Radionuclide detecors chart of what elements and isotopes are floating
in the wind. Of all the detection methods, says Lay, "radionuclides
are the least ambiguous. There is no natural process that produces certain
Xenon isotopes. Where they see them, they know a nuclear reaction has taken
The six-foot-by-five-foot metal boxes contain a big pump constantly sucking
air, blowing it through sticky paper. "Every day, they take the paper
and fold it up and put it in a mass spectrometer to see if it's glowing,"
says Lay. "It's pretty crude."
Yet, says Peter Marshall, "that's the method that is really the
'smoking gun'." Wisps of radioactive material eventually escape to
the surface of even the most well-buried explosions. By sniffing the air
then backtracking based on weather patterns, scientists can draw a footprint
of where a nuclear blast could have been detonated.