Radiation

• Isotopes

  Different forms of an element, with the same number of protons but different numbers of neutrons
• Only one or two of an element's isotopes are stable, while the rest are unstable and undergo radioactive decay
• Types of nuclear radiation

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

  • Made up of two protons and two neutrons, the same as a helium nucleus
  • Don't have any electrons, so have an overall charge of two plus
  • Easily stopped by collisions with other molecules, can only travel a few centimeters in air and are absorbed by a single sheet of paper
  • Strongly ionizing, can easily knock electrons off atoms they collide with
• Beta particles

  • Just electrons
  • Emitted when a neutron in an atom decays into a proton and an electron
  • Moderately ionizing and penetrate moderately far into materials, stopped by several meters of air or about 5 millimeters of aluminium
• Gamma rays

  • Waves of electromagnetic radiation, not particles
  • Often emitted after alpha or beta radiation as a way for the nucleus to get rid of extra energy
  • Don't have any mass or charge, so tend to pass straight through materials rather than colliding with atoms
  • Only weakly ionizing, can penetrate thick materials like lead or concrete
• Neutron emission

  • Occurs when a nucleus contains too many neutrons, making it unstable, and it throws out a neutron to increase stability
• Radioactive Decay

  The process of an atoms unstable nucleus becoming more stable over time by randomly emitting ionising radiation.
• In radioactive decay, we cannot predict when an individual atom will emit (produce) ionising radiation.
• Alpha Radiation

  • Produced by alpha decay. Releases helium nuclei, also known as alpha particles.
• Beta Radiation

  • Produced by beta decay. Releases electrons, also known as beta particles.
• Gamma Radiation

  Produced by gamma decay. It is a high-energy electromagnetic wave with a higher frequency than X-Rays.
• What are beta particles?

  Electrons
• What are Alpha particles?

  Helium nuclei
• How many types of ionising radiation are there?

  Three — Alpha radiation, Beta radiation, Gamma radiation
• What is Gamma Radiation?

  Electromagnetic waves produced by gamma decay
• Primary ways of detecting radioactivity

  • Geiger counter (Geiger-Muller tube)
  • Photographic film
  • Cloud chamber

  
• Geiger counter (Geiger-Muller tube)

  1. Ionising radiation enters a tube full of low pressure gases

  2. It ionises the atoms in the gas, knocking electrons out of the atoms

  3. The gas can now conduct electricity and completes an electric circuit

  4. Current flows between electrodes

  5. The current produces a clicking noise
• Count-rate

  The number of decays recorded each second
• Photographic film

  • Ionising radiation has the same effect on photographic film as light
  • A bright spot appears wherever the ionising radiation hits the film
• Cloud chamber

  • A container full of air containing alcohol vapour
  • Ionising radiation enters the air and leaves a trail of ionised air molecules
  • The alcohol vapour condenses on the ionised air molecules, showing the trail of radiation
• All elements have different isotopes, but there are usually only one or two stable ones.

  The other unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable.
• Radioactive Decay

  Unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable (balance the number of protons and neutrons in their nucleus or get rid of any excess energy ).
• Radioactive substances spit out one or more types of ionising radiation from their nucleus.
• They can also release neutrons when they decay to rebalance the number of protons and neutrons
• Ionising radiation

  Ionising radiation is radiation that knocks electrons off atoms, creating positive ions.
• Ionising power

  The ionising power of a radiation source is how easily it can knock electrons off atoms.
• Nuclear equations

  Nuclear equations are a way of showing radioactive decay by using element symbols
• Nuclear equations

  Nuclear equations are written in the from:

  atom before decay  → atom after decay + radiation emitted
• Ionising vs Penetration

  More strongly ionising radiation is less able to penetrate materials. It interacts with (damages) materials much more, so it comes to a stop sooner.
• Which is the most penetrating type of radiation?

  Gamma radiation
• The more ionising radiation is, the les penetrating it will be
• Radioactive decay

  During alpha, beta and gamma radioactive decay, an unstable nucleus becomes more stable
• Alpha Decay

  In alpha decay, a nucleus loses an alpha particle - made of 2 protons and neutrons. Because 2 protons have been lost, we now have a new element
• Beta Decay

  In beta decay, a neutron in the nucleus decays to form a proton and electron. This electron is then ejected out if the nucleus
• Gamma Decay

  In gamma decay, the composition of nucleus is unchanged. The nucleus is said to be “relaxing” from one state into another with lower energy.
• Which form of decay doesn’t create a new element?

  Gamma decay
• Nuclear equations for alpha, beta, and gamma radiation

  1. Alpha particles consist of two protons and two neutrons

  2. Unstable nucleus undergoes alpha decay and emits alpha particle

  3. Subtract 4 from mass number and 2 from atomic number

  4. Resulting element is different, check periodic table

  5. Add emitted helium
• Beta decay

  1. Neutron turns into proton and emits fast moving electron (beta particle)

  2. Atomic number increases by 1, mass number stays the same

  3. Represent beta particle with beta symbol and charge of -1
• Gamma radiation

  1. Pure energy, no mass or charge

  2. Does not change anything in the nucleus

  3. Represent with gamma symbol