22.0 RADIOACTIVITY

Radioactivity is the spontaneous emission of particles or energy from the nucleus of an unstable atom. This phenomenon, discovered by Henri Becquerel and studied by Marie Curie, reveals the hidden power within atoms. This chapter explores the three main types of radiation, the concept of half-life, nuclear reactions (fission and fusion), and the applications and hazards of radioisotopes in medicine, industry, and energy production.

22.1 ALPHA, BETA, AND GAMMA RADIATIONS

Unstable atomic nuclei undergo radioactive decay by emitting one or more types of radiation. The three main types are alpha (α), beta (β), and gamma (γ) radiation. They differ in nature, penetrating power, ionizing ability, and behavior in electric and magnetic fields.

22.1.1 Alpha (α) Radiation

• Nature: A helium nucleus consisting of 2 protons and 2 neutrons (⁴₂He).
• Charge: +2 (positive).
• Mass: 4 atomic mass units (relatively heavy).
• Speed: About 5–7% of the speed of light (slowest of the three).
• Penetrating power: Very low – stopped by a sheet of paper or a few centimeters of air. Cannot penetrate human skin (but dangerous if ingested/inhaled).
• Ionizing ability: Very high – collides with many atoms along its path, causing ionization. This is why it is highly damaging to living cells.
• Effect on nucleus: When an atom emits an alpha particle, its mass number decreases by 4 and its atomic number decreases by 2.
• Example: R