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Atoms

Life Cycle of Stars
1. clouds of DUST & GAS - gravity makes gas/dust spiral together = protostar
  1. gravitational energy converted to heat energy = temp. rises - when temp.'s high enough, hydrogen nuclei - nuclear fusion = helium nuclei = heat & light
    1. long stable period - heat created = outward pressure to balance gravity pulling inwards - millions of years - massive amounts of hydrogen = MAIN SEQUENCE STARS
      1. eventually hydrogen = runs out - stars swells = RED GIANT (small star) - RED SUPER GIANT (big star)
        small-medium star (like Sun) - becomes unstable & ejects outer layer of dust & gas as PLANETARY NEBULA
        hot dense solid core = WHITE DWARF - cools down = BLACK DWARF - disappears
        big stars - glows brightly again - fusion & expand/contract several times = heavy elements like iron in nuclear reactions - explode in SUPERNOVA (=elements heavier than iron) - ejects to form new planets & stars
        exploding supernova - throws outer layer of dust & gas - very dense core - NEUTRON STAR - star = big enough = BLACK HOLE
HALF-LIFE = AVERAGE TIME it takes for the NUMBER OF NUCLEI in RADIOACTIVE ISOTOPE SAMPLE to HALVE
1. time it takes for count rate to halve
Nuclear Fission & Fusion
1. Nuclear Fission - Splitting Up - big nuclei
  1. nuclear power station - nuclear reactors - uranium-235/plutonium-239
    1. chain reaction = nuclei split up & release heat energy - heats water - steam turbine - generator
2. Chain Reactions
  1. slow moving neutron - absorbed by nucleus - unstable nucleus = split
    1. uranium/plutonium splits up - two/tree neutrons released = hit another nucleus = split = chain reaction
      1. two new smaller nuclei = radioactive - "wrong" no. of neutrons
        splitting (fission) = lots of energy
3. Nuclear Fusion - Joining - small nuclei
  1. light nuclei (e.g. hydrogen) - join
    1. releases lots of energy (- more than fission)
  2. energy from stars - from fusion
  3. less radioactive waste - plenty of hydrogen as fuel
  4. big problem = high temp. - 10 million°C
    1. need strong magnetic field - to hold hydrogen at high temps/pressure
Ionising Radiation
1. radioactive isotopes - decay into other elements & give out radiation
2. Radioactive = Random
  1. radioactive substances - give out radiation from nuclei - no matter what's done to them
  2. can't say when any one of them will decay & can't make decay happen
    1. unaffected by physical conditions - temp. & chemical bonding
  3. spit out - alpha/beta/gamma
3. Background Radiation - present always
  1. 1. unstable isotopes - all around us - air, food, building materials & rocks
  2. 2. space - cosmic rays - the Sun
  3. 3. man-made sources - nuclear accidents / dumped nuclear waste
4. Alpha Particle = helium nucleus - big/heavy/slow moving
  1. don't penetrate far - stopped quickly - even in air
  2. strongly ionising - bash into & knock electrons off
5. Beta Particle = Electrons - quite fast
  1. penetrate moderately - long range in air - moderately ionising
  2. for each b-particle - neutron → proton
6. Gamma Rays = Short EM Waves
  1. penetrate far into materials - straight through air
  2. weakly ionising - only pass through (don't bash)
7. Radiation Damage Depends on Radiation Dose = higher risk of cancer
  1. underground rocks - can release radioactive radon gas - gets trapped in houses
  2. nuclear industry & uranium miners - 10 times - protective clothing/face masks - no touch/inhale - monitor with regular check-ups
  3. radiographers - lead aprons - stand behind lead screens - no prolonged exposure
  4. high altitudes (- jet planes) - cosmic rays - pilots risk
8. Alpha&Beta - Deflected by Electric & Magnetic Fields
  1. alpha = larger charge & feel greater force - deflected less - greater mass
Atomic Structure
1. J J Thompson - "plum pudding" - atoms = spheres of positive charge with electrons stuck in them
  1. Rutherford & Marsden - fired alpha particles at thin gold foil - positively charged alpha would slightly deflect
  2. most went straight through but few bounced back = shocking
    1. most atom mass = centre in nucleus most atom = empty space
2. Nuclear Model
  1. radius of nucleus = 10 000 times smaller than atom radius

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