Radioactivity Flashcards
What happens if a nucleus is unstable?
It decays and emits radiation (so is radioactive)
What are the three kinds of radiation?
Alpha, beta and gamma
Where are 4 ways background radiation is caused?
- From substances on earth e.g. building materials, rocks, soil
- Space (cosmic rays)
- Living things
- Human activity, like nuclear waste
How does nuclear radiation cause ionisation?
By bashing into atoms, knocking electrons off them. Atoms (no charge) are turned into ions (charged)
How can ionising radiation be detected?
With a Geiger-Muller detector or photographic film
What are alpha particles made up of?
2 protons and 2 neutrons (Helium nuclei)
What are the characteristics of an alpha particle? (size, speed, ionising, penetration, charge)
- Big, heavy and slow
- Strongly ionising
- Don’t penetrate far into materials
- Positively charged so deflected by electric and magnetic fields
What are the characteristics of a beta particle? (size, speed, ionising, penetration, charge)
- Small and quite fast
- Moderately penetrating and ionising
- Negatively charged, so are deflected by electric and magnetic fields
What are beta particles made up of?
Electrons
What are the characteristics of a gamma ray? (size, speed, ionising, penetration, charge)
- Have no mass or charge, just energy
- Penetrate far into materials
- Weakly ionising, as they tend to pass through rather than collide with atoms
What are alpha, beta and gamma particles stopped by?
Alpha - paper/skin/few cm of air
Beta - thin metal
Gamma - thick lead or concrete
What does Rutherford’s model of the atom say? (mass, size, charge)
- Most of the mass must be concentrated in the centre, most of the atom it empty space since most particles pass through
- Nucleus must be small since very few alpha particles are deflected by much
- Positively charged as atoms can repel +vely charged alpha particles
The faster the alpha particle is travelling, the ______ it will be deflected
Less
The more positively charged a nucleus is, the _____ the alpha particle will be deflected
More
The closer the alpha particle passes to the nucleus, the _____ it will be deflected
More
What is half-life?
The time taken for half of the radioactive atoms now present to decay
What is radioactivity measured in?
Becquerels
What types of radiation do medical tracers use and why?
Beta or Gamma - they can penetrate skin and other body tissues
What type of radiation do industrial tracers use and why?
Gamma - it’s not easily blocked (like alpha and beta)
How is gamma radiation used to detect a leak in a pipe?
- Insert gamma source into pipe, let it flow along
- Go along the outside with a detector
- If there’s a leak, the gamma will collect outside the pipe –> extra high reading on radioactivity detector
Which types of radiation are more hazardous when outside the body? and inside the body?
Outside - beta and gamma
Inside - alpha
What can lower doses of radiation do to body cells?
Damage them, which causes mutations
What can higher doses of radiation do to body cells?
Kills cells completely, causing radiation sickness if a large part of your body is affected at the same time
What does the extent of the harmful effects of radiation depend on?
How much exposure you’ve had to the radiation, its energy and its penetration
Which type of radiation is used to treat cancer?
Gamma
How is low-level radioactive waste disposed of safely?
Buried in secure landfill sites
How is high-level radioactive waste disposed safely of?
Put in glass blocks, inside metal canisters and buried deep underground somewhere that is geologically stable
What precautions must you take when working with radioactive materials?
- No skin contact, hold with tongs at arm’s length
- Point source away from body
- Store in a sealed lead box
- Wear lead aprons/screens
What is nuclear fission?
The splitting of an atom, which releases energy (nuclear power)
When does a nucleus (eg U-235) split in nuclear fission?
When it absorbs a slow-moving neutron
What is formed when U-235 splits in two?
Two daughter nuclei
What is the main problem with nuclear power?
It produces huge amounts of radioactive waste which is difficult and expensive to dispose of safely
In a nuclear reactor, what is the moderator made of and what does it do?
Usually made of graphite or water - slows neutrons so they can successfully collide with uranium nuclei and sustain the chain reaction
What are the control rods made of and what do they do?
Boron - limit the rate of fission y absorbing excess neutrons
What gas is pumped through the reactor and why?
Carbon dioxide - to carry away the heat generated
What are the products of the fission of a uranium nuclei?
Thermal energy, nuclei, neutrons
