Thermonuclear weapon

Thermonuclear weapons, also called fusion weapons or hydrogen bombs, are very strong types of nuclear weapons. They use a process named nuclear fusion to make explosions bigger than older nuclear weapons. These weapons can be smaller and lighter but still give out a lot of energy.

The first full test of a thermonuclear weapon happened in the United States in 1952. After that, many countries made these kinds of weapons. They work in two steps, with the first step helping to start the second step that makes most of the energy.

These weapons are the strongest ever made, with some able to give out energy like millions of tons of explosive. Because they are so powerful, they have been very important in history, especially during the Cold War, and still matter today for how countries keep themselves safe.

Terminology

Thermonuclear, fusion, and hydrogen weapons are special types of nuclear weapons. They use a process called radiation implosion, linked to the Teller-Ulam design made by scientists.

These weapons get their power from thermonuclear fusion. In fusion, tiny parts called nuclei join together at very high temperatures. This is different from regular nuclear weapons, which use neutrons to create an explosion. Some simpler thermonuclear weapons get power from a process called fast fission in materials like natural or depleted uranium.

Basic principle

Main article: Nuclear weapon design

A thermonuclear weapon has different parts that work together in steps. The first part, called the primary, is a smaller bomb that uses fission, or splitting atoms, to explode. This explosion gives off energy.

The energy moves to the second part, called the secondary. The secondary contains fusion fuel, which is special material that can join atoms together to release more energy. The energy from the primary squeezes the fusion fuel tightly and heats it up, causing a fusion reaction. This process can release a lot of energy. Some designs also have a third part that adds even more energy to the explosion.

Compression of the secondary

How the energy moves from the first part of the bomb to the second part has been discussed, but it is believed that X-rays and gamma rays from the first part are responsible. This energy helps squeeze the second part tightly.

There are three ideas about how the X-rays create this squeezing pressure:

• Radiation pressure from the X-rays. This was the first idea suggested.
• Plasma pressure from a special foam inside the bomb. This was a later idea.
• Ablation pressure from the outer layer of the bomb. This idea seems best supported by science.

Each of these ideas explains how the bomb's second part gets compressed to create a powerful explosion. The ablation idea suggests that the outer layer heats up so much that it flies off, pushing the rest of the bomb inward with great force.

Current reviews of the foam plasma pressure idea suggest it may not create as much pressure as thought, because the foam does not absorb much of the X-ray and gamma ray energy. This leads to the third idea: ablation.

Simple calculations show that the ablation effect can create very high pressure.

The ablation pressure seems much stronger than the other two ideas.

In one famous bomb, a thin layer of plastic foam was placed inside the outer casing to delay ablation. Without this foam, the metal would fly off too quickly. The foam helps keep the bomb together longer, allowing a bigger explosion.

Design variations

Different designs for these special weapons have been suggested. One idea is to use a special material called ²³⁵U in the outer part of the weapon. This material can help make the explosion bigger.

Some designs include extra parts to shield the main part of the weapon from tiny particles called neutrons that come from the first explosion.

Most of these weapons have two main parts that explode, but scientists have tested designs with three parts. One example is a powerful weapon tested by the United States.

These weapons usually work in two steps: first, a small explosion makes a central part split apart, creating a lot of energy. Then, that energy starts a second reaction that creates even more power. This method can be used again with more parts, but it is not always done.

For destroying larger areas like cities, it is often better to spread the explosion over a wider space instead of making one very big blast. Because of this, many modern weapons are made to have smaller explosions that can be spread out over an area.

Ivy Mike

In a book called Dark Sun: The Making of the Hydrogen Bomb, author Richard Rhodes shares details about a special test named "Ivy Mike." This test used heat from the first explosion, foam, and other materials to create a bigger explosion.

Ripple

The Ripple design was tested in 1962 and was noted for being very efficient. It used a special mix of gases and materials to create a clean and powerful explosion. However, it was large and not easy to carry on smaller missiles.

W88

In 1999, a report shared details about the W88 weapon used on certain missiles. This weapon has a special shape that allows it to be smaller but still very powerful. Its design lets more of these weapons fit on a single missile, improving how far and how fast the missile can travel.

History

First tests

United States

The idea of a thermonuclear fusion bomb started with Enrico Fermi and Edward Teller in 1941 at Columbia University. Teller worked on this idea during the Manhattan Project, preferring it to the atomic bomb. After World War II ended, there was less reason to focus on the "Super," as it was called.

The first atomic bomb test by the Soviet Union in 1949 surprised the Americans. This led to debates in the US about whether to develop a more powerful Super. Some, like Robert Oppenheimer, warned of the dangers. But in 1950, President Harry S. Truman decided to move forward.

Teller and other US scientists worked hard to create a working design. Stanislaw Ulam made important discoveries that helped. The "George" test in 1951 showed the idea could work on a small scale. In 1952, the "Mike" test proved the concept with a very powerful explosion. Later tests led to smaller, more practical designs that could fit in missiles.

Soviet Union

The Soviet Union's first fusion design, called the Sloika, was different from the US design. It used layers of materials but could not create very large explosions. The first test in 1953 had some fusion but was not very powerful. After seeing the US test in 1952, the Soviets looked for a better design. By 1955, they tested a new design that showed great power. In 1961, they tested the largest nuclear weapon ever made.

United Kingdom

In 1954, the UK started work on its own fusion bomb. They had little information and were not sharing details with the US. They observed US tests and learned important lessons. In 1957, their first test did not work well, but a later test using a very large fission bomb was successful. By 1958, they had a powerful test and later received help from the US.

China

China tested a full-scale thermonuclear bomb in 1967, just 32 months after its first atomic bomb. They had help from the Soviet Union early on, but then worked independently. They tested smaller designs before the successful 1967 test.

France

After its first nuclear test in 1960, France focused on developing delivery systems. In 1966, they felt pressure to catch up with China. French scientists learned from British expertise that their designs needed to change. In 1968, they successfully tested their first multistage thermonuclear weapon.

India

In 1998, India announced it had tested a thermonuclear bomb. Some experts believed it worked, while others had doubts. India claims it can build thermonuclear weapons of various sizes.

Israel

Israel is thought to have thermonuclear weapons, but it has never tested any. Edward Teller advised Israel on nuclear matters for many years.

North Korea

North Korea claimed to have tested a thermonuclear bomb in 2016 and again in 2017. However, seismic data suggested these tests might not have been true thermonuclear explosions. The 2017 test was larger than previous ones, but estimates of its power vary.

Public knowledge

Classification

Information about how nuclear weapons work is kept secret in most countries. In the United States, this knowledge is called "Restricted Data" and can be kept secret even if made by people not working for the government. Some details are considered "born secret" as soon as they are created.

The United States Department of Energy usually does not say when secret weapon information is leaked, because doing so might confirm that the information is true. In the past, the government has tried to stop news reports about these secrets, but with limited success.

Unclassified knowledge

While some general facts about nuclear weapons have been shared, many details remain unclear. Most of what the public knows comes from guessing based on known science, comparisons with related fields, and a few official statements.

US Department of Energy statements

In 1972, the United States government shared that thermonuclear weapons use a fission "primary" to start a fusion reaction in a "secondary" part. In 1979, they added that radiation from the fission part can be used to compress and ignite the fusion fuel. However, they said any more details would stay secret.

In 1991, they admitted that some parts of the weapon may contain special materials, but did not say where or how they are used.

United States v. The Progressive

Main article: United States v. The Progressive

Much of what is known today about how hydrogen bombs work became public after a magazine article in 1979. An activist named Howard Morland tried to explain the "secret" of these weapons. He used information from books, interviews with scientists, and his own thinking.

The government tried to stop the article from being published, claiming it was too secret. However, the case became weaker when it turned out some of the information had been published before. Eventually, the government let the article be published. Morland later changed some of his ideas about how the bomb worked.

Morland’s work is seen as partly correct because the government tried to stop it, which is rare. However, it is unclear how much of his explanation was fully accurate. Other countries found it difficult to build these weapons, suggesting that understanding the basic idea is not enough to make them.

Notable accidents

There have been some accidents with nuclear weapons in the past.

In 1958, a training plane lost a nuclear bomb near Savannah, Georgia. The U.S. Air Force said the bomb could not explode.

In 1966, two planes crashed in Palomares, Spain. The explosion spread material from the bombs, but the danger was controlled.

In 1968, a plane crashed in Greenland while landing. This caused radioactive contamination, and some parts of the bombs were not found.