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 "STREET-SMARTS" 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 set-up 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!