Laboratori Nazionali del Gran Sasso
Laboratori Nazionali del Gran Sasso is the largest underground research center in the world. Situated below Gran Sasso mountain in Italy, it is well known for particle physics research by the INFN. In addition to a surface portion of the laboratory, there are extensive underground facilities beneath the mountain; the nearest towns are Teramo. The facility is located about 120 km from Rome; the primary mission of the laboratory is to host experiments that require a low background environment in the fields of astroparticle physics and nuclear astrophysics and other disciplines that can profit of its characteristics and of its infrastructures. The LNGS is, like the three other European underground astroparticle laboratories, Laboratoire Souterrain de Modane, Laboratorio subterráneo de Canfranc, Boulby Underground Laboratory, a member of the coordinating group ILIAS; the laboratory consists of a surface facility, located within the Gran Sasso and Monti della Laga National Park, extensive underground facilities located next to the 10 km long Traforo del Gran Sasso freeway tunnel.
The first large experiments at LNGS ran in 1989. There are three main barrel vaulted experimental halls, each 20 m wide, 18 m tall, 100 m long; these provide 3×20×100=6,000 m2 of floor space and 3×20××100=95,100 m3 of volume. Including smaller spaces and various connecting tunnels, the facility totals 17,800 m2 and 180,000 m3; the experimental halls are covered by about 1400 m of rock, protecting the experiments from cosmic rays. Providing about 3400 metres of water equivalent shielding, it is not the deepest underground laboratory, but the fact that it can be driven to without using mine elevators makes it popular. Since late August 2006, CERN has directed a beam of muon neutrinos from the CERN SPS accelerator to the Gran Sasso lab, 730 km away, where they are detected by the OPERA and ICARUS detectors, in a study of neutrino oscillations that will improve on the results of the Fermilab to MINOS experiment. In May 2010, Lucia Votano, Director of the Gran Sasso laboratories, announced that "he OPERA experiment has reached its first goal: the detection of a tau neutrino obtained from the transformation of a muon neutrino, which occurred during the journey from Geneva to the Gran Sasso Laboratory."
This finding indicates a deficiency in the Standard Model of particle physics, as neutrinos would have to have mass for this change to occur. An effort to determine the Majorana/Dirac nature of the neutrino, called CUORE, is operating in the laboratory; the detector is be shielded with lead recovered from an ancient Roman shipwreck, due to the ancient lead's lower radioactivity than minted lead. The artifacts were given to CUORE from the National Archaeological Museum in Cagliari. In September 2011, Dario Autiero of the OPERA collaboration presented findings that indicated neutrinos were arriving at OPERA about 60 ns earlier than they would if they were travelling at the speed of light; this Faster-than-light neutrino anomaly was not explained. The results were subsequently confirmed to be wrong, they were caused by a flawed optic fiber cable in OPERA receiver of the laboratory, resulting in late arrival of the clock signal to which the neutrinos' arrivals were compared. In 2014 Borexino measured directly, for the first time, the neutrinos from the primary proton-proton fusion process in the Sun.
This result is published on Nature. This measurement is consistent with the expectations derived from the standard solar model of J. Bahcall along with the theory of solar neutrino oscillations as described by MSW theory, it can be regarded as a cornerstone for our understanding of the PP-chain. Astroparticle physics Fazia Gran Sasso National Laboratory CNGS - CERN neutrino to Gran Sasso Slide Show ILIAS
The European Organization for Nuclear Research, known as CERN, is a European research organization that operates the largest particle physics laboratory in the world. Established in 1954, the organization is based in a northwest suburb of Geneva on the Franco–Swiss border and has 23 member states. Israel is the only non-European country granted full membership. CERN is an official United Nations Observer; the acronym CERN is used to refer to the laboratory, which in 2016 had 2,500 scientific and administrative staff members, hosted about 12,000 users. In the same year, CERN generated 49 petabytes of data. CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research – as a result, numerous experiments have been constructed at CERN through international collaborations; the main site at Meyrin hosts a large computing facility, used to store and analyse data from experiments, as well as simulate events. Researchers need remote access to these facilities, so the lab has been a major wide area network hub.
CERN is the birthplace of the World Wide Web. The convention establishing CERN was ratified on 29 September 1954 by 12 countries in Western Europe; the acronym CERN represented the French words for Conseil Européen pour la Recherche Nucléaire, a provisional council for building the laboratory, established by 12 European governments in 1952. The acronym was retained for the new laboratory after the provisional council was dissolved though the name changed to the current Organisation Européenne pour la Recherche Nucléaire in 1954. According to Lew Kowarski, a former director of CERN, when the name was changed, the abbreviation could have become the awkward OERN, Werner Heisenberg said that this could "still be CERN if the name is ". CERN's first president was Sir Benjamin Lockspeiser. Edoardo Amaldi was the general secretary of CERN at its early stages when operations were still provisional, while the first Director-General was Felix Bloch; the laboratory was devoted to the study of atomic nuclei, but was soon applied to higher-energy physics, concerned with the study of interactions between subatomic particles.
Therefore, the laboratory operated by CERN is referred to as the European laboratory for particle physics, which better describes the research being performed there. At the sixth session of the CERN Council, which took place in Paris from 29 June - 1 July 1953, the convention establishing the organization was signed, subject to ratification, by 12 states; the convention was ratified by the 12 founding Member States: Belgium, France, the Federal Republic of Germany, Italy, the Netherlands, Sweden, the United Kingdom, Yugoslavia. Several important achievements in particle physics have been made through experiments at CERN, they include: 1973: The discovery of neutral currents in the Gargamelle bubble chamber. In September 2011, CERN attracted media attention when the OPERA Collaboration reported the detection of faster-than-light neutrinos. Further tests showed that the results were flawed due to an incorrectly connected GPS synchronization cable; the 1984 Nobel Prize for Physics was awarded to Carlo Rubbia and Simon van der Meer for the developments that resulted in the discoveries of the W and Z bosons.
The 1992 Nobel Prize for Physics was awarded to CERN staff researcher Georges Charpak "for his invention and development of particle detectors, in particular the multiwire proportional chamber". The 2013 Nobel Prize for Physics was awarded to François Englert and Peter Higgs for the theoretical description of the Higgs mechanism in the year after the Higgs boson was found by CERN experiments; the World Wide Web began as a CERN project named ENQUIRE, initiated by Tim Berners-Lee in 1989 and Robert Cailliau in 1990. Berners-Lee and Cailliau were jointly honoured by the Association for Computing Machinery in 1995 for their contributions to the development of the World Wide Web. Based on the concept of hypertext, the project was intended to facilitate the sharing of information between researchers; the first website was activated in 1991. On 30 April 1993, CERN announced. A copy of the original first webpage, created by Berners-Lee, is still published on the World Wide Web Consortium's website as a historical document.
Prior to the Web's development, CERN had pioneered the introduction of Internet technology, beginning in the early 1980s. More CERN has become a facility for the development of grid computing, hosting projects including the Enabling Grids for E-sciencE and LHC Computing Grid, it hosts the CERN Internet Exchange Point, one of the two main internet exchange points in Switzerland. CERN operates a network of a decelerator; each machine in the chain increases the energy of particle beams before delivering them
Brașov is a city in Romania and the administrative centre of Brașov County. According to the latest Romanian census, Brașov has a population of 253,200 making it the 7th most populous city in Romania; the metropolitan area is home to 382,896 residents. Brașov is located in the central part of the country, about 166 kilometres north of Bucharest and 380 kilometres from the Black Sea, it is part of the historical region of Transylvania. The city is notable for being the regional capital of the Transylvanian Saxons of the Burzenland administrative area in the past, a large commercial hub on the trade roads between East and West, it is the birthplace of the national anthem of Romania. According to Balázs Orbán, the name Corona - a Latin word meaning "crown" - is first mentioned in the Catalogus Ninivensis in 1235 AD, stating a monastic quarter existed in the territory of the Roman Catholic Diocese of Cumania. Pál Binder supposing it is a reference to the St. Catherine's Monastery. Others suggest the name derives from the old coat of arms of the city, as it is symbolized by the German name Kronstadt meaning "Crown City".
The two names of the city and Corona, were used in the Middle Ages, along with the Medieval Latin Brassovia. According to Dragoș Moldovanu, the name of Brașov came from the name of local river named Bârsa, adopted by Slavs and transformed in Barsa and in Barsov and in Brasov According to Pál Binder, the current Romanian and the Hungarian name Brassó are derived from the Turkic word barasu, meaning "white water" with a Slavic suffix -ov. Other linguists proposed various etymologies including an Old Slavic anthroponym Brasa; the first attested mention of this name is Terra Saxonum de Barasu in a 1252 document issued by Béla IV of Hungary. According to some historians, Corona was name of the city-fortess while Brassó was referreing to the county, while others consider both names may refer to the city and the county as well. Another historical name used for Brașov is Stephanopolis, lit. "Stephenstown". From 1950 to 1960, during part of the Communist period in Romania, the city was called Orașul Stalin, lit.
"Stalin City", after the Soviet leader Joseph Stalin. Brașov has a humid continental climate; the oldest traces of human activity and settlements in Brașov date back to the Neolithic age. Archaeologists working from the last half of the 19th century discovered continuous traces of human settlements in areas situated in Brașov: Valea Cetății, Pietrele lui Solomon, Șprenghi, Tâmpa, Dealul Melcilor, Noua; the first three locations show traces of Dacian citadels. The last two locations had their names applied to Bronze Age cultures -- Noua. German colonists known as the Transylvanian Saxons played a decisive role in Brașov's development; these Germans were brought by Hungarian kings to develop towns, build mines, cultivate the land of Transylvania at different stages between 1141 and 1300. The settlers came from the Rhineland and the Moselle region, with others from Thuringia, Bavaria and France. In 1211, by order of King Andrew II of Hungary, the Teutonic Knights fortified the Burzenland to defend the border of the Kingdom of Hungary.
On the site of the village of Brașov, the Teutonic Knights built Kronstadt – the city of the crown. Although the crusaders were evicted by 1225, the colonists they brought in remained, along with local population, as did three distinct settlements they founded on the site of Brașov: Corona, around the Black Church. Germans living in Brașov were involved in trade and crafts; the location of the city at the intersection of trade routes linking the Ottoman Empire and Western Europe, together with certain tax exemptions, allowed Saxon merchants to obtain considerable wealth and exert a strong political influence. They contributed a great deal to the architectural flavor of the city. Fortifications around the city were erected and continually expanded, with several towers maintained by different craftsmen's guilds, according to medieval custom. Part of the fortification ensemble was restored using UNESCO funds, other projects are ongoing. At least two entrances to the city, Poarta Ecaterinei and Poarta Șchei, are still in existence.
The city center is marked by the mayor's former office building and the surrounding square, which includes one of the oldest buildings in Brașov, the Hirscher Haus. Nearby is the "Black Church", which some claim to be the largest Gothic style church in Southeastern Europe. In 1689, a great fire destroyed the walled city entirely, its rebuilding lasted several decades. Besides the German population living in the walled city and in the northern suburbs, Brașov had a significant Romanian and Bulgarian population, some Hungarian population; the cultural and religious importance of the Romanian church and school in Șchei is underlined by the generous donations received from more than thirty hospodars of Moldavia and Wallachia, as well as that from Elizabeth of Russia. In the 17th and 19th centuries, t
Quantum computing is the use of quantum-mechanical phenomena such as superposition and entanglement to perform computation. A quantum computer is used to perform such computation, which can be implemented theoretically or physically; the field of quantum computing is a sub-field of quantum information science, which includes quantum cryptography and quantum communication. Quantum Computing was started in the early 1980s when Richard Feynman and Yuri Manin expressed the idea that a quantum computer had the potential to simulate things that a classical computer could not. In 1994, Peter Shor shocked the world with an algorithm that had the potential to decrypt all secured communications. There are two main approaches to physically implementing a quantum computer analog and digital. Analog approaches are further divided into quantum simulation, quantum annealing, adiabatic quantum computation. Digital quantum computers use quantum logic gates to do computation. Both approaches use quantum qubits.
Qubits are fundamental to quantum computing and are somewhat analogous to bits in a classical computer. Qubits can be in a 0 quantum state, but they can be in a superposition of the 1 and 0 states. However, when qubits are measured they always give a 0 or a 1 based on the quantum state they were in. Today's physical quantum computers are noisy and quantum error correction is a burgeoning field of research. Quantum supremacy is the next milestone that quantum computing will achieve soon. While there is much hope and research in the field of quantum computing, as of March 2019 there have been no commercially useful algorithms published for today's noisy quantum computers. A classical computer has a memory made up of bits, where each bit is represented by either a one or a zero. A quantum computer, on the other hand, maintains a sequence of qubits, which can represent a one, a zero, or any quantum superposition of those two qubit states. In general, a quantum computer with n qubits can be in any superposition of up to 2 n different states..
A quantum computer operates on its qubits using measurement. An algorithm is composed of a fixed sequence of quantum logic gates and a problem is encoded by setting the initial values of the qubits, similar to how a classical computer works; the calculation ends with a measurement, collapsing the system of qubits into one of the 2 n eigenstates, where each qubit is zero or one, decomposing into a classical state. The outcome can, therefore, be at most n classical bits of information. If the algorithm did not end with a measurement, the result is an unobserved quantum state. Quantum algorithms are probabilistic, in that they provide the correct solution only with a certain known probability. Note that the term non-deterministic computing must not be used in that case to mean probabilistic because the term non-deterministic has a different meaning in computer science. An example of an implementation of qubits of a quantum computer could start with the use of particles with two spin states: "down" and "up".
This is true. A quantum computer with a given number of qubits is fundamentally different from a classical computer composed of the same number of classical bits. For example, representing the state of an n-qubit system on a classical computer requires the storage of 2n complex coefficients, while to characterize the state of a classical n-bit system it is sufficient to provide the values of the n bits, that is, only n numbers. Although this fact may seem to indicate that qubits can hold exponentially more information than their classical counterparts, care must be taken not to overlook the fact that the qubits are only in a probabilistic superposition of all of their states; this means that when the final state of the qubits is measured, they will only be found in one of the possible configurations they were in before the measurement. It is incorrect to think of a system of qubits as being in one particular state before the measurement; the qubits are in a superposition of states before any measurement is made, which directly affects the possible outcomes of the computation.
To better understand this point, consider a classical computer that operates on a three-bit register. If the exact state of the register at a given time is not known, it can be described as a probability distribution over the 2 3 = 8 different three-bit strings 000, 001, 010, 011, 100, 101, 110, 111. If there is no uncertainty over its state it is in one of these states with probability 1. However, if it is a probabilistic computer there is a possibility of it being in any one of a number of different states; the state of a three-qubit quantum computer is described by an eight-dimensional vector (
Cluj-Napoca known as Cluj, is the fourth most populous city in Romania, the seat of Cluj County in the northwestern part of the country. Geographically, it is equidistant from Bucharest and Belgrade. Located in the Someșul Mic River valley, the city is considered the unofficial capital to the historical province of Transylvania. From 1790 to 1848 and from 1861 to 1867, it was the official capital of the Grand Principality of Transylvania; as of 2011, 324,576 inhabitants lived within the city limits, marking a slight increase from the figure recorded at the 2002 census. The Cluj-Napoca metropolitan area has a population of 411,379 people, while the population of the peri-urban area exceeds 420,000 residents; the new metropolitan government of Cluj-Napoca became operational in December 2008. According to a 2007 estimate provided by the County Population Register Service, the city hosts a visible population of students and other non-residents—an average of over 20,000 people each year during 2004–2007.
The city spreads out from St. Michael's Church in Unirii Square, built in the 14th century and named after the Archangel Michael, the patron saint of Cluj-Napoca; the boundaries of the municipality contain an area of 179.52 square kilometres. Cluj-Napoca experienced a decade of decline during the 1990s, its international reputation suffering from the policies of its mayor at the time, Gheorghe Funar. Today, the city is one of the most important academic, cultural and business centres in Romania. Among other institutions, it hosts the country's largest university, Babeș-Bolyai University, with its botanical garden. Cluj-Napoca held the titles of European Youth Capital in 2015 and European City of Sport in 2018. On the site of the city was a pre-Roman settlement named Napoca. After the AD 106 Roman conquest of the area, the place was known as Municipium Aelium Hadrianum Napoca. Possible etymologies for Napoca or Napuca include the names of some Dacian tribes such as the Naparis or Napaei, the Greek term napos, meaning "timbered valley" or the Indo-European root *snā-p-, "to flow, to swim, damp".
The first written mention of the city's current name – as a Royal Borough – was in 1213 under the Medieval Latin name Castrum Clus. Despite the fact that Clus as a county name was recorded in the 1173 document Thomas comes Clusiensis, it is believed that the county's designation derives from the name of the castrum, which might have existed prior to its first mention in 1213, not vice versa. With respect to the name of this camp, it is accepted as a derivation from the Latin term clausa – clusa, meaning "closed place", "strait", "ravine". Similar senses are attributed to the Slavic term kluč, meaning "a key" and the German Klause – Kluse; the Latin and Slavic names have been attributed to the valley that narrows or closes between hills just to the west of Cluj-Mănăștur. An alternative hypothesis relates the name of the city to its first magistrate, Miklus – Miklós / Kolos; the Hungarian form Kolozsvár, first recorded in 1246 as Kulusuar, underwent various phonetic changes over the years. Its Saxon name Clusenburg/Clusenbvrg appeared in 1348.
The Romanian name of the city used to be spelled alternately as Cluj or Cluș, the latter being the case in Mihai Eminescu's Poesis. In 1974, the communist authorities added "-Napoca" to the city's name as a nationalist gesture, emphasising its pre-Roman roots; the full name is used outside of official contexts. In Yiddish it is known as קלאזין or קלויזענבורג; the nickname "treasure city" was acquired in the late 16th century, refers to the wealth amassed by residents, including in the precious metals trade. The phrase is kincses város in Hungarian, given in Romanian as orașul comoară; the Roman Empire conquered Dacia in AD 101 and 106, during the rule of Trajan, the Roman settlement Napoca, established thereafter, is first recorded on a milestone discovered in 1758 in the vicinity of the city. Trajan's successor Hadrian granted Napoca the status of municipium as municipium Aelium Hadrianum Napocenses. In the 2nd century AD, the city gained the status of a colonia as Colonia Aurelia Napoca. Napoca became thus the seat of a procurator.
The colonia was evacuated in 274 by the Romans. There are no references to urban settlement on the site for the better part of a millennium thereafter. At the beginning of the Middle Ages, two groups of buildings existed on the current site of the city: the wooden fortress at Cluj-Mănăștur and the civilian settlement developed around the current Piața Muzeului in the city centre. Although the precise date of the conquest of Transylvania by the Hungarians is not known, the earliest Hungarian artifacts found in the region are dated to the first half of the 10th century. In any case, after that time, the city became part of the Kingdom of Hungary. King Stephen I made the city the seat of the castle county of Kolozs, King Saint Ladislaus I of Hungary founded the abbey of Cluj-Mănăștur, destroyed during the Tatar invasions in 12
Transylvania is a historical region, located in central Romania. Bound on the east and south by its natural borders, the Carpathian mountain range, historical Transylvania extended westward to the Apuseni Mountains; the term sometimes encompasses not only Transylvania proper, but parts of the historical regions of Crișana and Maramureș, the Romanian part of Banat. The region of Transylvania is known for the scenery of its Carpathian landscape and its rich history, it contains major cities such as Cluj-Napoca, Brașov, Sibiu, Târgu Mureș, Bistrița. The Western world associates Transylvania with vampires, because of the influence of Bram Stoker's novel Dracula and its many film adaptations. Historical names of Transylvania are: Latin: Ultrasilvania, Transsilvania Romanian: Ardeal, Transilvania Russian: Ардял, translit. Ardjal, Трансильвания Transil'vanija Hungarian: Erdély Ukrainian: Семигород, translit. Semyhorod, Залісся Zalissja, Трансильванія Transyl'vanija Serbian: Ердељ, translit. Erdelj, Трансилванија Transilvanija Croatian: Sedmogradska, Transilvanija Bulgarian: Седмоградско, translit.
Sedmogradsko, Трансилвания Transilvanija Slovak: Sedmohradsko German: Siebenbürgen, Transsilvanien Transylvanian Saxon: Siweberjen Polish: Siedmiogród, Transylwania Turkish: Erdel, Transilvanya Romani: TransilvaniyaIn Romanian, the region is known as Ardeal or Transilvania. The earliest known reference to Transylvania appears in a Medieval Latin document in 1075 as ultra silvam, meaning "beyond the forest". Transylvania, with an alternative Latin prepositional prefix, means "on the other side of the woods". Hungarian historians claim that the Medieval Latin form Ultrasylvania Transsylvania, was a direct translation from the Hungarian form Erdő-elve; that was used as an alternative name in German überwald and Ukrainian Залісся. The German name Siebenbürgen means "seven castles", after the seven Transylvanian Saxons' cities in the region; this is the origin of the region's name in many other languages, such as the Croatian Sedmogradska, the Bulgarian Седмиградско, Polish Siedmiogród and the Ukrainian Семигород.
The Hungarian form Erdély was first mentioned in the 12th-century Gesta Hungarorum as Erdeuleu or Erdő-elve. The word Erdő means forest in Hungarian, the word Elve denotes a region in connection with this to the Hungarian name for Muntenia. Erdel, Erdelistan, the Turkish equivalents, or the Romanian Ardeal were borrowed from this form as well; the first known written occurrence of the Romanian name Ardeal appeared in a document in 1432 as Ardeliu. The Romanian Ardeal is derived from the Hungarian Erdély. Transylvania has been dominated by several different countries throughout its history, it was once the nucleus of the Kingdom of Dacia. In 106 AD the Roman Empire conquered the territory. After the Roman legions withdrew in 271 AD, it was overrun by a succession of various tribes, bringing it under the control of the Carpi, Huns, Gepids and Slavs. From 9th to 11th century Bulgarians ruled Transylvania, it is a subject of dispute whether elements of the mixed Daco–Roman population survived in Transylvania through the Post-classical Era or the first Vlachs/Romanians appeared in the area in the 13th century after a northward migration from the Balkan Peninsula.
There is an ongoing scholarly debate over the ethnicity of Transylvania's population before the Hungarian conquest. The Magyars conquered much of Central Europe at the end of the 9th century. According to Gesta Hungarorum, the Vlach voivode Gelou ruled Transylvania before the Hungarians arrived; the Kingdom of Hungary established partial control over Transylvania in 1003, when king Stephen I, according to legend, defeated the prince named Gyula. Some historians assert Transylvania was settled by Hungarians in several stages between the 10th and 13th centuries, while others claim that it was settled, since the earliest Hungarian artifacts found in the region are dated to the first half of the 10th century. Between 1003 and 1526, Transylvania was a voivodeship in the Kingdom of Hungary, led by a voivode appointed by the King of Hungary. After the Battle of Mohács in 1526, Transylvania became part of the Kingdom of János Szapolyai. In 1570, the kingdom transformed into the Principality of Transylvania, ruled by Calvinist Hungarian princes.
During that time, the ethnic composition of Transylvania transformed from an estimated near equal number of the ethnic groups to a Romanian majority. Vasile Lupu estimates their number more than one-third of the population of Transylvania in a letter to the sultan around 1650. For most of this period, maintaining its internal autonomy, was under the suzerainty of the Ottoman Empire; the Habsburgs acquired the territory shortly after the Battle of Vienna in 1683. In 1687, the rulers of Transylvania recognized the suzerainty of the Habsburg emperor Leopold I, the region was attached to the Habsburg Empire; the Habsburgs acknowledged Principality of Transylvania as one of the Lands of the Crown of Saint Stephen, but the territory of principality was administratively separa
A neutrino is a fermion that interacts only via the weak subatomic force and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small that it was long thought to be zero; the mass of the neutrino is much smaller than that of the other known elementary particles. The weak force has a short range, the gravitational interaction is weak, neutrinos, as leptons, do not participate in the strong interaction. Thus, neutrinos pass through normal matter unimpeded and undetected. Weak interactions create neutrinos in one of three leptonic flavors: electron neutrinos, muon neutrinos, or tau neutrinos, in association with the corresponding charged lepton. Although neutrinos were long believed to be massless, it is now known that there are three discrete neutrino masses with different tiny values, but they do not correspond uniquely to the three flavors. A neutrino created with a specific flavor is in an associated specific quantum superposition of all three mass states.
As a result, neutrinos oscillate between different flavors in flight. For example, an electron neutrino produced in a beta decay reaction may interact in a distant detector as a muon or tau neutrino. Although only differences of squares of the three mass values are known as of 2016, cosmological observations imply that the sum of the three masses must be less than one millionth that of the electron. For each neutrino, there exists a corresponding antiparticle, called an antineutrino, which has half-integer spin and no electric charge, they are distinguished from the neutrinos by having opposite signs of lepton chirality. To conserve total lepton number, in nuclear beta decay, electron neutrinos appear together with only positrons or electron-antineutrinos, electron antineutrinos with electrons or electron neutrinos. Neutrinos are created by various radioactive decays, including in beta decay of atomic nuclei or hadrons, nuclear reactions such as those that take place in the core of a star or artificially in nuclear reactors, nuclear bombs or particle accelerators, during a supernova, in the spin-down of a neutron star, or when accelerated particle beams or cosmic rays strike atoms.
The majority of neutrinos in the vicinity of the Earth are from nuclear reactions in the Sun. In the vicinity of the Earth, about 65 billion solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun. For study, neutrinos can be created artificially with nuclear reactors and particle accelerators. There is intense research activity involving neutrinos, with goals that include the determination of the three neutrino mass values, the measurement of the degree of CP violation in the leptonic sector. Neutrinos can be used for tomography of the interior of the earth; the neutrino was postulated first by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy and angular momentum. In contrast to Niels Bohr, who proposed a statistical version of the conservation laws to explain the observed continuous energy spectra in beta decay, Pauli hypothesized an undetected particle that he called a "neutron", using the same -on ending employed for naming both the proton and the electron.
He considered that the new particle was emitted from the nucleus together with the electron or beta particle in the process of beta decay. James Chadwick discovered a much more massive neutral nuclear particle in 1932 and named it a neutron leaving two kinds of particles with the same name. Earlier Pauli had used the term "neutron" for both the neutral particle that conserved energy in beta decay, a presumed neutral particle in the nucleus; the word "neutrino" entered the scientific vocabulary through Enrico Fermi, who used it during a conference in Paris in July 1932 and at the Solvay Conference in October 1933, where Pauli employed it. The name was jokingly coined by Edoardo Amaldi during a conversation with Fermi at the Institute of Physics of via Panisperna in Rome, in order to distinguish this light neutral particle from Chadwick's heavy neutron. In Fermi's theory of beta decay, Chadwick's large neutral particle could decay to a proton and the smaller neutral particle: n0 → p+ + e− + νeFermi's paper, written in 1934, unified Pauli's neutrino with Paul Dirac's positron and Werner Heisenberg's neutron–proton model and gave a solid theoretical basis for future experimental work.
The journal Nature rejected Fermi's paper, saying that the theory was "too remote from reality". He submitted the paper to an Italian journal, which accepted it, but the general lack of interest in his theory at that early date caused him to switch to experimental physics. By 1934 there was experimental evidence against Bohr's idea that energy conservation is invalid for beta decay: At the Solvay conference of that year, measurements of the energy spectra of beta particles were reported, showing that there is a strict limit on the energy of electrons from each type of beta decay; such a limit is not expected if the conservation of energy is invalid, in which case any amount of energy would be statistically available in at least a few decays. The natural explanation of the beta decay spectrum as first measured in 1934 was that only a limited amount of en