One of three meson factories in the world, the TRIUMF complex, situated on the University of British Columbia campus, houses the world's largest cyclotron.

At the frontiers of knowledge
TRIUMF's intense beams of particles lead the world in many of the frontier areas of research into subatomic science. They are used to probe the structure of matter and search for nature's basic building blocks and measure the fundamental forces between them.

Matter in our world consists primarily of molecules which, in turn, are made of atoms. The atom consists of a heavy central nucleus surrounded by electrons. Atoms are bound together by electric forces between the negatively charged electrons and positively charged nuclei. The nucleus appears to consist of positively charged protons and uncharged neutrons. This binding is an example of the "electromagnetic" force between electrons and nuclei.

Protons and neutrons in the nucleus of an atom are influenced by two kinds of special nuclear forces called "strong" and "weak". The "strong" force, within the nuclei, binds protons and neutrons to form the nucleus. It appears to act through the exchange of a particle called the pion. The "weak" force is responsible for the radioactive decay of many nuclei and subatomic particles.

What are protons, neutrons, pions and other subatomic particles made of? In the past three decades a remarkable answer to this question has emerged in terms of two basic building blocks called "quarks" and "leptons". This is explained in a theory now called the Standard Model. Many of TRIUMF's experiments pursue the myriad of questions raised by the Standard Model.

In the Standard Model, there are two families of particles - quarks and leptons. The family of leptons consists of a number of pairs of particles which participate in the "electromagnetic" and "weak" interactions. The other family, called quarks, has a similar number of pairs of particles which participate, in addition, in the "strong" interactions.

Protons and neutrons are each made of three quarks; pions are made of a quark and an "antiquark". (Each particle in nature appears to have an opposite antiparticle.) Because there are many different combinations of quarks, there are a host of different subatomic particles. Some are similar to pions and are called mesons while others are similar to the neutron and proton and are called baryons.

The further understanding of quarks and leptons and their interactions is currently one of the most exciting frontiers of human knowledge. Its impact encompasses the understanding of the whole subatomic world and answers many important questions relating to technology. TRIUMF is a mixture of people and ideas, at the highest international levels of excellence, each working to extend our knowledge of this exciting frontier.

Hydrogen ions
The simplest substance in nature is hydrogen. Hydrogen atoms are composed of a single positively charged proton orbited by a negatively charged electron. The positive and negative charges balance out to make a neutral atom. It is possible to add a second orbiting electron to produce a negatively charged hydrogen ion.

Accelerating particles
A television set creates pictures by accelerating particles (electrons) up to 30 thousand electron volts. (By comparison, a 1.5 volt flashlight battery would accelerate an electron to 1.5 electron volts.) Negatively charged hydrogen ions in the TRIUMF cyclotron reach energies up to 520 million electron volts (520 MeV). The ions are accelerated by repeatedly applying "kicks" of electric voltage 23 million times per second. After only 3000 of these kicks, the ions move at 75% of the speed of light and can be directed out of the cyclotron into experimental areas where they are used for scientific studies.

TRIUMF's beams are not restricted to energies of 520 MeV. By moving a special stripping foil along a track inside the cyclotron, beams of lower energies can be extracted - from as low as 60 MeV up to 520 MeV and almost anywhere in between. (The stripping foil removes the two electrons from each hydrogen ion and allows the remaining bare protons to be channelled out of the accelerator.) By using more stripping foils, two or three proton beams can be extracted at the same time - each with a different energy and intensity. This versatility makes TRIUMF unique among the meson factories.

Once outside the accelerator, TRIUMF's proton beams are directed into pipes (called beam lines) which carry the speeding particles to experimental stations located in two large experimental halls called the meson hall and the proton hall. (Similar to the way lenses direct light inside a telescope, electromagnets guide and direct the proton beam inside the beam line pipes.)

In the meson hall, the proton beam is first made to strike targets of solid carbon (or beryllium, or copper, or water). The fast-moving protons "knock out" short-lived particles called "pi-mesons" from the target atoms. The mesons are then used for studies at the hall's seven experimental stations. In the proton hall, the beam of protons is used directly in studies that measure and analyze the properties of nuclei.

From the point of creation of the hydrogen ions, through the cyclotron, down the beam lines as far as the experimental stations, the particles are travelling in a continuous high vacuum. This ensures that particles are not scattered out of the beam due to collisions with air molecules.

Visit our Research Areas web page to see some of the work being done here at TRIUMF.