TOPIC: PHYSICS OF RADIATION
🌟 IMPORTANT POINTS TO REMEMBER
🔹John Dalton in 1808 developed his famous ‘Theory of Atom’.
🔹Elemental matter: It is made up of a combination of a single type of atom, e.g. hydrogen atom.
🔹Compound matter: It is composed of recurring units of a specific number of atoms in a definite arrangement and at least two are different atoms. For example, sodium and chlorine combine to form a compound called sodium chloride, better known as common salt.
🔹Bragg effect: Ionisation is more concentrated at the end of the particle path. This is called the Bragg effect. At the end of the particle path, velocity drops very rapidly.
🔹Electron: The lightest negatively charged particles are called electrons or electron is a subatomic particle that carries 1 unit negative charge (1.602 × 10−19 C) and has a mass (9.1 × 10−31 kg) equal to 1/1837th of that of the hydrogen atom.
🔹Proton: The lightest/smallest positive particle is known as a proton, or it is defined as a subatomic particle that carries 1 unit positive charge (1.602 × 10−19 C) and has a mass (1.67 × 10−27 kg) equal to that of an atom of hydrogen.
🔹Neutron: It is a subatomic particle having mass (1.675 × 10−27 kg) equal to that of the hydrogen atom and carrying no electrical charge.
🔹Molecule: A molecule is formed either by the transfer of electrons amongst or by the sharing of electrons by the outermost shell of the atom. An example of a simple molecule is water (H2O).
🔹In 1869, Mendeleev classified the elements according to their properties. Later, it was known as ‘the periodic table’.
🔹Einstein equation: The relation between mass and energy is given by the following equation: E = m × c2, where c is the velocity of light (about 3 × 108 m/s). The principal quantum number is denoted by n.
🔹Pauli exclusion principle: The maximum number of electrons in the given shell is 2n2. In addition, the outermost shell of any atom in the ground state can never contain more than eight electrons, even though it is assigned a greater number by the Pauli exclusion principle.
🔹Binding energy: The electrostatic force of attraction between the positively charged nucleus and the negatively charged electron balances the centrifugal force associated with a rapidly revolving electron and maintains it in its orbit around the nucleus. It is called binding energy.
🔹Ionisation: The process of converting an atom into an ion is called ionisation. When an atom loses an electron it is called a positive ion, and when an atom gains the electron it is called a negative ion.
🔹Linear energy transfer: The rate of loss of energy from a particle as it moves along its track through the irradiated matter is called linear energy transfer.
🔹Particulate radiation: It consists of atomic nuclei or subatomic particles that transmit kinetic energy by means of their small masses moving at high velocity. Alpha rays, beta rays and cathode rays are examples of particulate radiation.
🔹Alpha rays: Alpha rays consist of a high-speed stream of doubly ionised helium nucleus. They are represented by ‘α’.
🔹Beta rays: Beta rays are streams of high-speed electrons. They are represented by ‘β’.
🔹Cathode rays: If the electrons are produced in the manufactured device, they are called cathode rays.
🔹Electromagnetic radiation: It is the movement of energy through space as a combination of electric and magnetic fields. It is generated when the velocity of an electrically charged particle is altered. Examples are cosmic rays, gamma rays, X-rays, UV rays, visible light, television, radar, microwaves and radio waves.
🔹Wave theory: Wave can be defined as a variation or disturbance that transfers radiant energy progressively from point to point in a medium.
🔹Quantum theory: This theory assumes that the transfer of energy by electromagnetic radiation is not in the form of waves but as a flux of quanta or photons. The quantum is a small packet or bundle of energy with its size proportional to the frequency of radiation.
🔹Isotopes: Isotopes are defined as atoms with the same atomic number but with different atomic mass number and hence different numbers of neutrons.
🔹Isobars: Atoms of different elements which have the same mass number but different atomic number are called isobars. They contain same number of neutrons and protons, but the number of sum of protons and neutrons individually is different.
🔹Radioactivity: The name radioactivity was given to be a phenomenon of the emission of certain radiation of an element capable of penetrating through a substance, ionising it and causing a photographic plate to darken; it can be classified as natural radioactivity and artificial radioactivity.
🔹Radioactivity disintegration: When an atom of a radioactive substance emits an alpha or beta particle, it gets converted into an atom of another element. This phenomenon is called radioactive disintegration or radioactive decay. The main types of radioactive decay include alpha decay, beta decay, electron decay and spontaneous fission.
🔹Half-life period: It can be defined as the time required for an atom of an element to decrease to half the original value. In other words, the time required for a given number of radioactive atoms to disintegrate to half of their initial value is known as the half-life period.
📌 MULTIPLE CHOICE QUESTIONS (MCQs)
1. Which of the following is a type of particulate radiation?
a. Beta rays
b. Gamma rays
c. Cathode rays
d. Both a and c
Answer : d
2. Alpha rays are made up of
a. Doubly ionised helium nucleus
b. High-speed electrons
c. Having no electrical charge
d. None of the above
Answer: a
3. Linear energy transfer is more in
a. Alpha rays
b. Beta rays
c. Both a and b
d. None of the above
Answer : a
4. Which of the following is a type of electromagnetic radiation?
a. Cathode rays
b. Gamma rays
c. X-rays
d. Both b and c
Answer :d
5. The maximum penetration is seen with
a. Gamma rays
b. Alpha rays
c. Cathode rays
d. Beta rays
Answer: a
6. Which of the following is a type of ionising radiation?
a. Visible light
b. Ultraviolet light
c. X-rays
d. None of the above
Answer : c
7. Wavelength of X-ray is
a. 1 to 10−2 Å
b. 0.1–1 Å
c. 103 –1 Å
d. 1010–1014 Å
Answer : b
8. Gamma rays were discovered by
a. Rutherford
b. Ritter
c. Herschel
d. Huygens
Answer : a
9. The degree of penetration of X rays depends on
a. Milliampere and kilovoltage peak
b. Wavelength of X-ray
c. Thickness of material
d. All of the above
Answer :d
10. Which of the following travels with the speed of light?
a. X-rays
b. Gamma rays
c. Cosmic rays
d. All of the above
Answer : a