DEVELOPMENT OF NUCLEAR WEAPONS
During World War II, the United States government created the Manhattan District, often called the Manhattan Project, to develop the first nuclear weapons. It brought together leading scientists to work on nuclear weapons and organized facilities for producing their nuclear ingredients. Physicist J. Robert Oppenheimer, a professor at the University of California at Berkeley, was chosen as the director of the Los Alamos Laboratory, which designed the first nuclear weapons.
The United States, fearing that Nazi Germany would get nuclear weapons first, constructed huge facilities to obtain two types of materials that can produce nuclear explosions by splitting (fissioning) the nucleus of certain atoms. The nucleus of an atom, consisting of protons and neutrons, accounts for most of the weight of an atom. The energy liberated in nuclear fission is huge. It is much greater than that in ordinary chemical reactions, which merely involve the lightweight electrons that surround the nucleus.
One facility at Oak Ridge, Tennessee, was constructed to separate a rare form of the element uranium, abbreviated U 235, from the more abundant form of uranium, U 238. A factory at Hanford, Washington, produced plutonium in nuclear reactors. Plutonium (abbreviated Pu) is a man-made element that is not present naturally on Earth today.
Most elements consist of different isotopes (or flavors) that differ only very slightly from one another. Consequently, they are difficult to separate. For example, all of the various isotopes of uranium consist of 92 protons and 92 electrons. The isotope U 235 of uranium contains 235 – 92 = 143 neutrons, whereas U 238 consists of 238 – 92 = 146 neutrons.
In 1938 Otto Hahn, Fritz Strassmann, and Lise Meitner of the Kaiser Wilhelm Institute for Chemistry in Berlin, bombarded uranium atoms with neutrons and discovered that they could be fissioned, or broken into much lighter elements. Meitner, who was Jewish, fled to the Netherlands with the help of Hahn in July 1938 and went on to Sweden. In November 1938 Hahn discussed the results of his ongoing experiments with Meitner and Danish physicist Niels Bohr. Meitner and her nephew Otto Robert Frisch worked out the basic mathematics of nuclear fission in Sweden; it was Frisch who called the process nuclear fission. They realized that mass, m, was converted into a vast amount of energy, E, by Einstein’s famous equivalence of energy and mass, E = mc2 where c is the speed of light.
In a second paper on the fissioning of uranium in February 1939, Hahn and Strassmann predicted the liberation of neutrons during the fission process. A chain reaction involving the continued fission of atoms was central to the liberation of immense amounts of energy and the development of nuclear weapons. A chain reaction occurs when a neutron causes an atom of U 235 to fission and to produce more neutrons, which go on to fission additional uranium atoms. Hahn and Strassmann, who did not leave Germany, received the Nobel Prize in 1944 for their discovery. Meitner should have been included.
Fission involves the breakdown of either the plutonium isotope Pu 239 or uranium U 235 into lighter elements, typically ones near the middle of the periodic table of elements, and the release of huge amounts of energy as nuclear mass is converted into energy. In contrast, chemical reactions involve the release of much smaller amounts of energy per pound (or kilogram) and do not involve the change of one element into others as in nuclear reactions.
During World War II, the United States quickly developed two types of nuclear weapons. An explosive device called the Gadget with a yield of 21 kilotons was tested in New Mexico on July 16, 1945. (A kiloton, or kt, is the equivalent energy released by 1000 tons of TNT.) Gadget consisted of 13.5 pounds (6.1 kg) of plutonium and about 5000 pounds (2270 kg) of high explosives to compress the plutonium into a denser mass. Ten seismic stations at distances of 270 to 700 miles (435 to 1130 km) recorded the explosion. An untested U 235 bomb called Little Boy was exploded over Hiroshima, Japan, on August 6, 1945. It weighed about 8000 pounds (3630 kg) and had a yield of about 13 kilotons.
A plutonium nuclear weapon called Fat Man was detonated over Nagasaki, Japan, on August 8, 1945 with the same yield as that of the New Mexico device. The two nuclear weapons helped to bring the Pacific war to an end and ushered in the atomic age. A large bomber could carry one of the nuclear weapons of 1945 vintage, but these bombs were extremely heavy. The U 235 weapon used against Hiroshima, though not tested in a nuclear explosion beforehand, was developed by a group of some of the best scientists from many nations and to exacting tolerances. It would be difficult even today for a nonnuclear state to count on a similar device working without being fully tested, and it would be too heavy to place on a relatively crude missile.
The United States government initiated a classified program called Long-Range Detection in 1947, under the direction of the Air Force, to monitor nuclear testing by other counties, especially the Soviet Union and later China. The classified monitoring network, called the Atomic Energy Detection System (AEDS), was, and still is, operated by the Air Force Technical Applications Center (AFTAC). Publications by AFTAC in 1997 and in 2009 by seismologist Carl Romney, who worked for them for many years, describe this early work on monitoring in more detail. In 1948 the United Kingdom and Canada were involved in monitoring nuclear tests set off by the United States on towers at Eniwetok Atoll in the western Pacific. Those explosions were detected by sampling airborne radioactivity but were not picked up by seismic stations at distances greater than 500 miles (800 km).
The Air Weather Service of the Air Force began flying military aircraft between Alaska and Japan with special filters to try to detect radioactive debris carried by winds from possible atmospheric nuclear explosions by the USSR. Radioactive debris was captured by one such flight on September 3, 1949, and by one from Guam to Japan two days later. U.S. experts on radioactive isotopes identified collected debris as having been generated by a Soviet explosion of a plutonium device sometime between August 26 and 29, 1949. Scientists used meteorological observations to backtrack its location to somewhere in Central Asia. President Truman announced to the public on September 23 that the Soviet Union had conducted a nuclear test.
When Premier Joseph Stalin learned about the Hiroshima explosion, he ordered the rapid development of atomic weapons by the USSR. Soon after World War II, the United States proposed the international control of fissionable materials and a halt to the arms race, but Stalin was not responsive. It was decades before it became known publicly that the Soviet explosion of 1949 was an exact copy of the U.S. Fat Man weapon of 1945.
British scientist Klaus Fuchs, who was present at Los Alamos during the Manhattan Project, obtained its design by espionage. He had been a member of the Communist Party in Germany before fleeing to England in the early 1930s. Returning to Britain after World War II, Fuchs confessed he was a spy in 1950 and was convicted. He served nine years in prison and then immigrated to East Germany, where he died in 1988. The USSR built a reactor in the Ural Mountains to obtain plutonium for the 1949 explosion.
The Soviet test of 1949 led Truman to order the rushed development of larger fission as well as thermonuclear weapons. The latter are often called “The Super” hydrogen or fusion weapons. The fusion of hydrogen takes place only at exceeding high temperatures, millions of degrees, like those in the sun. Stars liberate vast amounts of energy primarily by converting hydrogen by fusion into helium. Fusion weapons involve the conversion of one or two of the heavy hydrogen isotopes, deuterium and tritium, into helium. Fusion converts mass into huge amounts of liberated energy.
The United States made several improvements in the yield-to-weight ratio of fission weapons. In a key development called “boosting,” heavy isotopes of hydrogen—deuterium and/or tritium—were used to increase the number of neutrons bombarding the fissile material in the core of a fission device. Boosting permitted the weight of a weapon to be reduced considerably. The United States tested a boosted device named Item with a yield of about 45 kilotons in May 1951.
In the Mike nuclear explosion of 1952 (figure 2.1), the United States tested the concept of igniting a full-scale fusion explosion with a small fission explosion, called either an initiator, a primary, or a trigger. A roomful of heavy equipment was needed to maintain its thermonuclear fuel, deuterium, at very low temperatures. Its yield of 10.4 megatons (Mt), or 10,400 kilotons, was about 800 times the yield of the Hiroshima explosion of 1945. Mike obliterated part of the Pacific island of Elugelab in the Marshall Islands. The arms race soon accelerated, and nuclear explosions of very high yield were developed and then deployed as weapons by the U.S. Air Force.
FIGURE 2.1
The Mike thermonuclear (hydrogen bomb) explosion.
Photo by U.S. Atomic Energy Commission.
The United States went on to develop fusion weapons with a solid fuel called lithium deuteride (the lightweight element lithium combined with one of the heavy isotopes of hydrogen called deuterium). That fuel is stable at room temperatures, meaning it could be used and deployed for fusion weapons. The United States tested this device first at Bikini Atoll in the Bravo explosion of March 1, 1954. Its yield of 15,000 kilotons (15 Mt) was much larger than expected, because the contribution of an isotope of lithium, Li 7, to fusion reactions was not foreseen. During the 1950s, the United States went on to develop and test a number of thermonuclear weapons in the megaton range.
Bravo produced large amounts of radioactive fallout, of which the nearby Japanese fishing boat Lucky Dragon received high levels. Twenty-three of its crew developed radiation sickness by the time the boat docked in Japan. Its captain died of leukemia six months later. Indian prime minister Jawaharlal Nehru made the first proposal that year for a halt to and a ban on nuclear testing.
The Soviets had not sat idle. They detonated two fission explosions in 1951 and their first thermonuclear device, with a yield of 400 kilotons, on August 12, 1953. Seismic stations in the United States and abroad recorded the test. In 1955 the USSR detonated a weaponized version of the 1953 device, with a yield of 215 kilotons, and their first thermonuclear device with a yield exceeding one megaton.
In 1957 and 1958 the Soviet Union and the United States conducted many thermonuclear tests, a number them in the megaton range. In 1952 the United Kingdom tested its first fission device, and in 1957 its first hydrogen bomb.
A megaton nuclear explosion would cause damage and deaths over a huge area from thermal radiation (heat), the atmosphere blast wave, and high-energy radiation, as illustrated in figure 2.2 for the New York City area.
FIGURE 2.2
Nuclear firestorm created by the detonation of an 800-kiloton weapon above New York City. M denotes midtown Manhattan. No one survives in the central fire zone (area 90 square miles, or 23,000 hectares) that includes most of the island of Manhattan; a firestorm is likely in the larger shaded area.
Computations courtesy of Theodore Postol of MIT, 2016.
SUMMARY OF NUCLEAR WEAPONS TESTS BY VARIOUS COUNTRIES AND LONG-RANGE (STRATEGIC) NUCLEAR WEAPONS OF RUSSIA AND THE UNITED STATES
Without testing, a country cannot be certain that a new nuclear weapon will work. Of course, many weapons would not have entered the stockpiles of various nations if a full ban on testing had been enacted in 1963, not when it was finally signed in 1996.
Table 2.1 lists the first fission test, the first fusion (hydrogen bomb) explosion, and the last underground test by the various nuclear powers as of late 2016. They have now conducted a total of more 2000 nuclear tests.
TABLE 2.1 Number of Nuclear Tests and Dates as of September 2016
| COUNTRY |
FIRST FISSION TEST |
FIRST FUSION TEST |
MOST RECENT TEST |
TOTAL TESTS |
| United States |
1945 |
1952 |
September 1992 |
1030* |
| Russia |
1949 |
1953 |
October 1990 |
715* |
| United Kingdom |
1952 |
1958 |
October 1991 |
45** |
| France |
1960 |
1968 |
January 1996 |
210 |
| China |
1964 |
1967 |
July 1996 |
45 |
| India |
1974 |
|
May 1998 |
4–6 |
| Pakistan |
May 1998 |
|
May 1998 |
2–6 |
| Israel & South Africa? |
September 1979? |
|
September 1979? |
|
| North Korea |
October 2006 |
|
September 2016 |
5 |
* Some tests involved two or more explosions close in time and location.
** Twenty-four were joint tests with the United States.
In their 2009 book The Nuclear Express, Thomas Reed and Danny Stillman argue that many of the countries that acquired nuclear weapons did so with the help of other nations. Nuclear weapons designers Reed and Stillman worked at the Livermore and Los Alamos weapons laboratories. Scientists from the United Kingdom helped develop the U.S. atomic bombs at Los Alamos and hence knew much about their design. The Soviet Union acquired the design of its first device from the United States by espionage. China initially received help from the USSR on its atomic bomb before Russia cut off aid over fear of what Mao might do with atomic weapons.
Reed and Stillman state that Britain aided France with the design of its hydrogen bomb; France helped Israel with its atomic weapons program. India obtained plutonium for its 1974 nuclear test from a reactor that Canada and the United States had supplied it under the Atoms for Peace program. They also conclude that the first Pakistani atomic device likely was tested at China’s Lop Nor site in 1990, but others disagree with their claim. Pakistani engineer A. Q. Khan transferred uranium enrichment technology to Libya, Iran, North Korea, and perhaps other states.
Table 2.2 lists the numbers of nuclear warheads of nine countries. Those that can be delivered at a moment’s notice are classified separately from those (“other”) held in reserve or being dismantled. Note that Russia and the United States have by far the greatest numbers of nuclear weapons. Figure 2.3 shows the sites of nuclear weapons tests.
TABLE 2.2 Numbers of Nuclear Weapons of Various Countries as of 2013
| COUNTRY |
DEPLOYED |
OTHER |
TOTAL 2012 |
TOTAL 2013 |
| United States |
2150 |
5550 |
8000 |
7700 |
| Russia |
1800 |
6700 |
10,000 |
8500 |
| United Kingdom |
160 |
65 |
225 |
225 |
| France |
290 |
10 |
300 |
300 |
| China |
|
250 |
240 |
250 |
| India |
|
90–110 |
80–100 |
90–110 |
| Pakistan |
|
100–120 |
90–110 |
100–120 |
| Israel |
|
80 |
80 |
80 |
| North Korea |
|
|
2 |
3 |
| Total* |
4400 |
12,865 |
19,000 |
17,265 |
FIGURE 2.3
Areas where nuclear explosives have been tested. The figure also includes the Hiroshima and Nagasaki explosions of 1945. Sites of Soviet and U.S. peaceful nuclear explosions are not shown. Whether a nuclear explosion was tested at the site shown in the southwestern Indian Ocean is discussed later.
Source: atomicarchive.com.
