The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform
Mark A. Silver - One of the best experts on this subject based on the ideXlab platform.
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Emergence of Californium as the second transitional element in the actinide series
Nature communications, 2015Co-Authors: Samantha K. Cary, Monica Vasiliu, Ryan Baumbach, Jared T. Stritzinger, Thomas D. Green, Kariem Diefenbach, Justin N. Cross, Kenneth L. Knappenberger, Guokui Liu, Mark A. SilverAbstract:A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of Californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of Californium(II) is responsible for many of the unusual properties of Californium including the green photoluminescence.
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Emergence of Californium as the second transitional element in the actinide series
Nature Communications, 2015Co-Authors: Samantha K. Cary, Monica Vasiliu, Jared T. Stritzinger, Thomas D. Green, Kariem Diefenbach, Justin N. Cross, Kenneth L. Knappenberger, Guokui Liu, Ryan E. Baumbach, Mark A. SilverAbstract:The chemistry of the post-plutonium actinides is thought to resemble lanthanides in that bonding is primarily ionic. Here, the authors show that a Californium(III) complex displays significantly different properties to those predicted for the free ion owing to a second break in actinide periodicity. A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5 f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of Californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of Californium(II) is responsible for many of the unusual properties of Californium including the green photoluminescence.
Samantha K. Cary - One of the best experts on this subject based on the ideXlab platform.
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Emergence of Californium as the second transitional element in the actinide series
Nature communications, 2015Co-Authors: Samantha K. Cary, Monica Vasiliu, Ryan Baumbach, Jared T. Stritzinger, Thomas D. Green, Kariem Diefenbach, Justin N. Cross, Kenneth L. Knappenberger, Guokui Liu, Mark A. SilverAbstract:A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of Californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of Californium(II) is responsible for many of the unusual properties of Californium including the green photoluminescence.
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Emergence of Californium as the second transitional element in the actinide series
Nature Communications, 2015Co-Authors: Samantha K. Cary, Monica Vasiliu, Jared T. Stritzinger, Thomas D. Green, Kariem Diefenbach, Justin N. Cross, Kenneth L. Knappenberger, Guokui Liu, Ryan E. Baumbach, Mark A. SilverAbstract:The chemistry of the post-plutonium actinides is thought to resemble lanthanides in that bonding is primarily ionic. Here, the authors show that a Californium(III) complex displays significantly different properties to those predicted for the free ion owing to a second break in actinide periodicity. A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5 f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of Californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of Californium(II) is responsible for many of the unusual properties of Californium including the green photoluminescence.
R. Ahuja - One of the best experts on this subject based on the ideXlab platform.
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Structural investigation of Californium under pressure
Physical Review B: Condensed Matter and Materials Physics, 2013Co-Authors: S. Heathman, T. Le Bihan, S. Yagoubi, B. Johansson, R. AhujaAbstract:The high-pressure structural behavior of Californium has been studied experimentally and theoretically up to 100 GPa. A valence change from divalent to trivalent forms was observed under modest pressure revealing Californium to be the only actinide to exhibit more than one metallic valence at near to ambient conditions as is the case for cerium in the lanthanide series. Three metallic valencies and four different crystallographic phases were observed in Californium as a function of pressure. High-pressure techniques, synchrotron radiation, and ab initio electronic structure calculations of total energies were used to investigate the material and to determine the role which Californium's 5f electrons play in influencing these transitions. The crystallographic structures observed are similar to those found in the preceding actinide elements, curium and americium, with the initially localized 5f states becoming completely delocalized under the influence of high pressure
R. C. Martin - One of the best experts on this subject based on the ideXlab platform.
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Production, Distribution, and Applications of Californium-252 Neutron Sources
1999Co-Authors: P.a. Balo, J.b. Knauer, R. C. MartinAbstract:The radioisotope {sup 252}Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-year half-life. A source the size of a person's little finger can emit up to 10{sup 11} neutrons/s. Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement, and minerals, as well as for detection and identification of explosives, laud mines, and unexploded military ordnance. Other uses are neutron radiography, nuclear waste assays, reactor start-up sources, calibration standards, and cancer therapy. The inherent safety of source encapsulations is demonstrated by 30 years of experience and by U.S. Bureau of Mines tests of source survivability during explosions. The production and distribution center for the U. S Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory (ORNL). DOE sells The radioisotope {sup 252}Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6- year half-life. A source the size of a person's little finger can emit up to 10 neutrons/s. Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement, and minerals, as well as for detection and identification of explosives, laud mines, and unexploded military ordnance. Other uses are neutron radiography, nuclear waste assays, reactor start-up sources, calibration standards, and cancer therapy. The inherent safety of source encapsulations is demonstrated by 30 years of experience and by U.S. Bureau of Mines tests of source survivability during explosions. The production and distribution center for the U. S Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory(ORNL). DOE sells {sup 252}Cf to commercial reencapsulators domestically and internationally. Sealed {sup 252}Cf sources are also available for loan to agencies and subcontractors of the U.S. government and to universities for educational, research, and medical applications. The REDC has established the Californium User Facility (CUF) for Neutron Science to make its large inventory of {sup 252}Cf sources available to researchers for irradiations inside uncontaminated hot cells. Experiments at the CUF include a land mine detection system, neutron damage testing of solid-state detectors, irradiation of human cancer cells for boron neutron capture therapy experiments, and irradiation of rice to induce genetic mutations.
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Biomedical neutron research at the Californium User Facility for Neutron Science
Journal of Radioanalytical and Nuclear Chemistry, 1998Co-Authors: R. C. Martin, T. E. Byrne, L. F. MillerAbstract:The Californium User Facility for Neutron Science has been established at Oak Ridge National Laboratory (ORNL). The Californium Use Facility (CUF) is a part of the larger Californium Facility, which fabricates and stores compact^252Cf neutron sources for worldwide distribution. The CUF can provide a cost-effective option for research with^252Cf sources. Three projects at the CUF that demonstrate the versatility of^252Cf for biological and biomedical neutron-based research are described: future establishment of a^252Cf-based neutron activation analysis system, ongoing work to produce miniature high-intensity, remotely afterloaded^252Cf sources for tumors therapy, and a recent experiment that irradiated living human lung cancer cells impregnated with experimental boron compounds to test their effectiveness for boron neutron capture therapy.
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Proposed Californium-252 user facility for neutron science at Oak Ridge National Laboratory
Applied Radiation and Isotopes, 1997Co-Authors: R. C. Martin, R.r. Laxson, J.b. KnauerAbstract:The Radiochemical Engineering Development Center (REDC) at ORNL has petitioned to establish a Californium-252 User Facility for Neutron Science for academic, industrial, and governmental researchers. The REDC Californium Facility (CF) stores the national inventory of sealed {sup 252}Cf neutron source for university and research loans. Within the CF, the {sup 252}Cf storage pool and two uncontaminated hot cells currently in service for the Californium Program will form the physical basis for the User Facility. Relevant applications include dosimetry and experiments for neutron tumor therapy; fast and thermal neutron activation analysis of materials; experimental configurations for prompt gamma neutron activation analysis; neutron shielding and material damage studies; and hardness testing of radiation detectors, cameras, and electronics. A formal User Facility simplifies working arrangements and agreements between US DOE facilities, academia, and commercial interests.
David D Haines - One of the best experts on this subject based on the ideXlab platform.
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Solvent effects on phytochemical constituent profiles and antioxidant activities, using four different extraction formulations for analysis of Bucida buceras L. and Phoradendron californicum
BMC Research Notes, 2015Co-Authors: Simon B. Iloki-assanga, Lidianys M. Lewis-luján, Claudia L. Lara-espinoza, Armida A. Gil-salido, Daniela Fernandez-angulo, Jose L. Rubio-pino, David D HainesAbstract:Background The present investigation evaluated 4 different solvent compositions for their relative capacity to extract total phenolic and total flavonoid (TF) components of the leaves, trunks, and stems of Bucida buceras L. (Combretaceae), and the stems of Phoradendron californicum (Viscaceae), plus mesquite and oak species endemic to the Southwestern United States, northern Mexico, and tropical regions of Central and South America, as well as to profile the composition of these plant materials and to measure their antioxidant capacity. Methods The total phenolic content of plant material used in the present investigation was measured using the Folin–Ciocalteau assay. Total flavonoids were assayed by AlCl_3 and 2,4-dinitrophenylhydrazin colorimetry. Nitroblue tetrazolium was utilized for scavenging of superoxide anion, and in vitro antioxidant activity was evaluated using the 2, 2-diphenyl-1-picrylhydrazyl and Ferric Reducing/Antioxidant Power assays. Results Phytochemical screening of each plant extract evaluated revealed the following major results: (1) No evidence of alkaloids for each of the extraction phases tested was detected in the hexanic, ethanolic, or aqueous phases of Bucida buceras and Phoradendron californicum (oak and mesquite); (2) Analysis of the hexane phase of B. buceras and P. californicum (mesquite) extracts revealed the presence of carotenes, triterpenes/steroids, and lactonic groups; (3) Analysis of the ethanol and aqueous extraction phases for both plants revealed the presence of a diverse range of compounds, including tripterpenes/steroids, lactonics groups, saponins, phenols/tannins, amines and/or amino acids, and flavonoids/anthocyanins; and (4) The highest total phenolic and flavonoid content were observed in P. californicum (oak): 523.886 ± 51.457 µg GAE/mg extract and 409.651 ± 23.091 µg/mg of extract for methanol and aqueous fractions, respectively. The highest flavonoid content was 237.273 ± 21.250 µg PNE/mg extract in the acetone extract of Bucida buceras stems; while the flavonol content (260.685 ± 23.031 µg CE/mg extract) was higher in the ethanol extract of P. californicum (oak). The acetone extract of B. buceras trunk extract showed the highest levels of DPPH radical-scavenging activity (IC_50 = 4.136 ± 0.446 µg/mL) and reducing power (4928.392 ± 281.427 µM AAE/mg extract). The highest superoxide radical scavenging activity (IC_50) was 55.249 ± 9.829 µg/mL, observed in acetone extracts of B. buceras leaves. Conclusions The results of the present investigation demonstrated the effects of extraction solvent on phenolic and flavonoid content yield—and antioxidant activities by Bucida buceras and Phoradendron californicum . The present investigation further revealed that Bucida buceras exhibited optimal antioxidant capacity when acetone was used as extraction solvent; and the highest yield of phenols and flavonoids were obtained from the P. californicum oak, using methanol and aqueous solvents, respectively.
