The goal of our project is to create a cloud chamber that captures cosmic rays that pass through. The theory behind the experiment is explained in detail in the attached files. We have made several attempts to construct the chamber. In our initial design, we used ice and plastic chambers as containers, which we proved that it doesn't work (the exact trials are described in detail in the steps described below). The eventual product has both the top plate and bottom plate replaced by metal conductors that transmit heat much faster, and we used dry ice to replace regular ice to create enough temperature gradient. In the attached videos we displayed many cosmic rays that we have observed. We also tested the performance of our chamber under the effect of a radioactive source.

Theory.pdf
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Supplies

List of items used:

Rubbermaid 1994227 Container, BPA-Free Plastic, Clear Brilliance Pantry Airtight $18.89 Food Storage, Open Stock, Sugar (12 Cup) * 2
Roscoe Gel Ice Pack and Ice Packs for Injuries Reusable, Ice Pack for Back, Shoulder, Knee, 11 x 14 Inches * 1
Flic-flac 8 x 8 inches (20cmx20cm) 1.4mm Thick Soft Felt Fabric Sheet Assorted Color Felt Pack DIY Craft Sewing Squares Nonwoven Patchwork * 28
Solimo 99% Isopropyl Alcohol For Technical Use, 16 Fl Oz * 12
Aluminum Tape, 2-inch x 65 Feet Foil Tape (3.9 mil), Insulation Adhesive Metal Tape, High-Temperature Heavy Duty HVAC Tape, Silver Tape Aluminum Foil Tape for Ductwork, Dryer Vent, HVAC * 1
Hot water at 60 Degrees Celsius.
Dry Ice Pellets: got from the Chemistry department.
Duct tapes
Hot glue
Metal Plate with 3-mm thickness and is large enough to cover the top of the container.
Some Ice packs.
Flashlights
Strontium-90 radioactive source.

Step 1: Let's Make a Prototype

Introduction:

As our prototype, we are trying only to create a temperature gradient and see a consistent cloud. In this prototype, we have tried three different methods to create the cold side of the temperature gradient: ice gel and ice pack outside, ice pack inside, and dry ice inside. We are inspired by the above youtube video that we don't really have to use dry ice to create a cloud chamber, and we decide to test this.

Method 1. Ice Gel and Ice Pack Outside:

We fold and cut out a felt of a proper size, and stick that to the outside of the bottom of one container with duct tapes.
Soak the felt with alcohol.
Get rid of the caps of both containers and put the one with the felt sticked to the bottom on top of the other.
Quickly and tightly seal the gaps between the two chambers with aluminum tapes.
Pour hot water in the top chamber.
Place the whole setup on top of the ice gel and put ice packs around the setup.
Wait for the cloud to form.
Then, use flashlights to observe the cloud and the traces.

Conclusion:

We didn't see a cloud, we suspect that this is because that our temperature gradient is not large enough to vaporize and condense the alcohol, and therefore, we are thinking of putting the ice pack inside the bottom container to make the the air there cooler.

Method 2. Ice Pack Inside

We fold and cut out a felt of a proper size, and stick that to the outside of the bottom of one container with duct tapes.
Soak the felt with alcohol.
Get rid of the caps of both containers and put ice cubes packed in sealed bags into the container.
Put the container with the felt sticked to the bottom on top of the other.
Quickly and tightly seal the gaps between the two chambers with aluminum tapes.
Pour hot water in the top chamber.
Place the whole setup on top of the ice gel and put ice packs around the setup.
Wait for the cloud to form.
Then, use flashlights to observe the cloud and the traces.

Conclusion:

We still didn't see a cloud, we suspect that this is because that our temperature gradient is not still large enough to vaporize and condense the alcohol. Eventually, without the setup in the video, we decide to go for dry ice.

Method 3. Dry Ice Inside:

We fold and cut out a felt of proper size, and stick that to the outside of the bottom of one container with duct tapes.
Soak the felt with alcohol.
Get rid of the caps of both containers and put dry ice into the container and wait for 1 minute such that air is pushed out by carbon dioxide. (The amount of dry ice can be varied.)
Put the container with the felt stuck to the bottom on top of the other.
Quickly and tightly seal the gaps between the two chambers with aluminum tapes.
Pour hot water into the top chamber.
Wait for the cloud to form.
Then, use flashlights to observe the cloud and the traces.

Conclusion:

We eventually get a cloud as well as some traces! However, although the cloud remained in the chamber for a long amount of time, we can only observe the traces for a short period of time. After approximately 2 minutes, all traces cease to exist. We need further modification to lengthen the time at which traces exists.

Step 2: And Make It Better...

Introduction:

Then, we try to make our cloud chamber sealed to remove huge turbulence and meanwhile, we also want to make our temperature gradient more uniform. Eventually, we make use of a metal plate to conduct heat away from the container to the dry ice uniformly.

Method:

We fold and cut out a felt of a proper size, and stick that to the inside of the bottom of one container with hot glue.
Soak the felt with alcohol.
Use the metal plate. (If your metal plate is not flat or has holes like ours, use aluminum tape to tape up the whole metal plate.)
Get rid of the cap of that container and put the metal plate on the top of the container, and seal the gap between them with aluminum tape.
Place the container upside down with the metal plate directly onto dry ice. The dry ice pellets should support the metal plate horizontally on the desk.
Wait for the cloud to form.
Then, use flashlights to observe the cloud and the traces.

Conclusion:

We tested this setup with a Sr-90 source and we indeed get some rays out of that. However, with this setup, we don't have place for hot water, and the resulting cloud is very thin and eventually cannot be nicely captured by our digital device. We came up a solution by turning the appratus upside down and giving a water bath at the bottom. This method works immediately and created a huge cloud, but it also brings huge turbulance that makes our obsercation of cosmic rays impossible. (We cannot even clearly see the electrons coming out of Sr-90 with this "improvement".) Therefore, we decide to cut from the top and put back the second container to heat up the alcohol.

Step 3: Final Design

Introduction:

As mentioned above, we removed the top layer of one of our chambers and put the other on top of that to create a thicker cloud.

Method:

We eventually cut one of the containers horizontally at a distance of 3-cm from the bottom. We should make sure that the cut is flat and smooth.
We fold and cut out a felt of proper size, and stick that to the outside of the bottom of the un-cutted container with hot glue.
Use the metal plate. (If your metal plate is not flat or has holes like ours, use aluminum tape to tape up the whole metal plate.)
Get rid of the cap of both containers and put the metal plate on the top of the cutted container, and seal the gap between them with hot glue.
Place the cutted container upside down with the metal plate in contact with the desk.
Soak the felt with alcohol.
Then, put the uncutted container in line with the cutting edge, with the felt completely inside the bottom container. Seal the gap tightly with aluminum tape.
Place the metal plate side on the dry ice. The dry ice pellets should support the metal plate horizontally on the desk.
Pour hot water into the top chamber.
Wait for the cloud to form.
Then, use flashlights to observe the cloud and the traces.

Conclusion:

We eventually created a long-lasting chamber that maintains the cloud for a long time and makes traces observable.

Step 4: What Particle Passes Through?

As can be seen in the video, we caught one particle spiraling through the chamber, this indicates it is charged (as expected) and reacting to a magnetic field. Since we see it spiraling around a north-south axis it is reasonable to assume it was reacting to the earth's magnetic field, additionally, since we see it spiral counterclockwise around the magnetic field lines we know it must be negatively charged. The most likely candidate is then naturally the electron. For circular motion, there must be an inwardly directed force of m*v^2/r, and a magnetic field will always exert a force on a charge qvB, where m is the mass of the particle, r is the radius of the circle, B is the magnetic field strength, q is the charge of the particle, and v is the velocity it spins about the axis of rotation. Setting these equal we see that for magnetically driven circular motion mv=qrB. Now assuming electron mass and charge (m=9.1093837 × 10-31 kilograms, q=1.60218 × 10^-19 Coulombs) and the earth's magnetic field strength (B=0.0000305 tesla) this gives us a direct relationship between the radius of curvature and particle velocity. Estimating the radius of the circle to be ~1 cm we see the velocity of the particle was around 5000 kilometers per second, around 2% the speed of light! This is actually quite slow for a cosmic ray or its remnants. This particle must be the last fading remnant of a particle shower. As you can see from the equations above since mv=qrB the velocity and radius of the circle are proportional so most of the particles we see will appear to move in straight lines because the circles they make around the earth's magnetic field lines are far bigger than our cloud chamber.

Conclusion:

We performed various different trials to construct a perfect cloud chamber with minimal cost and is convenient to set up at home. Throughout each trial, we observe the outcome, drew new conclusions, and took actions to improve it. During the process, we proved that certain design is infeasible and vetoed them (For example, we proved that the temperature gradient is too small if we use ordinary ice). Eventually, we ended up in a chamber that is much better than what we started that captures cosmic rays.