|
|
NOVA scienceNOW: CERN
|
|
|
|
Viewing Ideas
|
|
|
Before Watching
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.
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.
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.
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
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. 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. 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. 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.
|
|
