Chapter 26: Nuclear Physics

Question 1

Mass defect

Answer 1

The difference between the total mass of all the nucleons separately compared to the mass of the nucleus

Question 2

Why is there a mass defect?

Answer 2

Energy is released as the nucleons bind together into a nucleus

Question 3

What is binding energy?

Answer 3

The energy required to separate a nucleus into its constituent parts
(numerically equal to the energy released when the nucleus binds, also mass defect)

Question 4

True or False: A low binding energy per nucleon will mean that an element is more stable

Answer 4

False
A low binding energy per nucleon means not much energy would be required to separate the nucleus

Question 5

What is nuclear fission?

Answer 5

Unstable nucleus splits into 2 smaller nuclei, often occurs with the larger nuclei

Question 6

What happens to the binding energy during nuclear fission

Answer 6

Binding energy per nucleon increases when fission occurs, so overall process releases energy

Question 7

Fusion

Answer 7

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

Question 8

Does fusion or fission release more energy?

Answer 8

Fusion releases a lot more energy per reaction
This is because the change in binding energy is very drastic

Question 9

Why is it difficult to make fusion occur on Earth?

Answer 9

Large repulsion between the two positively charged nuclei, a lot of energy required to overcome the repulsion and fuse together

Question 10

How is fission used in nuclear reactors?

Answer 10

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

Question 11

What is the purpose of a moderator?

Answer 11

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

Question 12

Why are control rods essential for a nuclear power station

Answer 12

Stop chain reaction from being out of control
They absorb neutrons so that only 1 neutron released in each reaction, stops it from overheating

Question 13

What material can be used as a moderator?

Answer 13

Water

Question 14

What is a chain reaction?

Answer 14

One neutron from each decay goes on to cause another decay, amount of energy released is constant

Question 15

How is nuclear waste disposed of?

Answer 15

Stored in cooling ponds
Then put in sealed steel containers and potentially stored deep underground

Question 16

Benefit and risk of Nuclear power

Answer 16

Benefit = no release of greenhouse gas, no contribution to global warming, no fossil fuels
Risks = leak or escape of material can be catastrophic