Topic 6 RADIATION

• atoms have no charge because of same number of proton and electron
• atom radius 1 x 10^-10
• radius of nucleus is smaller 1 x 10^-14
• isotopes are atoms of same element with different number of neutrons(same atomic number but different mass number)
• isotope have unstable nucleus so it decays to be more stable
• isotopes of element have slightly different mass numbes because of different number of proton
• dalton thought atoms were tiny neutral solid spheres which couldn't be broken into smaller pieces(theory untrue because after electron was discovered)
• thompson did plum pudding theory(1904) atoms had randomly placed electrons in a positive mixture, still a tiny neutral sphere
• rutherford did alpha scattering experiment (1908-1911), he fired 1000s of positive alpha particles at thin gold foil
• what did Rutherford find out

  • most went straight through- most of atom is empty space
  • Tiny few rebound-nucleus heavy and tiny
  • Some were deflected- nucleus must be positive since 2 positive repel
• radioactive decay

  • atom nuclei changes to become stable(because some atom nuclei are made)
• its a random process can't predict or influence when nucleus will decay
• Half- life is the time taken for half of the nuclei in a sample to decay
• half-life is the time it takes for activity/count rate to halve
• decay is random so we don't know which nuclei will decay but we know how long it takes half of them to decay
• it takes the same time to half number for element
• What is activity?

  number of decays in 1 second/amount of radioactive decay in time of 1 second
• How to detect radioactive decay?

  geiger-muller, geiger, or GM tube and a counter/speaker
• How to protect yourself from radioactive decay?

  use/wear dose tube
• What is background radiation?

  Radiation which doesn't come from the source being tested
• Background radiation comes from:

  • stars- cosmic radiation
  • rocks because they release random gas
  • food and drinks
  • hospital nuclear departments
  • nuclear testing/power stations
• we need to measure and subtract background radiation counts when we test activity of the source
• What does line on half-life graph look like

  Curve
• Half-life of sample is 40 hours there 3,000,000 radioactive nuclei in the sample. How many nuclei remains after 5 days


  375,000