NUCLEAR WEAPONS Paul Sneller

History 1905 – Einstein’s Theory of Special Relativity. 1932 – The Neutron is Discovered by James Chadwick. 1938 – Otto Hahn and Fritz Strassman are able to split a uranium atom by bombarding it with neutrons. 1942 – First self sustaining nuclear reaction is produced by scientists at the University of Chicago. 1945 – First Nuclear Weapon detonated at Trinity, New Mexico. 1945 – Nuclear Weapons are dropped on the cities of Hiroshima and Nagasaki. 1952 – First Teller-Ulam hydrogen bomb detonated.

Nuclear Fission A nuclear reaction in which an atomic nucleus splits into fragments. Fission occurs readily in U-235 and Pu-239 when bombarded with neutrons. The sum of the product masses is less than the mass of the original atom. The lost mass is converted directly into energy. The fission of a single Uranium-235 nucleus generates about 3.36E-11J

Nuclear Fusion The combination of two nuclei to form a single atom. The product’s mass is less than the mass of the original atoms. Fusion occurs most readily in a combination of the hydrogen isotopes deuterium and tritium. Temperature in the millions of degrees is required to initiate fusion. A Deuterium-Tritium fusion generates about 2.8E-12J of energy

Criticality In order for a nuclear reaction to be self-sustaining, there must be a “critical mass” of fissile material. This is the mass necessary so that, on average, at least one neutron produced by every fission goes on to trigger another fission. Having less than critical mass will cause the bomb to “fizzle” and have a very low efficiency. Actual mass required for criticality depends on the density of the mass, the shape of its configuration, and the presence/effectiveness of the neutron reflector. Due to natural emission of neutrons, any critical mass has a chance of beginning a nuclear chain reaction.

The Fission Bomb To prevent premature detonation of a weapon, the nuclear material must be separated into two or more sub critical masses. The mechanism which combines these masses is the most important part of the weapon. The mechanism must combine the sub critical masses into one supercritical mass fast enough that the mass is fully assembled before there is any chance of the chain reaction blowing the fissile material apart and causing the bomb to fizzle.

The Neutron Generator In order to ensure that a chain reaction begins, there has to be free neutrons present in the fissile material when the critical mass is assembled. A combination of Po-210 which emits alpha particles, and Beryllium, which emits neutrons when struck by an alpha particle. The two substances can be separated by a foil which blocks alpha particles and is designed to break when the bomb is triggered.

The Tamper The tamper is a thick layer of heavy material which is designed to produce pressure on the fissionable core as the bomb detonates, allowing more fissions to occur before the materials are blown apart by the energy release. The tamper is usually constructed out of U-238 and doubles as a neutron reflector, redirecting neutrons back into the core and increasing the efficiency of the reaction. The most effective tamper is Be-9 which actually produces two neutrons when struck by a single neutron.

Weapon Designs Gun-triggered fission Implosion-triggered fission Fusion Bombs

Gun-triggered This is the simplest form of nuclear weapon. A bullet of U-235 is propelled by explosives into a U-235 sphere. Because of the relatively slow combination of the critical mass, this method works only with U-235. This is the type of bomb that destroyed the Japanese city of Hiroshima.

Gun-triggered

Implosion-triggered A sub critical sphere of plutonium is surrounded by explosives, when the explosives detonate they create a shockwave which compresses the core. The increased density of the core causes it to become supercritical, and the nuclear reaction begins. This method can be used with both U-235 and Pu-239. This is the type of weapon detonated at the Trinity site, and on the Japanese city of Nagasaki. To properly compress instead of blowing it apart, it is necessary to use explosive lenses, which create a concave shockwave that fits the surface of the core.

Implosion Triggered

Teller-Ulam Bomb The first true fusion bomb design. Utilizes a fission weapon to provide the necessary energy to cause fusion. The massive amount of X-rays released by the fission, which travel much faster than the actual explosion, are contained by a thick tamper and used to provide the heat to initiate a fusion reaction before the explosion has a chance to blow apart the bomb. Uses lithium deuterate as a fuel. When lithium is struck by a neutron it produces an alpha particle and tritium, which readily fuses with the deuterium in the extreme temperature created by the fission bomb. Can be scaled to nearly limitless power.

Teller-Ulam Bomb

Teller-Ulam Bomb

The Effects Standard Nuclear weapons emit approximately 50% of their total energy as blast energy, 35% as thermal energy, and 15% as radiation. The actual effects of the weapon vary greatly depending on the yield, and the detonation point. Detonation in the upper atmosphere can create massive EMPs, severely damaging many electronics. Detonation in the lower atmosphere results in enormous pressure damage over a larger area. Surface Detonation results in blast and thermal damage, and large amounts of fallout. Subterranean detonation results in large shockwaves, but minimizes most of the effects, provided the blast does not break the surface

10 Kiloton Surface Blast 1/3 mile radius: All but the sturdiest of buildings are completely destroyed, those that remain are merely empty shells, fatality rate is nearly 100% 3/4 mile radius: Anyone directly exposed to the blast receives a lethal radiation dose, all buildings suffer heavy damages, fatality rate is approximately 50% with 45% injured. 1 mile radius: Heat wave causes widespread fires and the area is ravaged by radiation. Approximately 5% of the population is killed, with 45% injured.

25 Megaton Airburst 6.5 mile radius: All but the sturdiest of buildings are destroyed, fatality rate is nearly 100% 10.7 mile radius: Buildings suffer heavy damage, approximately 50% of the population is dead and 45% injured. 20 mile radius: Windows, and many of the occupants of large buildings are blown out, small buildings are heavily damaged or destroyed, approximately 5% dead and 45% injured. 30.4 mile radius: Buildings are slightly damaged, approximately 25% of the population is injured.

Construction Feasibility To produce a functional gun-triggered nuclear weapon, there are only 4 main requirements. Access to a sufficient quantity of weapons grade material, or the equipment needed to enrich uranium ore. Precision machine tools. Safety equipment to protect against radiation. High explosives.

Construction Feasibility Due to the widespread availability of resources such as explosives, machine tools, and protective gear, sufficient monetary resources make such items trivial. The only real impediment to non-nuclear nations and terrorists is the availability of weapons grade Uranium.

Uranium Acquisition Although Uranium is actually fairly common in nature, Uranium-235, the isotope required for nuclear weapons, accounts for only .71% of all naturally occurring Uranium. Any sizable amount of Uranium-235 is closely monitored by international agencies, therefore the most feasible means of obtaining weapons grade uranium is to enrich uranium ore.

Uranium Enrichment There are several methods to enriching Uranium The most efficient method is by combining uranium with fluorine to Uranium hexafluoride and then using a gas centrifuge to separate the isotopes. Other methods include electromagnetic isotope separation (EMIS) and gaseous diffusion. All of these methods require a significant amount of electricity, some specialized equipment, a larger supply of uranium ore, and a good deal of time, as each process only slightly increases the percentage of U-235, and concentrations of over 90% are necessary for nuclear weapons.

Conclusion Nuclear weapons are one of modern science’s greatest achievements, harnessing the conversion of mass to energy. They range from fairly simple, to extremely complex, but they all are extremely powerful and deadly. Although construction of a basic nuclear weapon is fairly straightforward, the logistical problems involved with obtaining sufficient nuclear fuel, the careful monitoring of nuclear development should prevent terrorists and third world nations from constructing them for quite some time.