TRIUMF: Canada's National Laboratory for Particle Physics
What Is TRIUMF?
TRIUMF is Canada's national laboratory for particle physics and accelerator-based science. It's also the site of the largest cyclotron in the world and an important creator of medical isotopes. The facility is located in Vancouver on the University of British Columbia campus. It's operated by a consortium of Canadian universities, however. Free tours are offered to visitors, who are welcome to take photographs. The laboratory is a fascinating place to explore and to learn about science.
In this article, I describe some of the equipment in the TRIUMF laboratory and include observations made during a guided tour of the facility with students. Many interesting things can be seen during the tour and the guides are knowledgeable. The sight of all the complex equipment used to explore the mystery and power of the subatomic world is awesome.
TRIUMF stands for Tri-University Meson Facility. The facility was originally run by three nearby universities—the University of British Columbia, Simon Fraser University, and the University of Victoria. Additional Canadian universities are now involved. A meson is one type of subatomic particle.
The Guided Tour
The guided tour for the general public takes place at 1 pm on Wednesdays and lasts for an hour. The TRIUMF website should be checked before a visit to see whether this information has changed. The tour is free but registration is required. Visitors can register online.
Based on my experience on my school's field trip, there are three main areas shown to visitors. After an explanation of the cyclotron model in the reception area, the first sight is a large hall filled with many types of equipment and multiple experiments in progress. It's fascinating to see, but to an inexperienced eye it looks a bit disorganized. The system is obviously effective, though, since TRIUMF does valuable work.
After seeing sights at multiple levels in the hall, the tour goes to the office area. Here the data centre with its many computers and multiple screens of information can be seen. The office area also includes interesting photos related to the facility.
The climax of the tour is the visit to Meson Hall. More experiments can be seen here, but the highlight is being close to the largest cyclotron in the world. The hall also describes the uses of the facility's cyclotrons in medicine.
Group tours of TRIUMF (consisting of six or more people) currently take place on Tuesdays and Thursdays at 10 am and 2 pm. They are free to attend but must be booked at least two weeks in advance.
The cyclotron is located underground in a site known as the cyclotron vault. It's too dangerous to visit the device when it's operating because of the radiation that's released as particles break down. The surface area near the operating cyclotron is safe for people, however. Staggered stacks of concrete blocks cover the area where the device is actually located and absorb the radiation.
The purpose of the cyclotron is to produce an intense beam of highly energetic protons moving at tremendous speed. The protons that emerge from the device have a maximum energy of 500 million eV (electron volts) and a maximum speed of 224,000 km per second, or three quarters of the speed of light. The protons are sent along beamlines to various places for experiments or for medical use.
Structure of a Cyclotron
Inside a cyclotron there is a cylindrical vacuum tank containing two semicircular, hollow, and D-shaped electrodes known as dees. The straight sides of the dees face each other, as shown in the video screen below. There is a narrow gap between the electrodes. At this gap, the dees are connected to a single alternating voltage source, or an oscillator. Each dee is connected to a different terminal of the oscillator. As a result, an electric potential difference and an electric field is created across the gap.
A large magnet is located both above the vacuum tank and below it. The magnets are arranged so that opposite poles face one other, thereby creating a magnetic field in the tank.
Beamlines send particles into the vacuum tank and remove them after their journey. Like the tank, the beamlines contain a vacuum to prevent the particles from colliding with those in air.
How a Cyclotron Works: A Basic Overview
Charged particles are dropped into the centre of the gap between the dees through a pipe known as an injection beamline. The particles enter a dee and travel through it via a circular path. A positive particle is drawn towards the dee having a negative potential and a negative particle is drawn towards the positive dee. The polarity over the gap between the dees is alternated each time the particle reaches the gap in order to draw the particle into the opposite dee.
As the particle goes through the electric field in the gap, it gains energy and accelerates. This process is repeated multiple times, causing the particle's energy and speed to gradually increase as it travels around the dees (although "gradually" is still a rapid process). Adding all the energy that the particle needs via one trip through an electrical field isn't practical because a tremendous voltage would be needed to create the field.
An accelerated particle in a magnetic field follows a curved path, which is why the particles follow a circular route through the dees. As the acceleration and energy of the particles increases, they travel along a circle of a wider and wider diameter and spiral outwards through the dees. When the particles reach the outermost part of the electrodes, they are withdrawn through a pipe known as an external beamline. The beam of highly energetic particles is then directed at atoms in a target.
An Overview of the TRIUMF Cyclotron
How Are the Accelerated Particles Used?
The particles released from the cyclotron are sometimes used to break up atoms in order to study their structure. Another purpose of the particles is to create and study exotic particles, which may help scientists to understand the universe and its creation. Yet another purpose of the particles is the creation of medical isotopes for the diagnosis and treatment of disease.
More Facts About the TRIUMF Cyclotron
The particles that are fed into the TRIUMF cyclotron are hydrogen ions. Each ion consists of one proton and two electrons. The electrons are stripped from the hydrogen ions at the end of their journey through the cyclotron, creating isolated protons. The electrons are removed as the hydrogen ions travel through a thin layer of foil, which removes the lightweight electrons.
The TRIUMF facility also contains smaller cyclotrons that produce particles with lower energy. In addition, some beamlines from the main cyclotron extract protons with lower energies than others.
One interesting trivia fact that is not on the display board below is that the cyclotron accelerates 1000 trillion particles per second.
A Magnetic Field
Although the radiation from the cyclotron is blocked and doesn't reach Meson Hall, a magnetic field does reach visitors. The field is harmless to the human body and doesn't damage credit cards or consumer electronic devices. TRIUMF recommends that people with implanted medical devices check with their doctor about the sensitivity of the devices to magnetic fields, however. Examples of devices whose function may be affected include pacemakers, shunts and stents, and infusion pumps.
One interesting effect of the magnetic field is the fact that paper clips stand on their end when they're dropped near the cyclotron. Even the senior students from my school enjoyed dropping and carrying paper clips to see the results.
If you'd like a tour preview or a substitute tour, the video below is a good one to watch. It includes views of standing paper clips near the beginning. TRUMF's website is also worth viewing. It announces special events that local people can attend and also has news that online visitors can read.
A TRIUMF Lab Walkthrough or Mini-Tour
Isotopes are forms of an element whose atoms have more neutrons than normal. Some isotopes are stable, but others break down soon after they form, releasing radiation in the process. These isotopes are known as radioactive isotopes or radioisotopes. Most radioisotopes are harmful to humans, but some are not harmful when used in tiny and very specific amounts and are actually helpful in medicine. Medical isotopes are used for both diagnosis and treatment.
Some radioisotopes are used to destroy cancerous tumours. Others are used as tracers that allow doctors to follow a particular process in the body. They are also used to provide a helpful view of a specific area in the body. The radioisotopes become incorporated into a process or area—often after being attached to a carrier substance that is normally present inside the body—and release radiation. The radiation doesn't harm the patient but can be detected, helping doctors to diagnose a health problem.
TRIUMF produces medical radioisotopes for PET (Positron Emission Tomography) imaging. A positron is the antimatter version of an electron. Positrons are released from the nucleus of the medical isotopes as they break down in the body. The positrons then interact with nearby electrons. This process destroys both the positrons and the electrons and triggers the release of radiation in the form of gamma rays. The radiation is detected in the imaging process.
Medical Isotopes at TRIUMF
For most people, there are no safety issues related to a visit to TRIUMF. There may be exceptions for some people, however. Young children must be prevented from touching things that they see, except for things that are meant to be touched, like paper clips. Since there are quite a lot of steps to climb during the tour, it might not be suitable for people with certain health or mobility problems. The potential effects of the magnetic field on medical implants is another possible safety issue, as mentioned above. More information about safety is given on the facility's website. The website also has information about getting to the facility.
When visitors leave the research area of the facility and walk back to reception, they pass through a radiation detector. All of the students and staff from my school had no detectable radiation in their bodies. The facility also performs regular checks of the environment surrounding the facility and finds no increased radiation beyond the normal background level. The staff are well aware of both the benefits and the potential dangers of their work and make sure that safety is maintained. I have no worries about taking a tour again and am looking forward to my next visit. TRIUMF is a fascinating place.
Questions & Answers
© 2016 Linda Crampton