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1. Nuclear Chemistry and
Applications of Radioactivity

2. Radioactivity
The phenomenon of spontaneous emission of sub atomic
particles or invisible radiations by nucleus or certain radioactive
substances like uranium, thorium, polonium etc. is called radioactivity.
The substances which emit radioactive rays like α- ray, β- ray, ϒ- ray etc.
are called radioactive substances.
Natural and Artificial Radioactivity
Natural Radioactivity
The type of radioactivity which occurs due to the spontaneous
emission of sub atomic particles or invisible radiations from heavier
elements is called natural radioactivity. In this type of radioactivity,
only a single nucleus is involved and finally results in the formation of
stable nucleus. Generally, nucleus with atomic number higher than 83
undergoes this type of radioactivity.
e.g. 92U 238
90 Th 234 + α- particle
The beginning radioactive isotope is called parent and the product is
called daughter.

3. Artificial or induced radioactivity
The type of radioactivity in which an element is converted into a
new radioactive isotope of a known element by artificial means is
called artificial radioactivity. Stable nucleus of light mass is
bombarded by the projectile like neutron, α- ray etc. to convert it
into unstable radioactive nucleus.
e.g. 7 N 14 + 2 He 4 ( α- particle) 8O17 + 1P1 ( proton)
13 Al 27 + 2He 4
15P30 + 0n1 ( neutron)

5. Types of Radiations (Rays)
a. Alpha (α) ray:
* Positive charged ray which consist of two units of positive charge
& mass of four times of hydrogen, denoted as 2He4.
* velocity is nearly 10% that of light.
* Has highest ionizing power but lowest penetrating power which
can be stopped by 0.1 mm thick aluminium foil.
b. Beta (β) ray:
*Negative charged ray which consist of -1 charge and zero mass,
denoted as -1e0.
* Velocity is about 99% of that of light.
* Ionizing power is lower than α-ray but have higher penetrating
power which can be stopped by 10 mm thick aluminium sheet.
c. Gamma (ϒ) ray:
* Charge less and mass less ray, which has the velocity of light.
* Ionizing power is lowest but has highest penetrating power,
which can be stopped by 200 mm thick aluminium sheet.

6. Cause of Radioactivity
Radioactivity is caused due to unstable nucleus which can be
determined by neutron to proton (n/p) ratio.
If the n/p ratio is 1, the nucleus is stable and non-radioactive.
e.g. 20Ca40 , n/p = 20/20 = 1
If the n/p ratio is either greater or lesser than 1, the nucleus
becomes unstable and hence radioactive. But as the ratio
approach 1.5, it again becomes stable.
e.g. 4Be9, n/p = 5/4 = 1.25 (radioactive)
6C14, n/p = 8/6 = 1.33 (radioactive)
82Pb206, n/p = 124/82 = 1.5 (stable)
Units of Radioactivity
It is measured in Becquerel, Curie and Rutherford unit. The
widely used unit is Curie (Ci), which is defined as the quantity of
any substance that produces 3.7 X 10 10 disintegration per
second (dps). i.e. 1 Ci = 3.7 X 10 10 dps

7. Small units are
1 millicurie ( mCi) = 3.7X 10 7 dps
1 microcurie ( μ) = 3.7 X 10 4 dps
Similarly,
1 Rutherford (rd) = 10 6 dps
The SI unit of radioactivity is Becquerel, and
1 Becquerel = 1 disintegration per second
Nuclear Reaction
The reactions in which the composition of certain nuclei undergo a
change are termed as nuclear reactions. There are two types of
nuclear reactions i.e. nuclear fission and nuclear fusion reaction.
i. Nuclear Fission Reaction:
The nuclear reaction in which a heavier nucleus is bombarded with
high energy particles to form lighter nuclei of almost similar mass with
a simultaneous release of huge amount of energy is called nuclear
fission reaction.
e.g. 92U235 + 0n1 [92U236] 56Ba141 + 36Kr92 + 3 0n1 + Energy
(unstable)

8. The energy liberated during nuclear fission reaction can be both
controlled or uncontrolled. Controlled form of energy can be
used as nuclear power and uncontrolled form of energy can be
used as atom bomb. The amount of energy released in this type
of nuclear energy is much lower than that in nuclear fusion
reaction.
ii. Nuclear fusion reaction:
The nuclear reaction in which nuclei of the lighter elements fuse
together to form a heavier nucleus is called nuclear fusion
reaction.
e.g. 1H2 + 1H2
2He4 + energy
Nuclear fusion reaction takes place only at very high
temperature (≈ 40 lakhs degree). So, nuclear fusion reaction is
also called as thermonuclear reaction. The amount of energy
released is very high as compared to that in nuclear fission
reaction. It can be used to produce hydrogen bomb.

9. Nuclear power and Nuclear weapons
Nuclear power is the use of nuclear reactions that release
nuclear energy to generate heat, which is then used in steam
turbines to produce electricity in a nuclear power plant. Nuclear
power can be obtained from nuclear fission, nuclear decay and
nuclear fusion reactions. The energy from nuclear power plant is
made into electricity, which can be used to power machines and
heat homes. They produce power by boiling water to create
steam that spins a turbine.
Nuclear weapon is an explosive device that derives its
destructive force from nuclear reactions, either fission or from a
combination of fission and fusion reactions ( thermonuclear
bomb). E.g. atom bomb, nuclear warhead, nuclear bomb etc.
Both bomb types release large quantities of energy from
relatively small amount of matter.

10. Industrial uses of radioactivity
Radioactive isotopes have many applications in industry both in
research and in process control. Some of the examples are given
below.
a) The wear and tear of piston rings and gears in engine and its
prevention by means of suitable lubricants has been studied
by radioactivity. A steel piston ring is made radioactive by
exposing it to neutrons in a nuclear reactor and is fitted into
the cylinder of an internal combustion engine which is
operated normally with a particular lubricating oil. By
determining the radioactivity removed by oil, the amount of
piston wear can be determined.
b) The phenomenon of self-diffusion in metal i.e. the
movement of the atoms of a metal within the crystal lattice
has been studied with the help of radio-isotopes.

11. c) Uniformity of mixing during the blending of petrol, lubricating
oils and greases etc. has been achieved by labeling one of the
constituents with a radioactive tracer.
d) ϒ-rays obtained from Co60 have been used as catalyst in the
manufacture of C2H5Br from ethylene and HBr.
e) By incorporating radioactive isotope in the metal, it is possible
to know as to what happens when a metal is subjected to a
particular treatment like case-hardening, annealing,
quenching, cold-rolling etc.
f) Radioactive isotopes have been used in studying the
mechanism of the effectiveness of various lubricants.
g) Radioactive carbon, C14 has been used as a tracer in studying
mechanisms involved in many reactions of industrial
importance such as alkylation, polymerization, catalytic
synthesis etc.

12. Medical Use of Radioactivity
Many radioisotopes find applications in the field of medicine.
a) Phosphorus-32 has been used for locating some forms of
cancer and malignant growths, as the fast growing cells tend
to accumulate phosphorus more than the normal cells.
b) It is also a cure for leukemia.
c) Radioactive iodine and arsenic have been used for locating
brain tumors for operation.
d) Iodine-131 is helpful in detecting disorders of thyroid gland.
e) Gold-198 is used for curing some forms of cancer.
f) Sodium-24 has been used for examining the circulation of
blood.
g) Co-60 (β-emitter) forms Ni-60 which is strong ϒ-emitter. This
intense ϒ-radiation is replacing use of radium for curing
cancer. It is cheaper and safer to use.

13. Radiocarbon Dating
The age of a piece of wood or animal fossil can be determined by
radio-carbon dating technique which is base on determination of
C14/C12 ratio. This technique was developed by Willard Libby who
was awarded Nobel Prize for this brilliant work. Plants take up CO2
from atmosphere. CO2 in nature also contains small amount of
radioactive C14 which is produced in the atmosphere by the
interaction of neutrons (formed from cosmic rays in the upper
atmosphere) with ordinary nitrogen.
i.e. 7N14 + 0n1
6C14 + 1H1
6C14 decays continuously as follows:
6C14
7N14 + -1e0 ( T1/2 = 5760 years)
and is replaced at a steady rate so that C14/C12 ratio remains
constant. After death of plants and animals, the disintegrating 6C14
is no longer replaced and C14/C12 ratio becomes smaller and
smaller. By measuring C14/C12 ratio and half life period, the age of
plant or animal can be determined as follows.

14. t =
2.303 𝑇
0.693
log
𝑎
𝑎 −𝑥
where, a = C14/C12 ratio in living plant and a- x = C14/C12 ratio in
dead plant.
Hence, it can be written as follows.
t =
2.303 𝑇
0.693
log
𝐶14
𝐶12
𝑟𝑎𝑡𝑖𝑜 𝑖𝑛 𝑙𝑖𝑣𝑖𝑛𝑔 𝑝𝑙𝑎𝑛𝑡
𝐶14
𝐶12
𝑟𝑎𝑡𝑖𝑜 𝑖𝑛 𝑑𝑒𝑎𝑑 𝑝𝑙𝑎𝑛𝑡
Thus, if the ratio of amount of C14 isotopes in the fresh and
dead wood is known, age can be calculated by above equation.

15. Harmful effect of Nuclear Radiations
One of the serious problems associated with the nuclear energy
programme is the disposal of radioactive waste and the monitoring of
environmental pollution that can be caused by the discharge of volatile
radioactive isotopes into the atmosphere and the leakage of radioactive
material into the water stream used as coolant and moderator. It is well
known that the radiations emitted by radioactive substances and
neutrons have harmful biological effects. They can cause genetic
mutations leading to skin cancer or leukemia. If radio nucleids are
ingested into the body accidentally, in addition to the damage caused by
nuclear radiation, there is a danger of certain elements tending to
accumulate in certain specific organs or tissue. For example, iodine-131
with a half life period of 8 days is rapidly taken up by the thyroid gland
from which it is eliminated only slowly. Its harmful effect can persist for
several months and can cause serious damage to the healthy thyroid
gland.
Because of the harmful effect of nuclear radiations, extreme care has
to be exercised while working with radioisotopes. Stringent safety
measure are necessary for the safe operation of nuclear reactors and in
the disposal of radioactive wastes.