Radiation and Nuclear Physics Study Notes

Types of Radiation

• Alpha Particles:
  • Made of a helium nucleus (2 protons + 2 neutrons).
  • High ionizing power.
  • Low penetration.
• Beta Particles (β-):
  • High-speed electrons.
  • Medium ionizing power.
  • Medium penetration.
• Gamma Rays (γ):
  • High-energy electromagnetic waves.
  • Low ionizing power.
  • High penetration.

Neutron to Proton Conversion

• Occurs during beta decay when a neutron converts into a proton.

Contamination vs. Irradiation

• Contamination: Radioactive source is inside the body.
• Irradiation: Radioactive source is outside the body; affects you only when near it.

Cloud Chamber

• A device used to detect charged particles.
• Different track sizes indicate different ionizing powers of particles.

Nuclear Equations

• Example: \text{Fe} \rightarrow \text{Co} + \beta

Half-Life

• The time it takes for half of a radioactive isotope's nuclei to undergo radioactive decay.
• A Geiger counter can be used to calculate the radioactivity of an isotope.

Uses of Radiation

• Sterilization:
  • Medical equipment and food are exposed to gamma rays to kill bacteria.
• Medical Irradiation:
  • Gamma rays are used to kill cancer cells and slow their growth by damaging DNA and stopping cell division.
• Leak Detection:
  • Gamma rays are mixed in water and flow through pipes; buildup indicates a leak (due to high penetration).
• Smoke Alarms:
  • Alpha particles (from Americium-241) are easily absorbed by smoke particles.
  • The alarm measures the rate/flow of alpha particles. When smoke enters, it absorbs alpha rays, reducing the flow and triggering the alarm.
• Thickness Gauges:
  • Radiation is absorbed when passing through materials.
  • The amount of radiation that passes through indicates the thickness of the material.
  • Beta particles are used for paper and aluminum thickness measurements.

Properties of Subatomic Particles

Dangers of Radiation in Medicine

• Can cause mutations by damaging DNA.

Background Radiation

• Cosmic Rays:
  • Present in Earth's atmosphere, blocked by Earth's magnetic field.
• Granite:
  • Found in areas like South West Wales, contains uranium, leading to varying ionizing levels.
• Radon Gas:
  • Hazardous gas naturally produced from granite rocks due to the decay of uranium.
• Medical sources.

Mass-Energy Equivalence

• E = mc^2

Particle Accelerators

• Charged particles are affected by magnetic fields (opposites attract).
• Electrical fields accelerate particles, increasing their kinetic energy.
• A constant force in a uniform electrical field accelerates particles in a straight line.
• Magnetic fields control the direction of particle beams.
• Cyclotrons are circular accelerators.

Quarks

• 6 types of quarks:
  • Up (charge: +2/3)
  • Down (charge: -1/3)
  • Charm (charge: +2/3)
  • Strange (charge: -1/3)
  • Top (charge: +2/3)
  • Bottom (charge: -1/3)

Leptons

• 6 types of leptons:
  • Electron (charge: -1)
  • Electron neutrino (charge: 0)
  • Muon (charge: -1)
  • Muon neutrino (charge: 0)
  • Tau (charge: -1)
  • Tau neutrino (charge: 0)

Quark Combinations

• Quarks are always found in pairs.
• All particles have antiparticles.

Baryons

• Made of 3 quarks.
• Protons and neutrons are baryons.

Mesons

• Made of a quark and an antiquark.

Beta Decay

• A neutron in the nucleus splits into a proton (which stays in the nucleus) and a high-speed electron (emitted).
• Example: \text{udd} \rightarrow \text{uud}

Color Charge

• Baryons and mesons are colorless when combined.
• Blue + green + red = colorless.
• Red + anti-red = colorless.

Ionization

• The process where an electron is added or taken away from an atom to create an ion.
• An ion is an atom with more or fewer electrons than protons.
• Isotopes are atoms with more or fewer neutrons.

Static Electricity: Van de Graaff Generator

• Electrons are transferred from the rubber belt to the dome.
• Electrons get transferred to the person touching the dome, and hair stands on end as electrons in hair repel (like charges).
• This only works when standing on an insulator so the electrons don't discharge but build up on the person.
• Only electrons can move.
• Positively charged objects have fewer electrons.
• Negatively charged objects have more electrons.

Charge Detection

• Geiger-Müller tubes or photographic film can detect ionizing radiation.

Charging

• Involves the transfer of electrons.

Induced Charge

• No transfer of electrons occurs.
• Caused by friction.
• Static charged objects induce a charge on nearby surfaces.
• Induced charge always attracts.
• Charges build up when two insulators rub together.

Sparking

• If the opposite charge is great enough, there is a large potential difference (voltage).
• The buildup of charge causes electrons in the air to be attracted and feel the force of the electric field.
• Electrons are pulled out of air molecules and hit other electrons, causing a sudden flow of electrons between two charged objects.

Refueling Airplanes: Static Charge Buildup

• Friction when fuel goes down the pipe causes a buildup of static charge, creating a large potential difference.
• This can cause a spark and explosion, especially since fuel is flammable.
• Earthing straps are used to ground the plane by connecting it to a metal rod to ground, preventing charge buildup.

Dangers of Ionizing Radiation

• Ionizing radiation knocks off electrons and damages DNA.
• Alpha, beta and gamma radiation can be cancerous.
• Low doses can cause mutations.
• High doses can be lethal.

Radioactive Waste Disposal

• Low radioactive waste is disposed of in landfill sites underground.
• High-level radioactive waste is stored in glass blocks and metal canisters underground, which could potentially leak.

Conductors

• Conductors have delocalized electrons, allowing them to conduct electricity.