Berkelium
Encyclopedia
Berkelium is a synthetic element
with the symbol Bk and atomic number
97, a member of the actinide
and transuranium element
series. It is named after the city of Berkeley, California
, the location of the University of California Radiation Laboratory where it was discovered in December 1949. This was the fifth transuranium element discovered after neptunium
, plutonium
, curium
and americium
.
The major isotope
of berkelium, berkelium-249, is synthesized in minute quantities in dedicated high-flux nuclear reactor
s, mainly at the Oak Ridge National Laboratory
in Tennessee
, USA, and at the Research Institute of Atomic Reactors
in Dimitrovgrad, Russia
. The production of the second-important isotope berkelium-247 involves the irradiation of the rare synthetic isotope curium-244 with high-energy alpha particle
s.
Just over one gram of berkelium has been produced in the United States since 1967. There is no practical application of berkelium outside of scientific research which is mostly directed at the synthesis of heavier transuranic elements and transactinides. A 22 milligram batch of berkelium-249 was prepared during a 250-day irradiation period and then purified for a further 90 days at Oak Ridge in 2009. This sample was used to synthesize the element ununseptium
for the first time in 2009 at the Joint Institute for Nuclear Research
, Russia
, after it was bombarded with calcium-48
ions for 150 days. This was a culmination of the Russia—US collaboration on the synthesis of elements 113 to 118.
Berkelium is a soft, silvery-white, radioactive metal. The berkelium-249 isotope emits low-energy electron
s and thus is relatively safe to handle. However, it decays with a half-life
of 330 days to californium
-249, which is a strong and hazardous emitter of alpha particles. This gradual transformation is an important consideration when studying the properties of elemental berkelium and its chemical compounds, since the formation of californium brings not only chemical contamination, but also self-radiation damage, and self-heating from the emitted alpha particles.
, isolated and identified in December 1949 by Glenn T. Seaborg
, Albert Ghiorso
and Stanley G. Thompson. They used the 60-inch cyclotron
at the University of California, Berkeley
. Similar to the nearly simultaneous discovery of americium
(element 95) and curium
(element 96) in 1944, the new elements berkelium and californium
(element 98) were both produced in 1949–1950.
The name choice for element 97 followed the previous tradition of the Californian group to draw an analogy between the newly discovered actinide
and the lanthanide
element positioned above it in the periodic table
. Previously, americium was named after a continent as its analogue europium
, and curium honored scientists Marie
and Pierre Curie
as the lanthanide above it, gadolinium
, was named after the explorer of the rare earth element
s Johan Gadolin
. Thus the discovery report by the Berkeley group reads: "It is suggested that element 97 be given the name berkelium (symbol Bk) after the city of Berkeley in a manner similar to that used in naming its chemical homologue terbium
(atomic number 65) whose name was derived from the town of Ytterby
, Sweden
, where the rare earth minerals were first found." This tradition ended on berkelium though as the naming of the next discovered actinide, californium
, was not related to its lanthanide analogue dysprosium
, but after the discovery place.
The most difficult steps in the synthesis of berkelium were its separation from the final products and the production of sufficient quantities of americium for the target material. First, americium (241Am) nitrate
solution was coated on a platinum
foil, the solution was evaporated and the residue converted by annealing to americium dioxide (AmO2). This target was irradiated with 35 MeV alpha particle
s for 6 hours in the 60-inch cyclotron at the Lawrence Radiation Laboratory, University of California, Berkeley. The (α,2n) reaction induced by the irradiation yielded the 243Bk isotope and two free neutron
s:
After the irradiation, the coating was dissolved with nitric acid
and then precipitated as the hydroxide
using concentrated aqueous ammonia solution
. The product was centrifugated
and re-dissolved in nitric acid. To separate berkelium from the unreacted americium, this solution was added to a mixture of ammonium
and ammonium sulfate
and heated to convert all the dissolved americium into the oxidation state
+6. Unoxidized residual americium was precipitated by the addition of hydrofluoric acid
as americium(III) fluoride
. This step yielded a mixture of the accompanying product curium and the expected element 97 in form of trifluorides. The mixture was converted to the corresponding hydroxides by treating it with potassium hydroxide
, and after centrifugation, was dissolved in perchloric acid
.
Further separation was carried out in the presence of a citric acid
/ammonium
buffer solution
in a weakly acidic medium (pH
≈3.5), using ion exchange
at elevated temperature. The chromatographic
separation behavior was then unknown for the element 97, but was anticipated by analogy with terbium (see elution curves). First results were disappointing as no alpha-particle emission signature could be detected from the elution product. Only the further search for characteristic X-rays
and conversion electron
signals resulted in the identification of a berkelium isotope. Its atomic number was uncertain between 243 and 244 in the initial report, but was later established as 243.
metal. In the periodic table
, it is located right to the actinide curium
, left to the actinide californium
and below the lanthanide terbium
with which it shares many similarities in physical and chemical properties. Its density of 14.78 g/cm3lies between those of curium (13.52 g/cm3) and californium (15.1 g/cm3), as does its melting point of 986 °C, below that of curium (1340 °C) but higher than that of californium (900 °C). Berkelium is relatively soft and has one of the lowest bulk moduli
among the actinides, at about 20 GPa
(2Pa).
Berkelium(III) ions shows two sharp fluorescence
peaks at 652 nanometers (red light) and 742 nanometers (deep red – near infrared) due to internal transitions at the f-electron shell
. The relative intensity of these peaks depends on the excitation power and temperature of the sample. This emission can be observed, for example, after dispersing berkelium ions in a silicate glass, by melting the glass in presence of berkelium oxide or halide.
Between 70 K and room temperature, berkelium behaves as a Curie–Weiss paramagnetic material with an effective magnetic moment of 9.69 Bohr magnetons (µB) and a Curie temperature of 101 K. This magnetic moment is almost equal to the theoretical value of 9.72 µB calculated within the simple atomic L-S coupling model
. Upon cooling to about 34 K, berkelium undergoes a transition to an antiferromagnetic
state. Enthalpy of dissolution
in hydrochloric acid
at standard conditions is −600 kJ/mol−1, from which the standard enthalpy change of formation
(ΔfH°) of aqueous Bk3+ ions is obtained as −601 kJ/mol−1. The standard potential Bk3+/Bk0 is −2.01 V. The ionization potential
of a neutral berkelium atom is 6.23 eV.
P63/mmc, lattice parameters of 341 pm and 1107 pm. The crystal has a double-hexagonal close packing structure with the layer sequence ABAC and so is isotypic with α-lanthanum and α-forms of actinides beyond curium. This crystal structure changes with pressure and temperature. When compressed at room temperature to 7 GPa, α-berkelium transforms to the beta modification, which has a face-centered cubic
(fcc) symmetry and space group Fmm. This transition occurs without change in volume, but the enthalpy
increases by 3.66 kJ/mol. Upon further compression to 25 GPa, berkelium transforms to an orthorhombic
γ-berkelium structure similar to that of α-uranium. This transition is accompanied by a 12% volume decrease and delocalization of the electrons at the 5f electron shell
. No further phase transitions are observed up to 57 GPa.
Upon heating, α-berkelium transforms into another "metastable" phase (that is at ambient temperature it gradually converts back to α-berkelium). This phase has an fcc lattice (but slightly different from β-berkelium), space group Fmm and the lattice constant of 500 pm; this fcc structure is equivalent to the closest packing with the sequence ABC. The temperature of the phase transition is believed to be quite close to the melting point.
s, berkelium dissolves in various aqueous inorganic acids, liberating gaseous hydrogen
and converting into the berkelium(III) state. This trivalent oxidation state
is the most stable, especially in aqueous solutions, but tetravalent and possibly divalent berkelium compounds are also known. The existence of divalent berkelium salts is uncertain and has only been reported in mixed lanthanum chloride-strontium chloride
melts. A similar behavior is observed for the lanthanide analogue of berkelium, terbium
. Aqueous solutions of Bk3+ ions are green in most acids. The color of the Bk4+ ions is yellow in hydrochloric acid
and orange-yellow in sulfuric acid
. Berkelium does not react rapidly with oxygen
at room temperature, possibly due to the formation of a protective oxide layer surface. However, it reacts with molten metals, hydrogen
, halogen
s, chalcogen
s and pnictogens to form various binary compounds.
s (excited states of an isotope) of berkelium have been characterized with the atomic numbers ranging from 235 to 254. All of them are radioactive. The longest half-lives
are observed for 247Bk (1,380 years), 248Bk (9 years) and 249Bk (330 days); the half-lives of the other isotopes range from microseconds to several days. The isotope which is the easiest to synthesize is berkelium-249. This emits mostly soft β-particles
which are inconvenient for detection. Its alpha radiation is rather weak – 1.45% with respect to the β-radiation – but is sometimes used to detect this isotope. The second important berkelium isotope, berkelium-247, is an alpha-emitter as most actinide isotopes.
berkelium, that is berkelium present on the Earth during its formation, should have decayed by now. On Earth, berkelium is mostly concentrated in certain areas, which were used for the atmospheric nuclear weapons tests between 1945 and 1980, as well as at the sites of nuclear incidents, such as Chernobyl disaster
, Three Mile Island accident
and 1968 Thule Air Base B-52 crash. Analysis of the debris at the testing site of the first U.S. hydrogen bomb, Ivy Mike
, (1 November 1952, Enewetak Atoll), revealed high concentrations of various actinides, including berkelium. For reasons of military secrecy, this result was published only in 1956.
Nuclear reactors produce mostly, among the berkelium isotopes, berkelium-249. During the storage and before the fuel disposal, most of it breaks down to californium-249. The latter has a long half-life, of 351 years, and is therefore undesirable in the disposal products.
(238U) or plutonium
(239Pu) with neutrons in a nuclear reactor
. In a more common case of uranium fuel, plutonium is produced first by neutron capture (the so-called (n,γ) reaction or neutron fusion) followed by beta-decay:
(the times are half-lives
)
Plutonium-239 is further irradiated by a source that has a high neutron flux
,several times higher than a conventional nuclear reactor, such as the 85-megawatt High Flux Isotope Reactor
(HFIR) at the Oak Ridge National Laboratory
in Tennessee, USA. The higher flux promotes fusion reactions involving not one but several neutrons, converting 239Pu to 244Cm and then to 249Cm:
Curium-249 has a short half-life of 64 minutes, and thus its further conversion to 250Cm has a low probability. Instead, it transforms by beta-decay into 249Bk:
The thus-produced 249Bk has a long half-life of 330 days and thus can capture another neutron. However, the product, 250Bk, again has a relatively short half-life of 3.212 hours and thus, does not yield higher actinides. Instead decays to the californium isotope 250Cf:
The above reactions illustrate that although 247Bk is the most stable isotope of berkelium, its production in nuclear reactors is very inefficient. This makes 249Bk the most accessible isotope of berkelium, which still, is available only in small quantities (only 0.66 grams have been produced in the US over the period 1967–1983) at a high price of the order 185 USD
per microgram.
The isotope 248Bk was first obtained in 1956 by bombarding a mixture of curium isotopes with 25 MeV α-particles. Although its direct detection was hindered by strong signal interference with 245Bk, the existence of a new isotope was proven by the growth of the decay product 248Cf which had been previously characterized. The half-life of 248Cf was estimated as 23 ± 5 hours and a more reliable value still is not known. Berkelium-247 was produced during the same year by irradiating 244Cm with alpha-particles:
Berkelium-242 was synthesized in 1979 by bombarding 235U with 11B, 238U with 10B, 232Th with 14N or 232Th with 15N. It converts by electron capture
to 242Cm with a half-life of 7.0 ± 1.3 minutes. A search for an initially suspected isotope 241Bk was then unsuccessful.
+4 in solids, and is relatively stable in this state in liquids greatly assists separation of berkelium away from many other actinides. These are inevitably produced in relatively large amounts during the nuclear synthesis and often favor the +3 state. This fact was not yet known in the initial experiments, which used a more complex separation procedure. Various oxidation agents can be applied to the berkelium(III) solutions to convert it to the +4 state, such as bromate
s (BrO3–), bismuthates (BiO3–), chromate
s (CrO42– and Cr2O72–), silver(I) thiolate , lead(IV) oxide (PbO2), ozone
, or photochemical oxidation procedures. Berkelium(IV) is then extracted with ion exchange
, extraction chromatography
or liquid-liquid extraction using HDEHP (bis-(2-ethylhexyl) phosphoric scid), amine
s, tributyl phosphate
or various other reagents. These procedures separate berkelium from most trivalent actinides and lanthanides, except for the lanthanide cerium
(lanthanides are absent in the irradiation target but are created in various nuclear fission
decay chains).
A more detailed procedure adopted at the Oak Ridge National Laboratory
was as follows: the initial mixture of actinides is processed with ion exchange using lithium chloride
reagent, then precipitated as hydroxide
s, filtered and dissolved in nitric acid. It is then treated with high-pressure elution
from cation exchange
resins, and the berkelium phase is oxidized and extracted using one of the procedures described above. Reduction of the thus-obtained berkelium(IV) to the +3 oxidation state yields a solution, which is nearly free from other actinides (but contains cerium). Berkelium and cerium are then separated with another round of ion-exchange treatment.
, Arco, Idaho
, US. It resulted in preparation of an eight-gram plutonium-239 target and in the first production of macroscopic quantities (0.6 micrograms) of berkelium by Burris B. Cunningham and Stanley G. Thompson in 1958, after a continuous reactor irradiation of this target for six years. This irradiation method was, and still is the only way of producing weighable amounts of the element, and most solid-state studies of berkelium have been conducted on microgram or submicrogram-sized samples.
The world's major irradiation sources are the 85-megawatt High Flux Isotope Reactor at the Oak Ridge National Laboratory
in Tennessee, USA, and the SM-2 loop reactor at the Research Institute of Atomic Reactors
(NIIAR) in Dimitrovgrad, Russia
, which are both dedicated to the production of transcurium elements (atomic number greater than 96). These facilities have similar power and flux levels, and are expected to have comparable production capacities for transcurium elements, although the quantities produced at NIIAR are not widely reported. In a "typical processing campaign" at Oak Ridge, tens of grams of curium
are irradiated to produce decigram quantities of californium
, milligram quantities of berkelium-249 and einsteinium
, and picogram quantities of fermium
. In total, just over one gram of berkelium-249 has been produced at Oak Ridge since 1967.
The first berkelium metal sample weighing 1.7 micrograms was prepared in 1971 by the reduction of berkelium(III) fluoride with lithium
vapor at 1000 °C; the fluoride was suspended on a tungsten wire above a tantalum
crucible containing molten lithium. Later, metal samples weighting up to 0.5 milligrams were obtained with this method.
Similar results are obtained with berkelium(IV) fluoride. Berkelium metal can also be produced by the reduction of berkelium(IV) oxide with thorium
or lanthanum
.
) crystal structure
. Berkelium(III) oxide is formed from BkO2 by reduction
with molecular hydrogen
:
It is a yellow-green solid with a melting point of 1920 °C and a body-centered cubic
(bcc) crystal lattice. Upon heating to 1200 °C, the cubic Bk2O3 transforms to a monoclinic structure, which further converts to a hexagonal phase at 1750 °C, and the latter transition is reversible. Such three-phase behavior is typical for the actinide sesquioxides. Berkelium(II) oxide, BkO, has been reported as a brittle gray solid with a face centered cubic
(fcc) structure, but its exact chemical composition remains uncertain.
s, berkelium assumes the oxidation states +3 and +4. The +3 state is the most stable, especially in solutions, while the tetravalent halides BkF4 and Cs2BkCl6 are only known in the solid phase. The coordination of berkelium atom in its trivalent fluoride and chloride is tricapped trigonal prismatic, with the coordination number
of 9. In trivalent bromide, it is bicapped trigonal prismatic (coordination 8) or octahedral
(coordination 6), and in the iodide it is octahedral.
Berkelium(IV) fluoride (BkF4) is a yellow-green ionic solid which crystallizes in the monoclinic crystal system
and is isotypic with uranium tetrafluoride
or zirconium(IV) fluoride
.
Berkelium(III) fluoride (BkF3) is also a yellow-green solid, but it has two crystalline structures. The most stable phase at low temperatures has an orthorhombic
symmetry, isotypic with yttrium(III) fluoride
. Upon heating to between 350 and 600 °C, it transforms to a trigonal structure found in lanthanum(III) fluoride.
Visible amounts of berkelium(III) chloride (BkCl3) were first isolated and characterized in 1962, and weighed only 3 billionths of a gram
. It can be prepared by introducing hydrogen chloride
vapors into an evacuated quartz tube containing berkelium oxide at a temperature about 500 °C. This green solid has a melting point of 600 °C, and crystallized in the hexagonal crystal system
isotypic with uranium(III) chloride
. Upon heating to nearly melting point, BkCl3 converts into an orthorhombic phase.
Two forms of berkelium(III) bromide are known: a monoclinic one with berkelium having coordination 6, and an orthorhombic one with coordination 8. The latter is less stable and transforms to the former phase upon heating to about 350 °C. An important phenomenon for radioactive solids has been studied on these two crystal forms: the structure of fresh and aged 249BkBr3 samples was probed by X-ray diffraction over a period longer than 3 years, so that various fractions of berkelium-249 had converted to californium-249. No change in structure was observed upon 249BkBr3—249CfBr3 transformation, even though the orthorhombic bromide was previously unknown for californium. However, other differences were noted for 249BkBr3 and 249CfBr3. For example, the latter could be reduced with hydrogen to 249CfBr2, but the former could be not – this result was reproduced on individual 249BkBr3 and 249CfBr3 samples, as well on the samples containing both bromides. The intergrowth of californium in berkelium occurs at a rate of 0.22% per day and is an intrinsic obstacle in studying berkelium properties. Beside a chemical contamination, 249Cf, as an alpha emitter brings undesirable self-damage of the crystal lattice and the resulting self-heating. The chemical effect however can be avoided by performing measurements as a function of time and extrapolating the obtained results.
, phosphorus
, arsenic
and antimony
. They crystallize in the rock-salt structure
and are prepared by the reaction of either berkelium(III) hydride (BkH3) or metallic berkelium with these elements at elevated temperature (about 600 °C) under high vacuum.
Berkelium(III) sulfide, Bk2S3, was prepared by either treating berkelium oxide with a mixture of hydrogen sulfide
and carbon disulfide
vapors at 1130 °C, or by directly reacting metallic berkelium with elemental sulfur. These procedures yielded brownish-black crystals with a cubic symmetry.
Berkelium(III) and berkelium(IV) hydroxides are both stable in 1 molar solutions of sodium hydroxide. Berkelium(III) phosphate
(BkPO4) has been prepared as a solid, which shows strong fluorescence
under excitation with a green light. Berkelium hydrides are produced by reacting metal with hydrogen gas at temperatures about 250 °C. They are non-stoichiometric with the nominal formula BkH2+x (0 < x < 1). Whereas the trihydride has a hexagonal symmetry, the dihydride crystallizes in an fcc structure. Several other salts of berkelium are known, including an oxysulfide (Bk2O2S), and hydrated nitrate
, chloride , sulfate
and oxalate
. Thermal decomposition at about 600 °C in an argon
atmosphere (to avoid oxidation to ) of yields the body-centered orthorhombic crystals of berkelium(III) oxysulfate . This compound is thermally stable to at least 1000 °C in inert atmosphere.
complex with three cyclopentadienyl
rings, which can be synthesized by reacting berkelium(III) chloride with the molten beryllocene (Be(C5H5)2) at about 70 °C. It has an amber color, an orthorhombic symmetry and a density of 2.47 g/cm3. The complex is stable to heating to at least 250 °C, and sublimates without melting at about 350 °C. The high radioactivity of berkelium gradually destroys the compound (within a period of weeks). One cyclopentadienyl ring in (η5–C5H5)3Bk can be substituted by chlorine to yield [Be(C5H5)2Cl]2. The optical absorption spectra of this compound are very similar to those of (η5–C5H5)3Bk.
, rutherfordium
and bohrium
. It is also useful as a source of the isotope californium-249, which is used for studies on the chemistry of californium
in preference to the more radioactive californium-252 that is produced in neutron bombardment facilities such as the HFIR.
A 22 milligram batch of berkelium-249 was prepared in a 250-day irradiation and then purified for 90 days at Oak Ridge in 2009. This target yielded the first 6 atoms of element ununseptium
at the Joint Institute for Nuclear Research
(JINR), Dubna
, Russia, after bombarding it with calcium ions in the U400 cyclotron for 150 days. This synthesis was a culmination of the Russia—US collaboration between JINR and Lawrence Livermore National Laboratory
on the synthesis of elements 113 to 118 which was initiated in 1989.
properties of berkelium are different from those of the neighboring actinides curium and californium, and they suggest berkelium to perform poorly as a fuel in a nuclear reactor. Specifically, berkelium-249 has a moderately large neutron capture cross section
of 710 barns
for thermal neutrons, 1200 barns resonance integral, but very low fission cross section for thermal neutrons. In a thermal reactor, much of it will therefore be converted to berkelium-250 which quickly decays to californium-250. In principle, berkelium-249 can sustain a nuclear chain reaction
in a fast breeder reactor. Its critical mass
is relatively high at 192 kg; it can be reduced with a water or steel reflector but would still exceed the world production of this isotope.
Berkelium-247 can maintain chain reaction both in a thermal-neutron and in a fast-neutron reactor, however, its production is rather complex and thus the availability is much lower than its critical mass, which is about 75.7 kg for a bare sphere, 41.2 kg with a water reflector and 35.2 kg with a steel reflector (30 cm thickness).
Most available berkelium toxicity data originate from research on animals. Upon ingestion by rats, only about 0.01% berkelium ends in the blood stream. From there, about 65% goes to the bones, where it remains for about 50 years, 25% to the lungs (biological half-life about 20 years), 0.035% to the testicles or 0.01% to the ovaries where berkelium stays indefinitely. The balance of about 10% is excreted. In all these organs berkelium might promote cancer, and in the skeletal system its radiation can damage red blood cells. The maximum permissible body burden for the isotope berkelium-249 in the human skeleton is 0.4 nanograms.
Synthetic element
In chemistry, a synthetic element is a chemical element that is too unstable to occur naturally on Earth, and therefore has to be created artificially. So far 30 synthetic elements have been discovered—that is, synthesized...
with the symbol Bk and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
97, a member of the actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...
and transuranium element
Transuranium element
In chemistry, transuranium elements are the chemical elements with atomic numbers greater than 92...
series. It is named after the city of Berkeley, California
Berkeley, California
Berkeley is a city on the east shore of the San Francisco Bay in Northern California, United States. Its neighbors to the south are the cities of Oakland and Emeryville. To the north is the city of Albany and the unincorporated community of Kensington...
, the location of the University of California Radiation Laboratory where it was discovered in December 1949. This was the fifth transuranium element discovered after neptunium
Neptunium
Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive metal, neptunium is the first transuranic element and belongs to the actinide series. Its most stable isotope, 237Np, is a by-product of nuclear reactors and plutonium production and it can be used as a...
, plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
, curium
Curium
Curium is a synthetic chemical element with the symbol Cm and atomic number 96. This radioactive transuranic element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie. Curium was first intentionally produced and identified in summer 1944 by the group of...
and americium
Americium
Americium is a synthetic element that has the symbol Am and atomic number 95. This transuranic element of the actinide series is located in the periodic table below the lanthanide element europium, and thus by analogy was named after another continent, America.Americium was first produced in 1944...
.
The major isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
of berkelium, berkelium-249, is synthesized in minute quantities in dedicated high-flux nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s, mainly at the Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...
in Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
, USA, and at the Research Institute of Atomic Reactors
Research Institute of Atomic Reactors
The Research Institute of Atomic Reactors is an institute for nuclear reactor research in Dimitrovgrad in Ulyanovsk Oblast, Russia. The institute houses eight nuclear research reactors: SM, Arbus , MIR.M1, RBT-6, RBT-10 / 1, RBT-10 / 2, BOR-60 and VK-50.-External links:* *...
in Dimitrovgrad, Russia
Dimitrovgrad, Russia
Dimitrovgrad is a city in Ulyanovsk Oblast, Russia, located on the Bolshoy Cheremshan River. Population: -History:It was founded in the beginning of the 18th century as a village for workers of the local distillery, which was closed in 1848. As of 1897, its population was 8,500, and in 1919...
. The production of the second-important isotope berkelium-247 involves the irradiation of the rare synthetic isotope curium-244 with high-energy alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
s.
Just over one gram of berkelium has been produced in the United States since 1967. There is no practical application of berkelium outside of scientific research which is mostly directed at the synthesis of heavier transuranic elements and transactinides. A 22 milligram batch of berkelium-249 was prepared during a 250-day irradiation period and then purified for a further 90 days at Oak Ridge in 2009. This sample was used to synthesize the element ununseptium
Ununseptium
Ununseptium is the temporary name of a superheavy artificial chemical element with temporary symbol Uus and atomic number 117. Six atoms were detected by a joint Russia–US collaboration at Dubna, Moscow Oblast, Russia, in 2009–10...
for the first time in 2009 at the Joint Institute for Nuclear Research
Joint Institute for Nuclear Research
The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow Oblast , Russia, is an international research centre for nuclear sciences, with 5500 staff members, 1200 researchers including 1000 Ph.D.s from eighteen member states The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, after it was bombarded with calcium-48
Calcium-48
Calcium-48 is a rare isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, the only radioactive decay pathway open to it is the extremely rare process of double beta decay...
ions for 150 days. This was a culmination of the Russia—US collaboration on the synthesis of elements 113 to 118.
Berkelium is a soft, silvery-white, radioactive metal. The berkelium-249 isotope emits low-energy electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s and thus is relatively safe to handle. However, it decays with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 330 days to californium
Californium
Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles at the University of California, Berkeley. It is the ninth member of the actinide series and was the...
-249, which is a strong and hazardous emitter of alpha particles. This gradual transformation is an important consideration when studying the properties of elemental berkelium and its chemical compounds, since the formation of californium brings not only chemical contamination, but also self-radiation damage, and self-heating from the emitted alpha particles.
History
Although very small amounts of berkelium were possibly produced in previous nuclear experiments, it was first intentionally synthesizedDiscoveries of the chemical elements
The discovery of the elements known to exist today is presented here in chronological order. The elements are listed generally in the order in which each was first defined as the pure element, as the exact date of discovery of most elements cannot be accurately defined.Given is each element's name,...
, isolated and identified in December 1949 by Glenn T. Seaborg
Glenn T. Seaborg
Glenn Theodore Seaborg was an American scientist who won the 1951 Nobel Prize in Chemistry for "discoveries in the chemistry of the transuranium elements", contributed to the discovery and isolation of ten elements, and developed the actinide concept, which led to the current arrangement of the...
, Albert Ghiorso
Albert Ghiorso
Albert Ghiorso was an American nuclear scientist and co-discoverer of a record 12 chemical elements on the periodic table. His research career spanned five decades, from the early 1940s to the late 1990s.-Early life:...
and Stanley G. Thompson. They used the 60-inch cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
at the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
. Similar to the nearly simultaneous discovery of americium
Americium
Americium is a synthetic element that has the symbol Am and atomic number 95. This transuranic element of the actinide series is located in the periodic table below the lanthanide element europium, and thus by analogy was named after another continent, America.Americium was first produced in 1944...
(element 95) and curium
Curium
Curium is a synthetic chemical element with the symbol Cm and atomic number 96. This radioactive transuranic element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie. Curium was first intentionally produced and identified in summer 1944 by the group of...
(element 96) in 1944, the new elements berkelium and californium
Californium
Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles at the University of California, Berkeley. It is the ninth member of the actinide series and was the...
(element 98) were both produced in 1949–1950.
The name choice for element 97 followed the previous tradition of the Californian group to draw an analogy between the newly discovered actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...
and the lanthanide
Lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...
element positioned above it in the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
. Previously, americium was named after a continent as its analogue europium
Europium
Europium is a chemical element with the symbol Eu and atomic number 63. It is named after the continent of Europe. It is a moderately hard silvery metal which readily oxidizes in air and water...
, and curium honored scientists Marie
Marie Curie
Marie Skłodowska-Curie was a physicist and chemist famous for her pioneering research on radioactivity. She was the first person honored with two Nobel Prizes—in physics and chemistry...
and Pierre Curie
Pierre Curie
Pierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. He was the son of Dr. Eugène Curie and Sophie-Claire Depouilly Curie ...
as the lanthanide above it, gadolinium
Gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is found in nature only in combined form. Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with...
, was named after the explorer of the rare earth element
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
s Johan Gadolin
Johan Gadolin
Johan Gadolin was a Finnish chemist, physicist and mineralogist. Gadolin discovered the chemical element yttrium...
. Thus the discovery report by the Berkeley group reads: "It is suggested that element 97 be given the name berkelium (symbol Bk) after the city of Berkeley in a manner similar to that used in naming its chemical homologue terbium
Terbium
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife...
(atomic number 65) whose name was derived from the town of Ytterby
Ytterby
Ytterby is a village on the Swedish island of Resarö, in Vaxholm Municipality in the Stockholm archipelago.The name of the village means "outer village", implying that its location is its most noteworthy feature....
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, where the rare earth minerals were first found." This tradition ended on berkelium though as the naming of the next discovered actinide, californium
Californium
Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles at the University of California, Berkeley. It is the ninth member of the actinide series and was the...
, was not related to its lanthanide analogue dysprosium
Dysprosium
Dysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime...
, but after the discovery place.
The most difficult steps in the synthesis of berkelium were its separation from the final products and the production of sufficient quantities of americium for the target material. First, americium (241Am) nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
solution was coated on a platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
foil, the solution was evaporated and the residue converted by annealing to americium dioxide (AmO2). This target was irradiated with 35 MeV alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
s for 6 hours in the 60-inch cyclotron at the Lawrence Radiation Laboratory, University of California, Berkeley. The (α,2n) reaction induced by the irradiation yielded the 243Bk isotope and two free neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s:
After the irradiation, the coating was dissolved with nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
and then precipitated as the hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
using concentrated aqueous ammonia solution
Ammonium hydroxide
Ammonia solution, also known as ammonium hydroxide, ammonia water, ammonical liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or simply ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3...
. The product was centrifugated
Centrifugation
Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...
and re-dissolved in nitric acid. To separate berkelium from the unreacted americium, this solution was added to a mixture of ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
and ammonium sulfate
Ammonium sulfate
Ammonium sulfate , 2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen as ammonium cations, and 24% sulfur as sulfate anions...
and heated to convert all the dissolved americium into the oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
+6. Unoxidized residual americium was precipitated by the addition of hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
as americium(III) fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
. This step yielded a mixture of the accompanying product curium and the expected element 97 in form of trifluorides. The mixture was converted to the corresponding hydroxides by treating it with potassium hydroxide
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
, and after centrifugation, was dissolved in perchloric acid
Perchloric acid
Perchloric acid is the inorganic compound with the formula HClO4. Usually encountered as an aqueous solution, this colourless compound is a strong acid comparable in strength to sulfuric and nitric acids. It is a powerful oxidizer, but its aqueous solutions up to appr. 70% are remarkably inert,...
.
Further separation was carried out in the presence of a citric acid
Citric acid
Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...
/ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
buffer solution
Buffer solution
A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a...
in a weakly acidic medium (pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
≈3.5), using ion exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
at elevated temperature. The chromatographic
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
separation behavior was then unknown for the element 97, but was anticipated by analogy with terbium (see elution curves). First results were disappointing as no alpha-particle emission signature could be detected from the elution product. Only the further search for characteristic X-rays
K-alpha
In X-ray spectroscopy, K-alpha emission lines result when an electron transitions to the innermost "K" shell from a 2p orbital of the second or "L" shell...
and conversion electron
Internal conversion
Internal conversion is a radioactive decay process where an excited nucleus interacts with an electron in one of the lower atomic orbitals, causing the electron to be emitted from the atom. Thus, in an internal conversion process, a high-energy electron is emitted from the radioactive atom, but...
signals resulted in the identification of a berkelium isotope. Its atomic number was uncertain between 243 and 244 in the initial report, but was later established as 243.
Physical
Berkelium is a synthetic, silvery-white, radioactive actinideActinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...
metal. In the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
, it is located right to the actinide curium
Curium
Curium is a synthetic chemical element with the symbol Cm and atomic number 96. This radioactive transuranic element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie. Curium was first intentionally produced and identified in summer 1944 by the group of...
, left to the actinide californium
Californium
Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles at the University of California, Berkeley. It is the ninth member of the actinide series and was the...
and below the lanthanide terbium
Terbium
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife...
with which it shares many similarities in physical and chemical properties. Its density of 14.78 g/cm3lies between those of curium (13.52 g/cm3) and californium (15.1 g/cm3), as does its melting point of 986 °C, below that of curium (1340 °C) but higher than that of californium (900 °C). Berkelium is relatively soft and has one of the lowest bulk moduli
Bulk modulus
The bulk modulus of a substance measures the substance's resistance to uniform compression. It is defined as the pressure increase needed to decrease the volume by a factor of 1/e...
among the actinides, at about 20 GPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
(2Pa).
Berkelium(III) ions shows two sharp fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
peaks at 652 nanometers (red light) and 742 nanometers (deep red – near infrared) due to internal transitions at the f-electron shell
Electron configuration
In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure...
. The relative intensity of these peaks depends on the excitation power and temperature of the sample. This emission can be observed, for example, after dispersing berkelium ions in a silicate glass, by melting the glass in presence of berkelium oxide or halide.
Between 70 K and room temperature, berkelium behaves as a Curie–Weiss paramagnetic material with an effective magnetic moment of 9.69 Bohr magnetons (µB) and a Curie temperature of 101 K. This magnetic moment is almost equal to the theoretical value of 9.72 µB calculated within the simple atomic L-S coupling model
Angular momentum coupling
In quantum mechanics, the procedure of constructing eigenstates of total angular momentum out of eigenstates of separate angular momenta is called angular momentum coupling. For instance, the orbit and spin of a single particle can interact through spin-orbit interaction, in which case the...
. Upon cooling to about 34 K, berkelium undergoes a transition to an antiferromagnetic
Antiferromagnetism
In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usuallyrelated to the spins of electrons, align in a regular pattern with neighboring spins pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism...
state. Enthalpy of dissolution
Enthalpy change of solution
The enthalpy of solution, enthalpy of dissolution, or heat of solution is the enthalpy change associated with the dissolution of a substance in a solvent at constant pressure resulting in infinite dilution....
in hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
at standard conditions is −600 kJ/mol−1, from which the standard enthalpy change of formation
Standard enthalpy change of formation (data table)
These tables include heat of formation data gathered from a variety of sources, including the primary and secondary literature, as well as the NIST Chemistry WebBook...
(ΔfH°) of aqueous Bk3+ ions is obtained as −601 kJ/mol−1. The standard potential Bk3+/Bk0 is −2.01 V. The ionization potential
Ionization energy
The ionization energy of a chemical species, i.e. an atom or molecule, is the energy required to remove an electron from the species to a practically infinite distance. Large atoms or molecules have a low ionization energy, while small molecules tend to have higher ionization energies.The property...
of a neutral berkelium atom is 6.23 eV.
Allotropes
At ambient conditions, berkelium assumes its most stable α form which has a hexagonal symmetry, space groupSpace group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
P63/mmc, lattice parameters of 341 pm and 1107 pm. The crystal has a double-hexagonal close packing structure with the layer sequence ABAC and so is isotypic with α-lanthanum and α-forms of actinides beyond curium. This crystal structure changes with pressure and temperature. When compressed at room temperature to 7 GPa, α-berkelium transforms to the beta modification, which has a face-centered cubic
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
(fcc) symmetry and space group Fmm. This transition occurs without change in volume, but the enthalpy
Enthalpy
Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.Enthalpy is a...
increases by 3.66 kJ/mol. Upon further compression to 25 GPa, berkelium transforms to an orthorhombic
Orthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
γ-berkelium structure similar to that of α-uranium. This transition is accompanied by a 12% volume decrease and delocalization of the electrons at the 5f electron shell
Electron shell
An electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" , followed by the "2 shell" , then the "3 shell" , and so on further and further from the nucleus. The shell letters K,L,M,.....
. No further phase transitions are observed up to 57 GPa.
Upon heating, α-berkelium transforms into another "metastable" phase (that is at ambient temperature it gradually converts back to α-berkelium). This phase has an fcc lattice (but slightly different from β-berkelium), space group Fmm and the lattice constant of 500 pm; this fcc structure is equivalent to the closest packing with the sequence ABC. The temperature of the phase transition is believed to be quite close to the melting point.
Chemical
Like all actinideActinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...
s, berkelium dissolves in various aqueous inorganic acids, liberating gaseous hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and converting into the berkelium(III) state. This trivalent oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
is the most stable, especially in aqueous solutions, but tetravalent and possibly divalent berkelium compounds are also known. The existence of divalent berkelium salts is uncertain and has only been reported in mixed lanthanum chloride-strontium chloride
Strontium chloride
Strontium chloride is a salt of strontium and chloride. It is a typical salt, forming neutral aqueous solutions. Like all compounds of Sr, this salt emits a bright red colour in a flame; in fact is used as a source of redness in fireworks...
melts. A similar behavior is observed for the lanthanide analogue of berkelium, terbium
Terbium
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife...
. Aqueous solutions of Bk3+ ions are green in most acids. The color of the Bk4+ ions is yellow in hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
and orange-yellow in sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
. Berkelium does not react rapidly with oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
at room temperature, possibly due to the formation of a protective oxide layer surface. However, it reacts with molten metals, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
s, chalcogen
Chalcogen
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
s and pnictogens to form various binary compounds.
Isotopes
About twenty isotopes and six nuclear isomerNuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
s (excited states of an isotope) of berkelium have been characterized with the atomic numbers ranging from 235 to 254. All of them are radioactive. The longest half-lives
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
are observed for 247Bk (1,380 years), 248Bk (9 years) and 249Bk (330 days); the half-lives of the other isotopes range from microseconds to several days. The isotope which is the easiest to synthesize is berkelium-249. This emits mostly soft β-particles
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
which are inconvenient for detection. Its alpha radiation is rather weak – 1.45% with respect to the β-radiation – but is sometimes used to detect this isotope. The second important berkelium isotope, berkelium-247, is an alpha-emitter as most actinide isotopes.
Occurrence
The longest-lived isotope of berkelium (247Bk) has a half-life of only 1,380 years. Therefore, all primordialPrimordial nuclide
In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...
berkelium, that is berkelium present on the Earth during its formation, should have decayed by now. On Earth, berkelium is mostly concentrated in certain areas, which were used for the atmospheric nuclear weapons tests between 1945 and 1980, as well as at the sites of nuclear incidents, such as Chernobyl disaster
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...
, Three Mile Island accident
Three Mile Island accident
The Three Mile Island accident was a core meltdown in Unit 2 of the Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania near Harrisburg, United States in 1979....
and 1968 Thule Air Base B-52 crash. Analysis of the debris at the testing site of the first U.S. hydrogen bomb, Ivy Mike
Ivy Mike
Ivy Mike was the codename given to the first United States test of a thermonuclear weapon, in which a major part of the explosive yield came from nuclear fusion. It was detonated on November 1, 1952 by the United States at on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy...
, (1 November 1952, Enewetak Atoll), revealed high concentrations of various actinides, including berkelium. For reasons of military secrecy, this result was published only in 1956.
Nuclear reactors produce mostly, among the berkelium isotopes, berkelium-249. During the storage and before the fuel disposal, most of it breaks down to californium-249. The latter has a long half-life, of 351 years, and is therefore undesirable in the disposal products.
Preparation of isotopes
Berkelium is produced by bombarding lighter actinides uraniumUranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
(238U) or plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
(239Pu) with neutrons in a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
. In a more common case of uranium fuel, plutonium is produced first by neutron capture (the so-called (n,γ) reaction or neutron fusion) followed by beta-decay:
(the times are half-livesHalf-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
)
Plutonium-239 is further irradiated by a source that has a high neutron flux
Neutron flux
The neutron flux is a quantity used in reactor physics corresponding to the total length travelled by all neutrons per unit time and volume . The neutron fluence is defined as the neutron flux integrated over a certain time period....
,several times higher than a conventional nuclear reactor, such as the 85-megawatt High Flux Isotope Reactor
High Flux Isotope Reactor
The High Flux Isotope Reactor is a nuclear research reactor located at Oak Ridge National Laboratory in Oak Ridge, Tennessee, United States...
(HFIR) at the Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...
in Tennessee, USA. The higher flux promotes fusion reactions involving not one but several neutrons, converting 239Pu to 244Cm and then to 249Cm:
Curium-249 has a short half-life of 64 minutes, and thus its further conversion to 250Cm has a low probability. Instead, it transforms by beta-decay into 249Bk:
The thus-produced 249Bk has a long half-life of 330 days and thus can capture another neutron. However, the product, 250Bk, again has a relatively short half-life of 3.212 hours and thus, does not yield higher actinides. Instead decays to the californium isotope 250Cf:
The above reactions illustrate that although 247Bk is the most stable isotope of berkelium, its production in nuclear reactors is very inefficient. This makes 249Bk the most accessible isotope of berkelium, which still, is available only in small quantities (only 0.66 grams have been produced in the US over the period 1967–1983) at a high price of the order 185 USD
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
per microgram.
The isotope 248Bk was first obtained in 1956 by bombarding a mixture of curium isotopes with 25 MeV α-particles. Although its direct detection was hindered by strong signal interference with 245Bk, the existence of a new isotope was proven by the growth of the decay product 248Cf which had been previously characterized. The half-life of 248Cf was estimated as 23 ± 5 hours and a more reliable value still is not known. Berkelium-247 was produced during the same year by irradiating 244Cm with alpha-particles:
Berkelium-242 was synthesized in 1979 by bombarding 235U with 11B, 238U with 10B, 232Th with 14N or 232Th with 15N. It converts by electron capture
Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
to 242Cm with a half-life of 7.0 ± 1.3 minutes. A search for an initially suspected isotope 241Bk was then unsuccessful.
Separation
The fact that berkelium readily assumes oxidation stateOxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
+4 in solids, and is relatively stable in this state in liquids greatly assists separation of berkelium away from many other actinides. These are inevitably produced in relatively large amounts during the nuclear synthesis and often favor the +3 state. This fact was not yet known in the initial experiments, which used a more complex separation procedure. Various oxidation agents can be applied to the berkelium(III) solutions to convert it to the +4 state, such as bromate
Bromate
The bromate anion, BrO, is a bromine-based oxoanion. A bromate is a chemical compound that contains this ion. Examples of bromates include sodium bromate, , and potassium bromate, .Bromates are formed many different ways in municipal drinking water...
s (BrO3–), bismuthates (BiO3–), chromate
Chromate
Chromate salts contain the chromate anion, CrO42−. Dichromate salts contain the dichromate anion, Cr2O72−. They are oxyanions of chromium in the oxidation state +6. They are moderately strong oxidizing agents.- Chemical properties :...
s (CrO42– and Cr2O72–), silver(I) thiolate , lead(IV) oxide (PbO2), ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
, or photochemical oxidation procedures. Berkelium(IV) is then extracted with ion exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
, extraction chromatography
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
or liquid-liquid extraction using HDEHP (bis-(2-ethylhexyl) phosphoric scid), amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
s, tributyl phosphate
Tributyl phosphate
Tributyl phosphate, known commonly as TBP, is an organophosphorus compound with the formula 3PO. This colourless, odorless liquid finds some applications as an extractant and a plasticizer. It is an ester of orthophosphoric acid with n-butanol.- Production :Tributyl phosphate is manufactured by...
or various other reagents. These procedures separate berkelium from most trivalent actinides and lanthanides, except for the lanthanide cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
(lanthanides are absent in the irradiation target but are created in various nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
decay chains).
A more detailed procedure adopted at the Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...
was as follows: the initial mixture of actinides is processed with ion exchange using lithium chloride
Lithium chloride
Lithium chloride is a chemical compound with the formula LiCl. The salt is a typical ionic compound, although the small size of the Li+ ion gives rise to properties not seen for other alkali metal chlorides, such as extraordinary solubility in polar solvents and its hygroscopic...
reagent, then precipitated as hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
s, filtered and dissolved in nitric acid. It is then treated with high-pressure elution
Elution
Elution is a term used in analytical and organic chemistry to describe the process of extracting one material from another by washing with a solvent ....
from cation exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
resins, and the berkelium phase is oxidized and extracted using one of the procedures described above. Reduction of the thus-obtained berkelium(IV) to the +3 oxidation state yields a solution, which is nearly free from other actinides (but contains cerium). Berkelium and cerium are then separated with another round of ion-exchange treatment.
Bulk metal preparation
In order to characterize chemical and physical properties of solid berkelium and its compounds, a program was initiated in 1952 at the Material Testing ReactorIdaho National Laboratory
Idaho National Laboratory is an complex located in the high desert of eastern Idaho, between the town of Arco to the west and the cities of Idaho Falls and Blackfoot to the east. It lies within Butte, Bingham, Bonneville and Jefferson counties...
, Arco, Idaho
Arco, Idaho
Arco is a city in Butte County, Idaho, United States. The population was 995 at the 2010 census. The city is the county seat of Butte County.Craters of the Moon National Monument is located along U.S. Route 20, southwest of the city. The Idaho National Laboratory is located east of Arco...
, US. It resulted in preparation of an eight-gram plutonium-239 target and in the first production of macroscopic quantities (0.6 micrograms) of berkelium by Burris B. Cunningham and Stanley G. Thompson in 1958, after a continuous reactor irradiation of this target for six years. This irradiation method was, and still is the only way of producing weighable amounts of the element, and most solid-state studies of berkelium have been conducted on microgram or submicrogram-sized samples.
The world's major irradiation sources are the 85-megawatt High Flux Isotope Reactor at the Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...
in Tennessee, USA, and the SM-2 loop reactor at the Research Institute of Atomic Reactors
Research Institute of Atomic Reactors
The Research Institute of Atomic Reactors is an institute for nuclear reactor research in Dimitrovgrad in Ulyanovsk Oblast, Russia. The institute houses eight nuclear research reactors: SM, Arbus , MIR.M1, RBT-6, RBT-10 / 1, RBT-10 / 2, BOR-60 and VK-50.-External links:* *...
(NIIAR) in Dimitrovgrad, Russia
Dimitrovgrad, Russia
Dimitrovgrad is a city in Ulyanovsk Oblast, Russia, located on the Bolshoy Cheremshan River. Population: -History:It was founded in the beginning of the 18th century as a village for workers of the local distillery, which was closed in 1848. As of 1897, its population was 8,500, and in 1919...
, which are both dedicated to the production of transcurium elements (atomic number greater than 96). These facilities have similar power and flux levels, and are expected to have comparable production capacities for transcurium elements, although the quantities produced at NIIAR are not widely reported. In a "typical processing campaign" at Oak Ridge, tens of grams of curium
Curium
Curium is a synthetic chemical element with the symbol Cm and atomic number 96. This radioactive transuranic element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie. Curium was first intentionally produced and identified in summer 1944 by the group of...
are irradiated to produce decigram quantities of californium
Californium
Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles at the University of California, Berkeley. It is the ninth member of the actinide series and was the...
, milligram quantities of berkelium-249 and einsteinium
Einsteinium
Einsteinium is a synthetic element with the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide.Einsteinium was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein...
, and picogram quantities of fermium
Fermium
Fermium is a synthetic element with the symbol Fm. It is the 100th element in the periodic table and a member of the actinide series. It is the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities,...
. In total, just over one gram of berkelium-249 has been produced at Oak Ridge since 1967.
The first berkelium metal sample weighing 1.7 micrograms was prepared in 1971 by the reduction of berkelium(III) fluoride with lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
vapor at 1000 °C; the fluoride was suspended on a tungsten wire above a tantalum
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...
crucible containing molten lithium. Later, metal samples weighting up to 0.5 milligrams were obtained with this method.
Similar results are obtained with berkelium(IV) fluoride. Berkelium metal can also be produced by the reduction of berkelium(IV) oxide with thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
or lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
.
Oxides
Two oxides of berkelium are known, with the berkelium oxidation state of +3 (Bk2O3) and +4 (BkO2). Berkelium(IV) oxide is a brown solid that crystallizes in a cubic (fluoriteFluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...
) crystal structure
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
. Berkelium(III) oxide is formed from BkO2 by reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
with molecular hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
:
It is a yellow-green solid with a melting point of 1920 °C and a body-centered cubic
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
(bcc) crystal lattice. Upon heating to 1200 °C, the cubic Bk2O3 transforms to a monoclinic structure, which further converts to a hexagonal phase at 1750 °C, and the latter transition is reversible. Such three-phase behavior is typical for the actinide sesquioxides. Berkelium(II) oxide, BkO, has been reported as a brittle gray solid with a face centered cubic
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
(fcc) structure, but its exact chemical composition remains uncertain.
Halides
In halideHalide
A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. Many salts are halides...
s, berkelium assumes the oxidation states +3 and +4. The +3 state is the most stable, especially in solutions, while the tetravalent halides BkF4 and Cs2BkCl6 are only known in the solid phase. The coordination of berkelium atom in its trivalent fluoride and chloride is tricapped trigonal prismatic, with the coordination number
Coordination number
In chemistry and crystallography, the coordination number of a central atom in a molecule or crystal is the number of its nearest neighbours. This number is determined somewhat differently for molecules and for crystals....
of 9. In trivalent bromide, it is bicapped trigonal prismatic (coordination 8) or octahedral
Octahedral molecular geometry
In chemistry, octahedral molecular geometry describes the shape of compounds where in six atoms or groups of atoms or ligands are symmetrically arranged around a central atom, defining the vertices of an octahedron...
(coordination 6), and in the iodide it is octahedral.
| Oxidation number |
F | Cl | Br | I |
|---|---|---|---|---|
| +4 | BkF4 (yellow) |
Cs2BkCl6 (orange) |
||
| +3 | BkF3 (yellow) |
BkCl3 (green) Cs2NaBkCl6 |
BkBr3 (yellow-green) |
BkI3 (yellow) |
Berkelium(IV) fluoride (BkF4) is a yellow-green ionic solid which crystallizes in the monoclinic crystal system
Monoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
and is isotypic with uranium tetrafluoride
Uranium tetrafluoride
Uranium tetrafluoride is a green crystalline solid compound of uranium with an insignificant vapor pressure and very slight solubility in water. Uranium in its tetravalent state is very important in different technological processes...
or zirconium(IV) fluoride
Zirconium(IV) fluoride
Zirconium fluoride is an inorganic chemical compound. It is a component of ZBLAN fluoride glass. It is insoluble in water. It is the main component of fluorozirconate glasses....
.
Berkelium(III) fluoride (BkF3) is also a yellow-green solid, but it has two crystalline structures. The most stable phase at low temperatures has an orthorhombic
Orthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
symmetry, isotypic with yttrium(III) fluoride
Yttrium(III) fluoride
Yttrium fluoride is an inorganic chemical compound with the chemical formula YF3. It is not known naturally in 'pure' form. The fluoride minerals containing essential yttrium include tveitite- 6Ca6Ca6F42 and gagarinite- NaCaY6...
. Upon heating to between 350 and 600 °C, it transforms to a trigonal structure found in lanthanum(III) fluoride.
Visible amounts of berkelium(III) chloride (BkCl3) were first isolated and characterized in 1962, and weighed only 3 billionths of a gram
Gram
The gram is a metric system unit of mass....
. It can be prepared by introducing hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
vapors into an evacuated quartz tube containing berkelium oxide at a temperature about 500 °C. This green solid has a melting point of 600 °C, and crystallized in the hexagonal crystal system
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
isotypic with uranium(III) chloride
Uranium(III) chloride
Uranium chloride , UCl3, is a chemical compound that contains the earth metal uranium and chlorine. UCl3 is used mostly to reprocess spent nuclear fuel. Uranium chloride is synthesized various ways from uranium chloride; however, UCl3 is less stable than UCl4.-Preparation:There are two ways to...
. Upon heating to nearly melting point, BkCl3 converts into an orthorhombic phase.
Two forms of berkelium(III) bromide are known: a monoclinic one with berkelium having coordination 6, and an orthorhombic one with coordination 8. The latter is less stable and transforms to the former phase upon heating to about 350 °C. An important phenomenon for radioactive solids has been studied on these two crystal forms: the structure of fresh and aged 249BkBr3 samples was probed by X-ray diffraction over a period longer than 3 years, so that various fractions of berkelium-249 had converted to californium-249. No change in structure was observed upon 249BkBr3—249CfBr3 transformation, even though the orthorhombic bromide was previously unknown for californium. However, other differences were noted for 249BkBr3 and 249CfBr3. For example, the latter could be reduced with hydrogen to 249CfBr2, but the former could be not – this result was reproduced on individual 249BkBr3 and 249CfBr3 samples, as well on the samples containing both bromides. The intergrowth of californium in berkelium occurs at a rate of 0.22% per day and is an intrinsic obstacle in studying berkelium properties. Beside a chemical contamination, 249Cf, as an alpha emitter brings undesirable self-damage of the crystal lattice and the resulting self-heating. The chemical effect however can be avoided by performing measurements as a function of time and extrapolating the obtained results.
Other inorganic compounds
The pnictides of berkelium-249 of the type BkX are known for the elements nitrogenNitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
and antimony
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
. They crystallize in the rock-salt structure
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
and are prepared by the reaction of either berkelium(III) hydride (BkH3) or metallic berkelium with these elements at elevated temperature (about 600 °C) under high vacuum.
Berkelium(III) sulfide, Bk2S3, was prepared by either treating berkelium oxide with a mixture of hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
and carbon disulfide
Carbon disulfide
Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non-polar solvent...
vapors at 1130 °C, or by directly reacting metallic berkelium with elemental sulfur. These procedures yielded brownish-black crystals with a cubic symmetry.
Berkelium(III) and berkelium(IV) hydroxides are both stable in 1 molar solutions of sodium hydroxide. Berkelium(III) phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
(BkPO4) has been prepared as a solid, which shows strong fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
under excitation with a green light. Berkelium hydrides are produced by reacting metal with hydrogen gas at temperatures about 250 °C. They are non-stoichiometric with the nominal formula BkH2+x (0 < x < 1). Whereas the trihydride has a hexagonal symmetry, the dihydride crystallizes in an fcc structure. Several other salts of berkelium are known, including an oxysulfide (Bk2O2S), and hydrated nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
, chloride , sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
and oxalate
Oxalate
Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...
. Thermal decomposition at about 600 °C in an argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
atmosphere (to avoid oxidation to ) of yields the body-centered orthorhombic crystals of berkelium(III) oxysulfate . This compound is thermally stable to at least 1000 °C in inert atmosphere.
Organometallic compounds
Berkelium forms a trigonal (η5–C5H5)3Bk metalloceneMetallocene
A metallocene is a compound typically consisting of two cyclopentadienyl anions bound to a metal center in the oxidation state II, with the resulting general formula 2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride, vanadocene dichloride...
complex with three cyclopentadienyl
Cyclopentadienyl complex
A cyclopentadienyl complex is a metal complex with one or more cyclopentadienyl groups . Based on the type of bonding between the metals and the cyclopentadienyl]] moieties, cyclopentadienyl complexes are classified into the following three categories: a) π-complexes, b) σ-complexes, and c) ionic...
rings, which can be synthesized by reacting berkelium(III) chloride with the molten beryllocene (Be(C5H5)2) at about 70 °C. It has an amber color, an orthorhombic symmetry and a density of 2.47 g/cm3. The complex is stable to heating to at least 250 °C, and sublimates without melting at about 350 °C. The high radioactivity of berkelium gradually destroys the compound (within a period of weeks). One cyclopentadienyl ring in (η5–C5H5)3Bk can be substituted by chlorine to yield [Be(C5H5)2Cl]2. The optical absorption spectra of this compound are very similar to those of (η5–C5H5)3Bk.
Applications
There is no use for any isotope of berkelium outside of basic scientific research. Berkelium-249 is a common target nuclide to prepare still heavier transuranic elements and transactinides, such as lawrenciumLawrencium
Lawrencium is a radioactive synthetic chemical element with the symbol Lr and atomic number 103. In the periodic table of the elements, it is a period 7 d-block element and the last element of actinide series...
, rutherfordium
Rutherfordium
Rutherfordium is a chemical element with symbol Rf and atomic number 104, named in honor of New Zealand physicist Ernest Rutherford. It is a synthetic element and radioactive; the most stable known isotope, 267Rf, has a half-life of approximately 1.3 hours.In the periodic table of the elements,...
and bohrium
Bohrium
Bohrium is a chemical element with the symbol Bh and atomic number 107 and is the heaviest member of group 7 .It is a synthetic element whose most stable known isotope, 270Bh, has a half-life of 61 seconds...
. It is also useful as a source of the isotope californium-249, which is used for studies on the chemistry of californium
Californium
Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles at the University of California, Berkeley. It is the ninth member of the actinide series and was the...
in preference to the more radioactive californium-252 that is produced in neutron bombardment facilities such as the HFIR.
A 22 milligram batch of berkelium-249 was prepared in a 250-day irradiation and then purified for 90 days at Oak Ridge in 2009. This target yielded the first 6 atoms of element ununseptium
Ununseptium
Ununseptium is the temporary name of a superheavy artificial chemical element with temporary symbol Uus and atomic number 117. Six atoms were detected by a joint Russia–US collaboration at Dubna, Moscow Oblast, Russia, in 2009–10...
at the Joint Institute for Nuclear Research
Joint Institute for Nuclear Research
The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow Oblast , Russia, is an international research centre for nuclear sciences, with 5500 staff members, 1200 researchers including 1000 Ph.D.s from eighteen member states The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow...
(JINR), Dubna
Dubna
Dubna is a town in Moscow Oblast, Russia. It has a status of naukograd , being home to the Joint Institute for Nuclear Research, an international nuclear physics research centre and one of the largest scientific foundations in the country. It is also home to MKB Raduga, a defence aerospace company...
, Russia, after bombarding it with calcium ions in the U400 cyclotron for 150 days. This synthesis was a culmination of the Russia—US collaboration between JINR and Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
on the synthesis of elements 113 to 118 which was initiated in 1989.
Nuclear fuel cycle
The nuclear fissionNuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
properties of berkelium are different from those of the neighboring actinides curium and californium, and they suggest berkelium to perform poorly as a fuel in a nuclear reactor. Specifically, berkelium-249 has a moderately large neutron capture cross section
Neutron cross-section
In nuclear and particle physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. In conjunction with the neutron flux, it enables the calculation of the reaction rate, for example to derive the thermal power...
of 710 barns
Barn (unit)
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...
for thermal neutrons, 1200 barns resonance integral, but very low fission cross section for thermal neutrons. In a thermal reactor, much of it will therefore be converted to berkelium-250 which quickly decays to californium-250. In principle, berkelium-249 can sustain a nuclear chain reaction
Nuclear chain reaction
A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes or the fusion of light isotopes...
in a fast breeder reactor. Its critical mass
Critical mass
A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The...
is relatively high at 192 kg; it can be reduced with a water or steel reflector but would still exceed the world production of this isotope.
Berkelium-247 can maintain chain reaction both in a thermal-neutron and in a fast-neutron reactor, however, its production is rather complex and thus the availability is much lower than its critical mass, which is about 75.7 kg for a bare sphere, 41.2 kg with a water reflector and 35.2 kg with a steel reflector (30 cm thickness).
Health issues
Little is known about the effects of berkelium on human body, and analogies with other elements may not be drawn because of different radiation products (electrons for berkelium and alpha particles and/or neutrons for most other actinides). The low energy of electrons emitted from berkelium-249 (less than 126 keV) hinders its detection, due to signal interference with other decay processes, but also makes this isotope relatively harmless to humans as compared to other actinides. However, berkelium-249 transforms with a half-life of only 330 days to the strong alpha-emitter californium-249, which is rather dangerous and has to be handled in a glove box in a dedicated laboratory.Most available berkelium toxicity data originate from research on animals. Upon ingestion by rats, only about 0.01% berkelium ends in the blood stream. From there, about 65% goes to the bones, where it remains for about 50 years, 25% to the lungs (biological half-life about 20 years), 0.035% to the testicles or 0.01% to the ovaries where berkelium stays indefinitely. The balance of about 10% is excreted. In all these organs berkelium might promote cancer, and in the skeletal system its radiation can damage red blood cells. The maximum permissible body burden for the isotope berkelium-249 in the human skeleton is 0.4 nanograms.