P2 Revision Booklet

More Radiation

Harder (Grade B-A*)

Q1.          (a)    Some rocks inside the Earth contain uranium-238, a radioactive isotope of uranium. When an atom of uranium-238 decays, it gives out radiation and changes into a thorium-234 atom.

(i)      What type of radiation is emitted when a uranium-238 atom decays?
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(1)

(ii)     From which part of a uranium-238 atom is the radiation emitted?
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(1)

(iii)    Uranium-235 is another isotope of uranium.
How is an atom of uranium-235 similar to an atom of uranium-238?
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(1)

(b)     Uranium-238 has a half-life of 4500 million years.
(i)      When the Earth was formed, there was twice as much uranium-238 in the rocks as there is now.
What is the age of the Earth?
...............................................................................................................
(1)

(ii)     Complete the graph to show how the number of nuclei in a sample of uranium-238 will change with time.
Initially, there were 100 000 nuclei in the sample.

(2)
(Total 6 marks)
Q2.          (a)     The diagram shows what can happen when the nucleus of a uranium atom absorbs a neutron.

(i)      What name is given to the process shown in the diagram?
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(1)

(ii)     Explain how this process could lead to a chain reaction.
         You may wish to add further detail to the diagram to help your answer.
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(2)

(iii)     How does the mass number of an atom change when its nucleus absorbs a neutron?
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(1)

(b)     Uranium-235 is used as a fuel in some nuclear reactors.

Source: adapted from ‘Physics Matters’, by Nick England. Published by
Hodder and Stoughton, 1989. Reproduced by permission of Hodder and Stoughton Ltd.
          The reactor contains control rods used to absorb neutrons.
          Suggest what happens when the control rods are lowered into the reactor.
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(2)
(Total 6 marks)
 Q3.          (a)     Nuclear power stations use the energy released by nuclear fission to generate electricity.
(i)      Explain what is meant by nuclear fission.
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(2)

(ii)     How does nuclear fission lead to a chain reaction?
         You may give your answer as a labelled diagram.

 
 
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(1)

(b)     Although nuclear fuels are relatively cheap the total cost of generating electricity using nuclear fuels is expensive. Why?
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(1)

(c)     The table compares the energy released from 1 kg of coal and 1 kg of uranium.
Coal	29 MJ	1 MJ = 1 000 000 joules	
Uranium	580 000 MJ	 	

          State one benefit to the environment of using a concentrated fuel like uranium to generate electricity rather than using the energy from coal.
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(1)
(Total 5 marks)
 Q4.          (a)     When an atom of thorium-232 decays, an alpha (α) particle is emitted from the nucleus. An atom of radium is left behind.
          An alpha particle consists of two protons and two neutrons.
          We can represent this radioactive decay in a special kind of equation:

          Thorium-228 is also radioactive.
          Atoms of this isotope also decay by emitting an alpha particle and producing an isotope of radium.
          Complete the equation for this decay.
          
(4)

(b)     An atom of radium-228 decays by emitting a beta (β) particle from the nucleus.
          A beta particle is in fact an electron (symbol).
          The effect of this is to change a neutron into a proton.
          An atom of actinium remains.

          This type of decay can also be represented by an equation:

          This isotope of actinium is radioactive.

          An atom of actinium-228 also decays by emitting a beta particle.
          An isotope of thorium is left behind.
          Complete the equation for this decay.
          
(4)

(c)     Thorium-232 eventually decays to the stable isotope lead-208.
          All the steps in this process can be shown on a diagram.

(i)      Complete the sentences:
         During the decay from (A) to (B) a .................... particle is emitted.
         During the decay from (B) to (C) a .................... particle is emitted.
         During the decay from (E) to (F) a .................... particle is emitted.
         During the decay from (I) to (J) a .................... particle is emitted.
(2)

(ii)     The table shows how long it takes for half of the atoms of each isotope to decay.

         A rock sample contains:
•        many atoms of thorium‑232
•        even more atoms of lead‑208
•        hardly any atoms of any of the other isotopes shown on the diagram

         Explain this as fully as you can.
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(3)
(Total 13 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)
More radiation-Mark scheme
M1.         (a)      (i)     alpha (particle)
1

(ii)     (unstable) nucleus 
accept (unstable) nuclei
do not accept middle
do not accept helium nucleus
1

(iii)    same number of protons
accept same number of electrons
accept same atomic / proton number
accept they both have 92 protons
same number of neutrons negates answer
1

(b)     (i)      4500 million years 
do not accept 4500 years
1

(ii)     curve starting at 100 000 with a correct general shape
1

passing through (4500, 50 000) and (9000, 25 000)
allow 1 mark for points plotted
or
line passing through (4500, 50 000) and (9000, 25 000)
1
[6]
 M2.          (a)     (i)      (nuclear) fission
accept fision providing clearly not fusion
1

(ii)     (released) neutrons are absorbed by further (uranium) nuclei
accept hit nuclei for absorbed / hit
do not accept atom for nuclei
1
         more neutrons are released (when new nuclei split)
accept for both marks a correctly drawn diagram
1
(iii)     increases by 1
         or goes up to 236
1

(b)     any two from:
•        (more) neutrons are absorbed
accept there are fewer neutrons
•        (chain) reaction slows down / stops
accept keeping the (chain) reaction controlled
•        less energy released
accept heat for energy
accept gases (from reactor) are not as hot
2
[6]
 M3.          (a)     (i)      (large) nucleus hit by a neutron
1
         splits into (smaller) nuclei and neutron(s) (+ energy)
1
(ii)     additional neutrons collide with nuclei causing further fission
allow full credit for a correct labelled diagram
accept 2 or more neutrons given out at each fission reaction
diagram shows 3 discernible sizes, with smaller nuclei and neutrons at same stage

1

(b)     cost of (building and) de-commissioning is very high or
cost of building is higher
accept a correct description of de-commissioning
accept high cost to keep the power station safe / secure
accept high cost of reprocessing / storage of nuclear waste
1

(c)     less pollution from transport carrying the fuel
accept coal produces more pollutant gases
accept correct named gases
accept more radiation pollution from coal than nuclear
accept more waste from coal than nuclear
do not accept any reference to burning uranium
do not accept answers in terms of global warming or acid rain unless developed
1
[5]

##
          (a)     

[Accept He2+ for α]
each  for 1 mark
4

(b)     

[Accept β for e]
each  for 1 mark
4

(c)     (i)      beta/ β              alpha/ α
alpha/ α            beta/ β
beta/ β    but     alpha/ α
alpha/ α            beta/ β
[i.e. consistent for 1; consistent and correct for 2]
gains 2 marks
2

(ii)     ideas that
•    many thorium atoms because they take so long to decay*
•    (many lead atoms because) the thorium has been decaying for
     so long/for billions of years
or (because) the rock is so/very/billions of years of years old
•    many lead atoms because this is the stable end product [of the decay series]
•    few atoms of other isotopes because they decay so quickly*
         [*N.B. credit answers in terms of half-life]
any three for 1 mark each
3
[13]
 M5.          (a)     sensible scales
full use of y axis
1
completely accurate plotting
1
          a smooth curve going through all bar one of the points
do not accept a dot-to-dot graph if two parts shown for curves accept the more correct
1

          at least one line or a clear mark showing how to obtain the half life
from the graph and obtaining between 13 and 15
at the bottom of the page cross or ticks in the order of the mark scheme
1

          (b)     (i)      to let the beta particles get through
accept must be there to let the radiation through or if thick they may be stopped
1
(ii)     alpha particles would be stopped by the glass or cannot penetrate glass
do not accept alphas are weak
1

          (c)     (i)      it will give more counts per minute for a small quantity or it does not last
so long so may not be as dangerous
accept answers in terms of 5 years assume it refers appropriately
1

(ii)     it will not be there long enough to act as a tracer or it could cause
radiation damage as all its activity will be in the first place it enters the system
accept answer in terms of 5 seconds 
accept not there long enough to work assume it refers appropriately
1
[8]