1. What is nuclear fusion. How is it different to fission?
Starter: Plants get their energy from the sun …. But where does the sun get it from? !

2. Nuclear Fusion
Video IP Why fusion?

3. explain that the fusion of small nuclei like hydrogen releases energy H: calculated using E = mc2
explain that, for fusion to occur, nuclei must be close and this requires energy because the positive nuclei repel each other
H: explain that there is a force, called the strong force, holding the protons and neutrons together

4. NUCLEAR FUSION
FUSION involves SMALL nuclei like hydrogen JOINING TOGETHER to form larger ones.
FUSION powers STARS and is the method by which all of the ELEMENTS in the Universe were formed from the original simple particles present after the BIG BANG

5. Conditions needed for a fusion reactionH 1 2
deuterium H 1 3
tritium n 1
neutron H 1 p
proton
In stars, the 3 isotopes of HYDROGEN are often involved in fusion
Conditions needed for a fusion reaction
If the TEMPERATURE is not high enough, the particles will simply collide and ‘rebound’ due to electrostatic repulsion.
Q: why do they repulse each other?

6. If the temperature is high enough, the particles have enough kinetic energy to overcome their repulsion and FUSE
2 protons
positron
(neutrino)
deuterium
As with fission, the products have slightly less mass than the reactants with the ‘missing’ mass being converted to energy
(the neutrino is a tiny neutral particle always created with a positron – antineutrinos are created with electrons) H 1 2 e + ν
Temperatures of MILLIONS OF DEGREES are needed to start the reaction.

7. Strong Force
When nuclei are fused they are held together by a strong force called the “strong force” which makes them stable.

8. In the core of a star, many fusion reactions are taking place at the same time
Gigantic amounts of energy are released.

9. Out of interest only

10. Nucleosynthesis means the creation of new heavier nuclei from lighter ones
As a star’s life cycle goes on, fusion in the core produces heavier and heavier elements.
The process continues until IRON (26 protons) is produced.

11. Older stars build up layers of heavier and heavier elements.
Eventually, fusion in the core stops and gravity suddenly collapses the star.
Elements up to iron
The collapse produces a devastating SUPERNOVA explosion.
In a supernova the conditions are so extreme that nuclei fuse to produce all of the elements heavier than iron which are then blasted into space, later to form new stars and planets
iron to uranium

12. NEWLY CREATED ELEMENTS ARE RECYCLED
Heavier elements from a dead star are thrown out by the supernova into space as gas and dust
New stars and planets form from the gas and dust

13. CAN NUCLEAR FUSION FILL THE ENERGY SUPPLY GAP BACK HERE ON EARTH?
Fossil fuels
SUPPLIES RUNNING OUT, POLLUTION
Nuclear fission
SAFETY CONCERNS, WASTE PROBLEM
Renewables
NOT ENOUGH ENERGY PRODUCED

14. Is it possible to create a little piece of the Sun here on Earth?
We already rely on a nuclear fusion reactor 150 million km away for virtually all of our energy, whether directly through solar heating or indirectly through wind, hydro, food and fossil fuels.
Is it possible to create a little piece of the Sun here on Earth?
Many scientists say that if we could successfully control nuclear fusion, we could produce, cleanly, more energy than we could ever need

15. Inside the JET (Joint European Torus) experimental fusion reactor at Culham in Berkshire, trying to fuse hydrogen nuclei from water to make helium.

16. After about 40 years research and billions of dollars of funding…..
JET / ITER / TOKAMAK
Magnetic confinement
Hydrogen is super heated. It loses its electrons which form a cloud of particles called plasma.
This is kept from touching the sides of the reactor by a very strong magnetic field.
After about 40 years research and billions of dollars of funding…..

17. NIF
Laser Ignition
…continuous controlled fusion in a reactor has still not been achieved.

18. Practise Question