P4 - Atomic Structure

P4 - Atomic Structure

1. Atomic Model

   • Radius of atom 1x10^-10
     • Nucleus radius 10000 times smaller
   • Electron -1 charge, almost no mass
   • Neutron 0 charge, mass of 1
   • Proton +1 charge, mass of 1

2. Isotopes

   • Atoms of element with same protons, different neutrons
   • Same atomic number, different mass number
   • Some isotopes unstable, decay into other elements and give out radiation

3. Nuclear radiation

   • Ionising radiation knocks electrons off atoms, creates positive ion, ionising power is how easily it can do this
   • Alpha particles
     • Helium nuclei
       • Two protons, two neutrons
     • Don't penetrate very far, stopped quickly (few cm of air or sheet of paper)
     • Strongly ionising due to size
     • Emitted from nucleus
   • Beta particles
     • Fast-moving electron released by nucleus
     • Moderately ionising, penetrate moderately (few m of air or sheet of aluminium)
     • For every beta particle emitted, neutron in nucleus turns into proton
   • Gamma rays
     • Waves of EM radiation
     • Penetrate far without stopping, travel long distance in air
     • Weakly ionising, tend to pass through atoms instead of colliding
     • Absorbed by thick sheets of lead or m of concrete

4. Half Life

   • Use Geiger-Muller tube and counter to measure count-rate of radiation
   • Time taken for the number of radioactive nuclei in an isotope to halve
     • Time taken for activity (count-rate) to fall to half of its initial value
   • Can be measured by using graph (activity against time)

5. Irradiation and contamination

   • Ionising radiation can enter living cells and ionise atoms within them
     • Can damage cells (cause cancer) or kill them
   • Exposure to radiation is irradiation
     • Does not make it radioactive
   • Keeping sources in lead-lined boxes and standing behind barriers can reduce effects of irradiation
   • In some industries source in a different room, rc arms used to handle it
   • Contamination is radioactive particles getting into objects

6. Nuclear Equations

   • Mass and atomic numbers have to balance
     • atom before decay = atom after decay + radiation emitted
   • Alpha decay decreases charge and mass of nucleus
   • Beta decay increases the charge of the nucleus
   • Gamma rays don't change the charge or mass