Triple Science
4 Atomic Structure
Higher Questions & Answers
Q1.
A student models the random nature of radioactive decay using 100 dice.
He rolls the dice and removes any that land with the number 6 facing upwards.
He rolls the remaining dice again.
The student repeats this process a number of times.
The table below shows his results.
Number of dice
Roll number
remaining
0 100
1 84
2 70
3 59
4 46
5 40
6 32
7 27
8 23
(a) Give two reasons why this is a good model for the random nature of radioactive
decay.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
(2)
(b) The student’s results are shown in Figure 1.
Figure 1
Use Figure 1 to determine the half-life for these dice using this model.
Show on Figure 1 how you work out your answer.
Half-life = ________________________ rolls
(2)
(c) A teacher uses a protactinium (Pa) generator to produce a sample of radioactive
material that has a half-life of 70 seconds.
In the first stage in the protactinium generator, uranium (U) decays into thorium (Th)
and alpha (α) radiation is emitted.
The decay can be represented by the equation shown in Figure 2.
Figure 2
Determine the atomic number of thorium (Th) 234.
Atomic number = ______________________
(1)
(d) When protactinium decays, a new element is formed and radiation is emitted.
The decay can be represented by the equation shown in Figure 3.
Figure 3
When protactinium decays, a new element, X, is formed.
Use information from Figure 2 and Figure 3 to determine the name of element X.
___________________________________________________________________
(1)
(e) Determine the type of radiation emitted as protactinium decays into a new element.
Give a reason for your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(f) The teacher wears polythene gloves as a safety precaution when handling
radioactive materials.
The polythene gloves do not stop the teacher’s hands from being irradiated.
Explain why the teacher wears polythene gloves.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(Total 10 marks)
Q2.
Electricity is generated in a nuclear power station.
Fission is the process by which energy is released in the nuclear reactor.
(a) Figure 1 shows the first part of the nuclear fission reaction.
Complete Figure 1 to show how the fission process starts a chain reaction.
Figure 1
(3)
(b) Figure 2 shows the inside of a nuclear reactor in a nuclear power station.
Figure 2
In a nuclear reactor a chain reaction occurs, which causes neutrons to be released.
The control rods absorb neutrons.
The control rods can be moved up and down.
Explain how the energy released by the chain reaction is affected by moving the
control rods.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(c) Figure 3 shows how the power output of the nuclear reactor would change if the
control rods were removed.
Figure 3
Calculate the rate of increase of power output at 10 minutes.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Rate of increase of power output = _________ MW / minute
(2)
(Total 7 marks)
Q3.
(a) There are many isotopes of the element molybdenum (Mo).
What do the nuclei of different molybdenum isotopes have in common?
___________________________________________________________________
(1)
(b) The isotope molybdenum-99 is produced inside some nuclear power stations from
the nuclear fission of uranium-235.
(i) What happens during the process of nuclear fission?
______________________________________________________________
______________________________________________________________
(1)
(ii) Inside which part of a nuclear power station would molybdenum be produced?
______________________________________________________________
(1)
(c) When the nucleus of a molybdenum-99 atom decays, it emits radiation and changes
into a nucleus of technetium-99.
Mo Tc + Radiation
What type of radiation is emitted by molybdenum-99?
__________________________________________________
Give a reason for your answer.
___________________________________________________________________
___________________________________________________________________
(2)
(d) Technetium-99 has a short half-life and emits gamma radiation.
What is meant by the term ‘half-life’?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(1)
(e) Technetium-99 is used by doctors as a medical tracer. In hospitals it is produced
inside a technetium generator by the decay of molybdenum-99 nuclei.
(i) The figure below shows how the number of nuclei in a sample of molybdenum-
99 changes with time as the nuclei decay.
Time in days
A technetium generator will continue to produce sufficient technetium-99 until
80% of the original molybdenum nuclei have decayed.
After how many days will a source of molybdenum-99 inside a technetium-99
generator need replacing?
Show clearly your calculation and how you use the graph to obtain your
answer.
______________________________________________________________
______________________________________________________________
______________________________________________________________
Number of days = ______________________
(2)
(ii) Medical tracers are injected into a patient’s body; this involves some risk to the
patient’s health.
Explain the risk to the patient of using a radioactive substance as a medical
tracer.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(iii) Even though there may be a risk, doctors frequently use radioactive
substances for medical diagnosis and treatments.
Suggest why.
______________________________________________________________
______________________________________________________________
(1)
(Total 11 marks)
Q4.
Many countries use nuclear power stations to generate electricity.
Nuclear power stations use the process of nuclear fission to release energy.
(a) (i) What is nuclear fission?
______________________________________________________________
______________________________________________________________
(1)
(ii) Plutonium-239 is one substance used as a fuel in a nuclear reactor. For
nuclear fission to happen, the nucleus must absorb a particle.
What type of particle must be absorbed?
______________________________________________________________
(1)
(b) Nuclear fusion also releases energy.
Nuclear fusion happens at very high temperatures. A high temperature is needed to
overcome the repulsion force between the nuclei.
(i) Why is there a repulsion force between the nuclei of atoms?
______________________________________________________________
______________________________________________________________
(1)
(ii) Where does nuclear fusion happen naturally?
______________________________________________________________
(1)
(c) In 1991, scientists produced the first controlled release of energy from an
experimental nuclear fusion reactor. This was achieved by fusing the hydrogen
isotopes, deuterium and tritium.
Deuterium is naturally occurring and can easily be extracted from seawater. Tritium
can be produced from lithium. Lithium is also found in seawater.
The table gives the energy released from 1 kg of fusion fuel and from 1 kg of fission
fuel.
Energy released from
Type of fuel
1 kg of fuel in joules
Fusion fuel 3.4 × 1014
Fission fuel 8.8 × 1013
(i) Suggest two advantages of the fuel used in a fusion reactor compared with
plutonium and the other substances used as fuel in a fission reactor.
1. ____________________________________________________________
______________________________________________________________
______________________________________________________________
2. ____________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii) Some scientists think that by the year 2050 a nuclear fusion power station
capable of generating electricity on a large scale will have been developed.
Suggest one important consequence of developing nuclear fusion power
stations to generate electricity.
______________________________________________________________
______________________________________________________________
______________________________________________________________
(1)
(d) Tritium is radioactive.
After 36 years, only 10 g of tritium remains from an original sample of 80 g.
Calculate the half-life of tritium.
Show clearly how you work out your answer.
___________________________________________________________________
___________________________________________________________________
Half-life = __________________ years
(2)
(Total 9 marks)
Q5.
Atoms are different sizes.
One of the heaviest naturally occurring stable elements is lead.
Two of its isotopes are lead-206 ( ) and lead-208 ( ).
(a) (i) What is meant by ‘isotopes’?
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii) How many protons are in the nucleus of a atom?
__________________
(1)
(iii) How many neutrons are in the nucleus of a atom?
__________________
(1)
(b) A nucleus can be accelerated in a particle accelerator and directed at a large
nucleus. This produces a heavy nucleus that will decay after a short time.
This is shown in Figure 1.
(i) In 1984, nuclei of iron (Fe) were directed at nuclei of lead (Pb). This produced
nuclei of hassium (Hs).
Complete the equation for this reaction by writing numbers in the empty
boxes.
(3)
(ii) Use the correct answer from the box to complete the sentence.
an electron a proton a neutron
The particle X in part (b)(i) is _________________________________ .
(1)
(iii) After acceleration the iron nuclei travel at a steady speed of one-tenth of the
speed of light.
The speed of light is 3.00 ˟ 108 m / s.
Calculate the time taken for the iron nuclei to travel a distance of 12 000 m.
______________________________________________________________
______________________________________________________________
Time taken = ____________________ s
(2)
(iv) Linear accelerators, in which particles are accelerated in a straight line, are
not used for these experiments. Circular particle accelerators are used.
Suggest why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(3)
(c) Hassium-265 ( ) decays by alpha emission with a half-life of 0.002 seconds.
(i) What is meant by ‘half-life’?
Tick ( ) two boxes.
Tick ( )
The average time for the number of nuclei to halve
The time for count rate to be equal to background
count
The time for background count to halve
The time for count rate to halve
(2)
(ii) Complete the equation for the decay of Hs-265 by writing numbers in the
empty boxes.
(2)
(d) The table below shows how the atomic radius of some atoms varies with atomic
number.
Atomic Atomic radius in
number picometres (pm)
15 100
35 115
50 130
70 150
95 170
1 pm = 10-12 m
(i) On Figure 2, use the data from the table above to plot a graph of atomic
radius against atomic number and draw a line of best fit.
Two points have been plotted for you.
Figure 2
(2)
(ii) Scientists believe that the element with atomic number 126 can be produced
and that it will be stable.
Use your graph in Figure 2 to predict the atomic radius of an atom with atomic
number 126.
Atomic radius = ____________________ pm
(1)
(Total 20 marks)
Q6.
(a) Brown dwarf stars are thought to have been formed in the same way as other stars.
They are too small for nuclear fusion reactions to take place in them.
Brown dwarf stars emit infrared radiation but are not hot enough to emit visible light.
(i) Describe how a star is formed.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii) Describe the process of nuclear fusion.
______________________________________________________________
______________________________________________________________
______________________________________________________________
(1)
(iii) Scientists predicted that brown dwarf stars existed before the first one was
discovered in 1995.
Suggest one reason why scientists are now able to observe and identify
brown dwarf stars.
______________________________________________________________
______________________________________________________________
______________________________________________________________
(1)
(b) In the 18th century some scientists suggested a theory about how the planets
formed in the Solar System. The theory was that after the Sun formed, there were
cool discs of matter rotating around the Sun. These cool discs of matter formed the
planets. The scientists thought this must have happened around other stars too.
(i) Thinking about this theory, what would the scientists have predicted to have
been formed in other parts of the Universe?
______________________________________________________________
______________________________________________________________
(1)
(ii) Since the 1980s scientists studying young stars have shown the stars to be
surrounded by cool discs of rotating matter.
What was the importance of these observations to the theory the scientists
suggested in the 18th century?
______________________________________________________________
______________________________________________________________
(1)
(c) The Earth contains elements heavier than iron.
Why is the presence of elements heavier than iron in the Earth evidence that the
Solar System was formed from material produced after a massive star exploded?
___________________________________________________________________
___________________________________________________________________
(1)
(Total 7 marks)
Mark schemes
Q1.
(a) cannot predict which dice / atom will ‘decay’
accept answers given in terms of ‘roll a 6’
1
cannot predict when a dice / atom will ‘decay’
1
(b) 3.6 to 3.7 (rolls)
allow 1 mark for attempt to read graph when number of dice
= 50
2
(c) 90
1
(d) uranium
1
(e) beta
1
proton number has gone up (as neutron decays to proton and e–)
1
(f) prevents contamination
or
prevents transfer of radioactive material to teacher’s hands
1
which would cause damage / irradiation over a longer time period.
1
[10]
Q2.
(a) Nucleus splitting into two fragments and releasing two or three neutrons
1
(at least one) fission neutron shown to be absorbed by additional large nucleus and
causing fission
1
two or three additional neutrons released from fission reaction
1
This diagram would gain all 3 marks:
(b) lowering the control rods increases the number of neutrons absorbed
accept converse description
1
(so) energy released decreases
1
allow changing the position of the control rods affects the
number of neutrons absorbed for 1 mark
(c) rate of increase between 240 and 276 (MW / min)
2
allow 1 mark for attempt to calculate gradient of line at 10
minutes
[7]
Q3.
(a) (same) number of protons
same atomic number is insufficient
1
(b) (i) nuclei split
do not accept atom for nuclei / nucleus
1
(ii) (nuclear) reactor
1
(c) beta
1
any one from:
• atomic / proton number increases (by 1)
accept atomic / proton number changes by 1
• number of neutrons decreases / changes by 1
• mass number does not change
(total) number of protons and neutrons does not change
• a neutron becomes a proton
1
(d) (average) time taken for number of nuclei to halve
or
(average) time taken for count-rate / activity to halve
1
(e) (i) 6.2 (days)
Accept 6.2 to 6.3 inclusive
allow 1 mark for correctly calculating number remaining as
20 000
or
allow 1 mark for number of
80 000 plus correct use of the graph (gives an answer of 0.8
days)
2
(ii) radiation causes ionisation
allow radiation can be ionising
1
that may then harm / kill healthy cells
accept specific examples of harm, eg alter DNA / cause
cancer
1
(iii) benefit (of diagnosis / treatment) greater than risk (of radiation)
accept may be the only procedure available
1
[11]
Q4.
(a) (i) splitting of a(n atomic) nucleus
do not accept splitting an atom
1
(ii) Neutron
1
(b) (i) nuclei have the same charge
or
nuclei are positive
accept protons have the same charge
1
(ii) (main sequence) star
accept Sun or any correctly named star
accept red (super) giant
1
(c) (i) any two from:
• easy to obtain / extract
• available in (very) large amounts
• releases more energy (per kg)
do not accept figures only
• produces little / no radioactive waste.
naturally occurring is insufficient
seawater is renewable is insufficient
less cost is insufficient
2
(ii) any one from:
• makes another source of energy available
• increases supply of electricity
• able to meet global demand
• less environmental damage
• reduces amount of other fuels used.
accept any sensible suggestion
accept a specific example
accept a specific example
1
(d) 12
allow 1 mark for obtaining 3 half-lives
2
[9]
Q5.
(a) (i) (atoms with the) same number of protons
allow same atomic number
or same proton number
1
(atoms with) different number of neutrons
allow different mass number
1
(ii) 82
1
(iii) 124
1
(b) (i)
1 mark for each correct box
3
(ii) (a) neutron
1
(iii) 4.0 × 10-4 (s)
or
0.0004
3.00 × 108 × 0.1 = 12 000 / t
gains 1 mark
2
(iv) particles need to travel a large distance
1
equipment would have to be very long
1
with circular paths long distances can be accommodated in a smaller
space
1
(c) (i) the average time for the number of nuclei to halve
1
the time for count rate to halve
1
(ii)
1 mark if top boxes total = 265
and bottom boxes total = 108
1 mark for 4 and 2 for alpha
2
(d) (i) 3 plotted points
± ½ small square
1
best line through points
1
(ii) 190−205 (pm)
or correct from student’s line
1
[20]
Q6.
(a) (i) (enough) dust and gas (from space) is pulled together
accept nebula for dust and gas
accept hydrogen for gas
accept gas on its own
dust on its own is insufficient
mention of air negates this mark
1
by:
gravitational attraction
or
gravitational forces
or
gravitaty
ignore any (correct) stages beyond this
1
(ii) joining of two (atomic) nuclei (to form a larger one)
do not accept atoms for nuclei
1
(iii) more sensitive astronomical instruments / telescopes
or
infrared telescopes developed
accept better technology
more knowledge is insufficient
1
(b) (i) (other) planets / solar systems
do not accept galaxy
moons is insufficient
1
(ii) provided evidence to support theory
accept proves the theory
1
(c) elements heavier than iron are formed only when a (massive) star explodes
accept materials for elements
accept supernova for star explodes
accept stars can only fuse elements up to (and including)
iron
1
[7]
