Alpha Decay

parent nucleus daughter nucleus

HeThU 42

23490

23892

Atomic number: -2mass number: -4

Beta Decay

How does electron emit from nucleus?

epn 01

11

10

Beta decay

Atomic number: +1

mass number: no change

ePaTh 01

23491

23490

Gamma

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

Random Decay

The process of disintegration is random 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

Radon-220 52s Sodium-24 15 hours Iodine-131 8 days Carbon-14 5600 years Uranium-235 700000000 years

Activity

When the no. of radioactive nuclei decreases, the rate of radiation emission also decreases.

Activity = no. of disintegration per second unit : Bq (becquerel)

Use of Radioisotope

Radiotherapy Tracer Sterilisation Thickness gauge Smoke detector Carbon dating

Radiotherapy

Kill cancer cells Circular treatment Use gamma: high penetrating power

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

Sterilisation

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

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

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.

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.

Use of Radioisotope

Radiotherapy Tracer Sterilization Thickness gauge Smoke detector Carbon dating Nuclear energy

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

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.

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

Nuclear Reactor

Nuclear Reactor

Fuel element: uranium rod moderator:

• keep neutron at suitable speed of fission (slow speed)

control rod• absorb neutrons• control rate of reaction

Safety of Nuclear Reactor

Thick reactor building Thick steel reactor Control rod Use pressurized water to avoid boiling

Monitor nearby surrounding’s background radiation.

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

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

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