RADIOACTIVITY WORKSHOP
OVERVIEW
I
STEP-BY-STEP GUIDE
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A.
Equipment list
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B.
Workshop guides
II
ADDITIONAL MATERIAL
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A.
Alpha and beta radiation trail pictures
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B.
Nuclei decay graph
III
HANDOUTS & WORKSHEETS
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A.
Radioactivity workshop student worksheet
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B.
Radiation chart
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I
STEP-BY-STEP GUIDE
A.
Preparation Before Workshop
A1. FULL EQUIPMENT
CHECKLIST
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B.
Geiger counter (one per
group)
Selection of radioactive
rocks (one per group)
Beta decay model from
particle zoo
Bag of 10 6+ sided dice
(one per student)
Radioactivity worksheet
(one per student)
Graph paper
Cloud chamber containers
Isopropanol alcohol
Dry ice
Desk lamp
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A2. OPTIONAL EQUIPMENT
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Radioactivity worksheet
(one per student)
Graph paper
Smoke alarms
Uranium marbles
UV torch
Workshop Guides
B1. Safety Notices
B2. Introduction to Radioactivity
B2.1 History of Radioactivity
B2.2 Structure of the Nucleus and Types of Radiation
B3. Measuring Radioactivity
B4. Half Life
B5. Cloud Chambers
KEY
WORK TO BE DONE
TALKING POINTS
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Spectral Workshop
B1. SAFETY NOTICES
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The radioactive rocks can be removed from the box they are stored
in, but must not be removed from their individual bags.
B2.1. HISTORY OF RADIOACTIVITY
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Ask the students if they know what radiation is. Radiation is the
process of an unstable atomic nucleus losing energy by ejecting
particles or emitting electromagnetic waves.
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Becquerel discovered radioactivity in 1896 when he left
uranium salts on top of some photographic plates in a drawer – when
the plates were developed, an image of the crystals was produced
(courtesy of radiation from the uranium).
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Scientists were initially completely ignorant to the dangers of
radioactivity. Marie Curie, one of the co-discoverers of radioactivity,
died from aplastic anemia – almost certainly a result of her regular
exposure to substantial radioactivity without the protection we now
know is necessary. Her papers – and even her cookbook – are too
radioactive to hold, even today, 100 years later.
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But radioactivity can also be very beneficial – it is used in
industry and health care.
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B2.2. STRUCTURE OF THE NUCLEUS AND TYPES OF RADIATION
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To understand radiation, we must understand the atom and it's
fundamental components. Ask the students what they know about
the atom. The central nucleus of an atom is made of tightly bound
protons and neutrons – two particles that are very similar apart from
that the proton is positively charged and the neutron neutrally
charged. This nucleus is surrounded by electrons – particles much
lighter than the proton and neutron but with an equal and opposite
charge to the electron.
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Before explaining the three types of radiation, ask the students
if they know about them and their features.
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The first type of radiation, alpha, is made of up two protons and
two neutrons from the atomic nucleus. Because of it's size, this type
of radiation travels slowly and can be stopped easily by something as
thin as a sheet of paper.
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The second type of radiation, beta, is a single energetic
electron. To produce an electron, one of the neutrons in the nucleus
changes into a proton (which stays in the nucleus) and an electron
(which leaves). Since the number of protons in an atom decides the
element the atom is, this means emitting beta radiation changes the
element! Because beta radiation is smaller than alpha, it travels
faster and is harder to stop – it takes a few centimetres of metal.
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The final type of radiation, gamma, is not a particle like alpha or
beta, but an electromagnetic photon. It is much harder to stop than
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Spectral Workshop
than alpha and beta – only something very dense such as lead will do
the job.
B3. MEASURING RADIOACTIVITY
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Ask the students if they know how radiation can be measured or
observed.
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One method is a Geiger counter, in which every piece of
radiation entering the detector tube starts a chain reaction that
becomes an electric pulse and is recorded.
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The student will now experiment in groups with several
radioactive rocks and Geiger counters. They will take measurements
of activity in the presence of each of the sources, and take a
measurement of the background. They will also investigate how the
count rate measured by the Geiger counter decreases when paper or
foil barriers are placed between the sample and the Geiger counter.
(See attached worksheet.)
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Another method is a cloud chamber, in which the path of
radiation as it interacts with a cloud of alcohol vapor can be viewed.
As the radiation interacts with the vapour, clouds form in the
transparent vapour around the particle – short and fat trails for
alpha, longer and thinner trails for beta.
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B4. HALF LIFE
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Ask the students if they know what half-life is. The half-life is
how long it takes (on average) for half the number of atoms in a
sample to decay, or radiate. For a sample sample this can vary wildly
as half-life has a random element to it, but for a large sample the
half-life will not deviate much from the accepted value.
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The students will now model radioactive decay and half-life with
a set of dice. Starting with ten dice, the students will repeatedly roll
the dice, discard any of a certain value (chosen beforehand) and
record how many they now have. Once all the dice have 'decayed',
the students will plot a graph of dice roll against number of dice (or
nuclei) remaining. The result will be an exponential decay curve, like
that for decaying nuclei.
B5. CLOUD CHAMBERS
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In groups, the students will create their own cloud chambers by
adding alcohol vapour (to the foam lining) and dry ice (to the
bottom) of a supplied container.
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Once the cloud chamber is assembled, a desk light is used to
illuminate the chamber and the students can observe – and try to
identify - trails created by background radiation.
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Spectral Workshop
The large cloud chamber can also be used for a better view.
II
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ADDITIONAL MATERIAL
Picture of the trail left in a cloud chamber by an alpha particle (left)
and some deviated beta particles (right):
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Nuclei decay graph, illustrating half life:
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