6.4.4: Nuclear fission and fusion

Question 1

Rest mass

Answer 1

The mass of an object or particle when it is stationary

Question 2

Mass defect

Answer 2

The difference between the mass of a nucleus and the sum of the masses of its nucleons if they were completely separated

Question 3

Binding energy

Answer 3

The minimum energy required to separate a nucleus into its constituent protons or neutrons

Question 4

Fission

Answer 4

When a large nucleus splits into two smaller nuclei after absorbing a neutron

Question 5

Fusion

Answer 5

When two smaller nuclei join together to form one larger nucleus

Question 6

Thermal neutrons

Answer 6

A neutron in a fission reaction that has a mean kinetic energy approximately equal to the thermal energy of the particles in the reactor core.
Also called a slow neutron

Question 7

Chain reaction

Answer 7

Initial neutrons in a fission reaction cause exponential increase in neutrons, which causes an exponential growth in the rate of fission reactions

Question 8

Reactor core

Answer 8

A concrete-steel encasement around the core of a nuclear reactor

Question 9

Coolant

Answer 9

A substance that is heated by energy from fission reactions and removes thermal energy from the reactor core

Question 10

Moderator

Answer 10

A substance in a fission reactor that slows down fast neutrons so they can be absorbed by U-235 to continue the nuclear reaction. Often made from graphite or water

Question 11

Control rods

Answer 11

Moveable rods inside the reactor core that absorb neutrons and are used to ensure exactly one neutron survives per fission reaction, or are used to stop the fission reaction