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I'm trying to understand this image of a particle tracing experiment (which can be found all over the net if you google for "bubble chamber"):

(Bubble chamber experiment

There are two things that I can't figure out:

  1. The background has some kind of pattern made up of irregularly sized, semi-rectangular patches. Where does that come from?

  2. There is a vertical line of 4 circles in the middle of the image, each marked with an X. These seem to be part of the setup, but what is their function? Also, the pattern in the background in these circles is not continuous w.r.t. to the outside pattern, although the traces are. Why?

In addition, if anyone has the original source or more information about that particular experiment then that would be very welcome, too.

EDIT: It seems that the image stems from a 1980 Fermilab experiment.

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up vote 2 down vote accepted

Have you read about the construction and operation of bubble chambers? They are large vessels (with at least one transparent side) and work by rapidly reducing the pressure in the contained fluid so that it is superheated for a time. Doing that requires plumbing; both for filling the chamber with working fluid, and for arranging the pressure drop.

As the working fluid is often cryogenic it was also probably kept in circulation so that it could be periodically re-cooled, calling for more plumbing.

As the working fluid is chosen to be transparent except where bubbles nucleate, you can see through to whatever occupies the far side chamber. (The figure is a negative image so the light background of the image represents a dark background space.)

I would not be surprised if those neat, uniform circles all in a line represent the plumbing in the vessel, and the rest of the structure in the background the panels and welds of the chamber.

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I guess you're right concerning the general background being the panels and welds of the chamber itself. I'm not so sure about the circles, though: Wouldn't plumbing require some sort of in- or outlet? Also, why the crosses? Note that there's also a high res version. – Florian Brucker Apr 13 '13 at 11:46
The physics analysis in the early days was done by hand, by non-physicists hired and trained to locate the start points and end points of features, compute bending radii and so on. By 1980 they may have been digitizing data for a computer analysis, but I think there were still humans in the loop for bubble chamber data. I assume the crosses are to mark features the scanners should not worry about. – dmckee Apr 13 '13 at 15:04

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