past paper questions

• Development of the Nuclear Model

  John Dalton = matter was made up of tiny spheres that could not be broken up. But each element was made up of a different type of atom

  
  

  JJ Thomson = electrons could be removed from atoms. He thought that atoms were spheres of positive charge with negative charge stuck in them (plum pudding model)

  
  

  Rutherford = fired alpha particles at gold foil (alpha scattering). The expected particles to go straight through. some were deflected more than expected and a few were deflected straight back at them. Idea of a positive 'nucleus' in the center of the atom was created.

  
  

  Atoms are nearly all empty space apart from the nucleus
• Current Model of the atom

  
• Charge and Mass of subatomic particles

  
• Isotopes

  same number of protons

  
  

  different number of electrons

  
  

  different mass number
• Unstable Isotopes


  tend to decay into other elements and give out radiation as they become more stable (this is radioactive decay)
• 3 types of ionising radiation

  Alpha, Beta and Gamma
• Alpha Radiation

  Alpha Radiation is when an alpha particle is emitted from the nucleus

  
  

  An alpha particle is 2 neutrons and 2 protons

  
  

  They don't penetrate very well and are stopped quickly (absorbed by a sheet of paper)

  
  

  Because of their size, they're strongly ionising

  
• Beta Radiation


  it is a fast moving electron released by the nucleus

  
  

  Virtually no mass and a charge of -1

  
  

  Moderately Ionsing

  
  

  Penetrate Modernity (stopped by a sheet of aluminium)

  
  

  for every beta particle emitted, a neutron in the nucleus turns into a proton
• Gamma Radiation


  EM Radiation released by the nucleus

  
  

  Good at penetrating (only absorbed by thick sheets of lead or meters of concrete)

  
  

  Weakly ionising
• Alpha Equations

  
• Beta Equations

  
• Gamma Equations

  it is a way of getting rid of excess energy from the nucleus

  
  

  there is NO change to the atomic mass or atomic number of the atom
• Randomness of Radioactivity

  radioactive substances give out radiation from the nuclei of their atoms - no matter what

  
  

  Measured with a Geiger-Muller Tube and Counter (it records the count rate)

  
  

  Radioactive decay is random
• Half Life Definition

  it is the time taken for the number of radioactive nuclei in an isotope to halve

  
• Decrease of radioactivity of a source

  radioactive nucleus decays to become more stable. The activity as a whole will decrease.

  
  

  Some take a few hours to decay, some take millions of years
• Short Half-Life =...

  activity falls quickly, because the nuclei are very unstable and will decay very quickly.

  
  

  they are dangerous because of the high amount of radiation
• Long Half-Life =...

  most nuclei in the substance will not decay for a long time, therefore it will release small amounts of radiation for a long amount of time.

  
  

  Thecanbe dangerous as certain areas are exposed to it for millions of years
• Measuring Half-Life


  find the time interval on the bottom axis corresponding to a halving of the activity on the vertical axis

  
• Sources of Background Radiation


  1. Unstable Isotopes = building materials, in the rocks under our feet.

  
  

  2. Cosmic Rays = from the sun, earth's atmosphere protects us from a lot of this radiation.

  
  

  3. Human Activity = Nuclear Waste or Nuclear Explosions
• What does Dose of Radiation tell you?

  it tells you rick of harm to the body tissues due to exposure to radiation.

  
  

  Measured in Sv
• Irridation


  objects near to a radioactive source are irradiated by it (they are exposed to it)

  
  

  keeping sources in lead-lined boxes will reduce the effects of irridation
• Contamination

  if unwanted radioactive atoms get onto or into an object , the object is said to be contaminated

  
  

  e.g. touching a radioactive source without wearing gloves

  
  

  Radioactive particles can get inside of your body

  
  

  Using gloves and tongs stop radioactive sources from touching your skin // ALSO PROTECTIVE SUITS
• Seriousness of Irradiation and Contamination depends on the source

  Outside the body, Beta and Gamma are the most effective due to the penetrating ability.

  
  

  but inside the body alpha is the most damaging due to the ionising power.

  
  

  Alpha = Contamination is the main concern

  
  

  Beta and Gamma = Irradiation is the main concern
• Risks to using Radiation

  1. it can enter cells and ionise atoms and molecules (it can lead to tissue damage).

  
  

  2. lower doses causes minor damage without killing cells, this can cause mutant cells which lead to cancerous cells.

  
  

  3. Higher Doses kill cells completely, causing radiation sickness
• Gamma Sources in Medical Tracers

  certain radioactive isotopes can be injected into people and their progress around the body can be followed by a detector.

  
  

  A computer can show were the strongest reading is coming from.

  
  

  e.g.Iodine-123is absorbed by the thyroid gland. But it gives out radiation which can be detected to indicate whether the thyroid gland is taking in iodine as it should.

  
  

  Usually GAMMA, as it passes out of the body and it is not very strong at ionising.

  
  

  They need to have a short half life so the radioactivity inside the patient disappears very quickly
• Radiotherapy

  since high doses of ionising radiation will completely kill living cells.

  
  

  it is used to treat cancer.

  
  

  They are directed at the cells at a certain dosage so normal cells are not affected.

  
  

  a small amount of damage to normal cells is inevitable (this can make them feel ill)
• Nucleur Fission

  it release energy from large/unstable atoms by splitting them into smaller ones.

  
  

  a neutron is fired at the nucleus and is absorbed.

  
  

  the atom splits and produces 2 smaller elements that are the same size.

  
  

  2 or 3 neutrons are also released, they can then be absorbed by another nucleus.

  
  

  This is aCHAIN REACTION

  
  

  EXTRA ENERGY USED TO - heat water to make steam in order to turn a turbine.

  
  

  Control Rods = lowered to absorb neutrons and to slow down the chain reaction.

  
  

  Nuclear Weapons = an uncontrolled chain reaction

  
• Nuclear Fission

  Opposite of Nuclear Fission.

  
  

  2 light nuclei collide at a high speed and fuse to create a larger nucleus.

  
  

  Some of the extra mass is converted into energy and is released as radiation

  
  

  Fusion Releases Energy