Atomic Structure

• Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
• Ions are charged atoms, they become positively charged when losing electrons and negatively charged when gaining electrons.
• Radiation is the process of moving energy by waves or particles.
• Unstable atoms have significantly more neutrons (isotopes) and release radiation to reach a more stable state, a process called Radioactive decay.
• Bequerell is the unit to measure radiation.
• Alpha radiation, symbolised as α, has a +2 charge and a mass of 4 (He).
• Alpha radiation is the most strongly ionising type of radiation.
• Alpha radiation is fast moving electron radiation, it is blocked by paper.
• Beta radiation, symbolised as β, has a -1 charge and a mass of 1/2000.
• Beta radiation has moderate ionising power and is the lightest type of radiation, it can be reduced by thick lead.
• Gamma radiation, symbolised as γ, has no charge and no mass.
• Gamma radiation is the least ionising type of radiation.
• Radiation is dangerous because it ionises atoms (turns them into ions, losing/gaining electrons) making them more unstable.
• When a neutron breaks apart as its unstable it becomes a proton and an electron (beta particle).
• Alpha Decay: A substance emits an alpha particle from the nucleus creating a new substance, mass number decreases by 4, atomic number decreases by 2.
• Beta Decay: A beta particle (electron) is emitted and a neutron changes into a proton, mass number doesn’t change, atomic number increases by 1.
• Background radiation comes from many sources and is constantly in the air around us, it is not harmful.
• Radiation can be detected by a Geiger-Müller tube.
• The number recorded on the counter in a Geiger-Müller tube is the radiation from the source minus the background radiation.
• • Half-life is defined as:

  The time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half
• • Contamination is defined as:

  The unwanted presence of materials containing radioactive atoms on other materials
• • Irradiation is defined as:

  The process of exposing a material to alpha, beta or gamma radiation
• Sources with short half-life are dangerous because they emit high radiation at the start.

  Sources with a long half-life can be dangerous because radiation is emitted for a long time.
• What is nuclear fission?


  Splitting a large, unstable nucleus into two daughter nuclei.
• How does spontaneous fission differ from induced fission?


  Spontaneous fission rarely happens, while induced fission occurs when a neutron is fired at a nucleus.
• What happens when an atom undergoes fission?


  Two or three neutrons are released, which can cause a chain reaction.
• What role do neutrons play in nuclear fission?


  They can cause a chain reaction if another nucleus absorbs them.
• What type of radiation is produced during nuclear fission?


  Gamma rays are produced.
• What is nuclear fusion?


  Joining of two smaller nuclei to create a larger, heavier nucleus.
• How do nuclei behave during nuclear fusion?


  They collide at high speed and fuse together.
• What happens to the mass of the new nucleus formed during fusion?


  It is less than the combined mass of the two separate nuclei because some mass is converted to energy.
• More energy is released in fusion than in fission. However, scientists have not found a way to use this to generate energy because the machines needed are very expensive.
• Which is fission and which is fusion?

  A) fission

  B) fusion