The Cloud Chamber of Secrets The Effect of Magnetic Fields on Radioactive Particle Velocities in a Cloud Chamber A Magical Physics Investigation by…

Dr. Roberta Gannett The particle tracker and media specialist

Dr. Allison Nishitani The measuring master

Dr. Cassie Miura The human compass

What is a Cloud Chamber? A cloud chamber is an apparatus that tracks particle’s paths. It works by cooling isopropyl alcohol vapor at the bottom of the chamber with dry ice, while the top of the chamber is at room temperature so the vapor falls downward. There is too much vapor in the air and it is super-cooled, meaning that it’s in the vapor form at a temperature that is below where vapor can normally exist. Because it is at this cooler temperature, the vapor will easily condense into a liquid. An electrical charge ionizes the vapor, which leaves positively charged atoms. The ionized atom attracts other atoms to begin condensation, then you can see a trail that the particles leave behind them.

How Do Make a Cloud Chamber? We went through several different models before finding one that works well. All of these didn’t work…

This is Our Working Cloud Chamber

Materials Plastic airtight chamber Sponge Black paint Rubber bands Hot glue Sheet metal RADIOACTIVE SOURCE (very dangerous) Isopropyl alcohol (very stinky) Dry ice (burns….burrrrrr) Cooler Ice pick Slide projector Digital camera TV VCR Dry erase marker Ruler Digital video camera with tripod Ice tray Strong magnet (neodymium) Hall effect probe

How to Make the Chamber Cut the bottom out of the container Paint the metal plate black Secure the metal plate with putty as the new base Remove the clamps from the lid Create a very thick hot glue barrier along the inner top part of the chamber (not the lid) Cut sponge into long strips about 1 cm tall Glue the sponge to the glue barrier Put Harry Potter on top

Laboratory Conditions Level surface that is resistant to cold temperatures Access to a sink and soap Dark room Constant temperature Room for all lab associates

Chamber Procedure While wearing gloves, crush the ice and level it in the ice tray Wet the sponges with the alcohol Place the radioactive source in the chamber Place the magnet under the chamber and record its position Secure the chamber lid with rubber bands Place the chamber on the ice Turn on and adjust the light source Turn off other lights Film for 15 minutes

Data Collection Find the best footage from the 3+ hours of video Mark magnet location on TV screen View chosen footage on TV in slow motion When a curved particle track appears, pause the video and complete the circle with the pen Measure the radius and the distance to the magnet from the center of the circle

Calculating the Magnetic Field Use the Hall Effect probe to measure the magnetic field produced by the magnet on the bottom of the chamber at intervals of.5 cm Find a regression formula to calculate the magnetic field at any distance

Calculations Convert the measurements from the TV into meters and find the real lengths by using the proportion from the diameter of the chamber on the TV and the diameter of the real chamber Calculate the velocity by using v=rqB/m

Error The chamber Not airtight Reduced visibility due to: distortion, reflection, condensation at the bottom Plastic not durable/resistant to 99.9% pure alcohol The Light source Spread Focus Intensity The Ice Not flat Not evenly exposed to the metal sheet Melted The source Metal base (attracted to the magnet) Obstructed the camera view The Magnet Position not visible through the metal sheet Hard to position Poles unknown The Camera Pause capabilities Frames per second Focus Detail

Error (continued) Chamber Data The circles weren’t perfect because we weren’t able to use a compass The dry erase marker could smear or rub off The dry erase marker was thick We didn’t know the exact position of the magnet on the TV screen The radius was hard to measure because it changed every second, so we had to guess at when we should pause the camera Magnetic Field Data The reading from the hall effect probe was constantly changing, so we had to approximate the readings The probe was large, so it was hard to take readings at small intervals along the chamber The magnet wasn’t exactly where it was during the experiment