Antimatter weapon
An antimatter weapon is a hypothetical device using antimatter as a power source, a propellant, or an explosive for a weapon. No antimatter weaponry is known to exist outside of fiction (such as Star Trek's photon torpedo). The United States Air Force, however, has been interested in military uses—including destructive applications—of antimatter since the Cold War, when it began funding antimatter-related physics research.
On March 24, 2004, Eglin Air Force Base Munitions Directorate official Kenneth Edwards spoke at the NASA Institute for Advanced Concepts[1]. During the speech, Edwards ostensibly emphasized a potential property of positron weaponry, a type of antimatter weaponry: Unlike thermonuclear weaponry, positron weaponry would leave behind "no nuclear residue", such as the nuclear fallout generated by the nuclear fission reactions which power nuclear weapons. According to an article in San Francisco Chronicle, Edwards has granted funding specifically for positron weapons technology development, focusing research on ways to store positrons for long periods of time, a significant technical and scientific difficulty.
There is considerable skepticisim within the physics community about the viability of antimatter weapons. University of Maryland professor Bob Park refers to the idea as the "doesn't-matter bomb".
According to an article on the website of the CERN laboratories, which produces antimatter on a regular basis, "There is no possibility to make antimatter bombs for the same reason you cannot use it to store energy: we can't accumulate enough of it at high enough density. (...) If we could assemble all the antimatter we've ever made at CERN and annihilate it with matter, we would have enough energy to light a single electric light bulb for a few minutes." [2]
There are two major obstacles on the way to the creation of antimatter weapons. First of all, creation of antimatter requires enormous amounts of energy. Even if it were possible to convert energy directly into particle/antiparticle pairs without any loss, a large-scale power plant generating 2000 MWe would take 25 hours to produce just one gram of antimatter. Given the average price of electric power around $50 per megawatt hour, this puts a lower limit on the cost of antimatter at $2.5 million per gram. Quantities measured in grams or even kilograms would be required to achieve destructive effect comparable with conventional nuclear weapons: one gram of antimatter is equivalent to 43 kilotons of TNT. In reality, all known technologies involve particle accelerators and they are highly inefficient, making the production of antimatter much more expensive. It is estimated that an antimatter factory could be operated at a cost of $25 billion per gram.
The second problem is the containment of antimatter. Antimatter annihilates with regular matter on contact, so it would be necessary to prevent contact, for example by producing antimatter in the form of solid charged or magnetized particles, and suspending them using electromagnetic fields in near-perfect vacuum. Another, more hypothetical method is the storage of antimatter inside a buckyball. Because of the repulsion of all the carbon atoms, the antimatter would never combine with its opposite and no energy release will occur.
In order to achieve compactness given macroscopic weight, the overall electric charge of the antimatter weapon core would have to be very small compared to the number of particles. For example, it's not feasible to construct the weapon using positrons only because of their mutual repulsion. The antimatter weapon core would have to consist primarily of neutral antiatoms. Extremely small amounts of antihydrogen have been produced in laboratories, but containing them (by cooling them to temperatures of several millikelvin and trapping them in a magnetic bottle) may take decades. And even if these proposed experiments were successful, they would only trap several antihydrogen atoms for research purposes, far too few for weapons or spacecraft propulsion. Heavier antimatter atoms have never been produced.
Effects of antimatter detonation
Over 99.9% of the mass of neutral antimatter is accounted for by antiprotons and antineutrons. Their annihilation with protons and neutrons is a complicated process. A proton-antiproton pair can annihilate into a number of charged and neutral relativistic pions. Neutral pions, in turn, decay almost immediately into gamma rays; charged pions travel a few tens of meters and then decay further into muons and neutrinos. Finally, the muons decay into electrons and more neutrinos. Most of the energy (about 60%) is thus carried away by neutrinos, which have almost no interaction with matter and thus escape into outer space.
The overall structure of energy output from an antimatter bomb is highly dependent on the amount of regular matter in the area surrounding the bomb. If the bomb is shielded by sufficient amounts of matter, the gamma rays are absorbed and the pions slow down before decaying. Part of the kinetic energy is thus transferred to the surrounding atoms, which heat up. In the event of an antimatter detonation in the open atmosphere, most of the energy will ultimately be carried away by the neutrinos, and the remainder by 10-100 MeV gamma rays. The neutrinos would pass through the earth without being attenuated, while gamma rays are relatively weakly absorbed by matter: they lose roughly half of their energy per 500-1000 m of air, compared to only 20 cm of concrete. The explosion would not cause much physical damage because its energy would be evenly dispersed over large area, although the gamma rays may harm people standing nearby. Thus even if the impossible problem of producing enough antimatter were solved, the antimatter bomb would not be as practical or destructive as a conventional nuclear weapon.
External links
- Spotlight on "Angels and Demons" A discussion at CERN's public website on the viability of the use of antimatter for energy and weaponry.