WHAT IS RADIATION? WHAT ARE ITS EFFECTS?
What is radioactivity?
We now know that every substance is a collection of tiny particles known as atoms. There are 92
different kinds of atoms present on the earth. The lightest of these is the hydrogen atom and the
heaviest is the uranium atom.
Generally, the heavier atoms are not so stable as the lighter atoms. These unstable atoms are known
as radioactive atoms. They become stable only by emitting some radiation. The emission of radiation
by them is referred to as radioactivity.
What is ionising radiation?
In the general sense, heat and light are also a form of radiation. But we are concerned here with other
forms, which are commonly known as `atomic radiation' or simply as radiation. Certain substances
such as uranium, thorium etc., by nature are unstable. The atoms of such substances attain stability
by throwing away the excess energy in the form of electromagnetic radiations or particles. These are
called nuclear radiations or ionising radiations.
What is half-life?
Half life is the time required for a radioactive substance to
reduce its strength to one half of its original activity through
emission of radiations. The half life ranges from a few milli
second to millions of years. This concept (delay and decay)
is being utilised for the management of radioactive wastes
containing radioactive substances with short half lives. A
majority of man made radioactive substances has short half
lives compared to naturally occurring radioactive substance.
Fraction remaining
1.0
0.8
0.5
0.3
0.0
1
2
3
4
5
6
7
8
9
10
No. of Half lives
What is special about ionising radiations?
The nuclear radiations are termed as ionising radiations since they are capable of converting the
neutral atoms of all substance in to positive and negative ions through interactions.
How do we detect the presence of radiation?
Nuclear radiation cannot be detected by our senses. We need to depend on indirect means for
detection. Radiation affects photo films just as light does. So, photo films are used to detect and
measure radiation levels. There are other substances, which produce light when exposed to radiation.
These are known as scintillators. The intensity of light emitted by the scintillator is proportional to the
radiation level. Another type of instrument is the
GM counter, which is the most commonly used
Natural 87%
instrument for easy and quick detection of
Manmade 13%
radiation. This measures the electric current
produced when radiation passes through a gas.
Foo
d
12%
Is radiation unique to nuclear power
stations?
We tend to associate radiation and radioactive
Ra
don
Air
51%
mic
C os
10 %
s
Mi
0.3
c.
%
.4% .2%
t 0
0
al
ou
l
l
on
Fa
ati
p
cu
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Medical
12%
Nuclear
0.1%
Terrestrial
14%
materials with reactors alone. Not many may be aware that radiation has always been present in the
environment. We must remember that radiation is also used in medicine to a very great extent. The
exposure we receive from radiation sources in nature and from applications of radiation in medicine
can serve as a reference level for comparison with exposures due to nuclear reactors.
Radioactive materials like uranium, thorium, radium and potassium are present in nature everywhereon land, in the sea, in the air around us and even in our own bodies. And not just that. Radiation is
also constantly streaming towards the earth from deep outer space. This is known as cosmic
radiation. All this was discovered only in the past hundred years. In some locations they are much
higher and the population living there receives proportionately higher exposures. The regions with the
highest radiation levels on the earth are found in Brazil, China, France and India. On the beaches of
southern Kerala and in adjacent Tamil Nadu the radiation levels are about six times higher than the
national average.
There is perhaps no one among us who has not had an X-ray picture taken of his chest. X-rays are
only one of the many kinds of radiation known which come under the class of atomic radiation. No
hospital is without an X-ray machine. When switched on, it produces a very intense beam of X-rays.
The machine is kept on only for a short time. Still during that brief period, it causes a radiation
exposure. There are other common medical procedures which expose the patient to radiation about a
thousand times as much as a chest X-ray. To diagnose certain intestinal ailments, the patient is first
asked to swallow a barium salt mixture. Then a number of X-ray pictures are taken to follow its path
through the stomach and the intestines. This helps identify the affected parts. In some heart disorders,
a tube is inserted into the body reaching right up to the heart for diagnosing the heart condition and
sometimes even for treatment purposes. As the tube progresses into the body, its position is identified
at each stage through X-ray pictures. In each of these procedures, the patient receives a very large
exposure to radiation.
How are we affected by radiation?
All living systems are made up of cells. Human body has about 1,00,000 billion cells. Most cells
undergo division cyclically. Body metabolism ensures a close balance between production of cells by
cell division and the loss of cells by elimination.
When radiation passes through the body, it breaks up some of the molecules in the cells. The body's
natural mechanism can repair and restore the original shape of such broken molecules (or if required
scavenge them). At low levels of radiation exposure the repair mechanism is almost always effective.
Very rarely, this repair action may result in the broken molecules joining together in wrong order.
Misrepair of molecules may persist across cell division and lead to adverse effects in the long run.
Appearance of cancer is the most important among the delayed effects. Among occupational workers
exposed to radiation, 1 in 1000 may develop cancer many years i.e. 10,20 or even 40 years later.
If the exposure to radiation is moderately high or high, and occurs in a short time, then the body's
repair mechanism may not be able to cope with the loss effectively. To start with, symptoms like
nausea and vomiting appear but there is no threat to life. But as the exposure increases, the chances
of recovery diminish.
Is radiation the only cause of cancer?
No. There are several causative agents for
induction of cancer in human, including various
toxic chemicals that are always present in the air
we breathe, the water we drink and the food we
eat. The pie chart indicates the cancer causing
agents and their relative magnitude. Natural
Cancer – the causative factors
Env. Med.
Radiation
1%
Food
33%
31%
Env. Pollution
2%
Industrial
Occupation 4%
Sexuality
7% Unknown
5%
Viral
Infection
10%
Alcohol
4%
Additives
Hereditary 1%
2%
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incidence of cancer in most developed countries is about 1 in 5. Radiation contributes to less than 1%
of the total incidence.
Is radiation exposure harmful at all levels?
Exposure to ionising radiation at very low levels does not manifest in serious biological effects. The
evidence for this is the exposure that we receive from the natural sources of radiation. Studies
conducted in the population living near the high background areas corroborate this fact.
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