Exam-style Questions: Radioactivity
Radioactive isotopes of elements can emit 3 types of radioactivity a, b and g.
a) Explain the term 'isotope'.
b) Complete the table below showing the properties of the three types of radioactivity:
Type of radioactivity: Nature: Charge: Ionising power: Penetrating power: a (i) +2 large Thin sheet of paper b (ii) (iii) medium (vi) g Electromagnetic waves (iv) (v) Many cm of lead
(Marks available: 4)
Answer outline and marking scheme for question: 1
a) An isotope of an element has the same number of protons in the nucleus but different numbers of neutrons.
(i) helium nuclei
(vi) a few mm of aluminium
(6 correct = 3 marks, 4 correct = 2 marks, 2 correct = 1 mark)
(Total = 4 marks)
The diagram below shows how radioactivity can be used to check the thickness of a plastic as it is manufactured.
a) What type of detector is used in this process?
b) What would happen to the radioactive count if the plastic sheet was too thin?
c) Which type of radioactivity could be used for this process?
Explain your answer.
(Marks available: 5)
Answer outline and marking scheme for question: 2
a) Gieger-Muller tube/G-M tube/Geiger counter
b) It would increase.
because all the a radioactivity would be stopped by the plastic (so a change in thickness would not be detected),
and g radioactivity would not be stopped at all by the plastic (and a change in thickness would not stop any more).
(Total = 5 marks)
When a radioactive isotope emits radioactivity a new substance can be made. Balance the following radioactive equations to identify the new element made.
(You may need to look at a periodic table to help you).
a) What is element X?
b) What is element Y?
(Marks available: 2)
Answer outline and marking scheme for question: 3
(Atomic number decreased by 2, atomic mass decreased by 4)
(Atomic number increased by 1, atomic mass is the same)
(Total = 2 marks)
A sample of wood from the British museum is sent for radiocarbon dating. In this process, the radioactivity emitted from the sample is compared to the count from a new piece of wood. The radioactivity is due to 14C, which has a half-life of 5600 years.
a) Explain the term 'half-life'.
b) The radioactive counts of the samples is shown below;
Sample: Radioactive count (counts/min/g): Old 5 New 20
Using this information, calculate the age of the old sample of wood.
(Marks available: 3)
Answer outline and marking scheme for question: 4
a) The half-life is the time taken for the radioactivity of a material to decrease by half.
b) Half-life of 14C is 5600 years.
Radioactive count has decreased from 20 to 5 = 2 half-lives.
(20 → 10 is one half-life, 10 → 5 is the second).
Age of wood = 2 x 5600 years = 11200 years.
(Total = 3 marks)