Nuclear Chemistry and Application of Radioactivity | Unit 21 Class 12 Chemistry

Unit 21: Nuclear Chemistry and Application of Radioactivity

Nuclear chemistry

It is the subfield of chemistry dealing with radioactivity and
nuclear processes like nuclear reactions and nuclear properties. It is
concerned with the structure and stability of the nucleus. It also deals
with the composition of the nucleus, the origin and separation of isotopes, their effects and their uses.

Radioactivity

The spontaneous disintegration of a heavy unstable nucleus to form a
lighter stable nucleus with the emission of certain radiation is called
radioactivity. It does not depend upon temperature, pressure, magnetic
field and electric field.

$U n s t a b l e n u c l e u s \to S t a b l e n u c l e u s + Radiations(α, β, γ)$

Radioactive radiations

The nature of radiation emitted by radioactive substances is first
discovered by Rutherford. He passed radioactive rays through the
electric and magnetic fields and observed three different types of
deflected rays.

Nature of radioactive rays

i. Those which bend towards the negative field are called alpha (α) particles.
ii. Those which bend towards the positive field are called beta (β) particles.
iii. Those which pass straight and are neutral in nature are called gamma (γ) rays.

Properties	α-particles	β-particles	γ-particles
Nature	Helium nucleus (₂He⁴)	Electrons (_-1e⁰)	Electromagnetic radiations
Charge	Positive	Negative	Chargeless
Mass	4 amu	1/1827 amu	massless
Velocity	1/10 velocity of light	10 times of α-particles	same as light
Penetrating Power	low	Intermediate	High
Ionizing power	High	Intermediate	Low

Natural and artificial radioactivity

i. Natural radioactivity

The spontaneous and uncontrolled disintegration of an unstable
nucleus of radioactive elements by virtue of its own accord is called
natural radioactivity. It is accompanied by the emission of α, β, γ rays. Natural radioactive elements are uranium(U), thorium(Th), radium(Ra), polonium(Po), etc.

$\begin{aligned} _{92} U^{238} & \to_{90} U^{234} + α (_{2} H e^{4}) \\ _{6} C^{14} & \to_{7} N^{14} + β (_{- 1} e^{0}) \end{aligned}$

ii. Artificial radioactivity

The disintegration of an unstable nucleus by artificial means through nuclear transmutation is called
artificial radioactivity. In the laboratory, when slow-moving neutrons are bombarded to certain stable
nuclei,
they become unstable and undergo disintegration. It was discovered by
Joliot and Curie upon bombarding alpha particles on aluminium.

$\begin{aligned} _{2} H e^{4} +_{13} A l^{27} & \to_{15} P^{30} +_{0} n^{1} \\ _{7} N^{14} +_{2} H e^{4} & \to_{8} O^{17} +_{1} H^{1} \\ _{4} B e^{9} +_{2} H e^{4} & \to_{6} C^{12} +_{0} n^{1} \end{aligned}$

Units of radioactivity

Becquerel (Bq): It is the SI unit of radioactivity. One Becquerel is
defined as the quantity of radioactive substance which undergoes 1
disintegration per second.
Curie (Ci): One Curie is defined as the quantity of radioactive substance which undergoes 3.7×10¹⁰ disintegration per second. It measures the radioactivity of radium.
Rutherford (Rd): One Rutherford is defined as the quantity of radioactive substance which undergoes 10⁶ disintegrations per second.

Nuclear reactions (transmutation)

It is the transformation of an element into another by bombarding highly energized particles like alpha
particles, beta particles, neutrons, protons, gamma rays, etc.

$_{7} N^{14} +_{2} H e^{4} \to_{8} O^{17} +_{1} H^{1}$

Types of nuclear reactions

1. Nuclear fission

The nuclear reaction in which a large nucleus splits into smaller
nuclei releasing a huge amount of energy is called nuclear fission.

$_{92} U^{235} +_{0} n^{1} \to_{56} B a^{139} +_{36} K r^{94} + 3_{0} n^{1} + e n e r g y$

2. Nuclear fusion

The nuclear reaction in which two or more lighter nuclei fuse
together to form a heavier nucleus releasing energy is called nuclear
fusion.
These types of reactions are difficult to occur. Here two
lighter nuclei should come close where positively charged nuclei repel
each other. Hence a huge amount of energy is required to overcome such
repulsion. Therefore a large amount of energy from a source like a sun
is required to initiate these reactions. So these reactions are also
called thermonuclear reactions.

$_{1} H^{1} +_{1} H^{1} \to_{2} H e^{4} +_{0} n^{1} + E n e r g y$

Differences between Nuclear Fission and Fusion

Nuclear Fission	Nuclear Fusion
Occurs only in nuclei of heavy elements.	Occurs in nuclei of lighter elements.
Heavy nucleus splits into lighter nuclei.	Lighter nuclei fuse to form heavy nucleus.
Carried out at room temp.	Carried out at high temp.
Can be controlled and used in constructive work.	Can’t be controlled and can’t be used in constructive work.
Relatively less amount of energy is released.	Relatively more amount of energy is released.
Takes place in nuclear reactors.	Takes place in sun.
Used in atom bomb.	Used in hydrogen bomb.

Nuclear power

Nuclear power is the application of nuclear reactions for the
generation of electricity. A nuclear power plant is a thermal power
station in which heat is generated from the nuclear reactor. As produced
heat is used to generate steam from water which can drive a steam
turbine and generates electricity. Production of electricity from the
nuclear reactor was started in 1951 at a capacity of 100 kV. As per the
report of the 2018 International atomic energy agency, there were 450
nuclear power reactors in 30 countries around the world. It is estimated
that nuclear power provides about 15% of the world’s electricity.

Nuclear power can be obtained from nuclear fission, nuclear decay and
nuclear fusion reactions. Presently, the vast majority of electricity
from nuclear power is produced by the nuclear fission of uranium and
plutonium in nuclear power plants. It is a low-carbon source of
electricity. Top nuclear power producer countries are the United States,
France, China, Russia and South Korea.

Advantages

It is a safe and sustainable source of energy.
It reduces carbon emissions and keeps the environment free from pollution.

Disadvantages

It is expensive to start.
It requires high technology with qualified technicians.
It causes great threats to the people.
The disposal of radioactive waste is a serious issue.

Nuclear weapons

Nuclear weapons are devices designed to release energy in an
explosive way by causing nuclear reactions. Fission types of weapons are
commonly called atomic bombs and fusion types of weapons are commonly
called thermonuclear or hydrogen bombs.

Nuclear weapons cause
catastrophic effects through blasts, fire and lethal ionizing radiation.
Therefore they are used for mass destruction propose. Nuclear weapons
have only twice been used in war, both times by the United States
against Japan near the end of World War II.

On August 6, 1945, the U.S.
Army Air Forces detonated a uranium gun-type fission bomb nicknamed
“Little Boy” over the Japanese city of Hiroshima; three days later, on
August 9, the U.S. Army Air Forces detonated a plutonium implosion-type
fission bomb nicknamed “Fat Man” over the Japanese city of Nagasaki.

These bombings caused injuries that resulted in the deaths of
approximately 200,000 civilians and military personnel. The ethics of
these bombings and their role in Japan’s surrender are subjects of
debate.

Industrial uses of radioactivity

The automobile industry–to test steel quality in the manufacture of
cars and to obtain the proper thickness of tin and aluminium.
The aircraft industry–to check for flaws in jet engines
Construction–to gauge the density of road surfaces and sub surfaces
Pipeline companies–to test the strength of welds
Oil, gas, and mining companies–to map the contours of test wells and mine bores, and
Cable manufacturers–to check ski lift cables for cracks.

Medical uses of radioactivity

Used in both diagnosis and therapy.

Radioactive iodine is used in imaging the thyroid gland.
Radioactive sodium is used in studying the pumping action of the heart.
Radioactive caesium is used in medical device sterilization.
Radioactive phosphorous is used to cure leukaemia and treatment of skin disease.
Radioactive gold is used for curing some forms of blood cancer.

Radioactive Isotopes

The isotopes of radioactive elements are called radioactive isotopes. e.g.. Co-60, I-131, As-74, C-P-32, O-18, etc.

Uses

To trace the root of the element.
To study the mechanism of the reaction.
Used in medicine to cure cancer disease and leukaemia.
To determine the age of various objects containing fossils (carbon dating).

Radiocarbon dating

Radiocarbon dating (also referred to as carbon dating or carbon-14
dating) is a method for determining the age of an object containing
organic material by using the properties of radiocarbon, a radioactive
isotope of carbon.

The method was developed in the late 1940s at the University of
Chicago by Willard Libby. It is based on the fact that radiocarbon
(C-14) is constantly being created in the Earth’s atmosphere by the
interaction of cosmic rays with atmospheric nitrogen.

The resulting C-14
combines with atmospheric oxygen to form radioactive carbon dioxide,
which is incorporated into plants by photosynthesis; animals then
acquire C-14 by eating the plants.

When the animal or plant dies, it
stops exchanging carbon with its environment, and thereafter the amount
of C-14 it contains begins to decrease as the C-14 undergoes radioactive
decay.

Measuring the amount of C-14 in a sample from a dead plant or animal,
such as a piece of wood or a fragment of bone, provides information
that can be used to calculate when the animal or plant died.

The older a
sample is, the less C-14 there is to be detected, and because the
half-life of C-14 (the period of time after which half of a given sample
will have decayed) is about 5,730 years, the oldest dates that can be
reliably measured by this process date to approximately 50,000 years
ago, although special preparation methods occasionally make an accurate
analysis of older samples possible. Libby received the Nobel Prize in
Chemistry for his work in 1960.

Harmful effects of nuclear radiation

1. Hair: Loss of hair fall occurs when exposure to radiation is higher than 200 rems.

2. Heart and Brain: Intense exposure to radiation from 1000 to 5000
rems will affect the functioning of the heart. Radiation kills nerve
cells and small blood vessels of the heart which may cause immediate
death. Brain cells are affected if the radiation exposure is greater
than 5000 rems.

3. Thyroid: Certain body parts are affected specifically when exposed
to different types of radiation sources. The thyroid gland may be
affected when exposed to radioactive iodine. If exposed to a
considerable amount of radioactive iodine, the whole or part of the
thyroid can be affected.

4. Blood System: A number of lymphocytic cells present in the blood
will be reduced if a person is exposed to 100 rems. This may cause
several immune problems. This is termed mild radiation sickness. As per
the reports from Nagasaki and Hiroshima, symptoms may be present more
than ten years after that exposure.

5. Reproductive Tract: As the cells of the reproductive tract divide
fastly, these are more prone to be affected even if the exposure is not
more than 200 rems.

Nuclear Chemistry and Application of Radioactivity | Unit 21 Class 12 Chemistry

Unit 21: Nuclear Chemistry and Application of Radioactivity

Nuclear chemistry