7D10.20 • Cloud Chamber
Location: 4.48 Attic
Concepts Conveyed:
- Energized charged alpha particles from the thoriated tungsten pass through the vapor, leaving behind trails of ionized molecules.
- The alcohol condenses around the ion trails, and forms condensation tracks visible to our eyes.
Instructions / Notes:
- Plug in the lid heating pad.
- Soak the felt side of the lid with ~30 mL of isopropyl alcohol.
- Pour ~4 L (full dewar) of LN2 into the styrofoam container. The level of the liquid should approach the height of the corner blocks at the bottom of the well.
- You can insert the bottom metal plate vertically into the well to see the height of the liquid.
- Place metal plate in the well (clean side facing down). If it is dusty, wipe it down for better viewing.
- Set radioactive sources on plate, then place plexiglass chamber on top of the plate (glue side down).
- Line LED lights around the outside of the chamber (lights shine inwards). The lowest brightness setting is recommended.
- Place the lid on top of the chamber (felt side down).
- Peak viewing time is around 5-10 minutes, but tracks can be seen for up to 20 minutes. It is recommended to perform this demo with the overhead lights off.
- Try not to disturb the chamber, as water vapor could enter and destabilize the setup.
Demo Staff:
- Allow the lid to dry after use.
- Use tweezers to remove sources and metal plate from the chamber.
- Wipe the bottom plate after use so no residual marks are left (better for viewing next time).
- In general, alpha particles are not dangerous unless the source is ingested\inhaled\enters through a wound, but it is recommended that you wash your hands after handling the tungsten rods.
Last updated on April 24, 2025