Marie Curie and the History of Radioactivity
CSEC Physics: The Revolutionary Discoveries
Essential Understanding: The discovery of radioactivity transformed our understanding of the atom and led to revolutionary applications in medicine, energy, and archaeology. Marie Curie's pioneering work earned her two Nobel Prizes and changed science forever.
The Remarkable Life of Marie Curie
Maria Sklodowska Curie (1867-1934)
Born: November 7, 1867, Warsaw, Poland
Died: July 4, 1934, France
Education: Physics degree (Sorbonne, Paris, 1893)
Known as: "Mother of Modern Physics"
Marie Curie was the first woman to win a Nobel Prize, the first person to win a Nobel Prize twice, and the only person to win Nobel Prizes in two different sciences!
Nobel Prize Achievements
1903 Nobel Prize in Physics:
- Shared with Henri Becquerel and Pierre Curie
- Awarded for research on radiation phenomena
- First woman to win a Nobel Prize
1911 Nobel Prize in Chemistry:
- Solo award for discovering polonium and radium
- First person to win two Nobel Prizes
- Isolation of pure radium
— Marie Curie
Discovery Timeline: The Road to Radioactivity
French physicist Henri Becquerel discovered that uranium salts emitted mysterious rays that could expose photographic plates. This was completely accidental - he had been studying phosphorescence but found that uranium compounds emitted radiation even without exposure to light!
Marie Curie chose radioactivity as her research topic for her doctoral thesis. Working in a converted shed with inadequate equipment, she began systematically testing all known elements for radioactivity.
Marie and Pierre Curie discovered two new elements in pitchblende ore:
- Polonium (Po): Named after Marie's native Poland
- Radium (Ra): Named for its intense radioactivity
They found that pitchblende was more radioactive than pure uranium, proving that other radioactive elements were present!
The Curies and Becquerel shared the Nobel Prize in Physics for their work on radioactivity. Marie was the first woman recipient. The prize money allowed Pierre to leave his teaching job and focus on research full-time.
Marie Curie won the Nobel Prize in Chemistry for her isolation of pure radium and polonium. She remains the only person to win Nobel Prizes in two different scientific fields.
Understanding Radioactive Emissions
Radioactive atoms are unstable - they emit particles or energy to become more stable. There are three main types of radiation, often called "alpha, beta, and gamma rays" based on their penetrating power.
The Three Types of Radiation
Alpha Particles (α)
What is it: A helium nucleus - 2 protons and 2 neutrons bound together
Symbol: \( \alpha \) or \( _{2}^{4}He \)
Charge: +2
Mass: 4 atomic mass units
Penetration: Low - Stopped by paper or skin
Ionization: High - Causes significant damage
Speed: Slow (about 5% speed of light)
Beta Particles (β)
What is it: A high-speed electron emitted from the nucleus
Symbol: \( \beta^- \) or \( _{-1}^{0}e \)
Charge: -1
Mass: Very small (1/1836 of proton)
Penetration: Medium - Stopped by aluminum foil
Ionization: Medium - Less than alpha
Speed: Fast (up to 99% speed of light)
Gamma Rays (γ)
What is it: High-energy electromagnetic radiation
Symbol: \( \gamma \)
Charge: 0 (no charge)
Mass: 0 (no mass)
Penetration: High - Requires thick lead or concrete
Ionization: Low - Penetrates deeply
Speed: Speed of light (c)
Interactive Radiation Simulation
Observe Radioactive Emissions
Objective: Click the buttons below to observe different types of radioactive emissions. Notice how each particle has different properties and penetration power!
Click a button above to emit particles
Observe the different types of radiation and their properties.
Comparison of Radiation Types
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| Nature | Helium nucleus (2p + 2n) | Electron | Electromagnetic wave |
| Symbol | \( _{2}^{4}He \) or α | \( _{-1}^{0}e \) or β⁻ | γ |
| Charge | +2 | -1 | 0 |
| Mass (u) | 4 | 1/1836 | 0 |
| Speed | ~5% of light | Up to 99% of light | Speed of light |
| Range in air | 5-10 cm | 1-2 meters | Hundreds of meters |
| Shielding | Paper, clothing | Aluminum foil | Thick lead, concrete |
| Ionization | Very high | Medium | Low |
Radioactive Decay Equations
When an atom undergoes radioactive decay, the total mass number (A) and atomic number (Z) must be conserved. This allows us to write balanced nuclear equations.
$$ _{92}^{238}U \rightarrow _{90}^{234}Th + _{2}^{4}He $$
Uranium-238 loses 2 protons and 2 neutrons, becoming Thorium-234.
$$ _{6}^{14}C \rightarrow _{7}^{14}N + _{-1}^{0}e $$
A neutron turns into a proton and an electron (beta particle) is emitted.
$$ _{88}^{226}Ra^* \rightarrow _{88}^{226}Ra + \gamma $$
An excited nucleus releases energy as gamma ray without changing identity.
The Concept of Half-Life
What is Half-Life?
The half-life (\( t_{1/2} \)) is the time taken for half of the radioactive nuclei in a sample to decay.
Where: N = remaining nuclei, N₀ = initial nuclei, n = number of half-lives
Visualizing Half-Life Decay
Objective: Observe how the amount of radioactive material decreases over time as half-lives pass.
Click a button to see how much remains after each half-life
Each half-life reduces the radioactive material by half.
Applications of Radioactivity
Archaeology & Dating
Carbon-14 Dating: Used to determine the age of ancient artifacts, fossils, and archaeological specimens up to 50,000 years old. Living organisms absorb Carbon-14, which decays after death.
Potassium-Argon Dating: Used to date very old rocks and geological formations (billions of years).
Medical Applications
Radiation Therapy: Cobalt-60 and other isotopes are used to treat cancer by destroying tumor cells.
Diagnostic Imaging: Technetium-99m is used in PET scans and other medical imaging techniques.
Thyroid Treatment: Iodine-131 is used to diagnose and treat thyroid disorders.
Industry & Research
Tracers: Radioactive isotopes are used to track the movement of materials in industrial processes and biological systems.
Sterilization: Gamma rays from Cobalt-60 are used to sterilize medical equipment and preserve food.
Power Generation: Nuclear reactors use Uranium-235 to generate electricity.
Safety Precautions with Radioactivity
Radioactive materials can be dangerous if not handled properly. Key safety measures include:
- Time: Minimize exposure time - less time means less radiation absorbed
- Distance: Maximize distance from source - radiation follows inverse square law
- Shielding: Use appropriate shielding (lead, concrete, water) depending on radiation type
- Monitoring: Use film badges and Geiger counters to detect radiation levels
- Containment: Never eat, drink, or smoke in radioactive areas
CSEC Practice Arena
Test Your Understanding
Alpha (α): A helium nucleus consisting of 2 protons and 2 neutrons. Relatively heavy, positively charged, low penetrating power.
Beta (β): A high-speed electron emitted from the nucleus when a neutron turns into a proton. Light, negatively charged, medium penetrating power.
Gamma (γ): High-energy electromagnetic radiation (photons) emitted from an excited nucleus. No mass, no charge, very high penetrating power.
$$ _{92}^{238}U \rightarrow ? + _{2}^{4}He $$
Conservation of Mass Number: 238 = A + 4, so A = 238 - 4 = 234
Conservation of Atomic Number: 92 = Z + 2, so Z = 92 - 2 = 90
Answer: $$ _{90}^{234}Th $$ (Thorium-234)
Complete equation: $$ _{92}^{238}U \rightarrow _{90}^{234}Th + _{2}^{4}He $$
Step 1: Calculate the number of half-lives
Number of half-lives = Total time ÷ Half-life = 17,190 ÷ 5,730 = 3 half-lives
Step 2: Calculate remaining amount
After 1 half-life: 100g ÷ 2 = 50g
After 2 half-lives: 50g ÷ 2 = 25g
After 3 half-lives: 25g ÷ 2 = 12.5g
Answer: 12.5g of Carbon-14 will remain.
Alpha particles are relatively heavy (4 atomic mass units) and carry a +2 charge. They interact strongly with matter and lose energy quickly through ionization. A few centimeters of air or a sheet of paper is enough to stop them.
Gamma rays are massless, chargeless electromagnetic waves that travel at the speed of light. They interact weakly with matter and can penetrate deeply. Thick lead (several centimeters) or concrete is needed to absorb them effectively.
1903 Nobel Prize in Physics: Shared with Henri Becquerel and Pierre Curie for their joint research on radiation phenomena. Marie was the first woman to win a Nobel Prize.
1911 Nobel Prize in Chemistry: Awarded for her discovery of the elements polonium and radium, and for the isolation of radium. Marie was the first person to win two Nobel Prizes.
Note: She remains the only person to win Nobel Prizes in two different scientific fields.
Chapter Summary
Key Discoveries
- Henri Becquerel discovered radioactivity (1896)
- Marie Curie discovered polonium and radium (1898)
- Marie Curie won two Nobel Prizes (1903, 1911)
Types of Radiation
- Alpha (α): 2p + 2n, +2 charge, stopped by paper
- Beta (β): electron, -1 charge, stopped by aluminum
- Gamma (γ): electromagnetic wave, no charge, needs lead
Remember!
Each half-life reduces the radioactive material by exactly half, regardless of the amount present.