Week 1: Introduction

Question 1

Define an isotope.

Answer 1

Nuclides with the same number of protons Z.

Question 2

Define an isotone.

Answer 2

Nuclides with the same number of neutrons N.

Question 3

Define an isobar.

Answer 3

Nuclides with the same mass number
A = Z + N.

Question 4

Name the 5 terms in the SEMF.

Answer 4

Volume
Surface
Coulomb
Symmetry
Pairing

Question 5

Give a basic description of the process of fission.

Answer 5

In heavy nuclei, the repulsive Coulomb force between the protons begins to dominate.

If the nucleus is disturbed sufficiently from its equilibrium shape, the Coulomb repulsion can irreversibly drive the nucleus to break down into two.

Question 6

Describe what the fission barrier is and sketch a plot of potential energy against distance to show the stages of fission.

Answer 6

The fission barrier is the energy required to overcome the barrier to fission. It is the energy required to split the nucleus.

(1)

Question 7

What happens when low energy neutrons are absorbed by a nucleus?

Answer 7

The nucleus is left in an excited state.

Question 8

What can happen if a neutron is absorbed by the nucleus?

Answer 8

The excitation energy might be released as gamma radiation and the neutron is captured.

The excitation energy from the addition of the neutron may exceed the activation energy causing fission. (Uranium-235)

Fission produces more neutrons, which can then go on to induce more fission.

Question 9

What is a chain reaction?

Answer 9

When neutrons from one fission go on to cause further fission reactions.

Question 10

Describe criticality.

Answer 10

An uncontrolled chain reaction in fission fuel can lead to an extremely large and fast energy release.

A controlled chain reaction is achieved by ensuring that the right number of neutrons from fission induce further fission.