Section 7 - Nuclear Physics Exam Questions

Question 1

State what happens to a neutron that is incident on the moderator (1)

Answer 1

Neutron collides elastically with nucleus and kinetic energy is reduced

Question 2

State what happens to a neutron that is incident on a control rod (1)

Answer 2

Nucleus absorbs neutron

Question 3

A slow moving neutron collides with a nucleus and causes fission
Describe what happens (3)

Answer 3

Nucleus is absorbed by the nucleus
Nucleus is split into two daughter nuclei fragments
Neutrons are released (plural is necessary for mark)

Question 4

A thermal nuclear reactor produces radioactive waste
State the source of this waste and discuss the problems faced in dealing with it at various stages
Include: main source of most dangerous waste, brief outline of how waste is treated, problems faced in dealing with waste and solutions for these problems (6)

Answer 4

Fission fragments from fission of U-235 or from spent fuel rods

Waste is initially placed in cooling ponds near reactor
Plutonium/Uranium is separated to be recycled
Waste is placed in bunkers stored deep underground

Waste is initially very hot so is cooled in water
Waste will be radioactive for thousands of years so storage must be stable, hence waste is vitrified

Question 5

What is the equation for mass defect? (1)

Answer 5

Mass of individual protons and neutrons minus nuclear mass of nucleus (measured in u)

Question 6

The Rutherford scattering experiment led to which discovery? (1)

Answer 6

Nucleus

Question 7

If a count rate from a Geiger counter is reduced by aluminium foil and thick steel only, what radiation is emitted by the source? (1)

Answer 7

Beta

Gamma

Question 8

Suggest, with a reason, which type of radiation is most appropriate for sterilising metallic surgical instruments (1)

Answer 8

Gamma

It can pass through all instruments

Question 9

Decay is modelled as water flow from a tube via a tap, how can the apparatus be changed to represent more nuclei (1)

Answer 9

Increase depth of water

Question 10

Decay is modelled as water flow from a tube via a tap, how can the apparatus be changed to represent a smaller decay constant (1)

Answer 10

Narrower tube

Question 11

Explain why there is an imbalance between proton and neutron numbers by referring to forces in the nucleus and include the forces’ ranges and the particles affected (4)

Answer 11

Strong nuclear force has a range up to 3 fm and affects neutrons and protons keeping them attracted but not too close as its repulsive under 1 fm
Electrostatic force is repulsive between protons and has a much larger range than strong nuclear force
More neutrons than protons to keep the forces balanced

Question 12

A thallium nucleus is formed in an excited state
Electromagnetic radiation is emitted from the atom
Explain the origin and location of two sources of this radiation (2)

Answer 12

Electron excited, releases photons on moving down energy levels
Nucleus excited, releases gamma

Question 13

Explain why metastable form of technetium is a radioactive source suitable for medical diagnosis (2)

Answer 13

Half life is stable enough for measurements to be made and fast enough to decay quickly after use
Only emits gamma radiation so is very safe

Question 14

What causes Brownian motion with smoke particles and air? (1)

Answer 14

Collisions between smoke particles and air molecules

Question 15

What is most often used as a moderator in a nuclear reactor? (1)

Answer 15

Water

Question 16

Explain why the public need not worry that irradiated surgical instruments become radioactive once sterilised (1)

Answer 16

To become radioactive the nucleus has to be affected which ionising radiation does not do

Question 17

Why might results not follow the inverse square law for measuring count rate with distance using a GM tube? (2)

Answer 17

Random nature of decay

Distance measured is not the real distance between source and detector