topic 6 - radioactivity

• what is an isotope


  • atoms of the same element that have the same number of protons but a different number of neutrons
• what is an atom made up of


  • a positively charged nucleus
  • positive protons and neutral neutrons
  • surrounded by negatively charged electrons
• when an electron moves further from the nucleus what does this mean for EM radiation


  atom has absorbed EM radiation
• when an electron moves closer to the nucleus, what does this mean for EM raditation


  the atoms have emitted EM radiation
• what are examples of background radiation?


  • cosmic rays
  • medical rays
  • nuclear fallout
  • radiation from underground rocks
• what are the properties of alpha radiation?


  • helium nucleus
  • highly ionising
  • weakly penetrating
• what are the properties of beta minus radiation?


  • medium ionising
  • medium penetration
• what are the properties of beta plus radiation?


  Positron emission.

  medium ionising

  medium pentrating
• what are the properties of gamma radiation 


  • low ionising
  • highly penetrating
• what are two methods of measuring radioactivity?


  • photographic film
  • Geiger - muller tube
• how does photographic film measure radiation


  • film goes darker when it absorbs radiation
  • worn as badges by people who work with radiation to see how much exposure the have
• how does the Geiger - Muller tube work to measure radioactivity ?


  • a tube can detect radiation
  • Each time it absorbs radiation - it transmits an electrical pulse to the machine which produces a clicking sound
  • greater number of clicks per second - the more radiation is present
• what is a half life?


  • the time taken for half the nuclei in a sample to decay
• what is the equation for net decline?


  initial number - number after x half lives / initial number
• what did Dalton discover in 1800


  everything was made of atoms
• what did JJ Thompson discover in 1897


  • Plum Pudding Model
  • discovered the electron
  • overall charge of an atom is neutral so the negative electrons were dispersed through the positive ' pudding' to cancel out the charges
• what did Rutherford do in 1911 and what were his results?


  • Gold foil experiment
  • most particles went straight through so most of an atom is empty space
  • some particles were slightly deflected so nucleus must be positive
  • few particle were deflected so nucleus must contain most of the mass
• what did the Rutherford model consist of in 1913?


  • a positive nucleus at the centre of the atom
  • negative electrons existing in a cloud around the nucleus
• what did the the final model created by Bohr in 1913 include?


  • electrons exist in fixed 'orbitals' - as if they were in a cloud they would get too close and cause the atom to collapse
• what is activity?


  • the number of decays in a sample per second
  • it deceases exponentially over time
• what is activity measured in?

  • Becquerel Bq
• alpha particle


  a positively charged particle consisting of two protons and two neutrons
• chain reaction


  the process of neutrons released by a fission reaction, being absorbed by another unstable, large nuclei, and including further fission
• radioactive contamination


  the unwanted presence of radioactive atoms on other materials. It is hazardous due to the decay of the contaminating atoms
• random nature of radioactive decay


  you cannot predict which nuclei in a radioactive sample will decay next , or when the next decay will occur - it is a random process
• PET scanner


  a medical imaging device that uses radioactive tracers and detectors to form internal body images
• fission products


  • fission products produce two smaller nuclei, two or three neutrons and gamma rays - all released with kinetic energy
• what are the two safety measures for patients and medical staff with radiation?

  • limiting patient dose - use tracers with a short half life
  • Medical staff leave the room during radioactive tests
• how do smoke alarms work?

  • Alpha particles ionise air particles and make them charged which produces a current
  • if smoke enters, current drops
  • alarm sounds
• What is irradiating food?

  • gamma rays transfer energy to kill bacteria and sterilise food
• how does beta radiation help trace and gauge thickness?

  • Beta can just pass through paper
  • Source and receiver placed on either side of the paper
  • Drop or rise in received electrons indicates thickness of the paper has changed
• what is a short half - life less risky?

  • Not strongly radioactive for long - little long term effects
• why is a long half - life safer?

  • Remains weakly radioactive for a long period of time
• what are control rods?

  Boron rods in the reactor core which absorb excess neutrons
• what are moderators? (chain reactions)

  • Water/graphite which slows down emitted neutrons to be absorbed by other fissions
• what are required conditions for fusion?

  • high temperature
  • high pressure
• what is irradiation

  the process of an object being exposed to nuclear radiation. The object does not become radioactive
• what is the random nature of radioactive decay?

  • you can not predict which nuclei in the radioactive sample will decay next, or when the next decay will occur, it is a random process
• what is radioactive contamination?

  the unwanted presence of radioactive atoms on other materials. It is hazardous due to the decay of the contaminating atoms