Ch26: Nuclear Physics

Question 1

Define mass defect.

Answer 1

The mass defect of a nucleus is the difference between the mass of the completely seperated nucleons and the mass of the nucleus.

Question 2

Define binding energy.

Answer 2

The minimum energy required to completely separate a nucleus into its constituent protons and neutrons.

Question 3

Does a greater binding energy per nucleon mean a nucleus is more or less stable?

Answer 3

More stable

Question 4

Briefly describe fission in terms of binding energy.

Answer 4

A high A number nucleus splits into two low A number nuclei. Energy is released because the two nuclei produced have higher binding energy so release more energy than is used to split the original nuclei.

Question 5

Briefly describe fusion in terms of binding energy.

Answer 5

Two low A number nuclei form a higher A number nucleus. This new nucleus has a far higher binding energy and so energy is released.

Question 6

Does forming a nucleus release or require energy?

Answer 6

Release

Question 7

Does splitting up a nucleus into its components require or release energy?

Answer 7

Require

Question 8

What is the biggest drawback of nuclear power?

Answer 8

The production of radioactive and hazardous waste.

Question 9

Describe nuclear fission in terms of the particles involved.

Answer 9

• A slow moving nucleus is absorbed by a stable nucleus (usually uranium)
• Making it unstable.
• In less than a microsecond, the nucleus splits into two daughter nuclei and releases 1 or more fast moving neutrons. (usually 3)

Question 10

What form/s is the energy released by fission in?

Answer 10

• Kinetic energies of particles produced

- Energy of photons and neutrinos emitted.

Question 11

What is the role of the moderator in a fission reactor? What other role does the moderator often take?

Answer 11

To slow down the fast moving neutrons so they are more likely to be absorbed by the fuel. This happens when the neutrons collide with particles and transfer kinetic energy.
- Moderator can also be the coolant.

Question 12

What is the role of control rods in a fission reactor? Why is their depth adjustable?

Answer 12

Control rods absorb fast moving neutrons so exactly one survives from each fission reaction; to do this they are made from a material which easily absorbs neutrons such as Boron.
- To slow or stop fission they can be lowered further into the reactor.

Question 13

Why do faster neutrons in a fission reactor cause environmental problems?

Answer 13

They are easily absorbed by Uranium 238 which beta decays into the incredibly hazardous plutonium 239.