The radioactivity seen with a thermoelectric cloud chamber
We’re used to radiation being invisible. With a Geiger counter, it gets turned into audible clicks. What you see above, though, is radiation’s effects made visible in a cloud chamber. In the center hangs a chunk of radioactive uranium, spitting out alpha and beta particles. The chamber also has a reservoir of alcohol and a floor cooled to -40 degrees Celsius.
This generates a supersaturated cloud of alcohol vapor. When the uranium spits out a particle, it zips through the vapor, colliding with atoms and ionizing them. Those now-charged ions serve as nuclei for the vapor, which condenses into droplets that reveal the path of the particle. The characteristics of the trails are distinct to the type of decay particle that created them. In fact, both the positron and muon were first discovered in cloud chambers!
Btw...the positron or antielectron is the antiparticle or the antimatter counterpart of the electron and the muon is an elementary subatomic particle similar to the electron but 207 times heavier - in case you were asking yourself ;)
Video & info source Cloudylabs
https://www.youtube.com/watch?v=XGNvAEtYZkw
Information source via FYFD
https://twitter.com/fyfluiddynamics
#physics #cloudchamber #radioactivity #science
And if you want to make your own cloud chamber, here are instructions: home.cern - How to make your own cloud chamber | CERN
ReplyDeleteThe source from a fire detector is quite sufficient to get good tracks, as is a chunk of thoriated tungsten, available at any welding supply company.
Cloud chambers were artwork. A pity they've been superseded. It's impressive that the clip gives the impression that we see all of the (alpha) particles escaping in the same general directions, giving us a sensual estimation of a rate of (alpha-)decay within human capacity to evaluate.
ReplyDeleteNice post. What is the actual frame rate of the camera, the slowing factor of the footage? If you wait enough and are lucky you can catch highly energetic cosmic rays too.
ReplyDeleteIn French it gives 'chambre à brouillard' (fog chamber). But I like the French name of a similar detector, the bubble chamber, more poetic: 'Chambre à bulles'. It isn't exactly the same system but it serves the same purpose: it's normally made by filling a large cylinder with a liquid heated to just below its boiling point. As particles enter the chamber, a piston suddenly decreases its pressure, and the liquid enters into a superheated, metastable phase....
We can add that the chambers can be placed into a magnetic field to curve the trajectories of the charged particles. The characteristics of the trajectory (curvature and density of the bubbles) then make it possible to deduce the mass and the charge of the particle.
But as Boris Borcic notices it, physicists don't use them anymore, they are historic (or artwork) now, it has been replaced by the time projection chamber (TPC) efficient for large surfaces of detection and with a high spatial resolution (less than 150 μm) or the (multi-)wire chamber (MWPC), invented in 1968 by the French national Georges Charpak, which earned him the Nobel Prize in Physics in 1992.
en.wikipedia.org - Wire chamber - Wikipedia
John Bump The radioactive source of a smoke detector is a tiny chunk (0.29 microgram) of non-isolated Americium-241 (Am), atomic number Z= 95, atomic mass= 241, when it desintegrates, the alpha particles (nuclei of the Helium element: 2 protons and 2 neutrons) it mainly emits are used by the smoke detectors:
ReplyDeleteThese α-nuclei, passing through the air, will ionize the atoms in the air. Normally (no smoke) these ions produce a small electric current, of only a few picoampères, but sufficient to be detected.
Alpha particles are easily stopped (a sheet a paper is enough...) and so they won't let a significant trace in a cloud chamber I guess.
Am 241 also desintegrates with a relatively little harmful gamma radiation (main ray at 60 KeV).
That is an excellent demonstration!
ReplyDeleteIt could serve as a machine vision assignment -- have your robot eye spit out an estimation of the radioactivity in Becquerels from looking at a cloud chamber like in the gif with rulers telling of the dimension of the chamber and a clock telling the time.
ReplyDeleteBoris Borcic Your interventions are always interesting :-) Any upgraded home intrusion-detection system (a camera with a software to detect any change in the picture) would make the trick, no need of a robot....
ReplyDeleteOr better, the night sky survey softwares and cameras developed by UFOlogists, coming from those used by the astronomers for asteroid detection, are more sensitive.
But in any case, what would we mesure? A planar image isn't always sufficient to characterize the type of particles, especially if you use a magnetic field to curve the trajectory of charged particules or if there are collisions between the sub-products into the chamber. We need a 3D analysis of the trajectories and a 2D image of only one camera isn't enough, with a second one, precisely adjusted in its spatial position into an orthogonal crossing plan and a (very) good software it would work but we are leaving the 'amateur' domain...
Bertrand Nelson: if you don't have a magnetic field, you could chuck in webcams any way you wanted and cal out their misalignment based on knowing that they're taking pictures of straight lines, then add in the magnetic field and use the calibration to calculate the trajectory curvature. (I'm thinking of how 3d scanners use a known-straight laser line to determine topology of an illuminated item, and how you calibrate them.)
ReplyDeleteBertrand Nelson The gif shows long trails of particles that traverse the cloud chamber in its wide horizontal dimensions, but particles leaving the sample vertically will barely or not show at all. However, having the dimensions of the tank, together with the assumption that radiation leaves the sample isotropically, will allow to figure out how much the sample radiates in all from how much it radiates in the directions that the cloud chamber best reveals.
ReplyDeleteThe task of the machine vision system would be mostly to count the trails... and perhaps it could infer the geometry of the chamber just from detailing the trails...
Boris Borcic You're right but the example shown in the GIF depicts a limited use of a chamber: it is a fixed radio-element which emits the particles. Usually chambers are used for incoming particles, with various speeds and angles, which could decay themselves in sub-particles during their courses and collisions between them can occur. It would be more difficult, and it is truly, to retrace backwards the events and all the process is extremely short in time.
ReplyDeleteJohn Bump The generalization of the use of a detection system should be taken in account too, for randomly incoming particles. Your solution is good but we can't assume that the trails are always in a plan in the general cases.
Have a good night, it's Saturday in Paris....
Bertrand Nelson We share time zone -- I am in Geneva. You english like a Nelson, do you french like a Bertrand? Bonne nuit.
ReplyDeleteBoris Borcic So we are neighbors... My maternal grandfather was from Lausanne... Although my last name is Nelson I'm a French national, born in Alsace (Mulhouse) not far from the 3 states border (France, Germany, Switzerland) where the Mulhouse-Bâle airport is located. People in Alsace speaks a German dialect so I'm used to hear a foreign langage since my youth but my English skills come first from my professional past in computing: in the 80s, there was no law to force the editors to translate in French the softwares and the manuals. Now I can watch English speaking TV channels without subtitles and understand English 'in the text' (without inner translation).
ReplyDeleteBonne nuit donc.