Atoms & Radiation

• Radioactivity


  Unstable atoms randomly emit ionising radiation to become stable
• Radioactive substances


  • Decay randomly, with no way to predict it
• Detecting radioactivity with a Geiger counter

  Radiation enters tube, ionises gas, conducts electricity, produces clicking noise
• Detecting radioactivity with photographic film

  Ionising radiation has same effect as light, creating bright spots
• Detecting radioactivity with a cloud chamber

  Ionising radiation enters air, ionises molecules, causing vapour to condense and show trail
• Background radiation is very common, from sources like rocks and food
• Radon gas emits alpha particles, which can reach lung tissue if breathed in
• Types of radioactive emission

  • Alpha radiation
  • Beta radiation
  • Gamma radiation
• There are 43 kinds of radioactive emission
• Alpha radiation


  Contains 2 protons and 2 neutrons, so has a radioactive mass of 4, strongly ionising since the particles are big and heavy, does a lot of damage but is stopped by a small amount (like paper)
• Beta radiation


  Made up of high-energy electrons, more ionising than gamma radiation
• Gamma radiation


  Weakly ionising, less damaging than alpha or beta radiation, only stopped by centimetres of lead or metres of concrete
• More strongly ionising radiation


  Is less able to penetrate materials, interacts with (damages) materials much more so it comes to a stop sooner
• Practical applications of radiation

  • Smoke detectors (alpha radiation)
  • Paper production (beta radiation)
  • Exploring internal organs (gamma radiation)
  • Sterilisation (gamma radiation)
• Smoke detectors (alpha radiation)


  1. Radioactive material fires alpha particles

  2. Smoke between radioactive material and detector reduces alpha particles reaching detector

  3. Fewer alpha particles set off smoke alarm
• Paper production (beta radiation)


  1. Fire beta particles through paper

  2. Detect changes in beta particles reaching detector to monitor paper thickness
• Exploring internal organs (gamma radiation)


  1. Put gamma-emitting isotope in patient's body

  2. Trace radiation movement around body

  3. Gamma radiation is most penetrating, can leave body without too much damage
• Sterilisation (gamma radiation)


  1. Use gamma radiation to sterilise medical equipment

  2. Kills bacteria and viruses
• Half life


  The average time it takes for half the nuclei to decay
• Calculate half life: half it
• The half-life of different isotopes can vary from less than a second to millions of years
• Isotopes with a small/short half-life

  • Very unstable, emit radiation very quickly, do not remain radioactive for long
• Isotopes with a long half-life

  • More stable, emit radiation slowly, remain radioactive for a long time, exposure is less hazardous
• the level of background radiation a person experiences varies depending on their: - location, as some, areas of the country have a higher amount of natural background

  - occupation, as in some Jobs you ave more likely to be exposed to radiation
• Fission

  Splitting of a large unstable nucleus
• Fusion

  Two light nuclei join together to form a heavier nucleus
• Fission

  1. Nucleus must absorb a neutron first

  2. Nucleus splits into 2 or 3 smaller nuclei

  3. Emits two or three neutrons, gamma rays and energy
• All the products of fission have kinetic energy
• Fission chain reaction in a nuclear reactor

  1. Neutrons emitted can be absorbed by another large unstable nucleus

  2. Chain reaction is controlled to give a constant, steady release of energy
• The explosion caused by a nuclear weapon is the result of an uncontrolled chain reaction
• Fusion

  1. Two light nuclei join together

  2. Some of the mass is converted into energy

  3. Energy and radiation may be emitted
• Fusion

  • Requires high temperatures and pressures to overcome electrostatic repulsion and bring nuclei close enough together