powerpoint slides ocr a level physics, Slides of Physics

Download powerpoint slides ocr a level physics and more Slides Physics in PDF only on Docsity!

Nuclear Physics

L3 Nuclear Fusion

In a Fusion reaction (like in Fission!) the products being made have to have a higher binding energy per nucleon compared to the elements or particles we start with. Recall that all the elements to the left of iron on the binding energy per nucleon graph are associated with the Fusion process, mainly inside stellar cores.

Temperature

An external factor in assisting fusion is temperature. The hotter it is, the faster particles are moving (possessing more kinetic energy), so this increases the chance of collision/fusion. In theory we could show use the idea of Kinetic Energy of the particles would have to exceed the potential energy at a specific separation of 3fm.

In reality…

• (^) The core temperature of the Sun is close to 1.4x 7 K and the particle density is 1.5x 5 kgm -
• (^) This high density also allows for a high number of fusion reactions per second.
• (^) Since the temperature of the Sun is far lower than the temperature required ( 7 K << 10 K) to overcome the Coulomb barrier, we say that quantum tunnelling is occurring.

We summarise this reaction in the following

way…

• (^) Two protons fuse together to produce a deuterium nucleus, a positron and neutrino, producing 2.2MeV of energy
• (^) Two single protons each have zero binding energy , since they aren’t actually “bound” to anything. Energy is released when the two particles become bound.
• (^) You could imagine bound particles as being trapped in a potential well - if the particles move closer together then this means potential energy is decreasing (becoming more negative). So the “lost” energy has to end up somewhere, and is transferred away from the system as heat.

Next, the deuterium nucleus fuses with another proton to form a Helium-3 nucleus, with 5.5MeV of energy released.

Nuclear Fusion on Earth

• (^) Fusion has been achieved, albeit briefly. Scientists have been able to accomplish a net energy gain, but this energy is nowhere near ready to be commercially available (for use in ‘power stations’). For example, in Feb 2022, JET (Joint European Torus) achieved 59MJ of energy from fusion was transferred over a 5 second period, which doubled previous records. Replicating fusion is tricky as it required millions of degrees Celsius, as well has having to confine a plasma using magnets or lasers.
• (^) In Feb 2024, NIF (National Ignition Facility) in the US achieved 5.2MJ from a 2.2MJ input, using a method of alpha-particle heating. A lot of experiments use powerful lasers to contain deuterium and tritium. JET

• (^) The use of fusion power plants could substantially reduce the environmental impacts of increasing world electricity demands since, like nuclear fission power, they would not contribute to acid rain or the greenhouse effect.
• (^) Fusion power could easily satisfy the energy needs associated with continued economic growth, given the ready availability of fuels. There would be no danger of a runaway fusion reaction as this is intrinsically impossible and any malfunction would result in a rapid shutdown of the plant (world-nuclear.org,

Try the summary questions first

Now try the exam questions!