atomic structure

• radius of an atom

  
  

  $1\cdot\ 10^{-10\ }m$
• radius of an nucleus

  
  

  less than 1/10000 of the radius of an atom
• nucleus is where most of the mass is concentrated
• energy levels futher away from the nucleus have alot of energy
• when electrons absorbs electromagnetic radiation (eg. light) electrons move to a higher energy level
• when an atom emits electromagnetic radiation the electrons return back and move to a lower energy level
• radioactive decay happens when an isotope with an unstable nucleus emits radiation to become stable
• carbon 14 is an example of a radioactive isotope
• radioactive decay is a random process
• ACTIVITY

  • activity is the rate at which an unstable nucleus decays
  • it is measured in bequerels
  • 1Bq = 1 decay per second
• activity can be measured using a geiger-muller tube
• count rate is the number of decays recorded each second by a detector
• alpha particles ( $\alpha$ )

  • same as a helium nucleus
  • 2 protons
  • 2 electrons
• beta particles ( $\beta$ )

  • electron ejected from the nucleus at high speeds
  • formed whena neutron turns into a proton then an electron
• gamma ray ( $\gamma$ )

  • electromagnetic radiation
• another example of a type radiation emitted are neutrons
• beta particle:

  • travels 15cm in air
  • stopped by a mm of aluminium
  • quite strongly ionising
• gamma rays:

  • travels several metres
  • stopped by several cm of lead
  • weakly ionising
• alpha decay

  • loses $He^4_2$
  • mass number decreases by 4
  • atomic number decreases by 2
• beta decay

  • emits $e^0_{-1}$
  • mass number stays the same
  • atomic number increases by 1
• half-life

  • time taken for number of nuclei to halve
  • time taken for coun rate (or activity) to halve
• radiation can be ionising this can increase the risk of cancer
• precautions of ionising radiation

  • for alpha radiation wear gloves
  • for beta and gamma radiation wear a lead apron
  • using a moniter to see how much radiation is being recieved
• contamination

  • alpha particles are highly ionising but easily stopped from entering by your skin cells however it is very dangerous when inhaled or swallowed
  • beta particles are less ionising but highly penetrating
  • gamma rays are weakly ionising and pass in and out the body
• peer review:

  • scientists explore the effects of radiation
  • they publish and share their findings
  • the findings are then checked by other scientists
• geiger-muller tubes can detect back round radiation
• natural sources of backround radiation:

  • certain rocks such as granite
  • cosmic rays from space
• man-made sources of backround radiation:

  • nuclear weapons testing
  • nuclear accidents
  • medecine
• doses of radiation is measured by

  • sieverts (Sv)
• exploring internal organs using a tracer :

  • eg. to check the thyroid glands which absorb iodine
  • patients drink radioactive iodine which emit gamma rays
  • too much or too little absorption will indicate an illness
• you can even do a bone scan using tracers to find tumours
• a controlled chain reaction is used in nucleus reactors
• uncontrolled chain reactions are used in nuclear explosions
• nuclear fusion

  • 2 light nuclei (hygdrogen) join to form a heavier nuclei
  • some of the mass is converted into energy which is released as radiation
  • this is the process that releases energy in stars like the sun
  • this is not a chain reaction
• what effects exposure:

  • occupation - cabin crew exposed to cosmic rays
  • location - cornwall
• irradiation

  • irradiation is when an object is exposed to radiation
  • the object does not become radioactive
  • irradiation is used to sterilise medical equipment if it cant be heated up
• issues with tracers:

  • they must emit radiation that can pass in and out the body
  • must not be highly ionising
  • must not decay into another radioactive isotope
  • must have a short half life
• contamination

  • contamination is when unwanted radioactive isotopes end up on other materials
  • this is hazardous and will decay leading to ionising radiation
• radiotherapy:

  • destroy cancers
  • gamma rays destroy cancers
  • ! - healthy tissues may be damaged
  • radioactive rods inserted will cause less damage to healthy tissues
• alpha particles:

  • travels only 5cm in the air
  • stopped by paper
  • highly ionising