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11,300 | and also in the now rare apothecaries' system (usually in the form ): but while Roman numerals for whole numbers are essentially decimal does not correspond to , as one might expect, but . | https://en.wikipedia.org/wiki?curid=25657 |
11,301 | The Romans used a duodecimal rather than a decimal system for fractions, as the divisibility of twelve makes it easier to handle the common fractions of and than does a system based on ten . Notation for fractions other than is mainly found on surviving Roman coins, many of which had values that were duodecimal fractions of the unit . Fractions less than are indicated by a dot (·) for each "twelfth", the source of the English words "inch" and "ounce"; dots are repeated for fractions up to five twelfths. Six twelfths (one half), is for "half". "Uncia" dots were added to for fractions from seven to eleven twelfths, just as tallies were added to for whole numbers from six to nine. The arrangement of the dots was variable and not necessarily linear. Five dots arranged like (⁙) (as on the face of a die) are known as a quincunx, from the name of the Roman fraction/coin. The Latin words ' and ' are the source of the English words "sextant" and "quadrant". | https://en.wikipedia.org/wiki?curid=25657 |
11,302 | Each fraction from to had a name in Roman times; these corresponded to the names of the related coins: | https://en.wikipedia.org/wiki?curid=25657 |
11,303 | During the centuries that Roman numerals remained the standard way of writing numbers throughout Europe, there were various extensions to the system designed to indicate larger numbers, none of which were ever standardised. | https://en.wikipedia.org/wiki?curid=25657 |
11,304 | One of these was the "apostrophus", in which 500 was written as , while 1,000 was written as . This is a system of encasing numbers to denote thousands (imagine the s and s as parentheses), which has its origins in Etruscan numeral usage. | https://en.wikipedia.org/wiki?curid=25657 |
11,305 | Each additional set of and surrounding raises the value by a factor of ten: represents 10,000 and represents 100,000. Similarly, each additional to the right of raises the value by a factor of ten: represents 5,000 and represents 50,000. Numerals larger than do not occur. | https://en.wikipedia.org/wiki?curid=25657 |
11,306 | Sometimes was reduced to for 1,000. Similarly, for 5,000 was reduced to ; for 10,000 to ; for 50,000 to (ↇ); and (ↈ) for 100,000 to . | https://en.wikipedia.org/wiki?curid=25657 |
11,307 | John Wallis is often credited for introducing the symbol for infinity , and one conjecture is that he based it on , since 1,000 was hyperbolically used to represent very large numbers. | https://en.wikipedia.org/wiki?curid=25657 |
11,308 | Another system was the "vinculum", in which conventional Roman numerals were multiplied by 1,000 by adding a "bar" or "overline". It was a common alternative to the apostrophic ↀ during the Imperial era: both systems were in simultaneous use around the Roman world (M for '1000' was not in use until the Medieval period). | https://en.wikipedia.org/wiki?curid=25657 |
11,309 | The use of "vinculum" for multiples of 1,000 can be observed, for example, on the milestones erected by Roman soldiers along the Antonine Wall in the mid-2nd century AD. The "vinculum" for marking 1,000s continued in use in the Middle Ages, though it became known more commonly as "titulus". | https://en.wikipedia.org/wiki?curid=25657 |
11,310 | Some modern sources describe the "vinculum" as if it were a part of the current "standard". However, this is purely hypothetical, since no common modern usage requires numbers larger than the current year (). Nonetheless, here are some examples, to give an idea of how it "might" be used: | https://en.wikipedia.org/wiki?curid=25657 |
11,311 | This use of lines is distinct from the custom, once very common, of adding both underline and overline (or very large serifs) to a Roman numeral, simply to make it clear that it "is" a number, e.g. | https://en.wikipedia.org/wiki?curid=25657 |
11,312 | Another medieval usage was the addition of "vertical" lines (or brackets) before and after the numeral to multiply it by 10: thus ' for 10,000 as an alternative form for '. In combination with the overline the bracketed forms might be used to raise the multiplier to ten thousand, thus: | https://en.wikipedia.org/wiki?curid=25657 |
11,313 | This same syntax may also have indicated multiplication by 100 so the above two examples are 800,000 and 2,000,000. | https://en.wikipedia.org/wiki?curid=25657 |
11,314 | The system is closely associated with the ancient city-state of Rome and the Empire that it created. However, due to the scarcity of surviving examples, the origins of the system are obscure and there are several competing theories, all largely conjectural. | https://en.wikipedia.org/wiki?curid=25657 |
11,315 | Rome was founded sometime between 850 and 750 BC. At the time, the region was inhabited by diverse populations of which the Etruscans were the most advanced. The ancient Romans themselves admitted that the basis of much of their civilization was Etruscan. Rome itself was located next to the southern edge of the Etruscan domain, which covered a large part of north-central Italy. | https://en.wikipedia.org/wiki?curid=25657 |
11,316 | The Roman numerals, in particular, are directly derived from the Etruscan number symbols: , , , , and for 1, 5, 10, 50, and 100 (They had more symbols for larger numbers, but it is unknown which symbol represents which number). As in the basic Roman system, the Etruscans wrote the symbols that added to the desired number, from higher to lower value. Thus the number 87, for example, would be written 50 + 10 + 10 + 10 + 5 + 1 + 1 = 𐌣𐌢𐌢𐌢𐌡𐌠𐌠 (this would appear as 𐌠𐌠𐌡𐌢𐌢𐌢𐌣 since Etruscan was written from right to left.) | https://en.wikipedia.org/wiki?curid=25657 |
11,317 | The symbols and resembled letters of the Etruscan alphabet, but , , and did not. The Etruscans used the subtractive notation, too, but not like the Romans. They wrote 17, 18, and 19 as 𐌠𐌠𐌠𐌢𐌢, 𐌠𐌠𐌢𐌢, and 𐌠𐌢𐌢, mirroring the way they spoke those numbers ("three from twenty", etc.); and similarly for 27, 28, 29, 37, 38, etc. However, they did not write 𐌠𐌡 for 4 (nor 𐌢𐌣 for 40), and wrote 𐌡𐌠𐌠, 𐌡𐌠𐌠𐌠 and 𐌡𐌠𐌠𐌠𐌠 for 7, 8, and 9, respectively. | https://en.wikipedia.org/wiki?curid=25657 |
11,318 | The early Roman numerals for 1, 10, and 100 were the Etruscan ones: , , and . The symbols for 5 and 50 changed from and to and at some point. The latter had flattened to (an inverted T) by the time of Augustus, and soon afterwards became identified with the graphically similar letter . | https://en.wikipedia.org/wiki?curid=25657 |
11,319 | The symbol for 100 was written variously as or , and was then abbreviated to or , with (which matched the Latin letter "C") finally winning out. It might have helped that "C" was the initial letter of "CENTUM", Latin for "hundred". | https://en.wikipedia.org/wiki?curid=25657 |
11,320 | The numbers 500 and 1000 were denoted by or overlaid with a box or circle. Thus 500 was like a superimposed on a . It became or by the time of Augustus, under the graphic influence of the letter . It was later identified as the letter ; an alternative symbol for "thousand" was a , and half of a thousand or "five hundred" is the right half of the symbol, , and this may have been converted into . | https://en.wikipedia.org/wiki?curid=25657 |
11,321 | The notation for 1000 was a circled or boxed : Ⓧ, , , and by Augustinian times was partially identified with the Greek letter "phi". Over time, the symbol changed to and . The latter symbol further evolved into , then , and eventually changed to under the influence of the Latin word "mille" "thousand". | https://en.wikipedia.org/wiki?curid=25657 |
11,322 | According to Paul Kayser, the basic numerical symbols were , , and (or ) and the intermediate ones were derived by taking half of those (half an is , half a is and half a is ). | https://en.wikipedia.org/wiki?curid=25657 |
11,323 | The Colosseum was constructed in Rome in CE 72–80, and while the original perimeter wall has largely disappeared, the numbered entrances from (23) to (54) survive, to demonstrate that in Imperial times Roman numerals had already assumed their classical form: as largely standardised in current use. The most obvious anomaly (a common one that persisted for centuries) is the inconsistent use of subtractive notation - while is used for 40, is avoided in favour of : in fact gate 44 is labelled . | https://en.wikipedia.org/wiki?curid=25657 |
11,324 | Lower case, or "minuscule", letters were developed in the Middle Ages, well after the demise of the Western Roman Empire, and since that time lower-case versions of Roman numbers have also been commonly used: , , , , and so on. | https://en.wikipedia.org/wiki?curid=25657 |
11,325 | Since the Middle Ages, a "" has sometimes been substituted for the final "" of a "lower-case" Roman numeral, such as "" for 3 or "" for 7. This "" can be considered a swash variant of "". Into the early 20th century, the use of a final "" was still sometimes used in medical prescriptions to prevent tampering with or misinterpretation of a number after it was written. | https://en.wikipedia.org/wiki?curid=25657 |
11,326 | Numerals in documents and inscriptions from the Middle Ages sometimes include additional symbols, which today are called "medieval Roman numerals". Some simply substitute another letter for the standard one (such as "" for "", or "" for ""), while others serve as abbreviations for compound numerals ("" for "", or "" for ""). Although they are still listed today in some dictionaries, they are long out of use. | https://en.wikipedia.org/wiki?curid=25657 |
11,327 | Chronograms, messages with dates encoded into them, were popular during the Renaissance era. The chronogram would be a phrase containing the letters , , , , , , and . By putting these letters together, the reader would obtain a number, usually indicating a particular year. | https://en.wikipedia.org/wiki?curid=25657 |
11,328 | By the 11th century, Arabic numerals had been introduced into Europe from al-Andalus, by way of Arab traders and arithmetic treatises. Roman numerals, however, proved very persistent, remaining in common use in the West well into the 14th and 15th centuries, even in accounting and other business records (where the actual calculations would have been made using an abacus). Replacement by their more convenient "Arabic" equivalents was quite gradual, and Roman numerals are still used today in certain contexts. A few examples of their current use are: | https://en.wikipedia.org/wiki?curid=25657 |
11,329 | In astronautics, United States rocket model variants are sometimes designated by Roman numerals, e.g. Titan I, Titan II, Titan III, Saturn I, Saturn V. | https://en.wikipedia.org/wiki?curid=25657 |
11,330 | In astronomy, the natural satellites or "moons" of the planets are traditionally designated by capital Roman numerals appended to the planet's name. For example, Titan's designation is Saturn . | https://en.wikipedia.org/wiki?curid=25657 |
11,331 | In chemistry, Roman numerals are often used to denote the groups of the periodic table. They are also used in the IUPAC nomenclature of inorganic chemistry, for the oxidation number of cations which can take on several different positive charges. They are also used for naming phases of polymorphic crystals, such as ice. | https://en.wikipedia.org/wiki?curid=25657 |
11,332 | In education, school grades (in the sense of year-groups rather than test scores) are sometimes referred to by a Roman numeral; for example, "grade " is sometimes seen for "grade 9". | https://en.wikipedia.org/wiki?curid=25657 |
11,333 | In entomology, the broods of the thirteen and seventeen year periodical cicadas are identified by Roman numerals. | https://en.wikipedia.org/wiki?curid=25657 |
11,334 | In law, Roman numerals are commonly used to help organize legal codes as part of an alphanumeric outline. | https://en.wikipedia.org/wiki?curid=25657 |
11,335 | In advanced mathematics (including trigonometry, statistics, and calculus), when a graph includes negative numbers, its quadrants are named using , , , and . These quadrant names signify positive numbers on both axes, negative numbers on the X axis, negative numbers on both axes, and negative numbers on the Y axis, respectively. The use of Roman numerals to designate quadrants avoids confusion, since Arabic numerals are used for the actual data represented in the graph. | https://en.wikipedia.org/wiki?curid=25657 |
11,336 | In military unit designation, Roman numerals are often used to distinguish between units at different levels. This reduces possible confusion, especially when viewing operational or strategic level maps. In particular, army corps are often numbered using Roman numerals (for example the American XVIII Airborne Corps or the WW2-era German III Panzerkorps) with Arabic numerals being used for divisions and armies. | https://en.wikipedia.org/wiki?curid=25657 |
11,337 | In pharmacy, Roman numerals were used with the now largely obsolete apothecaries' system of measurement: including to denote "one half" and to denote "zero". | https://en.wikipedia.org/wiki?curid=25657 |
11,338 | In photography, Roman numerals (with zero) are used to denote varying levels of brightness when using the Zone System. | https://en.wikipedia.org/wiki?curid=25657 |
11,339 | In seismology, Roman numerals are used to designate degrees of the Mercalli intensity scale of earthquakes. | https://en.wikipedia.org/wiki?curid=25657 |
11,340 | In sport the team containing the "top" players and representing a nation or province, a club or a school at the highest level in (say) rugby union is often called the "1st ", while a lower-ranking cricket or American football team might be the "3rd ". | https://en.wikipedia.org/wiki?curid=25657 |
11,341 | In theology and biblical scholarship, the Septuagint is often referred to as , as this translation of the Old Testament into Greek is named for the legendary number of its translators ("septuaginta" being Latin for "seventy"). | https://en.wikipedia.org/wiki?curid=25657 |
11,342 | Some uses that are rare or never seen in English speaking countries may be relatively common in parts of continental Europe and in other regions (e.g. Latin America) that use a European language other than English. For instance: | https://en.wikipedia.org/wiki?curid=25657 |
11,343 | Capital or small capital Roman numerals are widely used in Romance languages to denote , e.g. the French ' and the Spanish ' mean "18th century". Slavic languages in and adjacent to Russia similarly favor Roman numerals (). On the other hand, in Slavic languages in Central Europe, like most Germanic languages, one writes "18." (with a period) before the local word for "century". | https://en.wikipedia.org/wiki?curid=25657 |
11,344 | Mixed Roman and Arabic numerals are sometimes used in numeric representations of dates (especially in formal letters and official documents, but also on tombstones). The is written in Roman numerals, while the day is in Arabic numerals: "4..1789" and ".4.1789" both refer unambiguously to 4 June 1789. | https://en.wikipedia.org/wiki?curid=25657 |
11,345 | Roman numerals are sometimes used to represent the in hours-of-operation signs displayed in windows or on doors of businesses, and also sometimes in railway and bus timetables. Monday, taken as the first day of the week, is represented by . Sunday is represented by . The hours of operation signs are tables composed of two columns where the left column is the day of the week in Roman numerals and the right column is a range of hours of operation from starting time to closing time. In the example case (left), the business opens from 10 AM to 7 PM on weekdays, 10 AM to 5 PM on Saturdays and is closed on Sundays. Note that the listing uses 24-hour time. | https://en.wikipedia.org/wiki?curid=25657 |
11,346 | Roman numerals may also be used for floor numbering. For instance, apartments in central Amsterdam are indicated as 138-, with both an Arabic numeral (number of the block or house) and a Roman numeral (floor number). The apartment on the ground floor is indicated as . | https://en.wikipedia.org/wiki?curid=25657 |
11,347 | In Italy, where roads outside built-up areas have kilometre signs, major roads and motorways also mark 100-metre subdivisionals, using Roman numerals from to for the smaller intervals. The sign thus marks 17.9 km. | https://en.wikipedia.org/wiki?curid=25657 |
11,348 | Certain romance-speaking countries use Roman numerals to designate assemblies of their national legislatures. For instance, the composition of the Italian Parliament from 2018 to 2022 (elected in the 2018 Italian general election) is called the XVIII Legislature of the Italian Republic (or more commonly the "XVIII Legislature"). | https://en.wikipedia.org/wiki?curid=25657 |
11,349 | A notable exception to the use of Roman numerals in Europe is in Greece, where Greek numerals (based on the Greek alphabet) are generally used in contexts where Roman numerals would be used elsewhere. | https://en.wikipedia.org/wiki?curid=25657 |
11,350 | The "Number Forms" block of the Unicode computer character set standard has a number of Roman numeral symbols in the range of code points from U+2160 to U+2188. This range includes both upper- and lowercase numerals, as well as pre-combined characters for numbers up to 12 (Ⅻ or ). One justification for the existence of pre-combined numbers is to facilitate the setting of multiple-letter numbers (such as VIII) on a single horizontal line in Asian vertical text. The Unicode standard, however, includes special Roman numeral code points for compatibility only, stating that "[f]or most purposes, it is preferable to compose the Roman numerals from sequences of the appropriate Latin letters". | https://en.wikipedia.org/wiki?curid=25657 |
11,351 | The block also includes some "apostrophus" symbols for large numbers, an old variant of "L" (50) similar to the Etruscan character, the Claudian letter "reversed C", etc. | https://en.wikipedia.org/wiki?curid=25657 |
11,352 | Parag Agrawal (; born 21 May 1984) is an Indian-American software engineer who was the CEO of Twitter, Inc. from November 2021 to October 2022. He was fired, along with three other top executives, on October 27, 2022, following Elon Musk’s purchase of the company. | https://en.wikipedia.org/wiki?curid=65507391 |
11,353 | Agrawal was born in Ajmer, Rajasthan. His father was a senior official in the Indian Department of Atomic Energy and his mother is a retired Economics professor from Veermata Jijabai Technological Institute in Mumbai. | https://en.wikipedia.org/wiki?curid=65507391 |
11,354 | In 2001, he completed his Class XII at Atomic Energy Junior College, Mumbai. In the same year, he secured a gold medal in the International Physics Olympiad held in Antalya, Turkey. | https://en.wikipedia.org/wiki?curid=65507391 |
11,355 | In 2005, Agrawal obtained his Bachelor of Technology degree in computer science and engineering from IIT Bombay. That year, he moved to the United States to pursue a PhD in computer science at Stanford University under the guidance of Jennifer Widom. His Stanford doctoral thesis, published in 2012, is titled "Incorporating Uncertainty in Data Management and Integration". | https://en.wikipedia.org/wiki?curid=65507391 |
11,356 | Agrawal held research internships at Microsoft Research and Yahoo! Research before joining Twitter as a software engineer in 2011. In October 2017, Twitter announced the appointment of Agrawal as chief technology officer following the departure of Adam Messinger. In December 2019, Twitter CEO Jack Dorsey announced that Agrawal would be in charge of Project Bluesky, an initiative to develop a decentralized social network protocol. | https://en.wikipedia.org/wiki?curid=65507391 |
11,357 | On November 29, 2021, Dorsey announced that he was resigning as CEO of Twitter and that Agrawal was replacing him immediately. As CEO, Agrawal was awarded annual compensation of $1 million as well as stock compensation worth $12.5 million. Agrawal was fired as CEO once Elon Musk completed his acquisition of the company on October 27, 2022. | https://en.wikipedia.org/wiki?curid=65507391 |
11,358 | In an interview with "MIT Technology Review" in November 2020, when asked about freedom of speech regarding Twitter, Agrawal said: "Our role is not to be bound by the First Amendment, but our role is to serve a healthy public conversation ... [and to] focus less on thinking about free speech, but thinking about how the times have changed." | https://en.wikipedia.org/wiki?curid=65507391 |
11,359 | Agrawal is married to Vineeta Agarwala, general partner at the venture capital firm Andreessen Horowitz. They have two children, born in 2011 and 2022. He took paternity leave as the CEO of Twitter for the birth of his second child. | https://en.wikipedia.org/wiki?curid=65507391 |
11,360 | A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter. | https://en.wikipedia.org/wiki?curid=21785 |
11,361 | 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 . Nuclear bombs have had yields between 10 tons TNT (the W54) and 50 megatons for the Tsar Bomba (see TNT equivalent). A thermonuclear weapon weighing as little as can release energy equal to more than . | https://en.wikipedia.org/wiki?curid=21785 |
11,362 | A nuclear device no larger than a conventional bomb 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. Nuclear weapons have been deployed twice in war, by the United States against the Japanese cities of Hiroshima and Nagasaki in 1945 during World War II. | https://en.wikipedia.org/wiki?curid=21785 |
11,363 | Nuclear weapons have only twice been used in war, both times by the United States against Japan near the end of World War II. On August 6, 1945, the U.S. Army Air Forces detonated a uranium gun-type fission bomb nicknamed "Little Boy" over the Japanese city of Hiroshima; three days later, on August 9, the U.S. Army Air Forces detonated a plutonium implosion-type fission bomb nicknamed "Fat Man" over the Japanese city of Nagasaki. These bombings caused injuries that resulted in the deaths of approximately 200,000 civilians and military personnel. The ethics of these bombings and their role in Japan's surrender are subjects of debate. | https://en.wikipedia.org/wiki?curid=21785 |
11,364 | Since the atomic bombings of Hiroshima and Nagasaki, nuclear weapons have been detonated over 2,000 times for testing and demonstration. Only a few nations possess such weapons or are suspected of seeking them. The only countries known to have detonated nuclear weapons—and acknowledge possessing them—are (chronologically by date of first test) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United Kingdom, France, China, India, Pakistan, and North Korea. Israel is believed to possess nuclear weapons, though, in a policy of deliberate ambiguity, it does not acknowledge having them. Germany, Italy, Turkey, Belgium and the Netherlands are nuclear weapons sharing states. South Africa is the only country to have independently developed and then renounced and dismantled its nuclear weapons. | https://en.wikipedia.org/wiki?curid=21785 |
11,365 | The Treaty on the Non-Proliferation of Nuclear Weapons aims to reduce the spread of nuclear weapons, but its effectiveness has been questioned. Modernisation of weapons continues to this day. | https://en.wikipedia.org/wiki?curid=21785 |
11,366 | There are two basic types of nuclear weapons: those that derive the majority of their energy from nuclear fission reactions alone, and those that use fission reactions to begin nuclear fusion reactions that produce a large amount of the total energy output. | https://en.wikipedia.org/wiki?curid=21785 |
11,367 | All existing nuclear weapons derive some of their explosive energy from nuclear fission reactions. Weapons whose explosive output is exclusively from fission reactions are commonly referred to as atomic bombs or atom bombs (abbreviated as A-bombs). This has long been noted as something of a misnomer, as their energy comes from the nucleus of the atom, just as it does with fusion weapons. | https://en.wikipedia.org/wiki?curid=21785 |
11,368 | In fission weapons, a mass of fissile material (enriched uranium or plutonium) is forced into supercriticality—allowing an exponential growth of nuclear chain reactions—either by shooting one piece of sub-critical material into another (the "gun" method) or by compression of a sub-critical sphere or cylinder of fissile material using chemically fueled explosive lenses. The latter approach, the "implosion" method, is more sophisticated and more efficient (smaller, less massive, and requiring less of the expensive fissile fuel) than the former. | https://en.wikipedia.org/wiki?curid=21785 |
11,369 | A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range from the equivalent of just under a ton to upwards of 500,000 tons (500 kilotons) of TNT (). | https://en.wikipedia.org/wiki?curid=21785 |
11,370 | All fission reactions generate fission products, the remains of the split atomic nuclei. Many fission products are either highly radioactive (but short-lived) or moderately radioactive (but long-lived), and as such, they are a serious form of radioactive contamination. Fission products are the principal radioactive component of nuclear fallout. Another source of radioactivity is the burst of free neutrons produced by the weapon. When they collide with other nuclei in the surrounding material, the neutrons transmute those nuclei into other isotopes, altering their stability and making them radioactive. | https://en.wikipedia.org/wiki?curid=21785 |
11,371 | The most commonly used fissile materials for nuclear weapons applications have been uranium-235 and plutonium-239. Less commonly used has been uranium-233. Neptunium-237 and some isotopes of americium may be usable for nuclear explosives as well, but it is not clear that this has ever been implemented, and their plausible use in nuclear weapons is a matter of dispute. | https://en.wikipedia.org/wiki?curid=21785 |
11,372 | 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. | https://en.wikipedia.org/wiki?curid=21785 |
11,373 | Only six countries—United States, Russia, United Kingdom, China, France, and India—have conducted thermonuclear weapon tests. Whether India has detonated a "true" multi-staged thermonuclear weapon is controversial. North Korea claims to have tested a fusion weapon , though this claim is disputed. Thermonuclear weapons are considered much more difficult to successfully design and execute than primitive fission weapons. Almost all of the nuclear weapons deployed today use the thermonuclear design because it is more efficient. | https://en.wikipedia.org/wiki?curid=21785 |
11,374 | Thermonuclear bombs work by using the energy of a fission bomb to compress and heat fusion fuel. In the Teller-Ulam design, which accounts for all multi-megaton yield hydrogen bombs, this is accomplished by placing a fission bomb and fusion fuel (tritium, deuterium, or lithium deuteride) in proximity within a special, radiation-reflecting container. When the fission bomb is detonated, gamma rays and X-rays emitted first compress the fusion fuel, then heat it to thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high-speed neutrons, which can then induce fission in materials not normally prone to it, such as depleted uranium. Each of these components is known as a "stage", with the fission bomb as the "primary" and the fusion capsule as the "secondary". In large, megaton-range hydrogen bombs, about half of the yield comes from the final fissioning of depleted uranium. | https://en.wikipedia.org/wiki?curid=21785 |
11,375 | Virtually all thermonuclear weapons deployed today use the "two-stage" design described above, but it is possible to add additional fusion stages—each stage igniting a larger amount of fusion fuel in the next stage. This technique can be used to construct thermonuclear weapons of arbitrarily large yield. This is in contrast to fission bombs, which are limited in their explosive power due to criticality danger (premature nuclear chain reaction caused by too-large amounts of pre-assembled fissile fuel). The largest nuclear weapon ever detonated, the Tsar Bomba of the USSR, which released an energy equivalent of over , was a three-stage weapon. Most thermonuclear weapons are considerably smaller than this, due to practical constraints from missile warhead space and weight requirements. | https://en.wikipedia.org/wiki?curid=21785 |
11,376 | Fusion reactions do not create fission products, and thus contribute far less to the creation of nuclear fallout than fission reactions, but because all thermonuclear weapons contain at least one fission stage, and many high-yield thermonuclear devices have a final fission stage, thermonuclear weapons can generate at least as much nuclear fallout as fission-only weapons. Furthermore, high yield thermonuclear explosions (most dangerously ground bursts) have the force to lift radioactive debris upwards past the tropopause into the stratosphere, where the calm non-turbulent winds permit the debris to travel great distances from the burst, eventually settling and unpredictably contaminating areas far removed from the target of the explosion. | https://en.wikipedia.org/wiki?curid=21785 |
11,377 | There are other types of nuclear weapons as well. For example, a boosted fission weapon is a fission bomb that increases its explosive yield through a small number of fusion reactions, but it is not a fusion bomb. In the boosted bomb, the neutrons produced by the fusion reactions serve primarily to increase the efficiency of the fission bomb. There are two types of boosted fission bomb: internally boosted, in which a deuterium-tritium mixture is injected into the bomb core, and externally boosted, in which concentric shells of lithium-deuteride and depleted uranium are layered on the outside of the fission bomb core. The external method of boosting enabled the USSR to field the first partially-thermonuclear weapons, but it is now obsolete because it demands a spherical bomb geometry, which was adequate during the 1950s arms race when bomber aircraft were the only available delivery vehicles. | https://en.wikipedia.org/wiki?curid=21785 |
11,378 | The detonation of any nuclear weapon is accompanied by a blast of neutron radiation. Surrounding a nuclear weapon with suitable materials (such as cobalt or gold) creates a weapon known as a salted bomb. This device can produce exceptionally large quantities of long-lived radioactive contamination. It has been conjectured that such a device could serve as a "doomsday weapon" because such a large quantity of radioactivities with half-lives of decades, lifted into the stratosphere where winds would distribute it around the globe, would make all life on the planet extinct. | https://en.wikipedia.org/wiki?curid=21785 |
11,379 | In connection with the Strategic Defense Initiative, research into the nuclear pumped laser was conducted under the DOD program Project Excalibur but this did not result in a working weapon. The concept involves the tapping of the energy of an exploding nuclear bomb to power a single-shot laser that is directed at a distant target. | https://en.wikipedia.org/wiki?curid=21785 |
11,380 | During the Starfish Prime high-altitude nuclear test in 1962, an unexpected effect was produced which is called a nuclear electromagnetic pulse. This is an intense flash of electromagnetic energy produced by a rain of high-energy electrons which in turn are produced by a nuclear bomb's gamma rays. This flash of energy can permanently destroy or disrupt electronic equipment if insufficiently shielded. It has been proposed to use this effect to disable an enemy's military and civilian infrastructure as an adjunct to other nuclear or conventional military operations. By itself it could as well be useful to terrorists for crippling a nation's economic electronics-based infrastructure. Because the effect is most effectively produced by high altitude nuclear detonations (by military weapons delivered by air, though ground bursts also produce EMP effects over a localized area), it can produce damage to electronics over a wide, even continental, geographical area. | https://en.wikipedia.org/wiki?curid=21785 |
11,381 | Research has been done into the possibility of pure fusion bombs: nuclear weapons that consist of fusion reactions without requiring a fission bomb to initiate them. Such a device might provide a simpler path to thermonuclear weapons than one that required the development of fission weapons first, and pure fusion weapons would create significantly less nuclear fallout than other thermonuclear weapons because they would not disperse fission products. In 1998, the United States Department of Energy divulged that the United States had, "...made a substantial investment" in the past to develop pure fusion weapons, but that, "The U.S. does not have and is not developing a pure fusion weapon", and that, "No credible design for a pure fusion weapon resulted from the DOE investment". | https://en.wikipedia.org/wiki?curid=21785 |
11,382 | Nuclear isomers provide a possible pathway to fissionless fusion bombs. These are naturally occurring isotopes (Hf being a prominent example) which exist in an elevated energy state. Mechanisms to release this energy as bursts of gamma radiation (as in the hafnium controversy) have been proposed as possible triggers for conventional thermonuclear reactions. | https://en.wikipedia.org/wiki?curid=21785 |
11,383 | Antimatter, which consists of particles resembling ordinary matter particles in most of their properties but having opposite electric charge, has been considered as a trigger mechanism for nuclear weapons. A major obstacle is the difficulty of producing antimatter in large enough quantities, and there is no evidence that it is feasible beyond the military domain. However, the U.S. Air Force funded studies of the physics of antimatter in the Cold War, and began considering its possible use in weapons, not just as a trigger, but as the explosive itself. A fourth generation nuclear weapon design is related to, and relies upon, the same principle as antimatter-catalyzed nuclear pulse propulsion. | https://en.wikipedia.org/wiki?curid=21785 |
11,384 | Most variation in nuclear weapon design is for the purpose of achieving different yields for different situations, and in manipulating design elements to attempt to minimize weapon size, radiation hardness or requirements for special materials, especially fissile fuel or tritium. | https://en.wikipedia.org/wiki?curid=21785 |
11,385 | Some nuclear weapons are designed for special purposes; most of these are for non-strategic (decisively war-winning) purposes and are referred to as tactical nuclear weapons. | https://en.wikipedia.org/wiki?curid=21785 |
11,386 | The neutron bomb purportedly conceived by Sam Cohen is a thermonuclear weapon that yields a relatively small explosion but a relatively large amount of neutron radiation. Such a weapon could, according to tacticians, be used to cause massive biological casualties while leaving inanimate infrastructure mostly intact and creating minimal fallout. Because high energy neutrons are capable of penetrating dense matter, such as tank armor, neutron warheads were procured in the 1980s (though not deployed in Europe, as intended, over the objections of NATO allies) for use as tactical payloads for US Army artillery shells (200 mm W79 and 155 mm W82) and short range missile forces. Soviet authorities announced similar intentions for neutron warhead deployment in Europe; indeed claimed to have originally invented the neutron bomb, but their deployment on USSR tactical nuclear forces is unverifiable. | https://en.wikipedia.org/wiki?curid=21785 |
11,387 | A type of nuclear explosive most suitable for use by ground special forces was the Special Atomic Demolition Munition, or SADM, sometimes popularly known as a suitcase nuke. This is a nuclear bomb that is man-portable, or at least truck-portable, and though of a relatively small yield (one or two kilotons) is sufficient to destroy important tactical targets such as bridges, dams, tunnels, important military or commercial installations, etc. either behind enemy lines or pre-emptively on friendly territory soon to be overtaken by invading enemy forces. These weapons require plutonium fuel and are particularly "dirty". Obviously they also demand especially stringent security precautions in their storage and deployment. | https://en.wikipedia.org/wiki?curid=21785 |
11,388 | Small "tactical" nuclear weapons were deployed for use as antiaircraft weapons. Examples include the USAF AIR-2 Genie, the AIM-26 Falcon and US Army Nike Hercules. Missile interceptors such as the Sprint and the Spartan also used small nuclear warheads (optimized to produce neutron or X-ray flux) but were for use against enemy strategic warheads. | https://en.wikipedia.org/wiki?curid=21785 |
11,389 | Other small, or tactical, nuclear weapons were deployed by naval forces for use primarily as antisubmarine weapons. These included nuclear depth bombs or nuclear armed torpedoes. Nuclear mines for use on land or at sea are also possibilities. | https://en.wikipedia.org/wiki?curid=21785 |
11,390 | The system used to deliver a nuclear weapon to its target is an important factor affecting both nuclear weapon design and nuclear strategy. The design, development, and maintenance of delivery systems are among the most expensive parts of a nuclear weapons program; they account, for example, for 57% of the financial resources spent by the United States on nuclear weapons projects since 1940. | https://en.wikipedia.org/wiki?curid=21785 |
11,391 | The simplest method for delivering a nuclear weapon is a gravity bomb dropped from aircraft; this was the method used by the United States against Japan. This method places few restrictions on the size of the weapon. It does, however, limit attack range, response time to an impending attack, and the number of weapons that a country can field at the same time. With miniaturization, nuclear bombs can be delivered by both strategic bombers and tactical fighter-bombers. This method is the primary means of nuclear weapons delivery; the majority of U.S. nuclear warheads, for example, are free-fall gravity bombs, namely the B61. | https://en.wikipedia.org/wiki?curid=21785 |
11,392 | Preferable from a strategic point of view is a nuclear weapon mounted on a missile, which can use a ballistic trajectory to deliver the warhead over the horizon. Although even short-range missiles allow for a faster and less vulnerable attack, the development of long-range intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) has given some nations the ability to plausibly deliver missiles anywhere on the globe with a high likelihood of success. | https://en.wikipedia.org/wiki?curid=21785 |
11,393 | More advanced systems, such as multiple independently targetable reentry vehicles (MIRVs), can launch multiple warheads at different targets from one missile, reducing the chance of a successful missile defense. Today, missiles are most common among systems designed for delivery of nuclear weapons. Making a warhead small enough to fit onto a missile, though, can be difficult. | https://en.wikipedia.org/wiki?curid=21785 |
11,394 | Tactical weapons have involved the most variety of delivery types, including not only gravity bombs and missiles but also artillery shells, land mines, and nuclear depth charges and torpedoes for anti-submarine warfare. An atomic mortar has been tested by the United States. Small, two-man portable tactical weapons (somewhat misleadingly referred to as suitcase bombs), such as the Special Atomic Demolition Munition, have been developed, although the difficulty of combining sufficient yield with portability limits their military utility. | https://en.wikipedia.org/wiki?curid=21785 |
11,395 | Nuclear warfare strategy is a set of policies that deal with preventing or fighting a nuclear war. The policy of trying to prevent an attack by a nuclear weapon from another country by threatening nuclear retaliation is known as the strategy of nuclear deterrence. The goal in deterrence is to always maintain a second strike capability (the ability of a country to respond to a nuclear attack with one of its own) and potentially to strive for first strike status (the ability to destroy an enemy's nuclear forces before they could retaliate). During the Cold War, policy and military theorists considered the sorts of policies that might prevent a nuclear attack, and they developed game theory models that could lead to stable deterrence conditions. | https://en.wikipedia.org/wiki?curid=21785 |
11,396 | Different forms of nuclear weapons delivery (see above) allow for different types of nuclear strategies. The goals of any strategy are generally to make it difficult for an enemy to launch a pre-emptive strike against the weapon system and difficult to defend against the delivery of the weapon during a potential conflict. This can mean keeping weapon locations hidden, such as deploying them on submarines or land mobile transporter erector launchers whose locations are difficult to track, or it can mean protecting weapons by burying them in hardened missile silo bunkers. Other components of nuclear strategies included using missile defenses to destroy the missiles before they land, or implementing civil defense measures using early-warning systems to evacuate citizens to safe areas before an attack. | https://en.wikipedia.org/wiki?curid=21785 |
11,397 | Weapons designed to threaten large populations or to deter attacks are known as "strategic weapons." Nuclear weapons for use on a battlefield in military situations are called "tactical weapons." | https://en.wikipedia.org/wiki?curid=21785 |
11,398 | Critics of nuclear war strategy often suggest that a nuclear war between two nations would result in mutual annihilation. From this point of view, the significance of nuclear weapons is to deter war because any nuclear war would escalate out of mutual distrust and fear, resulting in mutually assured destruction. This threat of national, if not global, destruction has been a strong motivation for anti-nuclear weapons activism. | https://en.wikipedia.org/wiki?curid=21785 |
11,399 | Critics from the peace movement and within the military establishment have questioned the usefulness of such weapons in the current military climate. According to an advisory opinion issued by the International Court of Justice in 1996, the use of (or threat of use of) such weapons would generally be contrary to the rules of international law applicable in armed conflict, but the court did not reach an opinion as to whether or not the threat or use would be lawful in specific extreme circumstances such as if the survival of the state were at stake. | https://en.wikipedia.org/wiki?curid=21785 |
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