radioactivity (SP6)

• when does the frequency of the generated radiation decrease?


  as you get further from the nucleus
• what happens if an outer electron absorbs radiation with enough energy?

  it can move so far that it leaves the atom
• what is an electron once it leaves the atom?

  a free electron and has been ionised. The atom is now a cation as it has more protons than electrons.
• what is radioactive decay?

  unstable isotopes tend to decay into other elements and gives out radiation as they try to become more stable.
• what happens once an electron that has moved up an energy level and then falls back down?

  will emit (lose) the same amount of energy it absorbed. The energy is carried away by EM radiation.
• when would an inner electron move up to a higher level?

  if it absorbs EM radiation with the right amount of energy
• what happens as you move further away from the nucleus in terms of electron shells?

  the energy levels get closer together so the difference in energy between 2 levels next to eachother get smaller.
• what do changes in the nucleus lead to?

  production of high energy, high frequency gamma rays.
• what is ionising radiation?

  radiation that can cause charged particles (ions) to be formed, it can cause tissue damage and DNA mutations.
• what about the nucleus of radioactive substance means it can easily decay?

  the nucleus is unstable.
• what happens when decay occurs?

  radiation is emitted which causes the nucleus to lose energy and become more stable. We cant predict when a nucleus will decay.
• what does an alpha particle contain?

  2 protons and 2 neutrons, just like the nucleus of a helium atom, they have a relative mass of 4 and a charge of 2+
• what are the 3 types of radiation that can be emitted by unstable nuclei?

  alpha particles, beta particles, gamma rays
• other than the 3 types of radiation, what else can be emitted from an unstable nucleus?

  neutrons, they have a relative mass of 1 and no electric charge.
• what can all types of ionising radiation do?

  penetrate materials.
• what happens when an electron moves up to a higher energy level (shell)?

  it moves to an empty or partially filled shell and is said to be "excited".
• what are positrons?

  high energy, high speed particles with the same mass of electrons but a charge of 1+
• how can positrons be written?

  e+
• what are gamma rays?

  high frequency EM waves, they travel at the speed of light and don't have an electric charge.
• where do the electrons that are beta particles come from?

  the nuclei of atoms when a neutron transforms into a proton.
• what do beta particles not do once they leave the nucleus?

  they don't ionise the atom they are leaving.
• what are beta particles?

  high energy, high speed electrons. They have a relative mass of 1/1835 and a charge of 1-
• how can beta particles be written?

  e-
• how can alpha particles be written?

  4

  He

  2
• what does alpha decay decrease?

  the charge and mass of the nucleus.
• what does beta-minus decay increase?

  the charge of the nucleus
• what does positron emission decrease?

  the charge of the nucleus.
• what does neutron emission decrease?

  the mass of the nucleus.
• how far can gamma rays penetrate?

  far into materials without being stopped and will travel long distance through air.
• how ionising are gamma rays?

  weakly ionising as they tend to pass through rather than collide with atoms. Eventually, they hit something and do damage.
• what can gamma rays be absorbed by?

  thick sheets of lead or metres of concrete.
• what is the equation for an atom before decay (nuclear equation)?

  atom before decay -> atom after decay + radiation emitted
• how ionising are B+/B- particles?

  moderately ionising
• how far can B- particles penetrate?

  range in air of a few centimetres and absorbed by sheets of alumunium (5mm thick).
• how far can B+ particles penetrate?

  smaller range than B- particles, when they hit an electron, they destroy each other and produce gamma rays. It's called annihilation and it's used in PET scanning.
• what happens after a nucleus has decayed?

  it often undergoes nuclear rearrangement and releases some energy. Gamma rays are waves of EM radiation released by the nucleus that carry away this energy.
• how many stable isotopes does an elemnt usually have?

  all elements have different isotopes, but there are usually only 1 or 2 stable ones.
• what happens to unstable isotopes?

  they tend to decay into other elements and give out radiation as they try to become more stable which is radioactive decay.
• how far can alpha particles penetrate?

  they don't penetrate very far into materials and are stopped quickly, they can only travel a few centimetres in air and are absorbed by a thin sheet of paper.
• how ionising are alpha particles?

  because of their size, they are strongly ionising.