question: what’s the difference between atomic bomb and hydrogen bomb ?
comment: At atom bomb, aka fission bomb, works by taking a heavy element such as uranium and breaking up its nucleus, releasing energy in the process. A hydrogen bomb, aka fusion bomb, works by fusing together hydrogen atoms to create heavier elements such as helium, also releasing a lot of energy in the process.
passages: The idea of the hydrogen bomb first came to public attention in 1949, when prominent scientists openly recommended against building nuclear bombs more powerful than the standard pure-fission model, on both moral and practical grounds. Their assumption was that critical mass considerations would limit the potential size of fission explosions, but that a fusion explosion could be as large as its supply of fuel, which has no critical mass limit. In 1949, the Soviets exploded their first fission bomb, and in 1950 U.S. President Harry S. Truman ended the H-bomb debate by ordering the Los Alamos designers to build one.
   In early news accounts, pure fission weapons were called atomic bombs or A-bombs and weapons involving fusion were called hydrogen bombs or H-bombs. Practitioners however favor the terms nuclear and thermonuclear, respectively.
  
  Section::::Nuclear reactions.
  
  Nuclear fission separates or splits heavier atoms to form lighter atoms. Nuclear fusion combines together lighter atoms to form heavier atoms. Both reactions generate roughly a million times more energy than comparable chemical reactions, making nuclear bombs a million times more powerful than non-nuclear bombs, which a French patent claimed in May 1939.
   Modern fusion weapons consist essentially of two main components: a nuclear fission primary stage (fueled by uranium-235 or plutonium-239) and a separate nuclear fusion secondary stage containing thermonuclear fuel: the heavy hydrogen isotopes deuterium and tritium, or in modern weapons lithium deuteride. For this reason, thermonuclear weapons are often colloquially called hydrogen bombs or H-bombs.
   In 1952, the 10.4-megaton Ivy Mike explosion was announced as the first hydrogen bomb test, reinforcing the idea that hydrogen bombs are a thousand times more powerful than fission bombs.
   Atomic bombs are based on the theory of nuclear fission, that when a large atom splits, it releases a massive amount of energy. Thermonuclear weapons, (colloquially known as "hydrogen bombs") use the energy from an initial fission explosion to create an even more powerful fusion explosion.
   This kind of thermonuclear weapon can produce up to 20% of its yield from fusion, with the rest coming from fission, and is limited in yield to less than one megaton of TNT (4 PJ) equivalent. Joe-4 yielded 400 kilotons of TNT (1.7 PJ). In comparison, a "true" hydrogen bomb can produce up to 97% of its yield from fusion, and its explosive yield is limited only by device size.
  
  Section::::Maintenance of gas boosted nuclear weapons.
   While every nuclear weapon design falls into one of the above categories, specific designs have occasionally become the subject of news accounts and public discussion, often with incorrect descriptions about how they work and what they do. Examples:
  
  Section::::Specific designs.:Hydrogen bombs.
  
  While all modern nuclear weapons (fission and fusion alike) make some use of D-T fusion, in the public perception hydrogen bombs are multi-megaton devices a thousand times more powerful than Hiroshima's Little Boy. Such high-yield bombs are actually two-stage thermonuclears, scaled up to the desired yield, with uranium fission, as usual, providing most of their energy.
   The U.S. tested three-stage bombs in several explosions (see Operation Redwing) but is thought to have fielded only one such tertiary model, i.e., a bomb in which a fission stage, followed by a fusion stage, finally compresses yet another fusion stage. This U.S. design was the heavy but highly efficient (i.e., nuclear weapon yield per unit bomb weight) 25 Mt B41 nuclear bomb. The Soviet Union is thought to have used multiple stages (including more than one tertiary fusion stage) in their 50 megaton (100 Mt in intended use) Tsar Bomba (however, as with other bombs, the fissionable jacket could be replaced with lead in such a bomb, and in this one, for demonstration, it was). If any hydrogen bombs have been made from configurations other than those based on the Teller–Ulam design, the fact of it is not publicly known. (A possible exception to this is the Soviet early "Sloika" design).
   In 1954, J. Robert Oppenheimer was labeled a hydrogen bomb opponent. The public did not know there were two kinds of hydrogen bomb (neither of which is accurately described as a hydrogen bomb). On May 23, when his security clearance was revoked, item three of the four public findings against him was "his conduct in the hydrogen bomb program." In 1949, Oppenheimer had supported single-stage fusion-boosted fission bombs, to maximize the explosive power of the arsenal given the trade-off between plutonium and tritium production. He opposed two-stage thermonuclear bombs until 1951, when radiation implosion, which he called "technically sweet", first made them practical. The complexity of his position was not revealed to the public until 1976, nine years after his death.
   Section::::Testing.:First series.
   In 1954, to explain the surprising amount of fission-product fallout produced by hydrogen bombs, Ralph Lapp coined the term fission-fusion-fission to describe a process inside what he called a three-stage thermonuclear weapon. His process explanation was correct, but his choice of terms caused confusion in the open literature. The stages of a nuclear weapon are not fission, fusion, and fission. They are the primary, the secondary, and, in a very few exceptional and powerful weapons no longer in service, the tertiary. Tertiary (three-stage) designs, such as the U.S. B41 nuclear bomb and the Soviet Tsar Bomba (discussed above), were developed in the late 1950s and early 1960s; all have since been retired, as the typical multi-megaton yields of tertiary bombs do not destroy targets efficiently, since they waste energy in a sphere above and below an area of land. For this reason, all tertiary bombs have given way in modern nuclear arsenals to multiple smaller two-stage bomb tactics (see for example, MIRV). Such two-stage bombs, even though less efficient in yield, are nevertheless more destructive for their total bomb weight, because they can be distributed over a roughly two-dimensional area of land at the target.
   The first hydrogen bombs were similarly massive and complicated. This ratio of one plane to one bomb was still fairly impressive in comparison with conventional, non-nuclear weapons, but against other nuclear-armed countries it was considered a grave danger. In the immediate postwar years, the U.S. expended much effort on making the bombs "G.I.-proof"—capable of being used and deployed by members of the U.S. Army, rather than Nobel Prize–winning scientists. In the 1950s, the U.S. undertook a nuclear testing program to improve the nuclear arsenal.
   Section::::Types.:Thermobaric.
  
  A thermobaric bomb is a type of explosive that utilizes oxygen from the surrounding air to generate an intense, high-temperature explosion, and in practice the blast wave typically produced by such a weapon is of a significantly longer duration than that produced by a conventional condensed explosive. The fuel-air bomb is one of the best-known types of thermobaric weapons.
  
  Section::::Types.:Nuclear fission.
   The other basic type of nuclear weapon produces a large proportion of its energy in nuclear fusion reactions. Such fusion weapons are generally referred to as thermonuclear weapons or more colloquially as hydrogen bombs (abbreviated as H-bombs), as they rely on fusion reactions between isotopes of hydrogen (deuterium and tritium). All such weapons derive a significant portion of their energy from fission reactions used to "trigger" fusion reactions, and fusion reactions can themselves trigger additional fission reactions.
   Nuclear weapons possess enormous destructive power from nuclear fission or combined fission and fusion reactions. Building on scientific breakthroughs made during the 1930s, the United States, the United Kingdom and Canada collaborated during World War II, in what was called the Manhattan Project, to counter the suspected Nazi German atomic bomb project. In August 1945, two fission bombs were dropped on Japan, standing to date as the only use of nuclear weapons in combat. The Soviet Union started development shortly thereafter with their own atomic bomb project, and not long after that both countries developed even more powerful fusion weapons known as "hydrogen bombs".
   The HPM concept is based on work from the 1950s, when the University of California Radiation Laboratory (currently the Lawrence Livermore National Laboratory) required a small nuclear fission device as the ignition charge for a thermonuclear weapon. The aim was to produce an explosion powerful enough to ignite it, while using only the minimum amount of fissile material. This was tried in operation Upshot–Knothole, where hydrogen was used to reduce the critical mass. The test explosions codenamed Ruth and Ray used in the core uranium hydride. Ruth used the hydrogen isotope protium (H) and Ray used the hydrogen isotope deuterium (H or D) as neutron moderators. The predicted yield was 1.5 to 3 kt TNT for Ruth and 0.5-1 kt TNT for Ray, however the tests produced only a yield of about 200 tons of TNT.
   Nuclear weapons are a staple element in science fiction novels. The phrase "atomic bomb" predates their existence, and dates back to H. G. Wells' "The World Set Free" (1914) when scientists had discovered that radioactive decay implied potentially limitless energy locked inside of atomic particles (Wells' atomic bombs were only as powerful as conventional explosives, but would continue exploding for days on end). Cleve Cartmill predicted a chain-reaction-type nuclear bomb in his 1944 science-fiction story "Deadline", which led to the FBI investigating him, due to concern over a potential breach of security on the Manhattan Project.
   The hydrogen bomb primarily has 2 units: a nuclear bomb, which was the primary unit, and a secondary energy unit. The first stage of the hydrogen bomb resembled the layer-cake design, except the main difference is that the explosion is carried out by a nuclear device, rather than a conventional explosive. This design was initially postulated by Enrico Fermi and Edward Teller in 1941. Teller insisted that they should ignite deuterium by some fission weapon. The hydrogen bomb was a challenge, and would be more powerful and destructive than the nuclear bomb. The fusion cell itself was not very powerful, coming out to about 17.6 MeV, but the quantity of hydrogen fuel can be scaled up to make the weapon as large as desired.
   A nuclear weapon (also called an atom bomb, nuke, atomic bomb, nuclear warhead, A-bomb, or nuclear bomb) is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or from a combination of fission and fusion reactions (thermonuclear bomb). Both bomb types release large quantities of energy from relatively small amounts of matter. The first test of a fission ("atomic") bomb released an amount of energy approximately equal to . The first thermonuclear ("hydrogen") bomb test released energy approximately equal to . A thermonuclear weapon weighing little more than can release energy equal to more than . A nuclear device no larger than traditional bombs can devastate an entire city by blast, fire, and radiation. Since they are weapons of mass destruction, the proliferation of nuclear weapons is a focus of international relations policy.
   The Tsar Bomba however differs from its parent design—the RN202—in a number of places. The Tsar Bomba was a three-stage bomb with Trutnev-Babaev second- and third-stage design, with a yield of . This is equivalent to about 1,570 times the combined energy of the bombs that destroyed Hiroshima and Nagasaki, 10 times the combined energy of all the conventional explosives used in World War II, one quarter of the estimated yield of the 1883 eruption of Krakatoa, and 10% of the combined yield of all nuclear tests to date. A three-stage hydrogen bomb uses a fission bomb primary to compress a thermonuclear secondary, as in most hydrogen bombs, and then uses energy from the resulting explosion to compress a much larger additional thermonuclear stage. There is evidence that the Tsar Bomba had several third stages rather than a single very large one.
   Nuclear explosion
  
  A nuclear explosion is an explosion that occurs as a result of the rapid release of energy from a high-speed nuclear reaction. The driving reaction may be nuclear fission or nuclear fusion or a multi-stage cascading combination of the two, though to date all fusion-based weapons have used a fission device to initiate fusion, and a pure fusion weapon remains a hypothetical device.
   A thermonuclear weapon is a type of nuclear bomb that releases energy through the combination of fission and fusion of the light atomic nuclei of deuterium and tritium. With this type of bomb, a thermonuclear detonation is triggered by the detonation of a fission type nuclear bomb contained within a material containing high concentrations of deuterium and tritium. Weapon yield is typically increased with a tamper that increases the duration and intensity of the reaction through inertial confinement and neutron reflection. Nuclear fusion bombs can have arbitrarily high yields making them hundreds or thousands of times more powerful than nuclear fission.
   Section::::Development.
   Section::::Organisation.
   The Soviet Union detonated its first "true" hydrogen bomb on November 22, 1955, which had a yield of 1.6 megatons. On October 30, 1961, the Soviets detonated a hydrogen bomb with a yield of approximately 58 megatons.
  
  Section::::Early Cold War.:Arms Race.
  
  With both sides in the "cold war" having nuclear capability, an arms race developed, with the Soviet Union attempting first to catch up and then to surpass the Americans.
  
  Section::::Early Cold War.:Delivery Vehicles.
  
  Strategic bombers were the primary delivery method at the beginning of the Cold War.
  