P4

• radius of atom ?

  1 x 10 -10 m
• energy levels which are further from the nucleus are at a higher energy than those which are closer to the nucleus
• • if the atom gains electromagnetic radiation, then an electron can move from a lower energy level to a higher energy level
  • the atom can now emit electromagnetic radiation and the electron returns back to the lower energy level
• • only one or two of an elements isotopes are stable
  • the other isotopes which are unstable tend to decay into other elements by emitting radiation like alpha, beta and gamma or sometimes they just emit neutrons and this process is called radioactive decay
• ionising :

  one of the outermost electrons should absorb so much energy that it is able to completely leave the atom

  this leaves the atom with more protons than electrons and so its left with a positive change which means now call it a positive ion rather than an atom
• ionising radiation- its able to knock electrons off atoms and so ionize them
• development of the atom- didnt do it cz its in chemistry
• radioactivity:

  • some isotopes have an unstable nucleus
  • to become stable, the nucleus gives out radiation
  • this is called radioactive decay
• radioactive decay is a random process which means you cannot prdect when a nucleus will decay
• • activity is the rate at which a source of unstable nuclei decay
  • activity is measured in becquerel
  • 1 Bq = 1 decay per second
• to measure the activity of a source we can use a Geiger muller tube
• the count rate is the number of decays recorded each second by a detector
• 4 types of radiation -

  • alpha
  • beta
  • gamma
  • neutron
• alpha particles consists of 2 neutrons and 2 protons that means it is the same as a helium nucleus
• a beta particle is an electron which is ejected from the nucleus at very high speed
• a beta particle is formed inside the nucleus when a neutron changes into a proton and an electron
• gamma rays are not particles
• gamma rays are a type of electromagnetic radiation from the nucleus
• • alpha particles are large
  • they can travel around 5cm in air before they collide with air particles and stop
• • beta particles can travel further
  • they can reach about 15cm in air before stopping
• gamma radiation travels several metres in air before stopping
• alpha particles are stopped by a single sheet of paper
• beta particles are stopped by a few mm of aluminium
• gamma radiation is stopped by several cm of lead
• alpha particles are easier to stop
• ionising power:

  • when radiation collides with atoms, that can cause the atoms to lose electrons and form ions
• alpha particles are very strongly ionising and that means they can produce a lot of ions when they collide with the material
• beta particles are quite strongly ionising
• gamma radiation is a little ionising
• • during alpha decay, the atomic number decreases by 2
  • during alpha decay, the mass number decreases by 4
• • in beta decay, a neutron changes to a proton and an electron
  • the electron is ejected from the nucleus
  • we call that a beta particle
• in beta decay, the atomic number increases by 1 but the mass number does not change
• in gamma decay, both the atomic number and the mass number are not changed at all
• the half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve
• the half-life is also the time it takes for the count rate or activity from a sample containing the isotope to fall to half its initial level
• ionising radiation can increase the risk of cancer in humans
• irradiation is exposing an object to nuclear radiation e.g. alpha
• people who work with radioactive isotopes have got to take precautions such as:

  • gloves can protect alpha radiation
  • beta and gamma can be reduced by a lead apron
  • lead walls
• • with a radiation monitor, we can measure how much radiation has been received
  • if the person has received too much radiation, we can stop them from working with radioactive isotopes
• • when unwanted radioactive isotopes end up on other materials, this is called contamination
  • this is hazardous as the radioactive atoms decay and emit ionising radiation