Sunday, April 12, 2020

Diffusion Cloud Chamber (Conclusion)

The Diffusion Cloud Chamber in operation!
 
The complete Cloud Chamber setup, ready for power up!

The clips bellows are from the very first test of the completed Cloud Chamber.
Best viewed in a full-screen mode!

The Cloud Chamber is capable of displaying only charged particles such as α-particles (Helium nuclei), β- particles (electron), β+ particles (positron), μ (muon), Cosmic Rays / proton clusters, etc..
It will not display neutrons, neutrinos and any other sub-atomic particles without a charge.
When I say "display", you don't see and you cannot see the actual particle but rather the ionized path and the resulting  condensation trails left behind a charged particle going thru the volume. 

I injected the Cloud Chamber with "Thoron" which is a short-lived isotop of Radon - 220Rn has a half-life of only 55.6 sec and it is an α-emitter (6405 keV). It is a daughter product of 224Ra, which, on the other hand is further down the decay chain of Thorium (232Th).
My son's reaction to this α-particle fireworks display was pretty rewarding!

Here is another example of Radon-220 ("Thoron") in the Cloud Chamber. To obtain the "Thoron", I placed a Thorium Gas Mantle (Thorium Dioxide - 232ThO2) inside a large syringe and capped it for a couple of days - no point of waiting more than that as it is a very short-lived isotop (55.6 sec) and it will decay quickly after it is produced by Radium-224 (one of the Thorium series decay daughter products) so no substantial accumulation will occur. (In a couple of days, inside the syringe, near an equilibrium state will take place - the concentration of 220Rn will become stable as new 220Rn will be generated to replace the one which is decaying at that moment.)
I lifted the edge of cover and gently injected the air and Radon mixture from the syringe into the Cloud Chamber.
Similar experiment can be done with another Rn isotop - 222Rn generated by Radium Watch hands but then it is worth waiting at least 3-4 days longer for more Radon-222 to accumulate inside the syringe - 222Rn has a half-life of 3.82 days.
As a side experiment, after removing the Thorium Mantle from the syringe and expelling the gas contents, the "empty" syringe was still producing an activity of around 150 CPM on the outside due to β- decay of other solid daughter products deposited after the Radon decay - namely 212Pb and 212Bi.
 This β- activity, as expected died out quickly, over the next few hours and normalized to background levels as the decay chain reached the stable 208Pb. 

The clip shows some high energy β- particles and some low energy β- are also visible. Around 0:08 there is nice Y-trace, showing an interaction with an atom by a high-energy β-. One leg of the Y is sort of zigzagging probably from the knocked off low-energy electron, the other leg of the Y is straighter, created by the original particle. There is also a nicely deflected low-energy β- at around 0:07.

An α-particle, then a low-energy β- particle and at the very end a high-energy β- or a muon (μ).

Some really nice particle interactions!

This is the equivalent of a "Sub-Atomic Particles Disco-Club". On the left is a Natural Uranium doped glass marble, emitting mainly alpha particles and some beta by daughter products. In the center is a pellet of 241Am (a very strong α emitter) and on the right is a vial filled with Tritium (3H) emitting very-low-energy β-.
This video is from an early test before the Light bars were fully constructed.

A tiny piece of Uranium Ore (Uraninite) attached to a Lego square. This piece produces only around 1000 CPM @ 1 cm from my GMC-600+ Geiger Counter. By the time this clip was filmed, the mineral was already covered with liquid alcohol condensate so not that many Alphas are able to escape but plenty of Betas can be seen, emitted by Uranium decay daughter products. The Cold Plate has been running at a steady -35.5℃ for over an hour -  the room temperature is +23.5℃.

This clip shows the Ion Scrubber in action and the difference it makes during operation! On the left side there is a tiny piece of Uraninite (UO2) attached to a Lego square. There is a distinctive loud "click" in the audio from the switch when the High Voltage (HV) is turned OFF or ON. The first 10 sec. of the video is with HV turned ON, then 10 sec. of HV turned OFF and then again 10 sec. of HV turned ON. One can note that when HV is OFF, the tracks become "fuzzy" and less defined. Currently, the Ion Scrubber operates at 4.3 kV but I am planing to add a circuit for voltage adjustment.
The background clicking is from a nearby Geiger Counter.

A word of Caution: Aside from Nuclear / Radiation Safety (dealing with radioactive materials is not something, I will encourage without the proper understanding and training!!!) one should be very careful not to contaminate the volume of the Cloud Chamber - this can affect later observations of the background / cosmic radiation!

I must say, this was a real fun project to work on and a true kitchen table / garage project! My son and I had great time designing and working on the Cloud Chamber and the results absolutely exceeded my expectations. It is a nice portable setup and I have the feeling my son will be bringing it to school more than once.
Unfortunately, the Science Fair, we built the Cloud Chamber for was postponed due to the COVID-19 Pandemic but this will give him time to prepare all of the supporting materials and diagrams.
On the bright side, besides being a Cloud Chamber, this instrument is a good platform to demonstrate, study and experiment with multi-stage Thermo-Electric Coolers.
The High-Voltage Power supply and adjustable electric field strength is also useful for experimentation with electric fields.
The Liquid Cooling Plant is quite useful too for various physics, chemistry or electronics experimentation.
Just as with a Telescope - now I wish the Cloud Chamber was a bit bigger :-)
Next project on the table - DIY Gamma-Spectroscopy!



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