On Tuesday President George W. Bush acknowledged that the al Qaeda network terrorist network has been attempting to acquire nuclear materials for use in terrorist plots against the West. Construction of a nuclear device from the ground-up, however, is not an easy task. The following excerpt from Tracking Nuclear Proliferation, A Guide in Maps and Charts 1998 provides insight into the level of expertise and technological sophistication that are required to build a nuclear weapon.

A state or group seeking to manufacture nuclear arms must complete a number of essential, often extremely demanding steps. The aspiring actor must:

• Develop a design for its nuclear device or obtain such a design from a weapon- holding state.

• Produce the fissile material for the core of the device or obtain it from an external source and then machine the fissile material to fabricate the nuclear parts of the weapon.

• Fabricate, or obtain from outside, the non-nuclear parts of the device, including the high-explosive elements and triggering components that will detonate the nuclear core.

• Verify the reliability of these various elements individually and as a system.

• Assemble all of these elements into a deliverable nuclear armament, commonly referred to as "weaponization."

Design

It is generally accepted today that designing an early generation atomic bomb—drawing a blueprint—is within the capabilities of most contemporary states. Indeed, a number of American college students have come up with plausible designs based on unclassified information. But developing a reliable, militarily-acceptable weapon would take a technical team with special facilities and financial support, and is not likely a project that could be carried out by an individual in a home workshop.

Acquiring Fissile Materials

The major technical barrier to making a nuclear device is obtaining the necessary fissile material, i.e., weapons-grade uranium or plutonium, for the weapon’s core.

How much fissile material would be needed for a nuclear weapon depends on the technical capabilities of the country involved and the size of the weapon it sought to produce. International Atomic Energy Agency (IAEA) regulations assume that 25 kg of weapons-grade uranium or 8 kg of plutonium are the minimum amounts that would constitute a "critical mass" (that could spontaneously fission) with a yield up to about 20 Kt (equivalent to the explosive force of 20,000 tons of TNT), roughly the size of the Nagasaki bomb. However, by utilizing more sophisticated designs that rely on high compression of the core material, neutron reflecting "tampers," or both, a state could build such a weapon with considerably less fissile material. According to one recent estimate, a country possessing a "low technical capability" could build a 20-Kt device with only 6 kg of plutonium or 16 kg of weapons-grade uranium. A state with a "high technological capability" could potentially build such a device with as little as 5 kg of weapons-grade uranium or 3 kg of plutonium; a 1 -Kt device, which would require considerable sophistication to manufacture, might need only about half these amounts.¹

Non-Nuclear Components, Assembly, Delivery

Finally, the manufacture of nuclear weapons requires the design and fabrication of: specially designed high-explosive components to compress the fissile-material core of the device; high-speed electronic firing circuits, or "triggering packages" to set off the high explosives uniformly at precisely the correct instant; and, in most designs, an "initiator"—an intense source of neutrons to initiate the nuclear chain reaction in the core. Developing all of these components necessitates considerable technical skill and, though less demanding than producing fissile material, can nonetheless be quite challenging. Iraq’s effort to develop these elements of nuclear weapons, for example, is known to have suffered considerable setbacks and had not succeeded prior to the 1991 Gulf War, despite several years of effort.

Assembly of the completed components of nuclear weapons and delivery by aircraft or as cargo by ship or truck are relatively less demanding. To produce nuclear warheads for ballistic missiles, however, additional steps are necessary, such as the development of reentry vehicles, the miniaturization and/or reconfiguration of nuclear weapons to fit into missile nose cones, and certifying the weapons to withstand the rigors of blast-off, extremely high altitudes, and reentry.

For an interactive web site with a wealth of information on the physics of nuclear fission, how nuclear bombs are designed and what happens after a nuclear explosion click here.

Click here for selected chapters and appendicies from the book Tracking Nuclear Proliferation: A Guide in Maps and Charts, 1998 (pdf)