QuarkNet 2010: Day 4

Today we built a very important part of the cloud chamber apparatus: the magnetometer.  This instrument will allow us to measure the strength of the magnetic field on the surface of our plate where the cosmic rays will be detected.

It's important to know the strength of the magnetic field so that we can calculate the momentum of the particles.  The greater the magnetic field strength, the more the charged particles will curve.

The construction of this apparatus required a lot of soldering, at least for someone who has never soldered before, like me.  Not to toot my own horn too much, but I think I did a pretty darn good job.  Decide for yourself:

The magnetometer has a Hall Effect Sensor which has current running through it.  The sensor is attached to a voltmeter, and when the sensor is inside a magnetic field the voltage changes, depending on the direction of the magnetic field.  A change in 1 mV in the voltage is equal to 1 guass.  The difference be the normal voltage and the experimental voltage gives you the magnetic field strength.  I found the max field strength near the center of the magnet to be about 740 gauss (the Earth's magnetic field is about 0.5 guass).

We had a picnic lunch outside the physics building, and when we came back in we were ready to cool down our chambers for the first time.  I didn't put enough alcohol in the ice box or in the reservoir in the tank, so I didn't see anything at first, but when I fixed those problems I started to see some tracks.

I wonder if a lot of the particles are being blocked because we are in the basement of a large building.  Maybe when I take it home or use it at school we will get more tracks.

Someone decided we needed a radioactive source so we would be able to see a lot of tracks.  We used the calibration source of a geiger counter to shoot gamma rays into one of the chambers.  Here's what it looked like:

In that clip you should see the "cloud" which looks like fog or rain. If you look carefully you will see wisps in the cloud, which is caused when a cosmic ray ionizes the alcohol.

This isn't my chamber, but they are all basically the same. This video was shot at 720p, and I wish it could be a little clearer, so the next time I'll try 1080p, and probably 720p at 60fps after that.

QuarkNet 2010: Day 3

Yesterday we didn't do much building at QuarkNet.  On Tuesday there weren't enough supplies for each of us to build two alcohol reservoirs, so many of us spent a few minutes in the morning building or second reservoir.

The magnets arrived yesterday, and after lunch we installed them.  Each magnet is about 6 cm by 12 cm, and I am pretty sure Helio said they are about 500 gauss.  It was a simple install.  They had brackets already made and holes already drillled.  All we had to do was add a little silicone adhesive to help hold it in place and screw the bracket to the underside of the plate.  See?

This magnet will create a magnetic field (duh) in the alcohol fog, which will cause the charged particles to travel in a curved path.  Negative particles will curve on way, and positive particles will curve the other way.  The amount that the particles curve depend on the mass of the particle, so by studying the particles path we will be able to calculate the momentum of the particle.

The rest of yesterday was taken up by a very interesting lecture by Helio, and a Q&A session in the afternoon.  Helio's lecture was great.  He is a soft spoken man, with a good sense of humor, and he is incredibly knowledgeable.  Better still, he is good at explaining things and is very patient.  We learned a lot about particle physics, which is my favorite aspect of physics.

Today we are going to build the magnetic field sensors, and I really hope we'll get to make some clouds today.  I saw someone bring in some dry ice, so that's promising.