Radioactivity Flashcards
What is the activity of a radioactive source?
The number of atoms that decay every second
What is the unit for activity?
Becquerel (Bq)
What is the half life of a radioactive isotope?
The time it takes for half of the unstable atoms to decay
Why is ionising radiation dangerous?
Mutation:
- Energy transferred by ionising radiation removes electrons from atoms to form ions
- Ions are very reactive and cause mutations to the DNA in cells
- Damage to DNA can lead to cancer
Radiation burns:
- Can also cause damage to self tissue in the form of radiation burns
- When its energy is high enough it can also kill cells
What are the precautions when coming into contact with ionising radiation?
- Limiting the time of exposure
- Wearing protective clothing, wearing a lead apron will absorb a lot of the ionising radiation
- Increasing the distance from the person to the radioactive source
What are medical tracers?
Substances that are used in biological processes in the body and contain a radioisotope
How are medical tracers used?
- They can be eaten, drunk or injected into the body
- The ionising radiation emitted by the tracer can be detected and the biological processes monitored
- Doctors content diagnose the nature and location of any health problems
How do PET scanners work?
- The tracer is a radioactive material that decays quickly by emitting positrons
- When positrons come into contact with electrons in the body the two particles annihilate each other
- This results in the formation of gamma rays
- These gamma rays are detected by the PET scanner and processed by a computer, an image is then displayed on the screen
- As the tracers decay quickly, they need to be produced close to where they are used
How are tumours treated internally?
- A radioactive source is injected or eaten/drunk by the patient
- It then targets the tumour without affecting the cells around it too much
How are tumours treated externally?
- Several beams of gamma rays are fired from different positions towards the cancer
- Each beam isn’t energetic enough to kill the tumour but damages it
- By moving the beam, the amount of ionising radiation received by the surrounding tissue is reduced
What are the steps of generating energy within a nuclear power station?
- Fuel rods containing uranium undergo nuclear fission, thermal energy is released
- A coolant (water) is pumped through the reactor, thermal energy from nuclear fission is taken by the coolant to heat water to produce steam 
- The steam causes turbines to rotate which turn the generator to generate electricity
- The steam is cooled back into water in the condenser so it can be used again
- Extra thermal energy is released from cooling towers or into the sea
What is the role of the moderator in a nuclear power station?
- It slows down the neutrons so that fission can occur
- It is often graphite or water
What is the role of control rods in a nuclear power station?
- They absorb excess neutrons
- Lowering a control rod reduces fission reactions as they will absorb more neutrons
How do you prevent stray neutrons and radiation from escaping the core?
Concrete shielding
How big is a typical atom?
10^-10m
How big is a typical molecule?
10^-9m
How big is the diameter of a typical nucleus?
10^-15m
How far can alpha particles travel in air?
Less than 5 cm
How far can beta particles travel in air?
A few metres
How far can gamma rays travel in air?
A few kilometres
What can alpha particles be stopped by?
Sheet of paper
Skin
What can beta particles be stopped by?
3 mm aluminium foil
What can gamma rays be stopped by?
Thick lead
What are the sources of background radiation on earth and from space?
- Radon gas
- Ground and buildings
- Food and drink
- Medical
- Nuclear power
- Cosmic rays (from space)
