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Radiation is a process in which a
body emits energy that propagates through a medium,
or through empty space, to be absorbed by other
bodies. It can be further classified as
Ionizing and Non Ionizing radiation.Ionizing
radiation consists of
subatomic particles or electromagnetic waves that
are energetic enough to detach electrons from atoms
or molecules, ionizing them. The occurrence of
ionization depends on the energy of the impinging
individual particles or waves, and not on their
number. An intense flood of particles or waves will
not cause ionization if these particles or waves do
not carry enough energy to be ionizing. Examples of
ionizing particles are energetic alpha particles,
beta particles, and neutrons. The ability of
electromagnetic waves (photons)) to ionize an atom
or molecule depends on their wavelength. Radiation
on the short wavelength end of the electromagnetic
spectrum � ultraviolet, x-rays, and gamma rays - is
ionizing. Non-ionizing radiation refers to
any type of electromagnetic radiation that does not
carry enough energy per quantum to ionize atoms or
molecules � that is, to completely remove an
electron from an atom or molecule. Instead of
producing charged ions when passing through matter,
the electromagnetic radiation has sufficient energy
only for excitation, the movement of an electron to
a higher energy state. Near,
visible light, infrared, microwave, radio waves, and low frequency
RF (longwave) are all examples of non-ionizing
radiation. The light from the Sun that reaches the earth is
largely composed of non-ionizing radiation, with the
notable exception of some ultraviolet rays. However,
most ionizing radiation is filtered out by the
atmosphere. Non-ionizing radiation is not mutagenic.
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Alpha (α)
radiation consists of Helium-4 (4He)
nuclei and is stopped by a sheet of paper. Beta
(β) radiation, consisting of electrons, is halted by an
aluminum plate. Gamma (γ) radiation,
consisting of energetic photons, is eventually
absorbed as it penetrates a dense material.
Neutron (n) radiation consists of free
neutrons which are blocked using light elements,
like hydrogen, which slow and/or capture them.
Radiation Sources
1. Natural sources
-cosmic
ray (radiation from outer spaces) and
-terrestrial radiation (naturally occurring
radioactive materials e.g. K-40, Rb-40
2. Man made sources
-X-ray machines
-Radio isotopes
-particle accelerators
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Exposure to ionizing radiation
produces free electrons by ionizing atoms/molecules.
These ionized entities are chemically active and can
form compounds, which interfere process of cell
division and metabolism.
Biological Effects:
Ionizing Radiation
1.
Delay in
cell division
2.
Chromosome
Breaks
3.
Cell Death
4.
Gene
Mutation
Non Ionizing Radiation
In terms of potential
biological effects, the non-ionizing portion of the
spectrum can be subdivided into:
- The optical
radiation portion, where electron excitation can
occur (visible light, infrared light)
- The portion where
the wavelength is smaller than the body, and
heating via induced currents can occur (MW and
higher-frequency RF).
- The portion where
the wavelength is much larger than the body, and
heating via induced currents seldom occurs
(lower-frequency RF, power frequencies, static
fields).
Interaction of Radiations with Matter
All radiation have
energy, either K.E as in the case of moving charged
particle, or inherent
energy
as in case of EM radiation. When radiation passes
through matter it may interact with
the
material, transferring some or all of its energy to
the atoms of the material.
At
atomic level the radiation can interact with
1.
Nuclear region
2.
Nuclear field or extra nuclear region
3.
Can pass straight through wide open spaces with in
atom, without interaction.
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Roentgen (R)
The roentgen is a unit used
to measure a quantity called exposure. This can only
be used to describe an amount of gamma and X-rays,
and only in air. One roentgen is equal to depositing
2.58 x 104 coulombs per kg of dry air. It is a
measure of the ionization of the molecules in a mass
of air. The main advantage of this unit is that it
is easy to measure directly, but it is limited
because it is only for deposition in air, and only
for gamma and x-rays.
Rad (radiation absorbed
dose)
The rad is a unit used to
measure a quantity called absorbed dose. This
relates to the amount of energy actually absorbed in
some material, and is used for any type of radiation
and any material. One rad is defined as the
absorption of 100 ergs per gram of material. The
unit rad can be used for any type of radiation, but
it does not describe the biological effects of the
different radiation.
Rem (roentgen equivalent
man)
The rem is a unit used to
derive a quantity called equivalent dose. This
relates the absorbed dose in human tissue to the
effective biological damage of the radiation. Not
all radiation has the same biological effect, even
for the same amount of absorbed dose. Equivalent
dose is often expressed in terms of thousandths of a
rem, or mrem. To determine equivalent dose (rem),
you multiply absorbed dose (rad) by a quality factor
(Q) that is unique to the type of incident
radiation.
Curie (Ci)
The curie is a unit used to
measure radioactivity. One curie is that quantity of
radioactive material that will have 3.7x1010
transformations in one second. Often radioactivity
is expressed in smaller units like: thousandths
(mCi), one millionth (mCi) or even billionths (nCi)
of a curie. The relationship between becquerels and
curies is 3.7 x 1010 Bq in one curie.
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The harmful effects of exposure to radiation
are due largely to its ionizing effects. Atoms and
molecules contain electrons that can be removed from
their orbits rather easily. For example, if a beta
particle passes through an atom, it has the ability to
repel any electrons in its path, ejecting them from
the atom.
The bonds that hold atoms together in
molecules are made of electrons. A molecule of water,
for example, consists of oxygen and hydrogen atoms
held together by electrons. If radiation passes
through or very near a molecule of water, it may cause
electrons to be ejected from the molecule. When that
happens, the water molecule may fall apart. The same
process occurs in any kind of molecule, including
proteins, lipids, nucleic acids, and carbohydrates,
the molecules of which living organisms are
constructed.
Damage to molecules of this kind can have two
general effects. First, when essential molecules are
destroyed, an organism is no longer able to carry on
all the normal functions it needs in order to stay
alive and to function properly. A person, for example,
may become sick if essential enzymes (substances that
speed up chemical reactions) in his or her body are
destroyed.
Some of the symptoms of radiation sickness
include actual burns to the skin, nausea, vomiting,
and diarrhea. The specific effects observed depend on
the kind of radiation to which the person was exposed
and the length of exposure. For example, a person
exposed to low doses of radiation may experience some
of the least severe symptoms of radiation sickness and
then get better. A person exposed to higher doses of
radiation may become seriously ill and even die.
Exposure to radiation can have long-term
effects as well. These effects include the development
of various kinds of cancer, leukemia being one of the
most common types. Damage to a person's
deoxyribonucleic acid (DNA) can also cause
reproductive defects, such as children who are born
deformed, blind, mentally impaired, or with other
physical or mental challenges. (DNA is a complex
molecule in the nucleus of cells that stores and
transmits genetic information.)
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The Health
Physics Group in the Centre was set up primarily for
monitoring and ensuring radiation safety of the
Accelerator facility as is mandatory by the Atomic
Energy Regulatory Board. The activities of the group
have grown in the direction of radiation research
beyond the routine regulatory duties. Over a decade,
this group has produced excellent output in research
and given the required support towards radiation
safety.
There are
around 20 universities and around 30 research
scholars, working with the health Physics group on
various interdisciplinary research activities. A few
NGO's and some Government Agencies have also used
these facilities. The universities associated with
this group are from all over the country.
Atomic Energy Regulatory Board (AERB) has accredited
Low Background Counting System for radioactivity
analysis such as 226Ra, 232Th,
40K. Indian Environmental Radiation
Monitoring network (IERMON) was installed with the
help of BARC. We are putting our best efforts to
make these activities par excellence in
co-ordination with the Atomic Energy Regulatory
Board (AERB) and the various universities involved
with the health physics group.
Research activities and facilities:
-
Low Background Counting
System (HPGE & Atomtex)
-
Dosimetry of neutron and
Gamma using Conducting Polymers and SSNTD�s
-
Low Beta Counting Setup
-
MRF and RF Enhancement
Setup for Hall Effect Studies & Dosimetry
-
Four Probe Setup
-
Development of new
Thermoluninescence Materials & its Dosimetry
Applications.
-
Development of Conducting
Polymers
-
Microscope for Track
Measurements
-
Alpha source for Thickness
Measurement
-
Centrifuge machine
-
Muffle furnace
(12000C)
-
Spark counter
-
TLD Reader
-
Electronic Balance
-
G M Counter
-
Distillation Set up
- Gamma Chamber
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