Chapter 2 properties of radiations and radioisotopes
PROPERTIES OF RADIATION AND
Electromagnetic radiation is a series of energy
waves composed of oscillating electric and
magnetic fields traveling at the speed of light
through a medium or space.
Two broad categories: ionizing and non-ionizing
The energy of the radiation shown on the
spectrum below increases from left to right as the
Type of radiation
Both ionizing and non-ionizing radiation can be
harmful to organisms and can result in changes to
the natural environment.
The different forms of electromagnetic radiation are
distinguished from each other by the amount of
energy they can transfer to matter, which depends
on their wavelength (frequency).
Radiations with enough high energy to ionize atoms.
Ionizing radiation has the power to create charged ions
by displacing electrons in atoms.
They have enough energy to remove tightly bound
electrons from atoms, thus creating ions.
They can cause chemical changes by breaking
chemical bonds. This effect can cause damage to living
Ionizing radiations include alpha, beta, x-ray and
Shorter wavelength u.v. radiation have enough
energy to break chemical bonds, hence are
classified as ionizing.
Uses include generation of electric power, killing of
cancerous cells, and in many manufacturing
Ionizing radiation can produce a number of
physiological effects, such as those associated with
risk of mutation or cancer.
Alpha, beta particles and gamma radiation
Type of radiation
Stopped by paper or skin
Stopped by thin metal
Reduced by many cms of No mass
lead or a few metres of
Alpha Beta Gamma:
Alpha particles - Fast moving helium atoms. They have
high energy, typically in the MeV range, but due to their
large mass, they are stopped by just a few inches of air,
or a piece of paper.
Beta - Fast moving electrons. They typically have
energies in the range of a few hundred keV to several
MeV. Since electrons are much lighter than helium
atoms, they are able to penetrate further, through
several feet of air, or several millimeters of plastic or
less of very light metals.
Gamma - These are photons, just like light, except of
much higher energy, typically from several keV to
several MeV. X-Rays and gamma rays are really the
same thing, the difference is how they were produced.
Depending on their energy, they can be stopped by a
Radiation with enough energy to move atoms in a
molecule around or cause them to vibrate, but not
enough to remove electrons from them.
They have the capacity to change the position of
atoms but not to alter their structure, composition,
Non-ionizing radiations include the spectrum of
ultraviolet (UV), visible light, infrared (IR),
microwave (MW), radio frequency (RF), and
extremely low frequency (ELF). Lasers commonly
operate in the UV, visible, and IR frequencies.
Extremely Low Frequency Radiation (ELF)
ELF radiation at 60 HZ is produced by power lines, electrical
wiring, and electrical equipment. Common sources of
intense exposure include ELF induction furnaces and highvoltage power lines.
Radiofrequency and Microwave radiation
Microwave radiation is absorbed near the skin, while
Radiofrequency (RF) radiation may be absorbed throughout
the body. At high intensities both will damage tissue through
heating. Sources of RF and MW radiation include radio
emitters and cell phones.
Infrared Radiation (IR)
The skin and eyes absorb infrared radiation (IR) as heat.
Workers normally notice excessive exposure through heat
sensation and pain. Sources of IR radiation include
furnaces, heat lamps, and IR lasers.
Visible Light Radiation
The different visible frequencies of the electromagnetic (EM)
spectrum are "seen" by our eyes as different colors. Good
lighting is conducive to increased production, and may help
prevent incidents related to poor lighting conditions.
Excessive visible radiation can damage the eyes and skin.
Ultraviolet Radiation (UV)
Ultraviolet radiation (UV) has a high photon energy range
and is particularly hazardous because there are usually no
immediate symptoms of excessive exposure. Sources of UV
radiation include the sun, black lights, welding arcs, and UV
Lasers typically emit optical (UV, visible light, IR) radiations
and are primarily an eye and skin hazard. Common lasers
include CO2 IR laser; helium - neon, neodymium YAG, and
ruby visible lasers, and the Nitrogen UV laser.
Microwave ovens use microwaves to heat food, toasters
use infrared waves to heat; televisions, cell phones, and
fm radios use radio waves.
Some forms of non-ionizing radiation can damage
tissues if we are exposed too much. For instance, too
much ultraviolet (UV) light from the sun is known to
cause some skin cancers.
Apart from the sun, UV radiation are emitted by lights
used in tanning beds, black lights, and lights used to
pasteurize fruit juices.
Some UV waves have an energy that is high enough to
cause a structural change within atoms.
Interaction of various radiations with matter
This is the spontaneous disintegration of an unstable
atomic nucleus and the emission of alpha or beta
particles and gamma rays.
It also be defined as the spontaneous disintegration of
an unstable nucleus to form a stable nucleus, with the
emission of alpha (α), beta (β) or gamma radiation (γ).
All naturally occurring elements with atomic numbers
greater than 83, as well as some isotopes of lighter
elements, are radioactive.
The emitting nuclide is known as the parent, and the
particles emitted with the stable nuclide formed are
known as daughter.
Radioactive decay is the process in which an
unstable atomic nucleus loses energy by
emitting radiation in the form of particles or
There are numerous types of radioactive decay.
The general idea:
An unstable nucleus releases
energy to become more stable
Two categories of radioactivity
Natural radioactivity: This is the spontaneous
disintegration of naturally occurring radio–nuclides
to form a more stable nuclide with the emission of
radiations of alpha, beta and gamma.
Artificial radioactivity: This is the spontaneous
disintegration of a nuclide when bombarded with a
fast moving thermal neutron to produce a new
nuclide with the emission of radiations of alpha, beta
and gamma and a large amount heat.
Derive radioactive decay
and half-life equations
Discuss the features of
radioactive decays (pg. 18
An example is the decay of Radon-222 (Rn-222) as
shown in the following equation:
A beta particle is essentially an electron that’s emitted
from the nucleus. Iodine-131 (I-131), which is used in
the detection and treatment of thyroid cancer, is a
beta particle emitter:
Alpha and beta particles have the characteristics of
matter: They have definite masses, occupy space,
and so on. However there is no mass change
associated with gamma emission.
Gamma radiation is similar to x-rays — high energy,
short wavelength radiation. Gamma radiation
commonly accompanies both alpha and beta
emission, but it’s usually not shown in a balanced
Some isotopes, such as Cobalt-60 (Co-60), give off
large amounts of gamma radiation. Co-60 is used in
the radiation treatment of cancer. Gamma rays are
focused on the tumor to destroy it.
A positron is essentially an electron that has a positive
charge instead of a negative charge.
It is formed when a proton in the nucleus decays into
a neutron and a positively charged electron. The
positron is then emitted from the nucleus.
This is a rare type of nuclear decay in which an electron
from the innermost energy level is captured by the
nucleus. This electron combines with a proton to form a
neutron. The atomic number decreases by one, but the
mass number stays the same.
The following equation shows the electron capture of
This creates an isotope of bismuth (Bi-204). The capture
of the 1s electron leaves a vacancy in the 1s orbitals.
Electrons drop down to fill the vacancy, releasing energy
in the X-ray portion of the electromagnetic spectrum.
Note that for any element:
Number of Electrons = Number of Protons = Atomic
Number of Neutrons (n) = Mass Number(A) - Atomic
Mass defect and Nuclear binding
Two forces exist in the nucleus: electrostatic
repulsion and strong force.
Electrostatic force is the repulsion between the
similarly charged protons.
Strong force is an attractive short range force.
If the electrostatic forces are greater than the strong
force, the nuclide becomes unstable.
For most atoms the strong forces are greater than
the electrostatic repulsion.
Binding energy is the energy holding protons and
neutrons together in an atomic nucleus.
This is obtained from the energy equivalence of
The mass of a nucleus is not the same as the sum
of the masses of its individual nucleons.
The mass of an atom is always slightly less than
the sum of the masses of its individual neutrons,
protons and electrons.
The difference between the mass of the atom and
the sum of the masses of its component protons,
neutrons and electrons is the mass defect (∆m).
The mass defect can be calculated using the
Neutron = 1.6749286*10-27 kg
Proton = 1.6726231*10-27 kg
Electron = 9.1093897*10-31 kg
Neutron = 939.56563 MeV
Proton = 938.27231 MeV
Electron = 0.51099906 MeV
1 amu = 1.6606 x 10-27 kg
What causes a nucleus to decay? What makes a
Arrange these emissions from least to greatest
penetrability: Gamma, Alpha, Beta.
What is the greatest source of exposure to
radioactivity in our everyday lives?
If I tell you that that the half-life of Fellmanium-250 is
10 days, how much would be left after 30 days if I
started with 1600 atoms?
Bombardment of atomic nuclei with energetic
particles, resulting in a change in the structure of
Nuclear reaction in which the nucleus of an atom
with a large mass number splits into smaller, lighter
nuclei, often producing free neutrons and photons
(gamma rays) and releasing a tremendous amount
It is induced by a slow moving neutron.
Energy released is in the form of both
electromagnetic radiation and kinetic energy of
It produces millions times the amount of energy
obtainable from the same mass of chemical fuels
such as petrol.
This makes it a very dense source of energy.
However, the products of nuclear fission are very
radioactive giving rise to nuclear waste problems.
Nuclear power plant convert energy in the nuclei of
atoms into electrical energy.
Nuclear fuels undergo fission when bombarded with
More neutrons are produced resulting in a self-
sustaining chain reaction that releases energy at a
controlled rate in a nuclear reactor,...
or at a very rapid uncontrolled rate in a nuclear
Reactor charge face
3m thick concrete biological shield
Hot gas out
Steam out to turbines
Cold water in
Boron control rods
Steel pressure vessel
Cold gas in
Fissionable material - enriched 3% uranium-235
and 97% uranium-238 in the form of pellets
encased in long tubes known as fuel rods.
Control rods - inserted between the fuel rods to
absorb neutrons. They moderate the chain
Pressurised water – flowing round fuel rods carries
away energy released and acts as a coolant. The
high pressure is to prevent extremely hot water
Pressurised water - also slows down the neutrons,
making them easy to be absorbed. This process is
known as thermalization or moderation.
The pressurised high temperature water is passed
through small tubes (primary loop) inside the
Feed-water from secondary tubes gets heated as
they flow over the small tubes.
This water is returned to the reactor to be heated
again and again till the temperature is about 2350C
and pressurised to about 68 atmospheres.
This steam is directed to turn turbines to generate
1kg of uranium U235 can potentially release
4.9x1013J of energy!
This is enough energy to heat a house, with a
5kW heater, 24 hours a day, 7 days a week, 52
weeks a year for over 300 years!
It is not quite that simple because its difficult to
get ALL the nuclei to split.
The combination of two light nuclei to form a single
heavier nucleus, with the release of a large amount
This reaction releases energy which is more than a
million times greater than that obtainable from a
typical chemical reaction.
The sum of the masses of the product nuclei is less
than the sum of the masses of the initial fusing
The mass deficit (‘lost mass’) is converted to
energy, carried away by the fusion products.
Most of this energy is released as kinetic energy of
the resulting particles.
Large electrostatic repulsion between reacting
nuclei since both are positively charged
Large initial energy is required to overcome
repulsion and start reaction.
When nuclei are close enough, repulsion is
overcome by the attractive strong nuclear force,
which is stronger at very short distances.
1 kg of deuterium can potentially release 8.45 x
1014 J of energy.
Peaceful uses of nuke reactions
Health hazards from radioactive
Applications of radioactivity.
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