Demos: 3E-05 Cloud Chamber

A box-like container has pads which can be soaked with an alcohol-water mixture, providing a source of water vapor. The box is placed over a tray containing pulverized dry ice. The air subsequently becomes supersaturated so that tracks of particles can be seen as the vapor condenses about the ions left in the particle’s wake.

Directions: NOTE: Because of the paperwork involved in obtaining dry ice from the Chemistry department, it is essential that you notify the lecture-demo technicians AT LEAST THREE DAYS IN ADVANCE if you are planning to perform this demonstration. IMPORTANT: It takes about thirty minutes for the apparatus to reach saturation and proper cooling for visible tracks to appear. You should notify the lecture-demo technician as to when you plan to introduce the demo in your lecture.

Place the box on top of the tray of dry ice. After about thirty minutes, visible tracks may be seen and can be projected by means of the overhead camera system. Tracks may be seen even if there is no “source” placed in the box. Ambient radiation seems to be sufficient.

Suggestions for Presentation: It might be of interest to the students to present a little history of the cloud chamber and its success in the early days of the study of ionizing radiation.

Applications: Historically, the cloud chamber played an important role in radioactivity studies. Also: cooling of saturated air has applications to weather systems.

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