It's Radioactive Saturday!
March 7, 2015 5:28 AM   Subscribe

Watch some U-238 decay in real time. The sample is placed in an alcohol cloud chamber, and transilluminated by a strip of LEDs. Hypnotic, after a while. After about 40 minutes, the sample begins to be coated by alcohol fumes and many of the emissions are absorbed on the surface.
posted by pjern (20 comments total) 50 users marked this as a favorite
 
That's fucking amazing.
posted by ZaneJ. at 5:35 AM on March 7, 2015 [4 favorites]


Interesting choice of music. :-)

Thanks for sharing this, I look forward to showing my child.
posted by anastasiav at 6:19 AM on March 7, 2015


You could have had one as a toy in the 1950's from Gilbert Scientific, maker of the slightly less dangerous Erector Set...
posted by jim in austin at 6:32 AM on March 7, 2015 [1 favorite]


Look, the Aether!

Forgive my ignorance: When I am seeing particles that do not seem to be coming from the sample, at right angles and further away, what is their origin? Are they ricochets from the U-238 or just random particles the cloud chamber is picking up?
posted by Faux Real at 6:59 AM on March 7, 2015


Faux Real those are most likely background radiation. Geiger counters (whose tubes are considerably smaller than this cloud chamber) usually deliver three or four clicks per minute in the absence of any nearby sample.
posted by localroger at 7:49 AM on March 7, 2015


The ones coming in at odd angles at a much lower rate are cosmic rays; you can see what a cloud chamber looks like without the sample in it in this video.
posted by apathy0o0 at 7:52 AM on March 7, 2015 [3 favorites]


Cloud Chamber injected with a puff of Radon gas. Redditor explains the V-shaped trails that appear.
posted by endotoxin at 8:09 AM on March 7, 2015 [4 favorites]


Whoa!
Trippy
posted by BlueHorse at 8:35 AM on March 7, 2015


I've heard of a cloud chamber before but I'm pretty sure this is the first time I've ever seen one, what a satisfying experience!
posted by furtive at 8:38 AM on March 7, 2015


Forgive my ignorance: When I am seeing particles that do not seem to be coming from the sample, at right angles and further away, what is their origin? Are they ricochets from the U-238 or just random particles the cloud chamber is picking up?

The ones coming in at odd angles at a much lower rate are cosmic rays; you can see what a cloud chamber looks like without the sample in it in this video.


I went back and forth over three of those, and their angles were all equal to an angle drawn from a point projected backward to the wall made with the sample -- angle of possible reflection equaled presumed angle of incidence, in other words -- so I think those were ricochets.

Which is, after all, exactly what Ernest Marsden was startled to observe when he shot alpha particles at a piece of gold foil in an experiment that led to the discovery of the nucleus.
posted by jamjam at 10:34 AM on March 7, 2015 [1 favorite]


The Exploratorium in San Francisco has a beautiful cloud chamber where you can watch cosmic rays. It's my favorite exhibit there. We are all being penetrated by cute little particles from space!
posted by njohnson23 at 10:35 AM on March 7, 2015 [2 favorites]


Alpha particles won't reflect off "the wall" as a coherent thing, they scatter off individual nuclei, so their resulting trajectories are set by their impact parameter relative to the specific nucleus rather than any bulk properties of the material.
posted by kiltedtaco at 11:07 AM on March 7, 2015


My comment does not depend on anything like "coherent" scattering as far as I can see; the mere fact that a projection of the path backward to a wall, and then drawing a line from that point to the sample results in equal angles argues persuasively for a ricochet from the wall, in my opinion, however rare or 'incoherent' such a reflection might be.

And in any case, I'm not sure your assertion remains true for very low angles of incidence (measured from the surface upward rather than the usual normal) on a very flat surface -- and float glass, the most common current production method, results in almost optically flat glass on one surface even without making a special effort to achieve that -- since on such a flat surface many nuclei will be found in a very good approximation to a plane parallel to that surface, and for very low angles of incidence, that greatly increases the probability the particle's path will intersect a nucleus, and that could result in something very like coherent reflection in that circumstance, I'd think.
posted by jamjam at 11:52 AM on March 7, 2015


Hmmm! Looking at this again, I don't think I do see equal wall angles for most of the anomalous tracks.
posted by jamjam at 12:46 PM on March 7, 2015


Very cool. Kind of reminds me of when I set up a kaleidoscope on my first computer to run when I played my music. Used to get stoned and watch that fucker for hours while listening to my favorite tunes. I enjoyed it more than my dad did his bug zapper.
posted by scottymac at 1:46 PM on March 7, 2015


"Alcohol Cloud Chamber" will be the name of my next trance/blues boy band.
posted by I-Write-Essays at 5:08 PM on March 7, 2015


jamjam, it's not possible for a gamma ray or alpha or beta particle to reflect from a wall the way light does because to such particles, the wall is just a collection of nuclei, all of which are tiny points and none of which has anything to do with the others.
posted by localroger at 6:09 PM on March 7, 2015


It's not the case that they only see the nuclei, but it is the case that if you want to see an elastic scattering it's going to have to be an alpha bounce off a nucleus (as in the classic Rutherford experiment). All three types will quite happily dump energy by ionising atoms - which is interactions with the electron cloud rather than the nucleus.
posted by edd at 8:46 PM on March 7, 2015


localroger: jamjam, it's not possible for a gamma ray or alpha or beta particle to reflect from a wall the way light does because to such particles, the wall is just a collection of nuclei, all of which are tiny points and none of which has anything to do with the others.
They may only be tiny points, but conservation of momentum still holds, so they're going to ricochet in ways that largely look like reflections when they hit a wall of nucleii too thick for them to penetrate - which a glass wall is.
posted by IAmBroom at 10:32 PM on March 7, 2015


but conservation of momentum still holds

What? While edd has a point that there is are ionization interactions, the point is that at the scale where these particles interact, there is no wall, only a collection of tiny solid points and tenuous clouds of electric field. This is in fact what Marsden observed in the very experiment JamJam brought up; the reflections aren't at equal angles but all over the place, because they're essentially reflecting off individual atoms, not a "wall."

Light reflects at equal angles because the wavelength of light is considerably longer than the distance between atoms in a solid, so the surface does in fact act like a surface at that scale.
posted by localroger at 6:16 AM on March 8, 2015


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