radiation

• what are atoms made up of?


  - positively charged protons

  - neutral neutrons

  - negatively charged electrons
• what orbits an atoms nucleus?


  electrons made up of protons and neutrons
• how are atoms neutral?


  - they contain equal numbers of positive protons and negative electrons

  - they have no overall charge
• ionisation


  the gain or loss of electrons from an atom
• what does ionisation result in?


  atoms becoming ions (charged particles)
• what happens if an atom gains a negative electron?


  it becomes a negative ion
• what happens if an atom loses a negative electron?


  it becomes a positive ion
• when does ionisation occur?

  ionisation can occur due to radioactive particles or waves, which are emitted from the nucleus of an unstable atom
• radioactive decay

  a random process (it cannot be predicted)
• alpha radiation

  - made up of two protons and two neutrons

  - has the same structure as the nucleus of a helium atom

  - have the greatest ionisation density of the three types of nuclear radiation

  - completely absorbed by a few centimetres of air or a single sheet of paper

  - least penetrative radiation
• beta radiation

  - a fast-moving electron ejected from the nucleus of an atom

  - result in a neutron in the nucleus becoming a proton

  - weakly ionising

  - absorbed by a few millimetres of aluminium
• gamma radiation

  - a gamma ray is a high-energy electromagnetic wave

  - travel through air at 3.0×10^8 ms-1, after being emitted from the nucleus of an atom

  - weakly ionising

  - mostly absorbed by several centimetres of lead

  - most penetrative radiation
• background radiation sources

  - the ground

  - the air

  - building materials

  - food

  - cosmic rays from space
• activity

  the number of nuclei in a radioactive substance which decay every second
• half-life

  the time taken for the activity of a radioactive source to decrease by half
• how to reduce the dose of nuclear radiation received

  - increase distance

  - decrease time

  - wear protective clothing

  - use shielding
• applications of nuclear radiation

  - electricity generation (fission and fusion)

  - cancer treatment (radiotherapy)

  - other industrial uses (thickness detection of materials)

  - other medical uses (sterilisation of medical equipment, tracers)

  - other applications (smoke detectors)
• absorbed dose

  - the energy absorbed per kilogram of tissue from radiation

  - measured in grays, Gy
• equivalent dose, H

  the biological effect (harm) of radiation on living things depends on ~

  - the type of radiation (α, β or γ)

  - the type of tissue exposed to the radiation

  - the absorbed dose

  - measured in sieverts, Sv
• equivalent dose rate, H (with a dot on top of the H)

  measured in Sv h-1 or Sv year-1 (or any other appropriate unit)
• average annual background radiation in the UK

  2.2 mSv
• annual effective dose limit for a member of the public

  1 mSv
• annual effective dose limit for a radiation worker

  20 mSv
• nuclear fission

  - the splitting of a large nucleus into smaller nuclei

  - this process releases energy

  - can be spontaneous, which means that it occurs at random at a time which cannot be predicted
• chain reaction

  - occurs when the neutrons released from a fission reaction split subsequent nuclei and the process continues

  - responsible for the production of energy in a nuclear reactor
• nuclear fusion

  - the joining of two smaller nuclei to form a larger nucleus

  - this process releases energy

  - the process by which stars produce heat
• state one advantage of generating electrical energy by a nuclear fission power station

  - a large amount of energy is produced for a small amount of fuel

  - no pollution is given off
• state conditions needed for nuclear fusion to occur

  - very high temperatures

  - a plasma confined by a magnetic field
• state one advantage that generating electrical energy by a nuclear fusion would have

  - a large amount of energy is produced for a small amount of fuel

  - no pollution is given off

  - no radioactive waste is produced
• what are benefits of developing nuclear fusion?

  - abundant fuel

  - less radioactive waste

  - safer
• what are challenges of developing nuclear fusion?

  - high temperature requirements

  - containment issues

  - high cost of development
• which type of radiation is suitable as a tracer in the human body?

  gamma radiation ~

  - least ionising

  - penetrates body tissues

  - detectable outside the body