Question 12
(a)
- (i) Define radioactivity.
(ii) If is a parent atom and E is the daughter atom of an element, write a balanced nuclear reaction to indicate;
(I) an alpha particle emission;
(II) a beta particle emission.
(B)(i) Define half-life of a radioactive element.
(ii) A radioactive element of mass 4.96 g has a half life of 32 hours. Calculate the mass of the element remaining after 224 hour.
(c)(i) Explain the term donor impurity.
(ii) Draw and label an energy band diagram of a semiconductor. Indicate the position of the extra energy level when an acceptor impurity is added
(ii) charge.
Part (a), candidates performance was below average.
Part (b), candidates performance was below average.
Part (c), candidates performance was below average
The expected answers are:
12.(a) (i) Definition of radioactivity
The (spontaneous) disintegration of an unstable atomic nucleus with the emission of radiations (a particle, b particle and γ rays) and energy.
(b) (i) Definition of half-life
The time taken for a quantity of a radioactive substance to decay/disintegrate to half its original/initial value.
OR
Time taken for half of the nuclides or atomic nuclei of a radioactive sample present to decay/disintegrate
