Radioactive Decay

• Radioactive Decay

  Unstable Nuclei

  • Some atomic nuclei are unstable
  • This is because of an imbalance in the forces within the nucleus
  • Forces exist between the particles in the nucleus
  • Carbon-14 is an isotope of carbon which is unstable
  • It has two extra neutrons compared to stable carbon-12
• Carbon-12 is stable, whereas carbon-14 is unstable. This is because carbon-14 has two extra neutrons

  
• • Some isotopes are unstable because of their large size or because they have too many or too few neutrons

  Radiation

  • Unstable nuclei can emit radiation to become more stable
  • Radiation can be in the form of a high energy particle or wave
• Unstable nuclei decay by emitting high energy particles or waves

  
• • As the radiation moves away from the nucleus, it takes some energy with it
  • This reduces the overall energy of the nucleus
  • This makes the nucleus more stable
  • The process of emitting radiation is called radioactive decay
  • Radioactive decay is a random process
  • This means it is not possible to know exactly when a particular nucleus will decay
• Types of Radioactive Decay

  • When an unstable nucleus decays it emits radiation, called nuclear radiation
  • There are different types of radiation that can be emitted:
  • Alpha
  • Beta
  • Gamma
  • Neutrons

  Alpha Particles

  • The symbol for alpha is α
  • An alpha particle is the same as a helium nucleus
  • This is because they consist of two neutrons and two protons
  • Alpha particles have a charge of +2
  • This means they can be affected by an electric field
• Types of Radioactive DecayBeta Particles

  • The symbol for beta is β
  • Beta particles are fast-moving electrons
  • They are produced in nuclei when a neutron changes into a proton and an electron
  • Beta particles have a charge of -1
  • This means they can be affected by an electric field

  Gamma Rays

  • The symbol for gamma is γ
  • Gamma rays are electromagnetic waves
  • They have the highest energy of the different types of electromagnetic waves
  • Gamma rays have no charge
• Neutrons

  • The symbol for a neutron is n
  • Neutrons are one of the two particles found in the nucleus of atoms
  • Neutrons are neutral, they have no charge
• Alpha particles, beta particles, gamma waves and neutrons can be emitted from unstable nuclei

  
• Activity

  • Objects containing radioactive nuclei are called sources of radiation
  • Sources of radiation decay at different rates which are defined by their activity
  • The activity is defined asThe rate at which the unstable nuclei from a source of radiation decays
  • Activity is measured in Becquerels
  • The symbol for Becquerels is Bq
  • 1 Becquerel is equal to 1 nucleus in the source decaying in 1 second
• Detecting Radiation

  • Radiation that is emitted from an unstable nucleus can be detected in different ways
  • For example, photographic film changes colour when exposed to radiation
  • A Geiger-Muller tube is a device used to detect radiation
• This Geiger-Muller Tube is connected to a Geiger Counter. This a common way of detecting radiation and measuring a count-rate

  
• • Within the Geiger-Muller tube, ions are created by radiation passing through it
  • The Geiger-Muller tube can be connected to a Geiger counter
  • This counts the ions created in the Geiger-Muller tube
  • Count-rate is the number of decays recorded each second by a detector
• Alpha, Beta & Gamma Decay

  Alpha Decay

  • During alpha decay an alpha particle is emitted from an unstable nucleus
  • A completely new element is formed in the process
• Alpha decay usually happens in large unstable nuclei, causing the overall mass and charge of the nucleus to decrease

  
• • An alpha particle is a helium nucleus
  • It is made of 2 protons and 2 neutrons
  • When the alpha particle is emitted from the unstable nucleus, the mass number and atomic number of the nucleus changes
  • The mass number decreases by 4
  • The atomic number decreases by 2
  • The charge on the nucleus also decreases by 2
  • This is because protons have a charge of +1 each
• Beta Decay

  • During beta decay, a neutron changes into a proton and an electron
  • The electron is emitted and the proton remains in the nuclei
  • A completely new element is formed because the atomic number changes
• Beta decay often happens in unstable nuclei that have too many neutrons. The mass number stays the same, but the atomic number increases by one

  
• • A beta particle is a high-speed electron
  • It has a mass number of 0
  • This is because the electron has a negligible mass, compared to neutrons and protons
  • Therefore, the mass number of the decaying nuclei remains the same
  • Electrons have an atomic number of -1
  • This means that the new nuclei will increase its atomic number by 1 in order to maintain the overall atomic number before and after the decay
• Gamma Decay

  • During gamma decay, a gamma ray is emitted from an unstable nucleus
  • The process that makes the nucleus less energetic but does not change its structure
• Gamma decay does not affect the mass number or the atomic number of the radioactive nucleus, but it does reduce the energy of the nucleus

  • The gamma ray that is emitted has a lot of energy, but no mass or charge