Physics module 2- Radiation

Physics module 2- Radiation

1. nuclear radiation

   • causes ionisation
     • when an unstable nucleus decays, it gives off one or more kinds of nuclear radiation
       • radioactive materials- give out nuclear radiation over time
         • alpha,beta and gamma
           • cause ionisation- radiation causes atoms to lose or gain electrons, turning those atoms into ions
             • ionisation can trigger chemical reactions
               • when radiation enters human cells it can ionise molecules and damage DNA
                 • causes mutations in cells that could lead to cancer
                   • the further the radiation can penetrate before hitting an atom, the less ionising it is
   • alpha particles
     • relatively big, heavy and slow moving
       • because of size-stopped quickly
         • stopped by skin or paper
           • means they're strongly ionising, less penetrating
             • bash into loads of atoms and knock electrons off them before they slow down
   • beta particles
     • electrons
       • they're small and move quite fast
         • penetrate moderately before colliding-moderately ionising, moderately penetraing
           • stopped by thin sheet of metal- few millimetres of aluminium
   • gamma rays
     • very high frequency electromagnetic waves
       • no mass and no charge
         • they can penetrate a long way into materials without being stopped
           • weakly ionising, most penetrating
             • stopped by thick concrete or a few centimetres of lead
   • radiation source and Geiger counter to test(detector)

2. radiation- the emission of energy as electromagnetic waves and particles from a source

3. how smoke detectors work

   • smoke detectors use alpha radiation
     • air is ionised so it conducts a very small current
       • current flows between the two electrodes
         • if smoke particles get in they will block the alpha particles so there is less ionisation
           • electric current will decrease, the circuit breaks
             • causing alarm to go off

4. uses

   • prepare a tracer
     • chemical which accumulates in target organ and emits gamma rays e.g radiopharmaceutical
       • inject into patient-time to flow around blood stream
         • patient is scanned by gamma camera-external radiation detector
           • show where strongest reading is coming from
             • doctors use beta or gamma emitters as tracers because this radiation passes out of the body
               • they also choose things that are only radioactive for a few hours- alpha never used
   • beta radiation is used in thickness control (thickness gauges)
     • direct radiation through the stuff being made (paper or cardboard)
       • and put a detector on the other side, connected to a control unit
         • when the amount of detected radiation goes down, it means the paper is coming out too thick
           • so the control unit pinches the rollers to make it thinner
             • if the reading goes up-paper is too thin, control unit opens the rollers out a bit
               • for this use, your radioactive substance mustn't decay away too quickly
                 • otherwise its strength would gradually fall- the control unit would keep pinching up the rollers trying to compensate
                   • you need to use a beta source- the paper or cardboard will partly block the radiation
                     • if it all goes through( or none of it does) then the reading wont change at all as the thickness changes
               • less radiation being absorbed
           • more radiation is being absorbed

5. medical and industrial uses

   • high doses of gamma rays will kill all living cells-used to treat cancer
     • rays have to be directed carefully so tumour recieves high dosage, but given in small doses, without damaging normal cells-radiotherapy
       • used to sterilise medical instruments-killing all microbes
         • need to use a strongly radioactive source that lasts a long time-doesn't need replacing too often
           • also used for non-destructive testing
             • airlines can check turbine blades of their jet engines
               • directing gamma rays at them
                 • if too much radiation gets through the blade to the detector
                   • know blade is cracked or there's a fault in the welding

6. Nuclear power

   • uses uranium as fuel
     • but with nuclear fission producing the heat to make steam
       • difference is in the boiler
         • atoms in the nuclear fuel( uranium) are split in to two- releasing lots of heat energy
           • water is used as a coolant to take away the heat produced by the fission process
             • this heat is used to produce steam to drive a turbine and generator
   • advanatges
     • make lots of energy without releasing Co2
       • nuclear reactions release a lot more energy than chemical reactions
         • e.g burning so it takes a lot less uranium to produce the same amount of power as fossil fuel
           • nuclear fuel is relatively cheap
             • still plenty of uranium left in the ground
   • disadvantages
     • expensive to build and maintain
       • longer to start up NP stations than FF power stations
         • processing the uranium before you start causes pollution
           • always a risk of leaks of radioactive material or even major - like chernobyl disaster
             • cause cancer and sickness
             • radioactive waste-difficult to dispose of and reprocess
               • when the stations are too old/ inefficient- have to be decommissioned- expensive
                 • uranium is non renewable source
                   • lot of money and energy to make it suitable for use in a reactor
               • when used uranium fuel is reprocessed
                 • left with more uranium and plutonium
                   • can reuse uranium in the power station
                     • plutonium can be used to make nuclear bombs

7. danger from radioactive material

   • radioactive sources stored in labelled lead box- can only be short amount of exposure
     • handle with tongs-never skin
       • keep at arms length, pointing away and avoid directly looking at it
         • industrial nuclear workers wear full protective suits to prevent tiny radioactive particles being inhaled
           • or lodging on the skin or under fingernails
             • lead lined suits, lead/concrete barriers and thick lead screens shield workers from gamma rays in highly radioactive areas
               • workers use remote controlled robot arms- tasks in highly radioactive areas
   • low level waste
     • paper,clothing,gloves,syringes etc from stations and hospitals
       • disposed of by burying it in secure landfill sits
         • high level waste
           • stays highly radioactive for tens of thousand of years
             • sealed in glass boxes then sealed in metal canisters-could be buried deep underground
               • difficult to find suitable places
                 • site has to be geologically stable-not prone to earthquakes- in case disturbance and leakage
                   • if material gets in to ground water- contaminate the soil, plants, rivers etc- get in to drinking water
                     • when do find suitable sites-people nearby object
                       • so at the moment, high level waste is kept on site at nuclear power stations
                       • some is reprocessed to reclaim useful radioactive material- but even this leaves waste behind
   • security
     • high fences and security checks on people going in and out
       • still target for terrorists
         • use stolen radioactive material-make bombs
           • strict regulations on how we dispose
             • rules could change- what might be low level waste could be high level in the future

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