Back to Teachers Home

NOVA scienceNOW: CERN

Viewing Ideas

Before Watching

1. Review terms related to atomic structure. Have students make flash cards and quiz one another on terms related to atomic structure. For example, have them define such words as electron, proton, neutron, nucleus, accelerate, magnetic field, mass, and matter.

2. Illustrate how a particle accelerator works. Particle accelerators are the largest machines ever built, which is ironic given that they investigate the smallest particles in the universe! These machines use electromagnets to accelerate particles, such as electrons and protons, to very high speeds and either smash them into a fixed target or force them to collide with each other. Physicists smash particles together in order to use the collision energy to "create" new particles—constituent particles that make up the larger particles. To help students understand the key features of a particle accelerator, draw a circle on the board and label it Particle Accelerator. Let students know that the particle accelerator at CERN is the biggest in the world—a tunnel over five miles in diameter and 16 miles in circumference. (The bigger a particle accelerator is, the faster it can make the particles go.) Tell them that in the tunnel at CERN, there are two pipes positioned side by side and surrounded by powerful electromagnets. These electromagnets accelerate protons to 99.9 percent of the speed of light and also keep them from blasting through the sides of the pipes.

   The protons in the two pipes travel in opposite directions. Draw four squares on the circle at the twelve, four, six, and eight o'clock positions. Label these the collision rooms. At these points in the accelerator, scientists can cause the two beams of protons to collide. The resulting collision has two times the energy of either beam, and the explosion smashes the protons apart. Instruments surrounding the point of explosion detect any particles resulting from the collision.

3. Demonstrate how a magnet can affect electrons. Particle accelerators use electromagnets to manipulate beams of particles. A familiar device that uses a particle beam is the cathode-ray tube, found in televisions and computer monitors. Unlike CERN's accelerator, which uses beams of protons, a cathode-ray tube uses a beam of electrons. A set of electromagnets moves this electron beam back and forth across the back of the television or computer screen. You can use the following demonstration to show that magnetic fields can be used to direct a beam of charged particles, such as a beam of protons or electrons. Find a junked television (either color or black and white) or computer monitor that still turns on. Plug it in and turn it on so that the screen either glows or shows an image. When you bring a magnet near the screen, students will see that the image distorts. This distortion occurs because the magnet deflects the electron beam, which is made up of negatively charged electrons. See how differently the magnet's north and south poles distort the image. You must use a junked television or monitor because a magnet can permanently damage a screen, especially a color screen. Make sure to tell students that you are using a discarded television or monitor and that they should not try this on their home sets. As an extension, make an electromagnet and use it to distort the image. You can also show that an electromagnet produces a field that can influence the behavior of objects, such as natural magnets or iron filings.

4. Introduce "The Standard Model of Fundamental Particles and Interactions." The Standard Model represents physicists' current understanding of the structure of matter. It shows that protons and neutrons, once thought to be the fundamental particles of matter, are themselves made up of smaller particles. Before introducing the Standard Model, first review the familiar Bohr model of the atom. Though newer models of atomic structure have replaced this one, the Bohr model is still useful for orienting students to the general structure of the atom. Ask the class to name the three main particles that make up ordinary matter: protons, neutrons, and electrons. Then ask the class if these are the smallest particles that exist or whether there are smaller ones that make up protons, neutrons, and electrons. (If the class knows that there are smaller particles, see how many they can name.)

   Next, introduce the particles of "The Standard Model," which identifies 12 different types of matter particles. Six of these are classified as quarks (named up, down, strange, charm, top, and bottom) and six are classified as leptons (named electron, electron neutrino, muon, muon neutrino, tau, tau neutrino). These particles are the fundamental building blocks of the universe. For example, a proton is a combination of three quarks (an up-up-down quark triplet). A neutron is an up-down-down quark triplet. There are other particles created in accelerator collisions, such as mesons (combinations of a quark and an anti-quark) and baryons (combinations of three quarks). However, only the neutron, proton, and electron are stable—the other particles are short-lived and decay into these stable particles. Consider making a chart so students can see the major categories of subatomic particles.

   If appropriate for your class, discuss the forces that act on quarks and leptons. There are four fundamental forces: the weak, strong, gravitational, and electromagnetic forces. There is an elementary particle that corresponds to each of these forces. For example, the photon is associated with the electromagnetic force. The graviton is associated with the gravitational force. The W and Z bosons are associated with the weak force. The gluon is associated with the strong force. Interestingly, these four particles have no mass. Even so, a large particle accelerator can detect the presence of photons, gravitons, bosons, and gluons. Along with the 12 fundamental particles, the Standard Model integrates three of the four fundamental forces (weak, strong, and electromagnetic). When these three forces interact with quarks and leptons, the photons, W and Z bosons, and gluons exchange quanta. The fact that the Standard Model does not include gravity suggests that it is incomplete. Ideally, a complete model would unify the relationship between the fundamental particles and the fundamental forces. If you made a chart of the categories of subatomic particles, consider adding the fundamental forces to the chart.

After Watching

1. Identify fundamental particles by examining particle tracks. Particle accelerators enable physicists to learn about the subatomic world by accelerating particles, such as protons and electrons, to high speeds and either smashing them into a fixed target or forcing them to collide with each other. The collisions break the particles into smaller particles, such as quarks and leptons. Various types of detectors record the behavior of these constituent particles as they scatter, and physicists use this behavior to identify different particles and to understand their properties. What do the data from scattering particles look like? How do physicists tell one particle from another? NOVA has developed an activity in which students learn how to interpret particle tracks recorded by one type of detector called a bubble chamber. The activity is a fun way of introducing students to how physicists look for and recognize some of the fundamental particles. Download the activity and student sheets from the NOVA Web site at www.pbs.org/wgbh/nova/teachers/
   activities/3012_elegant_05.html.

2. Discuss the merits of investing $4 billion in a single research project. The CERN particle accelerator is one of the largest, most expensive machines in the world. Its size enables it to probe into the nature of matter more deeply than any other particle accelerator can. Its cost—about $4 billion for the machine and $1 billion for the experiments and computer analysis of the data—is so great that there is undeniably less money for other science research. For comparison, the entire 2006 budget of the National Science Foundation, a major funder of scientific research in the United States, was $5.6 billion. In preparation for a general class discussion, ask students to jot down their opinions and reasoning about whether or not committing so many research dollars to a single project is in the best interest of advancing scientific understanding. On one hand, CERN is a gamble—it may not reveal anything new. On the other hand, there is a possibility that CERN will unlock new secrets of the universe. As students formulate their positions, write two headings on the board: CERN is worth the cost; and CERN is not worth the cost. Then, ask students to share their ideas. Write their reasons under the appropriate heading. Next, use the list of reasons as the basis of a class discussion about the two points of view. Conclude the discussion by having the class take a vote. Tell students that the science communities in the countries managing CERN, such as the United Kingdom, France, and Germany, have each debated the merits of allocating a significant share of their annual research budget to a single project. Tell students that their solution was to pool resources and work collaboratively. Discuss the advantages and disadvantages of tackling any project, large or small, using a collaborative, team-base approach rather than an independent, go-it-alone approach.

3. Sign up for a distributed computing project to help CERN process its data. When the largest particle accelerator at CERN is operating at full capacity, there will be 400 million proton collisions every second, producing 40,000 gigabytes of data per second! The data to be generated in one year is estimated at ten times that of all the data currently available on the World Wide Web! Given such a profusion of data, how will physicists ever detect a new particle? CERN is enlisting the help of the world's idle computers. Using an approach called distributed computing, CERN is one of a growing number of "data-rich" projects that use people's idle, Web-enabled computers to help process vast amounts of data. People sign on to a distributed computing project by downloading software from the project site. The project splits its huge data set into small chunks and sends these manageable sets of data to the participating computers. After it sits idle for a few minutes, a computer begins processing the data set. Once it finishes processing the data set, the computer automatically sends the processed data back to the project site and receives a new data set to process. Given the number of computers in the world and the amount of time they sit idle, distributed computing can offer a project the equivalent processing power of several super computers, depending on how many people have signed on. Learn more about distributed computing projects, such as CERN's particle accelerator project, by visiting such Web sites as the Berkeley Open Infrastructure for Network Computing (boinc.berkeley.edu) or World Community Grid (www.worldcommunitygrid.org). Some schools' computer policies do not allow a school's computers to be involved in distributed computing projects. In that case, consider enrolling your personal computer, giving yourself a front-row seat to some of the world's most exciting, cutting-edge science.

4. Research the history of particle physics. Students can make a timeline of key events in our understanding of particle physics. They can make two kinds of timelines to tell the story—one based on the people involved, or one based on the major phases in the development of our understanding of the Standard Model. For the first kind, major figures include Democritus, Newton, Faraday, the Curies, Thompson, Planck, Einstein, Rutherford, Bohr, Chadwick and Bieler, Compton, Schroedinger, Dirac, Pauli, Fermi, Yukawa, Glaser, Yang and Mills, Schwinger, Gell-Mann and Zweig, Weinberg and Salam, Bjorken and Feynman, and Iliopoulos. Major phases are framed according to our understanding of atomic particles before and after the advent of particle accelerators. Physicists began using accelerators to investigate subatomic particles in the 1940s. Major topics in the second kind of timeline include the discovery of subatomic particles, postulating and confirming the existence of the quark, the development of the Standard Model, and describing the subatomic forces and interactions (i.e., gravitational, electromagnetic, strong, and weak forces). While the Standard Model answers many questions about the structure and stability of matter, it leaves many other questions unanswered. For example, do quarks and leptons themselves have a substructure? Are there new particles and forces to be discovered? Physicists hope that large particle accelerators can provide answers, or at least clues, to just these kinds of questions.

Web Sites

Evolution Library: Permian-Triassic Extinction
www.pbs.org/wgbh/evolution/library/03/2/l_032_02.html
Presents a short video segment in which rock layers laid down during the Permian and Triassic periods are analyzed.

NOVA scienceNOW
http://www.pbs.org/nova/sciencenow/3410/02.html
Offers CERN-related resources, including additional activities, streamed video, and reports by experts.

Official CERN Website
http://public.web.cern.ch/Public/Welcome.html
A complete introduction of the world's largest particle physics laboratory that includes a history, photographs, current news; as well as resources for teachers, students, and the general public.

Exploratorium Page on CERN
http://www.exploratorium.edu/origins/cern/
The Exploratorium tours CERN's particle accelerators, meets the scientists, and webcasts from inside the Antiproton Decelerator.

The Particle Adventure
http://www.particleadventure.org/
Interactive tour of the inner workings of the atom and the tools for discovery, with student art, humor, quizzes.

Books

The Anniversary of CERN's Discoveries and a Look into the Future
by Roger Cashmore, Luciano Maiani, Jean-Pierre Revol. Springer, 2004.
The articles collected in this book have been written by distinguished physicists who contributed in a crucial way to the developments in particle physics made possible by CERN.

Atoms & Molecules: Building Blocks of the Universe (Exploring Science)
By Darlene R. Stille. Compass Point Books, 2007.
Learn about the discoveries of physicists and chemists while you explore the invisible world of atoms and molecules.

Atoms and Molecules (Usborne Understanding Science)
By Roxbee Cox. Usborne Publishing Limted, 1993.
This book reveals the inner workings of the atom and includes the background to some historic discoveries and inventions, such as the atom bomb.