Radiation+Half life

• Radioactivity

  A totally random process
• Important facts about radioactivity

  • Radioactive substances give out radiation from the nuclei of their atoms no matter what
  • Radiation can be measured with a Geiger-Muller tube and counter, which records the count-rate (the number of radiation counts reaching it per second)
  • Radioactive decay is entirely random, so you can't predict exactly which nucleus in a sample will decay next, or when any one of them will decay
• Half-life


  The time it takes for the amount of radiation emitted by a source to halve
• Activity

  The rate at which a radioactive source decays, measured in becquerels (Bq) where 1 Bq is 1 decay per second
• The radioactivity of a source decreases over time as radioactive nuclei decay to become stable nuclei
• Factors affecting how quickly a radioactive source decays

  • Some isotopes have a short half-life, so their activity falls quickly because the nuclei are very unstable and rapidly decay
  • Some isotopes have a long half-life, so their activity falls more slowly because most of the nuclei don't decay for a long time
• Calculating final activity as a percentage of initial activity after two half-lives

  1. Find the activity after each half-life

  2. Divide the final activity by the initial activity, then multiply by 100 to make it a percentage
• A graph of activity against time will always be shaped like an exponential decay curve
• Sources of background radiation


  • Radioactivity of naturally occurring unstable isotopes in the air, food, building materials, and rocks
  • Radiation from space (cosmic rays)
  • Radiation due to human activity (e.g. fallout from nuclear explosions)
• Radiation dose

  The risk of harm to body tissues due to exposure to radiation, measured in sieverts (Sv)
• Exposure to radiation is called irradiation, which does not make an object radioactive
• Contamination

  Unwanted radioactive atoms getting onto or into an object
• Dangers of contamination vs irradiation

  • Outside the body, beta and gamma sources are most dangerous as they can penetrate the body
  • Inside the body, alpha sources are most dangerous as they do all their damage in a very localised area
  • Contamination is a major concern with alpha sources as the radioactive particles could get inside the body
• Research on how radiation affects the body is important to improve protection when using radioactive sources
• Background Radiation


  The low-level radiation that's around us all the time
• Background radiation should always be measured and subtracted from results to avoid systematic errors
• Sources of background radiation


  • Radioactivity of naturally occurring unstable isotopes
  • Radiation from space (cosmic rays)
  • Radiation due to human activity (e.g. fallout from nuclear explosions or nuclear waste)
• Radiation dose

  Measure of the risk of harm to body tissues due to exposure to radiation, measured in sieverts (Sv) or millisieverts (mSv)
• The dose from background radiation is small
• Irradiation

  Exposure to radiation
• Irradiating something does not make it radioactive
• Contamination

  Radioactive particles getting onto or into an object
• Contamination is especially dangerous because radioactive particles could get inside your body
• Radiation types

  • Beta and gamma are the most dangerous outside the body as they can penetrate it
  • Alpha is less dangerous outside the body as it can't penetrate the skin
  • Alpha sources are the most dangerous inside the body as they do all their damage in a very localised area
  • Beta sources are less damaging inside the body as radiation is absorbed over a wider area and some passes out
  • Gamma sources are the least dangerous inside the body as they mostly pass straight out
• The more we understand how radiation affects our bodies, the better we can protect ourselves when using it
• Research about radiation effects is peer-reviewed and can quickly become accepted, leading to improvements in the use of radioactive sources
• Radiation

  Can be useful but also has dangers
• Risks of using radiation

  • Radiation can enter living cells and ionise atoms and molecules, leading to tissue damage
  • Lower doses can cause minor damage without killing cells, leading to mutant cells which divide uncontrollably, causing cancer
  • Higher doses can kill cells completely, causing radiation sickness (vomiting, fatigue, hair loss)
• Gamma sources used in medical tracers

  • Certain radioactive isotopes can be injected or swallowed, and their progress around the body can be followed using an external detector
  • Example: iodine-123 is absorbed by the thyroid gland and its radiation can be detected
  • Isotopes used are usually gamma-emitters so the radiation passes out of the body without causing much ionisation
• Radiotherapy

  • High doses of ionising radiation can be directed at cancer cells to kill them, while minimising damage to normal cells
  • Radiation-emitting implants can also be placed near or inside tumours
  • However, some damage to normal cells is inevitable, causing side effects for the patient
• Weighing up risks and benefits of using radioactive materials

  • For every situation, both the benefits and risks should be considered
  • Tracers can diagnose life-threatening conditions, while the risk of cancer from one use is very small
  • For cancer patients, the benefits of radiotherapy may outweigh the risks and side effects, as it may get rid of their cancer entirely
  • Perceived risk can vary from person to person and may not match the actual risk