alpha decay parent nucleus daughter nucleus atomic number: -2 mass number: -4
TRANSCRIPT
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Alpha Decay
parent nucleus daughter nucleus
HeThU 42
23490
23892
Atomic number: -2mass number: -4
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Beta Decay
How does electron emit from nucleus?
epn 01
11
10
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Beta decay
Atomic number: +1
mass number: no change
ePaTh 01
23491
23490
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Gamma
Waves are emitted from the nucleus atomic number and mass number no change
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Random Decay
The process of disintegration is random The no. of radioactive nuclei decreases
No. of radioactive nuclei
time
Decay curve
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Half Life
The half life is the time for half of the radioactive nuclei to decay.
No. of radioactive nuclei
time
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Half Life
Radon-220 52s Sodium-24 15 hours Iodine-131 8 days Carbon-14 5600 years Uranium-235 700000000 years
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Activity
When the no. of radioactive nuclei decreases, the rate of radiation emission also decreases.
Activity = no. of disintegration per second unit : Bq (becquerel)
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Use of Radioisotope
Radiotherapy Tracer Sterilisation Thickness gauge Smoke detector Carbon dating
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Radiotherapy
Kill cancer cells Circular treatment Use gamma: high penetrating power
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Tracer
Inject radioactive source into body Let the body absorb the radioactive source Detect the radiation outside body
• e.g. Iodine-131 to detect thyroid gland
Sodium-24 to detect blood clot
Use gamma or beta: penetrate through body Short half life: several hours to several days
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Sterilisation
Use radiation to kill bacteria in food Sterilize syringes Use gamma ray: high penetrating power
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Thickness Gauge
Check thickness of materials Use beta ray If too thin, more beta particle penetrate
through and the count rate increase If too thick, less beta particle penetrate
through and the count rate decrease
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Smoke Detector
Radioactive source produces ions in both chamber
two equal current produced If there is fire, more ions enter the open
chamber. Two current not equal. Alarm on.
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Carbon-14 Dating
Every living things contain C-12 and C-14 with specific ratio.
When living things died, C-14 decays and become less and less.
Ratio of C-12 and C-14 can be used in archaeological dating.
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Use of Radioisotope
Radiotherapy Tracer Sterilization Thickness gauge Smoke detector Carbon dating Nuclear energy
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Nuclear Fission
When neutron bombard uranium nucleus, it splits into smaller parts.
Energy is released in the process.
This is called fission. 1kg uranium releases 100000000000000J
energynnKrBanU 10
10
9036
14456
10
23592
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Chain Reaction The neutrons emitting in the
fission can cause more uranium nucleus to have fission.
Chain reaction takes place very quickly if the mass is larger than the critical mass.
Huge amount of energy will be released.
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Atomic Bomb vs Nuclear Reactor
Atomic Bomb: uncontrolled fission
Nuclear reactor: controlled fission• fission heat up water• hot water boils secondary water• steam turns turbine of generator
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Nuclear Reactor
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Nuclear Reactor
Fuel element: uranium rod moderator:
• keep neutron at suitable speed of fission (slow speed)
control rod• absorb neutrons• control rate of reaction
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Safety of Nuclear Reactor
Thick reactor building Thick steel reactor Control rod Use pressurized water to avoid boiling
Monitor nearby surrounding’s background radiation.
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Fusion
When two light nuclei join together to form heavy nucleus, energy is released.
This is called fusion. 1kg of hydrogen gives 600000000000000J.
energynHeHH 10
42
31
21
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Fusion’s Adv. And Disadv.
Advantage: • many fuel• less pollution• more energy released
Disadvantage: • requires very high temperature (like the Sun)• difficult to find container
Uncontrolled fusion: hydrogen bomb• Start by atomic bomb
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Nuclear Energy Debate Pros
• Solve world’s energy problem• Cheaper than coal or oil• Less pollution than coal or oil
Cons• Unacceptable hazard if exploded• Many nuclear waste• Lead to nuclear weapon, nuclear war• Other better energy resources available