Question 12
(a) (i) Define natural radioactivity.
(ii) State the relationship between the decay constant λ, and the half-life, , of a radioactive decay process
(iii) A radioactive element has a decay constant of 4.6 x 10-2 atoms per minute. The initial reading on a detector for the radiations of this element is 1600 per minute. Calculate the time taken for the rate to fall to 100 per minute.
(b)(i) What are cathode rays?
(ii) State four properties of cathode rays.
(c)(i) State the energy transformations which take place during the operation of -ray tube.
(ii) State two uses of rays.
Observation
Part (a) Well attempted by most candidates.
Part (b) Many candidates attempted this question correctly.
Part (c) Candidates performance was average.
The expected answers are:
(a)(i) Characteristics of nuclear reaction
- Mass is converted to energy
- Not affected by pressure
- Not affected by temperature
- Does not depend on the state of the nuclide
- Charge is conserved
(ii) Applications of atomic radiation
- Treatment of (malignant) tumours
- Study of crystal structure
- Preservation of food stuffs
- Detection of fracture
(b) (i) The relationship between T½ andl of a radioactive element
