Nuclear physics

Question 1

Describe how the strong nuclear force between two nucleons varies with the
separation of the nucleons quoting suitable values for separation. (3 marks)

Answer 1

• SNF ACTS OVER A SHORT RANGE
• Repulsive less than 0.5fm then attractive after this
• Attractive from a range of 0.5-3fm
• Attraction quickly drops at a distance further than 3fm

Question 2

State the nature of an alpha particle (1 mark)

Answer 2

A helium nucleus

Question 3

Under suitable conditions, a γphoton may be converted into two other particles rather than
an electron and positron.
Give an example of the two other particles it could create.

Answer 3

-any pairing of a particle with its corresponding

antiparticle eg proton & antiproton

Question 4

Explain what is meant by a thermal neutron. (2 marks)

Answer 4

• Slow moving neutrons

- That are in thermal equilibrium with the moderator

Question 5

Name the substance used as the moderator in a pressurised water reactor
(PWR). (1 mark)

Answer 5

Water

Question 6

Properties of nuclear reactor:

Answer 6

• Collisions are not always elastic

- Collisions in a reactor are rarely head on

Question 7

The wooden block is replaced by a steel block of the same mass.
The experiment is repeated with the steel block and an identical pellet. The pellet
rebounds after striking the block.
Discuss how the height the steel block reaches compares with the height of 0.63 m
reached by the wooden block. In your answer compare the energy and momentum
changes that occur in the two experiments. (4 marks)

Discuss which experiment is likely to give the more accurate value for the velocity of
the pellet. (2 marks)

Answer 7

-As pellet rebounds, change in momentum of pellet greater and therefore the
change in momentum of the block is greater
-Initial speed of block is greater
-Initial KE of block greater
-Therefore height reached by steel block is greater than with wooden block

2nd part:

-Calculation of steel method will need to assume that collision is elastic so that
change of momentum can be calculated
-This is unlikely due to deformation of bullet, production of sound etc.

Question 8

Explain what is meant by electron capture (3 marks)

Answer 8

• an atomic/orbital/shell electron
• interacts with a proton in the nucleus
• neutron formed (and neutrino released)