radioactivity

• how to use a gm tube?

  • Remove all known sources of radioactivity from the room.
  • Set the counter to zero.
  • Switch on and start a stop clock.
  • After 20 minutes switch off. Record the count.
  • Divide the count by 20 to calculate the count rate per minute.
• the graphite core and movable rods?

  • graphite core - graphite slows down the fast moving neutrons so that they are more likely to be absorbed by uranium nuclei in nearby fuel rods and cause further fission
  • control rods - these are raised and lowered to stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction or stop it altogether. On average, only one of the fission neutrons goes on to produce further fission;
• what did jj thompsons plum pudding model show?

  . a ball of positive charge with discrete electrons
• What did rutherford so in his experiment?

  • fired particles around a thin sheet of gold
  • if the positive charge in the gold sheet was spread out, the particles would have gone right through
  • however, he found the opposite
  • some of the alpha particles were refracted to the side and some back where they came from
• what model did rutherfords experiment conclude in?

  the nuclear model - there was a nucleus that contained the positive charge and electrons in the outer shell
• what does the mass number show?

  the total number of protons and neutrons
• what does the atomic number show?

  the amount of protons in the element
• what is an isotope?

  atoms with the same number of protons but a different number of neutrons
• what happens to electrons as their energy level increases?

  they jump into a shell that is further away from the nucleus as its energy level increases , after some time it falls back and remits energy
• what is ionisation?

  when one of the outermost electrons gain so much energy is leaves the electron shell completely, making a positive ion
• what are the properties of alpha beta and gamma rays?

  Alpha: Helium nucleus, low penetration, stopped by paper. Highly ionising . has a (+2 charge)

  Beta: High-speed electrons, moderate penetration, stopped by aluminum. moderately ionising ,(-1 charge)

  Gamma: Electromagnetic waves, high penetration, stopped by lead. weakly ionising. (no charge)
• what happens during alpha decay?

  it looses 2 protons and 2 neutrons
• what happens in beta decay?

  the atomic number decreases by 1 and the mass number stays the same
• what happens in gamma decay?

  the radioactive particle stays the same
• What happens in neutron emisison?

  the mass number decreases by 1 and the atomic number stays the same
• what is half life?


  the time taken for the number of the radioactive nuclei in the sample to halve
• what is irradiation?


  when objects are exposed to radiation
• What is contammination?

  when radioactive particles get onto other objects
• why is irratiation on or inside the body dangerous?

  they can interact with the molecules inside our cells and can lead to mutations
• what do medical tracers do?


  track movement of isotopes around the body
• what happens when you receive cancer treatment externally?


  it emmits gamma rays that are targeted at the cancer site and it receive the highest dose
• What happens when you receive the dose internally?

  the radioactive source inside the body next to the cancer , however it isnt too dangerous as beta rays aren't too penetrative, so they cant travel far into the body
• fusion?


  hydrogen nuclei fuse to gather to form helium three as well as some of the mass

  adv

  doesn't produce radioactive waste

  only happens in high pressure and temp
• fission?


  large unstable nuclei and slow moving neutron is fired towards it , making it more unstable and splits it into daughter nuclei and releases a lot of energy