Chapter 26: Nuclear Physics Flashcards
Mass defect
The difference between the total mass of all the nucleons separately compared to the mass of the nucleus
Why is there a mass defect?
Energy is released as the nucleons bind together into a nucleus
What is binding energy?
The energy required to separate a nucleus into its constituent parts
(numerically equal to the energy released when the nucleus binds, also mass defect)
True or False: A low binding energy per nucleon will mean that an element is more stable
False
A low binding energy per nucleon means not much energy would be required to separate the nucleus
Greater binding energy means a more stable nucleus
What is nuclear fission?
Unstable nucleus splits into 2 smaller nuclei, often occurs with the larger nuclei
What happens to the binding energy during nuclear fission
Binding energy per nucleon increases when fission occurs, so overall process releases energy
Fusion
When two smaller nuclei fuse together to create a larger nuclei, larger binding energy per nucleon than the old nuclei therefore energy is released in the process
Does fusion or fission release more energy?
Fusion releases a lot more energy per reaction
This is because the change in binding energy is very drastic
Why is it difficult to make fusion occur on Earth?
Large repulsion between the two positively charged nuclei, a lot of energy required to overcome the repulsion and fuse together
How is fission used in nuclear reactors?
Rods of Uranium-235 absorb neutrons and become unstable and then split into two daughter nuclei
Releases 2 or 3 more neutrons, which then get absorbed by another Uranium-235
What is the purpose of a moderator?
To slow down the neutrons so they travel slow enough to be absorbed by the uranium
Done through elastic collisions between moderator and the nucleus
Why are control rods essential for a nuclear power station
Stop chain reaction from being out of control
They absorb neutrons so that only 1 neutron released in each reaction, stops it from overheating
What material can be used as a moderator?
Water
What is a chain reaction?
One neutron from each decay goes on to cause another decay, amount of energy released is constant
How is nuclear waste disposed of?
Stored in cooling ponds
Then put in sealed steel containers and potentially stored deep underground
Benefit and risk of Nuclear power
Benefit = no release of greenhouse gas, no contribution to global warming, no fossil fuels
Risks = leak or escape of material can be catastrophic
How can you interpret a binding energy curve?
Elements below Fe, in mass number, are more likely to undergo fusion
Elements above Fe, in mass number, are more likely to undergo fission
Fe has the highest binding energy per nucleon
What happens to binding energy during nuclear fission
Total binding energy increases as the daughters are more stable than the parents
Excess energy is released by the reaction
Advantages of Nuclear Fusion
Very little radioactive waste
Unlimited supply of raw material (hydrogen in sea)
Releases much more energy than nuclear fission for a given mass
Disadvantages of Nuclear Fusion
Difficult to maintain high temp for long time
Apparatus that induce fusion requires more input energy in the form of electricity that it could provide output
Why does nuclear fusion work on stars?
Intense gravitational fields can overcome Coulomb repulsion force between protons
