Cosmic Rays: Introducing Magnetic Fields

This page describes trying to introduce fairly strong magnetic fields into the cloud chamber in order to observe the deflection of paths of charged particles.  One 'holy grail' of this maneuver is to produce and observe a helical track or 'corkscrew'. Early on in these first cloud chamber runs I thought I did see one, but of course it wouldn't count (given the ephemeral nature of the tracks) unless I could capture it on film...

Note 1: I do not have time at the moment to reduce the size of these images. Therefore the page size will be well over 1 Megabyte and I apologize that it will be slow to download over a dialup connection.

Note 2: My web-skills being what they are, these frames are not animated. However an ad hoc movie-effect can be created by carefully sizing the browser window and jump-scrolling using the cursor.

Note 3: The features in the photos below are definite but faint. They will be easier to see either by dimming other lights or if the author eventually changes the contrast to enhance them.

The gold 'cube magnets' seen in some of these early photos are very strong NIB magnets, rated at something like 1 Gauss (?). They are strong enough to pinch fingers and smash themselves apart when handled carelessly (they are also pretty fragile).  The trick is to place them in the chamber precisely in the illuminated area, which is smaller than the chamber itself. This placement with some photographs of resulting tracks will have to be compared to a no-magnet test to establish whether they are strong enough to affect particle paths. If not I'll have to resort to electromagnet coils.

Update
The last runs in the initial series of tests (November 2004--February 2005) involved three radioactive sources. The first of these is (putatively) Trinitite, which I understand to be sand acquired from the site of the first nuclear test (Trinity). I took about 400 photos during this test, trying to refine illumination angles, focus, exposure time, and so on.  The camera captures about four frames per second which resulted in an interesting series of ten photos, as follows with brief notes.

First, here is the full camera frame:

frame 01: null

The main features of this photo: The stack of four magnets are used to pinch some sample bags in place. The illumination and camera focus are set to highlight the region inside the chamber to the left of the sources/magnets. There are no strong track-features clearly visible in this photo.

01 null

Same as above; cropped field of view, no major tracks visible.

02 feature 1

Straight nearly-vertical track appears at center-right.

03 feature 1 falls and distorts

Feature is falling (gravity acting on condensation) and deforming.
A guess: Residual ions are affected by the strong local magnetic field.

04 more distortion

Feature continues to fall and deform.

05

Again, deforming and starting to lose coherent structure.

06

A new feature has appeared from center-low to center-left, shape suggests a corkscrew.

07

The corscrew is slightly better-defined in this next frame.

08

Corscrew is falling and starting to lose coherence.

09

Corscrew most dissolved, other suggestive tracks at low-center and low-center-right.

10

Final frame. The entire sequence spans about two seconds.

Interpretation
This sequence of photos captures two (presumably) unrelated events: The short straight track and the corsckrew track. The short straight track deformed as it dissolved, either due to "micro-conditions" in the chamber or possibly because residual ions interacted with the magnetic field from the gold-cube magnets as they fell.

Considerably more interesting is the corkscrew path; did it spiral inwards as the particle moved from right to left?  Or did the radius of curvature increase as it traveled from left to right? The magnetic field strength changes with distance from the magnets and this is certainly also an important factor. In either case we have the distinct possibility that a charged particle was moving at just the right speed relative to the strength of the magnetic field that it went through 3--4 complete gyrations of increasing/decreasing radius before coming to rest.

Cosmic Rays
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