physical science 9 - rio hondo prep

0804 Chapter 7.2 1

Physical

Science 9 Fusion and Fission

0804 Chapter 7.2 2

Physical


In 1939, two German scientists

were attempting to make heavier

nuclei by bombarding uranium

atoms with neutrons.

Otto Hahn and Fritz Strassman

totally failed in their attempt.

However, they discovered

something very interesting…

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Instead of creating heavier

nuclei, they actually produced

smaller atoms.

After reviewing their data, others

discovered that the neutrons that

had been fired at the atoms had

SPLIT the atoms.

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It was from this experiment (and

others) that scientists

discovered that a strong nuclear

force held the particles in the

nucleus together.

This force was greater

than the repulsion of the

positively charged

protons. A Japanese

chemist, Hideki Yukawa,

was the first to realize

this.

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However, there is a limit to the

amount of neutrons an atom can

hold before it becomes

unstable.

Unstable atoms

undergo decay.

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Fission occurs when a nucleus splits into two

or more fragments, releasing neutrons and

energy.

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The energy released by a fission reaction is

twice as much as the energy released by the

explosion of TNT,

After a fission reaction, the amount of mass

of the products is less than the mass of the

reactants. This seems to violate the law of

conservation of matter, but Albert Einstein

was able to explain the missing mass with

his mass energy equation…

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Physical


E=mc2

The energy released is

equal to the mass time the

speed of light squared!

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E=mc2

This equation states that if you were to

convert 1kg of matter into energy, it would

produce 9 x 1016 J of energy – equivalent to 8

million TONS of TNT.

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E=mc2

Putting that into perspective, 1 gram (about

the weight of a one dollar bill) converted to

energy would produce enough energy to

provide electricity to Arcadia for about 2

weeks.

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Fission only takes place if the neutrons are

moving slow enough. To slow down the

neutrons, graphite rods and water are used.

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If you have a high enough concentration of

uranium, the released neutrons can go on to

split other Uranium nuclei, causing a chain

reaction.

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If you have a high enough concentration of

uranium, the released neutrons can go on to

split other Uranium nuclei, causing a chain

reaction.

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Fission is used in nuclear power plants, as

well as in atomic weapons.

Two separate masses

of U-235 are kept

separate in a bomb.

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When the bomb is

detonated, explosives

are used to jam the

two masses together.

If the combined

masses exceed the

“critical mass”, a chain

fission chain reaction

will occur.

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Fortunately, the amount of Uranium-235

found in nature is very low; regular Uranium

must be “enriched” with extra neutrons in

order to become U-235.

There are very few countries in the world with

the technology to enrich Uranium; so only a

few countries are able to build nuclear

weapons.

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Science 9 Countries with Nuclear Weapons

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Science 9 Fusion Nuclear Reactors

Nuclear radiation can be

beneficial. Nuclear

reactors are used by

many countries to

generate electricity.

Although not as clean as

hydro power, wind or

solar power, it is far

better for the

environment than coal

burning power plants.

San Onofre

Arizona

Coal

Power

Plant

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Physical

Science 9 Fusion Nuclear Reactors

California has banned

coal burning power

plants, and does not

purchase power from

coal burning power

plants in other states.

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Physical

Science 9

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Physical

Science 9

Fusion

Fission is relatively easy to do. Fusion

reactions are much more difficult to start and

sustain.

Fusion occurs when very light nuclei

combine at extremely high temperatures to

form heavier nuclei.

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Physical

Science 9

Fusion

Fusion reaction produce tremendous amounts

of energy as well.

Stars (like our sun) use fusion reactions to

produce energy that warms our planet.

Solar fusion involves “fusing” four hydrogen

nuclei together to form a heavier helium and

an enormous amount of electromagnetic

radiation.

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Science 9

Fusion

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Physical

Science 9

Fusion

Fusion requires a tremendous amount of

energy to start and sustain a reaction, so its

use has yet to be viable on Earth.

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Physical

Science 9

Fusion

physical science 9 - rio hondo prep

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