Physics Flashcards

What are the three main types of radiation and their basic properties?

Alpha (α) Radiation:

• Helium nuclei (2 protons, 2 neutrons)

• Highly ionizing, low penetration

• Stopped by paper or skin

Beta (β) Radiation:

• High-energy electrons or positrons

• Moderately ionizing and penetrating

• Stopped by aluminum foil

Gamma (γ) Radiation:

• Electromagnetic waves (photons)

• Low ionizing, high penetration

• Requires lead or thick concrete to stop

Write the radioactive decay formula for alpha decay.

Alpha Decay Formula:

²³⁸U₉₂ → ²³⁴Th₉₀ + ⁴He₂

General form:
ᴬX_Z → ᴬ⁻⁴Y_(Z-2) + ⁴He₂

• Mass number decreases by 4

• Atomic number decreases by 2

• Alpha particle = helium nucleus

Write the radioactive decay formula for beta decay.

Beta Minus Decay:
¹⁴C₆ → ¹⁴N₇ + e⁻ + ν̄ₑ

Beta Plus Decay:
¹¹C₆ → ¹¹B₅ + e⁺ + νₑ

General forms:
β⁻: ᴬX_Z → ᴬY_(Z+1) + e⁻
β⁺: ᴬX_Z → ᴬY_(Z-1) + e⁺

• Mass number stays the same

• Atomic number changes by ±1

Write the radioactive decay formula for gamma decay.

²³⁴Th₉₀* → ²³⁴Th₉₀ + γ

General form:
ᴬX_Z* → ᴬX_Z + γ

• No change in mass number

• No change in atomic number

• Nucleus releases excess energy

• * indicates excited state

• Often follows alpha or beta decay

What is the difference between electromagnetic waves and particle radiation?

Electromagnetic Waves:

• Gamma rays and X-rays

• No mass, no charge

• Travel at speed of light

• Energy = hf (photons)

Particle Radiation:

• Alpha particles (helium nuclei)

• Beta particles (electrons/positrons)

• Have mass and often charge

• Travel slower than light

• Kinetic energy = ½mv²

How do you calculate the number of half-lives when emission rate changes?

Where:

• N = final number of nuclei

• N₀ = initial number of nuclei

• n = number of half-lives

To find n:
n = log(N₀/N) / log(2)

Example:
If activity drops from 800 to 100 counts/min:
n = log(800/100) / log(2) = 3 half-lives

How do you determine half-life from a decay graph?

Steps:

1. Find the initial activity (A₀)

2. Calculate half of this value (A₀/2)

3. Find the time when activity = A₀/2

4. This time is the half-life (t₁/₂)

Alternative method:
Pick any point, find when it halves

Remember:
Half-life is constant regardless of starting point on the curve

What is the mathematical relationship for radioactive decay?

Exponential Decay Law:
N(t) = N₀e^(-λt)

Half-life relationship:
t₁/₂ = ln(2)/λ = 0.693/λ

Activity equation:
A(t) = A₀e^(-λt)

Where:

• λ = decay constant

• t = time

• A = activity (decays/second)

What are the effective precautions against alpha radiation?

Alpha Radiation Protection:

• Distance: Few centimeters in air

• Shielding: Paper, clothing, or skin

• Time: Minimize exposure time

• Containment: Prevent inhalation/ingestion

Key Points:

• Most dangerous if inside the body

• Cannot penetrate skin externally

• Very high ionizing power

What are the effective precautions against beta radiation?

Beta Radiation Protection:

• Distance: Several meters in air

• Shielding: Aluminum foil, plastic, glass

• Time: Limit exposure duration

• Clothing: Lab coats and gloves

Special Considerations:

• Can penetrate skin but not deep tissue

• Avoid dense materials (produce X-rays)

• Use low-Z materials for shielding

What are the effective precautions against gamma radiation?

Gamma Radiation Protection:

• Distance: Inverse square law applies

• Shielding: Lead, concrete, or thick steel

• Time: Minimize exposure time

• ALARA: As Low As Reasonably Achievable

Shielding Requirements:

• High-Z materials most effective

• Thickness depends on energy

• Never completely stopped, only attenuated

Explain the three mechanisms of heat transfer.

Conduction:
Heat transfer through direct contact in solids

Convection:
Heat transfer by movement of fluids (liquids/gases)

Radiation:
Heat transfer by electromagnetic waves

Key Differences:

• Conduction: needs matter, no bulk motion

• Convection: needs fluid motion

• Radiation: works through vacuum

Which state of matter is most effective for conduction and why?

Solids are most effective for conduction

Reasons:

• Particles are closely packed

• Strong intermolecular forces

• Efficient energy transfer between particles

• No bulk movement of particles

Ranking:
Solids > Liquids > Gases

Best conductors: Metals (free electrons)

Compare conduction in different states of matter.

Solids:

• Excellent conduction (especially metals)

• Vibrating particles transfer energy

• No particle movement

Liquids:

• Moderate conduction

• Particles can move slightly

• Less efficient than solids

Gases:

• Poor conduction

• Large spaces between particles

• Convection usually dominates

Why are different materials used in specific thermal applications?

Good Thermal Conductors (metals):

• Cooking pans, heat sinks, radiators

• Need rapid heat transfer

Thermal Insulators:

• Building insulation, clothing, thermos

• Prevent heat loss/gain

Material Properties Matter:

• Thermal conductivity

• Specific heat capacity

• Density and structure

What is the relationship between temperature and kinetic energy of molecules?

Direct Proportional Relationship:

Formula: KE_avg = (3/2)kT

Where:

• k = Boltzmann constant

• T = absolute temperature (Kelvin)

Key Points:

• Higher temperature = more kinetic energy

• Temperature measures average kinetic energy

• All particles don't have same energy

• Absolute zero = minimum possible energy

How do you calculate energy required to change temperature using specific heat capacity?

Formula: Q = mcΔT

Where:

• Q = heat energy (Joules)

• m = mass (kg)

• c = specific heat capacity (J/kg°C)

• ΔT = temperature change (°C)

Example:
Heat 2 kg water by 50°C (c = 4200 J/kg°C)
Q = 2 × 4200 × 50 = 420,000 J = 420 kJ

How do you calculate heat required for phase changes using latent heat?

Formula: Q = mL

Where:

• Q = heat energy (Joules)

• m = mass (kg)

• L = latent heat (J/kg)

Types of Latent Heat:

• L_f = latent heat of fusion (melting/freezing)

• L_v = latent heat of vaporization (boiling/condensing)

Example:
Melt 0.5 kg ice (L_f = 334,000 J/kg)
Q = 0.5 × 334,000 = 167,000 J

What is the complete calculation for heating a substance through multiple phases?

Multi-step Process:

Example: Ice (-10°C) to Steam (110°C)

1. Heat ice: Q₁ = mc_ice × ΔT

2. Melt ice: Q₂ = mL_fusion

3. Heat water: Q₃ = mc_water × ΔT

4. Vaporize water: Q₄ = mL_vaporization

5. Heat steam: Q₅ = mc_steam × ΔT

Total: Q_total = Q₁ + Q₂ + Q₃ + Q₄ + Q₅

Temperature constant during phase changes!

Identify the different states of matter and their characteristics.

Solid:

• Fixed shape and volume

• Particles vibrate in fixed positions

• Strong intermolecular forces

Liquid:

• Fixed volume, takes shape of container

• Particles can move past each other

• Moderate intermolecular forces

Gas:

• No fixed shape or volume

• Particles move freely

• Weak intermolecular forces

Define fusion and vaporization processes.

Fusion (Melting):

• Solid → Liquid

• Occurs at melting point

• Requires latent heat of fusion

• Temperature remains constant

Vaporization (Boiling):

• Liquid → Gas

• Occurs at boiling point

• Requires latent heat of vaporization

• Temperature remains constant

Reverse processes: Freezing, Condensation

What happens to temperature during phase changes?

Temperature remains constant during phase changes

Why?

• Energy goes into breaking/forming bonds

• Not increasing kinetic energy

• Called latent heat (hidden heat)

On heating curves:

• Flat horizontal lines = phase changes

• Sloped lines = temperature changes

• Different slopes = different specific heats

Energy still being added, just not increasing temperature!

Uses of medical radiation

Cancer Treatment: Radiation therapy delivers focused high-energy beams to destroy cancer cells while minimising damage to healthy tissue. Techniques include external beam radiation and brachytherapy (internal radiation sources).

Uses of processing radiation

Sterilisation: Medical equipment, pharmaceuticals, and cosmetics are sterilised using gamma rays or electron beams, ensuring they're free from microorganisms without heat damage.

Uses of engineering radiation

Ionisation Smoke Detectors use a small amount of americium-241, a radioactive isotope that emits alpha particles.

What is background radiation and what causes it

Background radiation is the naturally occurring ionising radiation that exists everywhere in our environment. It's a constant, low-level exposure that all living things on Earth experience throughout their lives.