Nuclear Fission

Prepared By Irtasam

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A Brief History

• Otto Hahn: Germany-Nobel Prize winner famous for his discovery of nuclear fission.

• Fritz Strassmann: German chemist who, with Otto Hahn in 1938, identified barium in the residue after bombarding uranium with neutrons.

• Enrico Fermi: Italy-Nobel Prize winner and famous for creating the world's first nuclear chain reaction.

What is Fission?• Fission is another word for splitting.

• It means division or splitting into two or more parts.

• In general, If a heavy particle or object splits into two or

more parts or fragments it is called fission.

Analogy

•  Nuclear Fission is similar to a liquid drop when excess energy is added to it .•When a liquid drop is given vibratory motion it

undergoes elongation and compression.•When vibrations become very fast the drop

splits into two.• Similar is the case of Uranium-235

Liquid Drop Model Fission

Nuclear Fission• When a nucleus(usually Uranium-235 fissions, it splits into

several smaller fragments.• These fragments, or fission products, are about equal to half

the original mass.• Two or three neutrons are also emitted.• The sum of the masses of these fragments is less than the

original mass.• This 'missing' mass has been converted into energy according

to Einstein's equation.• Fission can occur when a nucleus of a heavy atom captures a

neutron, or it can happen spontaneously.

Diagram

+Energy

Neutrons may1 - Cause another fission by colliding with a U235 nucleus

2 - Be absorbed in other material3 - Lost in the system

If sufficient neutrons are present, we may achieve a chain reaction

Each split (fission) is accompanied by a large quantity of E-N-E-R-G-Y

• Creates two smaller nuclides and free neutrons.• The free neutrons potentially collide with nearby U235 nuclei

Steps In Nuclear Fission• The 235U nucleus captures a thermal (slow-moving)

neutron.• The capture results in the formation of 236U*, and

the excess energy of this nucleus causes it to undergo violent oscillations.• The 236U* nucleus becomes highly elongated, and

the force of repulsion between protons in the two halves of the dumbbell-shaped nucleus tends to increase the distortion.• The nucleus splits into two fragments, emitting

several neutrons in the process.

FISSION CAN BE USED

• GOOD• A controlled chain reaction in a reactor used in

nuclear power plants to produce electricity.

• EVIL• An uncontrolled chain reaction is used to

create incredibly powerful weapons – the atomic bombs dropped on Japan.

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A neutron travels at slow speed towards a uranium-235 nucleus

The Fission Process

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A neutron travels at slow speed towards a uranium-235 nucleus

The Fission Process

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A neutron travels at slow speed towards a uranium-235 nucleus

The Fission Process

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The neutron strikes the nucleus which then captures the neutron

The Fission Process

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The nucleus changes from being uranium-235 to uranium-236 as it has captured a neutron

The Fission Process

The uranium-236 nucleus formed is very unstable It transforms into an elongated shape for a short time

The Fission Process

The Fission Process

It transforms into an elongated shape for a short time

The uranium-236 nucleus formed is very unstable

The Fission Process

It transforms into an elongated shape for a short time

The uranium-236 nucleus formed is very unstable

It then splits into 2 fission fragments and releases neutrons

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The Fission Process

It then splits into 2 fission fragments and releases neutrons

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The Fission Process

It then splits into 2 fission fragments and releases neutrons

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The Fission Process

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The Fission ProcessThe mass that was “lost” became energy