GCSE SCIENCE PHYSICS HIGH SCHOOL - Stars - Life Cycle - What is Fusion? - Hydrogen becomes Helium - Nuclear Reaction

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Stars - Life Cycle - Birth - Fusion.

At very high temperatures, a nuclear reaction called fusion
occurs in stars. Fusion is the joining together of two nuclei
to make a bigger nucleus. Fusion is not the same as fission.

It has been possible to create a fusion reaction on Earth
in the laboratory but so far it has not been possible to use
fusion as a way of releasing enough energy to run a
power station because of the very high temperature needed.

A nuclear reaction changes the number of protons inside
the nucleus. The original element is changed into a
new element (for further information see radioactivity).
If you are unsure what a proton or nucleus is, see the
information about atoms on the GCSE Chemistry site.

In main sequence stars, the fusion reaction turns hydrogen
into helium. The nucleus of a hydrogen atom is a positively
charged proton. When two protons approach each other
they repel each other because they have the same charge.
The protons must be moving very very fast if they are
to have enough energy to overcome the force of repulsion.
This only happens at very high temperatures.
The two protons can then join together to form a new
nucleus. The joining together is called fusion.

The new nucleus with two protons is an atom of helium.
Those of you who are familiar with the elements will
know that helium has two neutrons as well as two protons.
The real process that turns hydrogen into helium is
more complicated than that given above. The good news
is that you don't need to know the detail for GCSE.
"Hydrogen turns into helium and gives out energy"
is all you need to say (continued on the next page).

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