1. Name two sources of natural background radiation.

1 ...................................................................................................................................
2 ...................................................................................................................................
(6)

Caesium-137 is a by-product of nuclear fission within a nuclear reactor. Complete the two boxes in the nuclear
equation below which describes the production of 137
55 Cs

U 01n137
55 Cs +

235
92

95

Rb +

1
0

n
(6)

The half-life of caesium-137 is 30 years. When the fuel rods are removed from a nuclear reactor core, the total
activity of the caesium-137 is 5.8 1015 Bq. After how many years will this activity have fallen to 1.6
106 Bq?
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Number of years = ......................................................... (12)
(Total 24 marks)

2. The graph shows the decay of a radioactive nuclide.

Determine the half-life of this radionuclide.

Use your value of half-life to calculate the decay constant of this radionuclide.
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Decay constant = ............................
(3)

Use the graph to determine the rate of decay dN/dt when N = 3.0 10 20.
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Rate of decay = ..............................
(9)

Use your value of the rate of decay to calculate the decay constant of this radionuclide.
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Decay constant = ............................
(6)

Explain which method of determining the decay constant you consider to be more reliable.
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(3)
(Total 27 marks)

3. Protactinium, Pa, decays to uranium U by emitting a beta-minus particle. The uranium produced is itself
radioactive and decays by alpha emission to thorium, 234
92 Th.

Mark and label the position of

234
92

U. Draw lines on the grid showing both the beta-minus and the alpha decays.
(Total 12marks)

4. Indium-115 (symbol In, proton number 49) decays by beta-minus emission to tin (symbol Sn). Write down a
nuclear equation representing this decay.
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(6)

Indium-115 has a half-life of 4.4 1014 years. Calculate its decay constant.
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Decay constant = ................................................
(6)

A radioactive source contains 2.3 1021 nuclei of indium-115. Calculate the activity of this source in
becquerels.
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Activity = ...................................................... Bq
State how this activity compares with a normal background count rate.
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(9)
(Total 21 marks)

5. (a) Use the data below to calculate the binding energy in MeV of a nucleus of oxygen,

16
8

Data: mass of proton = 1.007 276 u mass of neutron = 1.008 665 u mass of
oxygen nucleus = 15.990 527 u

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Binding energy = ............................................ MeV (4)
Calculate the binding energy per nucleon of . O168
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Binding energy per nucleon = .................................. (1)
On the axes below sketch a graph of binding energy per nucleon against nucleon
number.

(2)

Show on the graph the approximate position of

238
92

U ,labelling this point U. (3) (Total 10 marks)

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(Class):________ (No):__________