RADIOACTIVITY

RADIOACTIVITY

1. at the centre of every atom is a nucleus

   • contains protons and neutrons
   • makes up most of the mass of the atom
   • takes up virtually no space
   • really small

2. isotopes are atoms with different numbers of neutrons

   • same atomic number
   • different mass number
   • usually each element has only one or 2 stable isotopes like carbon 12
     • does not emit radioactive material
   • other isotopes tend to be radioactive
     • nucleus is unstable
     • it decays and emits radiation
     • carbon 14 is an unstable isotope of carbon

3. radioactive decay is a radom process

   • it is unaffected by physical conditions like temperature or chemical bonding
   • when it does decay it spits out one or more of the 3 types of radiation
     • beta
     • gamma
     • alpha
   • in the process the nucleus often changes into a new element

4. background radiation is everywhere all the time

   • substances here on earth
     • food
     • air
     • building materials
     • soil
     • rocks
   • radiation from space
     • cosmic rays
       • come from sun
   • living things
     • little bit of radioactive material in all things
   • radiation due to human acivity
     • nuclear waste
       • small proportion

5. nuclear radiation causes ionisation

   • by bashing into atoms and knocking off the electrons
   • atoms with no overall charge are turned into ions which are charged
   • the further the radiation can penetrate before hitting an atom and getting stopped the less damage it will do along the way and so the less ionising it is
   • we can detect ionising radiation with photographic film or a Geiger muller detector

6. alpha particles

   • helium nuclei
   • 2 protons and 2 neutrons
   • big, heavy and slow moving
   • don't penetrate far into materials but are stopped quickly
   • strongly ionising
     • bash into a lot of atoms and knock electrons off them before they slow down which creates lots of ions
   • electrically charge +
   • are deflected by electric and magnetic fields
   • the emition of a alpha particle decreases the atomic number of the nucleus by 2 and the mass number by 4

7. beta particles

   • electrons
   • when it has been emitted the nass numbers stays the same but the atomic number increase by 1
   • move quite fast
   • quite small
   • they penetrate moderately before colliding and are moderately ionising too
   • negatively charged
   • deflected by electric and magnetic fields

8. gamma rays

   • very short em waves
   • no mass
   • just energy
   • penetrate a long way into materials without being stopped
   • weakly ionising
   • no charge
   • not deflected by electric or magnetic fields
   • has no effect on the atomic or mass numbers of the isotope

9. you can identify the type by its penetrating power

   • alpha
     • blocked by paper, skin or a few cm of air
   • beta particles are stopped by thin metal
   • gamma
     • thick lead or very thick oncrete

10. half life

    • the time it takes for half of the radioactive atoms now present to decay
    • the older the sample the less radiation it will emit
    • a short half life
      • the activity falls quickly because there is lots of nuclei decay quickly
    • long half life
      • activity falls slower

11. uses of nuclear radiation

    • medical tracer use beta or gamma radiation
      • a source is injected into the patient
        • the radiation penetrates the body tissues and can be detected externally
          • as it move the radiographer can use a detector to monitor the progress or to get a snap shot of its distribution
            • a computer converts the reading to an on screen display showing where the radiation is coming from
              • doctors se it to check whether the organs of the body are working as they should
              • the radioactive source has to have a short half life so you can use less of the radioactive source you still get a reading on the detector
                • an alpha source would be worse than useless as a medical tracer useless because it would be stopped by the body tissues so you con never detect it externally
                • it's strong ionising power makes alpha radiation really harmful if it gets inside you
    • gamma radiation is used in industrial tracers
      • squirt a gamma source into the pipe
        • let it flow down the pipe
          • go along the outside with a detector
            • gamma radiation will penetrate through a metal pipe but some of it is absorbed
              • if there is a crack the gamma source will collect outside the pipe and your detector will show extra high radioactivity
      • must be a gamma emitter so that the radiation can be detected even through any rocks or earth surrounding the pipe alpha and beta radiation would be too easily blocked
      • should have a short half life so it will not cause a long term hazard if it collects somewhere
    • radioactive dating of rocks and archaeological specimens
      • work out he age of rocks, fossils and archaeological specimins
      • compare the relative proportion of potassium 40 to trapped argon gas

12. ionising radiation can damage cells and tissues

    • beta and gamma can penetrate the skin and soft tissues to reach the delicate organs inside the body
    • this makes beta and gamma sources more hazardous than alpha when outside the body
    • if they get inside the body their radiation mostly passes straight out without doing much damage
    • alapha radiation can't penetrate the skin but it is very dangerous if it gets inside the body
    • alpha sources do all their damage in a very localised area
    • lower doses tend to cause minor damage without killing the cell
      • this can cause mutation in cells which then divide uncontrollably
        • this is cancer
    • higher doses tend to kill cells completely causing radiation sickness if a large part of your body is affected at the same time
    • the extent of the harmful effects depends on how much exposure you have to the radiation and its energy and penetration

13. radiation is also used to treat cancer

    • radiotherapy
      • used to kill the cancer cells and stop them divinging
      • high dose of gamma rayse
      • carefully directed to zap the cells in the tumour while minimising the dose to the rest of the body

14. radioactive waste is difficult to dispose of sfely

    • most radioactive waste from nuclear power stations and hospitals is low level slightly radioactive
      • clothing ,syringes
      • disposed of burying in a secure landfill site
    • high level
      • really dangerous stuff
      • stay reactive for tens of thousands of years
      • disposed how
        • sealed in glass blocks and then into metal canisters
          • buried deep underground
            • needs to be geographically stabel
              • no earthquakes
              • so none is leaked out
              • not in groundwater
                • could contaminate the soil, plants, rivers etc. and get into the drinking water

15. use protection if you are working with radioactive materials

    • no skin contact
    • always hold d with tongs and at arm's length
    • keep the source pointed away from the body and avoid looking at it directly
    • keep in sealed lead box when ever they are not being used

16. people who regularly need to take extra precautions

    • wearer lead aprons
    • stand behind lead screens during procedure
    • industrial
      • full protective suits
    • workers
      • use remote controlled robot arms

17. nuclear power stations use nuclear fission

    • nuclear fission is the splitting of an atom which releases energy
    • powered by nuclear reactors
    • controlled chain reaction

18. fission chain reactions

    • the fuel that split in a nuclear reactor is usually uranium 235
    • if a slow moving neutron gets absorbed by a uranium 235 nucleus the nucleus can split
    • each time a uranium 235 splits up it releases a small number of neutrons and it is repeated again and again
      • chain reaction
      • also releases 2 daughter nuclei
        • lighter elements than uranium
          • very reactive
            • means that it is expensive to dispose of safely
    • each nucleus splitting gives out energy
      • converted to heat energy in the reactor by collisions with other atoms

19. nuclear reactor

    • free neutrons in the reactor start the fission process
    • the atoms produced then collide with other atoms causing the temp to rise
    • the moderator slows neutrons so they collide with uranium nuclei and sustain the chain reaction
    • control rods
      • made of boron
      • limit the rate of fission by absorbing excels neutrons
    • co2 is pumped through the reactor to carry out heat generatoed
    • turbine tuns producing electricity