of dead skin cells.

13. BETA PARTICLES
• A nucleus with a slightly unstable ratio
of neutrons to protons may decay
through the emission of a high speed
electron called a beta particle.
• When a radioactive nucleus
disintegrates by emitting a β−particle,
the atomic number increases by one
and the mass number remains the
same.
• The penetrating power of β rays is
greater than that of α−rays; but can be
stopped by thin aluminium. It can
penetrate skin a few centimeters,
posing somewhat of an external
radiation hazard.

14. BETA PARTICLE- Positron
• When the neutron-to-proton ratio of a radionuclide
is too low and α emission is not possible, the nucleus
may under certain conditions attain stability by
emitting a positron.
• A Positron (positive e⁻) is a β particle (similar to
ordinary electron) whose charge is positive.

15. GAMMA RADIATION
• Following a radioactive transformation, the atoms go to the
excited state and reach the ground state by emitting the excitation
energy in the form of gamma radiation.
• During α or β−decay, the daughter nucleus is mostly in the excited
state. It comes to ground state with the emission of γ−rays.
• Emission of γ rays does not affect atomic or mass no.
• They travel with the velocity of light.
• Gamma rays are electromagnetic photons with discrete energy
levels & very high penetrating power.
• Hence γ radiation is a significant radiation hazard.

16. TYPES OF RADIATION
•The higher frequencies of EM radiation, consisting of x-rays and gamma
rays, are types of ionizing radiation.
•Lower frequency radiation, consisting of ultraviolet (UV), infrared (IR),
microwave (MW), Radio Frequency (RF), and extremely low frequency (ELF)
are types of non-ionizing radiation.

17. RADIOACTIVITY
• Radioactivity is the process by which an unstable atomic
nucleus loses energy by emitting radiation, such as an
alpha particle, beta particle, gamma ray.
• It is the characteristic of various materials to emit
ionizing radiation.
• This phenomenon is related to nucleus of the atom.
• E.g. When tritium emits a β particle, it becomes helium.
• Radioactivity is unaffected by temperature, pressure or
any other physical or chemical changes experienced by
atom

18. IONISING RADIATION
• Ionizing radiation is radiation with enough energy so that
during an interaction with an atom, it can remove tightly
bound electrons from the orbit of an atom, causing the
atom to become charged or ionized.
• Direct Ionization Caused By:
• Alpha Particles
• Beta Particles
• Positron Particles
• Indirect Ionization Caused By:
• Neutrons
• Gamma Rays
• X-Rays

19. X-RAYS
• X-rays are also a part of electromagnetic spectrum and
are similar to gamma rays with the primary difference
being that they originate from the electron cloud.
• This is generally caused by energy changes in an
electron, such as moving from a higher energy level to a
lower one, causing the excess energy to be released.
• X-Rays have longer-wavelength and lower energy than
gamma radiation.

20. NON - IONISING RADIATION
• Non-ionizing radiation refers to any type of electromagnetic
radiation that does not carry enough energy to ionize atoms or
molecules.
Types of non-ionizing electromagnetic radiation
– Near ultraviolet radiation.
– Visible light.
– Infrared.
– Microwave.
– Radio waves.

21. LINEAR ENERGY TRANSFER
• LET (linear energy transfer) is the amount of energy
deposited by a radioactive particle or wave while
travelling through a matter.
• Unit : kiloelectron volt per micrometer (keV/µm)
• LET is used to classify radiations as:
• High LET Radiations
• Low LET Radiations
High LET Radiation:
– This is a type of ionizing radiation that deposit a large amount of energy.
– E.g. alpha particles
Low LET Radiation:
– This is a type of ionizing radiation that deposit less amount of energy.
– E.g. x-rays, gamma rays

22. FLUORESCENCE
• Light of low wavelength incident on specific
fluorochromes is excited and in the process of coming to
the original sate emits light of a particular wavelength.
• Fluorescence exists as long as the fluorescing substance
remain exposed to incident light (UV) and re-emission of
light stops as soon as incident light is cut off.

23. PHOSPHORESCENCE
• Phosphorescence, emission of light from a substance
exposed to radiation and persisting as an afterglow
after the exciting radiation has been removed.

24. CHEMILUMINESCENCE
• Chemiluminescence is the production of light from a
chemical reaction.
• Two chemicals react to form an excited (high-energy)
intermediate, which breaks down releasing some of
its energy as photons of light.
A + B -> AB* -> Products + Light
Chemiluminescence in forensics:
• Forensic scientists use the reaction of luminol to
detect blood at crime scenes.

25. UNITS OF RADIATION

26. RADIOACTIVITY
• It is the process by which a nucleus of an unstable
atom loses energy by emitting ionizing radiation.
• Old unit - Curie(Ci)
• SI unit - Becquerel(Bq)
• One Curie refers to the quantity of radioactive nuclei
which disintegrates at a rate of 3.7x1010
disintegrations per second.
1Bq = 1 disintegrations per second
1 C = 3.7*1010 dps

27. EXPOSURE (In air)
• Exposure is defined as the amount of ionization in air produced by
x-rays.
Old unit- Roentgen (R)
SI unit - X Unit [coulomb per kilogram (C/kg)]
•One roentgen is equal to the amount of x- radiation or γ radiation
that will produce one electrostatic unit of charge of either signs
within a volume of 1 cu.cm of air at NTP.
•The X unit is defined as quantity of x-radiation or γ radiation which
will produce 1 coulomb of charge of either signs in 1Kg of air at NTP.
X Unit = 1C/Kg

28. EXPOSURE MEDIUM
ABSORBED DOSE:
• Dose can be defined as the amount of energy absorbed by any
medium for any radiation type.
Old unit - Radiation absorbed dose (rad)
SI unit - Gray (Gy)
Gray: 1 Gy can be defined as energy absorption of 1 J/Kg of any
medium.

29. DOSE EQUIVALENT (HT )
• Dose equivalent is defined as the same degree of biological effect
irrespective of radiation type.
• Standard unit- rem
SI unit - Sievert (Sv)
HT = Absorbed Dose * WR
RADIATION WEIGHTING FACTOR ( WR ) Or QUALITY FACTOR ( QF )
• WR for x-rays, γ rays, β rays = 1
• WR for α rays = 5-20 WR
• Any radiation with high WR has more biological effect.

30. EFFECTIVE DOSE
• Effective dose provides an approximate indicator of
potential detriment from ionizing radiation.
Effective Dose = HT* WT
• Where HT = Absorbed Dose (D) * WR
• SI unit - Sievert (Sv)
• Tissue Weighting Factor (WT)is a relative measure of
the risk of stochastic effects that might result from
irradiation of that specific tissue.
• Bone marrow, stem cells are senitive to radiation
have high WT

31. DOSE RATE
• Rate at which the radiation is emitted from a
radioactive source.
• Dose emitted/unit time
• Dose rate is usually presented in terms of R/hour,
rem/hour, etc.

32. EFFECT OF RADIATION
• The radiation causes its effects by ionization.
• Ionization is the process of ejecting one or more electrons
from an atom.
– Directly Ionizing: when absorbed in material, they directly cause
ionization leading to damage. Eg. Electrons, α-particles, β-particles
– Indirectly ionizing: when absorbed in material, they give up their
energy to produce fast moving charged particles which produce the
damage. This happens by formation of FREE RADICALS. Their life
span is 10-10 Sec. E.g. Electromagnetic radiation