I caught up with my guest today, Arms Control Association president Daryl Kimball from his hotel in Vienna. Daryl, along with hundreds of diplomats around the world were gathered for the 20th anniversary of the Comprehensive Test Ban Treaty.   This is a treaty that bans the testing of nuclear weapons and establishes a global monitoring system to ensure that no one can secretly test a nuclear bomb. The treaty was signed by the USA and most countries on the planet back in 1996, but it has not been ratified by some key countries, including the United States, and accordingly has not formally entered into force.    Despite that, Daryl Kimball explains how the CTBT has become a very effective treaty over the past two decades, in particular through deployment of a system of monitoring stations around the world that can detect anomalous seismic activity and radioactive discharge into the atmosphere. We also discusses the implications of the continues non-ratification of the treaty by the USA.