Every second, about 34  cosmic rays from the Sun (and some from distant supernovae) zip through your body.  That's 3 million cosmic rays penetrating you a day.

Typically we are totally oblivious, unaware of the stunning particle symphony enveloping us.  However, we can make that all change.  You can see cosmic rays with your own eyes! See them clearly for the first time with these easy direction listed below. It will forever change the way you think about your surroundings.

Auroras as seen by the International Space Station. When cosmic rays strike the upper atmosphere's oxygen and nitrogen it excites electrons, releasing photons. (Image by NASA.)

First-What is A Cosmic Ray?

A high energy charged particle that comes from highly energetic cosmic events that blow apart atoms, sending hydrogen and helium nuclei, electrons, and even the very special muons (more on these below) zipping towards us at nearly the speed of light.  Examples of such events include solar flares and supernovas.  Like a constant particle rain, they pour down on Earth.  These particles can cause mutations when they hit DNA.  Fortunately, Earth's magnetic field protects much of the Earth from the full brunt of cosmic rays.

The doughnut shaped magnetosphere funnels much of the cosmic rays sent towards Earth to the poles, exciting electrons in the atmosphere enough to produce light - the auroras. Listen to Brian Cox wax eloquent about how the cosmic rays from supernovas shooting through his ancestor's bodies created the mutations that lead to him.

Amazing Facts About Cosmic Rays:

Here are just a few facts about cosmic rays and reasons why they are important:

  • As cosmic rays travel through your body they can cause DNA  mutations, which sometimes lead to cancer or even evolutionary changes. As Carl Sagan famously pointed out, there is a reasonable chance that cosmic rays from supernova have had an important role in crafting human evolution by causing mutations that might have given our ancestors a selective advantage.
  • The dazzling light shows at the poles (known as the aurora) are caused by cosmic rays.
  • Cosmic rays are the cause of much of the white noise interference on radios and televisions.
  • Cosmic rays are often the culprits behind blocked satellite/GPS signals.
  • Your last dropped call might have even been caused by cosmic rays.
  • The rays can help your car pick up charge while driving, since the cosmic rays ionize the atmosphere flowing over your car.
  • Neutrino detectors are built deep underground within old mines because of cosmic rays.  Closer to the surface of Earth, there is too much interference, so the detectors need to go far underground because muons can penetrate  tens of meters of rock.
  • Cosmic rays cause nitrogen in the atmosphere to turn into the radioactive carbon-14 used in artifact dating.
  • Even doing something as simple as sipping a cup of tea may be affected, as you see cosmic rays zipping and dancing through the steam rising from your mug.

How The Test Works in Relation to Relativity:

Some of the cosmic rays hitting Earth strike the nuclei of gas in our atmosphere.  Some of these collisions produce pions, which then decay into muons (a negatively charged particle with mass).  Muons are unstable and have a half life of 2.2 microseconds.  That means that they should decay after traveling only 660 meters/2165.35 ft; although these particles travel pretty quick, they should almost never reach the surface of Earth.

Go fast and time slows down as compared to the time of an outside observer.
Image via The World as Computation.

However, 34 just shot through you this second. By another estimation, about 10,000 reach every square meter of the surface of Earth.  So these particles are making it much, much  farther through our atmosphere than would be expected. How is this possible? Well, it's all rather simple. First, they are traveling 98% of the speed of light, because they are traveling at relativistic speeds (speeds approaching the speed of light) time is slowed down, which allows them to reach Earth's surface and shoot through your body Let me repeat that for emphasis: the particle detector you build works (in part) because of relativity.

Muons reach it because time is slowed down due to relativity, and their life is extended long enough to make it through the atmosphere to you.  These simple cloud chambers are, in essence, testing relativity.

Why Do the Cloud Contrails Form?

As the cosmic ray shoots through the atmosphere it ionizes the air molecules (hence, it's called "ionizing radiation").  That means that it is so energetic that it causes electrons to disassociate from their nucleuses.  These free agent ionized particles then act as nucleation sites for the alcohol vapor to condense upon - the opposite charges get "sticky" with each other.  So, the cosmic ray contrails share more than just superficial resemblance to the contrails produced by airplanes, which is droplets forming on the burnt fuel nucleation sites.

Image by Cloudylabs.

Materials To Conduct the Experiment:

  • Vapor source: any alcohol will work: Methanol, ethanol (denatured or very high proof alcohol), propanol, or isopropyl.
  • Container: Used to trap the vapor.  I have seen the following used effectively: A petri dish, pyrex, tuperware, an aquarium, or even a plastic cup.
  • Absorbent material: This will be soaked with the alcohol: A sponge, paper towel, felt, etc.  It will need to be fixed on the top of the container using tape, clay, pins, or other material (see steps below for more details).
  • Dry ice: used to supersaturate the vapor, allowing for small contrail clouds to form.
  • Black base for container: this allows for contrast to see the contrail clouds (maybe a pan or something similar).
  • Light source: This is used to illuminate the contrails.  The brighter, the better.  Experiment with which angle illuminates the droplets best.
  • Hot water bottle (optional): if your container is large enough, such as an aquarium, you can use a hot water bottle to heat the alcohol, saturating the air.  This increases the amount of vapor in the air, but it also may raise the saturation level.
  • Source of radioactivity (optional): You don't have to have this, but it's awesome if you do.  You'll see quite clearly the alpha and beta particle decays.  Common sources of radioactivity: smoke detectors (Americium-241), propane gas lamps (the fabric gas mantles often contain thorium dioxide), orange Fiestaware (uranium), old glow in the dark clocks/watches/instrument dials (radium), antique 19th century yellow/green vaseline or canary glass, some rocks/stone counter tops, etc.
  • Magnet (optional): These are charged particles we are dealing with.  If you introduce a magnetic field they will be attracted to one pole and repelled by the other, depending on their charge.
  • Sealant (optional): If you want to trap the vapor more effectively you could use clay or vaseline around the edge where the container and the base meet.

Step-by-step Guide:

Here are a few video explanations of the construction process:  This is the best and simplest video explanation.  See what it looks like to use a radioactive source (lead).  Here's a video description of the first cloud chamber (which was the first time subatomic particles were observed!!) that used a vacuum to supersaturate air with water vapor.  Here is how to make such an expansion cloud chamber (much more complex than the diffusion cloud chamber described below).

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  1. Prepare the base by filling it with dry ice.  Having styrofoam beneath the base will allow for extended viewing.
  2.  Insert what you are using to absorb the alcohol into the viewing container.  Soak it thoroughly with alcohol.
  3.  Put the two pieces together, sealing as you are able.
  4. Shine your light through the side of the container, adjusting to get the best view.
  5. Wait and be patient, allowing time for the alcohol to saturate the container's air.
  6. Change your undergarments because you just sh*t your pants it was so awesome.  Actually, your results will likely be very subtle.  Please remember that while your results may be faint, their implications are massive.
  7.  Share this with others!  This is a very simple experiment that reveals a side of reality that is mind blowing when understood properly.  From this one experiment, you can you can jump off to exploring more about subatomic particles, solar flares, supernovas, time dilation,  chemical volatility, weather/condensation/nucleation, carbon dating, electromagnetism, how cosmic rays affect radio/TV/cellphones/satellite signals, ionization, radioactive decay, magnetism/magnetosphere, and probably a bunch of stuff I haven't thought of (please comment your ideas!)!!  It's like the ultimate experiment - easy to do, mind blowing implications, and covers a stunning array of topics.   Consider hosting a science themed party and having this as one of your activities!  I did and it was awesome!  Take pictures and please comment how it went!!
  8. See the world in a whole new light!!!  Fossil dating, time dilation, auroras, mutations, cancer, using a cell phone, listening to the radio, watching the TV, driving your car, seeing the sunlight, and sipping a cup of tea will never be the same!  It's amazing.

Teachers/parents/whoever, click on these for curriculum from Fermilab and Cornell.

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