GCSE Questions: Radioactivity
(a) The graph shows how a sample of barium-143, a radioactive isotope with a short half-life, decays with time.
(i) What is meant by the term isotope?
Isotopes of an element have equal number of protons but different number of neutrons
Isotopes of an element have the same atomic/proton number but a different mass/nucleon number
(ii) What is meant by the term half-life?
Half-life is the time taken for activity (or 'count rate' or 'number of nuclei') to decrease to half.
(iii) Use the graph to find the half-life of barium-143.
(b) Humans take in the radioactive isotope carbon-14 from their food. After their death, the proportion of carbon-14 in their bones can be used to tell how long it is since they died. Carbon-14 has a half-life of 5700 years.
(i) A bone in a living human contains 80 units of carbon-14. An identical bone taken from a skeleton found in an ancient burial ground contains 5 units of carbon-14.
Calculate the age of the skeleton.
Show clearly how you work out your answer.
80 to 40 - First half life
40 to 20 - Second half life
20 to 10 - Third half life
10 to 5 - Fourth half life
4 half lives = 4 x 5700 = 22800 years
(ii) Why is carbon-14 unsuitable for dating a skeleton believed to be about 150 years old?
The decay of carbon-14 over 150 years is insignificant there is very little decay the change is too small
(c) The increased industrial use of radioactive materials is leading to increased amounts of radioactive waste.
Some people suggest that radioactive liquid waste can be mixed with water and then safely dumped at sea.
Do you agree with this suggestion?
Explain the reason for your answer.
massive dilution of waste within the ocean
reduces concentration (within a given volume) to insignificant levels
dumped distant from human habitation
pollution (of the sea/beach)
mutation or harm caused to living things (animals/plants)
effect on food chain
long period of time necessary for radioactive isotopes to be harmless
(Total 9 marks)