Nuclear Fusion and Fission

Nuclear Fission• Division of Nuclei– Splitting of nucleus into

smaller fragments when bombarded with neutrons

– This is the reaction that takes place in nuclear reactors such as the one in San Onofre

Nuclear Fusion

• The combination or addition of nuclei– The reaction that powers the sun

Energy Released:

• Matter can be changed into energy.

E = mc2

• E = energy• m = mass• c = speed of light

The energy released by fusion is three to four times greater than the energy released by fission.

Why? The amount of mass transformed into energy is that much greater in a fusion reaction than in a fission reaction.

E = mc2

Nuclear Force

The nucleus is held together by the strong nuclear force.

• The strong nuclear force acts between:– protons– neutrons– protons and neutrons

Nuclear Force• Has a limited range comparable to the size of

an atomic nucleus. • Able to overcome the mutual electrostatic

repulsion of the protons only when the protons and neutrons are near each other as they are in the nucleus of an atom.

Fission Bombs

• Fission bomb : assemble a supercritical mass of fissile material, and a chain reaction will rapidly produce neutrons that, in turn, generate more fission and neutrons.

• The challenge is to bring two subcritical masses together quickly before the energy released by the initial fission blows the masses apart and stops the chain reaction.

The physicists had to answer two fundamental questions: how much fissile material would be required for the weapons, and how much time would be needed for an effective detonation.

Fusion Bombs

• H-Bombs– Rely on the fusion of the

isotopes of hydrogen

Radiation in Your Life

3 methods of Identifying Radiation:– Geiger Counter: Detects Beta radiation– Scintillation counter: Detects all types of radiation – Film Badge: Layers of photographic film that can

be developed to determine strength and type of radiation

Applications of radioisotopes in research and medicine

• Tracers– Used to study chemical reaction mechanisms– Test effects in agriculture

• Diagnose diseases (Iodine – thyroid problems)• Treatment of cancer

The End