Chapter 26 Nuclear Physics

Question 1

What is the concept of mass energy?

Answer 1

This is the concept that mass and energy are the same thing.

Question 2

What is annihilation?

Answer 2

It is the concept that when a particle and antiparticle collide the entire mass of one is transformed into energy

Question 3

What is the equation linking mass and energy?

Answer 3

E = mc^2

Question 4

What happens to the mass of the person as they run?

Answer 4

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

Question 5

How can unstable nuclei decay?

Answer 5

By emitting photons (gamma) or by emitting particles (electrons or photons)

Question 6

What is alpha radiation?

Answer 6

It is a helium nucleus (two protons and two neutrons). The proton number decreases by 2 and the mass number decreases by 4

Question 7

What is beta radiation?

Answer 7

This is an electron that is fired from the nucleus. And in the nucleus a neutron becomes a proton.

Question 8

What is gamma radiation?

Answer 8

It is a high frequency photon

Question 9

How can the kinetic energy of a released particle be calculated?

Answer 9

The change in mass is equal to the change in energy

Question 10

What is annhilation?

Answer 10

This is when a particle and an antiparticle meet and they destroy each other and release energy

Question 11

How can the energy released between an electron and positron be calculated?

Answer 11

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

Question 12

What is the opposite of annhilation?

Answer 12

Pair production

Question 13

What is pair production?

Answer 13

This is when a photon turns into two particles. (one particle and one antiparticle)

Question 14

What is deuterium?

Answer 14

This is an isotope of hydrogen which has one proton and one neutron and it is held together with the strong nuclear force

Question 15

Talk about deuterium and its mass when it is together vs when it is separated

Answer 15

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.

Question 16

What is mass defect?

Answer 16

This is the difference between the mass of the joined nucleons and the separated nucleuons

Question 17

What is the binding energy?

Answer 17

This is the minimum energy required to completely separate a nucleuses nucleuons

Question 18

What is the equation for binding energy and mass defect?

Answer 18

Binding energy of nucleus = mass defect of nucleus x c^2

Question 19

What happens if the binding energy is greater?

Answer 19

This means that the nucleons are more tightly held together. It also means that the nucleus is more stable

Question 20

What are the trends of the binding energy of nuclei?

Answer 20

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

Question 21

What is the process for induced fission?

Answer 21

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

Question 22

What is the probability of a uranium-238 or uranium-235 nucleus decaying?
What about uranium-236?

Answer 22

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

Question 23

Where does the energy in fission come from?

Answer 23

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

Question 24

What forms of energy are released in a fission decay?

Answer 24

Kinetic energy
Photons
Neutrinos

Question 25

How are uranium fissions made sustainable? and why?

Answer 25

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.

Question 26

What are the components of a fission reactor?

Answer 26

Moderators
Control rods
Coolant
Fuel rods

Question 27

What are moderators?

Answer 27

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

Question 28

What are control rods?

Answer 28

They are made of a material like boron and absorb neutrons so this prevents a chain reaction from occuring

Question 29

What are fuel rods?

Answer 29

They contain enriched uranium. Uranium that has a higher percentage of U-235 than naturally found. It is usually around 2-3%

Question 30

What is the environmental impact of nuclear energy?

Answer 30

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

Question 31

What is nuclear fusion?

Answer 31

This is when two or more lighter nuclei fuse to make a heavier nuclei

Question 32

What is required for fusion to happen?

Answer 32

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

Question 33

What are some examples of fusion reactions?

Answer 33

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

Question 34

Where is current fusion technology at?

Answer 34

Fusion has been recreated on earth but the quantity of energy put in is larger than the energy released