Nuclear Fission and Fusion

Question 1

What is the decay constant of an isotope?

Answer 1

The probability of decay of a nucleus per unit time.

Question 2

What is induced nuclear fission?

Answer 2

The splitting of a (uranium) nucleus as a neutron is absorbed (into two fragment nuclei and neutrons).

Question 3

What is the role of the moderator in a nuclear reactor?

Answer 3

The moderator slows down the fast-moving neutrons.

The neutrons lose significant amount of their kinetic energy when colliding with moderator nuclei.

Question 4

What is the role of the control rods in a nuclear reactor?

Answer 4

The control rods absorb the neutrons thus the rate of fission reactions is reduced.

Question 5

Describe the process and conditions for fission

Answer 5

A neutron is absorbed by the nucleus causing it to split into two (major) fragments and several/two/three neutrons.
Rate can be varied/controlled by absorbing and or slowing released neutrons in reactor where chain reaction is occurring.

Question 6

Describe similarities of fission and fusion.

Answer 6

1. release of energy 2. total (rest) mass decrease 3. ‘increase’ in binding energy 4. conservation of charge/mass-energy.

Question 7

Major disadvantage of fission reactors?

Answer 7

Fission reactors produce radioactive by-products which affect future generations and the environment in terms of possible contamination/exposure to humans and animals.

Question 8

Describe differences of fission and fusion.

Answer 8

1. cold, hot 2. heavy, light nuclei 3. large (200 MeV), small (30 MeV) energy release per reaction.

Question 9

Describe the process and conditions for fusion.

Answer 9

Two light nuclei (moving rapidly enough) overcome the Coulomb repulsion between them and fuse.
It needs a very hot and sufficiently dense and plentiful plasma for random fusion collisions to occur, e.g. inside Sun/star.