Frequently Asked Questions
About Matter and Antimatter
I know that single electrons have been trapped for study many years ago. Have there been any experiments using trapped positrons, which would then be released from the trap, and allowed to free-fall ? Everyone expects them to behave identically as electrons do, but I hear the jury is still out. Jim Bogan - Oregon, US
We noticed that during a nuclear fusion between two protons, which fuse into a deuterium atom, a positron and a neutrino are released. We wondered where those particles were coming from. Jasper Vogel & Timo Pleus - Adriaan Roland Holst College, Netherlands
About studying at CAMS
What is Antimatter?
The world is made up of matter in the form of (mostly) atoms and molecules. Of course, atoms themselves can be broken down into several fundamental particles, the proton, neutron and electron. There are many other fundamental particles that we know of and scientists have long been trying to come up with a comprehensive theory that will describe all of them, and their interactions.
For every matter particle, there is a corresponding antiparticle — these antiparticles collectively are what we know as antimatter. They have properties that are similar but opposite to their corresponding matter particles — for example the same mass and the same magnitude but opposite sign of charge. When a particle and its antiparticle meet, they annihilate — disappearing in a burst of energy. What happens in between can be quite interesting, and is the focus of CAMS.
Where do you get antimatter?
Most forms of antimatter are quite hard to come by and can only be seen at big accelerator facilities, such as CERN in Switzerland (or in deep outer space). However, the electron's antiparticle, the positron, is reasonably accessible. It has the same mass as en electron but has a positive charge, rather than a negative charge. This is either through generating positrons using a (relatively) small accelerator called a LINAC, or by using an artificially made radioactive isotope which emits positrons, such as 22Na. CAMS uses radioactive sources to give us the positrons to study interactions of antimatter with matter.
What is a Positron?
A positron is the antiparticle of the electron. It has the same mass but opposite charge (positive instead of negative). When it annihilates with an electron, they turn into gamma rays.
What is Positronium?
Positronium is when a positron and an electron are bound together. In a normal atom, there is a heavy nucleus with a positive charge, with electrons orbiting around it. In the case of positronium, the positive nucleus is replaced by the positive positron. Essentially it is an exotic type of atom. It is very light, as the positron is not heavy like an ordinary nucleus and it only lives for 120 picoseconds or 142 nanoseconds, depending on the configuration. You can even make molecules out of it!
Annihilate, what's that?
Remember E=mc2? When an antiparticle meets its corresponding particle, the mass is converted into energy, and sometimes other particles. In the case of a positron and electron annihilating, the energy is carried by gamma rays, usually either two or three gamma rays are emitted per annihilation event.
Can't you use antimatter for bombs, space drives and that sort of thing?
Not really. For anything like that you would need enormous amounts of antimatter, which you just can't find here on Earth. If you tried to make it, you'd soon find it took a VERY long time and is VERY expensive, a nanogram (one thousandth millionth of a gram) of 22Na costs about $35,000 (Aussie dollars). Even to get a gram, you would need about twice the GDP of the USA (in 2004).
What is a proton?
A proton is a form of matter. It is found in the nucleus (inside of atoms) and has a positive charge that attracts electrons and keeps them stuck to the atoms. The mass of protons (along with neutrons) makes up most of the mass of an atom. Some experiments use protons to smash into atoms or other protons, like the Large Hadron Collider at CERN.
What is a neutron?
A neutron is also a form of matter, but is neutral, meaning it has no charge. It can also be found in the nucleus of atoms. Neutrons are used by some scientists to study the structure of materials. They are also very important in nuclear reactors, where they help sustain the nuclear reaction used to produce electrical power.
What is an electron?
An electron is the third constituent of an atom and has a negative charge. In an atom, electrons form a cloud around the nucleus. Electrons are also the particles that can carry charge around in metals, giving us electricity.
What is a gamma ray?
A gamma ray is a form of light, but with much higher energy than visible light. Gamma rays are produced is nuclear decay and when matter and antimatter annihilate.
What does 22-Na mean?
Na is the chemical symbol for sodium, one of the elements in table salt (sodium chloride). The "22" refers to the mass of the atom. Normal sodium has a mass of 23 (23-Na). 22-Na is unstable and decays to give us 22-Ne (neon) plus a positron. 22-Ne is also unstable and has further radiactive decays.
What is annihilation good for?
Annihilation can tell us when and where a positron dies. By carefully analysing the annihilation radiation (gamma rays) we can get information about material properties and positron interactions.
What would you use a positronium molecule for?
Positronium molecules have only been formed and studied a few times. While they don't have any specific use, they are important to help us try and understand the fundamentals of quantum mechanics and the laws of physics.
What can antimatter be used for?
Antimatter is currently used in medicine for PET scans. "PET" stands for Positron Emission Tomography (the positrons are antimatter) and is used to located cancer sites in the body. PET is also used to monitor brain activity. Positrons can also be used to measure certain material properties which are important for polymers and material damage.
Why should we study antimatter?
Antimatter can give us information about fundamental physics that helps us understand the universe better. It is also used for some applications, so research into antimatter can help improve the way we live. It also lets you play with some really cool toys!
Is antimatter dangerous?
If you met your "antiself" then you would both disappear, via annihilation, in a flash of light (actually, gamma rays). So, in principle, antimatter can be dangerous. In practice, however, antimatter is so rare (at least in this part of the Universe) that the small quantities available do not present any danger to anyone.
I heard that the Large Hadron Collider (LHC) is doing research into antimatter. Does CAMS have anything to do with this?
CAMS is not involved in the research going on at the Large Hadron Collider. That research falls under the field of "particle physics" and is quite different from our own research focus. They do interesting things there too, and get to play with some pretty amazing toys!
I know that single electrons have been trapped for study many years ago. Have there been any experiments using trapped positrons, which would then be released from the trap, and allowed to free-fall ? Everyone expects them to behave identically as electrons do, but I hear the jury is still out.
Excellent question Jim. Using charged particles to study the effects of gravity is virtually impossible. This is because the force of gravity is so much weaker than the electromagmetic force. Any small stray electric or magnetic fields (and they're extremely difficult to get rid of) mean that the results of trying to drop a positron or electron would be fatally contaminated. However, using neutral antimatter, you don't have to worry about that. And you are right, we don't know for sure if antimatter will fall "up" or "down". There are two experiments trying to trap neutral antimatter at CERN (antihydrogen, to be precise). Once they achieve that, one of the interesting things will be to see which way it goes when they let it out. My bet - antimatter will fall down...
We noticed that during a nuclear fusion between two protons, which fuse into a deuterium atom, a positron and a neutrino are released. We wondered where those particles were coming from.
Another good question. When 2 protons fuse to form dueterium, the total charge of the system goes from +2 units to +1 unit. Charge is a conserved quantity, so there must be some way to get rid of the extra +1. For this case, most of the time, a positron is produced, which carries the extra charge away from the dueterium. Where does the positron come from? Well as we all know E=mc2 - there needs to be eonugh energy in the intitial reaction to create a positron from nothing. Not only can mass get converted to energy, but energy can be converted to mass. So, there are no positrons "hiding" in the protons, they are created in the reaction. The neutrino also comes about in this way, and is needed to balance out the momentum in the reaction. There is also a small chance that instead of producing a positron the protons will capture and electron (charge -1 unit) to neutralise the extra charge. In this case, the mass of the electron needs to be converted to energy and the reaction gives off the extra energy (an exothermic reaction). There is a neutrino produced in this reaction too.
How do I get in contact with CAMS?
Please visit our contacts page and use the addresses, email addresses and phone numbers there.
What is the ARC?
The Australian Research Council is a statutory authority within the Australian Government's Innovation, Industry, Science and Research (IISR) portfolio. Its mission is to deliver policy and programs that advance Australian research and innovation globally and benefit the community.
You can learn more at http://www.arc.gov.au/
What is a Centre of Excellence?
The Centres of Excellence program is administered by the Australian Research Council. ARC Centres of Excellence are prestigious hubs of expertise through which high-quality researchers maintain and develop Australia's international standing in research areas of national priority. Through ARC Centres of Excellence, a high level of collaboration occurs between universities and other organisations in Australia and overseas.
To find out more, visit http://www.arc.gov.au/ncgp/ce/ce_default.htm.
Why are so many universities working together in CAMS?
One of the strengths of CAMS is the high levels of collaboration between different universities and other institutions around Australia. The facilities at each institution is called a "research node". Each research node in CAMS brings a unique strength with some nodes specializing in theoretical studies, others in experimental studies and applications. With each research node working together, CAMS has an output and relevance which is much greater than the sum of its parts.
What is your logo about?
Our logo represents a positron and an electron forming positronium. The curved line between the two circles represents a gamma ray (check the Greek alphabet symbol for gamma). Understanding and using the interaction of matter and antimatter, including the production of positronium is fundamental to the work of CAMS.
What sort of student programs are there at CAMS?
CAMS has programs for all levels of University students. Please see our student pages for more details.
Who should I contact to ask about studying at CAMS?
Are there scholarships available?
There are scholarships available for study with CAMS at all levels. Please check out our student pages for more details.
What background do I need to study at CAMS?
CAMS is interested in students with backgrounds in physics, chemistry and biology. Each project has its own unique requirements. Please check out our student pages, and then contact us to discuss further.
I'm interested in Science Communication. Are there opportunities for me to study at CAMS?
Yes! At CAMS we're very interested in communicating the results of our research. Please contact us for more information.