title: Biotechnology

text: The field of modern biotechnology is generally thought of as having been born in 1971 when Paul Berg's (Stanford) experiments in gene splicing had early success. Herbert W. Boyer (Univ. Calif. at San Francisco) and Stanley N. Cohen (Stanford) significantly advanced the new technology in 1972 by transferring genetic material into a bacterium, such that the imported material would be reproduced. The commercial viability of a biotechnology industry was significantly expanded on June 16, 1980, when the United States Supreme Court ruled that a genetically modified microorganism could be patented in the case of "Diamond v. Chakrabarty". Indian-born Ananda Chakrabarty, working for General Electric, had modified a bacterium (of the genus "Pseudomonas") capable of breaking down crude oil, which he proposed to use in treating oil spills. (Chakrabarty's work did not involve gene manipulation but rather the transfer of entire organelles between strains of the "Pseudomonas" bacterium).


title: Biotechnology

text: The MOSFET (metal-oxide-semiconductor field-effect transistor) was invented by Mohamed M. Atalla and Dawon Kahng in 1959. Two years later, Leland C. Clark and Champ Lyons invented the first biosensor in 1962. Biosensor MOSFETs were later developed, and they have since been widely used to measure physical, chemical, biological and environmental parameters. The first BioFET was the ion-sensitive field-effect transistor (ISFET), invented by Piet Bergveld in 1970. It is a special type of MOSFET, where the metal gate is replaced by an ion-sensitive membrane, electrolyte solution and reference electrode. The ISFET is widely used in biomedical applications, such as the detection of DNA hybridization, biomarker detection from blood, antibody detection, glucose measurement, pH sensing, and genetic technology.


title: Biotechnology

text: By the mid-1980s, other BioFETs had been developed, including the gas sensor FET (GASFET), pressure sensor FET (PRESSFET), chemical field-effect transistor (ChemFET), reference ISFET (REFET), enzyme-modified FET (ENFET) and immunologically modified FET (IMFET). By the early 2000s, BioFETs such as the DNA field-effect transistor (DNAFET), gene-modified FET (GenFET) and cell-potential BioFET (CPFET) had been developed.


title: Biotechnology

text: A factor influencing the biotechnology sector's success is improved intellectual property rights legislation—and enforcement—worldwide, as well as strengthened demand for medical and pharmaceutical products to cope with an ageing, and ailing, U.S. population.


title: Biotechnology

text: Rising demand for biofuels is expected to be good news for the biotechnology sector, with the Department of Energy estimating ethanol usage could reduce U.S. petroleum-derived fuel consumption by up to 30% by 2030. The biotechnology sector has allowed the U.S. farming industry to rapidly increase its supply of corn and soybeans—the main inputs into biofuels—by developing genetically modified seeds that resist pests and drought. By increasing farm productivity, biotechnology boosts biofuel production.


title: Biotechnology

text: Biotechnology has applications in four major industrial areas, including health care (medical), crop production and agriculture, non-food (industrial) uses of crops and other products (e.g., biodegradable plastics, vegetable oil, biofuels), and environmental uses.


title: Biotechnology

text: For example, one application of biotechnology is the directed use of microorganisms for the manufacture of organic products (examples include beer and milk products). Another example is using naturally present bacteria by the mining industry in bioleaching. Biotechnology is also used to recycle, treat waste, clean up sites contaminated by industrial activities (bioremediation), and also to produce biological weapons.


title: Biotechnology

text: A series of derived terms have been coined to identify several branches of biotechnology, for example:


title: Biotechnology

text: In medicine, modern biotechnology has many applications in areas such as pharmaceutical drug discoveries and production, pharmacogenomics, and genetic testing (or genetic screening).


title: Biotechnology

text: Pharmacogenomics (a combination of pharmacology and genomics) is the technology that analyses how genetic makeup affects an individual's response to drugs. Researchers in the field investigate the influence of genetic variation on drug responses in patients by correlating gene expression or single-nucleotide polymorphisms with a drug's efficacy or toxicity. The purpose of pharmacogenomics is to develop rational means to optimize drug therapy, with respect to the patients' genotype, to ensure maximum efficacy with minimal adverse effects. Such approaches promise the advent of "personalized medicine"; in which drugs and drug combinations are optimized for each individual's unique genetic makeup.


title: Biotechnology

text: Biotechnology has contributed to the discovery and manufacturing of traditional small molecule pharmaceutical drugs as well as drugs that are the product of biotechnology – biopharmaceutics. Modern biotechnology can be used to manufacture existing medicines relatively easily and cheaply. The first genetically engineered products were medicines designed to treat human diseases. To cite one example, in 1978 Genentech developed synthetic humanized insulin by joining its gene with a plasmid vector inserted into the bacterium "Escherichia coli". Insulin, widely used for the treatment of diabetes, was previously extracted from the pancreas of abattoir animals (cattle or pigs). The genetically engineered bacteria are able to produce large quantities of synthetic human insulin at relatively low cost. Biotechnology has also enabled emerging therapeutics like gene therapy. The application of biotechnology to basic science (for example through the Human Genome Project) has also dramatically improved our understanding of biology and as our scientific knowledge of normal and disease biology has increased, our ability to develop new medicines to treat previously untreatable diseases has increased as well.


title: Biotechnology

text: Genetic testing allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a child's parentage (genetic mother and father) or in general a person's ancestry. In addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders. Genetic testing identifies changes in chromosomes, genes, or proteins. Most of the time, testing is used to find changes that are associated with inherited disorders. The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person's chance of developing or passing on a genetic disorder. As of 2011 several hundred genetic tests were in use. Since genetic testing may open up ethical or psychological problems, genetic testing is often accompanied by genetic counseling.


title: Biotechnology

text: Genetically modified crops ("GM crops", or "biotech crops") are plants used in agriculture, the DNA of which has been modified with genetic engineering techniques. In most cases, the main aim is to introduce a new trait that does not occur naturally in the species. Biotechnology firms can contribute to future food security by improving the nutrition and viability of urban agriculture. Furthermore, the protection of intellectual property rights encourages private sector investment in agrobiotechnology.


title: Biotechnology

text: Examples in food crops include resistance to certain pests, diseases, stressful environmental conditions, resistance to chemical treatments (e.g. resistance to a herbicide), reduction of spoilage, or improving the nutrient profile of the crop. Examples in non-food crops include production of pharmaceutical agents, biofuels, and other industrially useful goods, as well as for bioremediation.


title: Biotechnology

text: Farmers have widely adopted GM technology. Between 1996 and 2011, the total surface area of land cultivated with GM crops had increased by a factor of 94, from to 1,600,000 km (395 million acres). 10% of the world's crop lands were planted with GM crops in 2010. As of 2011, 11 different transgenic crops were grown commercially on 395 million acres (160 million hectares) in 29 countries such as the US, Brazil, Argentina, India, Canada, China, Paraguay, Pakistan, South Africa, Uruguay, Bolivia, Australia, Philippines, Myanmar, Burkina Faso, Mexico and Spain.


title: Biotechnology

text: Genetically modified foods are foods produced from organisms that have had specific changes introduced into their DNA with the methods of genetic engineering. These techniques have allowed for the introduction of new crop traits as well as a far greater control over a food's genetic structure than previously afforded by methods such as selective breeding and mutation breeding. Commercial sale of genetically modified foods began in 1994, when Calgene first marketed its Flavr Savr delayed ripening tomato. To date most genetic modification of foods have primarily focused on cash crops in high demand by farmers such as soybean, corn, canola, and cotton seed oil. These have been engineered for resistance to pathogens and herbicides and better nutrient profiles. GM livestock have also been experimentally developed; in November 2013 none were available on the market, but in 2015 the FDA approved the first GM salmon for commercial production and consumption.


title: Biotechnology

text: There is a scientific consensus that currently available food derived from GM crops poses no greater risk to human health than conventional food, but that each GM food needs to be tested on a case-by-case basis before introduction. Nonetheless, members of the public are much less likely than scientists to perceive GM foods as safe. The legal and regulatory status of GM foods varies by country, with some nations banning or restricting them, and others permitting them with widely differing degrees of regulation.


title: Biotechnology

text: GM crops also provide a number of ecological benefits, if not used in excess. However, opponents have objected to GM crops per se on several grounds, including environmental concerns, whether food produced from GM crops is safe, whether GM crops are needed to address the world's food needs, and economic concerns raised by the fact these organisms are subject to intellectual property law.


title: Biotechnology

text: Industrial biotechnology (known mainly in Europe as white biotechnology) is the application of biotechnology for industrial purposes, including industrial fermentation. It includes the practice of using cells such as microorganisms, or components of cells like enzymes, to generate industrially useful products in sectors such as chemicals, food and feed, detergents, paper and pulp, textiles and biofuels. In the current decades, significant progress has been done in creating genetically modified organisms (GMOs) that enhance the diversity of applications and economical viability of industrial biotechnology. By using renewable raw materials to produce a variety of chemicals and fuels, industrial biotechnology is actively advancing towards lowering greenhouse gas emissions and moving away from a petrochemical-based economy.


title: Biotechnology

text: Synthetic biology is considered one of the essential cornerstones in industrial biotechnology due to its financial and sustainable contribution to the manufacturing sector. Jointly biotechnology and synthetic biology play a crucial role in generating cost-effective products with nature-friendly features by using bio-based production instead of fossil-based. Synthetic biology can be used to engineer model microorganisms, such as "Escherichia coli", by genome editing tools to enhance their ability to produce bio-based products, such as bioproduction of medicines and biofuels. For instance, "E. coli" and "Saccharomyces cerevisiae" in a consortium could be used as industrial microbes to produce precursors of the chemotherapeutic agent paclitaxel by applying the metabolic engineering in a co-culture approach to exploit the benefits from the two microbes.


title: Biotechnology

text: Another example of synthetic biology applications in industrial biotechnology is the re-engineering of the metabolic pathways of "E. coli" by CRISPR and CRISPRi systems toward the production of a chemical known as 1,4-butanediol, which is used in fiber manufacturing. In order to produce 1,4-butanediol, the authors alter the metabolic regulation of the "Escherichia coli" by CRISPR to induce point mutation in the "glt"A gene, knockout of the "sad" gene, and knock-in six genes ("cat"1, "suc"D, "4hbd", "cat"2, "bld", and "bdh"). Whereas CRISPRi system used to knockdown the three competing genes ("gab"D, "ybg"C, and "tes"B) that affect the biosynthesis pathway of 1,4-butanediol. Consequently, the yield of 1,4-butanediol significantly increased from 0.9 to 1.8 g/L.


title: Biotechnology

text: Environmental biotechnology includes various disciplines that play an essential role in reducing environmental waste and providing environmentally safe processes, such as biofiltration and biodegradation. The environment can be affected by biotechnologies, both positively and adversely. Vallero and others have argued that the difference between beneficial biotechnology (e.g., bioremediation is to clean up an oil spill or hazard chemical leak) versus the adverse effects stemming from biotechnological enterprises (e.g., flow of genetic material from transgenic organisms into wild strains) can be seen as applications and implications, respectively. Cleaning up environmental wastes is an example of an application of environmental biotechnology; whereas loss of biodiversity or loss of containment of a harmful microbe are examples of environmental implications of biotechnology.


title: Biotechnology

text: The regulation of genetic engineering concerns approaches taken by governments to assess and manage the risks associated with the use of genetic engineering technology, and the development and release of genetically modified organisms (GMO), including genetically modified crops and genetically modified fish. There are differences in the regulation of GMOs between countries, with some of the most marked differences occurring between the US and Europe. Regulation varies in a given country depending on the intended use of the products of the genetic engineering. For example, a crop not intended for food use is generally not reviewed by authorities responsible for food safety. The European Union differentiates between approval for cultivation within the EU and approval for import and processing. While only a few GMOs have been approved for cultivation in the EU a number of GMOs have been approved for import and processing. The cultivation of GMOs has triggered a debate about the coexistence of GM and non-GM crops. Depending on the coexistence regulations, incentives for the cultivation of GM crops differ.


title: Biotechnology

text: In 1988, after prompting from the United States Congress, the National Institute of General Medical Sciences (National Institutes of Health) (NIGMS) instituted a funding mechanism for biotechnology training. Universities nationwide compete for these funds to establish Biotechnology Training Programs (BTPs). Each successful application is generally funded for five years then must be competitively renewed. Graduate students in turn compete for acceptance into a BTP; if accepted, then stipend, tuition and health insurance support are provided for two or three years during the course of their PhD thesis work. Nineteen institutions offer NIGMS supported BTPs. Biotechnology training is also offered at the undergraduate level and in community colleges.


title: Colombia national football team

text: The Colombia national football team () represents Colombia in men's international football and is managed by the Colombian Football Federation, the governing body for football in Colombia. They are a member of CONMEBOL and are currently ranked 17th in the FIFA World Rankings. The team are nicknamed "Los Cafeteros" due to the coffee production in their country. Notably, the national team has been a symbol of nationalism, pride, and passion for many Colombians worldwide. Colombia is known for having a passionate fan base, and the team's dances during goal celebrations have been symbolic.


title: Colombia national football team

text: The Colombian team has participated in six World Cups (1962, 1990, 1994, 1998, 2014 and 2018). In the 2014 edition held in Brazil, the team achieved its best World Cup performance, reaching the quarter-finals and coming fifth in the final standings. Its greatest international achievement is winning the Copa América in 2001 as hosts, also setting a new record with no goals conceded and every match won; it has also finished runner-up in 1975 and finished third five times: in 1987, 1993, 1995, 2016, and 2021. Furthermore, the team managed to make outstanding appearances at the continental level, obtaining from the Central American and Caribbean Games the gold and bronze medals in 1946 and 1938 respectively, and in the Bolivarian Games the team obtained the gold medal in 1951 and the silver medal in 1961, 1973 and 1981.


title: Colombia national football team

text: Colombia had its strongest period during the 1990s. A 1993 match which resulted in a 5–0 win over Argentina began a special "mutual respect" rivalry between both nations. The goalkeeper René Higuita achieved fame from his eccentric scorpion kick clearance against England at Wembley Stadium in 1995. Stars from Colombia's team playing in top European leagues included Carlos Valderrama, who shined in Ligue 1, Faustino Asprilla, who shined in the Serie A and Premier League, and Freddy Rincón, who played in Serie A, La Liga, and the Brazilian Championship. During this era Colombia qualified for 1990, 1994, and 1998 World Cups, only reaching the second round in 1990. Following the murder of Andrés Escobar after the 1994 World Cup, Colombia's performances faded in the latter half of the 1990s and early half of the 2000s, and although Colombia was the champion of the 2001 Copa América, which they hosted, the nation missed three World Cups between 2002 and 2010. Colombia was the first team to win FIFA best mover in 1993 where the achievement was first introduced and the second team after Croatia to win it twice in 2012.


title: Colombia national football team

text: A new era began for Colombia with the arrival of Argentine manager José Pékerman in January 2012. During the 2014 World Cup qualifiers, Colombia showed improvement over the 2011 Copa América, bringing its rank up from 40th to the top ten for the first time since 2002 and into the top five consistently for the first time since 2004. After a 16-year-long wait, in 2014 Colombia finally returned to the World Cup, where they were able to advance to the quarter-finals, the furthest Colombia has ever made it in a World Cup. Colombia's star midfielder James Rodríguez won two awards that tournament, the Golden Boot for most goals (6) and Best Goal of the Tournament, his long-range strike against Uruguay.


title: Colombia national football team

text: The development of football in Colombia is debated by many. Most historians agree that the Caribbean Region was the place where football spread. It is believed that its origins go back to 1900, by English railway engineers from The Colombia Railways Company.


title: Colombia national football team

text: It was not until 1924 that the Colombian Football Federation was formed, initially under the name Liga de Fútbol, that gained the affiliation with FIFA and CONMEBOL in 1936. Colombia played its first international match on 17 February 1926 against Costa Rica at the Julio Torres Stadium in Barranquilla, obtaining a 4–1 victory against the Central Americans.


title: Colombia national football team

text: In 1937, Colombia formed a national team for the "Juegos del IV Centenario de Cali" (Games of the IV Centenary of Cali). Colombia played four matches at the recently opened Estadio Olímpico Pascual Guerrero: against Mexico (3–1), Argentina (1–3), Ecuador (5–0), and Cuba (1–3).


title: Colombia national football team

text: Despite becoming a FIFA member in 1936, Colombia withdrew from the 1938 World Cup in France. Instead, Colombia played at the 1938 Central American and Caribbean Games. The Colombia national football team was composed mostly by all the players of the "Club Juventud Bogotana" (now Millonarios). Alfonso Novoa was the manager of Colombia until 23 February. The first game was played on 10 February 1938 against Mexico. Colombia was defeated 1–3; Luis Argüelles, Luis de la Fuente and Horacio Casarín scored for Mexico, while Marcos Mejía scored for Colombia. Colombia was able to obtain the bronze medal, with two wins and three losses. The same year, Colombia played at the I Bolivarian Games in Bogotá, where they finished fourth with one win and three losses. Fernando Paternoster was the manager of Colombia, the side's first foreign manager.


title: Colombia national football team

text: Colombia did not play again until 1945 when they participated for the first time at the South American Championship, finishing in fifth place. This time, Colombia was composed by players of Junior de Barranquilla except for Antonio de la Hoz (who played for Sporting de Barranquilla) and Pedro Ricardo López (who played for Boca Juniors de Cali). Roberto Meléndez was player and coach of Colombia throughout the tournament. Despite Colombia's debut at the tournament, the country withdrew from the 46' edition.


title: Colombia national football team

text: Under manager Lilo Taioli, Colombia returned to the South American Championship in 1947 where they finished last of the tournament with only 2 points.


title: Colombia national football team

text: The first match of Colombia in the professional era was played on 6 April in the 1949 South American Championship, a 3–0 defeat against Paraguay. Austrian coach Friedrich Donenfeld was the manager of Colombia during the tournament; he had moved with his family to Colombia due to World War II, and Atlético Junior would be his first team as a coach. As Junior was chosen to represent Colombia in the tournament, he became in the first European manager of the Colombia national team. The team, however, repeated their losing streak since, as in the previous tournament, ended eighth with two draws and five losses, scoring four goals.


title: Colombia national football team

text: Colombia chose to not enter the qualification process for the 1950 FIFA World Cup held in Brazil. For the following World Cup in 1954, Colombia was banned from participating due to the controversial El Dorado era which witnessed the Colombia football league's breaking away from FIFA.


title: Colombia national football team

text: Colombia withdrew from three consecutive South American Championship tournaments before returning for the 57' edition held in Peru under manager Pedro López where the team finished fifth.


title: Colombia national football team

text: Colombia participated for the first time in qualifying for the 1958 FIFA World Cup in Sweden. Their first match was on 16 June 1957 against Uruguay in Bogotá, a 1–1 draw. Colombia lost their next matches, leaving them at the bottom of the group.


title: Colombia national football team

text: Under Argentine coach Adolfo Pedernera, Colombia qualified for the 1962 World Cup, its first-ever FIFA World Cup by eliminating Peru 2–1 on aggregate.


title: Colombia national football team

text: At the 1962 World Cup, Colombia was drawn into a tough group containing Uruguay, Soviet Union and Yugoslavia; both had achieved notable results comparing to Colombia. Colombia lost its first match, 2–1 against Uruguay. Luis Cubilla and Jorge Sasía scored for Uruguay at the 56th and 75th minute respectively, while Francisco Zuluaga scored a 19th-minute penalty goal for Colombia to give the Colombians their first-ever World Cup goal and a shock lead. In the second match, they earned a 4–4 draw with the USSR, champions of the 1960 European Nations' Cup. In this game, Colombia scored four goals against Soviet goalkeeper Lev Yashin, widely considered the best goalkeeper in football history. Also in that game, Marco Coll scored the only in World Cup history so far. Unfortunately, the Colombian campaign in 1962 ended with a 5–0 defeat against Yugoslavia, who finished in fourth place in the tournament. After the 1962 World Cup, Colombia didn't qualify for over 28 years before they returned in the 1990 edition.


title: Colombia national football team

text: After withdrawing the two editions of the South American Championship in Argentina and Ecuador, Colombia participated in the 1963 South American Championship in Bolivia. Colombia finished last in the tournament with a draw and five defeats. Delio Gamboa was the goalscorer of Colombia with three goals.


title: Colombia national football team

text: For the 1966 FIFA World Cup qualifiers, Colombia was placed in a group against Ecuador and Chile. The team finished in the bottom of their group with 2 points, only with a 2–0 win over Chile in Bogotá. The following year, Colombia had to play qualifying for the 1967 South American Championship against Chile, but was eliminated with a 5–2 defeat in Santiago and a 0–0 draw in Bogotá.


title: Colombia national football team

text: Colombia participated for qualifying for the 1970 FIFA World Cup in Group 2, with Brazil, Paraguay and Venezuela. The team finished 3rd with one win, one draw and four defeats. In 1970, before the start of the World Cup in Mexico, England prepared a friendly against Colombia to prepare the team for the high altitudes of Mexico. England beat Colombia 4–0, but their victory was overshadowed by the Bogotá Bracelet incident.


title: Colombia national football team

text: For the 1974 FIFA World Cup qualifiers, Colombia faced Uruguay and Ecuador. Colombia was able to obtain a win and three draws, tied on 5 points with Uruguay, but Uruguay would be the one who qualified to the next stage due to better goal difference.


title: Colombia national football team

text: In the 1975 Copa America Colombia was placed in Group C with Paraguay and Ecuador. Colombia won all four games with 7 goals for and 1 against, advancing to the semifinals against Uruguay. Colombia won 3–0 at home and lost 1–0 away, but the 3–1 aggregate score allowed them to advance to the final for the first time in their history, where they faced Peru. Colombia won at home 1–0, but lost 2–0 away, so that the champion was defined on neutral ground (in Caracas) where Peru beat Colombia with a 25th-minute goal from Hugo Sotil. Colombian Ernesto Díaz tied with Argentinian Leopoldo Luque as the top goalscorer of the tournament with 4 goals.


title: Colombia national football team

text: For the 1978 FIFA World Cup qualifiers, Colombia shared Group 1 with Brazil and Paraguay and failed to qualify after finishing last with just two points.


title: Colombia national football team

text: Under the orders of Blagoje Vidinić, Colombia disputed the 1979 Copa América, where they shared Group A with Chile and Venezuela. Despite finishing with the same points as first-placed Chile, Colombia were knocked out of the tournament due to goal difference.


title: Colombia national football team

text: Prior to the 1980s, the Colombian national football team was widely recognized as a weak team, and lack of fans, due to neglected investment for the national team by the Colombian Football Federation, national tragedies like La Violencia, and widespread criminal activities that destabilized the country. Their lack of participation also added to this sporadic support, and despite having qualified for the 1962 FIFA World Cup, the national team remained underrated and under-achieved than the rest of South America, particularly to those of Chile, Peru, Bolivia and Paraguay outside traditional powers Uruguay, Brazil and Argentina, in spite of their youth football successes.


title: Colombia national football team

text: Since the mid-1980s, with the influx of drug money into football, a new generation of football stars emerged, with René Higuita, Faustino Asprilla, Carlos Valderrama, Andrés Escobar and Arnoldo Iguarán. Following with it, the national team has become a symbol fighting the country's negative reputation. This has made the sport popular and made the national team a sign of nationalism, pride and passion for many Colombians worldwide. Colombia is known for having a passionate fan base, often attend in large number whatever the national team of Colombia play elsewhere.


title: Colombia national football team

text: Shortly before the 1987 Copa América, Francisco Maturana was hired. Colombia had a good tournament, winning both of their matches against Bolivia and Paraguay, before losing to Chile in the semi-finals. However, they won the third-place match against Argentina to finish in the top three for the first time in their history.


title: Colombia national football team

text: For the 1990 World Cup qualifiers, South America was allocated three-and-a-half berths at the 1990 finals. The continent's nine remaining sides were split into three groups with the two automatic qualifying berths going to the two best group winners, in this instance Uruguay and Brazil. The group winner with the worst record would advance to the CONMEBOL / OFC Intercontinental Play-off. Thus Colombia had to take on the winners of the Oceania zone. Curiously, this turned out to be Israel, after they finished ahead of Australia and New Zealand in the final qualifying group. Colombia qualified for their first FIFA World Cup since Chile 1962 after winning in Barranquilla 1–0, and tying in Israel 0–0, with most of the players coming from Atlético Nacional, who Maturana was also managing at the time.


title: Colombia national football team

text: At the 1990 World Cup, Colombia was once again drawn with the Yugoslavs, alongside United Arab Emirates and powerhouse West Germany. Colombia defeated the United Arab Emirates 2–0 to achieve its first-ever win in the World Cup, then lost to Yugoslavia 1–0, but earned their place in the Round of 16 after a respectable 1–1 draw with West Germany, who would later win the World Cup. Colombia would be eliminated in their next match against Cameroon with a 2–1 defeat in extra time, a match which is remembered for an mistake from goalkeeper René Higuita. Shortly after this defeat, Maturana left his post as Colombia manager. However, this world cup marked the rise of a generation known as the first Colombian Golden Generation.


title: Colombia national football team

text: Shortly before the 1993 Copa América, Maturana returned for his second spell as Colombia manager. Colombia began their tournament campaign by topping their group undefeated. In the quarter-finals, they beat Uruguay on penalties, and lost to eventual winners Argentina in the semi-finals on penalties, but won the third place match against Ecuador to finish third for the second time in their history.


title: Colombia national football team

text: For the 1994 World Cup, Colombia finished top of their qualifying group without having lost a match, which included a historic 0–5 victory over Argentina in Buenos Aires. Expectations of the team were high, some even naming them as favorites to win the tournament, as they had only lost one official match from July 1992 going into the World Cup. Colombia was assigned to Group A with the hosts United States, Romania, and Switzerland. During the tournament, internal conflict within Colombia proved to be detrimental and harmful for the Colombian squad as the team was distracted from their main goal. Colombia only earned one win over Switzerland and suffered two losses, which would eliminate them in the first phase. The first match against Romania ended with a 3–1 defeat that resulted in cartels' threats to relatives of Colombian players and manager Maturana. During the match against the United States, an unwanted incident occurred, when Andrés Escobar scored an own goal, leading to Colombia's elimination as they lost 2–1. Escobar was later murdered in Colombia a few days after the own goal, and this traumatic incident would lead to the demise of Colombia's first Golden Generation.


title: Colombia national football team

text: Colombia ended their qualification for the 1998 World Cup in third place with 28 points, two points below first-place Argentina with 30 points. Colombia was assigned to the Group G alongside Tunisia, England and once again, Romania. Romania, like in the 1994 edition, obtained a 1–0 victory in the first match. Colombia's second match was a 1–0 win against Tunisia, with a goal from Léider Preciado. In the last match, however, England won the game 2–0, thereby eliminating Colombia from the tournament.


title: Colombia national football team

text: Prior to the Copa América to be hosted in Colombia in 2001, the national team was invited to participate at the 2000 CONCACAF Gold Cup hosted in the United States. The team managed to advance to the final of the tournament after eliminating the host United States on penalties in the quarterfinals, and beating Peru 2–1 in the semi-finals. The team would match up against Canada in the final, however, Colombia failed to lift the trophy after losing 2–0 with goals from Jason de Vos and Carlo Corazzin.


title: Colombia national football team

text: The 2001 Copa América was the first Copa América held in Colombia. Prior to the tournament, meetings were held by CONMEBOL authorities who were concerned about potential security issues in Colombia, and the tournament was canceled on 1 July, just ten days before the opening match. On 6 July, CONMEBOL decided to reinstate the tournament, which was held on schedule. Canada had already disbanded its training camp and released its players, so Costa Rica (a CONCACAF invitee) was invited to the tournament. Claiming that Argentine players had received death threats from terrorist groups, the Argentine Football Association decided to withdraw from the competition the day before the first game, with Honduras (a CONCACAF invitee) hastily invited and flown in by the Colombian Air Force to participate. There were no terrorist incidents throughout the competition.


title: Colombia national football team

text: Colombia began the tournament strongly, topping their group consisting of Venezuela, Chile and Ecuador. They eliminated Peru and Honduras on their way to winning their first Copa América title by defeating Mexico (a CONCACAF invitee) in the final with a goal from Iván Córdoba in the second half. The team also broke a Copa America record of not conceding any goals and winning every game. Colombian striker Víctor Aristizábal finished as the tournament's top scorer, with six goals, and the team won the fair play award as well.


title: Colombia national football team

text: For the 2002 World Cup, Colombia only managed to place sixth in the qualification round, tied with Uruguay but failing to qualify due to goal difference. This was the first time that Colombia had failed to qualify for a World Cup since the team's three consecutive qualifications that began in 1990.


title: Colombia national football team

text: Although the Colombian Golden Generation was exhibiting its declining years for the Colombian squad, the country had an acceptable performance at the 2004 Copa América under Reinaldo Rueda, beginning by topping their group. The team eliminated Costa Rica in the quarter-finals and then lost to Argentina in the semi-finals. They ended up earning fourth place after losing the third place match.


title: Colombia national football team

text: Colombia also participated in the 2005 Gold Cup. The team performed poorly in the group stage, placing third with one win, and two losses. Even though it qualified to the next round as the best third-placed team and beat defending champions Mexico in the quarter-finals, the team was eventually eliminated by Panama, who Colombia had already lost to in the group stage. Many people thought Colombia would be one of the tournament favorites, and another failure was shown after not making the final.


title: Colombia national football team

text: Colombia would also eventually fail to qualify for the 2006 edition in Germany while by a single point thanks to Uruguay's win over Argentina. Had Uruguay and Argentina drawn, Colombia would've qualified to the playoff spot with their 1–0 away win over Paraguay, and they had superior goal difference to Uruguay as well.


title: Colombia national football team

text: Colombia had one of its worst ever Copa América performances in the 2007 Copa América. The team finished third in the group with one win and two losses, including a 5–0 loss to Paraguay, and didn't qualify for the knockout stages.


title: Colombia national football team

text: For the 2010 World Cup qualifiers, Colombia exeprienced a similar situation to their previous qualification campaign and failed to qualify by a point despite winning their final match against Paraguay. Thus, Colombia had failed to qualify for the World Cup for the third time a row. These failures to qualify for the World Cup were mainly a result of constantly changing formations and managers, combined with the struggle to score goals in the last games of the qualification.


title: Colombia national football team

text: In June 2011, Colombia has its worst ranking ever: 54th. Despite this ranking, In the 2011 Copa América, Colombia made a good run, topping their group and achieving a draw to the host nation Argentina, who were the favorites. In the next round, Colombia would be eliminated in a 2–0 loss against Peru in extra time. "Los Cafeteros" ended the year 2011 36th in the FIFA Rankings.


title: Colombia national football team

text: In September 2011, the Colombian side gained Leonel Álvarez as the new coach following the resignation of Hernán Darío Gómez, but he was sacked after three games with disappointing results, which led to the hiring of José Pékerman in January 2012. Pékerman's first match was a 2–0 win over Mexico in Miami, and his first official match was a 1–0 victory against Peru in June. In October 2012, Colombia moved back into the top 10 of the FIFA Rankings for the first time since July 2002, after the wins against Chile (3–1) and Uruguay (4–0). The team climbed to 9th place, up 13 places. At the end of the year, the team were in 5th.


title: Colombia national football team

text: Under Pékerman, the squad would break a personal qualifying best record by finishing in second with 30 points, and raise their FIFA ranking consistently into the top ten, which allowed them to qualify for the World Cup for the first time in 16 years. The qualification was secured with a 3–3 draw against Chile, after having trailed 0–3 at the half. Although World Cup qualification was already secured, Colombia ended their qualifying campaign with a 2–1 victory against Paraguay in Asunción, with two goals from captain and defender Mario Yepes. Celebrations broke throughout the nation, as many neutrals hailed Colombia as a dark-horse towards being a World Cup contender. Often, Colombia were noted by many Colombian figures such as Carlos Valderrama as a team that could become the most successful Colombian squad in history. Throughout the qualification process, Colombia only conceded 12 goals, which was the second-best defensive record behind Argentina.


title: Colombia national football team

text: Colombia topped off their return in the 2014 World Cup after a 16-year absence by defeating Greece 3–0. Colombia then edged a 2–1 victory over the Ivory Coast to dispute Group C's top spot days later. On the same day, Japan and Greece drew 0–0 and automatically qualified Colombia to the round of 16 for the first time in 24 years since the 1990 World Cup. In its final group stage game, Colombia defeated Japan 4–1 to win Group C and become the third South American team (following Brazil and Argentina) to win all three group stage games in World Cup history. The Japan match also saw goalkeeper Faryd Mondragón, the last active player from the country's previous World Cup appearance in 1998, become the oldest player ever to appear in a World Cup. Colombia went on to defeated Uruguay 2–0 on 28 June in the round of 16, securing a spot in the quarter-finals for the first time in their history. Colombia then fell to hosts Brazil 2–1 in the quarter-final round in controversy, where media and figures such as Diego Maradona criticized FIFA and Carlos Velasco Carballo for "favoring" Brazil and being biased in disallowing a goal from Mario Yepes and allowing too many fouls by the Brazilians to occur without any yellow cards being shown.


title: Colombia national football team

text: Despite the elimination, the national team was greeted by tens of thousands of Colombians in Bogotá, welcoming them back as heroes and restoring pride to the nation. Colombia would then receive the FIFA Fair Play Trophy and have James Rodríguez and Juan Cuadrado end as the World Cup's leading goal scorer and assist leader, respectively.


title: Colombia national football team

text: Colombia had a disappointing 2015 Copa América, having won only a single game during the group stage match against Brazil, with their only goal of the tournament. Colombia would be eliminated by Argentina in the next round via penalty shootout, ending their campaign with one win, two draws, and one loss. Their only goal throughout the tournament was scored by Jeison Murillo, who would later win the tournament's Best Young Player award and be included in the tournament's Star XI.


title: Colombia national football team

text: Colombia began their 2016 Copa América Centenario campaign with a 0–2 victory against hosts United States. Days later they sealed their qualification to the quarter finals with a 2–1 victory against Paraguay. In the final group game however, they fell to Costa Rica 2–3 and finished second in the group following a completely rotated squad. On 17 June, they advanced to the semi-finals with a win against Peru on penalties 4–2 in front of 79,000 fans at MetLife Stadium. Colombia would then lose to eventual tournament winners Chile following mistakes by their defense. Colombia, however, won the third place match against the hosts United States to seal their best result since winning the 2001 edition.


title: Colombia national football team

text: Colombia qualified for the 2018 FIFA World Cup by finishing fourth in CONMEBOL qualifying and drew a challenging group; playing with Japan, Poland and Senegal. The team was nevertheless considered the group favorites, but began their campaign with an unexpected 2–1 controversial defeat to Japan, with Carlos Sánchez being sent off after just three minutes of play. Colombia resurrected their hopes of advancing from the group with a 3–0 win over Poland, whose own chances of advancing were ended with the defeat. After the match, head coach José Pékerman dedicated the win to Carlos Sánchez. On 28 June, Colombia beat Senegal by a scoreline of 1–0, topping their group and advancing into the round of 16, and eliminated Senegal in process as well. On 3 July in Moscow, Colombia were knocked out by England in the round of 16; the game finished 1–1 after extra time, with England winning 4–3 on penalties.


title: Colombia national football team

text: Match referee Mark Geiger proved to be controversial, with criticism from both sets of teams. Colombia captain Radamel Falcao and manager José Pékerman both accused Geiger of favouring the England team during the match. Diego Maradona once again claimed favouritism against Colombia, saying, "England's penalty was a terrible call and that the ref won the match for England," and that Colombia were victims of a "monumental robbery". In response, FIFA said Maradona's comments were "entirely inappropriate" and insinuations about the referee "completely unfounded". A FIFA statement read, "Following comments made by Diego Armando Maradona in relation to yesterday's round of 16 game, Colombia vs England, FIFA strongly rebukes the criticism of the performance of the match officials which it considers to have been positive in a tough and highly emotional match. Furthermore, it also considers the additional comments and insinuations made as being entirely inappropriate and completely unfounded." Maradona subsequently apologized to FIFA and its president, admitting some of things he said were unacceptable: "I said a couple of things and, I admit, some of them are unacceptable."


title: Colombia national football team

text: Following the federation's choice to not renew Pekerman's contract, former Iran manager Carlos Queiroz was hired to coach the national team. After an impressive 8 goal run, winning 3 out of 4 of their pre-Copa America friendlies as well as conceding only 2 goals in only one, optimism for the Portuguese coach and the team itself was strong.


title: Colombia national football team

text: Starting off their 2019 Copa América campaign, Colombia defeated favorites Argentina in a shocking 2–0 win, marking their first victory over the "La Albiceleste" since 2007. Days later, they would face a very defensive Asian Cup champions and 2022 World Cup hosts Qatar with a 1–0 victory to become the first team in the group stages to advance to the next round. Colombia would end their group stage run in perfect fashion with a 1–0 victory over Paraguay, resting a majority of their starters and finishing with nine points with four goals scored and none conceded throughout the group stage. Colombia also became the only team since the 2001 edition to advance out of the group stage with a 100% perfect run. Despite this achievement, Colombia was then eliminated by Chile in a penalty shootout during the quarter-finals match where Colombia performed poorly, only to be saved by the referee over two disallowed Chilean goals.


title: Colombia national football team

text: In the 2021 Copa América, Colombia started with a 1–0 victory against Ecuador. Days later, they faced Venezuela, where the match ended with a 0–0 draw. Then, they would face Peru, where the first half ended with a victory for Peru with a goal in the 17th minute. In the second half, Colombia was able to tie with a penalty goal for an action by Peruvian goalkeeper Pedro Gallese against Miguel Borja. However, in the 64th minute, a mistake by Yerry Mina caused him to score an own goal after a corner kick by Peru, goalkeeper David Ospina clawed the ball away but the referee ruled the goal valid, ending the match with a score of 1–2. Finally, Colombia faced Brazil, with Luis Díaz scoring the first goal of the match in just 10 minutes into the game, which was considered the best goal of the Copa América by some media and fans. However, in the 78th minute, Brazil scored a controversial goal shortly after the ball touched referee Nestor Pitana, without him stopping play. Brazil scored another goal in the finale minutes of the game, causing the score to end 1–2. Even so, Colombia finished in third place in the Group B table and qualified for the quarterfinals, where they faced Uruguay, where the match was defined with a 4–2 victory for Colombia through penalties after a 0–0 draw. In the semifinals, Colombia contested with Argentina, where they drew 1–1. Argentina won 3–2 in the penalty shoot-out. Colombia managed to win the match for third place against Peru, with the score 3–2, where the last two goals that Luis Díaz scored along with one in the final 93rd minute of the game made him the top scorer of the Copa América, along with Lionel Messi. The third-place victory for Colombia marks their best result since also winning the third place in the Copa América Centenario.


title: Colombia national football team

text: Colombia began the 2022 World Cup qualifiers with hope to make it third in a row for the second time, and Colombia appeared to be on the right path where they beat neighbor Venezuela and held Chile. However, when matches resumed following COVID-19 pandemic, Colombia's performance slipped disastrously, with a 0–3 home loss to Uruguay (its worst ever home loss for 82 years) before being shockingly thrashed 1–6 by Ecuador, marking the end of Carlos Queiroz's reign as Colombia's coach in December 2020.


title: Colombia national football team

text: On 14 January 2021, the Colombian Football Federation announced Reinaldo Rueda's return to the national team. He made his returning debut in the match against Peru for the second time in the 2022 FIFA World Cup qualification, having faced the same opponent in the same qualification as coach of Chile. After a break, Colombia managed to defeat Peru again, this time with a 3–0 victory in Lima. Colombia then picked up points in all of four of their next qualifying matches, including a 2–2 draw against Argentina, a 1–1 draw against Bolivia at Estadio Hernando Siles in low oxygen conditions, and a convincing 3–1 win against Chile. However, after the game with Chile, Colombia fell into a goal drought, drawing 0–0 with Uruguay, Brazil and Ecuador consecutively, before losing 1–0 away to Brazil. Colombia again drew goalless with Paraguay, and lost at home 1–0 against Peru, which greatly diminished their hopes for qualifying to the World Cup, since they would have to depend on other results to qualify. Another 1–0 loss to Argentina extended their drought to seven official matches without scoring. In the next two matchdays Colombia finally secured goals, winning 3–0 against Bolivia, and 1–0 against Venezuela on the final matchday. However, due to other results, mainly Paraguay's defeat to Peru, Colombia finished in sixth place and failed to qualify for the World Cup. Rueda left his post as the Colombian team manager shortly after.


title: Colombia national football team

text: Colombia's main geopolitical rival has always been Venezuela. However, the rivalry is historically very one-sided for Colombia. This state of affairs started to change from the late 1990s, when football slowly began replacing baseball as Venezuela's main sport.


title: Colombia national football team

text: In 2001, Coach Luis Garcia was sacked for only managing a draw in an away game in San Cristóbal which ended 2–2 when a victory had been taken for granted. This was just a sign of things to come. Four years later in the 2006 World Cup qualifiers, Venezuela stunned the continent by defeating Colombia in Barranquilla 0–1. The game showed the new direction of the rivalry: while Colombia remains ahead on all rankings and competitions, Venezuela always outperform themselves when meeting each other. Former captain Valderrama started calling the games a ""classic"" and stated ""Venezuela kill themselves "[do their best]" playing against us.""


title: Colombia national football team

text: As of 2021, Colombia has not been able to win on Venezuelan soil since 1996. They would win in Venezuela during 2022 World Cup qualifying which marked their first win in Venezuela since 1996. During Jose Pekerman's coaching for the 2014 FIFA World Cup qualification, considered the rebirth of Colombian football, Venezuela still managed to win their game at home, which was one of only three defeats the Argentinean suffered. Venezuela also won the group stage game against Colombia in the 2015 Copa America which were their only three points, although Colombia still managed to advance to the knockout stage while Venezuela ended last. However, the matches are still not as popular as the rival matches against Argentina.


title: Colombia national football team

text: The historical Colombian 5–0 victory in 1993, beating host Argentina in the 1994 World Cup qualifiers, was the very first time Argentina lost in its home stadium Estadio Monumental during a qualifying match for a World Cup. Argentina had come to the qualifiers as a World Cup champion and finalist in the most recent editions (1986 and 1990). It caused a huge upset and start of a respective rivalry. Unlike other rivalries full of hostility, the Colombian–Argentine rivalry is more based on "respect" than a "hated" relationship, always attracting great interest between both nations. After the wane of Valderrama's generation, the rivalry became one-sided again until recent years, when the majority of the games started resulting in draws. Colombia and Argentina faced each other in ten matches during the past years, with Colombia winning once and Argentina twice, and 7 matches ending in draws. Tensions flourished again in 2021 after the semi final match of the 2021 Copa America, a match which ended in a defeat for Colombia after the penalty shootout when Emiliano Martínez, the Argentinean goalkeeper, utilized provocative gestures and phrases to distract the Colombian players, which were broadcast on live television. The episode sparked widespread controversy and reject from the Colombian side while it was praised from the Argentinian one, adding up to the already heated relationship of the teams.


title: Colombia national football team

text: Colombia had a more hostile rivalry against Brazil due to the 2014 FIFA World Cup encounter, where Brazil defeated Colombia 2–1 overshadowed by Neymar's injury and referee's favoritism towards Brazil against Colombia; This would later cause matches between the two national teams to be more intense, aggressive and to a certain extent, played with great hostility with numerous violent incidents, especially during the 2015 Copa América, where Neymar was sent off during a brawl after the final whistle after the Brazilian side suffered defeat, as well during the quarter-final match of the football tournament of the 2016 Summer Olympics between the two teams. The rivalry would soon improve in a less hostile manner after the 2016 Copa Sudamericana Finals when Atlético Nacional asked CONMEBOL to award the trophy for Associação Chapecoense de Futebol due to the LaMia Flight 2933 crash; Nonetheless, it remains a competitive rivalry between the two which often sparks heated episodes among players of both teams.


title: Colombia national football team

text: Although the head-to-head record showcases a one-sided advantage for Colombia, the increase of the footballing level in the neighboring nation of Ecuador during recent years has ended in close matches between the two teams. After Colombia was unable to obtain more than one point from six possible during the 2022 qualifiers (when the side often obtained four or six points from the encounters), including a historic 6-1 defeat against Ecuador in 2020, media began calling the match the new classic of the region, citing its potential for continuing to bring close matches with no clear favorites added to a new competitive atmosphere between both teams.


title: Colombia national football team

text: Colombia plays their qualifying matches and friendlies at the Estadio Metropolitano Roberto Melendez in Barranquilla and has the Estadio el Campin in Bogota as a second alternative.


title: Colombia national football team

text: Traditionally, Colombia's home colours are yellow shirts with navy trim and navy or white shorts and socks, with their away colours being normally navy shirts. They wore their first ever red kit at the 2014 FIFA World Cup. Colombia used red as their home colours in the 20th century, although in Copa América Centenario the team played in an all-white kit for the first time in their history, before reverting to the yellow and navy kit thereafter.


title: Hombale Films

text: Hombale Films (pronunciation: Hom-Baa-Lay) is an Indian film production company mainly known for the "K.G.F" franchise and blockbuster film Kantara. It was founded by Vijay Kiragandur.


title: Hombale Films

text: Hombale Films was founded by Vijay Kiragandur and Chaluve Gowda, entrepreneurs from Bangalore. Hombale Films' first production endeavour was the Kannada film "Ninnindale" in 2014, starring Puneeth Rajkumar. Their next venture was "Masterpiece", starring Yash, in 2015. Their third venture "Raajakumara" was directed by Santhosh Ananddram, and became the top grossing Kannada film at the time. It reportedly grossed more than Rs. 75 crores in the Karnataka box office and was an industry hit.


title: Hombale Films

text: Hombale Films' fourth film was "" directed by Prashanth Neel of "Ugramm" fame. This film was released in five languages across India: Kannada, Telugu, Tamil, Malayalam, and Hindi. "K.G.F: Chapter 1" was very successful at the box office, becoming the first Kannada film to enter the Rs. 200 crore club worldwide, and collected more than 250 crores.


title: Hombale Films

text: Hombale Films' next venture was "Yuvarathnaa" in 2021, which marked their third collaboration with Puneeth Rajkumar, and second collaboration with director Santhosh Ananddram. "Yuvarathnaa" released on 1 April 2021 in Kannada and Telugu, and was made available on Amazon Prime Video shortly after due to the COVID-19 pandemic. "Yuvarathnaa" marked Hombale Films' first foray into music production, under the label Hombale Music.


title: Hombale Films

text: Hombale Films' next film was "" directed by Prashanth Neel, which is the sequel to "", which was released in 2018. Yash reprised his lead role from the first film and Hindi actor Sanjay Dutt was the antagonist, marking his debut in Kannada. The film released on 14 April 2022 in 5 languages with extraordinary reports and collected more than ₹1200 Crore (₹12 Billion) from worldwide box-office.


title: Hombale Films

text: Hombale Films produced Kantara, directed by Rishabh Shetty, on September 30, 2022. It has currently grossed 400 crores in Kannada.


title: Nuclear fission

text: Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay.


title: Nuclear fission

text: Nuclear fission of heavy elements was discovered on Monday 19 December 1938, by German chemist Otto Hahn and his assistant Fritz Strassmann in cooperation with Austrian-Swedish physicist Lise Meitner.


title: Nuclear fission

text: Hahn understood that a "burst" of the atomic nuclei had occurred. Meitner explained it theoretically in January 1939 along with her nephew Otto Robert Frisch. Frisch named the process by analogy with biological fission of living cells. For heavy nuclides, it is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). Like nuclear fusion, for fission to produce energy, the total binding energy of the resulting elements must be greater than that of the starting element.


title: Nuclear fission

text: Fission is a form of nuclear transmutation because the resulting fragments (or daughter atoms) are not the same element as the original parent atom. The two (or more) nuclei produced are most often of comparable but slightly different sizes, typically with a mass ratio of products of about 3 to 2, for common fissile isotopes. Most fissions are binary fissions (producing two charged fragments), but occasionally (2 to 4 times per 1000 events), "three" positively charged fragments are produced, in a ternary fission. The smallest of these fragments in ternary processes ranges in size from a proton to an argon nucleus.


title: Nuclear fission

text: Apart from fission induced by a neutron, harnessed and exploited by humans, a natural form of spontaneous radioactive decay (not requiring a neutron) is also referred to as fission, and occurs especially in very high-mass-number isotopes. Spontaneous fission was discovered in 1940 by Flyorov, Petrzhak, and Kurchatov in Moscow, in an experiment intended to confirm that, without bombardment by neutrons, the fission rate of uranium was negligible, as predicted by Niels Bohr; it was not negligible.


title: Nuclear fission

text: The unpredictable composition of the products (which vary in a broad probabilistic and somewhat chaotic manner) distinguishes fission from purely quantum tunneling processes such as proton emission, alpha decay, and cluster decay, which give the same products each time. Nuclear fission produces energy for nuclear power and drives the explosion of nuclear weapons. Both uses are possible because certain substances called nuclear fuels undergo fission when struck by fission neutrons, and in turn emit neutrons when they break apart. This makes a self-sustaining nuclear chain reaction possible, releasing energy at a controlled rate in a nuclear reactor or at a very rapid, uncontrolled rate in a nuclear weapon. In their second publication on nuclear fission in February of 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction.


title: Nuclear fission

text: The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very dense source of energy. The products of nuclear fission, however, are on average far more radioactive than the heavy elements which are normally fissioned as fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem. However, the seven long-lived fission products make up only a small fraction of fission products. Neutron absorption which does not lead to fission produces Plutonium (from ) and minor actinides (from both and ) whose radiotoxicity is far higher than that of the long lived fission products. Concerns over nuclear waste accumulation and the destructive potential of nuclear weapons are a counterbalance to the peaceful desire to use fission as an energy source. The thorium fuel cycle produces virtually no plutonium and much less minor actinides, but - or rather its decay products - are a major gamma ray emitter. All actinides are fertile or fissile and fast breeder reactors can fission them all albeit only in certain configurations. Nuclear reprocessing aims to recover usable material from spent nuclear fuel to both enable uranium (and thorium) supplies to last longer and to reduce the amount of "waste". The industry term for a process that fissions all or nearly all actinides is a "closed fuel cycle".


title: Nuclear fission

text: Nuclear fission can occur without neutron bombardment as a type of radioactive decay. This type of fission (called spontaneous fission) is rare except in a few heavy isotopes.


title: Nuclear fission

text: In engineered nuclear devices, essentially all nuclear fission occurs as a "nuclear reaction" — a bombardment-driven process that results from the collision of two subatomic particles. In nuclear reactions, a subatomic particle collides with an atomic nucleus and causes changes to it. Nuclear reactions are thus driven by the mechanics of bombardment, not by the relatively constant exponential decay and half-life characteristic of spontaneous radioactive processes.


title: Nuclear fission

text: Many types of nuclear reactions are currently known. Nuclear fission differs importantly from other types of nuclear reactions, in that it can be amplified and sometimes controlled via a nuclear chain reaction (one type of general chain reaction). In such a reaction, free neutrons released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fission.


title: Nuclear fission

text: The chemical element isotopes that can sustain a fission chain reaction are called nuclear fuels, and are said to be 'fissile'. The most common nuclear fuels are U (the isotope of uranium with mass number 235 and of use in nuclear reactors) and Pu (the isotope of plutonium with mass number 239). These fuels break apart into a bimodal range of chemical elements with atomic masses centering near 95 and 135 u (fission products). Most nuclear fuels undergo spontaneous fission only very slowly, decaying instead mainly via an alpha-beta decay chain over periods of millennia to eons. In a nuclear reactor or nuclear weapon, the overwhelming majority of fission events are induced by bombardment with another particle, a neutron, which is itself produced by prior fission events.


title: Nuclear fission

text: Nuclear fission in fissile fuels is the result of the nuclear excitation energy produced when a fissile nucleus captures a neutron. This energy, resulting from the neutron capture, is a result of the attractive nuclear force acting between the neutron and nucleus. It is enough to deform the nucleus into a double-lobed "drop", to the point that nuclear fragments exceed the distances at which the nuclear force can hold two groups of charged nucleons together and, when this happens, the two fragments complete their separation and then are driven further apart by their mutually repulsive charges, in a process which becomes irreversible with greater and greater distance. A similar process occurs in fissionable isotopes (such as uranium-238), but in order to fission, these isotopes require additional energy provided by fast neutrons (such as those produced by nuclear fusion in thermonuclear weapons). While "some" of the neutrons released from the fission of are fast enough to induce another fission in , "most" are not, meaning it can never achieve criticality. While there is a very small (albeit nonzero) chance of a thermal neutron inducing fission in , neutron absorption is orders of magnitude more likely.


title: Nuclear fission

text: The liquid drop model of the atomic nucleus predicts equal-sized fission products as an outcome of nuclear deformation. The more sophisticated nuclear shell model is needed to mechanistically explain the route to the more energetically favorable outcome, in which one fission product is slightly smaller than the other. A theory of fission based on the shell model has been formulated by Maria Goeppert Mayer.


title: Nuclear fission

text: The most common fission process is binary fission, and it produces the fission products noted above, at 95±15 and 135±15 u. However, the binary process happens merely because it is the most probable. In anywhere from 2 to 4 fissions per 1000 in a nuclear reactor, a process called ternary fission produces three positively charged fragments (plus neutrons) and the smallest of these may range from so small a charge and mass as a proton ("Z" = 1), to as large a fragment as argon ("Z" = 18). The most common small fragments, however, are composed of 90% helium-4 nuclei with more energy than alpha particles from alpha decay (so-called "long range alphas" at ~ 16 MeV), plus helium-6 nuclei, and tritons (the nuclei of tritium). The ternary process is less common, but still ends up producing significant helium-4 and tritium gas buildup in the fuel rods of modern nuclear reactors.


title: Nuclear fission

text: The fission of a heavy nucleus requires a total input energy of about 7 to 8 million electron volts (MeV) to initially overcome the nuclear force which holds the nucleus into a spherical or nearly spherical shape, and from there, deform it into a two-lobed ("peanut") shape in which the lobes are able to continue to separate from each other, pushed by their mutual positive charge, in the most common process of binary fission (two positively charged fission products + neutrons). Once the nuclear lobes have been pushed to a critical distance, beyond which the short range strong force can no longer hold them together, the process of their separation proceeds from the energy of the (longer range) electromagnetic repulsion between the fragments. The result is two fission fragments moving away from each other, at high energy.


title: Nuclear fission

text: About 6 MeV of the fission-input energy is supplied by the simple binding of an extra neutron to the heavy nucleus via the strong force; however, in many fissionable isotopes, this amount of energy is not enough for fission. Uranium-238, for example, has a near-zero fission cross section for neutrons of less than 1 MeV energy. If no additional energy is supplied by any other mechanism, the nucleus will not fission, but will merely absorb the neutron, as happens when U absorbs slow and even some fraction of fast neutrons, to become U. The remaining energy to initiate fission can be supplied by two other mechanisms: one of these is more kinetic energy of the incoming neutron, which is increasingly able to fission a fissionable heavy nucleus as it exceeds a kinetic energy of 1 MeV or more (so-called fast neutrons). Such high energy neutrons are able to fission U directly (see thermonuclear weapon for application, where the fast neutrons are supplied by nuclear fusion). However, this process cannot happen to a great extent in a nuclear reactor, as too small a fraction of the fission neutrons produced by any type of fission have enough energy to efficiently fission U (fission neutrons have a mode energy of 2 MeV, but a median of only 0.75 MeV, meaning half of them have less than this insufficient energy).


title: Nuclear fission

text: Among the heavy actinide elements, however, those isotopes that have an odd number of neutrons (such as U with 143 neutrons) bind an extra neutron with an additional 1 to 2 MeV of energy over an isotope of the same element with an even number of neutrons (such as U with 146 neutrons). This extra binding energy is made available as a result of the mechanism of neutron pairing effects. This extra energy results from the Pauli exclusion principle allowing an extra neutron to occupy the same nuclear orbital as the last neutron in the nucleus, so that the two form a pair. In such isotopes, therefore, no neutron kinetic energy is needed, for all the necessary energy is supplied by absorption of any neutron, either of the slow or fast variety (the former are used in moderated nuclear reactors, and the latter are used in fast-neutron reactors, and in weapons). As noted above, the subgroup of fissionable elements that may be fissioned efficiently with their own fission neutrons (thus potentially causing a nuclear chain reaction in relatively small amounts of the pure material) are termed "fissile". Examples of fissile isotopes are uranium-235 and plutonium-239.


title: Nuclear fission

text: Typical fission events release about two hundred million eV (200 MeV) of energy, the equivalent of roughly >2 trillion kelvin, for each fission event. The exact isotope which is fissioned, and whether or not it is fissionable or fissile, has only a small impact on the amount of energy released. This can be easily seen by examining the curve of binding energy (image below), and noting that the average binding energy of the actinide nuclides beginning with uranium is around 7.6 MeV per nucleon. Looking further left on the curve of binding energy, where the fission products cluster, it is easily observed that the binding energy of the fission products tends to center around 8.5 MeV per nucleon. Thus, in any fission event of an isotope in the actinide mass range, roughly 0.9 MeV are released per nucleon of the starting element. The fission of U by a slow neutron yields nearly identical energy to the fission of U by a fast neutron. This energy release profile holds true for thorium and the various minor actinides as well.


title: Nuclear fission

text: By contrast, most chemical oxidation reactions (such as burning coal or TNT) release at most a few eV per event. So, nuclear fuel contains at least ten million times more usable energy per unit mass than does chemical fuel. The energy of nuclear fission is released as kinetic energy of the fission products and fragments, and as electromagnetic radiation in the form of gamma rays; in a nuclear reactor, the energy is converted to heat as the particles and gamma rays collide with the atoms that make up the reactor and its working fluid, usually water or occasionally heavy water or molten salts.


title: Nuclear fission

text: When a uranium nucleus fissions into two daughter nuclei fragments, about 0.1 percent of the mass of the uranium nucleus appears as the fission energy of ~200 MeV. For uranium-235 (total mean fission energy 202.79 MeV), typically ~169 MeV appears as the kinetic energy of the daughter nuclei, which fly apart at about 3% of the speed of light, due to Coulomb repulsion. Also, an average of 2.5 neutrons are emitted, with a mean kinetic energy per neutron of ~2 MeV (total of 4.8 MeV). The fission reaction also releases ~7 MeV in prompt gamma ray photons. The latter figure means that a nuclear fission explosion or criticality accident emits about 3.5% of its energy as gamma rays, less than 2.5% of its energy as fast neutrons (total of both types of radiation ~6%), and the rest as kinetic energy of fission fragments (this appears almost immediately when the fragments impact surrounding matter, as simple heat). In an atomic bomb, this heat may serve to raise the temperature of the bomb core to 100 million kelvin and cause secondary emission of soft X-rays, which convert some of this energy to ionizing radiation. However, in nuclear reactors, the fission fragment kinetic energy remains as low-temperature heat, which itself causes little or no ionization.


title: Nuclear fission

text: So-called neutron bombs (enhanced radiation weapons) have been constructed which release a larger fraction of their energy as ionizing radiation (specifically, neutrons), but these are all thermonuclear devices which rely on the nuclear fusion stage to produce the extra radiation. The energy dynamics of pure fission bombs always remain at about 6% yield of the total in radiation, as a prompt result of fission.


title: Nuclear fission

text: The total "prompt fission" energy amounts to about 181 MeV, or ~89% of the total energy which is eventually released by fission over time. The remaining ~11% is released in beta decays which have various half-lives, but begin as a process in the fission products immediately; and in delayed gamma emissions associated with these beta decays. For example, in uranium-235 this delayed energy is divided into about 6.5 MeV in betas, 8.8 MeV in antineutrinos (released at the same time as the betas), and finally, an additional 6.3 MeV in delayed gamma emission from the excited beta-decay products (for a mean total of ~10 gamma ray emissions per fission, in all). Thus, about 6.5% of the total energy of fission is released some time after the event, as non-prompt or delayed ionizing radiation, and the delayed ionizing energy is about evenly divided between gamma and beta ray energy.


title: Nuclear fission

text: In a reactor that has been operating for some time, the radioactive fission products will have built up to steady state concentrations such that their rate of decay is equal to their rate of formation, so that their fractional total contribution to reactor heat (via beta decay) is the same as these radioisotopic fractional contributions to the energy of fission. Under these conditions, the 6.5% of fission which appears as delayed ionizing radiation (delayed gammas and betas from radioactive fission products) contributes to the steady-state reactor heat production under power. It is this output fraction which remains when the reactor is suddenly shut down (undergoes scram). For this reason, the reactor decay heat output begins at 6.5% of the full reactor steady state fission power, once the reactor is shut down. However, within hours, due to decay of these isotopes, the decay power output is far less. See decay heat for detail.


title: Nuclear fission

text: The remainder of the delayed energy (8.8 MeV/202.5 MeV = 4.3% of total fission energy) is emitted as antineutrinos, which as a practical matter, are not considered "ionizing radiation". The reason is that energy released as antineutrinos is not captured by the reactor material as heat, and escapes directly through all materials (including the Earth) at nearly the speed of light, and into interplanetary space (the amount absorbed is minuscule). Neutrino radiation is ordinarily not classed as ionizing radiation, because it is almost entirely not absorbed and therefore does not produce effects (although the very rare neutrino event is ionizing). Almost all of the rest of the radiation (6.5% delayed beta and gamma radiation) is eventually converted to heat in a reactor core or its shielding.


title: Nuclear fission

text: Some processes involving neutrons are notable for absorbing or finally yielding energy — for example neutron kinetic energy does not yield heat immediately if the neutron is captured by a uranium-238 atom to breed plutonium-239, but this energy is emitted if the plutonium-239 is later fissioned. On the other hand, so-called delayed neutrons emitted as radioactive decay products with half-lives up to several minutes, from fission-daughters, are very important to reactor control, because they give a characteristic "reaction" time for the total nuclear reaction to double in size, if the reaction is run in a "delayed-critical" zone which deliberately relies on these neutrons for a supercritical chain-reaction (one in which each fission cycle yields more neutrons than it absorbs). Without their existence, the nuclear chain-reaction would be prompt critical and increase in size faster than it could be controlled by human intervention. In this case, the first experimental atomic reactors would have run away to a dangerous and messy "prompt critical reaction" before their operators could have manually shut them down (for this reason, designer Enrico Fermi included radiation-counter-triggered control rods, suspended by electromagnets, which could automatically drop into the center of Chicago Pile-1). If these delayed neutrons are captured without producing fissions, they produce heat as well.


title: Nuclear fission

text: In fission there is a preference to yield fragments with even proton numbers, which is called the odd-even effect on the fragments' charge distribution. However, no odd-even effect is observed on fragment mass number distribution. This result is attributed to nucleon pair breaking.


title: Nuclear fission

text: In nuclear fission events the nuclei may break into any combination of lighter nuclei, but the most common event is not fission to equal mass nuclei of about mass 120; the most common event (depending on isotope and process) is a slightly unequal fission in which one daughter nucleus has a mass of about 90 to 100 u and the other the remaining 130 to 140 u. Unequal fissions are energetically more favorable because this allows one product to be closer to the energetic minimum near mass 60 u (only a quarter of the average fissionable mass), while the other nucleus with mass 135 u is still not far out of the range of the most tightly bound nuclei (another statement of this, is that the atomic binding energy curve is slightly steeper to the left of mass 120 u than to the right of it).


title: Nuclear fission

text: Nuclear fission of heavy elements produces exploitable energy because the specific binding energy (binding energy per mass) of intermediate-mass nuclei with atomic numbers and atomic masses close to Ni and Fe is greater than the nucleon-specific binding energy of very heavy nuclei, so that energy is released when heavy nuclei are broken apart. The total rest masses of the fission products () from a single reaction is less than the mass of the original fuel nucleus (). The excess mass is the invariant mass of the energy that is released as photons (gamma rays) and kinetic energy of the fission fragments, according to the mass-energy equivalence formula .


title: Nuclear fission

text: The variation in specific binding energy with atomic number is due to the interplay of the two fundamental forces acting on the component nucleons (protons and neutrons) that make up the nucleus. Nuclei are bound by an attractive nuclear force between nucleons, which overcomes the electrostatic repulsion between protons. However, the nuclear force acts only over relatively short ranges (a few nucleon diameters), since it follows an exponentially decaying Yukawa potential which makes it insignificant at longer distances. The electrostatic repulsion is of longer range, since it decays by an inverse-square rule, so that nuclei larger than about 12 nucleons in diameter reach a point that the total electrostatic repulsion overcomes the nuclear force and causes them to be spontaneously unstable. For the same reason, larger nuclei (more than about eight nucleons in diameter) are less tightly bound per unit mass than are smaller nuclei; breaking a large nucleus into two or more intermediate-sized nuclei releases energy.


title: Nuclear fission

text: Also because of the short range of the strong binding force, large stable nuclei must contain proportionally more neutrons than do the lightest elements, which are most stable with a 1 to 1 ratio of protons and neutrons. Nuclei which have more than 20 protons cannot be stable unless they have more than an equal number of neutrons. Extra neutrons stabilize heavy elements because they add to strong-force binding (which acts between all nucleons) without adding to proton–proton repulsion. Fission products have, on average, about the same ratio of neutrons and protons as their parent nucleus, and are therefore usually unstable to beta decay (which changes neutrons to protons) because they have proportionally too many neutrons compared to stable isotopes of similar mass.


title: Nuclear fission

text: This tendency for fission product nuclei to undergo beta decay is the fundamental cause of the problem of radioactive high-level waste from nuclear reactors. Fission products tend to be beta emitters, emitting fast-moving electrons to conserve electric charge, as excess neutrons convert to protons in the fission-product atoms. See Fission products (by element) for a description of fission products sorted by element.


title: Nuclear fission

text: Several heavy elements, such as uranium, thorium, and plutonium, undergo both spontaneous fission, a form of radioactive decay and "induced fission", a form of nuclear reaction. Elemental isotopes that undergo induced fission when struck by a free neutron are called fissionable; isotopes that undergo fission when struck by a slow-moving thermal neutron are also called fissile. A few particularly fissile and readily obtainable isotopes (notably U, U and Pu) are called nuclear fuels because they can sustain a chain reaction and can be obtained in large enough quantities to be useful.


title: Nuclear fission

text: All fissionable and fissile isotopes undergo a small amount of spontaneous fission which releases a few free neutrons into any sample of nuclear fuel. Such neutrons would escape rapidly from the fuel and become a free neutron, with a mean lifetime of about 15 minutes before decaying to protons and beta particles. However, neutrons almost invariably impact and are absorbed by other nuclei in the vicinity long before this happens (newly created fission neutrons move at about 7% of the speed of light, and even moderated neutrons move at about 8 times the speed of sound). Some neutrons will impact fuel nuclei and induce further fissions, releasing yet more neutrons. If enough nuclear fuel is assembled in one place, or if the escaping neutrons are sufficiently contained, then these freshly emitted neutrons outnumber the neutrons that escape from the assembly, and a "sustained nuclear chain reaction" will take place.


title: Nuclear fission

text: An assembly that supports a sustained nuclear chain reaction is called a critical assembly or, if the assembly is almost entirely made of a nuclear fuel, a critical mass. The word "critical" refers to a cusp in the behavior of the differential equation that governs the number of free neutrons present in the fuel: if less than a critical mass is present, then the amount of neutrons is determined by radioactive decay, but if a critical mass or more is present, then the amount of neutrons is controlled instead by the physics of the chain reaction. The actual mass of a "critical mass" of nuclear fuel depends strongly on the geometry and surrounding materials.


title: Nuclear fission

text: Not all fissionable isotopes can sustain a chain reaction. For example, U, the most abundant form of uranium, is fissionable but not fissile: it undergoes induced fission when impacted by an energetic neutron with over 1 MeV of kinetic energy. However, too few of the neutrons produced by U fission are energetic enough to induce further fissions in U, so no chain reaction is possible with this isotope. Instead, bombarding U with slow neutrons causes it to absorb them (becoming U) and decay by beta emission to Np which then decays again by the same process to Pu; that process is used to manufacture Pu in breeder reactors. In-situ plutonium production also contributes to the neutron chain reaction in other types of reactors after sufficient plutonium-239 has been produced, since plutonium-239 is also a fissile element which serves as fuel. It is estimated that up to half of the power produced by a standard "non-breeder" reactor is produced by the fission of plutonium-239 produced in place, over the total life-cycle of a fuel load.


title: Nuclear fission

text: Fissionable, non-fissile isotopes can be used as fission energy source even without a chain reaction. Bombarding U with fast neutrons induces fissions, releasing energy as long as the external neutron source is present. This is an important effect in all reactors where fast neutrons from the fissile isotope can cause the fission of nearby U nuclei, which means that some small part of the U is "burned-up" in all nuclear fuels, especially in fast breeder reactors that operate with higher-energy neutrons. That same fast-fission effect is used to augment the energy released by modern thermonuclear weapons, by jacketing the weapon with U to react with neutrons released by nuclear fusion at the center of the device. But the explosive effects of nuclear fission chain reactions can be reduced by using substances like moderators which slow down the speed of secondary neutrons.


title: Nuclear fission

text: Critical fission reactors are the most common type of nuclear reactor. In a critical fission reactor, neutrons produced by fission of fuel atoms are used to induce yet more fissions, to sustain a controllable amount of energy release. Devices that produce engineered but non-self-sustaining fission reactions are subcritical fission reactors. Such devices use radioactive decay or particle accelerators to trigger fissions.


title: Nuclear fission

text: Critical fission reactors are built for three primary purposes, which typically involve different engineering trade-offs to take advantage of either the heat or the neutrons produced by the fission chain reaction:


title: Nuclear fission

text: While, in principle, all fission reactors can act in all three capacities, in practice the tasks lead to conflicting engineering goals and most reactors have been built with only one of the above tasks in mind. (There are several early counter-examples, such as the Hanford N reactor, now decommissioned). Power reactors generally convert the kinetic energy of fission products into heat, which is used to heat a working fluid and drive a heat engine that generates mechanical or electrical power. The working fluid is usually water with a steam turbine, but some designs use other materials such as gaseous helium. Research reactors produce neutrons that are used in various ways, with the heat of fission being treated as an unavoidable waste product. Breeder reactors are a specialized form of research reactor, with the caveat that the sample being irradiated is usually the fuel itself, a mixture of U and U.


title: Nuclear fission

text: For a more detailed description of the physics and operating principles of critical fission reactors, see nuclear reactor physics. For a description of their social, political, and environmental aspects, see nuclear power.


title: Nuclear fission

text: One class of nuclear weapon, a "fission bomb" (not to be confused with the "fusion bomb"), otherwise known as an "atomic bomb" or "atom bomb", is a fission reactor designed to liberate as much energy as possible as rapidly as possible, before the released energy causes the reactor to explode (and the chain reaction to stop). Development of nuclear weapons was the motivation behind early research into nuclear fission which the Manhattan Project during World War II (September 1, 1939 – September 2, 1945) carried out most of the early scientific work on fission chain reactions, culminating in the three events involving fission bombs that occurred during the war. The first fission bomb, codenamed "The Gadget", was detonated during the Trinity Test in the desert of New Mexico on July 16, 1945. Two other fission bombs, codenamed "Little Boy" and "Fat Man", were used in combat against the Japanese cities of Hiroshima and Nagasaki on August 6 and 9 (respectively) of 1945.


title: Nuclear fission

text: Even the first fission bombs were thousands of times more explosive than a comparable mass of chemical explosive. For example, Little Boy weighed a total of about four tons (of which 60 kg was nuclear fuel) and was long; it also yielded an explosion equivalent to about 15 kilotons of TNT, destroying a large part of the city of Hiroshima. Modern nuclear weapons (which include a thermonuclear "fusion" as well as one or more fission stages) are hundreds of times more energetic for their weight than the first pure fission atomic bombs (see nuclear weapon yield), so that a modern single missile warhead bomb weighing less than 1/8 as much as Little Boy (see for example W88) has a yield of 475 kilotons of TNT, and could bring destruction to about 10 times the city area.


title: Nuclear fission

text: While the fundamental physics of the fission chain reaction in a nuclear weapon is similar to the physics of a controlled nuclear reactor, the two types of device must be engineered quite differently (see nuclear reactor physics). A nuclear bomb is designed to release all its energy at once, while a reactor is designed to generate a steady supply of useful power. While overheating of a reactor can lead to, and has led to, meltdown and steam explosions, the much lower uranium enrichment makes it impossible for a nuclear reactor to explode with the same destructive power as a nuclear weapon. It is also difficult to extract useful power from a nuclear bomb, although at least one rocket propulsion system, Project Orion, was intended to work by exploding fission bombs behind a massively padded and shielded spacecraft.


title: Nuclear fission

text: The strategic importance of nuclear weapons is a major reason why the technology of nuclear fission is politically sensitive. Viable fission bomb designs are, arguably, within the capabilities of many, being relatively simple from an engineering viewpoint. However, the difficulty of obtaining fissile nuclear material to realize the designs is the key to the relative unavailability of nuclear weapons to all but modern industrialized governments with special programs to produce fissile materials (see uranium enrichment and nuclear fuel cycle).


title: Nuclear fission

text: The discovery of nuclear fission occurred in 1938 in the buildings of the Kaiser Wilhelm Society for Chemistry, today part of the Free University of Berlin, following over four decades of work on the science of radioactivity and the elaboration of new nuclear physics that described the components of atoms. In 1911, Ernest Rutherford proposed a model of the atom in which a very small, dense and positively charged nucleus of protons was surrounded by orbiting, negatively charged electrons (the Rutherford model). Niels Bohr improved upon this in 1913 by reconciling the quantum behavior of electrons (the Bohr model). Work by Henri Becquerel, Marie Curie, Pierre Curie, and Rutherford further elaborated that the nucleus, though tightly bound, could undergo different forms of radioactive decay, and thereby transmute into other elements. (For example, by alpha decay: the emission of an alpha particle—two protons and two neutrons bound together into a particle identical to a helium nucleus.)


title: Nuclear fission

text: Some work in nuclear transmutation had been done. In 1917, Rutherford was able to accomplish transmutation of nitrogen into oxygen, using alpha particles directed at nitrogen N + α → O + p.  This was the first observation of a nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. Eventually, in 1932, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues Ernest Walton and John Cockcroft, who used artificially accelerated protons against lithium-7, to split this nucleus into two alpha particles. The feat was popularly known as "splitting the atom", and would win them the 1951 Nobel Prize in Physics for ""Transmutation of atomic nuclei by artificially accelerated atomic particles"", although it was not the nuclear fission reaction later discovered in heavy elements.


title: Nuclear fission

text: After English physicist James Chadwick discovered the neutron in 1932, Enrico Fermi and his colleagues in Rome studied the results of bombarding uranium with neutrons in 1934. Fermi concluded that his experiments had created new elements with 93 and 94 protons, which the group dubbed ausonium and hesperium. However, not all were convinced by Fermi's analysis of his results, though he would win the 1938 Nobel Prize in Physics for his "demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons". The German chemist Ida Noddack notably suggested in print in 1934 that instead of creating a new, heavier element 93, that "it is conceivable that the nucleus breaks up into several large fragments." However, Noddack's conclusion was not pursued at the time.


title: Nuclear fission

text: After the Fermi publication, Otto Hahn, Lise Meitner, and Fritz Strassmann began performing similar experiments in Berlin. Meitner, an Austrian Jew, lost her Austrian citizenship with the "Anschluss", the union of Austria with Germany in March 1938, but she fled in July 1938 to Sweden and started a correspondence by mail with Hahn in Berlin. By coincidence, her nephew Otto Robert Frisch, also a refugee, was also in Sweden when Meitner received a letter from Hahn dated 19 December describing his chemical proof that some of the product of the bombardment of uranium with neutrons was barium. Hahn suggested a "bursting" of the nucleus, but he was unsure of what the physical basis for the results were. Barium had an atomic mass 40% less than uranium, and no previously known methods of radioactive decay could account for such a large difference in the mass of the nucleus. Frisch was skeptical, but Meitner trusted Hahn's ability as a chemist. Marie Curie had been separating barium from radium for many years, and the techniques were well-known. Meitner and Frisch then correctly interpreted Hahn's results to mean that the nucleus of uranium had split roughly in half. Frisch suggested the process be named "nuclear fission", by analogy to the process of living cell division into two cells, which was then called binary fission. Just as the term nuclear "chain reaction" would later be borrowed from chemistry, so the term "fission" was borrowed from biology.


title: Nuclear fission

text: News spread quickly of the new discovery, which was correctly seen as an entirely novel physical effect with great scientific—and potentially practical—possibilities. Meitner's and Frisch's interpretation of the discovery of Hahn and Strassmann crossed the Atlantic Ocean with Niels Bohr, who was to lecture at Princeton University. I.I. Rabi and Willis Lamb, two Columbia University physicists working at Princeton, heard the news and carried it back to Columbia. Rabi said he told Enrico Fermi; Fermi gave credit to Lamb. Bohr soon thereafter went from Princeton to Columbia to see Fermi. Not finding Fermi in his office, Bohr went down to the cyclotron area and found Herbert L. Anderson. Bohr grabbed him by the shoulder and said: “Young man, let me explain to you about something new and exciting in physics.” It was clear to a number of scientists at Columbia that they should try to detect the energy released in the nuclear fission of uranium from neutron bombardment. On 25 January 1939, a Columbia University team conducted the first nuclear fission experiment in the United States, which was done in the basement of Pupin Hall. The experiment involved placing uranium oxide inside of an ionization chamber and irradiating it with neutrons, and measuring the energy thus released. The results confirmed that fission was occurring and hinted strongly that it was the isotope uranium 235 in particular that was fissioning. The next day, the Fifth Washington Conference on Theoretical Physics began in Washington, D.C. under the joint auspices of the George Washington University and the Carnegie Institution of Washington. There, the news on nuclear fission was spread even further, which fostered many more experimental demonstrations.


title: Nuclear fission

text: In their second publication on nuclear fission in February of 1939, Hahn and Strassmann used the term "Uranspaltung" (uranium fission) for the first time, and predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction.


title: Nuclear fission

text: During this period the Hungarian physicist Leó Szilárd realized that the neutron-driven fission of heavy atoms could be used to create a nuclear chain reaction. Such a reaction using neutrons was an idea he had first formulated in 1933, upon reading Rutherford's disparaging remarks about generating power from his team's 1932 experiment using protons to split lithium. However, Szilárd had not been able to achieve a neutron-driven chain reaction with neutron-rich light atoms. In theory, if in a neutron-driven chain reaction the number of secondary neutrons produced was greater than one, then each such reaction could trigger multiple additional reactions, producing an exponentially increasing number of reactions. It was thus a possibility that the fission of uranium could yield vast amounts of energy for civilian or military purposes (i.e., electric power generation or atomic bombs).