Name: _______________________________________________
P2 Topic 6 Radioactivity Higher
Date:
Time: 31 minutes
Total marks available: 31
Total marks achieved: ______
Questions
Q1.
(a)
In some countries food is sold with this label.
This food has been deliberately exposed to gamma radiation.
Complete the sentence by putting a cross (
The gamma radiation is used to
) in the box next to your answer.
(1)
A
produce cancer cells in the food
B
kill cancer cells in the food
C
kill microbes in the food
D
make the food radioactive.
(b) Cobalt-60 is one source of gamma radiation used for food irradiation. This graph shows how the
activity of a sample of cobalt-60 changes over 10 years.
(i) Use the graph to find the half-life of cobalt-60.
(2)
half-life = ........................................................... years
(ii) The cobalt-60 has to be replaced when its activity has fallen below 1000 Bq.
Estimate how long it takes for the activity to fall from 8000 Bq to 1000 Bq.
(1)
half-life = ........................................................... years
(c) The cobalt-60 sources used to irradiate the food are small metal rods about the size of a pencil.
They are made from stable cobalt-59 which is put inside a nuclear reactor. Some of the cobalt-59 is
turned into cobalt-60 by the radiation in the reactor.
(i) The nuclei of the two isotopes can be represented as
Compare these two isotopes of cobalt.
(2)
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*(ii) When it is time to replace the cobalt-60 rods there are two options.
 The rods can be disposed of.
 The rods can be transported to a nuclear reactor to turn more of the cobalt-59 into cobalt-60 so
that they can be used again.Discuss the hazards in these two options.
(6)
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(Total for Question = 12 marks)
Q2.
Radioactivity, its uses and problems
(a) Radioactivity is used in medicine to diagnose and treat cancer.
State two other uses of radioactivity.
(2)
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(b) Which of these is the correct definition for the half-life of a radioactive isotope?
Put a cross (
) in the box next to your answer.
(1)
A it is the time it takes for half of an atom to decay
B it is the number of atoms left when half have decayed
C it is the time taken for half the undecayed nuclei to decay
D it is half of the time it takes for all the undecayed nuclei to decay
(c) (i) Iodine-131 emits beta particles.
State what a beta particle is.
(1)
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(ii) The graph shows how the activity of iodine-131 varies with time.
A sample of iodine-131 has a mass of 100 mg.
How much iodine-131 will remain after 24 days?
(3)
mass of iodine-131 = ...................................... mg
(d) Scientists in Finland are building a facility for the storage of radioactive waste.
They plan to bury radioactive waste deep underground.
Describe some of the issues that need to be considered when planning to bury nuclear waste.
(3)
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Q3.
(a) A scientist uses a Geiger counter to measure the radioactivity of a sample.
She writes down the results in her notebook.
The Geiger counter gives a count rate of 120 counts per minute.
The average background radiation in her laboratory is 10 counts per minute.
(i) What should she write down for the count rate of this sample?
Put a cross (
) in the box next to your answer.
(1)
A
12 counts per minute
B
110 counts per minute
C
130 counts per minute
D 1200 counts per minute
(ii) Name one source of background radiation.
(1)
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(iii) Explain why some people are exposed to more background radiation than others.
(2)
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(iv) Complete the sentence by putting a cross (
) in the box next to your answer.
The recommended safe limit for exposure to radiation has been reduced over the last 80 years.
This is because now
(1)
A better instruments allow scientists to make measurements more quickly
B global warming has increased the rate of decay of radioactive materials
C humans release more radioactive materials into the environment
D scientists have a better understanding of the dangers of radiation
(b) After the accident at the Fukushima nuclear plant in Japan, some drinking water became
contaminated with radioactive
iodine-131.
The graph shows how the activity of a sample of iodine-131 changes over two weeks.
(i) Use the graph to estimate the half-life of the iodine-131.
Show your working clearly.
(2)
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(ii) The recommended safe limit for a sample of this size is 100 Bq.
How long did it take for the activity of the sample to decay until it was below the safe limit?
(1)
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(iii) When iodine-131 decays, it emits beta radiation.
State one possible danger to health from exposure to beta radiation.
(1)
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(Total for Question is 9 marks)
Examiner's Report
Q1.
(b)
It was pleasing to see that so many candidates could interpret the graph and correctly read the scale to
arrive at a value between 5.1 and 5.5. The most common error was to look for the activity at 5 years (ie
half-way along the time axis) or to simply give 5 years.
In the second part, the majority of candidates recognised that three half-life periods were required for the
activity to fall from 8000 Bq to 1000 Bq. Those that had an incorrect value in part (i) could carry that error
forward for full credit in part (ii) if they showed appropriate working. Some candidates attempted to
extrapolate the graph. Credit was given if they arrived at a value between 15.5 and 16.5, but this was rare
to see.
Results Plus: Examiner Comments
This is a clear answer worth 3 marks.
Results Plus: Examiner Comments
2 marks were awarded for the first part but no mark was given for trying to continue the
curve outside of the margin of the paper.
Results Plus: Examiner Tip
The examiner will not expect you to continue a graph outside of the given scale.
(c) (i)
Isotopes were well understood by most candidates and very many could give the correct number
of neutrons and protons in each nucleus. It was noticeable that fewer candidates mentioned
electrons (which are not relevant in this context) than in previous years.
(c) (ii)
Most candidates fully engaged with this question. The hazards of radioactive materials were well
known and candidates were able to write extensively on this topic. Level 1 answers were able to
describe some of the hazards; most frequently the effect of radiation on living organisms. For
level 2, examiners were looking for a more detailed response. This might be an expansion on the
particular properties of the (gamma) radiation from the pencils or the duration for which they
would emit significant amounts of radiation. It might also include details about how these hazards
could be addressed such as shielding or particular storage, transport or handling arrangements.
Level 3 responses contained a detailed discussion which included both storage and
reprocessing.
As with the previous extended response question, there was sufficient space on the paper for a
well-structured answer at level 3. Unfortunately, many candidates did not structure their answers
but appeared to simply write down everything they could think of. It was common to read of
possible disposal methods such as sending into space or disposal at sea which are no longer
seriously considered as viable options. It was also very common for candidates to write about
dangers of nuclear reactors in general: often quoting named examples of recent accidents. They
would then often state that putting the spent cobalt pencils into a nuclear reactor would increase
the likelihood of such accidents.
Once again, these responses frequently tended to go outside of the allocated space and onto
continuation sheets with little mark-worthy content.
This is a well-constructed answer.
Results Plus: Examiner Comments
The candidate has given detail about the hazards and considered how they may be
dealt with in both storage and transport. The answer addresses the question concisely.
This is a level 3 answer. The quality of written communication was appropriate for this
level and scored 6 marks.
Results Plus: Examiner Comments
This level 1 answer gives a simple description of the health hazard of disposal of the
(radioactive) material but does not expand on either the nature of the radiation, how
long it might be dangerous nor how the hazard could be addressed. There is a mention
of transport but does not describe how this might be hazardous apart from mentioning it
being 'spilt'.
Q2.
No Examiner's Report available for this question
Q3.
(a) (ii)
Most of the candidates were able to name a source of background radiation. The most popular
responses were radon gas and cosmic rays.
(a) (iii)
Examiners were looking for an understanding that background radiation has regional variations.
A person who flies a lot would also be subject to more cosmic rays. A mark was given for stating
that a person's exposure to background radiation depended on their individual circumstances
such as where they live or their lifestyle. A further mark was awarded for an explanation of why
that led to more background radiation. Many of the candidates scored full marks but a significant
number of the candidates cited where a person lived as a reason for increased background
radiation but lost marks failing to explain why and often simply repeated the stem without further
explanation.
Most candidates related increased background radiation to where a person lives.
Results Plus: Examiner Comments
This is a clear answer which scores 2 marks.
Results Plus: Examiner Comments
This answer does not explain why background radiation might be more in one place
rather than another and scores 1 mark only.
Some candidates knew that certain jobs could expose a person to more radiation.
Results Plus: Examiner Comments
This answer does not say why a particular job might increase exposure to radiation. It
only scored 1 mark.
(b) (i)
The vast majority of candidates correctly found the half life from the graph. The most common
error was to look for 70Bq ( half of the axis maximum rather than the activity at 0 days).
(b) (ii)
The acitivity fell to 100Bq point at 2.2 days. Answers between 2 and 2.5 days were accepted.
Many candidates, however, seemed to think that days can only be a whole number and gave an
answer of the next full day ( ie 3 days).
(b) (iii)
Dangers to health from beta radiation were well known and, compared with the previous
examination series, candidates were more precise in their answers. Most scored the mark.
Mark Scheme
Q1.
Q2.
Question
Number
(a)
Question
Number
(b)
Question
Number
(c)(i)
Answer
Acceptable answers
Any two from the
following points
• smoke alarms (1)
• irradiating food (1)
• dating (e.g.
radiocarbon) (1)
• sterilisation of
equipment (1)
• tracing and
gauging thickness
(1)
Answer
credit any specific
examples but must
be from two different
areas for 2 marks
C
Answer
(fast moving)
electron
Mark
Acceptable answers
(2)
Mark
Acceptable answers
(1)
Mark
(1)
Question
Number
(c)(ii)
Question
Number
(d)
Answer
Acceptable answers
Mark
half life = 8 days (1)
24 days = 3 half lives
(1) 12.5 (mg) (1)
bald 3 half lives for 2
marks give full marks
for correct answer,
no working
Acceptable answers
(3)
Mark
Answer
A description
including three of
the following points
• the long time taken
for decay (of
long-lived
radionuclides)
• water causing
corrosion / leaks
• transportation of
radioactive material
• need for
geologically stable
rock formation
• public perception of
waste • security from
terrorist activity
idea of planning for
conditions hundreds
/thousands of years
from now public do
not want waste
buried near where
they live (so
limitation on
available sites)
Answer
Acceptable
answers
B
Any one of the
following
Rocks
Food
Radon gas
Cosmic rays
Own bodies
Fall-out
Sun/stars
(1)
(1)
Plausible named
food such as coffee,
brazil nut, bananas
Space
Specified
medical/industrial
use of x-rays Ignore
smoke alarms,
power stations (in
normal use)
(3)
Q3.
(a) (i)
(a) (ii)
(a) (iii)
(1)
An explanation
linking
 personal
circumstances such
as
geographical
location nature of
their work lifestyle
(1)
 the
consequences such
as
radiation from radon
gas/particular
Mark
(2)
rocks/fallout (eg
Chernobyl)
greater exposure to
x-rays greater
exposure to cosmic
rays
(a) (iv)
(b) (i)
(1)
D
From the graph
Time taken to fall
(from 120 to) 60
(1)
= 8 days
(b) (ii)
(b) (iii)
(1)
2.2 (days)
(1)
Any one of the
following:
 Mutation of dna
 Ionisation of cells
 (Increases risk
of)
cancer
(1)
Any other suitable
pair of readings from
graph 8.1, 8.2
Full marks for correct
answer even if no
working is evident
between 2.0 and 2.5
2
damage / mutate
cells
(1)
(2)
(1)
(1)