7D30.60 - Cloud Chamber
Demonstrate the detection of subatomic and high energy particles.
Place pump in small section of ice cooler. Feed cables through holes in cooler and secure in place with removable bar. Fill cooler with ice and add about 1-2 liters of water. Add isopropyl alcohol (90% or better) to the walls inside the cloud chamber until they are saturated and there is about ~1-2mm layer of liquid in the bottom of the cloud chamber. Start the circulation pump and thermoelectric cooler by holding down the momentary contact button. Hold down the button until all of the bubbles are out of the system and the flow indicator ball is circulating. Place the small computer fan so that it is blowing over the surface of the cloud chamber in order to reduce the development of condensation on the window. Set up a camera to view the inside of the chamber using the enclosed felt strip to shield the cloud chamber top from stray reflections. After the water in the thermoelectric cooler has come down to temp, you may need to add additional ice. The cooler should be full of ice before it is moved into the classroom. If too much ice has melted, you may need to remove some of the water before adding additional ice to the cooler. If the water is not cold enough, the thermoelectric cooler will not chill down the chamber enough to allow for the tracks to form. It takes about 30-45 minutes until tracks are visible. If you see alcohol rain inside of the chamber, the unit is close to beginning to work. The system will turn off if the water flow through the thermoelectric cooler stops, so be sure to keep and eye on this.
The radioactive source used is a thoriated welding rod. Make sure the camera is up for the students to view the inside of the chamber. Alpha, beta, and gamma rays are all produced. Magnetic field is present to show the charged particles curved paths. You can also see electron-positron pair production when you see two tracks twist away in opposite directions. The radial tracks are coming from the welding rod. If the lights are off, then the system has turned off and let the Demo Lab staff know asap if you want to still show it in the same class period.