nuclear

• Thomas plum pudding model - a sphere of positive charge, with small areas of negative charge evenly distributed throughout.
• Rutherfords scattering proved the existence of a nucleus. It involved an alpha source and gold foil in an evacuated chamber which was covered in a fluorescent coating. Which allows you to see where alpha particles hit.
• What was observed in Rutherfords scattering:

  . most alpha particles passed straight through the foil - suggests the atom is mostly empty space

  . A small amount of alpha particles were deflected by a large angle - suggests that the centre of the atom is positively charged

  . Very few particles were deflected back by more than 90 degrees - suggests that the centre of the atom is very dense.
• . Alpha is highly ionising absorbed by paper range: 2-10 cm

  . beta is weakly ionising absorbed by aluminium range: 1m

  . gamma is very weakly absorbed by concrete or lead range: infinite

  Deflected by E and M fields:

  . alpha - yes

  . beta - yes

  . gamma - no
• Geiger muller tube is used to detect gamma radiation.

  You can measure the count rate of a gamma source at diff distances from the geiger muller tube.

  However background radiation is around us constantly. So measure that first then minus it from the the total count to get the corrected count.
• Radioactive decay is random and unpredictable.
• The activity of a radioactive sample is the number of nuclei that decay per second.

  time taken for activity to half is the half life.
• Nuclei are held together by the strong nuclear force. Protons experience a force of repulsion due to the electrostatic force, if the forces are out of balance the nuclei becomes unstable.

  4 reasons a nuclei might become unstable:

  . too many neutrons - beta minus emission

  . too many protons - beta plus emission

  . too many nucleons - decays through alpha emission

  . too much energy - decays through gamma emission
• Mass defect is that the mass of the nucleus is less that the mass of its constituents. The mass that is loss is converted into energy and released when the nucleons fuse to form a nucleus.
• Binding energy is the energy required to separate the nucleus into its constituents.
• Nuclear fission is the splitting of a large nucleus into 2 daughter nuclei.
• Nuclear fusion is where 2 smaller nuclei join together to form one larger nucleus. It only occurs at high temperatures and releases far more energy than fission.