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Contents 1 Discussion 1 2 Discussion 2 3 Discussion 3 4 Discussion 4 5 Magnetic Field Map at 3 cm 6 It is Alive! 7 About momentum analysis

Discussion 1

We discussed briefly how to build our chamber. The requirements are the following

1. Magnetic field to deflect electrons
2. Good top view so we can make movies
3. Reasonably compact and portable

Notes February 8th class.

• Ken Tiu found a 8" diameter plexyglass tube in McMaster catalog for a reasonable price. So we could build the round chamber by gluing a round disk on top.
• We discussed the magnet - There are a couple of ideas. First we talked about a solenoidal magnet. Simple but perhaps not enough magnetic field. Adam suggests multiple coils under the cold plate. We discussed the possibility of using an iron plate instead of aluminum and have it magnetized using a coil around it.
• Helio mentioned the use of Hall Probes used in electronic ignition to map out magnetic field. This was used by Joe Sundermier to map the magnetic field of a much larger magnet.

So here's other ideas to investigate.

1. Do a historical research on how Carl Anderson, the discoverer of positron, built his cloud chamber
2. Do a rough estimate of magnetic field for a solenoid and a solenoid with iron.
3. How about using permanent magnets? crazy?

Discussion 2

(Class March 1, 2006)

Topics for discussion:

• Read about Cloud Chamber and edit the text for typos and incorrect statements.
• A cheap and inexpensive gauss meter
• How to estimate electron energy seeing in a cloud chamber
• Permanent Magnets (Ken Tiu)
• Designing a magnet for the cloud chamber

Discussion 3

(Class March 8, 2006)

• Ken Tiu's magnet are very strong. We will need to map the magnetic field. This procedure involves locating a gauss probe in different places in space and measuring the magnetic field. Based on the measurements we will have a better idea of how much particles will be bent.
• I will bring the cloud chamber to see the mechanical fit of the existing magnets
• Bill L and Tom T have the Allegro sensor and will wire, so we can measure magnetic field
• Jeremy T will bring a gauss meter
• Helio will also bring a gauss meter
• Maps will be done using Excel

What happened? Basically we measured the magnetic field produced by the permanent magnets that Ken Tiu broght in last class. To measure the magnetic field we used an inexpensive gaussmeter that Bill Leacock put it together.

	To determine which side of the magnet is the North (or South) pole we came up with this interesting method. We floated the magnet on a container and let it orient with earth magnetic field. This magnet is quite heavy and it took some doing until we were able to equilibrate it.
	Then the problem was to separate the 3 other magnets that we glued together. After several frustrating attempts, Bill Fisher came up with a solution. To use a screw driver and wedge it between the magnets. Because we didn't have a hammer we used a Rock. You can see it in the picture. It worked extremely well.
	Here's an attempt to fix the magnet at the bottom of the cloud chamber. We concluded that this is not a good setup since the large gaps between magnets creates a reverse polarity field between them. So we decided to rearrange the magnets and thermal fingers for the chamber.

Tom found a cooler that will be better than the one we have to hold dry ice. So pieces are coming together. The base of the chamber is back to BNL for mechanical adjustments.

Discussion 4

(Class March 22, 2006)

• Today we map the magnetic field.

	Bill brought his magic wand and a nice wooden platform. Bill's innovative design of the platform allowed for measurement at three different levels. We could not measure the field directly on the aluminum plate as it saturated the instrument.
	Jeremy created the grid on the platform. This made the data collection simple, yet effective.
	We're not playing Ouija or Chess here - we're measuring the magnetic field!
	How many physicists does it take to measure a B field? Ken places the wand, Elizabeth reads the voltage, and Rich holds the platform steady.
	Adam handled the data collection and number crunching.
	B field level two...
	Tom and Bill worked together to modify the cooling bath. Since the cooler is too deep to fill with dry ice, they cut two styromfoam false bottoms to put in the cooler. This maintained the integrity of the outside shell while using a lot less dry ice.

Magnetic Field Map at 3 cm

The magnetic field map shows that the field strenght is amazingly concentrated in the center. But this begs the question. Is this correct?

It is Alive!

The chamber is shown in the picture in its full glory. Before firing the chamber, all parts were cleaned with alcohol (95% alcohol). The bottom plated where the magnets are glued was cleaned and all excess epoxy scraped with a razor blade. Pure Alcohol (200 proof, absolute) was sprayed onto black felts and the two cylinders filled up to 1/4 of its capacity. The fish tank was lowered and sealed. Sealing is very important as allows for the environment to be isolated from the outside. A plastic liner was put in place to hold the mixture of dry ice and alcohol. This styrofoam container is very good as it keeps the mixture cold for many hours. We've improvised the illumination using an old overhead projector. This works extremely well since light is colimated. (It also shows that biology books can be useful sometimes). The inital worries were that magnets would come loose during cool down because of different thermal expansion coefficients between the aluminum and magnets. This doesn't seem to be the case as the magnets seemed to survive the cool down and warm up cycles. We noticed that the edges cool down much faster than the middle and it takes about 15 minutes for the whole system to reach thermal equilibrium. Ah, it is important to note where the chamber was operated. We were in room 42 at LIGASE. The room is located in the basement of the Life Science building at Stony Brook University. Why is this important? Cosmic rays are absorbed by the building above us. Apparently not that much, as the rate of events were very high. Perhpas we should repeat the experiment somewhere high???

A video camera (30 fps) was mounted initially overhead to record events. Later the camera was moved around to record event under different light conditions. After about 15 min waiting period, a fine mist formed, and tracks were visible. Success! Lots of curved tracks were observed! Many different events could be seen and now the task of analyzing the 45 minutes of recording will start. While working, the chamber shows many, many tracks. The presence of the magnetic field allows us to classify events very nicely. So what can we look for? electron-positron pairs, muon decay, production of delta rays, protons, and new particles. So stay tuned for few events that we will be posting when they become available.

About momentum analysis

For a given magnetic field B(in Tesla) the radius of curvature R (in meters) for a particle of charge z.e and momentum p (in GeV/c) is given by:

So, for a particle with p = 1 MeV/c, z=1 in a region with B=0.03T (close to our case), the radius of curvature will be R=0.10 m. Of course, you can use the equation above in your favorite units....