Clandestine weapons: New ways to detect covert nuclear weapons are being developed, which could help inspectors monitor Iran’s nuclear deal
AS NUCLEAR blasts go, North Korea’s first test in 2006 was small. The detonation of an underground device produced an explosive force well below one kiloton (less than a tenth of the size of the bomb dropped on Hiroshima in 1945). Even so, the vibrations it caused were recorded half a world away in the centre of Africa. Advances in the sensitivity of seismic sensors and monitoring software are now good enough to distinguish between a distant nuclear detonation and, say, a building being demolished with conventional explosives, says Lassina Zerbo, head of the Preparatory Commission for the Comprehensive Test-Ban-Treaty Organisation (CTBTO), the international organisation that seeks to enforce the agreement ratified, so far, by 163 nations.
The CTBTO operates 170 seismic stations worldwide, 11 underwater hydroacoustic centres detecting sound waves in the oceans, 60 listening stations for atmospheric infrasound (low-frequency acoustic waves that can travel long distances) and 96 labs and radionuclide-sampling facilities. More sensors are being installed. Crucially, however, the optimal number for global coverage was recently reached. It is now impossible, reckons Dr Zerbo, to test even a small nuclear weapon in secret anywhere on Earth. And on top of that, the United States Air Force runs a detection network that includes satellites that can spot nuclear-weapons tests.
It is better, though, to discover a secret weapons programme before testing. Once a country has a nuclear bomb or two, there is not much other governments can do to stop it from making more, says Ilan Goldenberg, a former head of the Iran team at the Pentagon. Plenty of states want such capabilities. The Defence Science Board, an advisory body to the Pentagon, concluded in a report last year that the number of countries that might seek nuclear weapons is higher now than at any time since the cold war. Those states include Saudi Arabia and other Sunni-Arab rivals of Iran, which in July, after long and tortuous negotiations, signed a nuclear deal with America and other nations to restrict its nuclear activities, and to allow enhanced monitoring and inspection of its facilities.
Some wonder how effective such monitoring measures will be—and that is with the benefit of agreed access to Iran’s facilities. The West’s record on detecting more covert nuclear work is spotty. A large North Korean centrifuge facility for uranium enrichment remained hidden until the regime gave a Stanford University professor a tour in 2010, letting the cat out of the bag. This troubles many. Enrichment is the biggest, trickiest step in bombmaking, so it should create the most evidence. By contrast, a roomful of scientists running mathematics software on offline computers to calculate the best way to detonate enriched uranium can keep a low profile, says Mr Goldenberg. It doesn’t help, he adds, that A.Q. Kahn, a metallurgist who made Pakistan’s nuclear weapons, circulated his designs.