# 6.7: Fusion

## Mike -The First Fusion Device

The first fusion device was tested by the United States on November 1st, 1952. On Elugelab Island located in the Marshall Islands, this nondeliverable weapon measured 20 feet in height and weighed over 140,000 pounds. During the eighth round of United States nuclear testing (named Operation Ivy), Mike (fusion weapon) vaporized the entire island where it was detonated. The 10.4 megaton blast was 500 times more powerful than the Nagasaki weapon and left a crater in the ocean that was 6,240 feet wide and 164 feet deep.

Example $$\PageIndex{1}$$:

From video and classroom discussion, answer the questions below:

A scene from our PBS documentary "Dr. Teller's Very Large Bomb" (with perhaps a bit too much information on how to build your own hydrogen bomb.) (Complete hour-long documentary available at www.foolishearthling.com)

1. Could the United States transported Mike by airplane? Was this bomb deliverable or nondeliverable?
2. What nuclear isotopes did this device contain?
3. What two types of nuclear reactions were used in Mike?
4. Is fission or fusion more technologically complex?
5. What was Teller's response after Mike exploded?
6. How far away were the observers of Mike?

Edward Teller, one of the Manhattan Project scientists, is credited designing the fusion bomb. Unlike J. Robert Oppenheimer, Teller felt it was important and necessary for the United States to pursue new nuclear weapons. After the dropping of Little Boy and Fat Man, Edward Teller testified against Oppenheimer in order to get his security clearance revoked at Los Alamos National Laboratory. He was successful in his testimony and Oppenheimer left Los Alamos for Princeton University. In 1963, Oppenheimer was presented with the Enrico Fermi Award. This accolade recognized international achievement in the field of energy. Only three years later, Oppenheimer died of throat cancer in Princeton, New Jersey.

Teller was not present for the testing of Mike. For personal and professional reasons, he left the south Pacific and head back to Berkley, California. At the university, he waited for Mike to affect the university's seismograph machine. This instrument detects earthquake activity due to natural or artificial causes. Before the bomb detonation, Teller had calculated the exact time the vibration would reach the University of California, Berkley.

## The Mechanics of Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process called fusion. The principal source of energy in the sun is a net fusion reaction in which four hydrogen nuclei fuse and produce one helium nucleus and two positrons. This is a net reaction of a more complicated series of events:

$\ce{4^1_1H ⟶ ^4_2He + 2 ^1_{0}n}$

A helium nucleus has a mass that is 0.7% less than that of four hydrogen nuclei; this lost mass is converted into energy during the fusion. This reaction produces about 3.6 × 1011 kJ of energy per mole of $$\ce{^4_2He}$$ produced. This is somewhat larger than the energy produced by the nuclear fission of one mole of U-235 (1.8 × 1010 kJ), and over 3 million times larger than the energy produced by the (chemical) combustion of one mole of octane (5471 kJ).

It has been determined that the nuclei of the heavy isotopes of hydrogen, a deuteron, $$^2_1H$$ and a triton, $$^3_1H$$, undergo fusion at extremely high temperatures (thermonuclear fusion). They form a helium nucleus and a neutron:

$\ce{^2_1H + ^3_1H ⟶ ^4_2He + 2 ^1_0n}$

This change proceeds with a mass loss of 0.0188 amu, corresponding to the release of 1.69 × 109 kilojoules per mole of $$\ce{^4_2He}$$ formed. The very high temperature is necessary to give the nuclei enough kinetic energy to overcome the very strong repulsive forces resulting from the positive charges on their nuclei so they can collide.

The most important fusion process in nature is the one that powers stars. In the 20th century, it was realized that the energy released from nuclear fusion reactions accounted for the longevity of the Sun and other stars as a source of heat and light. The fusion of nuclei in a star, starting from its initial hydrogen and helium abundance, provides that energy and synthesizes new nuclei as a byproduct of that fusion process. The prime energy producer in the Sun is the fusion of hydrogen to form helium, which occurs at a solar-core temperature of 14 million kelvin. The net result is the fusion of four protons into one alpha particle, with the release of two positrons, two neutrinos (which changes two of the protons into neutrons), and energy (Figure $$\PageIndex{2}$$).

## Overview of Ivy Mike's Mechanism

Fusion requires extreme temperatures. In order to achieve this, all fusion weapons contain a primary fission component. U-235 or Pu-239 are detonated first and the resulting heat fuses the deuterium and tritium components of a thermonuclear weapon.

Initially, the fission reaction of the primary releases gamma and x-ray, neutrons, and heat to produce the high temperatures required for following the fusion reactions. The fuel for the fusion is lithium deuteride, $$\ce{^6_3Li^2_1H}$$. The neutrons react with lithium to produce tritium, $$\ce{_1^3H}$$, and alpha radiation.

$\ce{_3^6Li} + \ce{_0^1n} →\ce{_1^3H} + \ce{_2^4He}$

At the high temperature created by fission of the primary, the tritium then undergoes fusion with the deuterium in the lithium deuteride fuel.

$\ce{^{3}_1H + ^{2}_1H → ^{4}_2He + ^{1}_0n} + \text{energy}$

The fusion reaction liberates a huge amount of energy and creates large numbers of high energy neutrons, which causes the additional fission of the uranium surrounding the secondary.

More recent fusion weapons utilize different mechanisms. Today's, warheads use a series of fission-fusion-fission chain reactions to produce yields several orders of magnitude greater than Little Boy or Fat Man. At this time, fusion weapons still require:

1. knowledge and construction of fission
2. isolation of H-2 and H-3 isotopes, and
3. extreme temperatures.

The five permanent members of the United Nations Security Council all possess the knowledge and the technology of fusion. These countries with their fusion device detonation dates are: United States (1952), the former Soviet Union (1953), the United Kingdom (1957), China (1967) and France (1968). Note that these dates refer to device detonations and not deliverable nuclear weapons. As of November 2017, it is still unclear if North Korea has detonated a fusion device.

In March of 1953, the United States dropped its largest fusion bomb over the Bikini Atoll in the Marshall Islands. Castle Bravo produced a punch equivalent to 15 megatons of TNT. The fallout isotopes affected over 11,000 square kilometers of area. Unfortunately, winds carried the lingering radiation to neighboring islands that were inhabited. Only 145 kilometers away from the epicenter, a Japanese fishing vessel (Lucky Dragon #5) was fishing with a crew of 24 people. Castle Bravo killed one person on the Lucky Dragon #5 and exposed the other crew members to extremely high dosages of radioactive isotopes (fallout).

## Tsar Bomba-The Largest Nuclear Weapon

The former Soviet Union is credited with dropping the largest fusion bomb in history. On October 30, 1961, a fifty megaton three staged fusion bomb was dropped over the Arctic Circle. This weapon was calculated to be 1570 times more powerful than Little Boy and Fat Man combined. Tsar Bomba weighed 27 metric tons and was 26 feet long with a 7 foot diameter. The resulting fireball reached a maximum height of 1000 km (620 miles). The mushroom cloud produced was 64 km (40 miles) in height with a maximum width of 95 km (59 miles). Lastly, the flash from the fireball could be seen from 270 km (170 miles) away and burns were experience up to 100 km (62 miles) from epicenter.

Discovery Channel - Ultimates - Explosions - Tsar bomb segment

## The Development of Nuclear Weapons after World War II

The use of nuclear weapons by the United States to hasten the end of the war initiated a nuclear arms race between the United States and the Soviet Union that lasted until the end of the Cold War in 1992. During this period, scientists in both countries developed powerful thermonuclear fusion weapons (hydrogen bombs) and more efficient fission bombs. Table $$\PageIndex{2}$$ compares the explosive power of current nuclear warheads. A nuclear weapon includes the warhead encased in a bomb or missile.

 Terrorist weapon (improvised nuclear device) < 3 kilotons Bunker buster or tactical nuclear weapon 3 to 5 kilotons Fission weapon (Pu-239 or U-235) 15 to 50 kilotons Boosted fission weapon 100 to 500 kilotons Thermonuclear weapon 1 to 57 megatons

Improvised nuclear devices (IND) are low yield weapons that might be assembled by non-state groups or “rogue” nations for a terrorist attack. The most likely scenario would be the acquisition of a critical mass of HEU and construction of a simple gun-type assembly mechanism.

Tactical nuclear warheads are placed in a variety of delivery systems such as artillery shells, torpedoes, cruise missiles, and bombs. These weapons may be defined by their range and types of targets. Tactical nuclear weapons are short-range weapons that are to be used on a battlefield or a a military target. On the other hand, strategic nuclear weapons are longer-range weapons that would disrupt the infrastructure of a country or a nation. Bunker busters are designed to deliver nuclear warheads to hardened, underground targets.

Nuclear weapons with yields greater than 5 kilotons of TNT are known as strategic weapons. They are designed to be used on targets such as missile launch sites, command and control centers, large cities, or industrial sites. The two types of early fission weapons have been discussed previously. Boosted warheads contain a small amount of deuterium and tritium (isotopes of hydrogen) gases, which undergo fusion with the initiation of the fission reaction.

$\ce{^{2}_1H + ^{3}_1H -> ^{4}_2He + ^{1}_1n} + \text{energy}$

The fusion releases an intense burst of high energy neutrons which amplifies the fission chain reaction, along with a small amount of energy This boosting allows increased yields from smaller, lighter warheads. Most current fission weapons contain boosted warheads. The 12 year half-life of tritium requires that these warheads be replenished at regular intervals.

Finally thermonuclear warheads, developed during the Cold War, use a series of fission-fusion-fission reactions to produce yields several orders of magnitude greater than those of fission devices . Weapons designers have also reduced the size of thermonuclear warheads so that multiple warheads could be carried by a single missile. Today, a ballistic missile submarine can carry 24 missiles each with 6 thermonuclear warheads.

A nuclear weapon can be modified from being tactical to strategic. In 1968, Los Alamos National Laboratory build the B61 thermonuclear bomb. This weapon was only twelve feet long and thirteen inches wide. The power range could be easily adjusted from .3 to 340 kilotons. B61 was a two stage thermonuclear weapon and over 3100 were constructed in the United States.

Some countries possess ICBMs which are intercontinental ballistic missiles. These weapons can travel a minimum of 3400 miles (5500 kilometers). ICBMs can contain chemical or nuclear weapons. Noted countries that have or have had ICBMs are: Russia, United States, India, China, Israel, France, and North Korea. In 2017, China presented the longest reaching ICBM to the world. This weapon can reach a destination of over 6000 miles.

## World Arsenals

According to the Arms Control Association October 2017's report, the countries contained in the table below possess nuclear warheads. This type of weapon would have a fission or fusion portion fastened to the front of a guided missile, rocket, or torpedo. In the world, there are approximately 15,000 nuclear warheads. Of this number, ninety percent are in military service while the remaining percent await dismantlement.

Table $$\PageIndex{2}$$: Stats for countries that possess nuclear weapons.
Russia 7000
United States 6800
France 300
China 270
United Kingdom 215
Pakistan 140
India 130
Israel 80
North Korea 10

At one time, former Soviet Union countries like Belarus, Kazakhstan, and the Ukraine stored nuclear weapons. Now, they do not possess any nuclear warheads. South Africa, Brazil, Iraq, Libya, Argentina, South Korea, and Taiwan have abandoned their nuclear weapon programs as well.

In August of 1949, the American monopoly on nuclear weapons technology ended. The USSR ignited a 20 kiloton Pu-239 weapon that they named First Lightning. American nuclear scientists code named this detonation to be Joe-1. The weapon was duplicate of the Trinity device that was tested by the Manhattan Project scientists in July of 1945. A spy ring of scientists and civilians passed implosion mechanics and hydrogen bomb technology to KGB agents. The most notable of these people were Klaus Fuchs and Julius and Ethel Rosenberg. During the Manhattan Project, Fuchs worked at the gaseous diffusion facility (University of Columbia) and Pu-239 implosion laboratory (Los Alamos). In addition, Fuchs assisted Edward Teller with hydrogen bomb research. Fuchs passed knowledge of implosion and fusion directly to KGB agents and through civilians, Ethel and Julius Rosenberg.

The USSR had started fission research in the mid to late 1930's. They primarily focused on uranium enrichment and determination of critical mass. After the bombings of Hiroshima and Nagasaki, Stalin pushed USSR scientists harder to obtain nuclear weapons technology. During the Manhattan Project, Stalin was aware that the United States was pursuing the development of fission weapons. Espionage provided USSR scientists with blueprints of the Trinity device and information regarding fusion. This data expedited the USSR to detonate their first fission device in 1949. Less than a year after the American testing of Mike (first fusion device), USSR exploded a 400 kiloton, H-bomb device named Joe-4 . Hans Bethe, an American Manhattan Project scientists, debated the nature of this explosion. Fragments and resulting isotopes did not indicate that a fusion device had exploded. In 1955, the USSR dropped their first fusion weapon which yielded energy within the megaton range.

Since the late 1960's, the United States and the former Soviet Union/Russia have signed several treaties to downside their nuclear arsenals. The START (Strategic Nuclear Arms Control Agreements) program has greatly reduced the numbers of nuclear weapons for both countries. For more information regarding START, click on this link.

Figure $$\PageIndex{8}$$:Nuclear Arsenals of the United States and USSR/Russia over the past sixty years. Image taken from: https://upload.wikimedia.org/wikiped...kpiles.svg.png

Requirements for Producing Nuclear Weapons

A nation seeking to produce nuclear weapons must complete the following basic steps:

• Develop a weapon design or obtain one from an external source.
• Produce highly enriched uranium or plutonium for the core of the device or obtain this material from an external source.
• Fabricate this material into the fissile component of the weapon.
• Fabricate or obtain from external sources the non-nuclear components of the weapon. These include high explosives and a triggering mechanism to detonate the nuclear core.
• Verify the reliability of all components individually and as a system.
• Assemble the components into a deliverable weapon.
• For fusion weapons, a through knowledge of fission is required. A fusion bomb must contain a fission counterpart.

## Nuclear Terrorism

Most recently, attention has centered on the possibility of “rogue” nations or terrorist groups obtaining a fission device. Two possibilities exist: the acquisition of an intact weapon or the construction of an improvised nuclear device (IND) device from components either stolen or acquired illegally from a rogue state. In the first case, an organized group must obtain the financial resources to initiate this act of extreme violence. The group must then acquire an intact weapon through purchase, theft, diversion, or as a gift. It then has to ascertain how to bypass or disable safeguards incorporated in the weapon to prevent its unauthorized use. Lastly, the weapon must be transported to a high value target and detonated. The challenges involved with the successful completion of each step are formidable.

The second case would also involve sizeable obstacles. As in the first case, an organization and funding would be required. The group would have to acquire sufficient fissile material, fabricate it into a fissile component, and assemble an IND. This would require significant technical expertise. A device similar to a uranium gun-type bomb (Figure 2) would be easier to build than a plutonium implosion weapon. Transport and detonation of an IND would involve greater risks than those associated with the intact weapon.

The lack of complete control of fissile materials and the economic conditions in the former Soviet Union have increased the possibility that HEU and plutonium from weapons programs might be available on the international black market. Several instances involving plutonium and enriched uranium smuggled from the former Soviet Union have been observed since 1994. The United States and Russia have had a “blend down” agreement since 1993 that renders excess HEU incapable of being fabricated into nuclear weapons. Under the terms of this agreement, the United States purchases from Russia uranium of which the concentration of U-235 has been reduced by mixing it with U-238 to that suitable for fueling nuclear power reactors.

Other nations also have quantities of HEU and plutonium from their weapon programs and the production of civilian nuclear power. Figures Figure $$\PageIndex{9}$$ and Figure $$\PageIndex{10}$$ show the global disposition and current status of HEU and plutonium.