Revision: Nuclear Physics Science SSLC (English Medium) Class 10 Tamil Nadu Board of Secondary Education

Definitions [11]

Define free electrons.

Electrons in outer orbits are weakly bound with the nucleus. In solids these weakly bound electrons leave their individual atom and become a part of it. These electrons are known as free electrons.

Define bound electrons.

As nucleus is positively charged it strongly attracts the negative charged electrons. The electron orbit close to the nucleus are tightly bound by strong attractive force of nucleus. These electrons are known as bound electrons.

Define the term radioactivity.

The phenomenon of spontaneous disintegration of an unstable nucleus of a naturally occurring isotope accompanied by emission of active radiations, α particles, β particles and γ radiations is called radioactivity.

Definition: Radioactivity

Radioactivity is a nuclear phenomenon. It is the process of spontaneous emission of α or β and γ radiations from the nucleus of atoms during their decay.

Definition: Beta (β) Radiations

Beta (β) radiations are the radiations which are negatively charged and turn to the right in a magnetic field or towards the positive plate in an electric field, and are deviated more than alpha particles.

Definition: Alpha (α) Radiations

Alpha (α) radiations are the radiations which are positively charged and turn to the left in a magnetic field or towards the negative plate in an electric field.

Definition: Gamma (γ) Radiations

Gamma (γ) radiations are the radiations which are uncharged (neutral) and pass undeviated in both magnetic and electric fields, and are electromagnetic waves similar to light waves.

Definition: Nuclear Fission

Nuclear fission is the process in which a heavy nucleus splits into two lighter nuclei of nearly the same size, when bombarded with slow neutrons. In each fission reaction, a tremendous amount of energy (≈ 190 MeV) is released.

Definition: Nuclear Fusion

Nuclear fusion is the process in which two light nuclei combine to form a heavy nucleus. In this process also, huge amount of energy is released.

Define the following form:

Moderator in nuclear reactor

Moderator of a nuclear reactor is a substance that slows down the speed of neutrons. In traditional nuclear reactors, the moderator is the same thing as that of coolant like water.

Define.

Nuclear fission

In nuclear fission, the atom of a heavy element is bombarded by a neutron to form an unstable isotope which further splits into two or more smaller nuclei releasing extra neutrons and large amount of energy and heat.

Key Points

Key Points: Properties of Alpha Particles

Alpha particles strongly ionise the gas through which they pass, and their ionising power is about 100 times that of beta particles.
Alpha particles have very small penetrating power, as they can penetrate only 3 to 8 cm in air and are stopped by a thin card sheet or thick paper.
Alpha particles are deflected by electric and magnetic fields, but their deflection is less than that of beta particles due to their larger mass.
Alpha particles affect a photographic plate and cause fluorescence on striking a fluorescent material.

Key Points: Properties of Beta Particles

The speed of beta particles is of the order of 10⁸ m s⁻¹, but always less than 3 × 10⁸ m s⁻¹.
The penetrating power of beta particles is more than that of alpha particles but less than that of gamma radiation.
Beta particles are negatively charged and get deflected in electric and magnetic fields more than alpha particles.
Beta particles produce X-rays when stopped by metals of high atomic number and high melting point.
Beta particles cause more biological damage than alpha particles as they can easily pass through the skin.

Key Points: Properties of Gamma Radiations

The speed of γ‑radiations is the same as the speed of light, i.e., 3 × 10⁸ m s⁻¹ in vacuum or air.
The ionising power of γ‑radiations is very low, being 1/10,000 times that of α‑particles.
The penetrating power of γ‑radiations is very high, and they can pass through thick sheets of lead or iron.
Gamma radiations are not deflected by electric and magnetic fields, as it is not a charged particle.
Gamma radiation can easily pass through the human body; therefore, it causes immense biological damage.

Key Points: Changes Within the Nucleus in Alpha, Beta and Gamma Emission

In alpha emission, the atomic number (Z) decreases by 2, and the mass number (A) decreases by 4.
In beta emission, the atomic number (Z) increases by 1 and the mass number (A) remains unchanged.
In gamma emission, there is no change in atomic number (Z) and mass number (A); only the energy of the nucleus changes.
Beta emission is often followed by the emission of an antineutrino (ν̅) to conserve energy and momentum.
The daughter nucleus may still be radioactive and can undergo further α or β emission until a stable nucleus is formed.

Key Points: Nuclear Fission

In nuclear fission of U‑235, a slow neutron is absorbed to form unstable U‑236, which splits into two nuclei with the release of three neutrons and energy.
Energy released in fission is due to loss of mass, and is given by Einstein’s mass‑energy relation, .
In each fission reaction, atomic number (Z) and mass number (A) remain conserved, though mass is converted into energy.
Fission of one U‑235 nucleus releases nearly 190 MeV energy, mainly as kinetic energy of fragments, neutrons, γ‑rays, heat, and light.

Key Points: Power Plants Based on Nuclear Energy

Working Principle: Nuclear fission of Uranium-235 or Plutonium releases heat, which is used to convert water into steam.
Electricity Generation: The high-pressure steam rotates the turbine, which drives the generator to produce electricity.
Energy Transformation: Nuclear energy → Thermal energy → Kinetic energy in steam → Kinetic energy in turbine → Electrical energy.
Advantages: No air pollution, efficient source of energy, and less fuel required compared to thermal power plants.
Problems: Produces radioactive nuclear waste and any accident can release harmful radiation.

Laws of Motion Atoms and Molecules