Topic 4: Atomic Structure - Subtopic 4: Nuclear Fission & Fusion

Question 1

What is nuclear fission?

Answer 1

The splitting of a large, unstable nucleus into two smaller nuclei

Question 2

Name two isotopes which undergo fission and are used as fuels in power stations

Answer 2

Uranium and Plutonium

Question 3

What happens during nuclear fission?

Answer 3

• When a neutron collides with an unstable nucleus, the nucleus splits into two smaller nuclei (called daughter nuclei) as well as two or three neutrons
• Gamma rays are also emitted

Question 4

What happens to the products of fission?

Answer 4

• Move away very quickly
• Energy transferred from nuclear potential energy to kinetic energy

Question 5

What is spontaneous fission?

Answer 5

Where nuclei undergoes fission without additional energy being put into nucleus

Question 6

What is induced fission>

Answer 6

Where the nuclei undergoes fission by absorbing a neutron

Question 7

Is fission a chain reaction?

Answer 7

Yes, the two or three neutrons produed can start another fission reaction, which again creates further excess neutrons

Question 8

What happens in a nuclear reactor?

Answer 8

• A chain reaction is required to keep the reactor running
• When the reactor is producing energy at the correct rate, the number of free neutrons in the reactor needs to be kept constant
• This means some must be removed from the reactor

Question 9

How are neutrons removed?

Answer 9

Control Rods
- Absorb neutrons without becoming dangerously unstable themselves

Question 10

Why are uncontrolled chain reactions dangerous?

Answer 10

• Each new fission reaction releases energy
• The number of neutrons available increases quickly, so the number of reactions does too

Question 11

What uses an uncontrolled chain reaction?

Answer 11

Nuclear Weapon
- Releases huge amount of energy in a short period of time as an explosion

Question 12

What is nuclear fusion?

Answer 12

When two light nuclei join to form a heavier nucleus

Question 13

Why is nuclear fusion hard to reproduce on Earth?

Answer 13

Process requires extremely high temperatures to maintain

Question 14

Where does nuclear fusion normally take place?

Answer 14

• Centre of stars
• Hydrogen Nuclei fuse into helium nuclei and release large amounts of energy