build a cloud chamber

P H Y S I C A L S C I E N C E S M A G A Z I N E

Build a Cloud Chamber for €10Sean Fogarty

Instructions for use:1. Set the plunger about two thirds of the way down from the

top and seal the chamber i.e. screw on the top. 2. Push the plunger towards the top to increase the pressure and

then pull back rapidly to cause sudden reduction of the chamber pressure and super saturation of the chamber with the alcohol/water vapour and ultimately formation of the cloud trails due to the beta particles.

There are many combinations of plunger position and motion ofthe plunger that may work and one should experiment to findwhich works best, if there is a better method please let me know!

Precaution:Wipe the plastic case with a cloth regularly, the static chargecreated by this will help to clear the tube of ions and it willperform better with clearer more distinct trails.

Trouble shootingA number of problems can cause the cloud chamber not tofunction correctly. The following list may assist if problems occur.

Possible cause Solutionof problemSponge dry Wet with a 50:50 mix of methanol and water

Too much vapour/ Open front valve (needle attachment point on condensation the syringe) and move plunge a few times to in Chamber clear air in chamber. Seal again and retry.

Condensation on If the chamber has not been used for a while the source condensation can form on the front of the

source. This moisture is sufficient to block the beta particles (which helps to prove that the thick walls of the syringe should stop any radiation hazard).The best way to clear this is to open the chamber and clean the source with a cotton bud or leave the chamber open to the air till all condensation is gone.

NOTESThe syringe used is a 50 ml veterinary syringe which has a usefulscrew on end and thick walls (they are designed to be washed andre-used). However you might like to try other models.

The photos show a black card been placed on one side of thesyringe, this helps to improve the visibility of the cloud trails. Inlater versions I found painting half the syringe with matt blackpaint more suitable.

In the version shown in the photos a hand held torch was held tothe base of the chamber however in later versions I added a whiteled and a button battery and switch (taken from an led torch)which were permanently attached to the syringe, this was handierbut not essential.

Any comments or suggestion on the design would be appreciated; you cancontact me at snjnfogarty@eircom.netSean Fogarty, Rocklands, Hempfield, Enniscorthy, Co Wexford

Step 1Fire alarm,ionizationtype, c. €5

Step 2Remove theplate withthe ‘sealed’source. This is a ß emitter.

Step 350 mlveterinarysyringe, €5.The syringewalls stopthe ßradiation.

Step 4Attach sourceto sponge andinsert insyringe.

Step 550:50 watermethanol onsponge.

Step 6Seal inlet,use a piece ofrubber.

Step 7Set plunger2/3 way down.Close seal andpull plunger.Use a light toilluminatechamber.

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