AS Science In Society 1.7
Teacher Notes
Introduction
This comprehension activity will help students to place their
study of radioactive decay into a real-life context.
The activity
This is a comprehension activity which uses an adaptation of a
newspaper report of a research paper. Students will read, and
answer questions, about the science behind the headline.
Extension: For more able students you could provide them
with the original research paper and ask them to compare and
contrast the newspaper article and the research.
How Science Works
Fb The popular media play a part in providing
information, setting the agenda and influencing
opinion on issues involving science and
technology.
Fc Media reports of scientific developments
are always simplified, and sometimes
inaccurate. A newspaper report of a new
development has not been through the
stringent peer review process that articles in
scientific journals must undergo (though it may
be reporting on work that has).
Additional Resources
The original research paper:
http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.
pone.0001529
A detailed explanation of the paper:
http://www.sciencedaily.com/releases/2008/01/080129201238.
htm
Suggested answers:
1. What is C-14 and how does it differ from Carbon -12?
A radioactive isotope of Carbon. It has 6 protons and 8
neutrons in its nucleus.
2. Radiocarbon dating depends on the half-life of a
radioactive material. What is half-life? Sketch a graph to
help explain your answer.
The half-life of a radioactive material is the time it takes for
the original activity (or number of nuclei) to decrease by
half. This value is the same for every halving – a
logarithmic scale.
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Science Explanations
Da Although all atoms of an element have the
same number of protons and electrons they
may have different numbers of neutrons.
Atoms of the same element with different
numbers of neutrons are called isotopes. Most
atoms are stable but some of these isotopes
have unstable atoms. A substance containing
unstable atoms is said to be radioactive.
Db Radioactive atoms decay, emitting
radiation. The decays occur randomly but with
a definite probability. As they proceed, the
number of radioactive atoms left in a sample
falls, so the rate of emission drops. The
number of emissions per second is called the
activity of the source (in becquerel). The time
which it takes for the activity of a sample of
radioactive isotope to fall from any initial value
to half of that value can be measured and is
called the half-life of the radioactive isotope.
The half-life is characteristic of the isotope
Dh Effects of radioactivity can be spread in
two ways: by irradiation (the emissions from a
radioactive substance striking and being
absorbed by another object); and by
contamination (the transfer of pieces of the
radioactive substance itself on to, or into,
another object).
Ed Most matter contains more than one
element or compound mixed together. The
proportions of the different substances in the
mixture will vary. For example the air is a
mixture of several gaseous elements and
compounds. The proportions of each can be
measured in parts per million, parts per billion
or other units.
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Teacher Notes
Graph to show half-life
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3. How does radiocarbon dating work?
Scientists know the ratio of C-14 to C-12 in the atmosphere. Every living object breathes in a small
amount of C-14 in the form of radioactive Carbon Dioxide. The radioactive carbon may then be fixed
in the tissues (in this case the crystallins in the lens). At this point the ratio of C-14 to C-12 in the
tissue starts to change as the C-14 undergoes radioactive decay. The older an object is the less C14 it will have. By looking at the amount of C-14 in a tissue, and comparing it with the amount
present in the atmosphere scientists can calculate how long ago the ratio of the isotopes were the
same.
4. Why has C-14 in the atmosphere returned to natural levels since 1960?
C-14 has been removed from the atmosphere due to photosynthesis ‘locking it up’ in biomass. Also,
some of the C-14 will have decayed.
5. Does this story give an example of radioactive contamination or irradiation? Explain your answer.
Contamination – radioactive isotope is inside the body.
6. The newspaper article suggests that this technique could be used to work out a person’s age.
a. Is this a likely use for the research? Why?
Unlikely as need to take a sample of the lens.
b. Suggest a different possible use for the research.
Could be used in forensic science to calculate the age of a recently deceased body.
Page 2
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Student sheets
The activity:
Read through the newspaper extract and answer the questions that follow.
Looking your Age?
IF YOU go through life lying about your age, science can now find you out – thanks to the radioactive
fallout from Cold War weapons testing.
Danish investigators have found that they can estimate your date of birth with a high degree of accuracy,
by subjecting protein from the lens of your eye to radiocarbon dating.
The transparent proteins, called crystallins, build up in babies’ eyes from birth until around the age of 2.
Once the construction is finished, the crystallins remain essentially unchanged for the rest of our lives.
Thus, they provide a record of the environment we spent our first days in – including the type of
radiation.
From the end of the Second World War until about 1960, the Cold War superpowers ran a series of
nuclear bomb tests in the atmosphere. These detonations have affected the content of radioactive
materials in the air and created what scientists refer to as the “C-14 bomb pulse”.
From the first nuclear bang until the nuclear test ban treaties were agreed, the quantity of C-14 in the
atmosphere doubled. Since 1960, it has slowly decreased to natural levels.
Scientists at the universities of Copenhagen and Aarhus report how the fallout got into the food chain and
thus into our crystallins. These proteins therefore reflect the content of C-14 present in the atmosphere at
the time of their creation, shortly after birth.
Using a large nuclear accelerator, the physicists can determine the amount of C-14 in as little as one
milligram of lens tissue and calculate the year of birth. Gotcha.
Adapted from:
http://women.timesonline.co.uk/tol/life_and_style/women/
body_and_soul/article3288379.ece
1. What is C-14 and how does it differ from Carbon -12?
2. Radiocarbon dating depends on the half-life of a radioactive material. What is half-life? Sketch a
graph to help explain your answer.
3. How does radiocarbon dating work?
4. Why has C-14 in the atmosphere returned to natural levels since 1960?
5. Does this story give an example of radioactive contamination or irradiation? Explain your answer.
Page 1
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Student sheets
6. The newspaper article suggests that this technique could be used to work out a person’s age.
c. Is this a likely use for the research? Why?
d. Suggest a different possible use for the research.
August 2008
Page 2
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges