Chapter 26 Nuclear Physics Flashcards
What is the concept of mass energy?
This is the concept that mass and energy are the same thing.
What is annihilation?
It is the concept that when a particle and antiparticle collide the entire mass of one is transformed into energy
What is the equation linking mass and energy?
E = mc^2
What happens to the mass of the person as they run?
When the person runs they gain kinetic energy and because mass is energy, the gain mass.
The mass change is so small that it isnt noticible
How can unstable nuclei decay?
By emitting photons (gamma) or by emitting particles (electrons or photons)
What is alpha radiation?
It is a helium nucleus (two protons and two neutrons). The proton number decreases by 2 and the mass number decreases by 4
What is beta radiation?
This is an electron that is fired from the nucleus. And in the nucleus a neutron becomes a proton.
What is gamma radiation?
It is a high frequency photon
How can the kinetic energy of a released particle be calculated?
The change in mass is equal to the change in energy
What is annhilation?
This is when a particle and an antiparticle meet and they destroy each other and release energy
How can the energy released between an electron and positron be calculated?
Calculate the change in mass: 2 x Mass of an electron
Change that mass into the energy equivalent: ΔE = Δmc^2
Therefore, the energy released is: 2Δmc^2
What is the opposite of annhilation?
Pair production
What is pair production?
This is when a photon turns into two particles. (one particle and one antiparticle)
What is deuterium?
This is an isotope of hydrogen which has one proton and one neutron and it is held together with the strong nuclear force
Talk about deuterium and its mass when it is together vs when it is separated
Deuterium together has less mass because work (energy) has to be done to separate them from the strong nuclear force.
So when they are separated more energy has been put into them so they have more mass. This is whey separated Deuterium has more mass.
What is mass defect?
This is the difference between the mass of the joined nucleons and the separated nucleuons
What is the binding energy?
This is the minimum energy required to completely separate a nucleuses nucleuons
What is the equation for binding energy and mass defect?
Binding energy of nucleus = mass defect of nucleus x c^2
What happens if the binding energy is greater?
This means that the nucleons are more tightly held together. It also means that the nucleus is more stable
What are the trends of the binding energy of nuclei?
A is the atomic mass
A < 56 then as A increases so does the binding energy
A > 56 then as A increases the binding energy reduces
There trend isnt perfect. Helium-4, Carbon-12 and oxygen-16 are very stable
What is the process for induced fission?
A uranium-235 nucleus absorbs a slow moving neutron (also called a thermal neutron) and this then causes the uranium to decay which releases more neutron
What is the probability of a uranium-238 or uranium-235 nucleus decaying?
What about uranium-236?
It is unlikely like U238 or U235 will decay naturally.
But U236 will decay spontaneously so by firing a neutron into a U235 it will become U236 and decay. This is induced fission
Where does the energy in fission come from?
Energy is released in the form of fast moving neutrons but this is from the change in the mass. The nuclei produced are more stable and have a higher binding energy. This binding energy is equal to the energy released
What forms of energy are released in a fission decay?
Kinetic energy
Photons
Neutrinos
How are uranium fissions made sustainable? and why?
The neutrons released from the fission of uranium are very fast so cannot be absorbed by another uranium nuclei so moderators are used to slow down the neutrons and make the process a chain reaction.
What are the components of a fission reactor?
Moderators
Control rods
Coolant
Fuel rods
What are moderators?
They slow down the speed of neutrons so that they can be absorbed by uranium nuclei. It is often made from water or carbon because they reduce the kinetic energy of the neutron and heat up. This is used to generate power
What are control rods?
They are made of a material like boron and absorb neutrons so this prevents a chain reaction from occuring
What are fuel rods?
They contain enriched uranium. Uranium that has a higher percentage of U-235 than naturally found. It is usually around 2-3%
What is the environmental impact of nuclear energy?
The waste that is generated at the end is often very radioactive and will continue to be for many thousands of years. So its disposal has to be done very carefully because it will affect people and the environment many thousands of years into the future
What is nuclear fusion?
This is when two or more lighter nuclei fuse to make a heavier nuclei
What is required for fusion to happen?
The nuclei need to come very very close together so that the strong nuclear force can attract them together.
At the same time positive nuclei will repel each other and it becomes stronger the closer the nuclei get to each other
What are some examples of fusion reactions?
Two protons combine to form deuterium nucleus and a positron and neutrino are released.
1,1P + 1,1P ==> 2,1H + 0+1e + v
A deuterium nucleus and a proton join to form helium
2,1H + 1,1P ==> 3,2He
2 Helium nuclei join to make more helium and release protons
3,2He + 3,2He ==> 4,2He + 2 1,1P
Then the process repeats
Where is current fusion technology at?
Fusion has been recreated on earth but the quantity of energy put in is larger than the energy released
