Bubble Chamber Detective

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Bubble Chamber Tracks and CERN from the air.
(Images courtesy of CERN.)

This lesson explores the tracks left behind by charged particles moving through a constant magnetic field. This lesson was developed from resources, from CERN Education and Peter Watkins at the University of Birmingham. I felt that teachers might need a bit more information and that the students need more opportunities to practise their detective skills than was provided in the original resources. The background information gives a brief summary of what you might want to know about bubble chambers.

Introductory Demo (5 minutes)
The bubble chamber consists of liquid hydrogen at a temperature just below its boiling point. The pressure is suddenly reduced so it is no longer stable. Bubbles are formed where the hydrogen is disturbed by moving charges. The early models used beer and you can demonstrate the physics with a bottle of soda water. Remove the label so the students can see the clear liquid. Unscrew the cap and suddenly there are bubbles everywhere. If you shake some salt into the soda water, visible trails will form. To show how magnets can bend the path of charged particle, bring a strong magnet (like one from an old speaker) near a black and white TV. Don't do this with a colour TV!

Interactive Lecture (25 minutes)
The PowerPoint lesson Bubble Chamber Detective: Part I, shows the students how to identify the presence of positive, negative and neutral particles by using conservation of momentum and charge and mv = qBr. They learn to use these tools to recognize decays, elastic collisions and particle reactions. Each student needs a copy of Bubble Photo I. The Bubble Notes I is a paper copy of the questions and answers in the lecture.

Interactive Lecture (15 minutes)
The PowerPoint lesson Bubble Chamber Detective: Part II, teaches the students how to recognize electrons, positrons and protons. They get a chance to review and practise their skills on a few more interactions. Each student needs a copy of Bubble Photo II. The Bubble Notes II is a paper copy of the questions and answers in the lecture.

Jigsaw Opportunity (20 minutes)
These are seven more photographs for students to analyse in small groups. There are no questions given, but key events are indicated by a letter. The students need to figure out whatever they can and be prepared to explain their reasoning. Be sure to photocopy the sheets without the answers! This could be done as a jigsaw excercise where each student works with several others to become the expert for a particular photo. They then return to their home group and each 'expert' presents the analysis of their particular photo to the others.
photo107 photo121 photo184 photo239 photo275 photo94 photo98

Worksheets (20 minutes)
The two CERN excercises provide two more photographs with specific questions that could be assigned for homework.

For more images and information about bubble chambers see CERN's bubble chamber resource.
For more information about CERN's resources go here.

Last modified Dec 2010 (Thanks to Steve Greer for noticing a bad link.)