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.

NEB Notes

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

Unit 21: Nuclear Chemistry and Application of Radioactivity