Sunday, November 6, 2011
Supercritical CO2 does not help visualize ionizing radiation
I tried to build a cloud chamber with supercritical CO2, thinking that ionizing radiation (alpha particles) would cause localized condensation of the CO2 at the point where the fluid is coming out of the supercritical state. It didn't work, unfortunately. I tested this idea with the americium-241 source from a smoke detector. I will continue experimenting with CO2 ionization chambers, and it might be possible to visualize the particles with superheated liquid CO2.
A helpful commenter pointed out that alpha particles will not travel very far in a fluid as dense as liquid CO2, so I will try again with a beta emitter.
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How far does the alpha radiation penetrate the CO2? Maybe it just isnt penetrating far enough to be seen.
ReplyDeleteI expect that your comments in the video are correct, Ben. I'm not sure how fast the whole process of c02 condensing into liquid is (the part that is sped up in the video), but ethanol cloud chambers are somewhat stable in that they develop a layer of supercritical ethanol vapor which is the only location where you can see interactions with particles. I'm sure you'll get it if you continue tweaking the parameters.
ReplyDeleteHi Ben,
ReplyDeleteAlpha particles from Am241 have energies of ~5.5MeV and will only travel a few tens of micrometers. Beta particles will travel ~10mm in water (depending on their energy). You can purchase a beta source from: http://www.imagesco.com/geiger/radioactive-sources.html. Another alternative is to look for a cosmic ray track. It might take several minutes for a cosmic ray muon to pass through the chamber as the flux is something like a muon per cm per minute.
Cheers,
Mark
Mark, thanks very much for your insight. I will try a strong beta emitter and post the results.
ReplyDeleteLooking forward to this one Ben.
ReplyDeleteHi Ben,
ReplyDeleteI was thinking about your bubble chamber experiment and recall that propane was used as the working fluid. If you Google bubble+chamber+propane you will get a lot of hits. One in particular (a PDF) has a nice graph of particle counts per second versus "superheat pressure" (=vapor pressure - operating pressure). Also shown is a schematic of a bubble chamber in which a buffer liquid (glycol) is floated on the supercritical fluid separating it from a working gas. Although not indicated I would think you could use helium or argon as the working gas and in this way you could adjust the pressure in the chamber independent of temperature (to some degree - pun intended). See: http://www-astro-theory.fnal.gov/Conferences/TeV/Sonnenschein.pdf
Cheers,
Mark
Maybe CO2 doesn't have enough of a cross-section?
ReplyDeleteEnergy source: evaporation – condensation. New idea (CO2 only):
ReplyDeletehttp://www.youblisher.com/p/850885-Energy-source-evaporation-condensation-Edited-version-2/
Regards, Emil Kutin