Caltech Partners with Local High Schools to Measure Subatomic Shrapnel

PASADENA, Calif. – They stream out of deep space, traveling at speeds close to that of light, constantly bombarding Earth and literally passing through our bodies: subatomic shrapnel, as one magazine described them, energetic bits of matter known as cosmic rays.

For the past year, Los Angeles-area high school students and their teachers have teamed up with a Caltech physicist to, in a sense, "catch" these ultrahigh-energy rays on their own campuses. Students and their science teachers from the Pasadena Unified School District, Los Angeles Unified School District, and other districts in Southern California, have been involved in the development and construction of detector hardware, the associated electronics, and the computer equipment to form a networked system among 30 Southern California high schools. The project is called the California High School Cosmic-Ray Observatory (CHICOS). Ultimately, says Caltech physics professor Robert McKeown, at least 90 detectors will be installed, scattered widely throughout Southern California.

A large array of detectors will enable the study of these ultrahigh-energy cosmic rays through the detection of "showers," several kilometers in radius, of secondary particles they create in the Earth's atmosphere. Such rays are the highest-energy particles ever observed in nature and have captured the fancy of the astrophysics and particle-physics community. Thus, while establishing a state-of-the-art experimental facility, the project is also providing an exceptional educational experience for local high school students. When a majority of the sites are operating, McKeown expects the project will yield enough significant science to be reported in the scientific journals.

Cosmic rays are comprised of protons, neutrinos (uncharged elementary particles), gamma ray photons (bits of light emitted spontaneously by a radioactive substance), and other subatomic "stuff." They are of interest to scientists for a couple of reasons. For one, studying their composition tells how the galaxy has continued to evolve chemically since the solar system was formed. This helps us to understand how the solar system got the chemical composition that it has, and, in turn, tells us something about our origin. Further, as energetic as they are, cosmic rays may emanate from cataclysms of staggering proportions, including the Big Bang, shock waves from supernovas collapsing into black holes, and matter that's accelerated as it is sucked into massive black holes. Knowing where these particles originate and how they attain such colossal energies will help scientists understand how these violent objects operate.

"The idea is, 'what do these things point back to?' " says McKeown. "And, can we learn something about where they come from as a result of that? This is real science. Maybe these things will point back to some exploding object in the sky, which is exciting to kids. And to me, for that matter."

The timing of when the showers hit the different schools is what tells scientists like McKeown a lot about where they came from. The cosmic rays will generate a "pancake" of rays that, as it falls, gets bigger and bigger. The particles will hit one detector first, then another one sometime later. The detectors at the center of the shower will have stronger signals than the detectors farther away.

Once the center of the shower is detected, the direction of the shower can be determined from the relative times. This is where the high school kids come in--using trigonometry, they can reconstruct the direction of the showers, taking into account the orientation of the earth at that time.

The program also incorporates a high-school-teacher education component coordinated by Dr. Ryoichi Seki at California State University, Northridge. Teachers are developing curriculum materials to help their students participate in this research. Caltech also hosts a summer workshop where physics teachers and students can participate in the construction of new detector stations for deployment at additional sites.

"One of the things I like to show the students and teachers is that this really is a current and ongoing research project," says McKeown, "so it's not an exercise out of a textbook but real science."