Atomic Structure (T4)

• What are isotopes?

  Isotopes are atoms of the same element that have different numbers of neutrons.
• Atoms of the same element have the same number of protons.
• What is the mass number?

  The total number of protons and neutrons in an atom's nucleus. (Top number)
• What is the atomic number?

  The number of protons in an atom's nucleus. ( Bottom number)
• How are unstable isotopes formed?

  When an element has extra neutrons or protons.
• Unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable. This process is called radioactive decay.
• Radioactive substances spit out different types of ionising radiation such as alpha, beta and gamma radiation.
• What is ionising radiation?

  Radiation that knocks electrons off atoms, creating positive ions. The ionising power of a radiation source is how easily it can do this.
• Alpha particles are Helium Nuclei. Alpha radiation is when an alpha particles is emitted from the nucleus.

  • It is two neutrons and two protons.
  • It can be written as Helium or $\alpha$
  • They can only travel a few cm in air and are absorbed by a sheet of paper.
  • They are strongly ionising because of their size.
• Beta Particles are high speed electrons.

  • They have almost no mass
  • -1 charge
  • moderately ionising
  • Penetrate moderately - few metres in the air and can be absorbed by a sheet of aluminium.
  • For every beta particle emitted, a neutron in the nucleus has turned into a proton.
• Gamma rays are electromagnetic waves with a short wavelength.

  • waves of EM radiation released by the nucleus
  • Very penetrative (long distance through air)
  • Weakly ionising (because they pass through rather than collide with atom. Eventually they hit something and do damage)
  • Can be absorbed by thick sheets of lead or metres of concrete
• How do you calculate Half life?

  Divide by two
• what is background radiation?

  Low-level radiation that’s around us all the time.
• What are the three background radiation?

  Naturally occurring unstable isotopes

  From space (cosmic rays)

  human activity e.g nuclear explosions
• Radiation dose tells you the risk of harm to body tissues due to exposure to radiation.
• Radiation is measured in sieverts (Sv)
• Exposure to radiation is called irradiation.
• Ionising radiation can cause damage to cells which may lead to cancer or genetic mutations.
• Contamination is radioactive particles getting onto objects.
• How could you protect yourself against radioactive sources?

  Lead shielding, gloves, tongs
• Outside the body, beta and gamma sources are the most dangerous. Inside the body, alpha sources are the most dangerous.
• What are some uses of radiation?

  Medical tracers

  Radiotherapy - treating cancer with radiation
• What are some risks of using radiation?

  Lower doses cause minor damage without killing the cells and can mutate the cells, causing cancer.

  • Higher doses tend to kill cells completely, causing radiation sickness
• How does gamma sources in medical tracers work?

  1. Radioactive isotopes are injected and their progress around the body can be tracked using an external detector.
  2. A computer shows where the strongest reading is coming from
• What is nuclear fission?

  Nuclear Fission is a type of nuclear reaction that is used to release energy from large and unstable atoms by splitting them into smaller atoms.
• How does Nuclear fission work?

  1. The nucleus absorbs a neutron.
  2. The atom splits and forms 2 new lighter elements that are roughly the same size.
  3. 2 or 3 neutrons are released when an atom splits. If any of these neutrons are moving slow enough to be absorbed by another nucleus, they can cause more fission to occur. This is a chain reaction.
• Uncontrolled chain reactions leads to lots of energy being released as an explosion.
• Nuclear fission is the splitting of a large, unstable nucleus.
• Nuclear fusion is the joining of small nuclei
• Explain how nuclear fission works.

  2 light nuclei collide at high speed and fuse (join) to crate a large, heavier nucleus.

  Some of the mass of the lighter nuclei is converted and released, so the heavier nucleus doesn’t have as much as both the light nuclei.
• How can you measure radiation?

  Geiger- muller tube and counter.
• What is half life?

  The time taken for the number of radioactive nuclei in an isotope to halve.
• The rate at which a source decays is its activity.
• Activity can be measured in becquerels (Bq)
• Radioactivity decreases over time because there are fewer unstable nuclei left to decay.