P6

• Nuclei


  Made up of protons and neutrons
• Protons


  Relative charge of +1
• Neutrons


  No charge
• Nuclei


  Have an overall positive charge
• Isotopes


  Atoms of the same element but with different numbers of neutrons
• Atomic number (Z)


  Determines what the element is (number of protons)
• Mass number (A)


  Neutrons + protons
• Charge (N)


  Number of electrons - number of protons
• The number of protons is fixed for each individual element, so it is a defining feature for each element
• Some nuclei are unstable leading to random decay
• Alpha decay


  • Occurs for nuclei that are too large, an alpha particle is emitted
• Beta decay


  • Occurs when an atom has too many neutrons, a neutron is turned into a proton and a beta particle is emitted
• Electron capture


  • Occurs when there are too many neutrons and the nucleus is too large, the nucleus absorbs a neutron and emits a neutron
• Gamma emission


  • If a nucleus has too much energy, a gamma ray is emitted, proton and neutron numbers do not change
• Electron excitation and ionisation

  1. Electrons absorb energy and become excited, rising to a higher energy level

  2. When outer electrons are given lots of energy, they can be lost from the atom, this is called ionisation
• Half-life


  The time taken for the number of unstable nuclei of an isotope in a sample to halve
• Half-life is used to show how long radioactive atoms will last for, and each half-life is specific to each isotope
• Radioactive dating


  Analysing the proportion of decayed and undecayed isotopes in a sample to work out the age of the sample
• Alpha radiation


  • Most ionising, least penetrating
• Beta radiation


  • Medium penetrating power and medium ionising power
• Gamma radiation


  • Least ionising power and most penetrating power
• Contamination


  Radioactive material lasts for a long period of time, transferring radiation to an object
• Irradiation


  Only lasts for a short period of time as the source emits radiation, which reaches the object
• Short half-life


  • The source presents less of a risk as it does not remain strongly radioactive for as long
• Long half-life


  • The source remains weakly radioactive for a long period of time
• Technetium as a medical tracer

  Has a half-life of 6 hours, decays into a safe isotope that can be excreted by the body, is a gamma emitter so can pass through body tissue without being absorbed
• Gamma emitters in chemotherapy


  Used to emit gamma radiation which can be directed onto cancerous cells to kill them, but also damages surrounding healthy cells
• Nuclear fission


  1. Unstable nuclei split into two smaller nuclei, releasing a neutron and energy

  2. The neutron may collide with another radioactive nucleus and be absorbed, causing it to split and release another neutron and more energy

  3. A chain reaction is set up as the energy released causes further splits
• Nuclear fusion


  Two small nuclei fuse to form a heavier nucleus, releasing large quantities of energy in the process