Number of nuclear weapons experiments worldwide until 2016

With the "Trinity" test on 16 July 1945 in the USA, a nuclear weapon was detonated for the first time in human history. Only one month later, nuclear weapons were detonated in military operations over Hiroshima and Nagasaki at the end of World War II.

Despite early considerations about international control of fissile material for the production of nuclear weapons, other nations acquired the ability to produce these weapons (Soviet Union: 1949, United Kingdom: 1952).

Start of nuclear weapons tests

In the 1950s, the USA and the Soviet Union began testing so-called thermonuclear weapons (colloquially referred to as "hydrogen bombs"), which have a higher explosive yield and correspondingly produce larger amounts of radioactive fallout.

Partial Test Ban Treaty

Among others, the criticism following these tests led to an agreement between the USA, the Soviet Union and the United Kingdom to ban tests in the atmosphere, under water and in outer space in 1963.

This outcome was laid down in an international treaty, the Partial Nuclear Test Ban Treaty (PTBT). France (first test in 1960) and China (first test in 1964), however, did not sign this treaty and conducted nuclear weapons tests in the atmosphere up until 1980.

From the partial to the comprehensive test ban

The International IMS measuring network Source: CTBTO

The states signatory to the PTBT complied with the rules of the treaty and consequently reduced the number of atmospheric (above-ground) tests and the associated radioactive fallout. However, the total number of nuclear weapons tests was not reduced, apart from conductiong them mostly below the Earth's surface. More than 2000 nuclear weapons tests have been counted to date.

After the PTBT had entered into force, a comprehensive test ban treaty was discussed at the diplomatic level and in 1976 the so-called "Group of Scientific Experts" (GSE) was established. Their task was to determine whether and how compliance with such a treaty could be verified. A reliable verification system is a crucial prerequisite for states to commit to a ban under international law. Initially, the experts' opinions on the possibilities and limits of scientific verification differed widely.

Comprehensive Nuclear-Test-Ban Treaty

It was the end of the Cold War before formal negotiations began at the United Nations Conference on Disarmament. The consultations in which experts from the BfS had been substantially involved, were completed already two years later and the CTBT opened for signature in 1996.

The parties to the negotiations, however, wanted to ensure that the signatories of the treaty did not enter into binding commitments until all states with nuclear installations - and consequently the capability to produce nuclear weapons - have joined. This is why the document contains a list of 44 states (so-called Annex 2 states) that have to ratify the treaty before it enters into force.

To this day, three out of these 44 states have yet to sign and ratify the treaty for it to enter into force (India, North Korea, Pakistan) and five countries that have already signed, still have to ratify the treaty (Egypt, China, Iran, Israel, USA).

Implementation of the Comprehensive Nuclear-Test-Ban Treaty

Once the Comprehensive Nuclear-Test-Ban Treaty (CTBT) has come into force, the verification of the ban has to be instantly possible. For this reason, the so-called Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) with its task to set up an international monitoring network with 337 monitoring stations was established in Vienna. This monitoring network allows to reliably verify compliance with the treaty.

Other tasks of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) include to preparing concepts for on-site inspections, to develop measurement methods for one-site inspections and to perform exercises.