atomic structure

• the number of protons is the same as the number of electrons
• john dalton believed elements were made up of tiny spheres called atoms
• jj thomson discovered the plum pudding model of the atom
• niels bohr developed the planetary model of the atom where electrons orbited around the nucleus like planets orbiting the sun
• rutherford experimented with the alpha particle and discovered that it was a helium nucleus
• alpha particles sometimes deflected in the experiment
• current model

  
• number of protons = atomic number
• number of protons + neutrons = mass number
• unstable isotopes decay into other elements by emitting radiation and neutrons to become stable
• half life - time taken for half of an unstable sample to decay
• alpha particles do not penetrate far into materials
• alpha particles are absorbed by paper
• alpha particles are strongly ionising
• gamma rays can pass through most materials, but can be blocked with lead
• alpha particles

  
• beta particles are moderately ionising
• beta particles can be absorbed by aluminium
• beta particles are moderately penetrating
• beta particle

  
• gamma rays can penetrate far into materials
• gamma rays are weakly ionising
• gamma rays are absorbed by thick lead or concrete
• alpha decay

  
• beta decay

  
• radiation can be measured with a geiger - muller tube, a detector that measures the number of decays per second
• half life graph

  
• ionising radiation can enter living cells and damage them
• keeping sources in lead - lined boxes are ways to reduce irradiation
• if an object is contaminated with a radioactive substance, it will emit radiation
• if your hand touches a contaminated item it can cause harm so you should wear gloves and use tongs
• beta and gamma particles can penetrate through skin damaging organs
• inside the body alpha particles do the most damage as it is in a very localised area
• gamma is the least damaging in the body as it is the least ionising