NUCLEAR FUSION &
NUCLEAR FISSION
Noadswood Science, 2012
Nuclear Fusion

Monday, April 13, 2015
To understand nuclear fusion & fission
On-line Lessons: The Birth and
Death of Stars
What are Stars?
 Stars are large balls of hot gas.
 They look small because they are a
long way away, but in fact many are
bigger and brighter than the Sun.
 The heat of the star is made in the
centre by nuclear fusion reactions.
 There are lots of different colours
The Birth and Death of Stars
Stars are made (or “born”) in
giant clouds of dust and gas.
 Sometimes part of the cloud
shrinks because of gravity.
 As it shrinks it becomes hotter
and when it is hot enough,
nuclear reactions can start in
the centre…..
 … and A Star is Born!
The Birth and Death of Stars
Watching stars being born
The Bubble Nebula
Here you can see the old dust
and gas being blown away by
the heat of the new star.
https://www.youtube.com/watch?
v=9EnBBIx6XkM
The Birth and Death of Stars
• The
When
a star of
begins
to exhaust its hydrogen
Death
A Star
supply, its life nears an end.
• The first sign of a star's old age is a swelling
and reddening of its outer regions.
• Such an aging, swollen star is called a red
giant.
• When all its fuel has been exhausted, a star
cannot generate sufficient pressure at its center
to balance the crushing force of gravity
• https://www.youtube.com/watch?v=44BwqpthXB
Nuclear Fusion
Why do stars shine?
 Stars release energy as a result of fusing small
nuclei such as hydrogen to form larger nuclei


The energy released by
this process is vast –
water contains lots of
hydrogen atoms
Fusion Reactions


2 small nuclei release energy when they are
fused together to form a single, larger nucleus
Energy must be supplied to create bigger
nuclei
Nuclear Fusion & Stars


The Sun consists of about 75% hydrogen (H) and
25% helium (He)
The core is so hot that it consists of a ‘plasma’ of bare
nuclei with no electrons – these nuclei move about and
fuse together when they collide
When they fuse they release
energy…

Nuclear Fusion & Stars


Nuclear fusion involves two atomic nuclei
joining to make a large nucleus – energy is
released when this happens
The Sun and other stars use nuclear fusion to
release energy
1
H +
1
2
H
1
3
He
2
Nuclear Fusion On Earth


It is technically very difficult to produce nuclear fusion
on Earth
This temperature is needed because 2 nuclei
approaching each other will try and repel each other
(due to the positive charge) – move them fast enough
(i.e. with temperature) then they will overcome this
force of repulsion, and fuse
Nuclear Fusion On Earth

There are some experimental reactors, however the
process is extremely complicated and currently they
only work for a few minutes: -
Powerful Future

Practical fusion reactions could meet all our energy
needs: -
 The
energy released could be
used to then generate electricity
Hydrogen Bomb


2
A hydrogen bomb is a uranium bomb, surrounded
by
1
the H isotope
When the uranium bomb explodes it makes the
surrounding hydrogen fuse and release even more
energy – a single hydrogen bomb would destroy
London
Hydrogen Bomb

2
https://www.youtube.com/watch?v=qjnm3V0xYjI
1
Nuclear Fission



Energy is released in a nuclear reactor as a result of
nuclear fission
The nucleus of an atom of a fissionable substance
splits into two smaller ‘fragment’ nuclei
This event can cause other fissionable nuclei to split,
leading to a chain reaction of fission events
Splitting Atoms

Fission is another word for splitting (splitting a
nucleus is called nuclear fission)
 The nucleus splits into two smaller nuclei,
which are radioactive
 Two
or three more neutrons are released
 Some
energy is released
Chain


The additional neutrons released may also hit other
uranium or plutonium nuclei and cause them to split –
even more neutrons are then released, which in turn
can split more nuclei
This is called a chain
reaction – in nuclear
reactors the chain reaction is
controlled, stopping it going
too fast
Chain Reaction
Krypton
n
n
n
Uranium
n
Barium
More
decays