Silencing the Bomb

By Lynn R. Sykes, Columbia University Press, New York, 283 pp., $35 (cloth), ISBN 9780231182485.

Almost from the first use of nuclear weapons in 1945 there have been attempts to limit them. One approach has been to limit the testing of these weapons in hopes that this would eliminate or, at least slow down, the development of new nuclear weapons. This book presents a detailed history of the attempts to limit testing. The author, Lynn Sykes, is a seismologist who has spent some fifty years working on limiting nuclear testing, which puts him in an excellent position to discuss it. He describes the arguments and issues involved in setting up the various test ban treaties.

The first approach was to limit testing in the atmosphere. In addition to its use in developing new, more destructive, nuclear weapons, testing in the atmosphere produced significant amounts of radioactive strontium 90. Sr 90 eventually got into the food chain where, because of its chemical similarity to calcium, it ended up in human bones and teeth around the world in the 1950s. Discussions between the United States and the Soviet Union led to the Limited Test Ban Treaty (LTBT) in 1963. This treaty banned testing in the atmosphere, in outer space, and under water. However it did not ban testing underground.

The reason that underground testing was not included in the LTBT was the difficulty of verification. At the time the only means of detecting underground explosions was by seismic waves. The US feared that, unless there were seismographs directly on Soviet territory the USSR could cheat. The USSR on the other hand feared that US monitoring posts would just be an excuse for spying. These fears did not apply to tests in the atmosphere or under water. Atmospheric tests can be detected from the generation of infrasound, very low frequency sound waves. Acoustic waves in the oceans allow the detection of underwater explosions. Both types of waves can be detected at great distances and do not require monitoring posts on the other’s territory. Sykes also mentions instruments for detecting explosions in outer space but gives no details.

Further consideration of underground testing raised several important questions. Could seismic waves be used to detect nuclear explosions and distinguish them from earthquakes? Is there a lower limit on the size of blasts that can be detected? And would it be possible to disguise a blast by exploding it in a large enough hole? Negotiations based on these considerations led to the Threshold Test Ban Treaty (TTBT) of 1974. This treaty limited underground nuclear tests to yields with an upper limit of 150 kilotons. At the urging of the Soviets the limit applied only to the testing of nuclear weapons and not to peaceful nuclear explosions (PNEs). PNEs were used by both the US and USSR to create large cavities in salt for storage, to break rock for petroleum recovery, and as energy sources for seismological studies.

Again the TTBT raised a number of problems. Were the Soviets cheating? They did try to hide one large explosion but were only partly successful. One cannot distinguish between a weapons test and a peaceful nuclear explosion. India, at least, did claim that its first weapons test was a PNE. This led to the Peaceful Nuclear Explosion Treaty of 1976, which stated that any explosion at a declared weapons test site would be considered a weapons test. Any explosion outside these sites would be considered peaceful.

What is the relation between the size of the seismic disturbance and the size of the explosion that produced the seismic waves? The seismic disturbance depends not only on the size of the explosion but also on the nature of the ground surrounding the explosion. This led to some overestimations of the size of Soviet explosions.

In the years since the TTBT, detection of underground explosions has greatly improved. The seismic signal of a nuclear explosion can be distinguished from an earthquake and the location of the source can be determined. If the source is sufficiently far underground it cannot be a nuclear explosion. Nuclear explosions produce small quantities of radioactive xenon which can be detected at great distances from atmospheric explosion and from some underground explosions. Furthermore, satellite imaging can show displacements of the ground caused by nuclear explosions or earthquakes.

These improvements in detection led to the Comprehensive Test Ban Treaty, which banned all nuclear tests in the atmosphere, underwater, underground, and in space. The treaty was signed in 1996 by over one hundred countries. The treaty requires all states possessing nuclear weapons or reactors to ratify it before it can go into effect. As of 2017, 183 nations including several nuclear nations have ratified the treaty. However, several nuclear nations including the United States have not yet ratified it.

Kenneth S. Mendelson
Professor emeritus of physics
Marquette University
Email: kenneth.mendelson@marrquette.edu

These contributions have not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the view of APS.