P7

• Half-life can be defined as the time taken for the number of radioactive nuclei in a sample to halve or for the activity to halve
• Decay process of radioactive isotopes

  Completely random decay process where unstable isotopes emit radiation like alpha particles, beta particles, or gamma rays to become more stable
• With a large enough sample of radioactive isotopes, the overall rate of decay (activity) can be determined
• Geiger Muller tubes record all decays that reach them each second, which is used to estimate the activity
• Radioactive materials contain unstable isotopes that decay by emitting radiation
• Radioactive materials come in various forms
• Half-life


  The time taken for either the number of radioactive nuclei in a sample to halve or for the activity to halve
• Activity

  The overall rate of decay of all isotopes in a sample, measured in becquerels where one becquerel represents one decay per second
• A Geiger Muller tube is used to measure the activity of radioactive samples
• Calculating half-life from a graph

  Find the time it takes for the activity to halve
• As radioactive nuclei decay, the overall rate of decay (activity) decreases
• Half-life is correlated with the decrease in the number of radioactive nuclei and the decrease in activity
• A graph of activity against time for a radioactive sample shows a curved decline
• In a question involving half-life, the number of remaining nuclei can be calculated by halving the initial number based on the number of half-lives
• Radioactive materials consist of unstable isotopes that can decay
• Alpha particles

  Consist of two protons and two neutrons, represented by helium's nuclear symbol He, have an overall charge of +2, are easily stopped by collisions with other molecules, and are strongly ionizing
• Only one or two of an element's isotopes are stable, while the rest are unstable and can undergo radioactive decay
• Neutrons can be emitted by a nucleus to increase stability if it contains too many neutrons
• Alpha particles


  Stopped by a single sheet of paper
• Radioactive decay

  Isotopes emit something to change slightly and become more stable
• Beta particles

  Just electrons with a charge of -1, emitted when an atom's neutron decays into a proton and an electron, moderately ionizing, and penetrate moderately far into materials
• Gamma rays


  Require a thick piece of lead to stop them
• Isotopes are different forms of an element with the same number of protons but a different number of neutrons
• Types of nuclear radiation

  • Alpha particles
  • Beta particles
  • Gamma rays
  • Neutrons
• Beta particles


  Stopped by a thin sheet of aluminium
• Gamma rays


  Waves of electromagnetic radiation, emitted after alpha or beta radiation, weakly ionizing, and can penetrate far into materials
• Determinants of how harmful radiation is

  • Type of radiation, location of exposure, and the amount of radiation received
• For external sources of radiation

  Beta and gamma radiation are the most dangerous as they can penetrate the skin
• Contamination

  When radioactive particles get onto other objects, leading to contamination. The real issue is the increased risk of irradiation from the radioactive material decaying
• Being irradiated does not cause mutation or make a person radioactive. Only being contaminated with a radioactive source can harm others
• For internal or contaminated sources of radiation

  Alpha radiation is the most dangerous as it can enter cells
• Ionizing radiation is generally more dangerous as it can enter living cells and interact with molecules, causing mutations and potentially leading to cancer
• Precautions around radioactive sources

  Wearing protective gear, handling items with tools, and storing items in lead-lined boxes to minimize irradiation and avoid contamination
• Order of harmfulness of different types of radiation

  • Alpha, Beta, Gamma, Ultraviolet, Microwave, Radio waves
• The amount of radiation exposure depends on the distance from the source, duration of exposure, and the radioactivity of the substance
• Irradiation


  The process by which an object is exposed to radiation, which could be ionizing radiation like alpha particles, beta particles, gamma rays, or x-rays, as well as non-ionizing radiation like ultraviolet or microwave radiation
• Radiation can be used to destroy particular cells like cancer cells, a process known as radiotherapy
• Cells receiving a large enough dose of radiation can be killed off completely
• Ionizing radiation can damage cells by ionizing the atoms and molecules within them
• Gamma rays are commonly used for medical tracers as they are less harmful than alpha or beta radiation