Q1.          Most elements have some isotopes which are radioactive.
(a)     What is meant by the terms:
(i)      isotopes
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(1)

(ii)     radioactive?
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(1)

(b)     The graph shows how the number of nuclei in a sample of the radioactive isotope plutonium-238 changes with time.

          Use the graph to find the half-life of plutonium-238.
          Show clearly on the graph how you obtain your answer.
Half-life = ............................ years
(2)

(c)     The Cassini spacecraft launched in 1997 took seven years to reach Saturn.
          The electricity to power the instruments on board the spacecraft is generated using the heat produced from the decay of plutonium-238.
(i)      Plutonium-238 decays by emitting alpha particles.
         What is an alpha particle?
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(1)

(ii)     During the 11 years that Cassini will orbit Saturn, the output from the generators will decrease.
         Explain why.
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(2)

(d)     Plutonium-238 is highly dangerous. A tiny amount taken into the body is enough to kill a human.
(i)      Plutonium-238 is unlikely to cause any harm if it is outside the body but is likely to kill if it is inside the body.
         Explain why.
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(2)

(ii)     In 1964, a satellite powered by plutonium-238 was destroyed, causing the release of radioactive material into the atmosphere.
         Suggest why some environmental groups protested about the launch of Cassini.
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(1)
(Total 10 marks)

 

Q2.          In 1986, a nuclear reactor exploded in a power station at Chernobyl in the Ukraine.
(a)     The table gives information about some of the radioactive substances released into the air by the explosion.
 
Radioactive
substance	Half-life	Type of radiation
emitted	
Iodine-131	8 days	beta and gamma	
Caesium-134	2 years	beta	
Caesium-137	30 years	beta	

(i)      How is the structure of a caesium-134 atom different from the structure of a caesium-137 atom?
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(1)

(ii)     What is a beta particle and from which part of an atom is a beta particle emitted?
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(1)

(iii)     Once a radioactive substance is dissolved in rainwater, it can enter the food chain.
         Following the Chernobyl explosion, some milk supplies were found to be radioactive.
         If one litre of milk contaminated with iodine-131 gives a count rate of 400 counts/second, how long will it take for the count rate to fall to 25 counts/second?
Show clearly how you work out your answer.
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Time taken = ................................................. days
(2)

(iv)    After 20 years, the caesium-137 emitted into the atmosphere is a more serious problem than the iodine-131.
Explain why.
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(2)

(b)     The bar chart compares the incidence of thyroid cancer in Ukrainian children, aged 0–14 years, before and after the Chernobyl explosion.

          Of the children that developed thyroid cancer, 64% lived in the areas most contaminated by the radiation.

          Considering this data, can you be certain that a child who developed thyroid cancer between 1986 and 1990 did so because of the Chernobyl explosion?
Explain the reason for your answer.
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(2)

(c)     In 1991, some scientists compared the health of two groups of people: a control group and a group that had been exposed to the radiation from Chernobyl.
What people would have been in the control group?
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(1)

(d)     Although there are some risks associated with nuclear power stations, it is likely that new ones will be built.
Give two reasons to justify the use of nuclear power.
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2 .................................................................................................................................
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(2)
(Total 11 marks)

 

Q3.          (a)     The table gives information about six radioactive isotopes.
 
Isotope	Type of radiation emitted	Half-life	
hydrogen-3	beta particle	12 years	
iridium-192	gamma ray	74 days	
polonium-210	alpha particle	138 days	
polonium-213	alpha particle	less than 1 second	
technetium-99	gamma ray	6 days	
uranium-239	beta particle	24 minutes	

(i)      What is an alpha particle?
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(1)

(ii)     Two isotopes of polonium are given in the table. How do the nuclei of these two isotopes differ?
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(1)

(iii)     A doctor needs to monitor the blood flow through a patient’s heart. The doctor injects a radioactive isotope into the patient’s bloodstream. The radiation emitted by the isotope is then detected outside the body.
         Which one of the isotopes in the table would the doctor inject into the bloodstream?
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         Explain the reasons for your choice.
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(3)

(b)     Igneous rock contains uranium-238 which eventually changes to the stable isotope lead-206. The graph shows how the percentage of uranium-238 nuclei present in an igneous rock changes with time.

          A rock sample is found to have seven atoms of uranium-238 for every three atoms of lead-206. Use the graph to estimate the age of the rock. Show clearly how you obtain your answer.
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Age of rock = .................................... million years
(2)
(Total 7 marks)

 

Q4.          A beta particle is a high-energy electron.
(i)      Which part of an atom emits a beta particle?
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(1)

(ii)      How does the composition of an atom change when it emits a beta particle?
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(1)
(Total 2 marks)

 

Q5.          Radon is a radioactive gas. Radon makes a major contribution to background radiation levels. Radon atoms decay by the emission of alpha particles.
          (a)     (i)      What is an alpha particle?
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(1)

(ii)     From which part of the radon atom does the alpha particle come?
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(1)

          (b)     (i)      A sample of air contains 40 000 radon atoms. The half-life of radon is four days. Draw a graph to show how the number of radon atoms present in a sample of air will change over a period of 12 days.

(3)

(ii)     After 20 days, how many of the radon atoms from the original sample of air will have decayed? Show clearly how you work out your answer.
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Number of radon atoms decayed = ..........................
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(c)     Fairly constant concentrations of radon gas have been found in some deep mine shafts. 
(i)      Suggest why the concentration of radon gas remains fairly constant although the radon gas decays.
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(1)

(ii)     Explain why the long term exposure to large concentrations of radon gas could be a danger to health.
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(2)
(Total 11 marks)

 

Q6.          The diagram below shows the paths of two alpha particles A and B into and out of a thin piece of metal foil.

(a)     The paths of the alpha particles depend on the forces on them in the metal.
Describe the model of the atom which is used to explain the paths of alpha particles aimed at thin sheets of metal foil.
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(3)

(b)     Scientists used to believe that atoms were made up of negative charges embedded in a positive ‘dough’. This is called the ‘plum pudding’ model of the atom.
The diagram below shows a model of such an atom.

(i)      Explain how the ‘plum pudding’ model of the atom can explain why alpha particle A is deflected through a very small angle.
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(ii)     Explain why the ‘plum pudding’ model of the atom can not explain the large deflection of alpha particle B.
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(3)

(c)     We now believe that atoms are made up of three types of particles called protons, neutrons and electrons.
          Complete the table below to show the relative mass and charge of a neutron and an electron. The relative mass and charge of a proton have already been done for you.
PARTICLE	RELATIVE MASS	RELATIVE CHARGE	
proton	1	+1	
neutron	 	 	
electron	 	 	

(2)

(d)     The diagrams below show the nuclei of four different atoms A, B, C and D.

(i)      State the mass number of C.                         ..................................................

(ii)     Which two are isotopes of the same element? .................... and .....................
         Explain your answer.
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(4)
(Total 14 marks)

 

##
          The isotope of sodium with a mass number of 24 is radioactive. The following data were obtained in an experiment to find the half-life of sodium-24.
Time in hours	Count rate in counts per minute	
0
10
20
30
40
50
60	1600
1000
600
400
300
150
100	

          (a)     Draw a graph of the results and find the half-life for the isotope. On the graph show how you obtain the half-life.

Half-life = ............................... hours
(4)

(b)     Sodium-24 decays by beta emission. The G.M. tube used in the experiment is shown in the diagram. Each beta particle which gets through the glass causes a tiny electric current to pass in the circuit connected to the counter.

(i)      Why must the glass wall of the G.M. tube be very thin?
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(1)

(ii)     Why is this type of arrangement of no use if the radioactive decay is by alpha emission?
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(1)

(c)     Sodium chloride solution is known as saline. It is the liquid used in ‘drips’ for seriously-ill patients. Radioactive sodium chloride, containing the isotope sodium-24, can be used as a tracer to follow the movement of sodium ions through living organisms.
          Give one advantage of using a sodium isotope with a half-life of a few hours compared to using an isotope with a half-life of:
(i)      five years; ........................................................................................................
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(1)
(ii)     five seconds. ....................................................................................................
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(1)
(Total 8 marks)