Comprehensive notes for Chapter 18 Atomic and Nuclear Physics. Covers Atomic Structure, Isotopes, Natural Radioactivity (Alpha, Beta, Gamma), Half-Life, Nuclear Fission, Fusion, and Hazards.
Atom: Consists of a central positive nucleus (Protons + Neutrons) and revolving electrons. $A = Z + N$ (Mass Number = Atomic Number + Neutron Number).
Isotopes: Atoms of the same element with same number of protons but different number of neutrons (e.g., Protium $^1H$, Deuterium $^2H$, Tritium $^3H$).
Definition: Spontaneous emission of radiation by unstable nuclei ($Z > 82$).
Types of Radiation:
Background Radiation: Radiation from environment (Cosmic rays, rocks, soil). Safe limit: 5 rem/year.
Definition: Time required for half of the radioactive nuclei to decay. Symbol: $T_{1/2}$.
Formula: Remaining atoms $N = N_o \times (\frac{1}{2})^n$, where $n = \frac{\text{Total Time}}{\text{Half Life}}$.
Radioisotopes Uses: Tracers (Diagnosis, Industry), Carbon Dating (Age of fossils using C-14, $T_{1/2} = 5730$ years).
Nuclear Fission: Heavy nucleus splits into two smaller nuclei with energy release (e.g., U-235 absorbs neutron). Chain Reaction: Neutrons released trigger further fission. Nuclear Reactor: Controlled fission for energy.
Nuclear Fusion: Light nuclei fuse to form heavier nucleus (e.g., Hydrogen to Helium in Sun). Releases more energy per nucleon than fission.
Hazards: Radiation burns, Genetic mutations, Cancer. Safety: Use lead shielding, tongs, and dosimeters.