Nuclear Test Ban
Several world leaders called for a comprehensive test ban, no more testing of nuclear weapons by any state and this call was taken seriously by the world’s nuclear powers.
The biggest hurdle in the negotiating a comprehensive test ban which is how to know that the other side will not carry on with the tests anyway?
Detecting atmospheric tests was the easiest, the radioactive isotopes they produced disperse in the atmosphere which could be detected thousands of kilometres away.
Underwater tests produce distinctive sounds that travel efficiently around a kilometre below the surface of the ocean and these can be picked up by hydrophones.
But underground tests are much harder to detect from a distance because their radiation is mostly contained. This is why when a test ban treaty was signed in 1963, it was only a partial ban (Partial-Test-Ban-Treaty). It banned testing underwater, in the atmosphere and in space, places where compliance could be verified, but it didn’t ban testing underground for the simple reason that it was almost impossible to verify compliance.