Atomic structure

• atom radius


  1x10-10m
• radioactive decay


  The process in which an unstable nucleus gives out radiation to become more stable
• Subatomic constituents of an atom

  proton

  neutron

  electron
• Most of the mass of an atom is concentrated in the nucleus
• Unstable nuclei

  • They undergo decay to become more stable
  • As they release radiation their stability increases
• How an atom's electron arrangement can change?

  1. Absorbing electromagnetic radiation
  2. Emitting electromagnetic radiation
• activity


  the rate of decay of a source of unstable nuclei
• How electron arrangement changes when atom absorbs EM radiation

  Electrons move further away from nucleus, to higher energy level
• How electron arrangement changes when atom emits EM radiation

  Electrons move closer to nucleus, to lower energy level
• why atoms have no overall change]

  Number of protons equals number of electrons, so charges cancel
• unit for radioactive activity?


  becquerel (Bq)
• atomic number?


  number of protons in an atom
• sources of background radiation

  1. rocks
  2. cosmic rays from space
  3. nuclear weapon testing
  4. nuclear accidents
• count rate


  the number of radioactive decays per sec for a radioactive source
• mass number


  total no of protons and neutrons in an atom
• how to deal with background radiation in calc

  Subtract the background count from any readings before calculations (half life etc.) are attempted
• units used to measure radiation dosage?

  Sv
• detector used to measure count-rate

  geiger muller tube
• How atoms turn into positive ions
?


  Lose one or more outer electrons, resulting in a positive charge
• 1000 millisieverts = 1 sievert
• Reasons why radiation dosage may differ for different people?

  • Some occupations involve working with radiation
  • Background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing
• New experimental evidence that doesn't agree with existing theory may lead to a scientific model being changed or replaced
• Types of nuclear radiation

  • alpha
  • beta
  • gamma
  • neutrons
• Factor that determines how dangerous a particular radioactive isotope is

  half-life of the isotope
• Isotopes with long half-lives

  • remain radioactive for much longer times
  • must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long
• uses of nuclear radiation in medicine?

  • tracer- to detect tumours
  • controlling and destroying unwanted tissue
• what is an alpha particle?

  2 neutrons and 2 protons
• uses of radiation in sterilisation?

  gamma emitters are used to kill bacteria on equipment
• Conclusions of alpha-scattering experiment: most mass concentrated in nucleus, nucleus positively charged
• Radiotherapy process

  1. Gamma emitters direct gamma rays at the cancerous cells.
  2. The cancerous cells absorb the radiation and are killed
• Medical tracers


  • short half life and decay into a stable isotope= can be excreted
  • release gamma radiation = weakly ionising n can easily pass thru body tissue without damage
• who discovered neutrons?


  chadwick
• Range of alpha particle through air?

  a few cm 3-5
• range of beta particle?

  metre
• range of gamma ray in air?

  1km ( several metres) can be absorbed by thick lead
• what stops beta radiation?

  • thin sheet of aluminium
  • several metres of air
• what stops alpha radiation?

  paper
• most - least ionising

  alpha, beta, gamma
• most - least penetration

  gamma, beta, alpha
• what is nuclear fission?

  the splitting of large unstable nuclei to form more smaller stable nuclei