What has caused this panda-face in a cloud chamber ?

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This image was posted on another forum , maybe someone here may be able to shed some light on the origin of the grinning-panda ...

Blurry, grainy photo of a cloud chamber showing a bright oval halo enclosing a dark pattern of blotches that resembles a face with two eyes and a wide mouth.


The the cloud chamber does not have an applied magnetic field.

The radioactive source is Americium 241 [ from smoke detector ? ].

The duration of the camera exposure cannot be greater than one second (so I am told).

Personally I think the panda-face is an artefact caused by the radioactive source which has a similar size and shape to the largest* ring, but maybe some series of atomic events has created the pattern ? , ( the circular forms in the absence of a strong magnetic field makes me think otherwise ).

(* which is less than 1cm in diameter),
 
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  • Blurry grainy photo of a cloud chamber showing a bright oval ring with dark blotches inside that roughly resemble a face, with a small bright spot above.
    grinning-panda-face-cloud.jpg
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Discussion

There is the magnetic field of the earth, it could be a low energy cosmic ray. Nice imagination to suggest a panda face !
 
Americium 241 does emit gamma rays, which can produce electron-positron pairs, which have circular/spiralling paths in a strong ( 0.1 T) magnetic field ...

Electron and positron spiralling tracks

Cloud chamber photo showing a dense tangle of white curved and straight particle tracks on a dark background, forming a large loop-like pattern with a bright blob on the lower left.

positron and electron being created by a gamma ray which came in from the top of the picture

Cloud chamber photograph on a dark background showing two spiral tracks curling inward, with a sharp V-shaped track meeting a bright point between them.

But the panda-face appeared in a home-made cloud chamber which does not have an added magnetic field.

Photo of a faint, roughly oval cloud-chamber track in a dark background, showing a pale ring with dark blotches inside that resemble a face.
 
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