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Cloud Chambers and
Cool Dry Ice
In this workshop:
 Using dry ice
 Making a large cloud chamber
 Safe radioactive sources
 Obtaining dry ice
 Other things to do with dry ice
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Dry ice
Solid carbon dioxide. Subliming at -78.4ºC

ALWAYS store dry ice in an area which is:
Well ventilated (it's an asphyxiant).

Preferably not below ground (because it's heavier than air).

Out of direct sunlight and sources of heat (so it lasts longer)

Secure – to prevent unauthorised access.
DO NOT handle dry ice with bare hands. It can cause severe
cold burns and frostbite.
DO NOT PLACE IN WORKING REFRIGERATOR / FREEZER
REMEMBER – A little bit of dry ice will sublime to a large
volume of CO2 gas.
CLEAPSS General Handbook Section 11.2
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Make a Risk Assessment

Managing Ionising Radiations and Radioactive
Substances in Schools, etc L93
http://www.cleapss.org.uk/download/L93.pdf

Radiation Protection in School Science:
Guidance for Employers Information for local
authorities (PS46A)
http://www.cleapss.org.uk/attachments/article/0/P
S46A.pdf?Secondary/Science/Guidance%20Leafl
ets/?Local%20Authority%20Officers/LA%20RPA
%20advice%20service/
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Who discovered
radioactivity?


Radioactivity was
discovered in the year:
 1857
By:
 Abel Niepce de
Saint Victor
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How science works






March 1, 1896: Henri Becquerel Discovers Radioactivity
An American Physical Society web page:
http://www.aps.org/publications/apsnews/200803/physicshistory.cf
m
Original papers:
http://gallica.bnf.fr/ark:/12148/cb343481087/date1858.langEN
http://gallica.bnf.fr/ark:/12148/bpt6k3004t.image.langEN.swf
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Cloud Chambers
The Nobel Prize in Physics 1927
was divided equally between Arthur
Holly Compton "for his discovery of
the effect named after him" and
Charles Thomson Rees Wilson "for
his method of making the paths of
electrically charged particles
visible by condensation of
vapour".
http://www.nobelprize.org/nobel_prizes/physics/laureates/1927/index.html
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More Nobel Prizes…
The Nobel Prize in Physics
1936 was divided equally
between Victor Franz Hess
and Carl David Anderson "for
his discovery of the positron"
which he photographed in a
cloud chamber.
The Nobel Prize in Physics 1948
was awarded to Patrick M.S.
Blackett "for his development of
the Wilson cloud chamber
method, and his discoveries
therewith in the fields of nuclear
physics and cosmic radiation".
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Cloud Chambers
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Making a Cloud Chamber
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Making a Cloud Chamber
1.
Cut a 2 cm wide length of felt about 1m long.
2.
Stick to the “bottom” of the plastic fish tank.
3.
Cut the lid of the fish tank.
4.
Put tape along the slots left in the lid.
5.
Tape the baking tray to the lid.
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You will need:
A fish tank
A baking tray
Scissors
Saw
Snips
Tape
Metre stick
Access to the roll of felt
A marker pen
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You are going to stick felt around the
“bottom” of the fish tank
Mark two 2.5 cm wide
bands the width of the
roll of felt and cut
them off.
Then cut these two
strips so that you
have pieces that fit
the ends and sides of
the tank.
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Peel the backing off the felt and stick it in place in the
“bottom” of the fish tank.
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You're going to cut out the central part of the “lid” that is
inside the lip.
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You should end up with something like this:
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Cover the slits along the sides with tape:
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Stick the lid to the baking tray with more tape:
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Put it all together:
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Using the Cloud Chamber
•
1. Soak the felt in the chamber with Isopropyl alcohol.
•
2. Get blu tac and a source and put them at one end of
the cloud chamber. Use the blu tac to have the source
about 5mm above the base.
•
3. Put dry ice in a tray. (With gloves).
•
4. Put the cloud chamber on the dry ice.
•
5. Arrange the lighting so trails will be lit from the side.
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What do you see?
The tracks from beta can be observed,
but they are much fainter; low-energy
beta emissions produce very irregular
tracks. Another way to identify beta
tracks is to take a number of
photographs at 1 second intervals with
a digital camera and flash, say 10 or
so, and then download the images to a
computer. Zoom in on the photographs
and with luck you may be able to pick
out some images that show beta
tracks. The contrast may be better if
the pictures are changed to greyscale.
Mostly alpha
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• A straight track that sharply "kinks" off to the
left or right. This is a decay of a muon particle.
The two dashed lines are particle called
neutrinos that your chamber is not able to
detect.
• Three tracks that meet at a single point. In
these events, one track is an incoming cosmic
ray, a particle called muon. This particle hits an
atomic electron. The electron and the outgoing
cosmic track are the two other tracks.
• A very windy, chaotic track. This is "multiple
scattering", as a low-energy cosmic ray
bounces off of one atom in the air to the next.
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Welding Electrode sources
http://www.practicalphysics.org/go/Apparatus_2298.html
Welding Electrode
Tungsten rod with 2% Thorium 232. Weakly
radioactive. No special precautions required.
Do not break or grind.
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Where to get dry ice
•
Online or by phone:
http://www.dryiceuk.com 0800 0842 040
http://www.chillistick.co.uk/ 08433 192 919
http://www.boconline.co.uk 0800 111 333
•
Around £60 for 20kg. They don't deliver on Mondays.
•
Or ask at pharmaceutical suppliers, airport food
companies, universities.
•
•
•
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Mad Scientist
•
•
•
1 litre measuring
cylinder
Dilute ammonia
solution and/or
dilute sodium
hydroxide
solution (Irritant),
0.1 mol dm-3
Universal
Indicator
http://www.practicalchemistry.org/experiments/indicators-and-dry-ice-demonstration,53,EX.html
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Floating bubbles


Place some dry ice in a bowl, and let it sublime. The
bowl will fill with a dense layer of carbon dioxide.
Now blow a soap bubble, gently, and try to get it to
rest, floating, on the layer of CO2
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Singing Spoons

Press a spoon against a piece of dry ice – the heat of
the spoon will make the dry ice sublime, squealing as it
rushes past.
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Make your own Comet!
http://www.practicalphysics.org/go/Experiment_1039.html
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Apparatus and materials
• Large polythene sheet to protect floor
• Mixing bowl
• Bin-liner bag, to line bowl and draw comet together
• Mallet, to crush some dry ice to powder
• Substantial plastic bag, in which to crush dry ice
• Gardening gloves (heavy duty type)
• Mixing spoon
• Balance, to find mass of comet (and hence calculate a hypothetical kinetic energy)
For two comets • Dry ice pellets, 10 kg
• Garden sand, 1 kg
• Water, 2 litres
• Soil, 1 handful (organic constituent)
• Worcestershire sauce (organic constituent)
• Smelling salts (organic constituent)
Technical notes
The essential ingredients are dry ice, sand and water. The other items represent the organic molecules
thought to be present in a comet.
If it feels as if the comet will not bind into a 'snowball', it is because you have not used enough water. There
is a natural tendency not to want to use too much water for fear of evaporating all the dry ice.
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Teaching Radioactivity
http://www.iop.org/education/teacher/resources/radioactivity/page_41558.html