How to Build a Cloud Chamber
sketch of our low-tech cloud chamber is shown here. Click the image to
see a large figure. The chamber consists of an upside down plastic jar
(#1 type plastic) with a metal lid. The metal lid becomes the floor of
the chamber. The jar is cut horizontally. Adhesive is applied to the cut
edge to make a flat surface on which a cover can be placed to seal the
chamber. The transparent cover can be a plate of glass or clear plastic
of a type that is not degraded by alcohol. Colorfast black absorbent paper
lines the floor and sides of the jar, with an open space on the side for
the light source. A small Styrofoam cooler cut to appropriate size contains
the dry ice for cooling the base of the chamber. The metal lid of the chamber
nests in a hole in the lid of the cooler, which rests, upside down, on
Methanol or ethanol wets the blotting paper. A temperature difference
is maintained by having only the bottom of the chamber on dry ice, so that
the alcohol evaporates in the warm, top end of the chamber and condenses
on air molecules ionized by radiation in lower cold half of the chamber.
Jar - We used a large Clausen Pickle jar. The lid diameter is 10
cm (4 in). The jar diameter is 12.75 cm (5 in). The jar is made of PETE,
a No. 1 type of plastic, which is not degraded by alcohol.
Flat cover - We chose PETG (also a No. 1 plastic) for the cover
because it is available in clear sheet stock. A thickness of 1/8 or 3/16
inch would be adequate, but ours is 1/4 inch thick because it was available
for $2.00 as a scrap piece. The cover was cut to 15 cm (6 in) square, large
enough to cover our jar. A hole was drilled in an extra cover to accommodate
a thermometer. Plexiglas (acrylic) is more commonly available, but it reacts
with alcohol and becomes cloudy over time.
Styrofoam - A small "double 6-pack" Styrofoam cooler works to hold
dry ice. Dimensions at the bottom are about 15 cm (6 in) by 22 cm (9in).
Dry Ice (solid carbon dioxide, CO2) - CAUTION! Dry ice (temperature
of -78 C) must be handled with gloves.
Alcohol - Methanol (CH2OH) and Ethanol (C2H5OH), 95% pure or better,
both worked in the temperature range of our chamber. Rubbing alcohol (70%
isopropanol) was not successful.
Thermometer - A thermometer is helpful to monitor temperature in
Radioactive sources - These are listed as optional, because tracks
of naturally occurring radiation (cosmic rays and radioactive decay of
natural substances on earth) can be seen in the chamber. Because natural
radiation occurs randomly, however, it may be difficult to know when the
cloud chamber is working.
|Plastic jar w/ lg. dia. metal lid
||(large Clausen Pickle jar)
|Flat cover, glass or PETG*
||*Laird Plastics, Seattle
|Silicone 'aquarium' adhesive
|Black colorfast absorbent paper
(Arches 100% cotton)
|Daniel & Smith Art Supplies
|Small Styrofoam cooler
|Solid CO2 (dry ice)
(~ 2 lbs. per use)
|Methanol or ethanol
(~ 1 oz per use)
|All World Scientific, Seattle
|Light source (200 - 300 W)
|Radioactive sources (optional)
Oakridge, Tennessee (school supplied)
|Radiation monitor (optional)
The radioactive sources used in our development work were:
*A curie is a unit measure of radioactivity equal to 37 billion disintegrations
Prolonged exposure to even low levels of radiation can be harmful. Minimize
exposure to radiation by use of safe sources and appropriate shielding.
See Radiation Saftey for information on penetration
of different types of radiation and appropriate shielding.
Only alpha and beta emitters are used in our demonstrations for the
Cut the plastic jar 7 to 10 cm from the metal lid. The plane of the cut
should be parallel to the flat surface of the lid. This distance will be
the height of the chamber. Apply a silicone adhesive to the cut edge of
the jar and place this coated edge on wax paper on a flat surface to cure
(dry). When the adhesive is cured, gently remove the wax paper.
Cut a circle of colorfast black absorbent paper to line inside of the metal
lid, and a strip to line the side of the jar. Leave a narrow slot about
2.5 cm (1 inch) on the side for the light source. We actually lined the
side of our jar with two strips. The first was equal in height to the height
of the chamber, and the length matched the circumference of the lid, minus
the space for the light. Our jar diameter however was larger and necked
down sharply to the lid. We placed a second strip less wide (high), but
longer to line the outside of the jar above its neck, thinking that this
might increase the reservoir of alcohol in the top of the chamber, and
thus improve the condensation results.
Cut the Styrofoam cooler to a height of about 15 cm (6 in). The "double
6-pack" cooler we used was trimmed at the transition between the smaller
lower portion of the chamber and the larger upper section.
Cut a circular hole in the center of the lid of the cooler to match
the diameter of the metal lid of your jar, so that the lid will nest in
this hole. The Styrofoam lid should fit upside down on the trimmed lower
portion of the Styrofoam cooler. The lid and rim of the cooler may need
to have a 2.5 cm (1 inch) wide cut on a side to allow the light beam to
enter at a low angle.
D. Cut Styrofoam blocks to place inside of the cooler to hold the dry
ice in position under the lid of the jar as shown here.
1. Wearing gloves, trim the dry ice to fit in the cooler. Scoring the ice
with a saw blade will help achieve clean breaks at desired locations. Place
the ice in the cooler with a flat surface up.
2. Place the cooler lid over the ice, upside down. The surface of the jar's
metal lid should contact the ice, when nested in the hole in the center
of the upside down foam cooler lid.
3. Position the blotting paper in the jar as shown under item B above.
Add enough methanol or ethanol to wet all the paper, but not so much that
it pools in the bottom of the chamber.
4. Place the clear flat cover on top of the chamber, and shim under the
cooler to level the floor of the chamber.
5. Position the light source so that it enters the chamber at a low angle
downward through the gap in paper on the side of the jar.
6. Now turn down the room lights and look for cloud tracks of naturally
If a known radioactive sample is used, place it to one side on the floor
of the chamber between Steps 3 and 4 above. Position the sample so that
the primary direction of emissions is horizontal across the floor of the
chamber and is perpendicular to the light beam direction.
If you are having trouble seeing tracks, check the trouble shooting
Trouble Shooting Tips
If no paths are visible:
Check for adequate alcohol in chamber.
The blotting paper should be wet with alcohol, but alcohol should not be
pooled in bottom of chamber. If the chamber is opened periodically, alcohol
vapor can escape and may need to be replenished. Check temperature gradient.
If the entire chamber is too cold, not enough alcohol will vaporize at
top of chamber. Warm top of chamber, e.g., with hands over exterior surface,
or by turning cover plate over.
The bottom of chamber needs to be cold enough. In our experiments, we got
clouds to form when the bottom of the chamber was below -15oF.
Check that bottom surface of the chamber is level.
If it is not level, convection currents may interfere with the cloud paths.
If the ice on which the metal lid rests is not level, the Styrofoam cooler
may be shimmed from the outside to make it level.
A shallow angle from horizontal seems to work best for the angle of illumination.
Adjusting the beam so that its reflection off the blotting paper is not
directly behind the location of expected paths, relative to line of sight,
may help. Adjusting the viewing angle may help too. Also check that ambient
light is dim or absent.
Apply an electrostatic charge to the cover plate of the chamber.
Charging the surface of the chamber helps make paths visible, e.g., with
a statically charged balloon or with an electrophorus and aluminum disk.
Radiation Safety, Range and Shielding
Prolonged exposure to ionizing radiation can be harmful because of its
ionizing properties. Living tissue is usually damaged when molecules of
the tissue are ionized by radiation. Bodies have repair mechanisms for
many types of damage, but not all. Thus, with accumulated doses the risk
of permanent damage to living tissue increases.
Typical ranges of travel and shields for alpha (), beta (), and gamma
() radiation are given below:
Although alpha particles produce 100 to 200 times the ionization caused
by betas, their short range makes them dangerous only in close proximity,
especially inside the body where they can damage much tissue. The Polonium
210 producing alpha emissions in our experiment has a range of 3.8 cm.
||Range in air
||Can be stopped by
||10 cm maximum
(3.8 cm for Po-210)
|A sheet of paper
||A few meters
||A few mm of aluminum
||A few hundred meters
||A few cm of lead
The range for beta particles is typically a few meters in air. It depends
on their energy, which varies a great deal for different beta sources.
Betas can usually be stopped by a few millimeters of aluminum.
Gamma rays (high frequency electromagnetic energy) produce only about
1/1000 of the ionization of alpha particles, but they are difficult to
stop, so they pose a threat from a distance.
If safe radioactive sources are used, store in a lead box or comparable
Know the range and shielding requirements for your radioactive sources.
Check range and shielding with radiation monitor.
Handle radioactive materials in a manner that minimizes exposure. Wash
hands if samples are touched.
Additional radiation safety information can be found at:
The Division of Oral and Maxillofacial
Radiology, Dalhousie University
Open Source Radioactive
Materials Safety Training, University of Illinois at Urbana-Champaign
Prepared by: Winnie Ng, Sharon Olds, Yu-Har Yam,
Advisor: *Robert Hobbs, Bellevue
*To whom correspondence should be addressed
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This page was last modified on 9/24/00.