IPFM International Panel on Fissile Materials

IPFM has produced a series of graphics for its reports and website. Some of these are available here for download and public use under GNU public license.

Explosive Chain Reaction

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An explosive fission chain-reaction releases enormous amounts of energy in one-millionth of a second. A neutron is absorbed by the nucleus of a fissile atom (uranium-235 in this example), which splits into two fission products (barium and krypton in this example). Additional neutrons are released in the process, which can set off a chain reaction in a critical mass of fissile materials. The energy set free is carried mainly by the fission products, which separate at high velocities. The chain reaction proceeds extremely fast; in a millionth of a second there can be 80 doublings of the neutron population, fissioning one kilogram of material and releasing an energy equivalent to 18,000 tons of high explosive (TNT).

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Making plutonium in a nuclear reactor. A neutron released by the fissioning of a chain-reacting U-235 nucleus is absorbed by the nucleus of a U-238 atom. The resulting U-239 nucleus decays with a half-life of 24 minutes into neptunium, which in turn decays into Pu-239. Each decay is accompanied by the emission of an electron and a neutrino.

Design of a Modern Thermonuclear Weapon

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A modern thermonuclear weapon usually contains both plutonium and highly-enriched uranium. Typically, these warheads have a mass of about 200-300 kg and a yield of several hundred kilotons, which corresponds to about one kilogram per kiloton of explosive yield. For comparison, the nuclear weapons that destroyed Hiroshima and Nagasaki weighed 300 kg per kiloton.

Source: Final Report of the Select Committee on U.S. National Security and Military/Commercial Concerns with the Peoples Republic of China, 3 January 1999, also known as the Cox Report. Original image credit: US News and World Report.

Gas Centrifuge for Uranium Enrichment

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The possibility of using centrifuges to separate isotopes was raised shortly after isotopes were discovered in 1919. The first experiments using centrifuges to separate isotopes of uranium (and other elements) were successfully carried out on a small scale prior to and during World War II, but the technology only became economically competitive in the 1970s. Today, centrifuges are the most economic enrichment technology, but also the most proliferation-prone.

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One-week average atmospheric Kr-85 concentrations measured at Tsukuba Japan, 1995-2001. Unless extraordinary precautions are taken, the reprocessing of spent fuel will release the radioactive gas, krypton-85, to the atmosphere. The spikes in the figure show the detection of krypton-85 released from upwind. No spikes are seen between April 1997 and July 2000 or from August to December 2000, periods during which the Tokai Mura plant was closed down. Original data courtesy of C. Schlosser and H. Sartorius, German Federal Office for Radiation Protection (BfS) Freiburg, private communication, May 2006.

Data originally published in: M. Hirota et al., Spatial and Temporal Variations of Atmospheric Kr Observed During 1995-2001 in Japan: Estimation of Atmospheric Kr-85 Inventory in the Northern Hemisphere, J. Radiat. Res., Vol. 45, 2004, pp. 405-413.

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Rise and fall of the U.S. and Russian nuclear weapon stockpiles. The Natural Resources Defense Council (NRDC) estimates suggest the number of U.S. warheads peaked at about 30,000 in the mid-1960s, and the Soviet/Russian warheads at 40,000 in the 1980s. Since then, the nuclear arsenals of both countries have dropped sharply. The United States and Russia are each committed to reducing their number of deployed strategic warheads to 1700-2200 by 2012. The NRDC estimates that the number of total operational warheads in the U.S. arsenal by that date will be about 6000, with the Russian operational arsenal likely to be no more than this same number. However, both countries may still at that time have many thousands of additional warheads and components in the dismantlement queue.