Antimatter, of course, is a fantastically interesting material. Being interested in a topic may be a good enough reason for a scientist to do endless research, but the average person usually needs a little more motivation. Why do we care about antimatter? What can antimatter do for us? It essentially explodes on interaction with regular matter, and it requires huge amounts of effort to produce. Why do we bother?
As physicists continue to study antimatter, more potential uses for antimatter are discovered. Below are some of the leading ways antimatter can be useful.
Medicine
As far as modern technology that makes use of antimatter, the most common example is positron emission tomography , or the PET scan (pictured left)[1]. A PET scan uses a radionuclide, an atom with an unstable nucleus that undergoes the previously mentioned beta decay, attached to a biological tracer molecule. When the radionuclide decays, it emits positrons, which then annihilate with nearby electrons. The gamma rays released from this event are then picked up by the machine, which produces a three-dimensional image of the body. The tracers vary according to what biological process is being observed. The most common process is fluorodeoxyglucose, which can be used to observe glucose uptake in various regions. This is used to check cancer metastasis , meaning the spread of cancer through the body.
Spaceships
One use for antimatter that is still in the hypothetical stage is as a potential fuel source, particularly for space travel. When antimatter annihilates, there is a 100% conversion from matter to energy. That gives an energy density of 8.99x1010 MJ/kg. To put this into perspective, take a look at the energy densities of common substances listed in Table 1
Because of this high energy density, several ways of using antimatter to drive space travel have been considered, from antimatter sails,pictured below3, to using antimatter as a trigger for nuclear fission.[2]
An example of an antimatter sail [5]
CREDIT: Hbar Technologies, LLC/Elizabeth Lagana
So why haven't any antimatter-fueled space expeditions been launched yet? The problem lies in finding a way to store larger quantities of antimatter. While only 30mg of antihydrogen would be enough fuel for 10kg payload to travel 250 astronomical units (about 4x1013m) in ten years (almost 5% of the speed of light), no one has yet developed a way to store antihydrogen. We really don't want the antimatter to annihilate with any part of the spacecraft, so the traditional containers for hydrogen won't work, since they are made of matter. Some methods of containment have been developed using electric and magnetic fields to store charged particles, confining them to the centre of an apparatus and preventing them from reaching the edges of the device.[5]This solution, however, only works for charged particles, such as antiprotons, positrons, or, hypothetically, ions of antimatter elements.
Other antimatter traps have been created that use the magnetic spin of the positrons and antiprotons themselves to contain neutral antihydrogen.[6] These traps are far more complex, and experience problems as the antihydrogen becomes more densely packed. When the atoms are pushed too close together, the positron's spin is capable of flipping, which results in it being lost from the trap, being annihilated at the walls and lost. With the recent interest in asteroid mining and space travel, this avenue of research will likely see a spike in activity.[7]
Explosions and Laser Beams
As may be gathered from the idea of annihilation, there is also the possibility of using antimatter as a weapon, most logically, as a bomb. This however involves two major stopping points: storage and quantity. Producing enough antimatter to be effective is no small task, and developing a method to store and transport that amount anywhere is just as difficult. However, several methods have been considered that could use much smaller quantities as parts of a larger military system. As mentioned above, antimatter can be used as a trigger for nuclear fusion, and has been considered as a potential power source for high-powered lasers. Other applications are also possible, and all of them read like deleted sections of a Star Trek script.[4]
