• Nuclear physics is the branch of physics that studies the interactions between atoms and their constituents.
• The branch of science that studies the structure of nuclei, their formation and stability.
• The application of nuclear physics is mostly in the field of power generation using nuclear energy.
• Splitting a nucleus to produce energy is called nuclear fission and combining two neutrons to produce energy is called nuclear fusion.

Atomic theory:

• Average atom diameter is 0.000000001m. or 1× 10-9m.
• Nanometer – A unit used to measure small lengths. One nanometer = 1× 10-9 m.
• Basic atomic particles
• Electron
• Proton
• Neutron

Protons (p):

• Located within the nucleus
• Positively charged particles.
• The value of their positive charge is equal to the value of negative charge acquired by the electrons.

Neutrons (n):

• Located within the nucleus.
• Does not contain electricity.
• All nuclei except hydrogen (protium) have neutrons.
• Protons + Neutrons = Nucleons.
• Its mass is equal to the mass of a proton and the mass of a neutron is 1.6 × 10-24 kg.

Electrons (e):

• Oppositely charged particles.
• They revolve around the nucleus in circular orbits.
• The mass of an atom depends only on the mass of protons and neutrons inside the nucleus

Atoms are neutral –

• The total negative charge of all the electrons outside the nucleus is equal to the total positive charge of the protons inside the nucleus.
• They knew that the protons in the nucleus of an atom determine what that element is.
• Example: A hydrogen atom if there is only one proton in the nucleus of an atom.
• An oxygen atom has eight protons in its nucleus.

Atomic number and mass number:

Atomic number (z):

• Atomic number is the total number of electrons or protons found in an atom.
• Denoted by the letter Z.
• If you know the atomic number, you can find the number of electrons or protons in that atom.

Mass Number (A):

• The total mass of an atom is found in its nucleus.
• The mass number is equal to the sum of the total number of protons and neutrons in the nucleus.
• Mass number or atomic mass = number of protons + number of neutrons
• A = p + n

Lithium mass number (A) = 3 + 4 = 7.

Sodium mass number (A) = 11 + 12 = 23.

Isotopes:

• Atoms of the same element have the same atomic number and different mass numbers. They are isotopes.
• For example the hydrogen atom has three isotopes.
• Protium (1H1), Deuterium (1H2), Tritium ( 1H3).

Isobars:

• Atoms having the same mass number and different atomic numbers are called isobars.
• g. Calcium (20Ca40) and Argon – (18Ar40).
• Competence
• Bonding ability is the ability of one atom to bond with another atom.
• It is measured by how many hydrogen atoms an atom can hold.
• Eg, one oxygen atom combines with two hydrogen atoms to form a water molecule. Therefore, the covalent bond of oxygen is two.

Nuclear principles:

Dalton’s Nuclear Principle:

• Published in 1808.
• Matter is made up of very small particles called atoms.
• An atom cannot be created or destroyed.
• Atom is the smallest indivisible particle.
• Did not give any explanation about the positive and negative charges found in the atom.

Limitations of the Dalton Atomic Principle:

• It is false that an atom is an indivisible particle.
• Atoms of the same element have different atomic masses (isotopes).
• Atoms of different elements have the same atomic mass (isobars).

Thomson’s Principles:

• Published in 1897.
• He compared the atom to a watermelon.
• He called opposite charges as electrons.
• According to this principle the atom has no electric charge.
• Awarded the Nobel Prize in 1906 for the discovery of the electron.

Limitations of the Thomson Atomic Principle:

• Unable to explain how a positively charged sphere protects itself from electro neutrality attracting negatively charged electrons.
• Describes protons and electrons only. Not talking about neutrons.

Rutherford’s Nuclear theory:

• He bombarded a thin gold plate with positively charged alpha rays. He issued a nuclear policy based on the test.
• An atom must contain mostly vacuum.
• The area from which the charged rays are reflected back must be charged throughout the area.
• He was awarded the Nobel Prize in Chemistry for this policy.
• Nucleus is electronegative. Most of the mass of the atom is located in the center.
• Electrons move in circular orbits around the nucleus.
• The nucleus is very small in size compared to the size of the atom.

Ions:

• Atoms that have a positive or negative charge are called ions.
• An atom gains a positive charge by losing one or more electrons. These are Nerayani
• An atom acquires an opposite charge by gaining one or more electrons. These are opposites

Chemical Addition Rules:

1. Law of Conservation of Mass.

• 1774
• Lavoisier
• The total mass of the products formed during a chemical reaction is equal to the total mass of the reactants”.
• “Mass cannot be created or destroyed by a chemical reaction”,
• This law can also be called law of mass extinction.
• Ammonia formation reaction from nitrogen and hydrogen (Haber method).

2. Law of Invariance.

• Year 1779
• Joseph Proust
• More than one element combines in a specific mass ratio to form a compound.”
• He discovered that compounds containing two or more elements contain the elements in the same proportions, regardless of where they are obtained and who prepares them.
• For example, whether we get water from rain, well, sea or river, the mass of hydrogen and oxygen in it is always in the ratio of 1:8.

3. Multiplying Ratio Law.
4. K- Lussac’s law of mass coupling.

Radioactivity:

Radiological discovery:

• Henri Beccorel 1896 observed that whenever a photographic plate was placed near uranium it was exposed to photochromic radiation.
• Realized that uranium emits some radiation.
• This phenomenon is called radiation.
• Uranium was identified as a radioactive element.
• Marie Curie, along with Pierre Curie, discovered radioactivity from a dark colored mineral called Pitch Blunt.
• Emits radioactivity similar to uranium. They named it Radium.
• Radioactive elements emit concentrated rays such as alpha, beta and gamma rays.

Definition of radioactivity:

• Nuclei of some elements are unstable.
• These nuclei disintegrate and become slightly more stable nuclei. The event itself is radiation.
• Radioactivity is the process by which nuclei decay and emit alpha, beta and gamma rays.
• All the elements that undergo this event are ‘radioactive elements’.
• Elements with atomic number greater than 82 are capable of spontaneously emitting radiation. E.g. Uranium, Radium,
• Technetium (43) and bromium (61) are the only two elements with atomic number less than 82 that are radioactive so far.
• So far 29 radioactive substances have been discovered

Artificial radiation:

• ‘Synthetic radioactivity’ is the process of induced conversion of some light elements into radioactive elements.
• Irene Curie and F. Joliet discovered

Natural radiation

1. It is a spontaneous fission phenomenon of nucleus.
2. Alpha, beta and gamma rays are emitted.
3. It is a spontaneous event.
4. These usually occur in elements with atomic numbers greater than 83.
5. It cannot be controlled.

Artificial radiation

• It is a phenomenon of induced decay of nucleus.
• Mostly elementary particles like neutron, positron are emitted.
• It is a triggered event.
• These usually occur in elements with atomic numbers less than 83.
• It can be controlled.

A unit of radioactivity

Curie:

• The archaic unit of radioactivity.
• A rate of 3.7 × 1010 decays per second from a radioactive substance is called one curie.
• This is roughly equivalent to the decay caused by 1 gram of radium 226.

1 Curie = Amount of radioactive element that gives 3.7 × 1010 decays in one second

Rutherford (Rd):

• Another unit of radioactivity.
• A radioactive substance is defined as one Rutherford if the amount of radioactive decay emitted per second is 106.

1 Rutherford (Rd) = dose of radioactive element that gives 106 disintegrations in one second

Beccoral (Bq):

• The international (SI) unit of radioactivity is the beccoral.
• It is defined as the amount of radioactive decay emitted per second as one pectoral.

Röntgen:

• A unit of radioactivity emitted by gamma (γ) and X rays.
• A roentgen is the quantity of radioactive material that produces 2.58 × 10-4 coulomb charges in 1 kilogram of air at constant pressure, temperature and humidity.
• Alpha, beta and gamma rays
• Radioactive nuclei emit dangerous rays.
• They are given as three radioactive particles.
• Alpha (α), beta (β) and gamma (γ) rays.

Law of radiative migration:

• Sadi and Fajan
• Nuclei are formed during α and β decay
• When an element emits an α-particle, its mass number is reduced by four and its atomic number by two, forming a new nucleus.
• When an element emits a β-particle, its mass number remains unchanged and its atomic number increases by one to form a new nucleus.

α – Decay

• The process by which an unstable parent nucleus emits an α particle to become a stable daughter nucleus is called α-decay.
• Example: Uranium 238 (U238) decays, emits an α particle, and becomes thorium – 234 (Th234).
• 92U238 → 90Th234 + 2He4 (α – decay)
• A parent nucleus undergoes α decay and its mass number decreases by four and atomic number by two to form a new nucleus.

β – Decay

• The process by which the unstable parent nucleus emits a β particle and becomes a stable daughter nucleus is called β-decay.
• Example: β – decay of phosphorus
• 15P32 → 16S32 + -1e0 (β – decay)
• During β – decay there is an increase in atomic number by one, with no change in mass number.
• Note: The nucleus of a new element appearing in a nuclear reaction is known by its atomic number, not its mass number.

γ – Gamach decomposition

• During Gamach decay only the ‘energy level’ of the nucleus changes.
• Its atomic number and mass number remain unchanged.

Nuclear fission

• Autobahn and F. Strassmann discovered in 1939.
• Nuclear fission occurs when the nucleus of a heavy atom splits into two smaller nuclei, releasing high-energy neutrons.

Example:

• Nuclear Fission of Uranium 235 (U235).
• 92U235 + 0n1 → 56Ba141 + 36Kr92 + 30n1 + Q (energy)
• An average energy of 3.2 × 10-11 J is released per fission.

Fissionable materials:

• A substance is fissionable if it absorbs neutrons and causes fission.
• Example: Uranium 235 (U235) Plutonium 239 and Plutonium 241 (Pu239 and Pu241)
• Not all isotopes of uranium undergo fission by absorbing neutrons. Uranium 238 does not undergo fission. Uranium 235 is a fissile material.
• Some non-fissile radioactive elements can be converted into fissile material by absorbing neutrons. These are called rich objects.
• Example: Uranium 238, Thorium 232, Plutonium 240

Continuity:

• Uranium (U-235) undergoes nuclear fission when struck with a neutron, releasing three neutrons.
• These three neutrons cause the next three uranium fissions to produce nine neutrons.
• These nine neutrons again cause the next 27 neutrons to be produced. Similarly, this event continues. Hence it is called a continuous action.
• The number of neutrons increases exponentially in the exponential series by the process of spontaneous diffusion.

1. a) Controlled Continuity

• In a controlled chain reaction the number of neutrons emitted is maintained at ‘one’.
• Of the neutrons emitted by the absorbing material, only one neutron is allowed to interact and the other neutrons are absorbed.
• The energy released through this interaction is used constructively.
• Controlled reactivity is used to generate steady, controlled power throughout a nuclear reactor.

1. b) Uncontrolled Continuity

• In this type of reaction neutrons multiply and due to this more fissile material is produced.
• At the end most of the energy is released within one second.
• Detonation of nuclear bomb is done using chain reaction.
• Atomic bomb
• Works on the principle of ‘Uncontrolled Continuity’.
• A large explosion occurs with high energy in a very short period of time.

System:

• A small fraction of fissionable matter of variable mass is placed in the nucleus.
• This compartment contains a cylindrical cavity.
• A cylindrical slitting material is placed to fit the vacuum.
• Its mass must be less than the transition mass.
• This cylinder is inserted into the vacuum for the detonation of the nuclear bomb.
• When these two parts come together and reach supercritical mass, a nuclear explosion occurs.
• During a nuclear explosion, very high energy levels of heat, light and radiation are released.
• Camac radiations are also released.
• In 1945, during World War II, such atomic bombs were dropped on Hiroshima and Nagasaki in Japan.
• The atomic bomb dropped on Hiroshima city was called “Little boy” and it was an atomic bomb containing uranium.
• The atomic bomb dropped on Nagasaki is known as “Fat man”. Contains plutonium.

Electron Volt:

• The electron volt [eV] is the unit for measuring the energy of small particles in nuclear physics.
• It is the energy of an electron accelerated using a voltage of one volt.

1eV = 1.602 × 10-19 joule.

1 million electron volts = 1 MeV = 106 eV

                                  (mega electron volt)

The average energy released by nuclear fission is 200 MeV.

Nuclear fusion:

• The phenomenon where two lighter nuclei combine to form a heavier nucleus is called “Nuclear Fusion”.
• Example: 1H2 + 1H2 → 2H4 + Q (energy)
• 1H2 stands for deuterium, an isotope of hydrogen.
• The average energy released during each nuclear fusion is 3.814 × 10-12 J.
• During nuclear reactions (fusion and fission) the mass of the resulting nucleus is less than the sum of the masses of the two parent nuclei.
• Mass – the ratio between the mass of the mother nucleus and the mass of the child nucleus. This material is converted into energy (mass-energy equation).
• This concept was proposed by Einstein in 1905 through the mass-energy equation.
• The mass-energy equation asserts that mass becomes energy and energy becomes mass.
• The relation for the mass-energy equation is E = mc2. where c is the speed of light. In vacuum its value is 3 × 108 mV-1.

Conditions for nuclear fusion:

• Nuclear fusion takes place only at very high temperatures of 107 to 109 K and at high pressures.
• In this case, the nuclei of the hydrogen atom move closer to each other and nuclear fusion takes place.
• This is called ‘thermonuclear fusion’.

Hydrogen bomb:

• Hydrogen bomb works on the principle of nuclear fusion.
• A nuclear bomb is detonated to create the required high temperature and pressure. After this, nuclear fusion takes place in the hydrogen, releasing an uncontrollable amount of energy.
• The energy produced by a hydrogen bomb (nuclear fusion) is greater than the energy produced by an atomic bomb (nuclear fission).

Nuclear fission:

• The process by which heavy nuclei split into lighter nuclei is called ‘nuclear fission’.
• This phenomenon can also occur at room temperature
• Alpha, beta and gamma rays are released.
• Nuclear fission emits gamma rays which induce genetic mutations in human genes and cause hereditary diseases.

Nuclear fusion:

• The phenomenon in which two light atoms combine to form heavier nuclei is called nuclear fusion.
• Nuclear fusion requires high temperature and pressure
• Alpha rays, positrons and neutrinos are emitted.
• Heat and light are emitted.
• 620 million metric tons of hydrogen nuclear fusion takes place in the Sun every second. 3.8 × 1026 Joules of energy are radiated in one second.

Uses of radioactivity:

Agriculture:

• Phosphorus isotope P-32 is used to increase crop production.
• Radioisotopes are also used to protect agricultural produce from spoilage by microorganisms such as insects and parasites.
• Keep onions and potatoes from rotting with a little radiation
• Can also protect pulses from sprouting during storage.

Medicine:

It is classified into two types and used in medicine.

• Diagnosis
• Radiation therapy
• Sodium – 24 (Na24) helps the heart to function properly.
• Iodine-131 (I131) helps in curing anterior cervical cancer.
• Iron – 59 (Fe59) helps in diagnosis and treatment of anemia.
• Phosphorus-32 (P32) is used in the treatment of skin diseases.
• Cobalt-60 (Co60) and gold-198 (Au198), an isotope of gold, are used to treat skin cancer.
• Irradiation of micro-organisms found in surgical instruments.

Factory:

• Californium – 252 (Cf252) – Used to detect explosives in aircraft cargo.
• Am241 (Am241) – Used as a smoke detector in factories.

Archaeological survey:

• Carbon dating estimates the age of objects by measuring the amount of radioactive carbon they contain.

Safety measures:

• Allowable amount
• A safe dose of radiation exposure for a year is 20 millisieverts.
• The radiation, expressed in roentgen units, should be 100 ml roentgen per week.
• Radiation exposure of 100 R can cause leukemia (destruction of red blood cells), a very serious complication. Radiation exposure is lethal at 600 R.

Preventive measures:

• Radioactive materials should be kept in thick-walled containers.
• Mandatory wearing of medical gloves and medical gown in irradiated areas.
• By wearing a dosimeter, the radiation dose can be measured from time to time.

Nuclear reactor:

• It is a place where controlled nuclear fission takes place and produces electricity.
• In 1942, the first nuclear reactor was built in Chicago, USA.
• Partial components of a nuclear reactor.
• Fuel: Fuel is the fissionable material. The most commonly used fuel is uranium.
• Attenuator: Attenuator is used to reduce high energy neutrons to low energy neutrons. Graphite and hard water are commonly used quenchers.
• Controlling salts: Boron and cadmium salts are mostly used as controlling salts. They are capable of absorbing neutrons.
• Cooler: Cooler is used to remove the heat generated inside the nuclear reactor. Some solvents are water, air, and helium.
• Barrier: A thick concrete wall is built around the nuclear reactor.
• Benefits of nuclear reactor
• Used for power generation.
• Used to make radioactive isotopes.
• Some nuclear reactors are used for research in the field of nuclear physics.
• Production reactors are used to convert non-fissile materials into fissile materials.

Indian nuclear power plants:

• The Indian Atomic Energy Commission (AEC) was set up in Mumbai in August 1948 by the Indian Department of Scientific Research.
• Homi Jahangir Baba was the first to take charge as the President.
• It is now known as Baba Atomic Research Center (BARC).
• In India’s power generation, nuclear power is the fifth resource.
• Tarapur Nuclear Power Plant is India’s first nuclear power plant.
• Maharashtra, Rajasthan, Gujarat, Uttar Pradesh and Karnataka have seven nuclear power plants, one each and Tamil Nadu has two nuclear power plants.
• Kalpakkam and Kudankulam are two nuclear power plants located in Tamil Nadu.
• Apsara was the first nuclear reactor built in Asia and India.
• There are currently 22 nuclear reactors in operation in India.