Glaser admits that the approach is “almost embarrassingly simple.” But the system contains hidden cleverness. If the host country offers up a fake warhead, another number besides N-max could be reached, which may reveal the number of preloaded bubbles being added. This could allow the inspector to work backward to find the signature, potentially releasing the host country’s nuclear secrets—added incentive not to cheat.
Although the theory seems sound, says Steve Fetter, a nuclear-control expert at the University of Maryland, he is not convinced such secrecy is necessary. Two states with advanced nukes don’t have much that they need to steal from one another, he notes. Tom Cochran, a physicist with the Natural Resources Defense Council, has concerns on other grounds. He brought up a testing system he proposed in the 1990s that measures the gamma rays nuclear warheads emit, which are more plentiful than neutrons and are statistically more likely to be accurate, he says. His system, however, relies on a computer to shield the classified information.
Glaser disputes the notion that better verification tests are unnecessary. As evidence that current systems are not adequate, he points to the U.S. Department of Defense’s 2010 Nuclear Posture Review that noted a need for “expanded work on verification technologies.”
Fetter concurs that as the number of warheads diminishes, governments will want to verify that reduction and that the neutron system may be a good option, although it is still a few years away from reality. “If these kinds of ideas are on the table, it should facilitate moving forward in negotiations,” Goldston says.