November 24, 2014 is a looming deadline for Iran, Israel, the United States and the world over its nuclear weapons program.
Under Secretary of State Wendy Sherman, leading the negotiations, has described them as “a forest of distrust.” At the same time, she declares, “Our bottom line is unambiguous … Iran will not, shall not obtain a nuclear weapon.”
As the world ponders Iran’s dash to enrich more kilograms of uranium, the underlying concern is not so much about the enrichment process itself, but the end product: a nuclear warhead. Iran has been developing its warhead for some sixteen years. That design is nearly perfected.
Compare the process to gunpowder. To use gunpowder, you need load it into a cartridge, load the cartridge and a bullet into a rifle, and then find a marksman. Iran has nearly mastered all those steps — but in nuclear terms.
Four technological achievements are key to completing Tehran’s nuclear weapon:
1) Accretion of enough nuclear materials, highly enriched to weapons-grade or 90 percent; 2) machining that material into metal for a spheroid warhead so it can fit into a missile nosecone; 3) developing a trigger mechanism to initiate the atomic explosion at a precise moment during missile reentry; and, of course, 4) a reliable delivery system.
Start with the nuclear material. Experts estimate that a single bomb would require approximately 25 kilograms of highly enriched uranium, or HEU, with a U-235 concentration of at least 90 percent. Much of Iran’s nuclear enrichment remains at 3.5 and 20 percent levels. But the numbers are deceiving. Enriching to 3.5 percent is 75 percent of the task of reaching weapons-grade. Once Iran has reached 20 percent, it has gone 90 percent of the distance. Today, Iran possesses enough nuclear material for a fast “break-out” that would finish the job, creating enough for five or ten bombs, in about six weeks.
Second, that HEU must be metalized and shaped into a dense spheroid compact enough to fit into a missile nosecone. Iran has mastered the metallurgical techniques using other high-density metals such as tungsten, which have been test-detonated in a special chamber to measure their explosive character.
Third, the spheroid must be detonated. Iran’s warhead design employs a R265 shock generator hemisphere drilled with 5mm boreholes that are filled with PETN — pentaerythritol tetranitrate, an organic high explosive favored by terrorists. When triggered with precision, the PETN array can cause a massive synchronized implosion. That will fire an internal exploding bridgewire which will in turn actuate an embedded neutron initiator to detonate the atomic reaction — and the mushroom cloud. This sequence of devices has been assembled and tested. Iran has some 500 exploding bridgewires.
Fourth, the warhead must be delivered. The Shabab-3 missile nosecone is large enough to accommodate the warhead. The outer radius of the R265 shock generator-encased warhead is 550 millimeters, less than the estimated payload chamber diameter of about 600 millimeters. Most of all, the Iranian military has selected the Shabab-3 not only because it possesses a range of 1200 kilometers, but because it can be detonated in an airburst some 600 meters off the ground on re-entry. The height of 600 meters was used in the Nagasaki explosion. Such a weapon cannot be crashed into the ground. It must be detonated while still airborne. Iran has a small fleet of Shahab-3 missiles.
Hence, Iran’s metronomic accretion of nuclear material is not just an ambiguous physics undertaking that should worry the West. It is part and parcel of a nuclear attack plan that the international community is determined to address.
Edwin Black is the author of 11 award-winning editions, including IBM and the Holocaust, and his most recent book Financing the Flames. He can be found at www.edwinblack.com.
