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|Weapons of mass destruction|
An antimatter weapon is a theoretically possible device using antimatter as a power source, a propellant, or an explosive for a weapon. Antimatter weapons are currently too costly and unreliable to be viable in warfare, as producing antimatter is enormously expensive (estimated at $6 billion for every 100 nanograms), the quantities of antimatter generated are very small, and current technology has great difficulty containing antimatter, which annihilates upon touching ordinary matter.
The paramount advantage of such a theoretical weapon is that antimatter and matter collisions result in the entire sum of their mass energy equivalent being released as energy, which is at least two orders of magnitude greater than the energy release of the most efficient fusion weapons (100% vs 0.4-1%). Annihilation requires and converts exactly equal masses of antimatter and matter by the collision which releases the entire mass-energy of both, which for 1 gram is ~9×1013 joules. Using the convention that 1 kiloton TNT equivalent = 4.184×1012 joules (or one trillion calories of energy), one half gram of antimatter reacting with one half gram of ordinary matter (one gram total) results in 21.5 kilotons-equivalent of energy (just over 40% more than the atomic bomb dropped on Hiroshima in 1945). 
Recent advances and physics obstacles
Research conducted in 2008 dramatically increased the quantity of positrons (antielectrons) that can be produced. Physicists at the Lawrence Livermore National Laboratory in California used a short, ultra-intense laser pulse to irradiate a millimeter-thick gold target which produced more than 100 billion positrons.
Even if it were possible to convert energy directly into particle/antiparticle pairs without any loss, a large-scale power plant generating 2000 W would take 25 hours to produce just one gram of antimatter. Given the average price of electric power of around US$50 per megawatt hour, this puts a lower limit on the cost of antimatter at $2.5 million per gram. This would make antimatter very cost-effective as a rocket fuel, as just one milligram would be enough to send a probe to Pluto and back in a year, a mission that would be completely unaffordable with conventional fuels. Most scientists, however, doubt whether such efficiencies could ever be achieved.
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, such as magnetic bottle in a near-perfect empty vacuum. The obvious solution of confining a charged object inside a similarly charged container is not feasible as the electric field inside is uniform. For this reason it is necessary to have charged objects moving relative to the container which can be confined to a central region by magnetic fields; for example, in the form of a toroid or Penning trap (see below).
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 is not feasible to construct a weapon using positrons alone, due to their mutual repulsion. The antimatter weapon core would have to consist primarily of neutral antiparticles. Extremely small amounts of antihydrogen have been produced in laboratories, but containing them (by cooling them to temperatures of several millikelvins and trapping them in a Penning trap) is extremely difficult. 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. Antimatter Helium-4 has also been created.
The difficulty of preventing accidental detonation of an antimatter weapon may be contrasted with that of a nuclear weapon. Whereas nuclear weapons are 'fail-safe', antimatter weapons are inherently 'fail-deadly': In an antimatter weapon, any failure of containment would immediately result in annihilation, which would damage or destroy the containment system and lead to the release of all of the antimatter material, causing the weapon to detonate entirely at full yield. By contrast, a modern nuclear weapon will explode with a significant yield if (and only if) the nuclear trigger is fired with absolute precision resulting in a neutron source wholly releasing promptly (< microseconds). In short, an antimatter weapon must be actively kept from detonating; whereas a nuclear weapon will not unless deliberately made to do so.
As of 2004[update], the cost of producing one millionth of a gram of antimatter was estimated at US$60 billion. By way of comparison, the cost of the Manhattan Project (to produce the first atomic bomb) is estimated at US$23 billion in 2007 prices.
Antimatter catalyzed weapons
Antimatter-catalyzed nuclear pulse propulsion proposes the use of antimatter as a "trigger" to initiate small nuclear explosions; the explosions provide thrust to a spacecraft. The same technology could theoretically be used to make very small and possibly "fission-free" (very low nuclear fallout) weapons (see pure fusion weapon). Antimatter-catalyzed weapons could be more discriminate and result in less long-term contamination than conventional nuclear weapons, and their use might therefore be more politically acceptable.
In popular culture
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The LLNL scientists created the positrons by shooting the lab's high-powered Titan laser onto a one-millimeter-thick piece of gold.
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- Spotlight on "Angels and Demons" – A discussion at CERN's public website on the viability of the use of antimatter for energy and weaponry
- "Air Force pursuing antimatter weapons: Program was touted publicly, then came official gag order"
- Page discussing the possibility of using antimatter as a trigger for a thermonuclear explosion
- Paper discussing the number of antiprotons required to ignite a thermonuclear weapon