Alpha Decay parent nucleus daughter nucleus Atomic number: -2 mass number: -4

Beta Decay w How does electron emit from nucleus?

Beta decay Atomic number: +1 mass number: no change

Gamma w Waves are emitted from the nucleus w atomic number and mass number no change

Random Decay w The process of disintegration is random w The no. of radioactive nuclei decreases No. of radioactive nuclei time Decay curve

Half Life The half life is the time for half of the radioactive nuclei to decay. No. of radioactive nuclei time

Half Life w Radon s w Sodium-2415 hours w Iodine-1318 days w Carbon years w Uranium years

Activity w When the no. of radioactive nuclei decreases, the rate of radiation emission also decreases. w Activity = no. of disintegration per second w unit : Bq (becquerel)

Use of Radioisotope w Radiotherapy w Tracer w Sterilisation w Thickness gauge w Smoke detector w Carbon dating

Radiotherapy w Kill cancer cells w Circular treatment w Use gamma: high penetrating power

Tracer w Inject radioactive source into body w Let the body absorb the radioactive source w Detect the radiation outside body e.g. Iodine-131 to detect thyroid gland Sodium-24 to detect blood clot w Use gamma or beta: penetrate through body w Short half life: several hours to several days

Sterilisation w Use radiation to kill bacteria in food w Sterilize syringes w Use gamma ray: high penetrating power

Thickness Gauge w Check thickness of materials w Use beta ray w If too thin, more beta particle penetrate through and the count rate increase w If too thick, less beta particle penetrate through and the count rate decrease

Smoke Detector w Radioactive source produces ions in both chamber w two equal current produced w If there is fire, more ions enter the open chamber. Two current not equal. w Alarm on.

Carbon-14 Dating w Every living things contain C-12 and C-14 with specific ratio. w When living things died, C-14 decays and become less and less. w Ratio of C-12 and C-14 can be used in archaeological dating.

Use of Radioisotope w Radiotherapy w Tracer w Sterilization w Thickness gauge w Smoke detector w Carbon dating w Nuclear energy

Nuclear Fission w When neutron bombard uranium nucleus, it splits into smaller parts. w Energy is released in the process. w This is called fission. w 1kg uranium releases J

Chain Reaction w The neutrons emitting in the fission can cause more uranium nucleus to have fission. w Chain reaction takes place very quickly if the mass is larger than the critical mass. w Huge amount of energy will be released.

Atomic Bomb vs Nuclear Reactor w Atomic Bomb: uncontrolled fission w Nuclear reactor: controlled fission fission heat up water hot water boils secondary water steam turns turbine of generator

Nuclear Reactor

w Fuel element: uranium rod w moderator: keep neutron at suitable speed of fission (slow speed) w control rod absorb neutrons control rate of reaction

Safety of Nuclear Reactor w Thick reactor building w Thick steel reactor w Control rod w Use pressurized water to avoid boiling w Monitor nearby surrounding’s background radiation.

Fusion w When two light nuclei join together to form heavy nucleus, energy is released. w This is called fusion. w 1kg of hydrogen gives J.

Fusion’s Adv. And Disadv. w Advantage: many fuel less pollution more energy released w Disadvantage: requires very high temperature (like the Sun) difficult to find container w Uncontrolled fusion: hydrogen bomb Start by atomic bomb

Nuclear Energy Debate w Pros Solve world’s energy problem Cheaper than coal or oil Less pollution than coal or oil w Cons Unacceptable hazard if exploded Many nuclear waste Lead to nuclear weapon, nuclear war Other better energy resources available