In the process of splitting, a great amount of thermal energy , as well as gamma rays and two or more neutrons, is released. Under certain conditions, the escaping neutrons strike and thus fission more of the surrounding uranium nuclei, which then emit more neutrons that split still more nuclei. This series of rapidly multiplying fissions culminates in a chain reaction in which nearly all the fissionable material is consumed, in the process generating the explosion of what is known as an atomic bomb. Many isotopes of uranium can undergo fission, but uranium, which is found naturally at a ratio of about one part per every parts of the isotope uranium, undergoes fission more readily and emits more neutrons per fission than other such isotopes.
Plutonium has these same qualities. These are the primary fissionable materials used in atomic bombs. A small amount of uranium, say 0. If more uranium is added to the assemblage, the chances that one of the released neutrons will cause another fission are increased, since the escaping neutrons must traverse more uranium nuclei and the chances are greater that one of them will bump into another nucleus and split it.
At the point at which one of the neutrons produced by a fission will on average create another fission, critical mass has been achieved, and a chain reaction and thus an atomic explosion will result. In practice, an assembly of fissionable material must be brought from a subcritical to a critical state extremely suddenly.
One way this can be done is to bring two subcritical masses together, at which point their combined mass becomes a critical one. This can be practically achieved by using high explosives to shoot two subcritical slugs of fissionable material together in a hollow tube. The core of an implosion-type atomic bomb consists of a sphere or a series of concentric shells of fissionable material surrounded by a jacket of high explosives, which, being simultaneously detonated, implode the fissionable material under enormous pressures into a denser mass that immediately achieves criticality.
An important aid in achieving criticality is the use of a tamper; this is a jacket of beryllium oxide or some other substance surrounding the fissionable material and reflecting some of the escaping neutrons back into the fissionable material, where they can thus cause more fissions. The fusionable material boosts the fission explosion by supplying a superabundance of neutrons.
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Fission releases an enormous amount of energy relative to the material involved. When completely fissioned, 1 kg 2. The detonation of an atomic bomb releases enormous amounts of thermal energy, or heat, achieving temperatures of several million degrees in the exploding bomb itself.
This thermal energy creates a large fireball, the heat of which can ignite ground fires that can incinerate an entire small city. Convection currents created by the explosion suck dust and other ground materials up into the fireball, creating the characteristic mushroom-shaped cloud of an atomic explosion. The detonation also immediately produces a strong shock wave that propagates outward from the blast to distances of several miles, gradually losing its force along the way. Such a blast wave can destroy buildings for several miles from the location of the burst. Large quantities of neutrons and gamma rays are also emitted; this lethal radiation decreases rapidly over 1.
Materials vaporized in the fireball condense to fine particles, and this radioactive debris, referred to as fallout , is carried by the winds in the troposphere or stratosphere. The radioactive contaminants include such long-lived radioisotopes as strontium and plutonium; even limited exposure to the fallout in the first few weeks after the explosion may be lethal, and any exposure increases the risk of developing cancer. Los Alamos was approved as the site for the main atomic bomb scientific laboratory on November 25, , by Brig. This last-moment arming is achieved by simple mechanical means, most commonly a small pinwheel on the bomb that turns as the air rushes past the falling projectile, and thereby arms the fuze.
Bombs first assumed military importance with the rapid development of zeppelins and aircraft in World War I , but the tonnages dropped in that conflict were insignificant, largely because the carrying capacity of the aircraft was so small. World War II saw the use of larger bombs in much greater numbers; more than 1.
Similar tonnages of bombs were used by the United States in the Korean and Vietnam wars, but by the time of the Persian Gulf War , tonnages had dropped owing to the increased use of highly accurate smart bombs.
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The Editors of Encyclopaedia Britannica. Learn More in these related Britannica articles: Atomic bomb , weapon with great explosive power that results from the sudden release of energy upon the splitting, or fission, of the nuclei of a heavy element such as plutonium or uranium. Thermonuclear bomb , weapon whose enormous explosive power results from an uncontrolled, self-sustaining chain reaction in which isotopes of hydrogen combine under extremely high temperatures to form helium in a process known as nuclear fusion. The high temperatures that are required for the reaction are….
Thermit , powdered mixture used in incendiary bombs, in the reduction of metals from their oxides, and as a source of heat in welding iron and steel and in foundry work. The powder consists of aluminum and the oxide of a metal such as iron. Napalm , the aluminum salt or soap of a mixture of naphthenic and aliphatic carboxylic acids organic acids of which the molecular structures contain rings and chains, respectively, of carbon atoms , used to thicken gasoline for use as an incendiary in flamethrowers and fire bombs. The thickened mixture, now also called…. London bombings of , coordinated suicide bomb attacks on the London transit system on the morning of July 7, An hour later 13 people were killed when a bomb detonated on the upper deck of a bus in….
External Websites Britannica Websites. Articles from Britannica Encyclopedias for elementary and high school students. Help us improve this article! Contact our editors with your feedback. Introduction Conventional bomb types Guidance and arming. You may find it helpful to search within the site to see how similar or related subjects are covered. The government did not move quickly.
It was not until mid that a program, authorized by Roosevelt, began to build the bomb. The Manhattan Project was the name given to the work by a division established within the Army Corps of Engineers. The sole purpose of this project was to develop the atomic bomb. The first nuclear bomb test was conducted on July 16, , in New Mexico. The test was a success, detonating a bomb as powerful as 20, tons of TNT explosives.
Within a month, two such bombs were dropped on Japan, killing an estimated , to , people and injuring another , or more. On August 15, six days after the second bomb was dropped, Japan announced its surrender, bringing World War II to an end. By , two thousand nuclear weapons existed across the globe. The Soviet Union and the United States owned 98 percent of them.
By the end of , there were still 26, nuclear warheads in existence; more than 95 percent belong to Russia and the United States. The mushroom-shaped cloud associated with the above-ground detonation of an atomic bomb is one of the most defining images and represents one of the most challenging moral imperatives to arise from the mid-twentieth century.
The scientific, technological, political, sociological, psychological, religious, and ethical ramifications of humankind's ability to harness and release in a fraction of a second fundamental forces of nature make the atomic bomb one of the preeminent issues of modern society and human existence. An atomic bomb is a weapon that derives its energy from a nuclear reaction in which a heavy nucleus of an atom such as uranium or plutonium splits into two parts and subsequently releases two or three neutrons along with a vast quantity of energy. These nuclear reactions, if they can be induced rapidly and in quick succession across a critical mass of material, produce a cataclysmic release of energy of prodigious dimensions from a very small quantity of initial material.
Advances in the design of these weapons have focused on efficiency and effectiveness, including ways to produce purer initial materials, induce and sustain more rapid reactions, and produce similar effects with smaller amounts of material. As a result, nuclear devices now available to the armed forces can yield effects from a small warhead on a missile that compare favorably to those generated in the s by weapons so large that bombers had to be specially adapted to haul and drop them.
Advances in weapons construction techniques further allow experts to assemble even relatively impure materials into "dirty" bombs with limited yield but severe environmental effects. Developments since the mids have posed new threats to world security as an ever-expanding set of nations gained access to suitable raw materials for constructing these devices.
Global monitoring of these materials has become increasingly more difficult and nongovernmental organizations have sought, and probably have obtained, previously unavailable raw materials to construct small-scale nuclear devices to advance sinister purposes. The technology behind atomic bombs dates to work in physics including the theoretical work of Albert Einstein at the beginning of the twentieth century and experimental work by Otto Hahn , Fritz Strassmann, Lise Meitner , Otto Robert Frisch , and others in Germany and Sweden in the late s.
Scientists in Germany, France, the United Kingdom, the Soviet Union , Japan, and the United States all realized that it might be possible to produce weapons of mass destruction as an extension of the work of the experimental physicists, but it was only in the United States that these efforts were organized and funded to achieve success.
The Hungarian refugee physicist Leo Szilard organized his physics colleagues in the United States to petition President Franklin Delano Roosevelt to sponsor work to build an atomic bomb out of fear that the Germans were already well advanced in their efforts. This claim was later shown to be completely erroneous. By Vannevar Bush , president of the Carnegie Institute of Washington, DC, had formed and chaired an Office of Scientific Research and Development to better harness the abilities of scientists in the United States to contribute substantially to the war effort.
A series of experiments at the University of California at Berkeley, the University of Chicago , and a remote location in Oak Ridge, Tennessee, during the period of to established that a fission reaction could be created and controlled, that new elements were created in such reactions that could also be useful as sources for bomb materials, and that uranium could be separated from the much more abundant but non-useful for bombs uranium via a number of different means.
Several of these separation techniques involved the use of highly reactive and corrosive materials, especially uranium-hexafluoride, in addition to a whole series of radioactive and dangerous by-products from the various processes associated with production of the basic materials needed for atomic bombs—by-products that continue to create problems of waste disposal and health impacts to this day. Bush appointed a secret National Academy of Sciences NAS committee in to recommend whether it was feasible to build an atomic bomb.
The committee, chaired by the Nobel Prize —winning physicist Arthur Holly Compton of the University of Chicago , concluded in May that an expanded six months of intensive research was needed before a decision could be rendered. Bush was dissatisfied with this report and responded by appointing more engineers to the committee and asking them to reconsider and produce a new report. This report, delivered on July 18, reached the same general conclusions as the prior one. By this point, Bush had a secret report from British scientists concluding that an atomic bomb could conceivably be built within the next few years.
Bush used this report and his own persuasive powers to convince President Roosevelt to give his full backing to proceeding with a large-scale effort to build the bomb. Roosevelt decreed that only four other people were to know: Army Chief of Staff George Marshall. Members of Congress were explicitly excluded from knowledge of the project and remained so throughout the war. Army Corps of Engineers ACE became the vehicle by which this massive endeavor would be hidden in the federal war budget because construction contracts were large and difficult to understand.
MED became known colloquially as the " Manhattan Project ," even though building the atomic bomb had little to do with the city of New York. Colonel Leslie Groves, the civil engineer who supervised the building of the Pentagon in record time, was promoted to brigadier general and given command of the Manhattan Project. General Groves swiftly commandeered equipment, supplies, human resources, and the best scientists who could be assembled, and created a series of centers in remote locations in Hanford, Washington; Oak Ridge; and Los Alamos , New Mexico in addition to maintaining work at many universities and over corporations including Stone and Webster, Dupont, Eastman Kodak, and Union Carbide.
At its peak in there were more than , employees working on the project. This workforce overcame tremendous scientific and technical problems in the push to build "the device," and the first atomic bomb performed superbly at Alamogordo, New Mexico , on July 16, Three weeks later the first atomic bomb was used in war as the Enola Gay bomber dropped a single kilogram device over Hiroshima, Japan, on August 6, Two days later the Soviets declared war on Japan and invaded Manchuria, and on August 9 a second atomic bomb weighing only 6.
The emperor of Japan announced his intent to accept the Potsdam Proclamation and surrender to the Allied forces on August 14, , with a formal surrender occurring on the 2nd of September. These first atomic bombs affected earth, water, air, and all living organisms in the targeted area. The Hiroshima bomb delivered the equivalent energy of The fireball radius was yards with a peak heat close to that of the center of the sun.
These bombs leveled the core of these cities with a huge shock wave moving at the speed of sound and heat radiation moving at the speed of light that, while sustained for only a few seconds, vaporized entire structures and human beings, seriously burned thousands of others, and sowed radiation poisoning in human and animal tissue, water supplies, building remains, and the very earth itself, which would affect generations to come. Robert Oppenheimer, the scientific leader of the Manhattan Project, when viewing the test site explosion at Alamogordo was reminded of the words of Shiva from the Bhagavad Gita, a Vedic text of India, "I am become death, the destroyer of worlds.
Many scientists associated with the Manhattan Project went on to take leading roles in organizations such as the American Nuclear Society, Federation of Atomic later American Scientists, Union of Concerned Scientists, and International Pugwash that sought to stop the spread of nuclear weapons and better educate the public about the brave new world humanity entered with the creation and use of these devices. Einstein expressed deep regret at his own key role in getting the ear of President Roosevelt for Szilard.
Einstein would later write, "the unleashed power of the atom has changed everything save our modes of thinking, and thus we drift toward unparalleled catastrophe Most nuclear scientists, however, went on to further government contract work on the construction of thermonuclear weapons that were more than one thousand times more powerful than those developed during the project or to work on peaceful uses of nuclear energy. Many scientists, joined by other scholars such as Pitirim Sorokin, Ruth Sivard, Alex Roland, Bruce Mazlish, Kenneth Waltz, and John Mearsheimer, agreed with the assessment of the nuclear scientist Donald York that providing these types of implements rendered war on a large scale too horrific to contemplate and consequently saved hundreds of millions of lives in the standoff between the United States and the Soviet Union known as the Cold War — Karl Jaspers , a noted German philosopher, argued in Atombombe und die Zunkunft des Menschen , that an entirely new way of thinking was required after the creation of the atomic bomb.
In the years following the development and deployment of the atomic bomb, the United States and other nations went on to develop more powerful weapons and to repeatedly test them above and below ground. Tens of thousands of civilians and military personnel were exposed to increased amounts of radiation, many unwittingly and unknowingly. The balance of evidence and the opinion of the majority of scientists with expertise who have studied this issue, suggest that for the most part the effects were quite minimal, although whether these low levels of exposure have long-term detrimental health effects can neither be demonstrated nor conclusively denied.
The government of the United States, throughout this period, consistently assured the American public that there were no risks, despite voluminous information from scientists and classified studies they had commissioned that showed such a claim to be preposterous. Various ethical arguments have been advanced against nuclear weapons. For example, some have argued that atomic weapons are "unnatural" and on this basis alone should be banned.
But all armaments beyond sticks and stones fall under the same charge. Massive fire bombings in World War II of British, German, and Japanese cities killed far more civilians and in ways every bit as horrendous. While an atomic weapon is more than the "beautiful physics" that Enrico Fermi declared when asked about any moral qualms he had about working on the bomb, it must be viewed on a long continuum of the technological evolution of warfare.
Whether nations holding nuclear technologies can, and should be able to, prohibit others from acquiring such devices remains an open question to be decided in sociopolitical processes that will include but not be wholly determined by ethical criticism. There is little question that human thought as expressed in writings across a wide range of other subject areas has also been profoundly influenced by the genesis and spread of nuclear weapons.
The future of the world is literally increasingly in the hands of a very small number of individuals.
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Scientists and the Development of Nuclear Weapons: This study portrays the scientific work, ethical and human dimensions, and societal interactions of scientists who worked on nuclear weapons over this period of time. The Nuclear Weapons Debate: Theological and Ethical Issues. Series of essays by theologians and philosophers who take up central issues concerning nuclear weapons.
Examines ramifications of a U. Literature, Physics and the First Atomic Bomb. University of Wisconsin Press. A detailed analysis of a variety of texts produced by physicists before, during and after World War II. Einstein on Peace , ed. Otto Nathan and Heinz Norden. A series of writings on peace by one of the most famous physicists of all time, including many reflections on the nuclear age.
People of the Bomb: Portraits of America's Nuclear Complex. University of Minnesota Press.
Atomic Bomb
A portrait based on fifteen years of research at weapons laboratories that shows how the military-industrial complex built consent for its programs and transformed public culture and personal psychology since the beginning of the nuclear age. University of California Press. A balanced portrait of weapons testing programs in the United States and their effects, including documentary evidence, clinical, and epidemiological studies.
Contains an extensive bibliography.
Hashmi, Sohail, and Steven Lee, eds. Ethics and Weapons of Mass Destruction: Religious and Secular Perspectives. Structured dialogues among representatives of various religious and secular traditions along with essays on weapons of mass destruction and an analysis of existing agreements among nations. Deterrence and the Crisis in Moral Theory: A systematic comparative study of the dominant views on nuclear arms. It suggests the weapons and the plans that accompany them challenge traditional moral reasoning and understandings of the relationship between intentions and actions.
The Making of the Atomic Bomb. The author won a Pulitzer Prize for this massive study that is rich in the human, political, and scientific dimensions of the making and use of the atomic bomb. A Peril and a Hope: The Scientists' Movement in America, —