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120-492: The primary purpose of the HFBR was to produce neutrons for multiple scientific uses. The reactor provided a source of neutrons for multidisciplinary scientific research in materials science, chemistry, biology, and physics. The reactor was used in the formulation of Nobel Prize -winning theories of cooperative ordering in large collections of atoms . The reactor first reached criticality on October 31, 1965. About twice as large as

240-425: A fermion with intrinsic angular momentum equal to ⁠ 1 / 2 ⁠   ħ , where ħ is the reduced Planck constant . For many years after the discovery of the neutron, its exact spin was ambiguous. Although it was assumed to be a spin  ⁠ 1 / 2 ⁠ Dirac particle , the possibility that the neutron was a spin  ⁠ 3 / 2 ⁠ particle lingered. The interactions of

360-408: A nuclear chain reaction . These events and findings led to the first self-sustaining nuclear reactor ( Chicago Pile-1 , 1942) and the first nuclear weapon ( Trinity , 1945). Dedicated neutron sources like neutron generators , research reactors and spallation sources produce free neutrons for use in irradiation and in neutron scattering experiments. A free neutron spontaneously decays to

480-484: A proton . Protons and neutrons constitute the nuclei of atoms . Since protons and neutrons behave similarly within the nucleus, they are both referred to as nucleons . Nucleons have a mass of approximately one atomic mass unit, or dalton (symbol: Da). Their properties and interactions are described by nuclear physics . Protons and neutrons are not elementary particles ; each is composed of three quarks . The chemical properties of an atom are mostly determined by

600-546: A (metric) ton [1000 kg] of Lanthanum oxide 99% (FOB China in USD/Mt) is given by the Institute of Rare Earths Elements and Strategic Metals (IREESM) as below $ 2,000 for most of the period from early 2001 to September 2010 (at $ 10,000 in the short term in 2008); it rose steeply to $ 140,000 in mid-2011 and fell back just as rapidly to $ 38,000 by early 2012. The average price for the last six months (April–September 2022)

720-401: A bottle, while the "beam" method employs energetic neutrons in a particle beam. The measurements by the two methods have not been converging with time. The lifetime from the bottle method is presently 877.75 s which is 10 seconds below the value from the beam method of 887.7 s A small fraction (about one per thousand) of free neutrons decay with the same products, but add an extra particle in

840-456: A cascade known as a nuclear chain reaction . For a given mass of fissile material, such nuclear reactions release energy that is approximately ten million times that from an equivalent mass of a conventional chemical explosive . Ultimately, the ability of the nuclear force to store energy arising from the electromagnetic repulsion of nuclear components is the basis for most of the energy that makes nuclear reactors or bombs possible; most of

960-544: A deuteron is formed by a proton capturing a neutron (this is exothermic and happens with zero-energy neutrons). The small recoil kinetic energy ( E r d {\displaystyle E_{rd}} ) of the deuteron (about 0.06% of the total energy) must also be accounted for. The energy of the gamma ray can be measured to high precision by X-ray diffraction techniques, as was first done by Bell and Elliot in 1948. The best modern (1986) values for neutron mass by this technique are provided by Greene, et al. These give

1080-643: A green-tinted light and were not very successful, and his first company, which established a factory in Atzgersdorf in 1887, failed in 1889. Modern uses of lanthanum include: Lanthanum has no known biological role in humans. The element is very poorly absorbed after oral administration and when injected its elimination is very slow. Lanthanum carbonate (Fosrenol) was approved as a phosphate binder to absorb excess phosphate in cases of end stage renal disease . While lanthanum has pharmacological effects on several receptors and ion channels, its specificity for

1200-401: A heavy mineral from the mine at Bastnäs , later named cerite . Thirty years later, the fifteen-year-old Wilhelm Hisinger , from the family owning the mine, sent a sample of it to Carl Scheele , who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral with Jöns Jacob Berzelius and isolated a new oxide which they named ceria after

1320-438: A hexagonal 7-coordinate structure that changes to the 6-coordinate structure of scandium oxide ( Sc 2 O 3 ) and yttrium oxide ( Y 2 O 3 ) at high temperature. When it reacts with water, lanthanum hydroxide is formed: a lot of heat is evolved in the reaction and a hissing sound is heard. Lanthanum hydroxide will react with atmospheric carbon dioxide to form the basic carbonate. Lanthanum fluoride

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1440-430: A leak of tritiated water was identified by routine sampling of groundwater from wells located adjacent to the reactor's spent fuel pool. Upon further investigation, a leak was discovered in the spent fuel pool that released tritium-contaminated water into the ground. The reactor remained shut for three years for safety and environmental reviews. In January 1998, all the spent fuel was removed and shipped off site to allow for

1560-454: A low to moderate level of toxicity and should be handled with care. The injection of lanthanum solutions produces hyperglycemia , low blood pressure, degeneration of the spleen and hepatic alterations. The application in carbon arc light led to the exposure of people to rare earth element oxides and fluorides, which sometimes led to pneumoconiosis . As the La ion is similar in size to

1680-488: A magnetic field to separate the neutron spin states. They recorded two such spin states, consistent with a spin  ⁠ 1 / 2 ⁠ particle. As a fermion, the neutron is subject to the Pauli exclusion principle ; two neutrons cannot have the same quantum numbers. This is the source of the degeneracy pressure which counteracts gravity in neutron stars and prevents them from forming black holes. Even though

1800-417: A mass spectrometer, the mass of a neutron can be deduced by subtracting proton mass from deuteron mass, with the difference being the mass of the neutron plus the binding energy of deuterium (expressed as a positive emitted energy). The latter can be directly measured by measuring the energy ( B d {\displaystyle B_{d}} ) of the single 2.224 MeV gamma photon emitted when

1920-416: A mean-square radius of about 0.8 × 10   m , or 0.8  fm , and it is a spin-½ fermion . The neutron has no measurable electric charge. With its positive electric charge, the proton is directly influenced by electric fields , whereas the neutron is unaffected by electric fields. The neutron has a magnetic moment , however, so it is influenced by magnetic fields . The specific properties of

2040-404: A neutron by some heavy nuclides (such as uranium-235 ) can cause the nuclide to become unstable and break into lighter nuclides and additional neutrons. The positively charged light nuclides, or "fission fragments", then repel, releasing electromagnetic potential energy . If this reaction occurs within a mass of fissile material , the additional neutrons cause additional fission events, inducing

2160-448: A neutron mass of: The value for the neutron mass in MeV is less accurately known, due to less accuracy in the known conversion of Da to MeV/ c : Another method to determine the mass of a neutron starts from the beta decay of the neutron, when the momenta of the resulting proton and electron are measured. The neutron is a spin  ⁠ 1 / 2 ⁠ particle, that is, it is

2280-543: A nucleon. The discrepancy stems from the complexity of the Standard Model for nucleons, where most of their mass originates in the gluon fields, virtual particles, and their associated energy that are essential aspects of the strong force . Furthermore, the complex system of quarks and gluons that constitute a neutron requires a relativistic treatment. But the nucleon magnetic moment has been successfully computed numerically from first principles , including all of

2400-489: A nucleus. The observed properties of atoms and molecules were inconsistent with the nuclear spin expected from the proton–electron hypothesis. Protons and electrons both carry an intrinsic spin of ⁠ 1 / 2 ⁠ ħ , and the isotopes of the same species were found to have either integer or fractional spin. By the hypothesis, isotopes would be composed of the same number of protons, but differing numbers of neutral bound proton+electron "particles". This physical picture

2520-417: A pair of protons, one with spin up, another with spin down. When all available proton states are filled, the Pauli exclusion principle disallows the decay of a neutron to a proton. The situation is similar to electrons of an atom, where electrons that occupy distinct atomic orbitals are prevented by the exclusion principle from decaying to lower, already-occupied, energy states. The stability of matter

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2640-444: A protective oxide coating like aluminium , scandium, yttrium, and lutetium. Lanthanum reacts with the halogens at room temperature to form the trihalides, and upon warming will form binary compounds with the nonmetals nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic. Lanthanum reacts slowly with water to form lanthanum(III) hydroxide , La(OH) 3 . In dilute sulfuric acid , lanthanum readily forms

2760-423: A proton, an electron , and an antineutrino , with a mean lifetime of about 15 minutes. Free neutrons do not directly ionize atoms, but they do indirectly cause ionizing radiation , so they can be a biological hazard, depending on dose. A small natural "neutron background" flux of free neutrons exists on Earth, caused by cosmic ray showers , and by the natural radioactivity of spontaneously fissionable elements in

2880-473: A radionuclide decay period not exceeding 65 years. The red and white, 320-foot-tall exhaust stack constructed for the BGRR in 1949 and later shared with the HFBR was a distinctive landmark for the area until its demolition in 2020. Neutrons The neutron is a subatomic particle , symbol n or n , that has no electric charge, and a mass slightly greater than that of

3000-419: A rare isotope carbon-13 with 7 neutrons. Some elements occur in nature with only one stable isotope , such as fluorine . Other elements occur with many stable isotopes, such as tin with ten stable isotopes, or with no stable isotope, such as technetium . The properties of an atomic nucleus depend on both atomic and neutron numbers. With their positive charge, the protons within the nucleus are repelled by

3120-403: A reactor beam line. Solid and gaseous fission products, including gaseous iodine-131 , had been produced during the experiment and were released in the fire. Smoke from the fire was identified by on-duty personnel approximately 2:20 a.m.; the reactor was shut down at 2:45 a.m. and the HFBR confinement evacuated at 3:47 a.m. At 4:51 a.m. BNL officials declared an Alert emergency,

3240-525: A sample of cerium nitrate by roasting it in air and then treating the resulting oxide with dilute nitric acid . That same year, Axel Erdmann , a student also at the Karolinska Institute, discovered lanthanum in a new mineral from Låven island located in a Norwegian fjord. Finally, Mosander explained his delay, saying that he had extracted a second element from cerium, and this he called didymium. Although he did not realise it, didymium too

3360-399: A secondary cooling loop of ordinary water which flowed through cooling towers located west of the HFBR confinement. Notably, the reactor produced its greatest neutron flux outside of the core, rather than within, which allowed for greatest options in the design of experiments. During 1993, the HFBR underwent safety upgrades as well as installation of new scientific instruments. External to

3480-481: A series of experiments that showed that the new radiation consisted of uncharged particles with about the same mass as the proton. These properties matched Rutherford's hypothesized neutron. Chadwick won the 1935 Nobel Prize in Physics for this discovery. Models for an atomic nucleus consisting of protons and neutrons were quickly developed by Werner Heisenberg and others. The proton–neutron model explained

3600-404: A simple nonrelativistic , quantum mechanical wavefunction for baryons composed of three quarks. A straightforward calculation gives fairly accurate estimates for the magnetic moments of neutrons, protons, and other baryons. For a neutron, the result of this calculation is that the magnetic moment of the neutron is given by μ n = 4/3 μ d − 1/3 μ u , where μ d and μ u are

3720-413: Is a consequence of these constraints. The decay of a neutron within a nuclide is illustrated by the decay of the carbon isotope carbon-14 , which has 6 protons and 8 neutrons. With its excess of neutrons, this isotope decays by beta decay to nitrogen-14 (7 protons, 7 neutrons), a process with a half-life of about 5,730 years . Nitrogen-14 is stable. "Beta decay" reactions can also occur by

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3840-403: Is an essential cofactor for the methanol dehydrogenase of the methanotrophic bacterium Methylacidiphilum fumariolicum SolV, although the great chemical similarity of the lanthanides means that it may be substituted with cerium, praseodymium, or neodymium without ill effects, and with the smaller samarium, europium, or gadolinium giving no side effects other than slower growth. Lanthanum has

3960-723: Is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead . In minerals such as monazite and bastnäsite , lanthanum composes about a quarter of the lanthanide content. It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923. Lanthanum compounds have numerous applications including catalysts , additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes , scintillators , and gas tungsten arc welding electrodes. Lanthanum carbonate

4080-492: Is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity. Lanthanum usually occurs together with cerium and the other rare earth elements. Lanthanum was first found by the Swedish chemist Carl Gustaf Mosander in 1839 as an impurity in cerium nitrate – hence the name lanthanum , from the ancient Greek λανθάνειν ( lanthanein ), meaning 'to lie hidden'. Although it

4200-403: Is essential to the production of nuclear power. In the decade after the neutron was discovered by James Chadwick in 1932, neutrons were used to induce many different types of nuclear transmutations . With the discovery of nuclear fission in 1938, it was quickly realized that, if a fission event produced neutrons, each of these neutrons might cause further fission events, in a cascade known as

4320-481: Is followed by reduction with alkali or alkaline earth metals in vacuum or argon atmosphere: Also, pure lanthanum can be produced by electrolysis of molten mixture of anhydrous LaCl 3 and NaCl or KCl at elevated temperatures. The first historical application of lanthanum was in gas lantern mantles . Carl Auer von Welsbach used a mixture of lanthanum oxide and zirconium oxide , which he called Actinophor and patented in 1886. The original mantles gave

4440-448: Is for one of the neutron's quarks to change flavour (through a Cabibbo–Kobayashi–Maskawa matrix ) via the weak interaction . The decay of one of the neutron's down quarks into a lighter up quark can be achieved by the emission of a W boson . By this process, the Standard Model description of beta decay, the neutron decays into a proton (which contains one down and two up quarks), an electron, and an electron antineutrino . The decay of

4560-402: Is insoluble in water and can be used as a qualitative test for the presence of La . The heavier halides are all very soluble deliquescent compounds. The anhydrous halides are produced by direct reaction of their elements, as heating the hydrates causes hydrolysis: for example, heating hydrated LaCl 3 produces LaOCl . Lanthanum reacts exothermically with hydrogen to produce

4680-444: Is relatively less soluble than other rare earth double salts and therefore stays in the residue. Care must be taken when handling some of the residues as they contain Ra , the daughter of Th , which is a strong gamma emitter. Lanthanum is relatively easy to extract as it has only one neighbouring lanthanide, cerium, which can be removed by making use of its ability to be oxidised to

4800-452: Is removed. After that, the solution is treated with ammonium oxalate to convert rare earths to their insoluble oxalates . The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid that excludes one of the main components, cerium , whose oxide is insoluble in HNO 3 . Lanthanum is separated as a double salt with ammonium nitrate by crystallization. This salt

4920-457: Is still unknown. Lanthanum meant for ingestion, typically as a chewable tablet or oral powder, can interfere with gastrointestinal (GI) imaging by creating opacities throughout the GI tract; if chewable tablets are swallowed whole, they will dissolve but present initially as coin-shaped opacities in the stomach, potentially confused with ingested metal objects such as coins or batteries. The price for

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5040-420: Is the nuclear magneton . The neutron's magnetic moment has a negative value, because its orientation is opposite to the neutron's spin. The magnetic moment of the neutron is an indication of its quark substructure and internal charge distribution. In the quark model for hadrons , the neutron is composed of one up quark (charge +2/3  e ) and two down quarks (charge −1/3  e ). The magnetic moment of

5160-438: Is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table , of which lanthanum is the first and the prototype. Lanthanum is traditionally counted among the rare earth elements . Like most other rare earth elements, its usual oxidation state is +3, although some compounds are known with an oxidation state of +2. Lanthanum has no biological role in humans but

5280-404: Is the most characteristic, forming square antiprismatic and dodecadeltahedral structures. These high-coordinate species, reaching up to coordination number 12 with the use of chelating ligands such as in La 2 (SO 4 ) 3 · 9(H 2 O) , often have a low degree of symmetry because of stereo-chemical factors. Lanthanum chemistry tends not to involve π -bonding due to

5400-443: Is the only stable isotope of lanthanum. The very rare isotope La is one of the few primordial odd–odd nuclei , with a long half-life of 1.05×10 years. It is one of the proton-rich p-nuclei which cannot be produced in the s- or r-processes . La , along with the even rarer Ta , is produced in the ν-process, where neutrinos interact with stable nuclei. All other lanthanum isotopes are synthetic : With

5520-435: Is to be mentioned. Naturally occurring lanthanum is made up of two isotopes, the stable La and the primordial long-lived radioisotope La . La is by far the most abundant, making up 99.910% of natural lanthanum: it is produced in the s-process (slow neutron capture, which occurs in low- to medium-mass stars) and the r-process (rapid neutron capture, which occurs in core-collapse supernovae ). It

5640-404: Is used as a phosphate binder to treat high levels of phosphate in the blood accompanied by kidney failure . Lanthanum is the first element and prototype of the lanthanide series. In the periodic table, it appears to the right of the alkaline earth metal barium and to the left of the lanthanide cerium. Lanthanum is generally considered the first of the f-block elements by authors writing on

5760-449: The Ca ion, it is sometimes used as an easily traced substitute for the latter in medical studies. Lanthanum, like the other lanthanides, is known to affect human metabolism, lowering cholesterol levels, blood pressure, appetite, and risk of blood coagulation. When injected into the brain, it acts as a painkiller, similarly to morphine and other opiates, though the mechanism behind this

5880-713: The Chicago Pile-1 at the University of Chicago in 1942, the first self-sustaining nuclear reactor . Just three years later the Manhattan Project was able to test the first atomic bomb , the Trinity nuclear test in July 1945. The mass of a neutron cannot be directly determined by mass spectrometry since it has no electric charge. But since the masses of a proton and of a deuteron can be measured with

6000-603: The Earth's crust . An atomic nucleus is formed by a number of protons, Z (the atomic number ), and a number of neutrons, N (the neutron number ), bound together by the nuclear force . Protons and neutrons each have a mass of approximately one dalton . The atomic number determines the chemical properties of the atom, and the neutron number determines the isotope or nuclide . The terms isotope and nuclide are often used synonymously , but they refer to chemical and nuclear properties, respectively. Isotopes are nuclides with

6120-451: The GABA receptor is unique among trivalent cations. Lanthanum acts at the same modulatory site on the GABA receptor as zinc , a known negative allosteric modulator. The lanthanum cation La is a positive allosteric modulator at native and recombinant GABA receptors, increasing open channel time and decreasing desensitization in a subunit configuration dependent manner. Lanthanum

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6240-578: The dwarf planet Ceres , which had been discovered two years earlier. Ceria was simultaneously independently isolated in Germany by Martin Heinrich Klaproth . Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist Carl Gustaf Mosander , who lived in the same house as Berzelius and studied under him: he separated out two other oxides which he named lanthana and didymia . He partially decomposed

6360-431: The +4 state; thereafter, lanthanum may be separated out by the historical method of fractional crystallization of La(NO 3 ) 3 · 2 NH 4 NO 3 · 4 H 2 O , or by ion-exchange techniques when higher purity is desired. Lanthanum metal is obtained from its oxide by heating it with ammonium chloride or fluoride and hydrofluoric acid at 300–400 °C to produce the chloride or fluoride: This

6480-486: The 1920s, physicists assumed that the atomic nucleus was composed of protons and "nuclear electrons", but this raised obvious problems. It was difficult to reconcile the proton–electron model of the nucleus with the Heisenberg uncertainty relation of quantum mechanics. The Klein paradox , discovered by Oskar Klein in 1928, presented further quantum mechanical objections to the notion of an electron confined within

6600-512: The 1944 Nobel Prize in Chemistry "for his discovery of the fission of heavy atomic nuclei". The discovery of nuclear fission would lead to the development of nuclear power and the atomic bomb by the end of World War II. It was quickly realized that, if a fission event produced neutrons, each of these neutrons might cause further fission events, in a cascade known as a nuclear chain reaction. These events and findings led Fermi to construct

6720-558: The American chemist W. D. Harkins first named the hypothetical particle a "neutron". The name derives from the Latin root for neutralis (neuter) and the Greek suffix -on (a suffix used in the names of subatomic particles, i.e. electron and proton ). References to the word neutron in connection with the atom can be found in the literature as early as 1899, however. Throughout

6840-400: The HFBR complex, consisting of multiple structures and systems to operate and maintain the reactor, was completed from 1999 until 2009. The control rod blades were removed and shipped offsite in 2009. The emptied and cleaned HFBR dome, which still contains the irradiated reactor vessel is maintained under surveillance. Final decommissioning of the HFBR confinement is to be performed at the end of

6960-425: The HFBR control room around the clock. In addition to the beam lines, seven sample irradiation thimbles for neutron activation experiments were provided which extended from the spherical reactor vessel towards the nuclear fuel. As a research reactor, HFBR never had a power conversion system to generate electricity. Heat from the nuclear reactions was transferred from the circulating heavy water moderator and coolant to

7080-494: The 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". In December 1938 Otto Hahn , Lise Meitner , and Fritz Strassmann discovered nuclear fission , or the fractionation of uranium nuclei into lighter elements, induced by neutron bombardment. In 1945 Hahn received

7200-450: The aquated tripositive ion [La(H 2 O) 9 ] : This is colorless in aqueous solution since La has no d or f electrons. Lanthanum is the strongest and hardest base among the rare earth elements , which is again expected from its being the largest of them. Some lanthanum(II) compounds are also known, but they are much less stable. Therefore, in officially naming compounds of lanthanum its oxidation number always

7320-453: The atmosphere from the vent stack serving BGRR and HFBR. The amount of radiation released was compared to a few seconds to typical background radiation. BNL officials and New York state health officials agreed that there was no danger posed to the public from the release. HFBR was shut down for multiple investigations until June 1994, then restarted. The TRISTAN experiment was permanently discontinued. The decontamination and decommissioning of

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7440-402: The balcony. The confinement building has four access points: a personnel airlock; a forklift airlock; and two tractor-trailer airlocks, one located on the experimental level and one on the equipment level. Nine neutron beam lines extended from the HFBR in a radial spoke pattern. Up to 15 experiments could be run concurrently on the nine beam lines. Two reactor operators and two supervisors crewed

7560-406: The beta decay process. The neutrons and protons in a nucleus form a quantum mechanical system according to the nuclear shell model . Protons and neutrons of a nuclide are organized into discrete hierarchical energy levels with unique quantum numbers . Nucleon decay within a nucleus can occur if allowed by basic energy conservation and quantum mechanical constraints. The decay products, that is,

7680-400: The capture of a lepton by the nucleon. The transformation of a proton to a neutron inside of a nucleus is possible through electron capture : A rarer reaction, inverse beta decay , involves the capture of a neutrino by a nucleon. Rarer still, positron capture by neutrons can occur in the high-temperature environment of stars. Three types of beta decay in competition are illustrated by

7800-438: The common chemical element lead , Pb, has 82 protons and 126 neutrons, for example. The table of nuclides comprises all the known nuclides. Even though it is not a chemical element, the neutron is included in this table. Protons and neutrons behave almost identically under the influence of the nuclear force within the nucleus. They are therefore both referred to collectively as nucleons . The concept of isospin , in which

7920-441: The complex behavior of quarks to be subtracted out between models, and merely exploring what the effects would be of differing quark charges (or quark type). Such calculations are enough to show that the interior of neutrons is very much like that of protons, save for the difference in quark composition with a down quark in the neutron replacing an up quark in the proton. The neutron magnetic moment can be roughly computed by assuming

8040-496: The configuration of electrons that orbit the atom's heavy nucleus. The electron configuration is determined by the charge of the nucleus, which is determined by the number of protons, or atomic number . The number of neutrons is the neutron number . Neutrons do not affect the electron configuration. Atoms of a chemical element that differ only in neutron number are called isotopes . For example, carbon , with atomic number 6, has an abundant isotope carbon-12 with 6 neutrons and

8160-406: The confinement building is a 5 ft. thick reinforced concrete mat bearing on the soil beneath the building. The interior of the confinement building contained the reactor and biological shield and was divided into equipment, experimental, balcony, and operations levels. The operations level contained the control room, instrument and maintenance shops, labs and offices. The equipment level contained

8280-552: The difference in mass represents the mass equivalent to nuclear binding energy, the energy which would need to be added to take the nucleus apart. The nucleus of the most common isotope of the hydrogen atom (with the chemical symbol H) is a lone proton. The nuclei of the heavy hydrogen isotopes deuterium (D or H) and tritium (T or H) contain one proton bound to one and two neutrons, respectively. All other types of atomic nuclei are composed of two or more protons and various numbers of neutrons. The most common nuclide of

8400-405: The dihydride LaH 2 , a black, pyrophoric , brittle, conducting compound with the calcium fluoride structure. This is a non-stoichiometric compound, and further absorption of hydrogen is possible, with a concomitant loss of electrical conductivity, until the more salt-like LaH 3 is reached. Like LaI 2 and LaI , LaH 2 is probably an electride compound. Due to

8520-412: The effects mentioned and using more realistic values for the quark masses. The calculation gave results that were in fair agreement with measurement, but it required significant computing resources. Lanthanum Lanthanum is a chemical element with the symbol La and the atomic number  57. It is a soft , ductile , silvery-white metal that tarnishes slowly when exposed to air. It

8640-436: The electron configuration of the element: thus its organometallic chemistry is quite limited. The best characterized organolanthanum compounds are the cyclopentadienyl complex La(C 5 H 5 ) 3 , which is produced by reacting anhydrous LaCl 3 with NaC 5 H 5 in tetrahydrofuran , and its methyl-substituted derivatives. In 1751, the Swedish mineralogist Axel Fredrik Cronstedt discovered

8760-459: The electron fails to gain the 13.6  eV necessary energy to escape the proton (the ionization energy of hydrogen ), and therefore simply remains bound to it, forming a neutral hydrogen atom (one of the "two bodies"). In this type of free neutron decay, almost all of the neutron decay energy is carried off by the antineutrino (the other "body"). (The hydrogen atom recoils with a speed of only about (decay energy)/(hydrogen rest energy) times

8880-405: The emitted particles, carry away the energy excess as a nucleon falls from one quantum state to one with less energy, while the neutron (or proton) changes to a proton (or neutron). For a neutron to decay, the resulting proton requires an available state at lower energy than the initial neutron state. In stable nuclei the possible lower energy states are all filled, meaning each state is occupied by

9000-593: The energy released from fission is the kinetic energy of the fission fragments. Neutrons and protons within a nucleus behave similarly and can exchange their identities by similar reactions. These reactions are a form of radioactive decay known as beta decay . Beta decay, in which neutrons decay to protons, or vice versa, is governed by the weak force , and it requires the emission or absorption of electrons and neutrinos, or their antiparticles. The neutron and proton decay reactions are: where p , e , and ν e denote

9120-432: The exception of La with a half-life of about 60,000 years, all of them have half-lives less than two days, and most have half-lives less than a minute. The isotopes La and La occur as fission products of uranium. Lanthanum oxide is a white solid that can be prepared by direct reaction of its constituent elements. Due to the large size of the La ion, La 2 O 3 adopts

9240-424: The f-block despite its anomalous ground-state configuration (which is merely the result of strong interelectronic repulsion making it less profitable to occupy the 4f shell, as it is small and close to the core electrons). The lanthanides become harder as the series is traversed: as expected, lanthanum is a soft metal. Lanthanum has a relatively high resistivity of 615 nΩm at room temperature; in comparison,

9360-445: The form of an emitted gamma ray: Called a "radiative decay mode" of the neutron, the gamma ray may be thought of as resulting from an "internal bremsstrahlung " that arises from the electromagnetic interaction of the emitted beta particle with the proton. A smaller fraction (about four per million) of free neutrons decay in so-called "two-body (neutron) decays", in which a proton, electron and antineutrino are produced as usual, but

9480-626: The insertion of a stainless steel liner in the spent fuel pool for the restart of the reactor. However, in November 1999, the Department of Energy decided to permanently shut down the HFBR. The HFBR was a heavy water cooled and moderated, enriched uranium fueled research reactor. The reactor core consisted of 28 individual fuel assemblies arranged in a close-packed array. The fuel material was enriched uranium alloyed in aluminum and clad with aluminum in curved plates. Heavy water (D 2 O) served as

9600-439: The lanthanides, lanthanum is exceptional as it has no 4f electrons as a single gas-phase atom. Thus it is only very weakly paramagnetic , unlike the strongly paramagnetic later lanthanides (with the exceptions of the last two, ytterbium and lutetium , where the 4f shell is completely full). However, the 4f shell of lanthanum can become partially occupied in chemical environments and participate in chemical bonding. For example,

9720-522: The large ionic radius and great electropositivity of La , there is not much covalent contribution to its bonding and hence it has a limited coordination chemistry , like yttrium and the other lanthanides. Lanthanum oxalate does not dissolve very much in alkali-metal oxalate solutions, and [La(acac) 3 (H 2 O) 2 ] decomposes around 500 °C. Oxygen is the most common donor atom in lanthanum complexes, which are mostly ionic and often have high coordination numbers over 6 : 8

9840-429: The largest atomic radius of the lanthanides. Hence, it is the most reactive among them, tarnishing quite rapidly in air, turning completely dark after several hours and can readily burn to form lanthanum(III) oxide , La 2 O 3 , which is almost as basic as calcium oxide . A centimeter-sized sample of lanthanum will corrode completely in a year as its oxide spalls off like iron rust , instead of forming

9960-474: The long-range electromagnetic force , but the much stronger, but short-range, nuclear force binds the nucleons closely together. Neutrons are required for the stability of nuclei, with the exception of the single-proton hydrogen nucleus. Neutrons are produced copiously in nuclear fission and fusion . They are a primary contributor to the nucleosynthesis of chemical elements within stars through fission, fusion, and neutron capture processes. The neutron

10080-437: The magnetic moments for the down and up quarks, respectively. This result combines the intrinsic magnetic moments of the quarks with their orbital magnetic moments, and assumes the three quarks are in a particular, dominant quantum state. The results of this calculation are encouraging, but the masses of the up or down quarks were assumed to be 1/3 the mass of a nucleon. The masses of the quarks are actually only about 1% that of

10200-476: The melting points of the trivalent lanthanides (all but europium and ytterbium) are related to the extent of hybridisation of the 6s, 5d, and 4f electrons (lowering with increasing 4f involvement), and lanthanum has the second-lowest melting point among them: 920 °C. (Europium and ytterbium have lower melting points because they delocalise about two electrons per atom rather than three.) This chemical availability of f orbitals justifies lanthanum's placement in

10320-518: The moderator/neutron reflector and primary coolant. The reactor vessel was fabricated from an aluminum alloy and contained the active core, reflector, and control rods. The vessel consists of an 82-inch diameter spherical section welded to a 46-inch diameter cylinder. The overall height of the vessel assembly was 24.75 feet. There were nine horizontal beam entry tubes that are integral parts of the vessel's spherical section. The core region provided space and access for 16 experimental facilities. The reactor

10440-406: The neutron and its magnetic moment both indicate that the neutron is a composite , rather than elementary , particle. The quarks of the neutron are held together by the strong force , mediated by gluons . The nuclear force results from secondary effects of the more fundamental strong force . The only possible decay mode for the neutron that obeys the conservation law for the baryon number

10560-401: The neutron and its properties is central to the extraordinary developments in atomic physics that occurred in the first half of the 20th century, leading ultimately to the atomic bomb in 1945. In the 1911 Rutherford model , the atom consisted of a small positively charged massive nucleus surrounded by a much larger cloud of negatively charged electrons. In 1920, Ernest Rutherford suggested that

10680-461: The neutron are described below in the Intrinsic properties section . Outside the nucleus, free neutrons undergo beta decay with a mean lifetime of about 14 minutes, 38 seconds, corresponding to a half-life of about 10 minutes, 11 s. The mass of the neutron is greater than that of the proton by 1.293 32   MeV/ c , hence the neutron's mass provides energy sufficient for the creation of

10800-401: The neutron can be modeled as a sum of the magnetic moments of the constituent quarks. The calculation assumes that the quarks behave like point-like Dirac particles, each having their own magnetic moment. Simplistically, the magnetic moment of the neutron can be viewed as resulting from the vector sum of the three quark magnetic moments, plus the orbital magnetic moments caused by the movement of

10920-434: The neutron is a neutral particle, the magnetic moment of a neutron is not zero. The neutron is not affected by electric fields, but it is affected by magnetic fields. The value for the neutron's magnetic moment was first directly measured by Luis Alvarez and Felix Bloch at Berkeley, California , in 1940. Alvarez and Bloch determined the magnetic moment of the neutron to be μ n = −1.93(2)  μ N , where μ N

11040-431: The neutron's magnetic moment with an external magnetic field were exploited to finally determine the spin of the neutron. In 1949, Hughes and Burgy measured neutrons reflected from a ferromagnetic mirror and found that the angular distribution of the reflections was consistent with spin  ⁠ 1 / 2 ⁠ . In 1954, Sherwood, Stephenson, and Bernstein employed neutrons in a Stern–Gerlach experiment that used

11160-431: The nucleus consisted of positive protons and neutrally charged particles, suggested to be a proton and an electron bound in some way. Electrons were assumed to reside within the nucleus because it was known that beta radiation consisted of electrons emitted from the nucleus. About the time Rutherford suggested the neutral proton-electron composite, several other publications appeared making similar suggestions, and in 1921

11280-420: The nucleus via the nuclear force , effectively moderating the repulsive forces between the protons and stabilizing the nucleus. Heavy nuclei carry a large positive charge, hence they require "extra" neutrons to be stable. While a free neutron is unstable and a free proton is stable, within nuclei neutrons are often stable and protons are sometimes unstable. When bound within a nucleus, nucleons can decay by

11400-446: The original particle is not composed of the product particles; rather, the product particles are created at the instant of the reaction. "Free" neutrons or protons are nucleons that exist independently, free of any nucleus. The free neutron has a mass of 939 565 413 .3  eV/ c , or 939.565 4133   MeV/ c . This mass is equal to 1.674 927 471 × 10   kg , or 1.008 664 915 88   Da . The neutron has

11520-464: The preceding BGRR, the HFBR initially operated at a thermal power level of 40 megawatts. Following an equipment upgrade in 1982, the reactor was operated at up to 60 megawatts thermal; a safety reanalysis resulted in the HFBR being shut down in 1989 and being limited to 30 megawatts thermal upon restart in 1991. The HFBR shut down in December 1996 for routine maintenance and refueling. During shutdown,

11640-592: The product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution. The procedure for monazite, which usually contains all the rare earths as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with sodium hydroxide to pH 3–4. Thorium precipitates out of solution as hydroxide and

11760-400: The proton and neutron are viewed as two quantum states of the same particle, is used to model the interactions of nucleons by the nuclear or weak forces. Because of the strength of the nuclear force at short distances, the nuclear energy binding nucleons is many orders of magnitude greater than the electromagnetic energy binding electrons in atoms. In nuclear fission , the absorption of

11880-406: The proton to a neutron occurs similarly through the weak force. The decay of one of the proton's up quarks into a down quark can be achieved by the emission of a W boson. The proton decays into a neutron, a positron, and an electron neutrino. This reaction can only occur within an atomic nucleus which has a quantum state at lower energy available for the created neutron. The story of the discovery of

12000-409: The proton, electron and electron anti- neutrino decay products, and where n , e , and ν e denote the neutron, positron and electron neutrino decay products. The electron and positron produced in these reactions are historically known as beta particles , denoted β or β respectively, lending the name to the decay process. In these reactions,

12120-464: The proton, electron, and anti-neutrino. In the decay process, the proton, electron, and electron anti-neutrino conserve the energy, charge, and lepton number of the neutron. The electron can acquire a kinetic energy up to 0.782 ± 0.013 MeV . Still unexplained, different experimental methods for measuring the neutron's lifetime, the "bottle" and "beam" methods, produce different values for it. The "bottle" method employs "cold" neutrons trapped in

12240-519: The puzzle of nuclear spins. The origins of beta radiation were explained by Enrico Fermi in 1934 by the process of beta decay , in which the neutron decays to a proton by creating an electron and a (at the time undiscovered) neutrino. In 1935, Chadwick and his doctoral student Maurice Goldhaber reported the first accurate measurement of the mass of the neutron. By 1934, Fermi had bombarded heavier elements with neutrons to induce radioactivity in elements of high atomic number. In 1938, Fermi received

12360-407: The rare earth metals except scandium and the radioactive promethium (mostly Ce, La, and Y). Bastnäsite is usually lacking in thorium and the heavy lanthanides, and the purification of the light lanthanides from it is less involved. The ore, after being crushed and ground, is first treated with hot concentrated sulfuric acid, evolving carbon dioxide, hydrogen fluoride , and silicon tetrafluoride :

12480-529: The rare earth minerals, and in their chemical formulae it is usually preceded by cerium. Rare examples of La-dominant minerals are monazite-(La) and lanthanite-(La). The La ion is similarly sized to the early lanthanides of the cerium group (those up to samarium and europium ) that immediately follow in the periodic table, and hence it tends to occur along with them in phosphate , silicate and carbonate minerals, such as monazite ( M PO 4 ) and bastnäsite ( M CO 3 F ), where M refers to all

12600-502: The reactor building, and shared with the previously constructed BGRR, was the Reactor Bypass Filter Facility (RBFF). This facility provided improved air cleaning prior to exhaust to the atmosphere in the unlikely event of a fuel element failure at either the BGRR or the HFBR. It also provided sufficient air cleaning to allow the use of air cooling as a method of combating a graphite fire at the BGRR. The facility

12720-429: The same atomic number, but different neutron number. Nuclides with the same neutron number, but different atomic number, are called isotones . The atomic mass number , A , is equal to the sum of atomic and neutron numbers. Nuclides with the same atomic mass number, but different atomic and neutron numbers, are called isobars . The mass of a nucleus is always slightly less than the sum of its proton and neutron masses:

12840-412: The second lowest of four emergency classifications. The fire self-extinguished after the electrical power supply to the experiment was turned off. Seven laboratory personnel were minimally contaminated by radionuclides entrained in the smoke from the fire. All seven were decontaminated at showers at the lab and released to return home. At the time of the fire, a minute amount of radiation was released to

12960-469: The single isotope copper-64 (29 protons, 35 neutrons), which has a half-life of about 12.7 hours. This isotope has one unpaired proton and one unpaired neutron, so either the proton or the neutron can decay. This particular nuclide is almost equally likely to undergo proton decay (by positron emission , 18% or by electron capture , 43%; both forming Ni ) or neutron decay (by electron emission, 39%; forming Zn ). Within

13080-424: The so-called "rare earth metals", lanthanum is thus not rare at all, but it is historically so-named because it is rarer than "common earths" such as lime and magnesia, and at the time it was recognized only a few deposits were known. Lanthanum is also ruefully considered a 'rare earth' metal because the process to mine it is difficult, time-consuming, and expensive. Lanthanum is rarely the dominant lanthanide found in

13200-429: The speed of light, or 250  km/s .) Neutrons are a necessary constituent of any atomic nucleus that contains more than one proton. As a result of their positive charges, interacting protons have a mutual electromagnetic repulsion that is stronger than their attractive nuclear interaction , so proton-only nuclei are unstable (see diproton and neutron–proton ratio ). Neutrons bind with protons and one another in

13320-477: The spent fuel pool water purification system, pumps and heat exchangers, cooling systems, and the spent fuel pool. The experimental level was for scientific users. The reactor biological shield, which surrounded the reactor, occupied the central portion of this level. A large open space surrounding the biological shield housed experimental equipment and there were labs and offices along the perimeter wall. Offices, locker rooms, toilets, and HVAC equipment were located on

13440-565: The subject. The 57 electrons of a lanthanum atom are arranged in the configuration [Xe]5d 6s , with three valence electrons outside the noble gas core. In chemical reactions, lanthanum almost always gives up these three valence electrons from the 5d and 6s subshells to form the +3 oxidation state, achieving the stable configuration of the preceding noble gas xenon . Some lanthanum(II) compounds are also known, but they are usually much less stable. Lanthanum monoxide (LaO) produces strong absorption bands in some stellar spectra . Among

13560-417: The theoretical framework of the Standard Model for particle physics, a neutron comprises two down quarks with charge − ⁠ 1 / 3 ⁠ e and one up quark with charge + ⁠ 2 / 3 ⁠ e . The neutron is therefore a composite particle classified as a hadron . The neutron is also classified as a baryon , because it is composed of three valence quarks . The finite size of

13680-435: The three charged quarks within the neutron. In one of the early successes of the Standard Model, in 1964 Mirza A.B. Beg, Benjamin W. Lee , and Abraham Pais calculated the ratio of proton to neutron magnetic moments to be −3/2 (or a ratio of −1.5), which agrees with the experimental value to within 3%. The measured value for this ratio is −1.459 898 05 (34) . The above treatment compares neutrons with protons, allowing

13800-439: The value for the good conductor aluminium is only 26.50 nΩm. Lanthanum is the least volatile of the lanthanides. Like most of the lanthanides, lanthanum has a hexagonal crystal structure at room temperature ( α -La). At 310 °C, lanthanum changes to a face-centered cubic structure ( β -La), and at 865 °C, it changes to a body-centered cubic structure ( γ -La). As expected from periodic trends , lanthanum has

13920-585: Was gamma radiation . The following year Irène Joliot-Curie and Frédéric Joliot-Curie in Paris showed that if this "gamma" radiation fell on paraffin , or any other hydrogen -containing compound, it ejected protons of very high energy. Neither Rutherford nor James Chadwick at the Cavendish Laboratory in Cambridge were convinced by the gamma ray interpretation. Chadwick quickly performed

14040-418: Was a contradiction, since there is no way to arrange the spins of an electron and a proton in a bound state to get a fractional spin. In 1931, Walther Bothe and Herbert Becker found that if alpha particle radiation from polonium fell on beryllium , boron , or lithium , an unusually penetrating radiation was produced. The radiation was not influenced by an electric field, so Bothe and Becker assumed it

14160-558: Was a mixture, and in 1885 it was separated into praseodymium and neodymium. Since lanthanum's properties differed only slightly from those of cerium, and occurred along with it in its salts, he named it from the Ancient Greek λανθάνειν [ lanthanein ] (lit. to lie hidden ). Relatively pure lanthanum metal was first isolated in 1923. Lanthanum makes up 39 mg/kg of the Earth's crust, behind neodymium at 41.5 mg/kg and cerium at 66.5 mg/kg. Despite being among

14280-446: Was housed within a confinement structure topped by a semi-hemispherical dome. The reactor sat inside a confinement building constructed of welded steel plates supported by an I-beam framework that rests on a cylindrical base. The inside diameter of the hemisphere at its base is 176 feet 8 inches. The cylindrical base is 22 feet 4 inches high and rests on a bed plate that is bolted to the reinforced concrete foundation ring. The foundation of

14400-542: Was placed into operation in 1965. On March 31, 1994, a small fire broke out in one of the beam line experiments being conducted on the experimental floor outside of the reactor and biological shield. The reactor, associated reactor operations systems, and safety systems were not involved in the fire. The experiment studying the decay of lanthanum -148, named TRISTAN, which burned contained a cylindrical capsule of 5 grams of uranium approximately 1 inch in diameter and 1 ½ inches tall. The capsule had been exposed to neutrons from

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