Nuclear detection is a complex process that requires a variety of tools and techniques to accurately identify the presence of radioactive materials. Radiation Portal Monitors (RPMs) are one of the most common methods used to detect the presence of low-radiation materials such as uranium. These devices typically consist of two pillars containing radiation detectors, which are monitored remotely from a display panel and emit alarms when radioactive materials are detected. Scientists can also detect isotopes such as xenon 131, xenon 135 and krypton 85 when they leak into the environment.
The Environmental Protection Agency (EPA) maintains a system of radiation monitors throughout the United States called RadNet. This system was originally designed to detect radionuclides released after the detonation of a nuclear weapon, but is now used to observe background radiation levels in many places in the United States. Background radiation is mainly from natural sources, such as natural radon and uranium. When it comes to detecting nuclear explosions, signal detection is the first step.
Scientists must then attempt to collect and associate all the signals recorded by several monitoring stations that originate from the same event. For example, in 1997, a small magnitude 3.5 seismic shock, along with an even smaller aftershock, was detected under the Kara Sea near Russia's former nuclear test site on the Arctic island of Novaya Zemlya. Detecting a test of a nuclear weapon has become so effective and reliable that no nation could hope to get away with secretly exploding a device of military importance. To detect nuclear explosions with lower yields, the number of seismic events that need to be examined increases.
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a legally binding global ban on the testing of nuclear explosives, and according to the National Academy of Sciences, a test of that size would be of little use to a testing country trying to manufacture larger nuclear weapons, particularly if the country has little prior experience with nuclear testing. There are many different ways to detect a nuclear detonation, including seismic, hydroacoustic and infrasound detection, air sampling, and satellites. Some studies estimate that cancer deaths due to global radiation doses from nuclear test programs in the atmosphere of the five nuclear-weapon States amount to hundreds of thousands. Detecting plutonium production is easier than detecting enriched uranium production for several reasons. Following the seismic detection of the Korean test and the announcement of the test by North Korea, radioactive matter in the air and on land in Asia, as well as leeward across the Pacific Ocean at an IMS station in Canada, decisively confirmed that the explosion was nuclear. Fortunately, the sensors needed to detect earthquakes can play a dual role in detecting bomb explosions.
In practice, with seismic monitoring alone, all nuclear explosions with one-kiloton yields can be detected with 90 percent reliability by examining between 50 and 100 seismic events per day.