Radioactivity and Nuclear Energy
1 Radioactivity
Definition: Radioactivity is the property of certain heavy elements to spontaneously break down or disintegrate, emitting invisible but highly energetic rays and forming new elements in the process. This transformation occurs naturally without any external trigger, making it a purely nuclear phenomenon.
Discovery:
- Henri Becquerel (1896) accidentally discovered radioactivity while studying the effects of sunlight on uranium salts.
- Later, Marie Curie and Pierre Curie investigated it in depth and coined the term radioactivity.
Cause: Atoms of heavy elements (with atomic numbers above 83) have unstable nuclei due to imbalance between the strong nuclear force and electrostatic repulsion between protons. This instability causes them to emit radiation to achieve stability.
Examples of radioactive elements: Uranium (U), Thorium (Th), Radium (Ra), Polonium (Po).
1.1 Becquerel Rays
When radioactive elements decay, they emit three main types of radiations, collectively called Becquerel rays:
- Alpha (α) rays – positively charged particles
- Beta (β) rays – negatively charged particles (electrons)
- Gamma (γ) rays – high-energy electromagnetic waves
Nature and Properties of α, β, and γ Rays
1. Alpha (α) Particles
- Nature: Nuclei of helium atoms (2 protons + 2 neutrons).
- Charge: +2
- Mass: 4 amu
- Speed: About 1/10th the speed of light.
- Penetrating Power: Very low – stopped by paper or skin.
- Ionising Power: Very high.
- Effect on Nucleus: Atomic number decreases by 2, mass number decreases by 4.
- Example decay: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
2. Beta (β) Particles
- Nature: High-speed electrons from the nucleus.
- Charge: –1
- Mass: 1/1837 amu
- Origin: Neutron changes to proton + electron; electron is emitted.
- Penetrating Power: Greater than α-particles; passes through thin aluminium foil.
- Ionising Power: Lower than α-particles.
- Effect on Nucleus: Atomic number increases by 1; mass number unchanged.
- Example decay: ¹⁴₆C → ¹⁴₇N + β⁻
3. Gamma (γ) Rays
- Nature: Electromagnetic radiation of very short wavelength.
- Charge: 0
- Mass: 0
- Speed: Equal to speed of light.
- Origin: Released when nucleus loses excess energy after α or β emission.
- Penetrating Power: Very high – can pass through lead and concrete.
- Ionising Power: Very low.
- Effect on Nucleus: No change in atomic or mass number.
Uses of Radioactivity
- Biochemical Research: Radioisotopes like C-14 trace biochemical pathways.
- Medical Applications: I-131 for thyroid treatment, Co-60 for cancer therapy, P-32 for leukemia.
- Archaeological Dating: C-14 dating for fossils and artifacts.
- Industrial Uses: Leak detection, material thickness measurement, sterilization.
2 Nuclear Energy
Definition: Nuclear energy is the energy stored in the nucleus of an atom, released during nuclear reactions – either by fission or fusion.
2.1 Mass Defect (Δm)
The mass defect is the difference between:
- The total mass of individual protons and neutrons.
- The actual measured mass of the nucleus.
The missing mass converts to binding energy.
2.2 Binding Energy
The energy needed to separate all nucleons from the nucleus.
Formula: E = Δm × 931 MeV (Δm in amu)
Higher binding energy per nucleon = more stable nucleus.
7.2.3 Nuclear Fission
- Process: Heavy nucleus splits into two lighter nuclei with energy release.
- Example: ²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3 ¹₀n + Energy
- Applications: Nuclear power plants, atomic bombs.
2.4 Nuclear Fusion
- Process: Two light nuclei combine to form a heavier nucleus, releasing energy.
- Example: ¹₁H + ¹₁H → ²₁H + Energy
- In Nature: Powers the Sun and stars.
- Advantages: More energy, less waste than fission.
- Disadvantage: Requires very high temperature and pressure.
2.5 Peaceful Uses of Nuclear Energy
- Electricity generation
- Medical diagnosis and treatment
- Scientific research
- Food preservation
2.6 Dangers & Safety Measures
Hazards: Radiation sickness, genetic mutations, environmental contamination.
Example Accident: Chernobyl Disaster (1986) – explosion and meltdown in Ukraine caused widespread radioactive contamination.
Safety Measures:
- Reactors far from populated areas
- Earthquake-resistant designs
- Thick concrete and lead shielding
- Safe radioactive waste disposal