Antimatter weapon

An antimatter weapon is a hypothetical device using antimatter as a power source, a propellant, or an explosive for a weapon. Antimatter weapons do not currently exist due to the cost of production and the limited technology available to produce and contain antimatter in sufficient quantities for it to be a useful weapon. 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. The primary theoretical advantage of such a weapon is that antimatter and matter collisions, though significantly limited by neutrino losses, still convert a larger fraction of the weapon's mass into explosive energy than a fusion reaction in a hydrogen bomb, which is on the order of only 0.7%.

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 skepticism within the physics community about the viability of antimatter weapons. 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]

Acquiring and storing antimatter

Antimatter production and containment are major obstacles to the creation of antimatter weapons. Quantities measured in grams will be required to achieve destructive effect comparable with conventional nuclear weapons; one gram of antimatter annihilating with one gram of matter produces 180 terajoules, the equivalent of 42.96 kilotons of TNT (approximately 3 times the bomb dropped on Hiroshima - and as such enough to power an average city for an extensive amount of time).

In reality, however, all known technologies for producing antimatter involve particle accelerators, and they are currently still highly inefficient and expensive. The production rate per year is only 1 to 10 nanograms. In 2008, the annual production of antiprotons at the Antiproton Decelerator facility of CERN was several picograms at a cost of $20 million. Thus, at the current level of production, an equivalent of a 10MT hydrogen bomb, about 250 grams of antimatter will take 2.5 million years of the energy production of the entire Earth to produce. A milligram of antimatter will take 100000 times the annual production rate to produce.(or 100000 years) It will take billions of years for the current production rate to make an equivalent of current typical hydrogen bombs. For example, an equivalent of the Hiroshima atomic bomb will take half a gram of antimatter, but will take CERN 2 billion years to produce at the current production rate.

Since the first creation of artificial antiprotons in 1955, production rates increased nearly geometrically until the mid-1980s; A significant advancement was made recently as a single anti-hydrogen atom was produced suspended in a magnetic field. Physical laws such as the small cross-section of antiproton production in high-energy nuclear collisions make it difficult and perhaps impossible to drastically improve the production efficiency of antimatter.

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. They suggest that 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. Incidentally the cost of the Manhattan Project (to produce the first atomic bomb) is estimated at $20 billion in 1996 prices Most scientists however would 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 in near-perfect vacuum. Another, more hypothetical method is the storage of antiprotons inside fullerenes. The negatively charged antiprotons would repel the electron cloud around the sphere of carbon, so they could not get near enough to the normal protons to annihilate with them.

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. Heavier antimatter atoms have yet to be produced.

The difficulty of preventing accidental detonation of an antimatter weapon may be contrasted with that of a nuclear weapon. In an antimatter weapon, any failure of containment would immediately result in energy release, which would probably further damage the containment system and lead to the release of all of the antimatter material, causing the weapon to explode at some very substantial fraction of its full yield. By contrast, a modern nuclear weapon will explode with a significant yield if and only if the chemical explosive triggers are fired at precisely the right sequence at the right time, and a neutron source is triggered at exactly the right time. In short, an antimatter weapon would have to be actively kept from exploding; a nuclear weapon will not explode unless active measures are taken to make it do so.

Effects of antimatter detonation

More than 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 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 any practical form however, the weapon could not simply be a ball of antimatter floating in space. There would have to be a significant amount of supporting hardware surrounding the antimatter. Also, in order to maximize the power of the bomb, it would be designed to mix the antimatter with matter in the least amount of time. The effect of a large antimatter bomb would likely be similar to that of a nuclear explosion of similar size. The reacting antimatter would release about half of its energy in a form immediately available to the environment, superheating the casing and components of the bomb and the surrounding air, and turning it into an ultrahot plasma which then emits Thermal Radiation in the full EM spectrum. A quantity as small as a kilogram of antimatter would release 1.8×10¹⁷ J (180 petajoules) of energy. Given that roughly half the energy will escape as non interacting neutrinos, that gives 90 petajoules of combined blast and EM radiation, or the rough equivalent of a 20 megaton thermonuclear bomb.

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 catalysed 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.

Igniting fusion fuel requires at least a few kilojoules of energy (for laser induced fast ignition of fuel precompressed by a z-pinch), which corresponds to around 10⁻¹³ gram of antimatter, or 10¹¹ anti-hydrogen atoms. Fuel compressed by high explosives could be ignited using around 10¹⁸ protons to produce a weapon with a one kiloton yield. These quantities are clearly more feasible than those required for "pure" antimatter weapons, but the technical barriers to producing and storing even small amounts of antimatter remain formidable.

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.
• "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.