CLOUD CHAMBER TIPS AND TRICKS
WARNING!!! CLOUD CHAMBERS CAN BE HOPELESSLY ADDICTING!!!
THIS MAY TURN OUT TO BE THE MOST EXCITING LAB EXPERIMENT
OF YOUR ENTIRE SCHOOL YEAR! DO NOT WORRY IF YOU HAVE NOT
HAD MUCH BACKGROUND IN TEACHING ABOUT SUBATOMIC
PARTICLES. YOUR STUDENTS ALREADY HAVE MORE “STREETSMARTS” ABOUT PARTICLES THAN EITHER YOU OR THEY REALIZE!
1. Cloud chamber labs are the most fun if they are treated as an EVENT! Group
enthusiasm is contagious. Plan on building enough cloud chambers so your students
are in groups of three to five. Cloud chamber enthusiasm stays higher for groups
than for partners or students working alone. With a group, you can count on
somebody seeing something exciting whenever another group member starts to lose
interest. NOTHING spurs on your entire class quite like a lab group suddenly and
unexpectedly SCREAMING out with excitement! If you are lucky, one or more
groups will observe a major event, where a straight-line vapor trail appears to
suddenly explode! The visual effect is similar to an exploding skyrocket, and it
almost always causes groups of students to scream! Occasionally, your entire lab
will experience a sudden flurry of vapor trail activity. I have had one occasion
where two lab groups observe major vapor trail explosions less than a minute apart.
For several minutes, all of the cloud chambers in the classroom went crazy with
vapor trail activity! We had many particle collisions causing vapor trails to split
into Y shapes. It was as if the Earth had received a sudden burst of particles from
some mysterious source out in the universe!
2. Successful cloud chamber operation depends on keeping the temperature cold at
the bottom and ever-so-slightly warm at the top. The most effective cloud chambers
have a good seal along the edge between the top viewing window and the edge of the
container. Cut the top edge of the container as carefully as possible. A smooth edge
makes it easy to form a good gasket. Sandpaper does wonders for a smooth edge. A
good edge is easier to create than you might think. The rest of the cloud chamber
construction procedure is almost trivial. By the time you’ve built your sixth or
seventh cloud chamber, you will be an expert!
3. Successful cloud chamber operation crosses that fine line between science and an
art form! Spend a weekend or two practicing with your cloud chambers at home,
before you bring them to school. AMAZE your family and friends. Think about it
for a minute… You’ve taken a few common household items and used them to trap
cosmic visitors from outer space! Students who are into science fiction think of a
cloud chamber like they think of a magic wand! For them, your cloud chambers
have harnessed magical powers! SCIENCE LABS DON’T GET ANY BETTER!
4. IMPORTANT NOTES ON CLOUD CHAMBER MATERIALS:
A. Plastic jars make great cloud chambers. They are cheap and unbreakable.
The plastic jar is turned upside-down, so the jar lid can act as the bottom of the
cloud chamber. The two best sources of cloud chamber jars are Claussen 32 oz.
jars of dill pickle spears and Skippy 4 pound jars of peanut butter.
B. Metal jar lids are crucial for good heat transfer between the jar lid and a
block of dry ice. The first ASTRONOMY IN THE ICE cloud chambers were
made from pickle jars, for the simple reason that some plastic pickle jars came
with metal lids, and virtually all other usable plastic food jars had plastic lids,
which are not very good at heat transfer.
For two glorious years, ASTRONOMY IN THE ICE cloud chambers were easy
to build. Cloud chamber builders bought half-gallon jars of Claussen dill pickle
spears at Sam’s Club. (The hard part of the project was eating all of those dill
pickle spears! Every picnic and holiday dinner had all the pickle spears you could
ever want!)
Then, the unthinkable happened! The Claussen Company switched to plastic
lids! Cloud chamber fans were devastated! …But fear not! Every cloud has a
metal lining! (pun intended, ha! ha!) Thanks to the generosity of an anonymous
corporate donor, the University of Wisconsin - River Falls now has a large
enough supply of metal jar lids to last for many years!
Now for the good news…
Since you no longer need to buy jars of pickles in order to get metal lids, other
products with suitable plastic jars can be used instead. The most popular of
these products is the four pound jar of SKIPPY peanut butter, which is readily
available at supermarkets everywhere!
C. CLOUD CHAMBER LIGHT SOURCE: As the ASTRONOMY IN THE
ICE cloud chambers increased in refinement, the cloud chamber light source was
recognized for its important secondary role as a heat source for the top of the
cloud chamber. Turn off the light for a few minutes, and the top viewing
window will fog up. Unfortunately, light sources are a lot like the three bears’
bowls of porridge. 110 volt desk lamps are too hot, and most flashlights are too
cold. 6 volt flashlights which use four AA batteries seem to be the only light
sources which generate the right amount of heat. Unfortunately, the 6 volt
flashlights guzzle electricity like a 1965 Buick guzzled gas! Think of those AA
batteries as being undersized fuel tanks. You just have to bite the bullet and
burn up two sets of batteries if you are running the cloud chamber lab all day!
The last thing you want to do is tell your students to turn off the flashlights
to save on batteries. Tell students to conserve batteries, and they will walk away
from the cloud chambers in 5 minutes! That’s hardly the way to create a
memorable learning experience! Fortunately, the 6 volt flashlights eliminate any
electrical hazards which might arise from mixing eighth graders with 110 volt
alternating current! It really does take two sets of AA batteries to get through a
full day of cloud chamber viewing.
D. ACRYLIC VIEWING WINDOW: Even though the standard
ASTRONOMY IN THE ICE cloud chamber is made from a transparent plastic
container, it was soon realized that irregularities in the wall of the plastic jar
made it difficult to see vapor trails through the side of the cloud chamber. The
best viewing is done through the cloud chamber’s top viewing window. Six inch
squares of single thickness acrylic storm door glazing is perfect.
NOTE: Alcohol vapors tend to cause stress cracks in the acrylic viewing
windows. A full day of cloud chamber viewing will cause the acrylic viewing
windows to crack while they are stored away. Plan to cut new acrylic viewing
windows every year. Don’t wait until the morning of your lab to find out you
have forgotten to cut new windows!
5. DO NOT PLAN ON PERFORMING THE CLOUD CHAMBER LAB ON A
MONDAY, UNLESS YOU FIND A DRY ICE SUPPLIER WHICH IS OPEN
ON SUNDAY AFTERNOONS! I drive to downtown St. Paul to buy dry ice
from a company which supplies dry ice to trucking companies. They are not
open on Sunday. They are not open early enough in the morning for me to
buy dry ice before school starts. They close by 4 p.m. on weekday
afternoons. I absolutely have to schedule my cloud chamber lab between
Tuesday and Friday! I generally leave school right after ,my last class to get
my dry ice. Once, I got caught in a freeway bottle-up and almost didn’t get
to the dry ice supplier on time! (REMEMBER MURPHY’S LAW WHEN
YOU RUN THIS LAB!)
6. Expect to spend SEVERAL hours setting up your cloud chamber lab equipment!
Part of the set-up can be done the night before you run the lab, but part of the setup has to be done in the morning before school starts. DO NOT let students apply
the petroleum jelly to the gaskets! They will just smear up your acrylic windows. If
two acrylic windows are allowed to sit for several hours with petroleum jelly
between them, they will stick together permanently! Do not let your students pour
the alcohol into the cloud chamber. They will pour in too much. (Also watch so
students don’t try to get high off of the alcohol fumes!) THIS IS A HIGH
MAINTENANCE LAB! You must constantly monitor your cloud chambers. The
biggest annoyance is when a cloud chamber stops producing vapor trails and a
student tries to fix it!