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VIENNA (Reuters) - While the U.N. atomic watchdog’s inspectors travel the globe to check that countries are not secretly developing nuclear weapons, that work hinges on meticulous analysis by two laboratories nestled in the Austrian countryside.

Samples taken in countries including Iran, where the International Atomic Energy Agency is policing the country’s nuclear deal with major powers, are sent to the IAEA’s labs in Seibersdorf near Vienna. There, state-of-the-art equipment scours them for minute traces of uranium and other chemicals.

On their visits, inspectors swipe surfaces to check for those telltale particles. They also take samples of chemicals produced and stored at declared facilities. The IAEA then checks that what it has found matches what the country has said it is doing.

“If you are for example in your kitchen and you cook something, you will always splatter something around like particles from an aerosol,” said Stephan Vogt, head of the IAEA’s Environmental Sample Laboratory, describing how nuclear work leaves telltale particles behind.

“Afterwards you clean but you will never be able to clean 100 percent. There will always be a little bit of material sticking to the surfaces and if someone else comes later on and takes a sample they can tell you what you had for dinner,” said Vogt, whose lab analyses the cloth squares swiped on surfaces.

His lab’s equipment includes powerful mass spectrometers, which break down particles to determine the precise level to which uranium has been enriched or their specific isotope.

“We’re here to basically serve as an auditor, independently verifying states’ declarations,” said Steve Balsley, head of the Nuclear Material Laboratory, which analyses uranium and plutonium samples from declared nuclear sites.

None of the samples come in with their geographical origin specified, ensuring that the scientists’ analysis is completely unbiased. The labs are also part of a broader network, with facilities in member states performing their own analyses and double-checking duplicate samples.

“Laboratory experts need to confirm that the uranium and plutonium content in the samples matches what a state has declared to the agency,” Balsley told reporters touring his lab.