P2 Energy from the nucleus

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  • Created by: Phoebe
  • Created on: 05-01-13 13:42

7.1 Nuclear fission

Nuclear fission is the splitting of a nucleus into two approximately equal and smaller nuclei and the release of two or three neutrons.

Nuclear fission occurs when a neutron hits a uranium-235 or plutonium-239 nucleus and the nucleus splits.

A chain reaction occurs when neutrons from the fission cause further fission events.

In a nuclear reactor, control rods absorb fission neutrons to ensure that, on average, only one neutron per fission goes on to produce further fission.

URANIUM-235 is closer to earth, PLUTONIUM-239 is four behind?

"Enriched" uranium contains 2-3% uranium-235

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7.2 Nuclear fusion

Nuclear fusion is the process of forcing two nuclei close enough together so they form a single, larger nucleus.

Nuclear fusion can be brought about by making two light nuclei collide at very high speed.

Energy is released when two light nuclei are fused together. Nuclear fusion in the Sun's core creates energy.

A fusion reactor needs to be at a very high temperature before nuclear fusion can take place.

The nuclei to be fused are very difficult to contain - they have to be contained by a magnetic field.

Nuclei approaching each other will repel one another due to their positive charges - they must be heated to very high temperatures to have enough energy to fuse.

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7.3 Nuclear issues

Radon gas is an alpha-emitting isotope that seeps into houses in certain areas through the ground.

There are thousands of fission reactors safely in use in the world. None of them are the same type as the Chernobyl reactors that exploded.

Nuclear waste is stored in safe and secure conditions for many years after unused uranium and plutonium (to be used in the future) is removed from it.

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7.4 The Early Universe

A galaxy is a collection of billions of stars held together by their own gravity. 

Before galaxies and stars were formed, the universe was formed of hydrogen and helium (first in periodic table- Eventually dust and gas were pulled together by gravitational attraction to form stars.

The resulting intense heat started off nuclear fusion reactions in the starts, so they began to emit visible light and other radiationn.

The distance between neighbouring stars is usually millions of times greater than the distance between planets in our solar system.

The distance between neighbouring galaxies is usually millions of times greater than the distance between stars in our galaxy.

Therefore the universe is mostly made up of empty space - LONELY

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7.5 The Life History of a Star

Gravitational forces pull clouds of dust and gas (LION KING) together to form a protostar that can go on to form a star.

Low mass star:

Potter Made Sure Rubeus the Giant and Warwick the Dwarf Beat Dumbledore

protostar - main sequence star - red giant - white dwarf - black dwarf.

High mass star:

Potter Made Super Sure Ron's Sister SawNobody Before Harry

protostar - main sequence star - red supergiant - supernova - black hole if sufficient mass

The Sun will eventually become a black dwarf (Bamf Dumbledore)

A supernova is the explosion of a supergiant after it collapses.

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The Life Cycle of a small star

For a star the size of our sun or smaller:

  • Gravitational forces pull clouds of dust and gas together to form a protostar
  • The protostar becomes denser and the nuclei of hydrogen atoms and other light elements start to fuse together
  • Energy is released in the process so the core gets hotter and brighter
  • Eventually a star runs out of hydrogen nuclei, swells, cools down and turns red
  • A star similar in size to our sun is now a red giant
  • Helium and other light elements fuse together to form heavier elements
  • Fusion stops and the star will contract to form a white dwarf
  • Eventuall no more light is emitted and the star becomes a black dwarf
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7.6 How the chemical elements formed

Elements as heavy as iron are formed inside stars as a result of nuclear fusion.

Elements heavier than iron are formed in supernovas, along with lighter elements.

The presence of heavier elements in the Sun and the Inner planets such as uranium is evidence that they were formed from the debris of a supernova.

In the process of fusion, light nuclei fuse to form heavier nuclei and energy is released. For elements heavier than iron to be formed there must be an input of energy.

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The Life Cycle of a bigger star

  • Gravitational forces pull clouds of dust and gas together to form a protostar
  • The protostar becomes denser and the nuclei of hydrogen atoms and other light elements start to fuse together
  • Energy is released in the process so the core gets hotter and brighter
  • Eventually a star runs out of hydrogen nuclei, swells, cools down and turns red
  • A star much larger than the sun will swell to become a red supergiant which continues to collapse
  • Eventually the star explodes in a supernova
  • The outer layers are thrown out into space, leaving the core as a neutron star
  • If this is massive enough it becomes a black gole, with a gravitational field so strong not even light can escape it
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