Module 6 Fission and Fusion Flashcards
Why is there a slight increase in mass when water at 100º is boiled to steam?
Gain in potential energy to separate particles. This is latent heat.
Plug into E=mc^2
Why is there a gain in mass during ionisation?
Energy is gained as electrostatic potential energy to separate opposite charges. Energy is converted to mass by E=mc^2.
Why can the mass gained during ionisation be ignored?
Negligible when compared to the original mass.
What can be said about the masses of particles during radioactive decay?
Total final mass is less than total initial mass.
What happens to the mass lost during nuclear decay?
Increases binding energy and gained as kinetic energy in products.
What is the symbol for a mass defect?
Δ m.
Why does a proton plus a neutron have higher mass than a deuterium nucleus?
There is a mass defect due to energy put in, to overcome the strong nuclear force.
What can you do when showing a diagram with three forces where RF=0?
Put it into a closed vector triangle.
How do you calculate the nuclear binding energy?
Find mass of original nucleus, find mass of separate protons and neutrons, find change in mass, plug into E=mc^2.
Define binding energy.
Minimum energy required to split a nucleus completely into its separate protons and neutrons.
Define mass defect.
[mass of protons + mass of neutrons] – mass of nucleus.
What is used to measure nuclear stability?
Binding energy per nucleon.
How do you calculate binding energy per nucleon?
Calculate binding energy, divide by A
(A is nucleon number)
What is the nucleon number of iron?
56.
What is the proton number of iron?
26.
What is the approximate value for the binding energy per nucleon of iron?
8.72 MeV.
What is the most stable nucleus?
Iron-56.
On binding energy per nucleon (y axis) against nucleon numer (x axis)
To what side of iron does fusion happen?
To the left side.
What happens during fusion?
Two nuclei fuse to form a larger one.
Explain, using binding energies, why fusion releases energy.
Two small nuclei join to form a larger one. Total binding energy increases. E=mc^2. Higher mass defect and so energy is released.
When is energy released during nuclear reactions?
Total final mass is less than initial mass. Mass defect (mass is lost). Energy is released according to E=mc^2 as kinetic energy of the products.
What must be done to calculate the energy released when two protons combine to form a hydrogen-2 atom?
Write out an equation. Find mass defect (mass of two protons) - (mass of hydrogen-2 and positron).
Find E using E=mc^2.
Positron will annihilate with an electron. Double mass of one electron and plug into equation E=mc^2.
Why is usually a very high temperature required for fusion?
High temperature to provide the high kinetic energy to overcome electrostatic repulsion so closest approach can be less than 3 fm and the strong nuclear force can come into play and bind nucleons.
Why is a high density required for nuclear fusion?
So there is a high probability of a head-on collision so maximum kinetic energy is transferred to electrostatic potential energy.
