Promoting physics, supporting physicists Cloud Chamber Workshop

Promoting physics, supporting physicists

Cloud Chamber Workshop


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Dry ice Solid carbon dioxide. Subliming at -78.4ºC

ALWAYS store dry ice in an area which is: Well ventilated (it's an asphyxiant). Preferably not below ground (because it's heavier than air). Out of direct sunlight and sources of heat (so it lasts longer) Secure – to prevent unauthorised access.

DO NOT handle dry ice with bare hands. It can cause severe cold burns and frostbite.

DO NOT PLACE IN WORKING REFRIGERATOR / FREEZER

REMEMBER – A little bit of dry ice will sublime to a large volume of CO2 gas.

CLEAPSS General Handbook Section 11.2


Cloud ChambersThe Nobel Prize in Physics 1927 was divided equally between Arthur Holly Compton "for his discovery of the effect named after him" and Charles Thomson Rees Wilson "for his method of making the paths of electrically charged particles visible by condensation of vapour".

http://www.nobelprize.org/nobel_prizes/physics/laureates/1927/index.html


More Nobel Prizes…The Nobel Prize in Physics 1936 was divided equally between Victor Franz Hess and Carl David Anderson "for their discovery of the positron" which they photographed in a cloud chamber.

The Nobel Prize in Physics 1948 was awarded to Patrick M.S. Blackett "for his development of the Wilson cloud chamber method, and his discoveries therewith in the fields of nuclear physics and cosmic radiation".


Making a Cloud Chamber


Making a Cloud Chamber

1. Cut a 2 cm wide length of felt about 1m long.

2. Stick to the “bottom” of the plastic fish tank.

3. Cut the lid of the fish tank.

4. Put tape along the slots left in the lid.

5. Tape the baking tray to the lid.


You will need:

A fish tankA baking tray

ScissorsSawSnipsTapeMetre stick

Access to the roll of feltA marker pen


You are going to stick felt around the “bottom” of the fish tank

Mark two 2.5 cm wide

bands the width of the

roll of felt and cut

them off.

Then cut these two

strips so that you

have pieces that fit

the ends and sides of

the tank.


Peel the backing off the felt and stick it in place in the “bottom” of the fish tank.


You're going to cut out the central part of the “lid” that is inside the lip.


You should end up with something like this:


Cover the slits along the sides with tape:


Stick the lid to the baking tray with more tape:


Put it all together:


Using the Cloud Chamber• 1. Soak the felt in the chamber with Isopropyl alcohol.

• 2. Get blu tac and a source and put them at one end of the cloud chamber. Use the blu tac to have the source about 5mm above the base.

• 3. Put dry ice in a tray. (With gloves).

• 4. Put the cloud chamber on the dry ice.

• 5. Arrange the lighting so trails will be lit from the side.


What do you see?The tracks from beta can be observed, but they are much fainter; low-energy beta emissions produce very irregular tracks. Another way to identify beta tracks is to take a number of photographs at 1 second intervals with a digital camera and flash, say 10 or so, and then download the images to a computer. Zoom in on the photographs and with luck you may be able to pick out some images that show beta tracks. The contrast may be better if the pictures are changed to greyscale.

Mostly alpha


• A straight track that sharply "kinks" off to the left or right. This is a decay of a muon particle. The two dashed lines are particle called neutrinos that your chamber is not able to detect.

• Three tracks that meet at a single point. In these events, one track is an incoming cosmic ray, a particle called muon. This particle hits an atomic electron. The electron and the outgoing cosmic track are the two other tracks.

• A very windy, chaotic track. This is "multiple scattering", as a low-energy cosmic ray bounces off of one atom in the air to the next.


Welding Electrode sources

http://www.practicalphysics.org/go/Apparatus_2298.html

Welding ElectrodeTungsten rod with 2% Thorium 232. Weaklyradioactive. No special precautions required. Do not break or grind.


Where to get dry ice

• Online or by phone:• http://www.dryiceuk.com 0800 0842 040 • http://www.chillistick.co.uk/ 08433 192 919• http://www.boconline.co.uk 0800 111 333

• Around £60 for 20kg. They don't deliver on Mondays.

• Or ask at pharmaceutical suppliers, airport food companies, universities.


Make your own Comet!http://www.practicalphysics.org/go/Experiment_1039.html


Apparatus and materials

• Large polythene sheet to protect floor• Mixing bowl• Bin-liner bag, to line bowl and draw comet together• Mallet, to crush some dry ice to powder• Substantial plastic bag, in which to crush dry ice• Gardening gloves (heavy duty type)• Mixing spoon• Balance, to find mass of comet (and hence calculate a hypothetical kinetic energy) For two comets -• Dry ice pellets, 10 kg• Garden sand, 1 kg• Water, 2 litres• Soil, 1 handful (organic constituent)• Worcestershire sauce (organic constituent)• Smelling salts (organic constituent)

Technical notes

The essential ingredients are dry ice, sand and water. The other items represent the organic molecules thought to be present in a comet. If it feels as if the comet will not bind into a 'snowball', it is because you have not used enough water. There is a natural tendency not to want to use too much water for fear of evaporating all the dry ice.


Teaching Radioactivityhttp://www.iop.org/education/teacher/resources/radioactivity/page_41558.html

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Promoting physics, supporting physicists Cloud Chamber Workshop