Question 12
- (i) Define decay constant
(ii) An isotope of Radon has a half-life of 3.8 days. Calculate its decay constant
- Mass defect;
- Binding energy of a nucleus.
- State the function and material used for each of the under listed components in a nuclear fission reactor
(i) moderator;
(ii) control rods;
(iii) coolant
- A nucleon of hydrogen -3 is formed when a neutron is absorbed by a nucleus of hydrogen -2. The table below give the masses of the particles in atomic mass unit (u)
- Write a balanced equation for the reaction
- Calculate the energy released in this reaction
Observation
Part (a): Performance was below average. Many candidates skipped the essential “time rate” to score zero in the definition of decay constant. In 12 (a) (i), many candidates failed to convert the “days” into “seconds”.
Part (b): Performance was above average as candidates gave acceptable responses to the question.
Part (c): Performance for (i), (ii), (iii) was generally below average. Many candidates scored zero for failure to include as a second product, a term representing the energy released
The expected answers are:
12.(a) (i) Decay Constant ()
The time rate of decay/disintegration per unit nucleus of a radioactive element at an instant.
OR
The ratio of the number of nuclei disintegrating per second to the number of nuclei in the source at that instant.
