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1

Protein carbon-13 spin systems by a single two-dimensional nuclear magnetic resonance experiment  

Microsoft Academic Search

By applying a two-dimensional double-quantum carbon-13 nuclear magnetic resonance experiment to a protein uniformly enriched to 26% carbon-13, networks of directly bonded carbon atoms were identified by virtue of their one-bond spin-spin couplings and were classified by amino acid type according to their particular single- and double-quantum chemical shift patterns. Spin systems of 75 of the 98 amino acid residues

B. H. Oh; W. M. Westler; P. Darba; J. L. Markley

1988-01-01

2

The 3'-keto-diol equilibrium of trospectomycin sulfate bulk drug and freeze-dried formulation: solid-state carbon-13 cross-polarization magic angle spinning (CP/MAS) and high-resolution carbon-13 nuclear magnetic resonance (NMR) spectroscopy studies.  

PubMed

Understanding how moisture interacts with a drug or formulation is a critical component of product development. This study demonstrates how water affects the 3'-gem-diol<==>3'-keto equilibrium in trospectomycin sulfate bulk drug and freeze-dried formulation, as probed by solid-state carbon-13 cross-polarization magic angle spinning (CP/MAS) and high-resolution nuclear magnetic resonance (NMR) spectroscopy. Drying the bulk drug or formulation to low water levels dehydrates trospectomycin sulfate from the diol to the keto form. Carbon-13 CP/MAS NMR spectroscopy measures the keto drug concentration in solid samples directly. The bulk drug, which contains approximately 16% water, is more than 90% in the 3'-diol form. Oven drying to < 3% water converts approximately 75% of the drug to the 3'-keto form. The drug is formulated as a freeze-dried, sterile powder that can contain up to 12% water depending on the freeze-drying conditions. These studies show that the 3'-keto concentration rises uniformly (up to 75%) with decreasing residual water in the freeze-dried cake. The keto-diol equilibrium was also studied in solution by high-resolution carbon-13 NMR experiments, and it was found that raising the temperature or using dimethyl sulfoxide (DMSO) as a solvent also dehydrates the drug. For example, in aqueous solution at 25 degrees C, nearly all (> 95%) of the drug is in the 3'-diol form. After equilibration at 60 degrees C, however, the 3'-keto content increases to 7%, and in d6-DMSO solvent at 25 degrees C the drug is mostly (60%) in the 3'-keto form. PMID:8430063

Likar, M D; Taylor, R J; Fagerness, P E; Hiyama, Y; Robins, R H

1993-01-01

3

The first observation of Carbon-13 spin noise spectra  

PubMed Central

We demonstrate the first 13C NMR spin noise spectra obtained without any pulse excitation by direct detection of the randomly fluctuating noise from samples in a cryogenically cooled probe. Noise power spectra were obtained from 13C enriched methanol and glycerol samples at 176 MHz without and with 1H decoupling, which increases the sensitivity without introducing radio frequency interference with the weak spin noise. The multiplet amplitude ratios in 1H coupled spectra indicate that, although pure spin noise prevails in these spectra, the influence of absorbed circuit noise is still significant at the high concentrations used. In accordance with the theory heteronuclear Overhauser enhancements are absent from the 1H-decoupled 13C spin noise spectra.

Schlagnitweit, Judith; Muller, Norbert

2012-01-01

4

NMR Investigations of Liquid Propellant Systems Consisting of Alkyl- and Hydroxylammonium Nitrates. Part 2. Measurement of Carbon-13 Spin-Lattice Relaxation Times and Activation Energies for Molecular Motion in Model Liquid Propellant Systems.  

National Technical Information Service (NTIS)

Carbon-13 spin-lattice relaxation times and nuclear Overhauser enhancements were measured in four alkylammonium nitrates, isopropyl-, triethanol-, trimeth trimethyl-, and n-butylammonium nitrates. The relaxation mechanism in these compounds was found to b...

R. L. Dudley S. Bulusu

1987-01-01

5

Carbon-13 nuclear magnetic resonance analysis of formaldehyde free preservatives.  

PubMed

Preservation of biomolecules is pivotal in increasingly important molecular diagnostics. Traditionally, formaldehyde is employed for such biomolecular preservation in spite of its carcinogenicity. Moreover, formaldehyde induced cross-linking during fixation is reported to alter structural and functional properties of the preserved biomolecules. Therefore, formaldehyde-free preservatives are advantageous because they are safer for laboratory personnel and they protect the structural and functional integrity of the biomolecules. Streck Cell Preservative and Cell-Free DNA BCT reagents are used as formaldehyde alternative preservatives. However, no studies have been carried out to evaluate formaldehyde concentrations in these preservatives. In this study, we evaluated the free formaldehyde concentrations of these reagents by carbon-13 ((13)C) NMR spectroscopic analysis. Chemically non-invasive NMR analysis is more reliable than the traditional derivatization based techniques in formaldehyde detection. (13)C NMR technique can be used for quantitative measurement by using (13)C NMR-relaxation agents. In this manuscript, we report an optimized NMR analysis method using Gadolinium diethylenetriaminepentaacetate. Additionally the data reported herein provide spectral analyses that indicate Streck Cell Preservative and Cell-Free DNA BCT reagents do not contain detectable free formaldehyde. Therefore, these preservatives are safer alternatives than formaldehyde for laboratory use, which can protect the overall integrity of the biomolecules within preserved samples. PMID:23261251

Das, Kausik; Dumais, Joseph; Basiaga, Sara; Krzyzanowski, Gary D

2012-12-21

6

Hydrogen bonding and related association in linear aliphatic amino alcohols as probed by carbon-13 spin-lattice relaxation times  

Microsoft Academic Search

Carbon-13 chemical shifts and spin-lattice relaxation data obtained in a number of solvents for five linear aliphatic amino alcohols are presented. The purpose of monitoring the relaxation behavior was to learn about inter- and intramolecular association as a function of concentration and solvent. An analyses of the Tâ, C13 spin-lattice relaxation time, data reveals that intermolecular OH-OH hydrogen bonding competes

Ulf Edlund; Clive Holloway; George C. Levy

1976-01-01

7

Quantitative carbon-13 nuclear magnetic resonance spectroscopic study of mobile residues in bacteriorhodopsin  

SciTech Connect

The authors have used quantitative carbon-13 nuclear magnetic resonance (NMR) spectroscopy to study the dynamic structure of the backbone of bacteriorhodopsin in the purple membrane of Halobacterium halobium R/sub 1/ and JW-3. NMR experiments were performed using an internal sucrose quantitation standard on purple membranes in which one of the following /sup 13/C'-labeled amino acids had been biosynthetically incorporated: glycine, isoleucine, lysine, phenylalanine, and valine. The results suggest that the C-terminus of the polypeptide chain backbone, and possibly one of the connecting loops, undergoes rapid, large angle fluctuations. The results are compared with previous NMR and fluorescence spectroscopic data obtained on bacteriorhodopsin.

Bowers, J.L.; Oldfield, E.

1988-07-12

8

SUBSTITUENT EFFECTS AND ADDITIVITY IN THE CARBON-13 NUCLEAR MAGNETIC RESONANCE SPECTRA OF CHLORINATED NAPHTHALENES AND THEIR CHLORINATED NAPHTHOL METABOLITES  

EPA Science Inventory

Carbon-13 and proton nuclear magnetic resonance spectra were obtained for 12 chlorinated naphthalenes and six chlorinated naphthols, some of which are metabolites of the naphthalenes. The validity of the use of additivity of chlorine and hydroxyl substituent effects to predict 13...

9

Characterization of the International Humic Substances Society standard and reference fulvic and humic acids by solution state carbon-13 (13C) and hydrogen-1 (1H) nuclear magnetic resonance spectrometry  

USGS Publications Warehouse

Standard and reference samples of the International Humic Substances Society have been characterized by solution state carbon-13 and hydrogen-1 nuclear magnetic resonance (NMR) spectrometry. Samples included the Suwannee River, soil, and peat standard fulvic and humic acids, the Leonardite standard humic acid, the Nordic aquatic reference fulvic and humic acids, and the Summit Hill soil reference humic acid. Aqueous-solution carbon-13 NMR analyses included the measurement of spin-lattice relaxation times, measurement of nuclear Overhauser enhancement factors, measurement of quantitative carbon distributions, recording of attached proton test spectra, and recording of spectra under nonquantitative conditions. Distortionless enhancement by polarization transfer carbon-13 NMR spectra also were recorded on the Suwannee River fulvic acid in deuterated dimethyl sulfoxide. Hydrogen-1 NMR spectra were recorded on sodium salts of the samples in deuterium oxide. The carbon aromaticities of the samples ranged from 0.24 for the Suwannee River fulvic acid to 0.58 for the Leonardite humic acid.

Thorn, Kevin A.; Folan, Daniel W.; MacCarthy, Patrick

1989-01-01

10

Carbon-13 nuclear magnetic resonance study on poly(ethylacrylate-co-sodium acrylate) ionomer  

NASA Astrophysics Data System (ADS)

The poly(ethylacrylate) (PEA) homopolymer and poly(ethylacrylate-co-sodium acrylate) ionomer that contain 8.4 mol % ionic groups (PEANa-8.4) were studied by 13C using cross polarization and magic angle spinning nuclear magnetic resonance (CP/MAS NMR). The 13C spin-lattice relaxation times in a rotating frame, T1?, were measured as functions of the temperature. Using these T1? spin-lattice relaxation times, we addressed the chain mobility, correlation time, and activation energy for carbon of the PEA homopolymer and the PEANa-8.4 ionomer. We found that the molecular motion in the PEA homopolymer needed a higher activation energy than that in the PEANa-8.4 ionomer. In addition, we observed that motion of the 1-methyl carbons in the PEANa-8.4 ionomer was distinctly different from that in the PEA homopolymer: the value of T1? for 1-methyl carbon is ascribed to stronger interactions between the polymer chains in the homopolymer.

Lim, Ae Ran; Kwark, Young-Je; Kim, Joon-Seop

2003-12-01

11

Natural abundance carbon 13 nuclear magnetic resonance spectroscopy of antifreeze glycoproteins  

SciTech Connect

Natural abundance /sup 13/C NMR spectroscopy (at 67.9 MHz) is used to study an aqueous solution of the antifreeze glycoproteins 3 to 6 from the Antarctic cod. Assignments of resonances to specific carbons of the known Ala-Ala-(..beta..Gal-(1 ..-->.. 3)-..cap alpha..-N-acetylgalactosamine)Thr repeating unit are presented. Some of the carbons of the proline residues of glycoprotein 6 are also identified. Spin-lattice relaxation times (at 30/sup 0/C), linewidths (at 35/sup 0/C), nuclear Overhauser enhancements (at 35/sup 0/C), and the temperature dependence of chemical shifts (from 0/sup 0/ to 75/sup 0/C) all strongly suggest that these antifreeze glycoproteins are predominantly or entirely flexible random coil polymers.

Berman, E. (Indiana Univ., Bloomington); Allerhand, A.; DeVries, A.L.

1980-05-25

12

Metal ion uptake from aqueous solution by olive stones: a carbon-13 solid-state nuclear magnetic resonance and potentiometric study.  

PubMed

The use of biomasses that result from the agriculture and food industries in removing heavy metals from wastewaters is attracting increasing interest. We present a joined potentiometric and cross polarization magic angle spinning (CP-MAS) carbon-13 (13C) nuclear magnetic resonance (NMR) study on the interaction of olive stones with copper(II), nickel(II), and cadmium(II). The potentiometric measurements allow both to distinguish two kind of basic sites in the olive stones and to postulate the coordination models for the three studied metals. The NMR spectral analysis allows the attribution of the different signals to the components of the olive stone matrix. A comparison of CP-MAS 13C NMR spectra of the samples after metal treatment suggests a specific complexation between metal ions and hydroxyl groups on guaiacyl and syringyl moieties. PMID:17966704

Nurchi, Valeria Marina; Floris, Costantino; Pinna, Rosalba; Fiol, Núria; Villaescusa, Isabel

2007-10-01

13

Characterization of Plasma Polymerized Hydrocarbons Using CP-MAS Carbon-13 NMR.  

National Technical Information Service (NTIS)

Plasma polymerized hydrocarbons made from ethane and methane were produced under different reactor conditions and probed by solid-state carbon-13 nuclear magnetic resonance (NMR) with cross-polarization and magic angle sample spinning. NMR experiments pro...

D. L. Cho F. D. Blum H. Yasuda R. J. Gambogi

1991-01-01

14

Carbon-13 nuclear magnetic resonance spectra of potassium (ethylenediaminetetraacetato)cobaltate(III) in organic solvents  

SciTech Connect

The carbon-13 NMR spectra of the (Co(edta))/sup /minus// (edta = ethylenediaminetetraacetate) anion were observed in water and a variety of organic solvents: ethylene glycol, methanol, formamide, ethanol, 2-propanol, chloroform, dichloromethane, dimethyl sulfoxide, acetonitrile, dimethylformamide, benzonitrile, and dimethylacetamide. The spectra in organic solvents were obtained after 1-2-h accumulations for the concentrated solutions (0.5 M) of the complex anion that were prepared by the addition of a macrobicyclic polyether, cryptand 222, to the solvents. The /sup 13/C NMR signals of the coordinated carboxylates are markedly shifted downfield in protic solvents in comparison with aprotic solvent (the greatest difference in chemical shift is 3.9 ppm), while the NMR chemical shifts of methylene carbons of ligands are not significantly influenced by solvent molecules. The magnitudes (/sigma/ values) of this downfield shift of the coordinated carboxylate /sup 13/C signals are found to be correlated linearly with the electrophilic ability of the solvent molecules. This finding leads to the conclusion that the (Co(edta))/sup /minus// anion interacts with solvent molecules through the hydrogen-bonding between solvent hydrogens and carboxyl oxygens of the complex anion. 10 references, 4 figures, 1 table.

Taura, Toshiaki

1988-08-10

15

Carbon-13 Nuclear Magnetic Resonance Spectra of Prostaglandins and Some Prostaglandin Analogs  

PubMed Central

High-resolution pulsed Fourier-transform nuclear magnetic resonance spectroscopy at 22.63 MHz was used to observe the proton-decoupled natural-abundance 13C nuclear magnetic resonance spectra of CDCl3 solutions of the methyl esters of prostaglandins F1?, 15-epi-F1?, F2?, F2?, E2, A2, 13-dehydro-F2?, 13-dehydro-F3?, two intermediates on the synthetic pathway to 13-dehydro-PGF3?, and of 7-oxa-PGF1?. All resonances were assigned by chemical shift comparisons and single-frequency offresonance proton decoupling. With two exceptions, all the lines of the spectra are well-resolved single-carbon resonances. Those due to the cyclopentane and vinyl carbons are most sensitive to structural changes. Some of these effects can be rationalized in terms of the preferred conformations of the molecules.

Cooper, Gary F.; Fried, Josef

1973-01-01

16

Nuclear-spin noise  

Microsoft Academic Search

The spectral density of the Nyquist noise current in a tuned circuit coupled to a sample of nuclear spins has been measured at He4 temperatures with a dc SQUID used as a rf amplifier. When the sample is in thermal equilibrium, a dip is observed in the spectral density at the Larmor frequency. For zero spin polarization, on the other

Tycho Sleator; Erwin L. Hahn; Claude Hilbert; John Clarke

1985-01-01

17

Optimum conditions for crude oil and petroleum product analysis by carbon-13 nuclear magnetic resonance spectrometry  

SciTech Connect

A general procedure to determine the optimum instrumental parameters in quantitative Fourier transform nuclear magnetic resonance (FT-NMR) analysis is described. Four couples of solvent and relaxation reagent have been tried; the couple C/sub 2/D/sub 2/Cl/sub 4//Fe(acac)/sub 3/ is shown to be about 3 to 5 times more efficient than the usual CDCl/sub 3//Cr(acac)/sub 3/ couples. Graphs are shown which allow the determination of the best conditions for obtaining either a given resolution in a minimum time, or the minimum time of operation, whatever the resolution may be. The procedure is applied to the carbon analysis of three crude oil heavy ends (Light Arabian). The time of operation may be reduced to about 1.5 and 12 h for a vacuum distillate (E = 370 to 535/sup 0/C) and an asphalt. In any case, the reagent must not be greater than 0.1 M. 6 figures, 1 table.

Gillet, S. (Universite de Nancy I, France); Delpuech, J.J.; Valentin, P.; Escalier, J.C.

1980-05-01

18

Mechanism of the backbone rearrangement of amino steroids. A carbon-13 and tritium nuclear magnetic resonance spectroscopic study of isoconessin, neoconessine, and the corresponding polydeuterated and polytritiated species  

SciTech Connect

Carbon-13 and tritium NMR spectroscopic data explaining the mechanism of the backbone rearrangement of some steroids, conessine into isoconessine and into neoconessine are reported. Treatment of conessine with D/sub 2/SO/sub 4/ or THSO/sub 4/ at O/sup 0/C yielded the epected mixture of polydeuterated isoconessine or polytritiated isoconessine. The complicated /sup 13/C NMR spectrum of isoconessine was highly complex as a result of the multiple partial labeling, carbon-deuterium spin-spin coupling and deuterium-induced isotope shifts. A somewhat detailed explanation of interpretation of the NMR spectrum and comparison spectra for labelled and unlabelled compounds are presented. (BLM)

Frappier, F. (Universite Pierre et Marie Curie, Paris, France); Audinot, M.; Beaucourt, J.P.; Sergent, L.; Lukacs, G.

1982-09-10

19

NMR (Nuclear Magnetic Resonance) Investigations of Liquid Propellant Systems Consisting of Alkyl- and Hydroxyl-Ammonium Nitrates. Part 1. Characterization of Carbon-13, Proton, and Nitrogen-15 NMR Spectra and Analytical Applications.  

National Technical Information Service (NTIS)

The proton, carbon-13, and nitrogen-15 (natural abundance) nuclear magnetic resonance (NMR) spectra of four aliphatic ammonium nitrates (AAN's) which could find application as the fuel components in liquid propellant systems and the nitriogen-15 NMR spect...

S. Bulusu R. L. Dudley

1986-01-01

20

Characterization of the International Humic Substances Society Standard and Reference Fulvic and Humic Acids by Solution State Carbon-13 (13C) and Hydrogen-1 (1H) Nuclear Magnetic Resonance Spectrometry.  

National Technical Information Service (NTIS)

Standard and reference samples of the International Humic Substances Society have been characterized by solution state carbon-13 and hydrogen-1 nuclear magnetic resonance (NMR) spectrometry. Samples included the Suwannee River, soil, and peat standard ful...

K. A. Thorn D. W. Folan P. MacCarthy

1989-01-01

21

Sensing single remote nuclear spins  

NASA Astrophysics Data System (ADS)

The detection of single nuclear spins would be useful for fields ranging from basic science to quantum information technology. However, although sensing based on diamond defects and other methods have shown high sensitivity, they have not been capable of detecting single nuclear spins, and defect-based techniques further require strong defect-spin coupling. Here, we present the detection and identification of single and remote 13C nuclear spins embedded in nuclear spin baths surrounding a single electron spin of a nitrogen-vacancy centre in diamond. We are able to amplify and detect the weak magnetic field noise (~10 nT) from a single nuclear spin located ~3 nm from the centre using dynamical decoupling control, and achieve a detectable hyperfine coupling strength as weak as ~300 Hz. We also confirm the quantum nature of the coupling, and measure the spin-defect distance and the vector components of the nuclear field. The technique marks a step towards imaging, detecting and controlling nuclear spins in single molecules.

Zhao, Nan; Honert, Jan; Schmid, Bernhard; Klas, Michael; Isoya, Junichi; Markham, Matthew; Twitchen, Daniel; Jelezko, Fedor; Liu, Ren-Bao; Fedder, Helmut; Wrachtrup, Jörg

2012-10-01

22

Transport, Compartmentation, and Metabolism of Homoserine in Higher Plant Cells . Carbon13- and Phosphorus31Nuclear Magnetic Resonance Studies  

Microsoft Academic Search

The transport, compartmentation, and metabolism of homoserine was characterized in two strains of meristematic higher plant cells, the dicotyledonous sycamore (Acer pseudoplatanus) and the mono- cotyledonous weed Echinochloa colonum. Homoserine is an inter- mediate in the synthesis of the aspartate-derived amino acids me- thionine, threonine (Thr), and isoleucine. Using 13C-nuclear magnetic resonance, we showed that homoserine actively entered the cells

Serge Aubert; Gilles Curien; Richard Bligny; Elisabeth Gout; Roland Douce

1998-01-01

23

Nuclear spin noise imaging  

PubMed Central

NMR images were obtained from the proton spin noise signals of a water-containing phantom, which was placed in the highly tuned, low-noise resonant circuit of a cryogenically cooled NMR probe in the presence of systematically varied magnetic field gradients. The spatially resolved proton spin density was obtained from the raw signal by a modified projection–reconstruction protocol. Although spin noise imaging is inherently less sensitive than conventional magnetic resonance imaging, it affords an entirely noninvasive visualization of the interior of opaque objects or subjects. Thus, tomography becomes possible even when neither x-ray nor radio frequency radiation can be applied for technical or safety reasons.

Muller, Norbert; Jerschow, Alexej

2006-01-01

24

Carbon-13 nuclear magnetic resonance analysis, lignin content and carbohydrate composition of humic substances from salt marsh estuaries  

NASA Astrophysics Data System (ADS)

13C nuclear magnetic resonance spectroscopy, CuO oxidation products of lignin and hydrolyzable carbohydrates were measured for fulvic and humic acids extracted from living and dead Spartina alterniflora and salt marsh sediments. With these methods, there was little evidence for early diagenetic alteration of the humic materials. No trends consistent for fulvic and humic acids were observed for either hydrolyzable carbohydrates or lignin derived phenols, and chemical measurements of these fractions did not agree with spectral estimates. Humic acids appear to contain secondary amide linkages typical of proteins and peptides.

Alberts, James J.; Hatcher, Patrick G.; Price, Mary T.; Filip, Zdenek

25

Molecular motions of [Beta]-carotene and a carotenoporphyrin dyad in solution. A carbon-13 NMR spin-lattice relaxation time study  

SciTech Connect

Analysis of [sup 13]C NMR spin-lattice relaxation times (T[sub 1]) yields information concerning both overall tumbling of molecules in solution and internal rotations about single bonds. Relaxation time and nuclear Overhauser effect data have been obtained for [Beta]-carotene and two related molecules, squalane and squalene, for zinc meso-tetraphenylporphyrin, and for a dyad consisting of a porphyrin covalently linked to a carotenoid polyene through a trimethylene bridge. Squalane and squalene, which lack conjugated double bonds, behave essentially as limp string, with internal rotations at least as rapid as overall isotropic tumbling motions. In contrast, [Beta]-carotene reorients as a rigid rod, with internal motions which are too slow to affect relaxation times. Modeling it as an anisotropic rotor yields a rotational diffusion coefficient for motion about the major axis which is 14 times larger than that for rotation about axes perpendicular to that axis. The porphyrin reorients more nearly isotropically and features internal librational motions about the single bonds to the phenyl groups. The relaxation time data for the carotenoporphyrin are consistent with internal motions similar to those of a medieval military flail. 31 refs., 3 figs., 5 tabs.

Li, S.; Swindle, S.L.; Smith, S.K.; Nieman, R.A.; Moore, A.L.; Moore, T.A.; Gust, D. (Arizona State Univ., Tempe, AZ (United States))

1995-03-09

26

Switched control of electron nuclear spin systems  

SciTech Connect

We study control of electron-nuclear spin dynamics at magnetic field strengths where the Larmor frequency of the nucleus is comparable to the hyperfine coupling strength. The quantization axis for the nuclear spin differs from the static B{sub 0} field direction and depends on the state of the electron spin. The quantization axis can be switched by flipping the state of electron spin, allowing for universal control of nuclear spin states. We show that by performing a sequence of flips (each followed by a suitable delay), we can perform any desired rotation of the nuclear spin, which can also be conditioned on the state of the electron spin. These operations, combined with electron spin rotations, can be used to synthesize any unitary transformation of the coupled electron-nuclear spin system. We discuss how these methods can be used for design of experiments for transfer of polarization from the electron to the nuclear spins.

Khaneja, Navin [Division of Engineering and Applied Science, Harvard University, 33 Oxford Street, Cambridge, Massachusetts 02138 (United States)

2007-09-15

27

A carbon-13 nuclear magnetic resonance spectroscopic study of inter-proton pair order parameters: a new approach to study order and dynamics in phospholipid membrane systems.  

PubMed Central

We report a simple new nuclear magnetic resonance (NMR) spectroscopic method to investigate order and dynamics in phospholipids in which inter-proton pair order parameters are derived by using high resolution 13C cross-polarization/magic angle spinning (CP/MAS) NMR combined with 1H dipolar echo preparation. The resulting two-dimensional NMR spectra permit determination of the motionally averaged interpair second moment for protons attached to each resolved 13C site, from which the corresponding interpair order parameters can be deducted. A spin-lock mixing pulse before cross-polarization enables the detection of spin diffusion amongst the different regions of the lipid molecules. The method was applied to a variety of model membrane systems, including 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/sterol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/sterol model membranes. The results agree well with previous studies using specifically deuterium labeled or predeuterated phospholipid molecules. It was also found that efficient spin diffusion takes place within the phospholipid acyl chains, and between the glycerol backbone and choline headgroup of these molecules. The experiment was also applied to biosynthetically 13C-labeled ergosterol incorporated into phosphatidylcholine bilayers. These results indicate highly restricted motions of both the sterol nucleus and the aliphatic side chain, and efficient spin exchange between these structurally dissimilar regions of the sterol molecule. Finally, studies were carried out in the lamellar liquid crystalline (L alpha) and inverted hexagonal (HII) phases of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). These results indicated that phosphatidylethanolamine lamellar phases are more ordered than the equivalent phases of phosphatidylcholines. In the HII (inverted hexagonal) phase, despite the increased translational freedom, there is highly constrained packing of the lipid molecules, particularly in the acyl chain region.

Urbina, J A; Moreno, B; Arnold, W; Taron, C H; Orlean, P; Oldfield, E

1998-01-01

28

Dressed qubits in nuclear spin baths  

SciTech Connect

We present a method to encode a dressed qubit into the product state of an electron spin localized in a quantum dot and its surrounding nuclear spins via a dressing transformation. In this scheme, the hyperfine coupling and a portion of a nuclear dipole-dipole interaction become logic gates, while they are the sources of decoherence in electron-spin qubit proposals. We discuss errors and corrections for the dressed qubits. Interestingly, the effective Hamiltonian of nuclear spins is equivalent to a pairing Hamiltonian, which provides the microscopic mechanism to protect dressed qubits against decoherence.

Wu Lianao [Department of Theoretical Physics and History of Science, Basque Country University (EHU/UPV), Post Office Box 644, ES-48080 Bilbao (Spain) and IKERBASQUE, Basque Foundation for Science, ES-48011 Bilbao (Spain)

2010-04-15

29

Isobaric Spin in Nuclear Physics.  

National Technical Information Service (NTIS)

A review is given of the state of isobaric spin studies in low energy physics. Topics include: isobaric spin quantum numbers; charge independance; isobaric spin impurities; selection rules for extranuclear reactions (beta decay, radiative transitions), di...

D. Robson

1966-01-01

30

Nuclear-spin noise and spontaneous emission  

Microsoft Academic Search

The spontaneous emission from nuclear spins has been observed at liquid-4He temperatures. The spins, 35Cl nuclei, are placed in the inductor of a tuned LCR circuit coupled to a dc superconducting quantum interference device used as a radio-frequency amplifier. When the spins are saturated and have zero polarization, the emission is observed at the nuclear quadrupole Larmor frequency as a

Tycho Sleator; Claude Hilbert; John Clarke

1987-01-01

31

Molecular determinants for drug-receptor interactions. 8. Anisotropic and internal motions in morphine, nalorphine, oxymorphone, naloxone and naltrexone in aqueous solution by carbon-13 NMR spin-lattice relaxation times  

NASA Astrophysics Data System (ADS)

Carbon-13 NMR spin-lattice relaxation times ( T1) were measured for morphine, oxymorphone, nalorphine, naloxone and naltrexone as hydrochloride salts in 2H 2O solution. The data refer to the molecules in the N-equatorial configuration. The experimental T1 values were interpreted using a model of anisotropic reorientation of a rigid body with superimposed internal motions of the flexible N-methyl, N-methyl-allyl and N-methyl-cyclopropyl fragments. The calculated internal motional rates were found to markedly decrease on passing from agonists to mixed (nalorphine) and pure (naloxone, naltrexone) antagonists. For these latter the observed trend of the internal flexibility about N?C and C?C bonds of the N-substituents is discussed in terms of a correlation with their relative antagonistic potencies. In fact, such an evidence of decreasing internal conformational dynamics in the order nalorphine, naloxone, naltrexone, appeared interestingly in line with the "two-state" model of opiate receptor operation mode proposed by Snyder.

Grassi, Antonio; Perly, Bruno; Pappalardo, Giuseppe C.

1989-02-01

32

A new way to use solid-state carbon-13 nuclear magnetic resonance spectroscopy to study the sorption of organic compounds to soil organic matter.  

PubMed

Several solid-state 13C nuclear magnetic resonance (NMR) techniques were used to characterize soil organic matter spiked with 13C-labeled organic compounds spanning a range of hydrophobicities (benzoic acid, benzophenone, naphthalene, phenanthrene, and palmitic acid). The chemical shifts of NMR resonances of the sorbed species were shifted by up to 3 ppm relative to those of the neat compounds. Sorption also resulted in increased resonance linewidth for the compounds containing a single 13C label, indicating the presence of a range of different chemical environments at the sites of sorption. On the other hand, sorption decreased the linewidth of the resonance of naphthalene, which was uniformly 13C-labeled. This was attributed to the removal of intermolecular 13C-13C dipolar coupling. Heterogeneity of the organic matter was demonstrated using the spectral editing technique proton spin relaxation editing (PSRE), which enabled the identification and quantification of charcoal-rich domains characterized by rapid rates of proton spin-lattice relaxation in the static frame (T1H), and humic domains characterized by slow rates of T1H relaxation. Furthermore it was demonstrated that the sorbed 13C-labeled molecules "inherit" the T1H "signature" of the organic matrix in their immediate vicinity. Thus PSRE on the spiked soils enabled evaluation of the relative affinity of the two domain types for the sorbate molecules. The charcoal-rich domains were shown to have a twofold to tenfold greater affinity for the organic compounds, with greater differences found for the more hydrophobic compounds. PMID:15942038

Smernik, Ronald J

2005-06-07

33

Nuclear rotation at low spin  

NASA Astrophysics Data System (ADS)

Two subjects related to nuclear rotation at low angular momentum are discussed. One is the ?-soft ``rotation'' in a microscopic calculation of the IBM-2, where it will be shown that we can reproduce ?-soft collective levels in a microscopic IBM-2 using a standard effective nucleon-nucleon Hamiltonian. The other is about the rotation of the axially-symmetric rotor. It is shown that, in and near the ground state, the proton and neutron deformed ellipsoids are rotating in the opposite directions, whereas they rotate about almost the same axis in states of higher spins. This holds, quite similarly, for angular-momentum-projected Nilsson wave functions and for wave functions in the Interacting Boson Model.

Takaharu, Otsuka; Mizusaki, T.; Honma, M.

1994-03-01

34

Carbon distribution in coals and coal macerals by cross polarization magic angle spinning carbon-13 nuclear magnetic resonance spectrometry  

SciTech Connect

Conventional and dipolar dephasing CP/MAS /SUP/ 1/SUP/3C NMR experiments are reported on 63 coals and coal macerals from lignite to anthracite ranks (from the US, the UK and Australia). Examination of the dipolar dephasing data reveals an overall increase in hydrogen aromaticity as the carbon aromaticity increases. While loss of substituents from aromatic rings with little aromatic cross-linking occurs until the anthracite stage is reached, the dipolar dephasing experiments also yield decay constants for different functional groups that are similar to the decay constants obtained with simple organic compounds.

Wilson, M.A.

1984-05-01

35

Conversion of Nuclear Spin Isomers of Ethylene  

NASA Astrophysics Data System (ADS)

A theoretical model of the nuclear spin isomer conversion in C2H4 induced by the intramolecular spin-spin interaction between hydrogen nuclei has been developed. In the ground electronic state, C2H4 has four nuclear spin isomers in contrast to two isomers in the molecules studied so far in this field of research. At the gas pressure of 1 Torr, the rate of conversion between isomers with the nuclear spin symmetries B1u and B2u was found to be 5.2 - 10-4 s-1, which coincides within experimental uncertainties with the rate recently measured by Sun et al. ( Science 2005, 310, 1938 ). It was determined that at low gas pressures the conversion is induced mainly by the mixing of only one pair of rotational states. The calculated pressure dependence of the conversion rate predicts that conversion slows down with increasing pressure at pressures higher than 300 Torr.

Chapovsky, P. L.; Zhivonitko, V. V.; Koptyug, I. V.

2013-10-01

36

Spins in silicon MOSFETs: electron spin relaxation and hyperpolarization of nuclear spins  

NASA Astrophysics Data System (ADS)

The spin degree of freedom of both mobile and localized electrons in silicon have extraordinary long spin relaxation times, making silicon an attractive candidate for spintronics applications and quantum information processing. In this talk, we will discuss recent results in measuring the conduction electron spin relaxation and coherence times in silicon MOS systems using electrically detected magnetic resonance. We will also discuss an all-electrical donor nuclear spin polarization method in silicon by exploiting the tunable interaction of donor bound electrons with conduction electrons, demonstrating that donor nuclear spins can be initialized through local gate control of electrical currents without the need for optical excitation.

Lo, C. C.; Weis, C. D.; van Tol, J.; Bokor, J.; Schenkel, T.; Morton, J. J. L.

2013-09-01

37

Nuclear spin conversion in diatomic molecules  

NASA Astrophysics Data System (ADS)

A mechanism of the internal interaction in dimers that mixes different nuclear spin modifications has been proposed. It has been shown that the intramolecular current associated with transitions between electronic terms of different parities can generate different magnetic fields on nuclei, leading to transitions between spin modifications and to the corresponding changes in rotational states. In the framework of the known quantum relaxation process, this interaction initiates irreversible conversion of nuclear spin modifications. The estimated conversion rate for nitrogen at atmospheric pressure is quite high (10-3-10-5 s-1).

Il'ichev, L. V.; Shalagin, A. M.

2013-07-01

38

Liquid-state nuclear spin comagnetometers.  

PubMed

We discuss nuclear spin comagnetometers based on ultralow-field nuclear magnetic resonance in mixtures of miscible solvents, each rich in a different nuclear spin. In one version thereof, Larmor precession of protons and 19F nuclei in a mixture of thermally polarized pentane and hexafluorobenzene is monitored via a sensitive alkali-vapor magnetometer. We realize transverse relaxation times in excess of 20 s and suppression of magnetic field fluctuations by a factor of 3400. We estimate it should be possible to achieve single-shot sensitivity of about 5×10(-9)??Hz, or about 5×10(-11)??Hz in ?1 day of integration. In a second version, spin precession of protons and 129Xe nuclei in a mixture of pentane and hyperpolarized liquid xenon is monitored using superconducting quantum interference devices. Application to spin-gravity experiments, electric dipole moment experiments, and sensitive gyroscopes is discussed. PMID:23004267

Ledbetter, M P; Pustelny, S; Budker, D; Romalis, M V; Blanchard, J W; Pines, A

2012-06-15

39

A New Way to Use Solid-State Carbon13 Nuclear Magnetic Resonance Spectroscopy to Study the Sorption of Organic Compounds to Soil Organic Matter  

Microsoft Academic Search

13 C-labeled. This was attributed to sorbing organic matter phases has remained elusive, partly the removalof intermolecular 13 C- 13 C dipolarcoupling. Heterogeneity due to the lack of techniques that can identify the loca- of the organic matter was demonstrated using the spectral editing tion of sorbed molecules in the heterogeneous organic technique proton spin relaxation editing (PSRE), which enabled

Ronald J. Smernik

2005-01-01

40

Hyperpolarization transfer from parahydrogen to deuterium via carbon-13  

NASA Astrophysics Data System (ADS)

Hyperpolarization arising from para-hydrogen (p-H2) can be transferred via carbon-13 to deuterium after hydrogenation of a perdeuterated substrate. The model compound is acetylene-d2, hydrogenated to yield ethylene-d2. Transfer to deuterium occurs in ALTADENA experiments (the hydrogenation reaction being performed outside the magnet of the NMR spectrometer prior to the insertion of the sample tube into the NMR probe). The proposed theory, limited to the case where the two p-H2 protons remain isochronous (same chemical shift), is based on the concept of a steady-state density operator which prevails subsequently to the hydrogenation reaction. The outcome quantity is the carbon-deuterium longitudinal spin order, denoted as IzCIzD. Calculations simply involve commutators of all relevant spin quantities with the J-coupling Hamiltonian (denoted as HJ). In particular, it is shown that the necessary condition for polarization transfer toward deuterium via carbon-13 is that IzCIzD does not commute with HJ. The structure of HJ is thus of prime importance and it appears that transfer to carbon-13 occurs for both types of experiments, ALTADENA and PASADENA (hydrogenation reaction in the presence of the NMR spectrometer magnetic field). Conversely, transfer toward deuterium via carbon-13 is possible only with ALTADENA experiments.

Aime, Silvio; Gobetto, Roberto; Reineri, Francesca; Canet, Daniel

2003-11-01

41

Detection and Control of Individual Nuclear Spins Using a Weakly Coupled Electron Spin  

SciTech Connect

We experimentally isolate, characterize, and coherently control up to six individual nuclear spins that are weakly coupled to an electron spin in diamond. Our method employs multipulse sequences on the electron spin that resonantly amplify the interaction with a selected nuclear spin and at the same time dynamically suppress decoherence caused by the rest of the spin bath. We are able to address nuclear spins with interaction strengths that are an order of magnitude smaller than the electron spin dephasing rate. Our results provide a route towards tomography with single-nuclear-spin sensitivity and greatly extend the number of available quantum bits for quantum information processing in diamond.

Taminiau, T.H.; Wagenaar, J.J.T.; van der Sar, T.; Jelezko, F.; Dobrovitski, Viatcheslav V.; Hanson, R.

2012-09-28

42

Assignments in the Carbon-13 Nuclear Magnetic Resonance Spectra of Vitamin B12, Coenzyme B12, and Other Corrinoids: Application of Partially-Relaxed Fourier Transform Spectroscopy  

PubMed Central

High-resolution Fourier transform NMR at 15.08 MHz was used to observe the proton-decoupled natural-abundance 13C spectra of aqueous solutions of cobinamide dicyanide (0.067 M), cyanocobalamin (0.024 M), dicyanocobalamin (0.14 M), and coenzyme B12 (0.038 M). Assignments were made with the aid of chemical shift comparisons, off-resonance single-frequency proton decoupling, partially-relaxed Fourier transform spectra, and splittings arising from 13C-31P coupling. As expected, the 13C spectra of the coronoids were appreciably more informative than the corresponding proton spectra. Nearly all the lines in the 13C spectra of the corrinoids were well-resolved single-carbon resonances, in spite of the structural complexity. Partially relaxed 13C Fourier transform NMR spectra, which yield spin-lattice relaxation times of each resolved resonance, were found to be a very useful addition to the arsenal of NMR techniques.

Doddrell, David; Allerhand, Adam

1971-01-01

43

Nuclear spin relaxation and intermolecular interactions  

Microsoft Academic Search

In order to specify what kind of information about intermolecular interactio~ls can be obtained by nuclear spin relaxation, we consider a suitable microscopic representation of a liquid. For reasons which will become clear below, this article is entirely confined to the treatment of the liquid phase. The molecular or microscopic picture of a liquid may be considered to be a

H G Hertz; A Kratochwill; H Weingärtner

1985-01-01

44

Readout and control of a single nuclear spin with a metastable electron spin ancilla.  

PubMed

Electron and nuclear spins associated with point defects in insulators are promising systems for solid-state quantum technology. The electron spin is usually used for readout and addressing, and nuclear spins are used as exquisite quantum bits and memory systems. With these systems, single-shot readout of single nuclear spins as well as entanglement, aided by the electron spin, have been shown. Although the electron spin in this example is essential for readout, it usually limits the nuclear spin coherence, leading to a quest for defects with spin-free ground states. Here, we isolate a hitherto unidentified defect in diamond and use it at room temperature to demonstrate optical spin polarization and readout with exceptionally high contrast (up to 45%), coherent manipulation of an individual excited triplet state spin, and coherent nuclear spin manipulation using the triplet electron spin as a metastable ancilla. We demonstrate nuclear magnetic resonance and Rabi oscillations of the uncoupled nuclear spin in the spin-free electronic ground state. Our study demonstrates that nuclei coupled to single metastable electron spins are useful quantum systems with long memory times, in spite of electronic relaxation processes. PMID:23793305

Lee, Sang-Yun; Widmann, Matthias; Rendler, Torsten; Doherty, Marcus W; Babinec, Thomas M; Yang, Sen; Eyer, Moritz; Siyushev, Petr; Hausmann, Birgit J M; Loncar, Marko; Bodrog, Zoltán; Gali, Adam; Manson, Neil B; Fedder, Helmut; Wrachtrup, Jörg

2013-06-23

45

Dissociation constants of phenothiazine drugs incorporated in phosphatidylcholine bilayer of small unilamellar vesicles as determined by carbon-13 nuclear magnetic resonance spectrometric titration.  

PubMed

The dissociation constants (pKms) of the phenothiazine drugs promazine, chlorpromazine, and triflupromazine, incorporated in the phosphatidylcholine (PC) bilayer of small unilamellar vesicles (SUV), were investigated by a 13C nuclear magnetic resonance (NMR) titration method employing their N-13CH3 (ionizable group) labelled derivatives. Use of the labelled drugs enabled direct observations of the ionization equilibrium of the N-dimethyl group. A second derivative spectrophotometric study proved that 95-98% of the phenothiazine species in the sample solutions (200 microM phenothiazine in the presence of 27 mM PC SUV) were incorporated into the PC bilayer, which simplified the calculation of pKm values by allowing that the phenothiazines in the aqueous phase could be neglected. The pKm values were calculated from the chemical shift dependence of the N-dimethyl 13C NMR signal on the pH value of sample solutions. The pKm values obtained were smaller than those measured in aqueous solutions by about one unit. The existence of cholesterol (30 mol%) in the PC bilayer showed little effect on the pKm values, suggesting that cholesterol in the bilayer does not largely affect the interfacial region where the N-dimethyl group of the incorporated phenothiazines is located. The results offered clear evidence for the pKm decrease and provided their precise values. PMID:14967475

Kitamura, Keisuke; Takegami, Shigehiko; Kobayashi, Takumi; Makihara, Kumi; Kotani, Chie; Kitade, Tatsuya; Moriguchi, Maki; Inoue, Yuki; Hashimoto, Tomoko; Takeuchi, Midori

2004-02-10

46

Carbon-13 nuclear-magnetic-resonance spectroscopy of whole cells and of cytochrome C from Neurospora crass grown with (S-Me-13C)methionine.  

PubMed Central

Neurospora crassa cytochrome C biosynthetically labelled with [S-Me-13C]methionine was prepared and analysed by 13C nuclear-magnetic-resonance spectroscopy. The methyl group of methionine is extensively incorporated into an N-trimethyl-lysine-72 residue arise from S-adenosylmethionine transmethylation, and that the methyl carbons of methionine residues are sufficiently close to the haem centre to experience chemical shifts from the ring currents of the tetrapyrrole pi electrons and broadening due to binding of methionine-80 with the haem, as well as interaction of the S-E113C]methyl groups with the paramagnetic iron centre. Although whole cells of the labelled Neurospora produced a 13C resonance at the expected position for the methionyl methyl group most of the methyl label was diverted into N-tetra-alkyl ammonium compounds. After an active state of growth these labelled N-methyl compounds appear, in the main, to be low-molecular-weight derivatives of choline which, if associated with membrane, are in a sufficiently fluid environment to have short rotational correlation times. During a subsequent dormant growth period these compounds become associated to some extent with relatively more immobile phases as a result of membrane binding or an increase in membrane rigidity.

Eakin, R T; Morgan, L O

1975-01-01

47

Nuclear spin selective laser control of rotational and torsional dynamics.  

PubMed

We explore the possibility of controlling rotational-torsional dynamics of non-rigid molecules with strong, non-resonant laser pulses and demonstrate that transient, laser-induced torsional alignment depends on the nuclear spin of the molecule. Consequently, nuclear spin isomers can be manipulated selectively by a sequence of time-delayed laser pulses. We show that two pulses with different polarization directions can induce either overall rotation or internal torsion, depending on the nuclear spin. Nuclear spin selective control of the angular momentum distribution may open new ways to separate and explore nuclear spin isomers of polyatomic molecules. PMID:22380044

Floss, J; Grohmann, T; Leibscher, M; Seideman, T

2012-02-28

48

Quantum computing with nuclear spins in semiconductors  

NASA Astrophysics Data System (ADS)

The successful implementation of a scalable, fault-tolerant quantum computer would introduce a type of information processing more powerful than any available today. Reciprocally, the discovery of a fundamental obstacle to such a system would be an important advance in the foundations of quantum theory. No such fundamental obstacles are currently known, but neither has any architecture been shown to be experimentally scalable. Many technologies have been considered for finding such an architecture; in this work I focus on nuclear spins in semiconductors. Semiconductors provide promising optical means for polarizing and measuring small nuclear spin ensembles, which are tasks that pose critical challenges to quantum computers based on nuclear magnetic resonance (NMR). At the same time, semiconductor nuclei are sufficiently coherent quantum oscillators to allow complex information processing using resonant radio-frequency pulse sequences. In particular, the isotopically clean and magnetically quiet environment of pure, high quality, bulk single-crystal silicon provides a nuclear environment allowing what may be the longest absolute coherence time of any solid-state qubit currently under consideration. I have experimentally tested this claim using high-power NMR pulse sequences to eliminate inhomogeneous dephasing and dipolar evolution among an ensemble of 29Si nuclei in isotopically modified silicon crystals. Intrinsic decoherence processes are only observed in polycrystalline silicon, where 1/f charging noise processes are likely to blame. In high-quality single crystal samples, nuclear coherence persists for over 25 seconds, a timescale limited only by pulse sequence imperfections. I will discuss an architecture that takes advantage of this clean nuclear environment, but I will also address its scalability limitations due to silicon's poor optical characteristics. These limitations will suggest new experiments employing nuclear spins in optically controlled semiconductor quantum dots, which may hold more promise for future scalable quantum computer architectures.

Ladd, Thaddeus D.

49

Nuclear spin conversion in H2O  

NASA Astrophysics Data System (ADS)

Nuclear spin conversion (NSC) in water molecules has often been investigated in the gas or solid phase. It has not been observed in the former yet because of the difficulty in producing an efficient disequilibrium of the spin isomer populations. Another, again failed, attempt at such an experiment is presented based on the supposed spin-selective adsorption ability of nanoporous materials. To explain the reason for so many failures, the NSC rate has been calculated in the framework of the quantum relaxation model, using the best available values of the energy levels of the vibrational ground state, the intramolecular magnetic interactions, and the collisional relaxation rates. The characteristic time of NSC in the gas phase is of the order of 1 s at ambient temperature. As NSC is observed in low-temperature matrices, the quantum relaxation model can be adapted to estimate the rate in such environments. Finally, some recent experimental results devoted to astrophysical problems are discussed.

Cacciani, P.; Cosléou, J.; Khelkhal, M.

2012-01-01

50

Electron spin decoherence by interacting nuclear spins in quantum dot II: Coherent control  

NASA Astrophysics Data System (ADS)

Due to the hyperfine interaction, the nuclear spins in a quantum dot, driven by nuclear spin pair-wise flip-flops, evolve in different pathways in the Hilbert space for different electron spin states, resulting in the electron-nuclei entanglement and hence the electron spin decoherence. When the electron spin is flipped by a pulse, the nuclear spin states for different electron spin states swap their pathways, and could intersect in the Hilbert space, which disentangles the electron and the nuclei and hence restores the electron spin coherence. The coherence restoration by disentanglement and the conventional spin echo in ensemble dynamics are fundamentally different and generally occur at different time. Pulse sequences can be applied to force the disentanglement to coincide with the spin echo, making the coherence recovery observable in ensemble dynamics. This work was supported by NSF DMR-0403465, NSA/ARO, and DARPA/AFOSR.

Liu, Ren-Bao; Yao, Wang; Sham, Lu J.

2006-03-01

51

Nuclear-spin polarimeter using photoelectron signals  

NASA Astrophysics Data System (ADS)

It is widely believed that the hyperfine states must be resolved in one way or the other to measure the degree of nuclear-spin polarization of atoms and ions. We theoretically show that the angle-resolved photoelectron signals produced by resonant multiphoton ionization by short and hence broadband two-color laser pulses, which cover all fine-structure and hyperfine manifold of the ground and resonant excited states, can serve as a new type of nuclear-spin polarimeter. Because of the use of time-delayed short laser pulses the proposed method has very high (subnanosecond) time resolution, and does not suffer from the Doppler broadening. Specific results are presented for the two-photon resonant three-photon ionization of hydrogen atoms using 205- and 410-nm laser pulses with picosecond to femtosecond pulse durations. The proposed scheme is immediately applicable to other unstable elements such as 11Be+, 27Mg+, and 35Ca+, etc.

Deng, Li; Iwasaki, Masahiko; Nakajima, Takashi

2013-07-01

52

Nuclear Spin-Lattice Relaxation in Magnetic Insulators.  

National Technical Information Service (NTIS)

First-order nuclear spin-lattice relaxation arises in magnetic insulators when a nuclear spin directly interacts with one or more spin waves via the hyperfine interaction. The direct process, in which a single magnon is emitted, is not ordinarily allowed ...

D. Beeman P. Pincus

1968-01-01

53

Copper Site Nuclear Spin Relaxation Anomaly and the Knight Shift  

Microsoft Academic Search

In the low doping limit, a high Tc cuprate preserves a two band structure. O2p electrons are itinerant, Cu3d electrons are localized. Therefore the two component model is suitable to describe nuclear spin relaxation at copper sites. In addition to the Korringa process, the hyperfine interaction between nuclear spins and local electron spins is considered, which gives rise to the

Wei Guo; Likun Wang; Rushan Han

2007-01-01

54

Detection and manipulation of nuclear spin states in fermionic strontium  

NASA Astrophysics Data System (ADS)

Fermionic 87Sr has a nuclear spin of I=9/2, higher than any other element with a similar electronic structure. This large nuclear spin has many applications in quantum simulation and computation, for which preparation and detection of the spin state are requirements. For an ultracold 87Sr cloud, we show two complementary methods to characterize the spin-state mixture: optical Stern-Gerlach state separation and state-selective absorption imaging. We use these methods to optimize the preparation of a variety of spin-state mixtures by optical pumping and to measure an upper bound of the 87Sr spin-relaxation rate.

Stellmer, Simon; Grimm, Rudolf; Schreck, Florian

2011-10-01

55

Detection and manipulation of nuclear spin states in fermionic strontium  

SciTech Connect

Fermionic {sup 87}Sr has a nuclear spin of I=9/2, higher than any other element with a similar electronic structure. This large nuclear spin has many applications in quantum simulation and computation, for which preparation and detection of the spin state are requirements. For an ultracold {sup 87}Sr cloud, we show two complementary methods to characterize the spin-state mixture: optical Stern-Gerlach state separation and state-selective absorption imaging. We use these methods to optimize the preparation of a variety of spin-state mixtures by optical pumping and to measure an upper bound of the {sup 87}Sr spin-relaxation rate.

Stellmer, Simon; Grimm, Rudolf [Institut fuer Quantenoptik und Quanteninformation (IQOQI), Oesterreichische Akademie der Wissenschaften, A-6020 Innsbruck (Austria); Institut fuer Experimentalphysik und Zentrum fuer Quantenphysik, Universitaet Innsbruck, A-6020 Innsbruck (Austria); Schreck, Florian [Institut fuer Quantenoptik und Quanteninformation (IQOQI), Oesterreichische Akademie der Wissenschaften, A-6020 Innsbruck (Austria)

2011-10-15

56

Electronic spin storage in an electrically readable nuclear spin memory with a lifetime >100 seconds.  

PubMed

Electron spins are strong candidates with which to implement spintronics because they are both mobile and able to be manipulated. The relatively short lifetimes of electron spins, however, present a problem for the long-term storage of spin information. We demonstrated an ensemble nuclear spin memory in phosphorous-doped silicon, which can be read out electrically and has a lifetime exceeding 100 seconds. The electronic spin information can be mapped onto and stored in the nuclear spin of the phosphorus donors, and the nuclear spins can then be repetitively read out electrically for time periods that exceed the electron spin lifetime. We discuss how this memory can be used in conjunction with other silicon spintronic devices. PMID:21164011

McCamey, D R; Van Tol, J; Morley, G W; Boehme, C

2010-12-17

57

Nuclear spin polarized H and D by means of spin-exchange optical pumping  

NASA Astrophysics Data System (ADS)

Optically pumped spin-exchange sources for polarized hydrogen and deuterium atoms have been demonstrated to yield high atomic flow and high electron spin polarization. For maximum nuclear polarization the source has to be operated in spin temperature equilibrium, which has already been demonstrated for hydrogen. In spin temperature equilibrium the nuclear spin polarization PI equals the electron spin polarization PS for hydrogen and is even larger than PS for deuterium. We discuss the general properties of spin temperature equilibrium for a sample of deuterium atoms. One result are the equations PI=4PS/(3+PS2) and Pzz=PS.PI, where Pzz is the nuclear tensor polarization. Furthermore we demonstrate that the deuterium atoms from our source are in spin temperature equilibrium within the experimental accuracy.

Stenger, Jörn; Grosshauser, Carsten; Kilian, Wolfgang; Nagengast, Wolfgang; Ranzenberger, Bernd; Rith, Klaus; Schmidt, Frank

1998-01-01

58

Harnessing nuclear spin polarization fluctuations in a semiconductor nanowire  

NASA Astrophysics Data System (ADS)

Soon after the first measurements of nuclear magnetic resonance in a condensed-matter system, Bloch predicted the presence of statistical fluctuations proportional to in the polarization of an ensemble of N spins. Such spin noise has recently emerged as a critical ingredient for nanometre-scale magnetic resonance imaging. This prominence is a consequence of present magnetic resonance imaging resolutions having reached less than (100nm)3, a size scale at which statistical spin fluctuations begin to dominate the polarization dynamics. Here, we demonstrate a technique that creates spin order in nanometre-scale ensembles of nuclear spins by harnessing these fluctuations to produce polarizations both larger and narrower than the thermal distribution. This method may provide a route to enhancing the weak magnetic signals produced by nanometre-scale volumes of nuclear spins or a way of initializing the nuclear hyperfine field of electron-spin qubits in the solid state.

Peddibhotla, P.; Xue, F.; Hauge, H. I. T.; Assali, S.; Bakkers, E. P. A. M.; Poggio, M.

2013-10-01

59

Nuclear spin selective alignment of ethylene and analogues.  

PubMed

We investigate the alignment of ethylene and of some of its analogues via short, non-resonant laser pulses and show that it depends crucially on the nuclear spin of the molecules. We calculate the time-dependent alignment factors of the four nuclear spin isomers of ethylene and analyze them by comparison with the symmetric top molecule allene. Moreover, we explore how the nuclear spin selective alignment depends on the asymmetry of the molecules and on the intensity of the laser pulse. As an application, we discuss how nuclear spin selective alignment could be applied in order to separate different isotopomers of ethylene. PMID:21639449

Grohmann, Thomas; Leibscher, Monika

2011-05-28

60

Increasing the electron spin coherence time by coherent optical control of the nuclear spin fluctuations  

NASA Astrophysics Data System (ADS)

A single electron spin plays a central role for spin-based quantum information science and electronic devices. One crucial requirement for the future success is to have a long quantum coherence time. It has been demonstrated that in III-V materials, the electron spin coherence time deteriorates rapidly due to the hyperfine coupling with the nuclear environment. Here, we report the increase of the electron spin coherence time by optical controlled suppression of nuclear spin fluctuations through coherent dark-state spectroscopy. The experiment is performed in a single negatively charged InAs self assembled quantum dot (SAQD). The dynamic nuclear spin polarization manifests itself as a hysteresis in the probe absorption spectrum and in the spectral position of the dark state as a function of the frequency scanning direction of the probe field. We demonstrated that the nuclear field can be locked to the maximum trion excitation by observing a flat-top of the trion absorption lineshape, and the switching of the nuclei from unstable to stable configurations by fixing the laser frequencies and monitoring the coherent optical response as a function of time. The optically controlled locking of the nuclear field leads to an enhancement of the electron spin coherence time, which is measured through dark state spectroscopy. The suppression of the nuclear field fluctuations result from a hole spin assisted dynamic nuclear spin polarization feed-back process. We further demonstrated the electron spin coherence enhancement by a three-beam measurement, where two-pump beams lock the nuclear field and the third probe measures the coherence time through the dark state. The inferred spin coherence time is increased by nearly 3 orders of magnitude compared to its thermal value. Our work lays the groundwork for the reproducible preparation of the nuclear spin environment for repetitive control and measurement of a single spin with minimal statistical broadening.

Xu, Xiaodong

2010-03-01

61

Coherence of single spins coupled to a nuclear spin bath of varying density  

NASA Astrophysics Data System (ADS)

The dynamics of single electron and nuclear spins in a diamond lattice with different C13 nuclear spin concentration is investigated. It is shown that coherent control of up to three individual nuclei in a dense nuclear spin cluster is feasible. The free-induction decays of nuclear spin Bell states and single nuclear coherences among C13 nuclear spins are compared and analyzed. Reduction in a free-induction-decay time T2? and a coherence time T2 upon increase in nuclear spin concentration has been found. For pure diamond, T2? as long as 30?s and T2 of up to 0.65 ms for the electron spin has been observed. The C13 concentration dependence of T2? is explained by Fermi contact and dipolar interactions with nuclei in the lattice. It has been found that T2 decreases approximately as 1/n , where n is C13 concentration, which corresponds to the reported theoretical line of T2 for an electron spin interacting with a nuclear spin bath.

Mizuochi, N.; Neumann, P.; Rempp, F.; Beck, J.; Jacques, V.; Siyushev, P.; Nakamura, K.; Twitchen, D. J.; Watanabe, H.; Yamasaki, S.; Jelezko, F.; Wrachtrup, J.

2009-07-01

62

Electron spin decoherence by interacting nuclear spins in quantum dot I: Quantum theory  

NASA Astrophysics Data System (ADS)

We present a quantum theory to the electron spin decoherence by a nuclear pair-correlation method for the electron-nuclear spin dynamics under a strong magnetic field and low temperature. The theory incorporates the electron nuclear hyperfine interaction, the intrinsic nuclear interactions, and the nuclear coupling mediated by the hyperfine interaction with the electron in question. Results for both single electron spin free-induction decay (FID) and ensemble electron spin echo will be discussed. Single spin FID is affected by both the intrinsic and the hyperfine-mediated nuclear interactions, with the dominance determined by the dot size and external field. The spin echo eliminates the hyperfine-mediated decoherence but only reduces the decoherence by the intrinsic nuclear interactions. Thus, the decoherence times for FID and spin echo are significantly different. Electron spin decoherence is explained in terms of the quantum entanglement with the pair-flip excitations in the nuclear spin environment. This work was supported by NSF DMR- 0403465, NSA/ARO, and DARPA/AFOSR.

Yao, Wang; Liu, R.-B.; Sham, Lu J.

2006-03-01

63

Ultrafast entangling gates between nuclear spins using photoexcited triplet states  

NASA Astrophysics Data System (ADS)

The representation of information within the spins of electrons and nuclei has been a powerful method in the ongoing development of quantum computers. Although nuclear spins are advantageous as quantum bits (qubits) because of their long coherence lifetimes (exceeding seconds), they exhibit very slow spin interactions and have weak thermal polarization. A coupled electron spin can be used to polarize the nuclear spin and create fast single-qubit gates, however, the permanent presence of electron spins is a source of nuclear decoherence. Here we show how a transient electron spin, arising from the optically excited triplet state of C60, can be used to hyperpolarize, manipulate and measure two nearby nuclear spins. Implementing a scheme that uses the spinor nature of the electron, we performed an entangling gate in hundreds of nanoseconds: five orders of magnitude faster than the liquid-state J coupling. This approach can be widely applied to systems comprising an electron spin coupled to multiple nuclear spins, such as nitrogen-vacancy centres in diamond, while the successful use of a transient electron spin motivates the design of new molecules able to exploit photoexcited triplet states.

Filidou, Vasileia; Simmons, Stephanie; Karlen, Steven D.; Giustino, Feliciano; Anderson, Harry L.; Morton, John J. L.

2012-08-01

64

Communication: Long-lived states of nuclear spins in solids.  

PubMed

We report an observation of extremely long-lived spin states in systems of dipolar-coupled nuclear spins in solids. The "suspended echo" experiment uses a simple stimulated echo pulse sequence and creates non-equilibrium states which live many orders of magnitude longer than the characteristic time of spin-spin dynamics T2. Large amounts of information can be encoded in such long-lived states and subsequently retrieved by an application of a single "reading" pulse. PMID:24028094

Turanov, A; Khitrin, A K

2013-09-01

65

Nuclear Spin Relaxation in Ellipsoids Undergoing Rotational Brownian Motion  

Microsoft Academic Search

The nuclear spin relaxation times T1 and T2 have been calculated for two identical nuclei of spin I = ½ fixed in an ellipsoid undergoing rotational Brownian motion. The ellipsoid is subject to small random changes in orientation in which the rotation probabilities about its three major axes are different. This anisotropic motion yields five nuclear correlation times; isotropic motion

D. E. Woessner

1962-01-01

66

Coulomb “Blockade” of Nuclear Spin Relaxation in Quantum Dots  

Microsoft Academic Search

We study the mechanism of nuclear spin relaxation in quantum dots due to the\\u000aelectron exchange with 2D gas. We show that the nuclear spin relaxation rate is\\u000adramatically affected by the Coulomb blockade and can be controlled by gate\\u000avoltage. In the case of strong spin-orbit coupling the relaxation rate is\\u000amaximal in the Coulomb blockade valleys whereas for

Y. B. Lyanda-Geller; I. L. Aleiner; B. L. Altshuler

2002-01-01

67

Repetitive readout of a single electronic spin via quantum logic with nuclear spin ancillae.  

PubMed

Robust measurement of single quantum bits plays a key role in the realization of quantum computation and communication as well as in quantum metrology and sensing. We have implemented a method for the improved readout of single electronic spin qubits in solid-state systems. The method makes use of quantum logic operations on a system consisting of a single electronic spin and several proximal nuclear spin ancillae in order to repetitively readout the state of the electronic spin. Using coherent manipulation of a single nitrogen vacancy center in room-temperature diamond, full quantum control of an electronic-nuclear system consisting of up to three spins was achieved. We took advantage of a single nuclear-spin memory in order to obtain a 10-fold enhancement in the signal amplitude of the electronic spin readout. We also present a two-level, concatenated procedure to improve the readout by use of a pair of nuclear spin ancillae, an important step toward the realization of robust quantum information processors using electronic- and nuclear-spin qubits. Our technique can be used to improve the sensitivity and speed of spin-based nanoscale diamond magnetometers. PMID:19745117

Jiang, L; Hodges, J S; Maze, J R; Maurer, P; Taylor, J M; Cory, D G; Hemmer, P R; Walsworth, R L; Yacoby, A; Zibrov, A S; Lukin, M D

2009-09-10

68

Nuclear Spin of Phosphorus Donors in Silicon: Spin Relaxation Times and Environmental Decoupling  

NASA Astrophysics Data System (ADS)

All shallow donors in silicon (and their various isotopes) have non-zero nuclear spins and thus, both the electron and nuclear spins of neutral donors have been proposed for coding, manipulating and storing quantum information. We have recently demonstrated that the spin of electrons bound to donors have extremely long coherence times of at least T2e= 60ms at liquid helium temperatures which permits 10^6 single-qubit operations before the electron spin decoheres [1]. Here we extend this work and demonstrate that spin states of both the electron and nucleus of a ^31P donor can be accurately controlled using resonant microwave and RF pulses in pulsed electron nuclear double resonance (ENDOR) experiments. We measure the spin relaxation times of the ^31P nuclear spin and observe long longitudinal relaxation times T1n= 70s at 6K, limited by hyperfine interaction with the electron spin residing on the donor. We implement a recently proposed bang-bang strategy which decouples the nuclear spin from a decohering environment, through repeated manipulation of the coupled electron spin [2]. This highlights the potential benefits of physical ‘qubit’ systems beyond the simple 2-level structure. [1] A. M. Tyryshkin et al. PRB, 68, 193207 (2003); [2] J. J. L. Morton et al. Nature Physics in press (2005)

Tyryshkin, Alexei; Lyon, Stephen; Morton, John; Ardavan, Arzhang

2006-03-01

69

Nonsecular resonances for the coupling between nuclear spins in solids  

NASA Astrophysics Data System (ADS)

Spin-spin relaxation in solid-state nuclear-magnetic resonance in strong magnetic fields is normally described only with the help of the secular part of the full spin-spin interaction Hamiltonian. This approximation is associated with the averaging of the spin-spin interaction over the fast motion of spins under the combined action of the static and the radio-frequency (rf) fields. Here, we report a set of conditions (nonsecular resonances) when the averaging over the above fast motion preserves some of the nonsecular terms entering the full interaction Hamiltonian. These conditions relate the value of the static magnetic field with the frequency and the amplitude of the rf field. When the above conditions are satisfied, the effective spin-spin interaction Hamiltonian has an unconventional form with tunable parameters. This tunable Hamiltonian offers interesting possibilities to manipulate nuclear spins in solids and can shed new light on the fundamental properties of the nuclear-spin-spin relaxation phenomenon.

Kropf, Chahan M.; Fine, Boris V.

2012-09-01

70

Spectrum of an electron spin coupled to an unpolarized bath of nuclear spins.  

PubMed

The main source of decoherence for an electron spin confined to a quantum dot is the hyperfine interaction with nuclear spins. To analyze this process theoretically we diagonalize the central spin Hamiltonian in the high magnetic B-field limit. Then we project the eigenstates onto an unpolarized state of the nuclear bath and find that the resulting density of states has Gaussian tails. The level spacing of the nuclear sublevels is exponentially small in the middle of each of the two electron Zeeman levels but increases superexponentially away from the center. This suggests to select states from the wings of the distribution when the system is projected on a single eigenstate by a measurement to reduce the noise of the nuclear spin bath. This theory is valid when the external magnetic field is larger than a typical Overhauser field at high nuclear spin temperature. PMID:21469823

Tsyplyatyev, Oleksandr; Loss, Daniel

2011-03-08

71

Spin Modes in Nuclei and Nuclear Forces  

SciTech Connect

Spin modes in stable and unstable exotic nuclei are studied and important roles of tensor and three-body forces on nuclear structure are discussed. New shell model Hamiltonians, which have proper tensor components, are shown to explain shell evolutions toward drip-lines and spin properties of both stable and exotic nuclei, for example, Gamow-Teller transitions in {sup 12}C and {sup 14}C and an anomalous M1 transition in {sup 17}C. The importance and the necessity of the repulsive monopole corrections in isospin T = 1 channel to the microscopic two-body interactions are pointed out. The corrections are shown to lead to the proper shell evolutions in neutron-rich isotopes. The three-body force, in particular the Fujita-Miyazawa force induced by {Delta} excitations, is pointed out to be responsible for the repulsive corrections among the valence neutrons. The important roles of the three-body force on the energies and transitions in exotic oxygen and calcium isotopes are demonstrated.

Suzuki, Toshio [Department of Physics and Graduate School of Integrated Basic Sciences, College of Humanities and Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550 (Japan) and Center for Nuclear Study, University of Tokyo, Hirosawa, Wako-shi, Saitama, 351-0198 (Japan); Otsuka, Takaharu [Department of Physics and Center for Nuclear Study, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

2011-05-06

72

Electron and Nuclear Spin Dynamics in Antiferromagnetic Molecular Rings  

SciTech Connect

We study theoretically the spin dynamics of antiferromagnetic molecular rings, such as the ferric wheel Fe{sub 10} . For a single nuclear or impurity spin coupled to one of the electron spins of the ring, we calculate nuclear and electronic spin correlation functions and show that nuclear magnetic resonance (NMR) and electron spin resonance (ESR) techniques can be used to detect coherent tunneling of the Neel vector in these rings. The location of the NMR/ESR resonances gives the tunnel splitting and its linewidth an upper bound on the decoherence rate of the electron spin dynamics. We illustrate the experimental feasibility of our proposal with estimates for Fe{sub 10} molecules.

Meier, Florian; Loss, Daniel

2001-06-04

73

Sensitive magnetic control of ensemble nuclear spin hyperpolarization in diamond.  

PubMed

Dynamic nuclear polarization, which transfers the spin polarization of electrons to nuclei, is routinely applied to enhance the sensitivity of nuclear magnetic resonance. This method is particularly useful when spin hyperpolarization can be produced and controlled optically or electrically. Here we show complete polarization of nuclei located near optically polarized nitrogen-vacancy centres in diamond. Close to the ground-state level anti-crossing condition of the nitrogen-vacancy electron spins, (13)C nuclei in the first shell are polarized in a pattern that depends sensitively upon the magnetic field. Based on the anisotropy of the hyperfine coupling and of the optical polarization mechanism, we predict and observe a reversal of the nuclear spin polarization with only a few millitesla change in the magnetic field. This method of magnetic control of high nuclear polarization at room temperature can be applied in sensitivity enhanced nuclear magnetic resonance of bulk nuclei, nuclear-based spintronics, and quantum computation in diamond. PMID:23736952

Wang, Hai-Jing; Shin, Chang S; Avalos, Claudia E; Seltzer, Scott J; Budker, Dmitry; Pines, Alexander; Bajaj, Vikram S

2013-01-01

74

Nuclear spin-induced Cotton-Mouton effect in molecules  

NASA Astrophysics Data System (ADS)

In nuclear magneto-optic spectroscopy, effects of nuclear magnetization are detected in light passing through a sample containing spin-polarized nuclei. An optical analogue of nuclear magnetic resonance (NMR) chemical shift has been predicted and observed in the nuclear spin optical rotation of linearly polarized light propagating parallel to the nuclear magnetization. A recently proposed magneto-optic analogue of the NMR spin-spin coupling, the nuclear spin-induced Cotton-Mouton (NSCM) effect entails an ellipticity induced to linearly polarized light when passing through a medium with the nuclear spins polarized in a direction perpendicular to the light beam. Here we present a first-principles electronic structure formulation of NSCM in terms of response theory as well as ab initio and density-functional theory calculations for small molecules. The roles of basis set (we use completeness-optimized sets), electron correlation, and relativistic effects are discussed. It is found that the explicitly temperature-dependent contribution to NSCM, arising from the partial orientation of the molecules due to the nuclear magnetization, typically dominates the effect. This part of NSCM is proportional to the tensor product of molecular polarizability and the NMR direct dipolar coupling tensor. Hence, NSCM provides a means of investigating the dipolar coupling and, thus, molecular structure in a formally isotropic medium. Overall ellipticities of the order of magnitude of 10-8...10-7 rad/(M cm) are predicted for fully polarized nuclei. These should be detectable with modern instrumentation in the Voigt setup.

Fu, Li-juan; Vaara, Juha

2013-05-01

75

Electrical detection of coherent nuclear spin oscillations in phosphorus-doped silicon using pulsed ENDOR.  

PubMed

We demonstrate the electrical detection of pulsed X-band electron nuclear double resonance (ENDOR) in phosphorus-doped silicon at 5 K. A pulse sequence analogous to Davies ENDOR in conventional electron spin resonance is used to measure the nuclear spin transition frequencies of the (31)P nuclear spins, where the (31)P electron spins are detected electrically via spin-dependent transitions through Si/SiO(2) interface states, thus not relying on a polarization of the electron spin system. In addition, the electrical detection of coherent nuclear spin oscillations is shown, demonstrating the feasibility to electrically read out the spin states of possible nuclear spin qubits. PMID:21635127

Hoehne, Felix; Dreher, Lukas; Huebl, Hans; Stutzmann, Martin; Brandt, Martin S

2011-05-03

76

Nuclear Spin-Lattice Relaxation in Dilute Paramagnetic Sapphire  

Microsoft Academic Search

The exchange of energy between nuclear spin system and lattice has been theoretically and experimentally studied for circumstances in which the nuclear Zeeman energy levels are not necessarily equally spaced. Starting from the master rate equations for the nuclear energy level populations, expressions are found for the population difference of an adjacent pair of energy levels as a function of

W. W. Simmons; W. J. O'Sullivan; W. A. Robinson

1962-01-01

77

Polarization of nuclear spins by a cold nanoscale resonator  

SciTech Connect

A cold nanoscale resonator coupled to a system of nuclear spins can induce spin relaxation. In the low-temperature limit where spin-lattice interactions are ''frozen out,'' spontaneous emission by nuclear spins into a resonant mechanical mode can become the dominant mechanism for cooling the spins to thermal equilibrium with their environment. We provide a theoretical framework for the study of resonator-induced cooling of nuclear spins in this low-temperature regime. Relaxation equations are derived from first principles, in the limit where energy donated by the spins to the resonator is quickly dissipated into the cold bath that damps it. A physical interpretation of the processes contributing to spin polarization is given. For a system of spins that have identical couplings to the resonator, the interaction Hamiltonian conserves spin angular momentum, and the resonator cannot relax the spins to thermal equilibrium unless this symmetry is broken by the spin Hamiltonian. The mechanism by which such a spin system becomes ''trapped'' away from thermal equilibrium can be visualized using a semiclassical model, which shows how an indirect spin-spin interaction arises from the coupling of multiple spins to one resonator. The internal spin Hamiltonian can affect the polarization process in two ways: (1) By modifying the structure of the spin-spin correlations in the energy eigenstates, and (2) by splitting the degeneracy within a manifold of energy eigenstates, so that zero-frequency off-diagonal terms in the density matrix are converted to oscillating coherences. Shifting the frequencies of these coherences sufficiently far from zero suppresses the development of resonator-induced correlations within the manifold during polarization from a totally disordered state. Modification of the spin-spin correlations by means of either mechanism affects the strength of the fluctuating spin dipole that drives the resonator. In the case where product states can be chosen as energy eigenstates, spontaneous emission from eigenstate populations into the resonant mode can be interpreted as independent emission by individual spins, and the spins relax exponentially to thermal equilibrium if the development of resonator-induced correlations is suppressed. When the spin Hamiltonian includes a significant contribution from the homonuclear dipolar coupling, the energy eigenstates entail a correlation specific to the coupling network. Simulations of dipole-dipole coupled systems of up to five spins suggest that these systems contain weakly emitting eigenstates that can trap a fraction of the population for time periods >>100/R{sub 0}, where R{sub 0} is the rate constant for resonator-enhanced spontaneous emission by a single spin 1/2. Much of the polarization, however, relaxes with rates comparable to R{sub 0}. A distribution of characteristic high-field chemical shifts tends to increase the relaxation rates of weakly emitting states, enabling transitions to states that can quickly relax to thermal equilibrium. The theoretical framework presented in this paper is illustrated with discussions of spin polarization in the contexts of force-detected nuclear-magnetic-resonance spectroscopy and magnetic-resonance force microscopy.

Butler, Mark C.; Weitekamp, Daniel P. [A. A. Noyes Laboratory of Chemical Physics, California Institute of Technology, MC 127-72, Pasadena, California 91125 (United States)

2011-12-15

78

Cooling Nuclear Spins in Diamond via Dark State Spectroscopy  

NASA Astrophysics Data System (ADS)

Optical cooling methods in atomic physics, developed over the last half century, enable reaching temperatures as low as a few nK. Some of these methods can be applied for cooling spin ensembles in solid state systems. We describe a method for cooling the nuclear spins of^ 13C impurities in diamond, via optical manipulation of the electronic spin associated with an NV^- center. We present the physical mechanism which leads to optical pumping of the nuclear spin ensemble into particular nuclear states. The method relies on optically driving three electronic levels in the ? configuration, and on using the formation of dark states under the conditions of Coherent Population Trapping, (CPT). The dynamics of the nuclear ensemble during this cooling process can be described analytically by using statistical tools, including anomalous random walk models and Levy flights. I survey the theoretical results of the model and discuss some predictions for experimental signatures of Levy flights in this system.

Pick, Adi; Gullans, Michael; Togan, Emre; Chu, Yiwen; Yelin, Susanne; Lukin, Mikhail

2012-02-01

79

All-Electrical Nuclear Spin Polarization of Donors in Silicon  

NASA Astrophysics Data System (ADS)

We demonstrate an all-electrical donor nuclear spin polarization method in silicon by exploiting the tunable interaction of donor bound electrons with a two-dimensional electron gas, and achieve over two orders of magnitude nuclear hyperpolarization at T=5K and B=12T with an in-plane magnetic field. We also show an intricate dependence of nuclear polarization effects on the orientation of the magnetic field, and both hyperpolarization and antipolarization can be controllably achieved in the quantum Hall regime. Our results demonstrate that donor nuclear spin qubits can be initialized through local gate control of electrical currents without the need for optical excitation, enabling the implementation of nuclear spin qubit initialization in dense multiqubit arrays.

Lo, C. C.; Weis, C. D.; van Tol, J.; Bokor, J.; Schenkel, T.

2013-02-01

80

All-electrical nuclear spin polarization of donors in silicon.  

PubMed

We demonstrate an all-electrical donor nuclear spin polarization method in silicon by exploiting the tunable interaction of donor bound electrons with a two-dimensional electron gas, and achieve over two orders of magnitude nuclear hyperpolarization at T=5 K and B=12 T with an in-plane magnetic field. We also show an intricate dependence of nuclear polarization effects on the orientation of the magnetic field, and both hyperpolarization and antipolarization can be controllably achieved in the quantum Hall regime. Our results demonstrate that donor nuclear spin qubits can be initialized through local gate control of electrical currents without the need for optical excitation, enabling the implementation of nuclear spin qubit initialization in dense multiqubit arrays. PMID:23414045

Lo, C C; Weis, C D; van Tol, J; Bokor, J; Schenkel, T

2013-01-31

81

Optical Control of Nuclear Spin Ensembles in Diamond  

NASA Astrophysics Data System (ADS)

We present new results on the hyperpolarization of ^13C nuclear spins in diamond through optically-oriented nitrogen vacancy (NV-) defects. Optical illumination of high NV- concentration diamonds at cryogenic temperatures and 9.4 Tesla results in a negative nuclear spin temperature with measured bulk-average polarization over 5%, although local polarization may be higher. The negative spin-temperature is attributed to a population inversion within the dipolar energy levels of the NV- spin ensemble. In our quantitative model, nuclei near defects equilibrate with the NV- dipolar energy reservoir and polarization is transported to the bulk material via spin diffusion. This model is tested by investigating a series of samples with varied defect density. We also investigate the nuclear hyperpolarization of NV- containing diamond nanocrystals. Such materials may be useful for surface transfer of polarization to target molecules for enhanced NMR sensitivity. Additionally, we investigate the dynamics and decoherence of the hyperpolarized nuclear spin ensemble and its interaction with electronic defect spins. Such phenomena are of fundamental interest to the use of diamond for quantum information applications.

King, Jonathan; Reimer, Jeffrey

2012-02-01

82

Experimental control of a nuclear spin quantum register in diamond with decoherence-protected gates  

NASA Astrophysics Data System (ADS)

Nuclear spins are one of the most promising candidates for long-lived quantum bits that store and process quantum information. Individual nuclear spins in diamond have been addressed using the nearby electron spin of a nitrogen vacancy center. However, the relatively fast decoherence of the electron spin limits coherent control to the nearest, strongly coupled, nuclear spins. Here, we employ decoherence-protected gates [1] to access individual spins embedded in a bath of nuclear spins that are weakly coupled to an electron spin [2]. We demonstrate the initialization, control and readout of the nuclear spins and discuss our recent progress in implementing two-qubit entangling operations between nuclear spins. These results greatly extend the number of available quantum bits in diamond and provide a way towards tomography with single nuclear spin sensitivity even in decohering environments. [1] T. van der Sar et al., Nature 484, 82 (2012). [2] T. H. Taminiau et al., Phys. Rev. Lett. 109, 137602 (2012).

Taminiau, Tim Hugo; van der Sar, Toeno; Dobrovitski, V. V.; Hanson, Ronald

2013-03-01

83

International conference on spin observables of nuclear probes: Summary talk  

SciTech Connect

A selected summary of the presentation and discussions at the 4th Telluride Conference is presented. The summary deals mainly with the effects of nuclear spin and isospin on the interaction between nucleons and their consequences in nuclear structure. 11 figs.

Garvey, G.T.

1988-01-01

84

Nuclear Moments of Inertia at High Spin.  

National Technical Information Service (NTIS)

The competition between collective motion and alignment at high spin can be evaluated by measuring two complementary dynamic moments of inertia. The first, I band, measured in gamma - gamma correlation experiments, relates to the collective properties of ...

M. A. Deleplanque

1982-01-01

85

Nuclear spin detection and optical pumping in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

Quantum memory devices and scalable quantum computers are important objectives of current research efforts. Quantum computers promise to solve certain problems which are intractable on classical computers and may provide insight into unanswered questions in computational theory. Quantum memory would provide coherent storage of a 'qubit' and could be used in conjunction with a quantum computer or in a quantum communication system. Both systems require a way of preparing qubits in a known state, a mechanism for measuring their states and addressing capability. Nuclear spins within a solid-state system have been proposed as one means for realizing a quantum computer. The preparation of nuclear spins in a known state and qubit readout remain a formidable challenge. Quantum dots provide a means of polarizing and measuring nuclear spins. We have observed the energy level shifts due to the nuclear spins in InAs quantum dots and we have measured the timescale for nuclear polarization to develop. Quantum dots are nano-scale regions of a small band-gap semiconductor embedded in a larger band-gap semiconductor which can trap a single electron-hole pair or exciton. The energy levels for the exciton are quantized and are affected by many parameters including hyperfine interactions with the nuclei from the lattice. There are between 104 and 105 nuclei within the dot and it is possible through optical pumping to align the nuclear spins in one direction. We can also use the interaction of the nuclear spins with the exciton to determine the average nuclear spin direction. Future work in this area may ultimately lead to useful applications for nuclear spins in the area of quantum information processing devices. In this thesis I will present results demonstrating nuclear polarization in InAs quantum dots. In addition, I will present background material and experimental details with the basic goal that a reader of this thesis could reproduce the results we have obtained. There is also a theoretical discussion in which I present a model for the nuclear polarization process and compare the predicted timescales to the measured results. I will also discuss work I carried out using sculpted ferromagnets with the goal of creating large magnetic field gradients. Such devices could be used in conjunction with quantum clots in order to do atomic plane imaging as discussed in Chapter 9. Chapter 4 provides a background to the discussion regarding magnetic field gradient calculations.

Goldman, Jonathan R.

86

Staggered-spin contribution to nuclear spin-lattice relaxation in two-leg antiferromagnetic spin-12 ladders  

NASA Astrophysics Data System (ADS)

We study the nuclear spin-lattice relaxation rate 1/T1 in the two-leg antiferromagnetic spin-1/2 Heisenberg ladder. More specifically, we consider the contribution to 1/T1 from the processes with momentum transfer (?,?). In the limit of weak coupling between the two chains, this contribution is of activation type with gap 2? at low temperatures (? is the spin gap), but crosses over to a slowly decaying temperature dependence at the crossover temperature T~?. This crossover possibly explains the recent high-temperature NMR results on ladder-containing cuprates by Imai et al.

Ivanov, D. A.; Lee, Patrick A.

1999-02-01

87

The Nuclear Cusp Condition in Spin-Polarized Thomas - Theory.  

NASA Astrophysics Data System (ADS)

Thomas-Fermi theory, which was introduced in the 1920s, was developed into rigorous mathematics in the 1970s by Lieb, Simon, Benilan, Brezis, and others. Later, Goldstein and Rieder extended rigorous Thomas-Fermi theory to a spin polarized context, to include the nuclear cusp condition, and to the case where a magnetic field is present. But they did not investigate incorporating the nuclear cusp condition into the spin polarized context. The purpose of my thesis is to do precisely that. I proved the existence and uniqueness of the problem of minimizing the energy functional by solving a non-linear elliptic partial differential equation on { bf R}^3 which arose from the Euler -Lagrange equation. A topological argument then related the Lagrange multipliers to the numbers of spin up and spin down electrons.

Lung, Chien-An.

88

Electrical injection of spin-polarized electrons and electrical detection of dynamic nuclear polarization using a Heusler alloy spin source  

NASA Astrophysics Data System (ADS)

We demonstrated electrical spin injection from a half-metallic Heusler alloy Co2MnSi electrode into a GaAs channel through observation of a spin-valve signal and a Hanle signal in the four-terminal nonlocal geometry. Furthermore, we electrically detected a nuclear field acting on electron spins, which was produced by the dynamic nuclear polarization, through observation of transient oblique Hanle signals. Samples with a Co2MnSi spin source exhibited higher spin-injection efficiency and a larger nuclear field compared to samples with a Co50Fe50 spin source, suggesting that the spin polarization of Co2MnSi is higher. This higher polarization is promising for realizing future spintronic devices and for understanding spin interactions as well as spin-dependent transport properties in a semiconductor channel.

Akiho, Takafumi; Shan, Jinhai; Liu, Hong-xi; Matsuda, Ken-ichi; Yamamoto, Masafumi; Uemura, Tetsuya

2013-06-01

89

Towards understanding global variability in ocean carbon-13  

Microsoft Academic Search

We include a prognostic parameterization of carbon-13 into a global ocean-biogeochemistry model to investigate the spatiotemporal variability in ocean carbon-13 between 1860 and 2000. Carbon-13 was included in all 10 existing carbon pools, with dynamic fractionations occurring during photosynthesis, gas exchange and carbonate chemistry. We find that ocean distributions of ?13CDIC at any point in time are controlled by the

Alessandro Tagliabue; Laurent Bopp

2008-01-01

90

Optimization of 1H spin density for dynamic nuclear polarization using photo-excited triplet electron spins  

Microsoft Academic Search

In dynamic nuclear polarization (DNP) using photo-excited triplet electron spins, known as Microwave-Induced Optical Nuclear Polarization (MIONP), the attainable 1H polarization is determined by the ratio of the buildup rate and the spin–lattice relaxation rate, in turn depend on the 1H spin density. It is shown that the final 1H polarization can be enhanced by diluting the 1H spins with

Akinori Kagawa; Yu Murokawa; Kazuyuki Takeda; Masahiro Kitagawa

2009-01-01

91

Cross polarization from spins I=12 to spins S=1 in nuclear magnetic resonance with magic angle sample spinning.  

PubMed

Spin locking of the nuclear magnetization of a spin with S=1 such as deuterium in the presence of a radio-frequency field under magic angle spinning (MAS) is described in terms of adiabatic modulations of the energy levels. In a brief initial period, part of the initial density operator nutates about the Hamiltonian and is dephased. The remaining spin-locked state undergoes persistent oscillatory transfer processes between various coherences with a periodicity given by the rotation of the sample. While all crystallites in the powder undergo such periodic transfer processes, the phases of the oscillations depend on the angle gamma of the crystallites. The angle gamma is the azimuthal angle defining the orientation of the unique axis of the quadrupolar interaction tensor in a rotor-fixed frame. The theory is extended to describe cross-polarization between spins S=1 and I=12 under MAS. There are four distinct Hartmann-Hahn matching conditions that correspond to four zero-quantum matching conditions, all of which are shifted and broadened compared to their spin S=12 counterparts. These matching conditions are further split into a family of sideband conditions separated by the spinning frequency. The theory allows the calculation of both shifts and broadening factors of the matching conditions, as verified by simulations and experiments. PMID:16729818

Gopalakrishnan, Karthik; Bodenhausen, Geoffrey

2006-05-21

92

Tritium isotope effects on carbon-13 NMR chemical shifts  

SciTech Connect

Deuterium isotope effects on carbon-13 NMR chemical shifts can be useful in making spectral assignments, and they are also interesting in their own right. The authors report here the first determination of tritium isotope effects on carbon-13 NMR spectra. 11 references, 2 tables.

Arrowsmith, C.H.; Baitzer, L.; Kresge, A.J.; Powell, M.F.; Tang, Y.S.

1986-03-19

93

Relaxation of the electron spin in a quantum dot due to interaction with nuclear spin bath  

NASA Astrophysics Data System (ADS)

Understanding the dynamics of electron spins in semiconducting nanostructures is important for novel applications in spintronics and in quantum information processing. An electron spin in a quantum dot is strongly affected by its interaction with the environmental degrees of freedom, in particular, with the nuclear spins. In this work we study the longitudinal relaxation of the electron spin component S^z by the nuclear spin bath for different applied fields and initial polarizations of the bath. We numerically simulate the motion of the compound system (the electron spin plus the bath) by explicitly solving the corresponding time-dependent Schrödinger equation using the method described in [1]. Typically, S^z exhibits a pronounced oscillation with subsequent saturation; at high fields, several such oscillations are observed. We compare our numerical results with the earlier analytical predictions [2], and discuss the agreements and differences. [1] V. V. Dobrovitski and H. A. De Raedt, Phys. Rev. E 67, 056702 (2003)[2] A. V. Khaetskii, D. Loss, and L. Glazman, Phys. Rev. Lett. 88, 186802 (2002); I. A. Merkulov, E. L. Efros, and M. Rosen, Phys. Rev. B 65, 205309 (2002).

Al-Hassanieh, Khaled; Dobrovitski, V. V.; Dagotto, E.; Harmon, B. N.

2005-03-01

94

Generating entanglement and squeezed states of nuclear spins in quantum dots.  

PubMed

We present a scheme for achieving coherent spin squeezing of nuclear spin states in semiconductor quantum dots. The nuclear polarization dependence of the electron spin resonance generates a unitary evolution that drives nuclear spins into a collective entangled state. The polarization dependence of the resonance generates an area-preserving, twisting dynamics that squeezes and stretches the nuclear spin Wigner distribution without the need for nuclear spin flips. Our estimates of squeezing times indicate that the entanglement threshold can be reached in current experiments. PMID:22181759

Rudner, M S; Vandersypen, L M K; Vuleti?, V; Levitov, L S

2011-11-08

95

Hole - Nuclear Spin Interaction in Semiconductor Quantum Dots  

NASA Astrophysics Data System (ADS)

Spins of localized electrons in semiconductor quantum dots (QDs) are attractive for future spintronic and quantum information devices since they are not subject to the classical spin relaxation mechanisms known for free carriers [1]. It is now well established that the main spin dephasing mechanism in QDs is due to the coupling of conduction electron spin with the randomly fluctuating nuclear spins (Fermi contact term) [2-5]. For a valence electron (or hole), this coupling is expected to be much weaker because of the p-symmetry of the valence band states and no experimental evidence of such a hole-nuclear spin interaction has been reported so far [6]. We have measured the carrier spin dynamics in p-doped InAs/GaAs quantum dots by pump probe and time-resolved photoluminescence experiments. We demonstrate that the hole spin dynamics in these QDs is governed by the interaction with randomly fluctuating nuclear spins [7]. Our calculations based on dipole-dipole coupling between the hole and the quantum dot nuclei lead to a hole spin dephasing time for an ensemble of dots of 15 ns in close agreement with experiments.[4pt] In collaboration with B. Eble, C. Testelin, F. Bernardot, and M. Chamarro, Institut des Nanosciences de Paris, Universit'e P. et M. Curie, CNRS, Paris, F-75015 France; A. Balocchi, T. Amand, and B. Urbaszek, Universit'e de Toulouse ; LPCNO, INSA-CNRS-UPS, 135 av. de Rangueil, 31077 Toulouse Cedex 4, France; and A. Lemaître, Laboratoire de Photonique et de Nanostructures, CNRS, Route de Nozay, F-91460, Marcoussis, France. [4pt] [1] Spin Physics in Semiconductors, edited by M. D'Yakonov (Springer, Berlin, 2008) [0pt] [2] I. Merkulov et al, Phys. Rev. B 65, 205309 (2002) [0pt] [3] P.-F. Braun, X. Marie et al, PRL 94, 116601 (2005) [0pt] [4] A. C. Johnson et al , Nature 435, 925 (2005) [0pt] [5] A. Greilich et al, Science 313, 341(2006) [0pt] [6] S. Laurent et al, Phys. Rev. Lett. 94, 147401 (2005) [0pt] [7] B. Eble et al, Phys. Rev. Lett. 102, 146601 (2009)

Marie, Xavier

2010-03-01

96

Snowballs of radioactive ions — nuclear spin polarization of core ions  

Microsoft Academic Search

Short-lived ions12B (beta-radioactive, T1\\/2=20.3 ms) sustaining nuclear spin polarization were introduced into superfluid helium at 1.7 K. It was found that the12B ions were transported as charged entities under a static electric field and that the nuclear polarization was maintained throughout the lifetime of12B nuclei. Polarization of12B was determined through beta-NMR method. “Snowball”, a singly charged microcluster of helium atoms

N. Takahashi; T. Shimoda; Y. Fujita; T. Itahashi; H. Miyatake

1995-01-01

97

Nuclear Spin Gyroscope Based on an Atomic Comagnetometer  

SciTech Connect

We describe a nuclear spin gyroscope based on an alkali-metal-noble-gas comagnetometer. Optically pumped alkali-metal vapor is used to polarize the noble-gas atoms and detect their gyroscopic precession. Spin precession due to magnetic fields as well as their gradients and transients can be cancelled in this arrangement. The sensitivity is enhanced by using a high-density alkali-metal vapor in a spin-exchange relaxation free regime. With a K-{sup 3}He comagnetometer we demonstrate rotation sensitivity of 5x10{sup -7} rad s{sup -1} Hz{sup -1/2}, equivalent to a magnetic field sensitivity of 2.5 fT/Hz{sup 1/2}. The rotation signal can be increased by a factor of 10 using {sup 21}Ne with a smaller magnetic moment. The comagnetometer is also a promising tool in searches for anomalous spin couplings beyond the standard model.

Kornack, T.W.; Ghosh, R.K.; Romalis, M.V. [Department of Physics, Princeton University, Princeton, New Jersey 08550 (United States)

2005-12-02

98

Dependence of nuclear spin singlet lifetimes on RF spin-locking power  

NASA Astrophysics Data System (ADS)

We measure the lifetime of long-lived nuclear spin singlet states as a function of the strength of the RF spin-locking field and present a simple theoretical model that agrees well with our measurements, including the low-RF-power regime. We also measure the lifetime of a long-lived coherence between singlet and triplet states that does not require a spin-locking field for preservation. Our results indicate that for many molecules, singlet states can be created using weak RF spin-locking fields: more than two orders of magnitude lower RF power than in previous studies. Our findings suggest that for many endogenous biomolecules, singlets and related states with enhanced lifetimes might be achievable in vivo with safe levels of RF power.

DeVience, Stephen J.; Walsworth, Ronald L.; Rosen, Matthew S.

2012-05-01

99

Dependence of nuclear spin singlet lifetimes on RF spin-locking power.  

PubMed

We measure the lifetime of long-lived nuclear spin singlet states as a function of the strength of the RF spin-locking field and present a simple theoretical model that agrees well with our measurements, including the low-RF-power regime. We also measure the lifetime of a long-lived coherence between singlet and triplet states that does not require a spin-locking field for preservation. Our results indicate that for many molecules, singlet states can be created using weak RF spin-locking fields: more than two orders of magnitude lower RF power than in previous studies. Our findings suggest that for many endogenous biomolecules, singlets and related states with enhanced lifetimes might be achievable in vivo with safe levels of RF power. PMID:22578548

DeVience, Stephen J; Walsworth, Ronald L; Rosen, Matthew S

2012-03-28

100

Creating nuclear spin entanglement using an optical degree of freedom  

SciTech Connect

Molecular nanostructures are promising building blocks for future quantum technologies, provided methods of harnessing their multiple degrees of freedom can be identified and implemented. Due to low decoherence rates, nuclear spins are considered ideal candidates for storing quantum information, while optical excitations can give rise to fast and controllable interactions for information processing. A recent paper [M. Schaffry et al., Phys. Rev. Lett. 104, 200501 (2010)] proposed a method for entangling two nuclear spins through their mutual coupling to a transient optically excited electron spin. Building on the same idea, we present here an extended and much more detailed theoretical framework, showing that this method is in fact applicable to a much wider class of molecular structures than previously discussed in the original proposal.

Schaffry, Marcus [Department of Materials, Oxford University, Oxford OX1 3PH (United Kingdom); Lovett, Brendon W. [Department of Materials, Oxford University, Oxford OX1 3PH (United Kingdom); SUPA, Department of Physics, Heriot Watt University, Edinburgh EH14 4AS (United Kingdom); Gauger, Erik M. [Department of Materials, Oxford University, Oxford OX1 3PH (United Kingdom); Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore)

2011-09-15

101

A silicon-based nuclear spin quantum computer  

Microsoft Academic Search

Quantum computers promise to exceed the computational efficiency of ordinary classical machines because quantum algorithms allow the execution of certain tasks in fewer steps. But practical implementation of these machines poses a formidable challenge. Here I present a scheme for implementing a quantum-mechanical computer. Information is encoded onto the nuclear spins of donor atoms in doped silicon electronic devices. Logical

B. E. Kane

1998-01-01

102

Nuclear tetrahedral configurations at spin zero  

SciTech Connect

The possibility of the existence of stable tetrahedral deformations at spin zero is investigated using the Skyrme-HFBCS approach and the generator coordinate method (GCM). The study is limited to nuclei in which the tetrahedral mode has been predicted to be favored on the basis of non-self-consistent models. Our results indicate that a clear identification of tetrahedral deformations is unlikely because they are strongly mixed with the axial octupole mode. However, the excitation energies related to the tetrahedral mode are systematically lower than those of the axial octupole mode in all the nuclei included in this study.

Zberecki, Krzysztof; Magierski, Piotr [Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, PL-00-662 Warsaw (Poland); Heenen, Paul-Henri [Service de Physique Nucleaire Theorique, U.L.B-C.P. 229, B-1050 Brussels (Belgium)

2009-01-15

103

Spin excitations in quantum Hall systems and their effect on nuclear spin relaxation and photoluminescence  

NASA Astrophysics Data System (ADS)

Two problems with respect to spin excitations in quantum Hall systems are studied by means of exact numerical diagonalization. The first one is related to the formation of reversed-spin quasielectrons (QER) in a two-dimensional electron gas (2DEG). The single-particle properties of QER's as well as the pseudopotentials of their interaction with one another and with Laughlin quasielectrons (QE's) and quasiholes (QH's) are calculated. Based on the short-range character of the QER-QE R and QER-QE repulsion, the partially unpolarized incompressible states at the filling factors nu = 411 and nu = 513 are postulated within Haldane's hierarchy scheme. To describe photoluminescence, the family of bound h(QER)n states of a valence hole h and n QE R's are predicted in analogy to the found earlier fractionally charged excitons hQEn. The binding energy and optical selection rules for both families are compared. The h QER is found radiative in contrast to the dark hQE, and the h(QER)2 is found nonradiative in contrast to the bright hQE2. The second problem involves the numerical study of the relaxation rates of nuclear spins coupled through the hyperfine interaction to a 2DEG at magnetic fields corresponding to both fractional and integral Landau level fillings nu. The spectral functions tau-1(E) describing the response of the 2DEG to the reversal of an embedded localized spin are calculated. In a (locally) incompressible nu = 1 or ? state, the finite Coulomb energy of short spin waves, together with the small nuclear Zeeman energy, prevent nuclear spin relaxation even in the limit of vanishing electron Zeeman energy (EZ). However, we find that the nuclear spins can couple to the internal excitations of mobile finite-size skyrmions that appear in the 2DEG at sufficiently low E Z and at nu slightly different from 1 or ?. The experimentally observed dependence of nuclear spin relaxation rate on E Z and nu is explained in terms of the occurrence of skyrmions and anti-skyrmions of various topological charge.

Szlufarska, Izabela Anna

104

Preparation of nonequilibrium nuclear spin states in double quantum dots  

NASA Astrophysics Data System (ADS)

We theoretically study the dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. In our prior work [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.104.226807 104, 226807 (2010)], we identified three regimes of long-term dynamics, including the buildup of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with the formation of so-called dark states, and the elimination of the difference field. In particular, when the dots are different sizes, we found that the Overhauser field becomes larger in the smaller dot. Here we present a detailed theoretical analysis of these problems, including a model of the polarization dynamics and the development of a numerical method to efficiently simulate semiclassical-central-spin problems. When nuclear spin noise is included, the results agree with our prior work indicating that large difference fields and dark states are stable configurations, while the elimination of the difference field is unstable; however, in the absence of noise, we find all three steady states are achieved depending on parameters. These results are in good agreement with dynamic nuclear polarization experiments in double quantum dots.

Gullans, M.; Krich, J. J.; Taylor, J. M.; Halperin, B. I.; Lukin, M. D.

2013-07-01

105

Selective polarization of nuclear spins in a wire-like quantum Hall system  

SciTech Connect

Nuclear spins are polarized selectively in a mesoscopic wire-like quantum Hall system by using the fractional quantum Hall system at Landau level filling factor nu = 2/3. The nuclear spin polarized region is limited by setting the filling factor in the wire to 2/3, while leaving the filling factor in the bulk away from 2/3. The longitudinal relaxation rate of selectively polarized nuclear spins probes electron spin properties in the wire.

Kobayashi, Takashi; Sasaki, Satoshi [NTT Basic Research Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198 (Japan); Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Kumada, Norio; Ota, Takeshi [NTT Basic Research Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198 (Japan); Hirayama, Yoshiro [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); ERATO-JST Nuclear Spin Electronics Project, 468-15 Aramaki Aza-Aoba, Aoba-ku, Sendai 980-0845 (Japan)

2010-01-04

106

Nuclear spin response studies in inelastic polarized proton scattering  

SciTech Connect

Spin-flip probabilities S/sub nn/ have been measured for inelastic proton scattering at incident proton energies around 300 MeV from a number of nuclei. At low excitation energies S/sub nn/ is below the free value. For excitation energies above about 30 MeV for momentum transfers between about 0.35 fm/sup /minus/1/ and 0.65 fm/sup / minus/1/ S/sub nn/ exceeds free values significantly. These results suggest that the relative ..delta..S = 1(..delta..S = 0 + ..delta..S = 1) nuclear spin response approaches about 90% in the region of the enhancement. Comparison of the data with slab response calculations are presented. Decomposition of the measured cross sections into sigma(..delta..S = 0) and sigma(..delta..S = 1) permit extraction of nonspin-flip and spin-flip dipole and quadrupole strengths. 29 refs., 11 figs.

Jones, K.W.

1988-01-01

107

Single shot NMR on single, dark nuclear spins  

Microsoft Academic Search

The electron and nuclear spins associated with the nitrogen-vacancy (NV)\\u000acenter in diamond are supposed to be building blocks for quantum computing\\u000adevices and nanometer scale magnetometry operating under ambient conditions.\\u000aFor every such building block precise knowledge of the involved quantum states\\u000ais crucial. Especially for solid state systems the corresponding hilbert space\\u000acan be large. Here, we experimentally

G. Waldherr; J. Beck; M. Steiner; P. Neumann; A. Gali; F. Jelezko; J. Wrachtrup

2010-01-01

108

Spin Density Matrices for Nuclear Density Functionals with Parity Violation  

NASA Astrophysics Data System (ADS)

Within the context of the radial density functional [1], we apply the spin density matrix (SDM) used in atomic and molecular physics [2] to nuclear physics. The vector part of the SDM defines a ``hedgehog'' situation, which exists only if nuclear states contain some amount of parity violation. Thus, looking for the vector profile of the SDM could be used as a test for parity violation in nuclei. The difference between the scalar profile and the vector profile of the SDM will be illustrated by a toy model. [4pt] [1] B. G. Giraud, Phys. Rev. C 78, 014307 (2008).[0pt] [2] A. Goerling, Phys. Rev. A 47, 2783 (1993).

Barrett, Bruce; Giraud, Bertrand

2010-11-01

109

Fast Nuclear Spin Hyperpolarization of Phosphorus in Silicon  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate a method for obtaining nuclear spin hyperpolarization, that is, polarization significantly in excess of that expected at thermal equilibrium. By exploiting a nonequilibrium Overhauser process, driven by white light irradiation, we obtain more than 68% negative nuclear polarization of phosphorus donors in silicon. This polarization is reached with a time constant of ˜150sec, at a temperature of 1.37 K and a magnetic field of 8.5 T. The ability to obtain such large polarizations is discussed with regards to its significance for quantum information processing and magnetic resonance imaging.

McCamey, D. R.; van Tol, J.; Morley, G. W.; Boehme, C.

2009-01-01

110

Large nuclear spin polarization in gate-defined quantum dots using a single-domain nanomagnet.  

PubMed

The electron-nuclei (hyperfine) interaction is central to spin qubits in solid state systems. It can be a severe decoherence source but also allows dynamic access to the nuclear spin states. We study a double quantum dot exposed to an on-chip single-domain nanomagnet and show that its inhomogeneous magnetic field crucially modifies the complex nuclear spin dynamics such that the Overhauser field tends to compensate external magnetic fields. This turns out to be beneficial for polarizing the nuclear spin ensemble. We reach a nuclear spin polarization of ?50%, unrivaled in lateral dots, and explain our manipulation technique using a comprehensive rate equation model. PMID:23679779

Petersen, Gunnar; Hoffmann, Eric A; Schuh, Dieter; Wegscheider, Werner; Giedke, Geza; Ludwig, Stefan

2013-04-26

111

Large Nuclear Spin Polarization in Gate-Defined Quantum Dots Using a Single-Domain Nanomagnet  

NASA Astrophysics Data System (ADS)

The electron-nuclei (hyperfine) interaction is central to spin qubits in solid state systems. It can be a severe decoherence source but also allows dynamic access to the nuclear spin states. We study a double quantum dot exposed to an on-chip single-domain nanomagnet and show that its inhomogeneous magnetic field crucially modifies the complex nuclear spin dynamics such that the Overhauser field tends to compensate external magnetic fields. This turns out to be beneficial for polarizing the nuclear spin ensemble. We reach a nuclear spin polarization of ?50%, unrivaled in lateral dots, and explain our manipulation technique using a comprehensive rate equation model.

Petersen, Gunnar; Hoffmann, Eric A.; Schuh, Dieter; Wegscheider, Werner; Giedke, Geza; Ludwig, Stefan

2013-04-01

112

Solid effect in magic angle spinning dynamic nuclear polarization  

PubMed Central

For over five decades, the solid effect (SE) has been heavily utilized as a mechanism for performing dynamic nuclear polarization (DNP). Nevertheless, it has not found widespread application in contemporary, high magnetic field DNP experiments because SE enhancements display an \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}\\omega _0 ^{ - 2}\\end{equation*} \\end{document}?0?2 field dependence. In particular, for nominally forbidden zero and double quantum SE transitions to be partially allowed, it is necessary for mixing of adjacent nuclear spin states to occur, and this leads to the observed field dependence. However, recently we have improved our instrumentation and report here an enhancement of ? = 91 obtained with the organic radical trityl (OX063) in magic angle spinning experiments performed at 5 T and 80 K. This is a factor of 6-7 higher than previous values in the literature under similar conditions. Because the solid effect depends strongly on the microwave field strength, we attribute this large enhancement to larger microwave field strengths inside the sample volume, achieved with more efficient coupling of the gyrotron to the sample chamber. In addition, we develop a theoretical model to explain the dependence of the buildup rate of enhanced nuclear polarization and the steady-state enhancement on the microwave power. Buildup times and enhancements were measured as a function of 1H concentration for both trityl and Gd-DOTA. Comparison of the results indicates that for trityl the initial polarization step is the slower, rate-determining step. However, for Gd-DOTA the spread of nuclear polarization via homonuclear 1H spin diffusion is rate-limiting. Finally, we discuss the applicability of the solid effect at fields > 5 T and the requirements to address the unfavorable field dependence of the solid effect.

Corzilius, Bjorn; Smith, Albert A.; Griffin, Robert G.

2012-01-01

113

Nuclear spin relaxation/resonance of 8Li in Al  

NASA Astrophysics Data System (ADS)

A low energy beam of spin polarized 8Li has been used to study the behaviour of isolated 8Li implanted into a 150 nm thick film of Al on an MgO substrate. The spin relaxation rate 1/T1 and ?-NMR lineshape were measured as a function of temperature in a large magnetic field of 4.1 T. The resonances from different sites are unresolved due to the large nuclear dipolar interaction with the host 27Al magnetic dipole moments. Nevertheless the temperature variation of the site averaged 1/T1 and Knight shift show evidence for a transition between the octahedral O and substitutional S sites at about 150 K, as observed in other fcc metals.

Wang, D.; Salman, Z.; Chow, K. H.; Fan, I.; Hossain, M. D.; Keeler, T. A.; Kiefl, R. F.; Levy, C. D. P.; Mansour, A. I.; Morris, G. D.; Pearson, M. R.; Parolin, T. J.; Saadaoui, H.; Smadella, M.; Song, Q.; Macfarlane, W. A.

2009-04-01

114

Pulsed Nuclear Pumping and Spin Diffusion in a Single Charged Quantum Dot  

NASA Astrophysics Data System (ADS)

We report the observation of a feedback process between the nuclear spins in a single charged quantum dot under coherently pulsed optical excitation and its trion transition. The optical pulse sequence intersperses resonant narrow-band pumping for spin initialization with off-resonant ultrafast pulses for coherent electron-spin rotation. A hysteretic sawtooth pattern in the free-induction decay of the single electron spin is observed; a mathematical model indicates a competition between optical nuclear pumping and nuclear spin-diffusion. This effect allows dynamic tuning of the electron Larmor frequency to a value determined by the pulse timing, potentially allowing more complex coherent control operations.

Ladd, Thaddeus D.; Press, David; de Greve, Kristiaan; McMahon, Peter L.; Friess, Benedikt; Schneider, Christian; Kamp, Martin; Höfling, Sven; Forchel, Alfred; Yamamoto, Yoshihisa

2010-09-01

115

Nuclear Hydrogen for Peak Electricity Production and Spinning Reserve  

SciTech Connect

Nuclear energy can be used to produce hydrogen. The key strategic question is this: ''What are the early markets for nuclear hydrogen?'' The answer determines (1) whether there are incentives to implement nuclear hydrogen technology today or whether the development of such a technology could be delayed by decades until a hydrogen economy has evolved, (2) the industrial partners required to develop such a technology, and (3) the technological requirements for the hydrogen production system (rate of production, steady-state or variable production, hydrogen purity, etc.). Understanding ''early'' markets for any new product is difficult because the customer may not even recognize that the product could exist. This study is an initial examination of how nuclear hydrogen could be used in two interconnected early markets: the production of electricity for peak and intermediate electrical loads and spinning reserve for the electrical grid. The study is intended to provide an initial description that can then be used to consult with potential customers (utilities, the Electric Power Research Institute, etc.) to better determine the potential real-world viability of this early market for nuclear hydrogen and provide the starting point for a more definitive assessment of the concept. If this set of applications is economically viable, it offers several unique advantages: (1) the market is approximately equivalent in size to the existing nuclear electric enterprise in the United States, (2) the entire market is within the utility industry and does not require development of an external market for hydrogen or a significant hydrogen infrastructure beyond the utility site, (3) the technology and scale match those of nuclear hydrogen production, (4) the market exists today, and (5) the market is sufficient in size to justify development of nuclear hydrogen production techniques independent of the development of any other market for hydrogen. These characteristics make it an ideal early market for nuclear hydrogen.

Forsberg, C.W.

2005-01-20

116

Solid-State Nuclear Spin-Flip Maser Pumped by Dynamic Nuclear Polarization  

Microsoft Academic Search

We report the observation of a coherent, maser-type rf radiation of the 27Al nuclear-spin system in Al2O3: Cr3+ pumped by dynamic nuclear polarization to negative temperature. A theoretical description is presented for the sharp, superradiant bursts which follow the fast tuning of a resonant LC circuit to a selected NMR line of 27Al. Experimental results are discussed which demonstrate the

P. Bösiger; E. Brun; D. Meier

1977-01-01

117

Nuclear Spins of Neutron-deficient Lanthanum and Cerium Isotopes  

Microsoft Academic Search

Nuclear spins of some neutron-deficient lanthanum and cerium isotopes have been measured by the atomic-beam magnetic resonance method. The results are: 131La (59 min) I=3\\/2, 132La (4.5 h) I=2, 132mLa (25 min) I=6, 133La (4.0 h) I=5\\/2, 135La (19.4 h) I=5\\/2, 136La (10 min) I=1, 130Ce (25 min) I=0, 132Ce (4.2 h) I=0, 133Ce (5.4 h) I=9\\/2, 133mCe (97 min)

S. Ingelman; C. Ekstroem; M. Olsmats; B. Wannberg

1973-01-01

118

Quantum Computing Using Pulse-Based Electron-Nuclear Double Resonance (endor):. Molecular Spin-Qubits  

NASA Astrophysics Data System (ADS)

Electrons with the spin quantum number 1/2, as physical qubits, have naturally been anticipated for implementing quantum computing and information processing (QC/QIP). Recently, electron spin-qubit systems in organic molecular frames have emerged as a hybrid spin-qubit system along with a nuclear spin-1/2 qubit. Among promising candidates for QC/QIP from the materials science side, the reasons for why electron spin-qubits such as molecular spin systems, i.e., unpaired electron spins in molecular frames, have potentialities for serving for QC/QIP will be given in the lecture (Chapter), emphasizing what their advantages or disadvantages are entertained and what technical and intrinsic issues should be dealt with for the implementation of molecular-spin quantum computers in terms of currently available spin manipulation technology such as pulse-based electron-nuclear double resonance (pulsed or pulse ENDOR) devoted to QC/QIP. Firstly, a general introduction and introductory remarks to pulsed ENDOR spectroscopy as electron-nuclear spin manipulation technology is given. Super dense coding (SDC) experiments by the use of pulsed ENDOR are also introduced to understand differentiating QC ENDOR from QC NMR based on modern nuclear spin technology. Direct observation of the spinor inherent in an electron spin, detected for the first time, will be shown in connection with the entanglement of an electron-nuclear hybrid system. Novel microwave spin manipulation technology enabling us to deal with genuine electron-electron spin-qubit systems in the molecular frame will be introduced, illustrating, from the synthetic strategy of matter spin-qubits, a key-role of the molecular design of g-tensor/hyperfine-(A-)tensor molecular engineering for QC/QIP. Finally, important technological achievements of recently-emerging CD ELDOR (Coherent-Dual ELectron-electron DOuble Resonance) spin technology enabling us to manipulate electron spin-qubits are described.

Sato, Kazuo; Nakazawa, Shigeki; Rahimi, Robabeh D.; Nishida, Shinsuke; Ise, Tomoaki; Shimoi, Daisuke; Toyota, Kazuo; Morita, Yasushi; Kitagawa, Masahiro; Carl, Parick; Höfner, Peter; Takui, Takeji

2009-06-01

119

Nuclear Spin Orientation Dependence of Magnetoconductance: A New Method for Measuring the Spin of Charged Excitations in the QHE  

SciTech Connect

A new method for measuring the spin of the electrically charged ground state excitations m the Q$j~j quantum Hall effect ia proposed and demonstmted for the tirst time in GaAs/AIGaAs nndtiquantum wells. The method is &sed on the nuclear spin orientation dependence of" the 2D dc conductivity y in the quantum Hall regime due to the nuclear hyperfine interaction. As a demonstration of this method the spin of the electrically charged excitations of the ground state is determined at filling factor v = 1.

Bowers, C.R.; Reno, J.L.; Simmons, J.A.; Vitkalov, S.A.

1998-12-01

120

Single-shot readout of multiple nuclear spin qubits in diamond under ambient conditions  

NASA Astrophysics Data System (ADS)

Nuclear spins are attractive candidates for solid-state quantum information storage and processing owing to their extremely long coherence time. However, since this appealing property results from a high level of isolation from the environment, it remains a challenging task to polarize, manipulate and readout with high fidelity individual nuclear spins. A promising approach to overcome this limitation consists in utilizing an ancillary single electronic spin to detect and control remote nuclear spins coupled by hyperfine interaction. In this talk, I will show how the electronic spin of a single Nitrogen-Vacancy (NV) defect in diamond can be used as a robust platform to observe the real-time evolution of surrounding single nuclear spins under ambient conditions. Using a diamond sample with a natural abundance of ^13C isotopes, we first demonstrate high fidelity initialization and single-shot readout of an individual ^13C nuclear spin. By including the intrinsic ^14N nuclear spin of the NV defect in the quantum register, we then report the simultaneous observation of quantum jumps linked to both nuclear spin species, providing an efficient initialization of the two qubits. These results open up new avenues for diamond-based quantum information processing (QIP) including active feedback in quantum error correction protocols and tests of quantum correlations with solid-state single spins at room temperature.

Jacques, Vincent

2013-03-01

121

Optimization of 1H spin density for dynamic nuclear polarization using photo-excited triplet electron spins  

NASA Astrophysics Data System (ADS)

In dynamic nuclear polarization (DNP) using photo-excited triplet electron spins, known as Microwave-Induced Optical Nuclear Polarization (MIONP), the attainable 1H polarization is determined by the ratio of the buildup rate and the spin-lattice relaxation rate, in turn depend on the 1H spin density. It is shown that the final 1H polarization can be enhanced by diluting the 1H spins with partial deuteration. The DNP experiments are demonstrated in 0.05 mol% pentacene-doped p-terphenyl for various 1H abundances. It is also shown that the 1H spin diffusion coefficient can be determined by examining the initial buildup rate of 1H polarization for various repetition rates of the DNP sequence.

Kagawa, Akinori; Murokawa, Yu; Takeda, Kazuyuki; Kitagawa, Masahiro

2009-03-01

122

Optimization of 1H spin density for dynamic nuclear polarization using photo-excited triplet electron spins.  

PubMed

In dynamic nuclear polarization (DNP) using photo-excited triplet electron spins, known as Microwave-Induced Optical Nuclear Polarization (MIONP), the attainable (1)H polarization is determined by the ratio of the buildup rate and the spin-lattice relaxation rate, in turn depend on the (1)H spin density. It is shown that the final (1)H polarization can be enhanced by diluting the (1)H spins with partial deuteration. The DNP experiments are demonstrated in 0.05 mol% pentacene-doped p-terphenyl for various (1)H abundances. It is also shown that the (1)H spin diffusion coefficient can be determined by examining the initial buildup rate of (1)H polarization for various repetition rates of the DNP sequence. PMID:19091611

Kagawa, Akinori; Murokawa, Yu; Takeda, Kazuyuki; Kitagawa, Masahiro

2008-11-27

123

Carbon-13 nuclear magnetic resonance characterization of network systems  

SciTech Connect

Solid-state C-13 NMR measurements are utilized to characterize the tetrafunctional epoxy, tetraglycidyl (diaminodiphenyl) methane, and the tetrafunctional amine, diaminodiphenyl sulfone. Intermolecular effective ether cross-links, amine junction points, and extent of reaction of the amine and epoxy are measured for the polymerization. Chemical reactions in the epoxy-amine system are discussed, and the reactivity ratio of the epoxy-amine system is calculated. Junction point measurements are made by the use of the dipolar dephasing relaxation experiment. The experimental data collected with C-13 NMR are then compared with the calculated data from a model developed in this laboratory. The information obtained in this study is sufficient to calculate the molecular weight between cross-links.

Mertzel, E.A.; Perchak, D.R.; Ritchey, W.M.; Koenig, J.L.

1988-04-01

124

Theory of single nuclear spin detection in magnetic resonance force microscopy  

NASA Astrophysics Data System (ADS)

We develop a theory for the measurement of a nuclear spin state in a paramagnetic atom with Oscillating Cantilever-Driven Adiabatic Reversals (OSCAR) in Magnetic Resonance Force Microscopy (MRFM). In this theory, we use a semi-classical approach where the electron-nuclear spin system, with hyperfine interaction, is treated quantum mechanically and the motion of the ferromagnetic particle on the cantilever tip is treated classically. Our computations support the idea of the measurement of a nuclear spin state by detection of a single electron spin.

Chemudupati, Srinivasa; Tsifrinovich, Vladimir

2008-10-01

125

High-fidelity readout and control of a nuclear spin qubit in silicon.  

PubMed

Detection of nuclear spin precession is critical for a wide range of scientific techniques that have applications in diverse fields including analytical chemistry, materials science, medicine and biology. Fundamentally, it is possible because of the extreme isolation of nuclear spins from their environment. This isolation also makes single nuclear spins desirable for quantum-information processing, as shown by pioneering studies on nitrogen-vacancy centres in diamond. The nuclear spin of a (31)P donor in silicon is very promising as a quantum bit: bulk measurements indicate that it has excellent coherence times and silicon is the dominant material in the microelectronics industry. Here we demonstrate electrical detection and coherent manipulation of a single (31)P nuclear spin qubit with sufficiently high fidelities for fault-tolerant quantum computing. By integrating single-shot readout of the electron spin with on-chip electron spin resonance, we demonstrate quantum non-demolition and electrical single-shot readout of the nuclear spin with a readout fidelity higher than 99.8 percent-the highest so far reported for any solid-state qubit. The single nuclear spin is then operated as a qubit by applying coherent radio-frequency pulses. For an ionized (31)P donor, we find a nuclear spin coherence time of 60 milliseconds and a one-qubit gate control fidelity exceeding 98 percent. These results demonstrate that the dominant technology of modern electronics can be adapted to host a complete electrical measurement and control platform for nuclear-spin-based quantum-information processing. PMID:23598342

Pla, Jarryd J; Tan, Kuan Y; Dehollain, Juan P; Lim, Wee H; Morton, John J L; Zwanenburg, Floris A; Jamieson, David N; Dzurak, Andrew S; Morello, Andrea

2013-04-18

126

Distal and proximal ligand interactions in heme proteins: Correlations between C-O and Fe-C vibrational frequencies, oxygen-17 and carbon-13 nuclear magnetic resonance chemical shifts, and oxygen-17 nuclear quadrupole coupling constants in C sup 17 O- and sup 13 CO-labeled species  

SciTech Connect

The authors have obtained the oxygen-17 nuclear magnetic resonance (NMR) spectra of a variety of C{sup 17}O-labeled heme proteins, including sperm whale (Physeter catodon) myoglobin, two synthetic sperm whale myoglobin mutants (His E7 {yields} Val E7; His E7 {yields} Phe E7), adult human hemoglobin, rabbit (Oryctolagus cuniculus) hemoglobin, horseradish (Cochlearia armoracia) peroxidase isoenzymes A and C, and Caldariomyces fumago chloroperoxidase, in some cases as a function of pH, and have determined their isotropic {sup 17}O NMR chemical shifts, {delta}{sub i}, and spin-lattice relaxation times, T{sub 1}. They have also obtained similar results on a picket fence prophyrin. The results show an excellent correlation between the infrared C-O vibrational frequencies, {nu}(C-O), and {delta}{sub i}, between {nu}(C-O) and the {sup 17}O nuclear quadrupole coupling constant, and as expected between e{sup 2}qQ/h and {delta}{sub i}. The results suggest the IR and NMR measurements reflect the same interaction, which is thought to be primarily the degree of {pi}-back-bonding from Fe d to CO {pi}* orbitals, as outlined previously.

Ki Deok Park; Guo, K.; Adebodun, F.; Chiu, M.L.; Sligar, S.G.; Oldfield, E. (Univ. of Illinois, Urbana (United States))

1991-03-05

127

Nuclear Spin-Dependent Parity Violation in Diatomic Molecules  

NASA Astrophysics Data System (ADS)

Nuclear spin-dependent parity violation (NSD-PV) effects arise from exchange of the Z^0 boson (parametrized by the electroweak coupling constants C2P,N) between electrons and the nucleus, and from the interaction of electrons with the nuclear anapole moment, a parity-odd magnetic moment. The latter scales with the nucleon number A of the nucleus as A^3/2, while the Z^0 coupling is independent of A; the former will be the dominant source of NSD-PV in nuclei with A greater than 20. NSD-PV effects can be dramatically amplified in diatomic molecules by bringing two levels of opposite parity close to degeneracy in a strong magnetic field. This opens the prospect for measurements across a broad range of nuclei. As a precursor to the measurement of the nuclear anapole moment of ^137Ba, we have experimentally observed and characterized opposite-parity level crossings in ^138BaF. These are found to be in excellent agreement with parameter-free predictions and indicate that the sensitivity necessary for NSD-PV measurements should be within reach.

Ammon, Jeffrey; Cahn, Sidney; Kirilov, Emil; Demille, David; Kozlov, Mikhail; Paolino, Richard

2012-06-01

128

A co-magnetometer-based nuclear spin gyroscope  

NASA Astrophysics Data System (ADS)

We describe a new atomic gyroscope based on an alkali metal--noble gas co-magnetometer. Unlike atomic and laser gyroscopes based on the Sagnac effect, nuclear spin gyroscopes do not require a large enclosed area and can be made quite compact. A high density alkali-metal magnetometer operating in a spin-exchange relaxation free (SERF) regime is used to polarize the noble gas atoms and detect their gyroscopic precession. In this arrangement it is also possible to cancel the response to the magnetic fields as well as their gradients and transients between the two atomic species, giving a clean signal proportional to the rotation. Using a K--^3He co-magnetometer we demonstrated rotation sensitivity of 2 x10-7 rad/sec/Hz^1/2. The rotation signal can be increased by an order of magnitude using Ne-21 atoms which have a smaller magnetic moment, while the fundamental limit on the gyroscope sensitivity is about 10-10 rad/sec/ Hz^1/2 for a 10 cm^3 measurement cell. We will also present data on the long-term stability of the gyroscope obtained during a search for Lorentz violation using the K--^3He co-magnetometer.

Kornack, Thomas

2005-05-01

129

Stable three-axis nuclear-spin gyroscope in diamond  

NASA Astrophysics Data System (ADS)

Gyroscopes find wide applications in everyday life from navigation and inertial sensing to rotation sensors in hand-held devices and automobiles. Current devices, based on either atomic or solid-state systems, impose a choice between long-time stability and high sensitivity in a miniaturized system. Here, we introduce a quantum sensor that overcomes these limitations by providing a sensitive and stable three-axis gyroscope in the solid state. We achieve high sensitivity by exploiting the long coherence time of the 14N nuclear spin associated with the nitrogen-vacancy center in diamond, combined with the efficient polarization and measurement of its electronic spin. Although the gyroscope is based on a simple Ramsey interferometry scheme, we use coherent control of the quantum sensor to improve its coherence time and robustness against long-time drifts. Such a sensor can achieve a sensitivity of ?˜0.5(mdegs-1)/Hzmm3 while offering enhanced stability in a small footprint. In addition, we exploit the four axes of delocalization of the nitrogen-vacancy center to measure not only the rate of rotation, but also its direction, thus obtaining a compact three-axis gyroscope.

Ajoy, Ashok; Cappellaro, Paola

2012-12-01

130

Distinguishing between nonorthogonal quantum states of a single nuclear spin.  

PubMed

An important task for quantum-information processing is optimal discrimination between two nonorthogonal quantum states, which until now has been realized only optically. Here, we present and compare experimental realizations of optimal quantum measurements for distinguishing between two nonorthogonal quantum states encoded in a single (14)N nuclear spin at a nitrogen-vacancy defect in diamond. Implemented measurement schemes are the minimum-error measurement (known as Helstrom measurement), unambiguous state discrimination using a standard projective measurement, and optimal unambiguous state discrimination [known as Ivanovic-Dieks-Peres (IDP) measurement], which utilizes a three-dimensional Hilbert space. This allows us to benchmark the IDP measurement against the standard projective measurements. Measurement efficiencies are found to be above 80% for all schemes and reach a value of 90% for the IDP measurement. PMID:23215260

Waldherr, Gerald; Dada, Adetunmise C; Neumann, Philipp; Jelezko, Fedor; Andersson, Erika; Wrachtrup, Jörg

2012-11-02

131

Carbon-13 magnetic resonance spectroscopy of drugs. Sulfonamides.  

PubMed

The natural abundance 13C magnetic resonance spectra of a series of sulfonamide drugs(sulfanilamide, sulfaguanidine,sulfathiazole, sulfasuxidine, sulfadiazine, sulfamerazine, sulfamethiazine, and sulfapyridine) have been determined at 25.15 MHz employing the pulse Fourier transform technique. The chemical shefts have been assigned with the aid of off-resonance and selective proton decoupling techniques, as well as by long-range carbon-13 proton coupling patterns. PMID:1151960

Chang, C; Floss, H G; Peck, G E

1975-05-01

132

Critical divergence of 55Mn nuclear spin relaxation rate in MnSi revealed by muon-núclear-spin double relaxation  

Microsoft Academic Search

The very short 55Mn nuclear spin relaxation time (0.5mus⪷TMn1⪷30mus) in the critical temperature region of MnSi was measured for the first time through zero-field mu+ spin relaxation, which reflects the nuclear spin dynamics. The observed temperature dependence of 1\\/TMn1 shows a clear divergent behaviour similar to that of the mu+ spin relaxation 1\\/Tmu1.

T. Matsuzaki; K. Nishiyama; K. Nagamine; T. Yamazaki; M. Senba; J. M. Bailey; J. H. Brewer

1987-01-01

133

Nuclear Spin-Lattice Relaxation in Ferromagnetic Insulators at Low Temperatures  

Microsoft Academic Search

A theoretical study of the nuclear spin-lattice relaxation in cubic ferromagnetic insulators at ultralow temperatures is presented. Calculations are performed for nuclei which belong to the magnetic atoms, considering only the direct processes. Three mechanisms are considered: the relaxation to mixed magnon-phonon modes, indirect nuclear-spin interaction modulated by lattice vibrations, and nuclear quadrupole energy modulated by lattice vibrations. The first

Akio Honma

1966-01-01

134

Electron and nuclear spin interactions in the optical spectra of single GaAs quantum dots.  

PubMed

Fine and hyperfine splittings arising from electron, hole, and nuclear spin interactions in the magneto-optical spectra of individual localized excitons are studied. We explain the magnetic field dependence of the energy splitting through competition between Zeeman, exchange, and hyperfine interactions. An unexpectedly small hyperfine contribution to the splitting close to zero applied field is described well by the interplay between fluctuations of the hyperfine field experienced by the nuclear spin and nuclear dipole/dipole interactions. PMID:11384450

Gammon, D; Efros, A L; Kennedy, T A; Rosen, M; Katzer, D S; Park, D; Brown, S W; Korenev, V L; Merkulov, I A

2001-05-28

135

Effects of Nuclear Spin Polarization on Reaction Dynamics in Photosynthetic Bacterial Reaction Centers  

PubMed Central

Singlet-triplet mixing in the initial radical-pair state, P[unk]I[unk], of photosynthetic bacterial reaction centers is due to the hyperfine mechanism at low magnetic fields and both the hyperfine and ?g mechanisms at high magnetic fields (>1 kG). Since the hyperfine field felt by the electron spins in P[unk]I[unk] is dependent upon the nuclear spin state in each radical, the relative probabilities of charge recombination to the triplet state of the primary electron donor, 3PI, or the ground state, PI, will depend on the nuclear spin configuration. As a result these recombination products will have non-equilibrium distributions of nuclear spin states (nuclear spin polarization). This polarization will persist until the 3PI state decays. In addition, due to unequal nuclear spin relaxation rates in the diamagnetic PI and paramagnetic 3PI states, net polarization of the nuclear spins can result, especially in experiments that involve recycling of the system through the radical-pair state. This net polarization can persist for very long times, especially at low temperatures. Nuclear spin polarization can have consequences on any subsequent process that involves re-formation of the radical-pair state. Numerical calculations of the nuclear polarization caused by both of these mechanics are presented, including the effect of such polarization on subsequent yields of 3PI, 3PI decay rates, the decay rate of the radical pair, and saturation behavior. The effect of this polarization under certain circumstances can be very dramatic and can explain previously noted discrepancies between experiments and theories that do not include nuclear spin polarization effects. Our analysis suggests new classes of experiments and indicates the need to reinterpret some past experimental results.

Goldstein, Richard A.; Boxer, Steven G.

1987-01-01

136

Electrically generated nuclear spin polarization in In.04Ga.96As  

NASA Astrophysics Data System (ADS)

The promises of lower power consumption and simple interfacing to magnetic storage has driven interest in the development of spintronics, in which devices could take advantage of electron spin as a means to store, move, and process data. Due to its long lifetime in moderate fields, nuclear polarization could serve as intermediate timescale data storage in both classical spintronic and quantum computation schemes. Here, we investigate the role of nuclear spins in materials with electrically driven spin polarization. The electron spin polarization generated by electrical current in a non-magnetic semiconductor is transferred via dynamic nuclear polarization to the nuclei. The resulting nuclear field is interrogated using Larmor magnetometry. We measure nuclear field as a function of current, applied magnetic field, and temperature. Polarization decay dynamics and the role of nuclei in devices are also discussed.

Trowbridge, Christopher; Norman, Benjamin; Kato, Yuichiro K.; Awschalom, David; Sih, Vanessa

2013-03-01

137

Mass Spectrometric Quantification of Polychlorinated Biphenyl Congeners Using Multiple Carbon-13 Internal Standards.  

National Technical Information Service (NTIS)

Multiple carbon-13 internal standards improve the precision and accuracy of the mass spectrometric analysis of polychlorinatedbiphenyl (PCB) congeners compared to analyses using a single carbon-13 internal standard. The mean percentage error in PCB congen...

F. L. Shore J. D. Martin L. R. Williams

1986-01-01

138

MASS SPECTROMETRIC QUANTIFICATION OF POLYCHLORINATED BIPHENYL CONGENERS USING MULTIPLE CARBON-13 INTERNAL STANDARDS  

EPA Science Inventory

Multiple carbon-13 internal standards improve the precision and accuracy of the mass spectrometric analysis of polychlorinatedbiphenyl (PCB) congeners compared to analyses using a single carbon-13 internal standard. The mean percentage error in PCB congener analysis on the microg...

139

Voltage control of electron-nuclear spin correlation time in a single quantum dot  

NASA Astrophysics Data System (ADS)

We demonstrate bias control of the efficiency of the hyperfine coupling between a single electron in an InAs quantum dot and the surrounding nuclear spins monitored through the positively charged exciton X+ emission. In applied longitudinal magnetic fields, we vary simultaneously the correlation time of the hyperfine interaction and the nuclear spin relaxation time and thereby the amplitude of the achieved dynamic nuclear polarization under optical pumping conditions. In applied transverse magnetic fields, a change in the applied bias allows a switch from the anomalous Hanle effect to the standard electron spin depolarization curves.

Nilsson, J.; Bouet, L.; Bennett, A. J.; Amand, T.; Stevenson, R. M.; Farrer, I.; Ritchie, D. A.; Kunz, S.; Marie, X.; Shields, A. J.; Urbaszek, B.

2013-08-01

140

Effects of Substituent Groups on Spin-Spin Coupling in Nuclear Magnetic Resonance.  

National Technical Information Service (NTIS)

The initial phases of this investigation were motivated by the observation that certain spin-spin coupling constants are directly additive whereas others are pairwise additive with respect to the substituent groups. During the study it has been found that...

E. R. Malinowski

1966-01-01

141

Accessing long-lived nuclear singlet states between chemically equivalent spins without breaking symmetry  

PubMed Central

Long-lived nuclear spin states could greatly enhance the applicability of hyperpolarized nuclear magnetic resonance. Using singlet states between inequivalent spin pairs has been shown to extend the signal lifetime by more than an order of magnitude compared to the spin lattice relaxation time (T1), but they have to be prevented from evolving into other states. In the most interesting case the singlet is between chemically equivalent spins, as it can then be inherently an eigenstate. However this presents major challenges in the conversion from bulk magnetization to singlet. In the only case demonstrated so far, a reversible chemical reaction to break symmetry was required. Here we present a pulse sequence technique that interconverts between singlet spin order and bulk magnetization without breaking the symmetry of the spin system. This technique is independent of field strength and is applicable to a broad range of molecules.

Feng, Yesu; Davis, Ryan M.; Warren, Warren S.

2013-01-01

142

Electrical current and coupled electron-nuclear spin dynamics in double quantum dots  

NASA Astrophysics Data System (ADS)

We examine electronic transport in a spin-blockaded double quantum dot. We show that by tuning the strength of the spin-orbit interaction the current flowing through the double dot exhibits a dip at zero magnetic field or a peak at a magnetic field for which the two-electron energy levels anticross. This behavior is due to the dependence of the singlet-triplet mixing on the field and spin-orbit amplitude. We derive approximate expressions for the current as a function of the amplitudes of the states involved in the transport. We also consider an alternative model that takes into account a finite number of nuclear spins and study the resulting coupled dynamics between electron and nuclear spins. We show that if the spin ensemble is in a thermal state there are regular oscillations in the transient current followed by quasichaotic revivals akin to those seen in a thermal Jaynes-Cummings model.

Giavaras, G.; Lambert, Neill; Nori, Franco

2013-03-01

143

Line Broadening in the Electron Resonance Spectra of Spin Probes Dissolved in Anisotropic Media: The Effect of Nuclear Spin Quantization  

Microsoft Academic Search

The line broadening in the electron resonance spectra of monoradicals dissolved in anisotropic media, such as liquid crystals, provides a valuable probe of both the orientational order and the molecular dynamics. However, the fast-motion relaxation theory employed to extract this information from the linewidths assumes that the nuclear spin is quantized along the direction of the magnetic field. This approximation

G. R. Luckhurst; C. Zannoni

1977-01-01

144

Coherent storage of photoexcited triplet states using 29Si nuclear spins in silicon.  

PubMed

Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the m(s)=±1 sublevels differs significantly from that of the m(s)=0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ~100% electron-spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor (29)Si nuclear spin. We measure the coherence time of the (29)Si nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance. PMID:22463668

Akhtar, Waseem; Filidou, Vasileia; Sekiguchi, Takeharu; Kawakami, Erika; Itahashi, Tatsumasa; Vlasenko, Leonid; Morton, John J L; Itoh, Kohei M

2012-02-27

145

New host-lattices for hyperfine optical hole burning: Materials of low nuclear spin moment  

Microsoft Academic Search

Optical hole burning (OHB) on lanthanides in inorganic host-lattices provides a promising method for optical storage application. To gain a high memory capacity, materials of low nuclear spin moments are of interest because of line broadening due to spin flip-flop processes in spin rich host-lattices. In this work, it is shown that only a small number of elements may be

A. Caprez; P. Meyer; P. Mikhail; J. Hulliger

1997-01-01

146

Dynamical nuclear spin polarization induced by electronic current through double quantum dots  

NASA Astrophysics Data System (ADS)

We analyse electron-spin relaxation in electronic transport through coherently coupled double quantum dots (DQDs) in the spin blockade regime. In particular, we focus on hyperfine (HF) interaction as the spin-relaxation mechanism. We pay special attention to the effect of the dynamical nuclear spin polarization induced by the electronic current on the nuclear environment. We discuss the behaviour of the electronic current and the induced nuclear spin polarization versus an external magnetic field for different HF coupling intensities and interdot tunnelling strengths. We take into account, for each magnetic field, all HF-mediated spin-relaxation processes coming from different opposite spin level approaches. We find that the current as a function of the external magnetic field shows a peak or a dip and that the transition from a current dip to a current peak behaviour is obtained by decreasing the HF coupling or by increasing the interdot tunnelling strength. We give a physical picture in terms of the interplay between the electrons tunnelling out of the DQD and the spin-flip processes due to the nuclear environment.

López-Monís, Carlos; Iñarrea, Jesús; Platero, Gloria

2011-05-01

147

Theory of nuclear spin interactions in ferromagnetic insulators. I. The thermodynamic properties  

Microsoft Academic Search

A field theoretical perturbation method is employed to investigate the low temperature thermodynamic properties of a ferromagnetic insulator in which there is a Heisenberg exchange interaction between neighbouring electronic spins and an additional hyperfine coupling between the nuclear and electronic spins. The calculations make use of the diagrammatic formalism of Vaks et al (1968), and the contributions are classified by

M. G. Cottam; M. J. Jones

1973-01-01

148

Theory of nuclear spin interactions in ferromagnetic insulators. II. The excitation spectrum  

Microsoft Academic Search

For pt. I see ibid., vol. 6, 1007 (1973). The method of the preceding paper is used to investigate the excitation spectrum of a Heisenberg ferromagnet in which there is a hyperfine coupling between the nuclear and electronic spins. This formalism employs a perturbation expansion in terms of the parameters 1\\/z, where z is the number of spins interacting with

M. G. Cottam; M. J. Jones

1973-01-01

149

Infrared Spectroscopy of Chloromethyl Radical in Solid Parahydrogen and Its Nuclear Spin Conversion  

NASA Astrophysics Data System (ADS)

We present high-resolution infrared absorption spectra of chloromethyl radical produced by in situ UV photolysis of chloroiodomethane isolated in solid parahydrogen. The radicals were stable over a few days in solid parahydrogen kept at 3.6 K. Analysis of the rotation-vibration spectra revealed that the radical exhibited quantized one-dimensional rotational motion about the C-Cl bond, while the ortho and para nuclear spin species were still clearly distinguishable in the spectra. Temporal change of the spectra indicated that the nuclear spin conversion between the ortho and para nuclear spin species of the radical in solid parahydrogen occurred in a time scale of a few hours at 3.6 K. It was also found that the nuclear spin conversion became significantly slower in a higher concentration of chloroiodomethane.

Miyamoto, Yuki; Tsubouchi, Masaaki; Momose, Takamasa

2013-10-01

150

Infrared Spectroscopy of Chloromethyl Radical in Solid Parahydrogen and its Nuclear Spin Conversion.  

PubMed

We present high-resolution infrared absorption spectra of chloromethyl radical produced by {\\it in situ} UV photolysis of chloroiodomethane isolated in solid parahydrogen. The radicals were stable over a few days in solid parahydrogen kept at 3.6 K. Analysis of the rotation-vibration spectra revealed that the radical exhibited quantized one-dimensional rotational motion about the C-Cl bond, while the {\\it ortho} and {\\it para} nuclear spin species were still clearly distinguishable in the spectra. Temporal change of the spectra indicated that the nuclear spin conversion between the {\\it ortho} and {\\it para} nuclear spin species of the radical in solid parahydrogen occurred in a time scale of a few hours at 3.6 K. It was also found that the nuclear spin conversion became significantly slower in a higher concentration of chloroiodomethane. PMID:23506119

Miyamoto, Yuki; Tsubouchi, Masaaki; Momose, Takamasa

2013-03-18

151

Nuclear spin selection rules in chemical reactions by angular momentum algebra  

NASA Astrophysics Data System (ADS)

The detailed selection rules for reactive collisions reported by Quack using molecular symmetry group are derived by using angular momentum algebra. Instead of the representations of the permutation inversion group for both nuclear spin and rovibronic coordinate wavefunctions, those of the rotation group for nuclear spin wavefunction only are used. The method allows more straightforward derivation of Quack’s results and further extension of the calculation for separating elementary reactions and application to higher proton systems.

Oka, Takeshi

2004-12-01

152

Application of Solid-State Nuclear Magnetic Resonance (NMR) to the Study of Skin Hydration  

Microsoft Academic Search

The solid-state nuclear magnetic resonance (NMR) technique of carbon-13 cross-polarization\\/magic angle spinning (CP\\/MAS) has been successfully used to obtain high-resolution spectra of whole-thickness, hairy rat skin and to characterize the influence of hydration on the efficiency of cross-polarization and the proton spin-lattice relaxation time in the rotating frame (T1?H). Spectra obtained with hydrated samples, which were obtained with 50% more

Timothy Wiedmann

1988-01-01

153

Description of 158Er at Ultrahigh Spin in Nuclear Density Functional Theory  

SciTech Connect

Rotational bands in 158Er at ultrahigh spin have been studied in the framework of relativistic and nonrelativistic nuclear density-functional theories. Consistent results are obtained across the theoretical models used but some puzzles remain when confronted with experiment. Namely, the many-body configurations which provide good description of experimental transition quadrupole moments and dynamic moments of inertia require substantial increase of the spins of observed bands as compared with experimental estimates, which are still subject to large uncertainties. If, however, the theoretical spin assignments turned out to be correct, experimental band 1 in 158Er would be the highest spin structure ever observed.

Afanasjev, A. V. [Mississippi State University/JIHIR, ORNL; Shi, Yue [Peking University; Nazarewicz, Witold [UTK/ORNL/University of Warsaw

2012-01-01

154

Quantum Hall charge sensor for single-donor nuclear spin detection in silicon  

NASA Astrophysics Data System (ADS)

We propose a novel optical and electrical hybrid scheme for the measurement of nuclear spin qubits in silicon. By combining the environmental insensitivity of the integer quantum Hall effect with the optically distinguishable hyperfine states of phosphorus impurities in silicon, our system can offer both nuclear spin measurement and robustness against environmental defects. 31P donor spins in isotopically purified 28Si are often discussed as very promising quantum memory qubits due to their extremely long decoherence times, and our proposed device offers an effective implementation for such a quantum memory system.

Sleiter, D.; Y Kim, N.; Nozawa, K.; Ladd, T. D.; Thewalt, M. L. W.; Yamamoto, Y.

2010-09-01

155

Nuclear magnetic resonance linewidth and spin diffusion in {sup 29}Si isotopically controlled silicon  

SciTech Connect

A nuclear magnetic resonance (NMR) study was performed with n-type silicon single crystals containing {sup 29}Si isotope abundance f ranges from 1.2% to 99.2%. The nuclear spin diffusion coefficient D has been determined from the linewidth of significantly enhanced {sup 29}Si NMR signals utilizing a developed dynamic nuclear polarization (DNP) method. The {sup 29}Si NMR linewidth depends linearly on f, at least when f<10%, and approaches {proportional_to}f{sup 1/2} dependence when f>50%. The estimated {sup 29}Si nuclear spin diffusion time T{sub sd} between phosphorus atoms used for DNP is more than ten times shorter than the nuclear polarization time T{sub 1}{sup p} of {sup 29}Si nuclei around phosphorus. Therefore, the regime of 'rapid spin diffusion' is realized in the DNP experiments.

Hayashi, Hiroshi; Itoh, Kohei M.; Vlasenko, Leonid S. [Department of Applied Physics and Physico-Informatics, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); A. F. Ioffe Physico-Technical Institute, 194021 Saint Petersburg (Russian Federation)

2008-10-15

156

Dynamical magnetic and nuclear polarization in complex spin systems: semi-magnetic II–VI quantum dots  

NASA Astrophysics Data System (ADS)

Dynamical magnetic and nuclear polarization in complex spin systems is discussed on the example of transfer of spin from exciton to the central spin of magnetic impurity in a quantum dot in the presence of a finite number of nuclear spins. The exciton is described in terms of electron and heavy-hole spins interacting via exchange interaction with magnetic impurity, via hyperfine interaction with a finite number of nuclear spins and via dipole interaction with photons. The time evolution of the exciton, magnetic impurity and nuclear spins is calculated exactly between quantum jumps corresponding to exciton radiative recombination. The collapse of the wavefunction and the refilling of the quantum dot with a new spin-polarized exciton is shown to lead to the build up of magnetization of the magnetic impurity as well as nuclear spin polarization. The competition between electron spin transfer to magnetic impurity and to nuclear spins simultaneous with the creation of dark excitons is elucidated. The technique presented here opens up the possibility of studying optically induced dynamical magnetic and nuclear polarization in complex spin systems.

Abolfath, Ramin M.; Trojnar, Anna; Roostaei, Bahman; Brabec, Thomas; Hawrylak, Pawel

2013-06-01

157

Increasing Hyperpolarized Spin Lifetimes Through True Singlet Eigenstates  

PubMed Central

The sensitivity limitations for magnetic resonance imaging of organic molecules have recently been addressed by hyperpolarization methods, which prepare excess nuclear spin polarization. This approach can increase sensitivity by orders of magnitude, but the enhanced signal relaxes away in tens of seconds, even in favorable cases. Here we show theoretically that singlet states between strongly coupled spins in molecules can be used to store and retrieve population in very-long-lived disconnected eigenstates, as long as the coupling between the spins substantially exceeds both the couplings to other spins and the resonance frequency difference between them. Experimentally, 2,3-carbon-13–labeled diacetyl has a disconnected eigenstate that can store population for minutes and is read out by hydration to make the two spins inequivalent.

Warren, Warren S.; Jenista, Elizabeth; Branca, Rosa Tamara; Chen, Xin

2010-01-01

158

Dynamics and thermalization of the nuclear spin bath in the single-molecule magnet Mn12-ac : Test for the theory of spin tunneling  

NASA Astrophysics Data System (ADS)

The description of the tunneling of a macroscopic variable in the presence of a bath of localized spins is a subject of great fundamental and practical interest, and is relevant for many solid-state qubit designs. Most of the attention is usually given to the dynamics of the “central spin” (i.e., the qubit), while little is known about the spin bath itself. Here, we present a detailed study of the dynamics of the nuclear spin bath in the Mn12-ac single-molecule magnet, probed by NMR experiments down to very low temperatures (T?20mK) . The results are critically analyzed in the framework of the Prokof’ev-Stamp theory of nuclear-spin-mediated quantum tunneling. We find that the longitudinal relaxation rate of the Mn55 nuclei in Mn12-ac becomes roughly T independent below T?0.8K and can be strongly suppressed with a longitudinal magnetic field. This is consistent with the nuclear relaxation being caused by quantum tunneling of the molecular spin, and we attribute the tunneling fluctuations to the minority of fast-relaxing molecules present in the sample. The transverse nuclear relaxation is also T independent for T<0.8K , and can be explained qualitatively and quantitatively by the dipolar coupling between like nuclei in neighboring molecules. This intercluster nuclear spin diffusion mechanism is an essential ingredient for the global relaxation of the nuclear spin bath. We also show that the isotopic substitution of H1 by H2 leads to a slower nuclear longitudinal relaxation, consistent with the decreased tunneling probability of the molecular spin. Finally, we demonstrate that even at the lowest temperatures—where only T -independent quantum tunneling fluctuations are present—the nuclear spins remain in thermal equilibrium with the lattice phonons, and we investigate the time scale for their thermal equilibration. After a review of the theory of macroscopic spin tunneling in the presence of a spin bath, we argue that most of our experimental results are consistent with that theory, but the thermalization of the nuclear spins is not. This calls for an extension of the spin-bath theory to include the effect of spin-phonon couplings in the nuclear-spin-mediated tunneling process.

Morello, Andrea; de Jongh, L. J.

2007-11-01

159

Spin-mediated consciousness theory: possible roles of neural membrane nuclear spin ensembles and paramagnetic oxygen  

Microsoft Academic Search

A novel theory of consciousness is proposed in this paper. We postulate that consciousness is intrinsically connected to quantum spin since the latter is the origin of quantum effects in both Bohm and Hestenes quantum formulism and a fundamental quantum process associated with the structure of space-time. That is, spin is the “mind-pixel”. The unity of mind is achieved by

Huping Hu; Maoxin Wu

2004-01-01

160

Electron spin coherence and electron nuclear double resonance of Bi donors in natural Si  

NASA Astrophysics Data System (ADS)

We have shown that the electron spin coherence times of Si:Bi donors in natural silicon are limited by the same mechanism of spectral diffusion as seen in Si:P, though the smaller Bohr radius of the Bi donor leads to ˜30% longer T2 times (up to 0.8 ms). We have mapped out the 36 ENDOR transitions observable at X-band arising from the I=9/2 nuclear spin of ^209Bi, going up to 1.3 GHz. We also demonstrate the transfer of electron spin coherence to and from the ^209Bi nuclear spin with a fidelity of ˜63%. Using pulsed ESR at W-band (100 GHz), we observe optically-induced dynamic nuclear polarisation, consistent with the mechanism of exciton capture proposed in by T. Sekiguchi et al.. Finally, we explore the zero-field splitting of 7.5 GHz in this system, within the context of coupling to superconducting resonators.

Morton, John; Simmons, Stephanie; George, Richard; Witzel, Wayne; Riemann, H.; Abrosimov, Nikolai; Notzel, N.; Thewalt, Mike

2011-03-01

161

Gauge invariance of the nuclear spin/electron orbit interaction and NMR spectral parameters.  

PubMed

A gauge transformation of the vector potential A(m(I)), associated to the magnetic dipole m(I) of nucleus I in a molecule, has been studied. The conditions for gauge invariance of nuclear magnetic shielding, nuclear spin/electron orbit contribution to spin-spin coupling between two nuclei, I and J, and electronic current density induced by m(I), have been expressed via quantum mechanical sum rules that are identically satisfied for exact and optimal variational wavefunctions. It is shown that separate diamagnetic and paramagnetic contributions to the properties transform into one another in the gauge transformation, whereas their sum is invariant. Therefore, only total response properties have a physical meaning. In particular, the disjoint diamagnetic and paramagnetic components of nuclear spin/electron orbit contributions to coupling constants are not uniquely defined. The diamagnetic contribution to the nuclear spin-spin coupling tensor, evaluated as an expectation value in the Ramsey theory, can alternatively be expressed as a sum-over-states formula, by rewriting the second-order Hamiltonian in commutator form à la Geertsen, as previously reported by Sauer. Other sum-over-states formulae are obtained via a gauge transformation, by a procedure formally allowing for a continuous translation of the origin of the m(I)-induced current density, analogous to those previously proposed for magnetizabilities and nuclear magnetic shielding. PMID:22920104

Lazzeretti, Paolo

2012-08-21

162

Small tip angle NMR as a probe of electron-mediated nuclear spin-spin couplings in YBa2Cu3O7  

NASA Astrophysics Data System (ADS)

We develop the theory and application of small tip angle NMR techniques that can be used to measure couplings between nuclear spins and multiple neighboring spins. We employ the techniques to measure indirect (electron-mediated) nuclear spin-spin couplings between neighboring 63,65Cu and 17O nuclear spins in the high-temperature superconductor YBa2Cu3O7. Predictions for the values of these couplings can be obtained from the existing phenomenological models of electronic spin susceptibility ?(q,?) and hyperfine couplings that have been used in attempts to understand the wide body of YBa2Cu3O7 NMR data gathered to date. We find that the measured couplings are incompatible with these models.

Pennington, C. H.; Yu, S.; Gorny, K. R.; Buoni, M. J.; Hults, W. L.; Smith, J. L.

2001-02-01

163

Nonconservation of the spin projection on the nuclear symmetry axis in neutron resonances, and Coriolis mixing  

SciTech Connect

It is shown that the effect of the Coriolis mixing in deformed nuclei grows as the nuclear level density increases and at sufficiently high excitation energies E/sub 0/ (E/sub 0/spin projection on the nuclear symmetry axis.

Kadmenskii, S.G.; Markushev, V.P.; Furman, V.I.

1982-02-01

164

Dynamic nuclear spin polarization in the resonant laser excitation of an InGaAs quantum dot.  

PubMed

Resonant optical excitation of lowest-energy excitonic transitions in self-assembled quantum dots leads to nuclear spin polarization that is qualitatively different from the well-known optical orientation phenomena. By carrying out a comprehensive set of experiments, we demonstrate that nuclear spin polarization manifests itself in quantum dots subjected to finite external magnetic field as locking of the higher energy Zeeman transition to the driving laser field, as well as the avoidance of the resonance condition for the lower energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear spin polarization originating from noncollinear hyperfine interaction and find excellent agreement between experiment and theory. Our results provide evidence for the significance of noncollinear hyperfine processes not only for nuclear spin diffusion and decay, but also for buildup dynamics of nuclear spin polarization in a coupled electron-nuclear spin system. PMID:23003088

Högele, A; Kroner, M; Latta, C; Claassen, M; Carusotto, I; Bulutay, C; Imamoglu, A

2012-05-09

165

Quenching of Nuclear Spin Diffusion in Strained GaAs-AlGaAs Multiple Quantum Wells  

NASA Astrophysics Data System (ADS)

NMR Knight shift and spin lattice relaxation measurements have recently provided new insight into the formation of charged spin texture excitations (i.e. Skyrmions) in the context of the quantum Hall effect in GaAs/AlGaAs quantum wells. Although the observable nuclei in these NMR experiments ( ^69Ga, ^71Ga and ^75As) all posses a nuclear quadrupole moment, no quadrupole splitting is observed due to the cubic symmetry of the lattice. We demonstrate that uniform and controlled strain can be useful to identify optically pumped NMR signal contributions from different layers in the sample and to determine the nuclear spin polarization. A uniform biaxial strain in the plane of wells can be induced by epoxy bonding of the GaAs/AlGaAs multilayer structure to a Si (100) support. The result is a quadrupole splitting of 55 kHz at 1.5-4.2 K. Differences in the spin lattice relaxation of the central versus satellite transitions of the ^71Ga signal are attributed to quenching of spin diffusion at the GaAs/AlGaAs boundary. Spin diffusion into the barrier regions influences the apparent nuclear spin lattice relaxation time in the wells, an effect we have modelled with the relaxation-diffusion equation. These calculations may be beneficial in NMR studies of the QHE.

Vitkalov, Sergey A.; Bowers, C. Russell; Reno, John L.; Simmons, Jerry A.

1998-03-01

166

Diamond nitrogen-vacancy center as a probe of random fluctuations in a nuclear spin ensemble  

NASA Astrophysics Data System (ADS)

New schemes that exploit the unique properties of nitrogen-vacancy (NV) centers in diamond are presently being explored as a platform for high-resolution magnetic sensing. Here we focus on the ability of a NV center to monitor an adjacent mesoscopic nuclear spin bath. For this purpose, we conduct comparative experiments where the NV spin evolves under the influence of surrounding 13C nuclei or, alternatively, in the presence of asynchronous alternating current fields engineered to emulate bath fluctuations. Our study reveals substantial differences that underscore the limitations of the semi-classical picture when interpreting and predicting the outcome of experiments designed to probe small nuclear spin ensembles. In particular, our study elucidates the NV center response to bath fluctuations under common pulse sequences, and explores a detection protocol designed to probe time correlations of the nuclear spin bath dynamics. Further, we show that the presence of macroscopic nuclear spin order is key to the emergence of semi-classical spin magnetometry.

Laraoui, Abdelghani; Hodges, Jonathan S.; Ryan, Colm A.; Meriles, Carlos A.

2011-09-01

167

Subsecond spin relaxation times in quantum dots at zero applied magnetic field due to a strong electron-nuclear interaction.  

PubMed

A key to ultralong electron spin memory in quantum dots (QDs) at zero magnetic field is the polarization of the nuclei, such that the electron spin is stabilized along the average nuclear magnetic field. We demonstrate that spin-polarized electrons in n-doped (In,Ga)As/GaAs QDs align the nuclear field via the hyperfine interaction. A feedback onto the electrons occurs, leading to stabilization of their polarization due to formation of a nuclear spin polaron [I. A. Merkulov, Phys. Solid State 40, 930 (1998)]. Spin depolarization of both systems is consequently greatly reduced, and spin memory of the coupled electron-nuclear spin system is retained over 0.3 sec at temperature of 2 K. PMID:17358564

Oulton, R; Greilich, A; Verbin, S Yu; Cherbunin, R V; Auer, T; Yakovlev, D R; Bayer, M; Merkulov, I A; Stavarache, V; Reuter, D; Wieck, A D

2007-03-07

168

Subsecond Spin Relaxation Times in Quantum Dots at Zero Applied Magnetic Field Due to a Strong Electron-Nuclear Interaction  

NASA Astrophysics Data System (ADS)

A key to ultralong electron spin memory in quantum dots (QDs) at zero magnetic field is the polarization of the nuclei, such that the electron spin is stabilized along the average nuclear magnetic field. We demonstrate that spin-polarized electrons in n-doped (In,Ga)As/GaAs QDs align the nuclear field via the hyperfine interaction. A feedback onto the electrons occurs, leading to stabilization of their polarization due to formation of a nuclear spin polaron [I. A. Merkulov, Phys. Solid State 40, 930 (1998).PSOSED1063-783410.1134/1.1130450]. Spin depolarization of both systems is consequently greatly reduced, and spin memory of the coupled electron-nuclear spin system is retained over 0.3 sec at temperature of 2 K.

Oulton, R.; Greilich, A.; Verbin, S. Yu.; Cherbunin, R. V.; Auer, T.; Yakovlev, D. R.; Bayer, M.; Merkulov, I. A.; Stavarache, V.; Reuter, D.; Wieck, A. D.

2007-03-01

169

Proposals of nuclear spin quantum memory in group-IV elemental and II-VI semiconductors  

NASA Astrophysics Data System (ADS)

Schemes for the nuclear spin quantum memory are proposed based on a system composed of two electrons or one electron coupled to a single nuclear spin in isotopically purified group-IV elemental and II-VI compound semiconductors. The qubit consists of the singlet state and one of the triplet states of two electrons or simply of an electron spin. These systems are free from the decoherence due to the nuclear dipole-dipole interaction and are advantageous for the long memory time. In the case of two electrons, the protocol for the quantum state transfer between the electron-spin qubit and the nuclear spin qubit is based on the magnetic or electric field tuning of the singlet-triplet state crossing and on the hyperfine coupling supplemented with a well-defined scheme to initialize the nuclear spin. In the case of a single-electron qubit, the quantum state transfer is driven by the hyperfine interaction itself without the need of the nuclear spin initialization. Many practical systems are considered, e.g., two electrons loaded on a Si or ZnSe quantum dot, a single-electron charged state in a Si quantum dot doped with a P atom, a single-electron charged S28i quantum dot doped with an isotope atom of S29i , and a localized electron system of Si:P and ZnSe:F in the bulk crystal. General aspects of these systems are investigated and a comparison of merits and demerits is made between the two-electron qubit and the single-electron qubit.

Çak?r, Özgür; Takagahara, Toshihide

2009-10-01

170

19F nuclear spin relaxation and spin diffusion effects in the single-ion magnet LiYF4:Ho3+  

NASA Astrophysics Data System (ADS)

Temperature and magnetic field dependences of the 19F nuclear spin-lattice relaxation in a single crystal of LiYF4 doped with holmium are described by an approach based on a detailed consideration of the magnetic dipole-dipole interactions between nuclei and impurity paramagnetic ions and nuclear spin diffusion processes. The observed non-exponential long time recovery of the nuclear magnetization after saturation at intermediate temperatures is in agreement with predictions of the spin-diffusion theory in a case of the diffusion limited relaxation. At avoided level crossings in the spectrum of electron-nuclear states of Ho3 + ions, rates of nuclear spin-lattice relaxation increase due to quasi-resonant energy exchange between nuclei and paramagnetic ions in contrast to the predominant role played by electronic cross-relaxation processes in the low-frequency ac-susceptibility.

Malkin, B. Z.; Vanyunin, M. V.; Graf, M. J.; Lago, J.; Borsa, F.; Lascialfari, A.; Tkachuk, A. M.; Barbara, B.

2008-11-01

171

Nuclear spin structure in dark matter search: The zero momentum transfer limit  

Microsoft Academic Search

We review the calculation of spin-dependent matrix elements relevant to\\u000ascattering of weakly interacting massive particles on nuclei. A comprehensive\\u000alist, to our knowledge, of the proton and neutron total spin expectation values\\u000a($<{\\\\bf S}_{p}>$ and $<{\\\\bf S}_{n}>$) calculated within different nuclear\\u000amodels is presented. These values allow a conclusion about the event rate\\u000aexpected in direct dark matter search

V. A. Bednyakov; F. Simkovic

2004-01-01

172

Intrinsic spin fluctuations reveal the dynamical response function of holes coupled to nuclear spin baths in (In,Ga)As quantum dots.  

PubMed

The problem of how single central spins interact with a nuclear spin bath is essential for understanding decoherence and relaxation in many quantum systems, yet is highly nontrivial owing to the many-body couplings involved. Different models yield widely varying time scales and dynamical responses (exponential, power-law, gaussian, etc.). Here we detect the small random fluctuations of central spins in thermal equilibrium [holes in singly charged (In,Ga)As quantum dots] to reveal the time scales and functional form of bath-induced spin relaxation. This spin noise indicates long (400 ns) spin correlation times at a zero magnetic field that increase to ?5???s as dominant hole-nuclear relaxation channels are suppressed with small (100 G) applied fields. Concomitantly, the noise line shape evolves from Lorentzian to power law, indicating a crossover from exponential to slow [?1/log(t)] dynamics. PMID:22681099

Li, Yan; Sinitsyn, N; Smith, D L; Reuter, D; Wieck, A D; Yakovlev, D R; Bayer, M; Crooker, S A

2012-05-03

173

Optical pumping of the electronic and nuclear spin of single charge-tunable quantum dots.  

PubMed

We present a comprehensive examination of optical pumping of spins in individual GaAs quantum dots as we change the net charge from positive to neutral to negative with a charge-tunable heterostructure. Negative photoluminescence polarization memory is enhanced by optical pumping of ground state electron spins, which we prove with the first measurements of the Hanle effect on an individual quantum dot. We use the Overhauser effect in a high longitudinal magnetic field to demonstrate efficient optical pumping of nuclear spins for all three charge states of the quantum dot. PMID:15783594

Bracker, A S; Stinaff, E A; Gammon, D; Ware, M E; Tischler, J G; Shabaev, A; Efros, Al L; Park, D; Gershoni, D; Korenev, V L; Merkulov, I A

2005-02-02

174

Synthesis of carbon-13 enriched disaccharides: lactose and sucrose  

SciTech Connect

Disaccharides can be prepared enzymatically and by chemical synthesis. Lactose enriched with carbon-13 at C-1 can be synthesized by reacting K/sup 13/CN with a sugar having a one fewer carbon than the desired product. Thus, a mixture of 4-O-..beta..-D-galactopyranosyl-D-(1-/sup 13/C)glucose ((1-/sup 13/C)lactose) and 4-O-..beta..-D-galactopyranosyl-D-(1-/sup 13/C)mannose can be synthesized from 3-O-..beta..-D-galactopyranosyl-D-arabinose and K/sup 13/CN. (/sup 13/C)Sucrose is conveniently prepared in gram quantities from D-(/sup 13/C)fructose and UDP-glucose in a reaction catalyzed by the enzyme sucrose synthetase. This reaction proceeds smoothly at 25/sup 0/ over a period of hours to give an equilibrium mixture which can be separated chromatographically. The glucose portion of sucrose can be labeled using enzymatically-prepared UDP-(/sup 13/C)glucose. Labeled sucrose is important for the preparation of labeled starches to be used for structural and metabolic studies.

Walker, T.E.; Unkefer, P.J.; Unkefer, C.J.; Ehler, D.S.

1986-05-01

175

Electronic structure and indirect spin-spin interactions in bournonite (CuPbSbS3) according to antimony nuclear quadrupole resonance  

NASA Astrophysics Data System (ADS)

A complex sulfide CuPbSbS3 (bournonite) has been studied by the nuclear quadrupole resonance on 121,123Sb. The temperature dependences of the spectroscopic and relaxation parameters in the temperature range of 10-295 K have been obtained. The crystallochemical features of the environment of the two non-equivalent Sb positions in the unit cell have been revealed from the nuclear quadrupole resonance spectra. The existence of the lattice vibrations with the frequency ? = 110 cm-1 has been demonstrated on the basis of the temperature dependence of the nuclear quadrupole resonance frequencies. Slow beats have been observed on the decay curve of the spin echo signal. Experimental data have been analyzed in order to reveal the existence of the indirect spin-spin interactions involving Sb atoms. The indirect spin-spin coupling constant has been estimated as J = 2.5 ± 0.5 kHz.

Orlova, A. Yu.; Gainov, R. R.; Dooglav, A. V.; Pen'kov, I. N.

2013-06-01

176

Theoretical aspects of dynamic nuclear polarization in the solid state--spin temperature and thermal mixing.  

PubMed

Dynamic nuclear polarization is a method which allows for a dramatic increase of the NMR signals due to polarization transfer between electrons and their neighboring nuclei, via microwave irradiation. These experiments have become popular in recent years due to the ability to create hyper-polarized chemically and biologically relevant molecules, in frozen glass forming mixtures containing free radicals. Three mechanisms have been proposed for the polarization transfer between electrons and their surrounding nuclei in such non-conducting samples: the solid effect and cross effect mechanisms, which are based on quantum mechanics and relaxation on small spin systems, and thermal mixing, which originates from the thermodynamic macroscopic notion of spin temperature. We have recently introduced a spin model, which is based on the density matrix formalism and includes relaxation, and applied it to study the solid effect and cross effect mechanisms on small spin systems. In this publication we use the same model to describe the thermal mixing mechanism, and the creation of spin temperature. This is obtained without relying on the spin temperature formalism. Simulations of small model systems are used on systems with homogeneously and inhomogeneously broadened EPR lines. For the case of a homogeneously broadened line we show that the nuclear enhancement results from the thermal mixing and solid effect mechanisms, and that spin temperatures are created in the system. In the inhomogeneous case the enhancements are attributed to the solid effect and cross effect mechanisms, but not thermal mixing. PMID:23160533

Hovav, Yonatan; Feintuch, Akiva; Vega, Shimon

2012-11-16

177

About long-lived nuclear spin states involved in para-hydrogenated molecules.  

PubMed

This study deals with a spin system constituted of three nonequivalent protons, two of them originating from para-hydrogen (p-H(2)) after a hydrogenation reaction carried out in the earth magnetic field. It is shown that three singlet states are created provided indirect (J) couplings exist between the three spins, implying hyperpolarization transfer toward the third spin. Upon insertion of the sample in the NMR (Nuclear Magnetic Resonance) high field magnet, the following events occur: (i) the longitudinal two-spin orders which are parts of the singlet states survive; (ii) the other two terms (of these singlet states) tend to be destroyed by magnetic field gradients but at the same time are partly converted into differences of longitudinal polarizations. Nuclear spin relaxation is studied by appropriate NMR measurements when evolution takes place in the high field magnet or in the earth field. In the former case, relaxation is classical although complicated by numerous relaxation rates associated with both longitudinal two-spin orders and longitudinal polarizations. In the latter case, an equilibration between the singlet states first occur, their disappearance being thereafter driven by relaxation rates which remain very small because of the absence of any dipolar contribution. Thus, even in the case of a three-spin system, long-lived states exist; this unexpected property could be very useful for many applications. PMID:17263430

Canet, Daniel; Bouguet-Bonnet, Sabine; Aroulanda, Christie; Reineri, Francesca

2007-02-01

178

Nuclear-Spin Selection Rules in the Chemistry of Interstellar Nitrogen Hydrides  

NASA Astrophysics Data System (ADS)

Nitrogen hydrides are at the root of the nitrogen chemistry in interstellar space. The detailed modeling of their gas phase formation, however, requires the knowledge of nuclear-spin branching ratios for chemical reactions involving multiprotonated species. We investigate in this work the nuclear-spin selection rules in both exothermic and near thermoneutral ion-molecule reactions involved in the synthesis of ammonia, assuming full scrambling of protons in the reaction complexes. The formalism of Oka [ J. Mol. Spectrosc. 2004, 228, 635 ] is employed for highly exothermic ion-molecule and dissociative recombination reactions. For thermoneutral reactions, a simple state-to-state statistical approach is suggested, which is in qualitative agreement with both quantum scattering and microcanonical statistical calculations. This model is applied to the seven atom reaction NH4+ + H2, of possible importance in the nuclear-spin thermalization of ammonia.

Rist, Claire; Faure, Alexandre; Hily-Blant, Pierre; Le Gal, Romane

2013-10-01

179

Nuclear magnetic relaxation in [sup 13]CH[sub 2] and [sup 13]CH[sub 3] coupled spin systems and variable angle spinning lineshape analysis for quadrupolar nuclei with half integer spins  

SciTech Connect

The carbon-13 multiplet spin-lattice relaxation in [sup 13]CH[sub 2] and [sup 13]CH[sub 3] spin systems is studied in detail by various nonselective and selective pulse techniques. Simultaneous fitting of the resulting relaxation curves with various rates and initial conditions allows for the extraction of both auto- and cross-correlated dipolar spectral densities which can provide detailed information on the molecular anisotropic reorientation. In addition, the [sup 13]CH[sub 3] coupled spin relaxation can characterize the methyl internal rotation dynamics. The cross-correlation between the dipolar and chemical shift anisotropy (CSA) interactions is found to be appreciable. Dipolar-CSA cross-correlated spectral densities introduce relaxation pathways that couple together magnetization modes with different spin inversion symmetries. Consideration of the dipolar-CSA cross-correlated spectral densities not only improves the accuracy of the measurement of dipolar spectral densities but also allows for the determination of the dipolar-CSA cross-correlated spectral densities themselves, providing a new measure of the anisotropy of the shielding tensor. NMR spectroscopy of quadrupolar nuclei in solids generally yields broad lines even when magic angle spinning is applied. Broadening of the central transition of quadrupolar nuclei with half integer spins is caused by the anisotropy of the second order quadrupolar interaction. A straightforward approach is presented that combines average Hamiltonian theory and a numerical solution of a classical banded matrix describing the equation of motion for a quadrupolar nucleus under variable angle sample spinning conditions. At either of two fourth rank magic angles, a simple three parameter lineshape is obtained, and the three breakpoints are related directly to the quadrupolar constant and its asymmetry parameter.

Zheng, Z.

1992-01-01

180

Theory for cross effect dynamic nuclear polarization under magic-angle spinning in solid state nuclear magnetic resonance: The importance of level crossings  

PubMed Central

We present theoretical calculations of dynamic nuclear polarization (DNP) due to the cross effect in nuclear magnetic resonance under magic-angle spinning (MAS). Using a three-spin model (two electrons and one nucleus), cross effect DNP with MAS for electron spins with a large g-anisotropy can be seen as a series of spin transitions at avoided crossings of the energy levels, with varying degrees of adiabaticity. If the electron spin-lattice relaxation time T1e is large relative to the MAS rotation period, the cross effect can happen as two separate events: (i) partial saturation of one electron spin by the applied microwaves as one electron spin resonance (ESR) frequency crosses the microwave frequency and (ii) flip of all three spins, when the difference of the two ESR frequencies crosses the nuclear frequency, which transfers polarization to the nuclear spin if the two electron spins have different polarizations. In addition, adiabatic level crossings at which the two ESR frequencies become equal serve to maintain non-uniform saturation across the ESR line. We present analytical results based on the Landau-Zener theory of adiabatic transitions, as well as numerical quantum mechanical calculations for the evolution of the time-dependent three-spin system. These calculations provide insight into the dependence of cross effect DNP on various experimental parameters, including MAS frequency, microwave field strength, spin relaxation rates, hyperfine and electron-electron dipole coupling strengths, and the nature of the biradical dopants.

Thurber, Kent R.; Tycko, Robert

2012-01-01

181

Theory for cross effect dynamic nuclear polarization under magic-angle spinning in solid state nuclear magnetic resonance: the importance of level crossings.  

PubMed

We present theoretical calculations of dynamic nuclear polarization (DNP) due to the cross effect in nuclear magnetic resonance under magic-angle spinning (MAS). Using a three-spin model (two electrons and one nucleus), cross effect DNP with MAS for electron spins with a large g-anisotropy can be seen as a series of spin transitions at avoided crossings of the energy levels, with varying degrees of adiabaticity. If the electron spin-lattice relaxation time T(1e) is large relative to the MAS rotation period, the cross effect can happen as two separate events: (i) partial saturation of one electron spin by the applied microwaves as one electron spin resonance (ESR) frequency crosses the microwave frequency and (ii) flip of all three spins, when the difference of the two ESR frequencies crosses the nuclear frequency, which transfers polarization to the nuclear spin if the two electron spins have different polarizations. In addition, adiabatic level crossings at which the two ESR frequencies become equal serve to maintain non-uniform saturation across the ESR line. We present analytical results based on the Landau-Zener theory of adiabatic transitions, as well as numerical quantum mechanical calculations for the evolution of the time-dependent three-spin system. These calculations provide insight into the dependence of cross effect DNP on various experimental parameters, including MAS frequency, microwave field strength, spin relaxation rates, hyperfine and electron-electron dipole coupling strengths, and the nature of the biradical dopants. PMID:22938251

Thurber, Kent R; Tycko, Robert

2012-08-28

182

Vector Model Of Electron Spin Echo Envelope Modulation Due To Nuclear Hyperfine And Zeeman Interactions  

SciTech Connect

The transverse electron spin magnetization of a paramagnetic center with effective spin S=? interacting with nonquadrupolar nuclei may be presented as a function of pairs of nuclei magnetization vectors which process around the effective magnetic field directions. Each vector of the pair starts its precession perpendicular to both effective fields. The FID signal is proportional to the scalar product of the vectors for nuclear spin I=?. The ESE signal can be described using two pairs of magnetization vectors. The ESE shape is not equal to two back-to-back FID signals except in the absence of ESE envelope modulation. A recursion relation is obtained which allows calculation of ESE signals for larger nuclear spins in the absence of NQI. This relation can be used to calculate the time course of the ESE signal for arbitrary nuclear spin as a function of the nuclear magnetization vectors. Although this formalism allows quantitative calculation of modulation from nuclei, it also provides a qualitative means of visualizing the modulation based on simple magnetization vectors.

Maryasov, Alexander G. (OFFICE OF FELLOWSHIP PROG); Bowman, Michael K. (BATTELLE (PACIFIC NW LAB)); Tsvetkov, Yuri D. (OFFICE OF FELLOWSHIP PROG)

2002-12-01

183

Fluorescence detection of single molecule magnetic resonance for pentacene in p-terphenyl. The hyperfine interaction of a single triplet spin with a single 13C nuclear spin  

NASA Astrophysics Data System (ADS)

We report the observation of the broadening of a magnetic-resonance transition between triplet sublevels of a single pentacene molecule owing to the interaction of the triplet electron spin with a single 13C nuclear spin. Analysis of this broadening allows the assignment of particular features in the fluorescence—excitation spectrum to pentacene molecules containing 13C isotopes in specific positions.

Köhler, J.; Brouwer, A. C. J.; Groenen, E. J. J.; Schmidt, J.

1994-09-01

184

Nuclear-Spin-Independent Short-Range Three-Body Physics in Ultracold Atoms  

SciTech Connect

We investigate three-body recombination loss across a Feshbach resonance in a gas of ultracold {sup 7}Li atoms prepared in the absolute ground state and perform a comparison with previously reported results of a different nuclear-spin state [N. Gross et al., Phys. Rev. Lett. 103, 163202 (2009)]. We extend the previously reported universality in three-body recombination loss across a Feshbach resonance to the absolute ground state. We show that the positions and widths of recombination minima and Efimov resonances are identical for both states which indicates that the short-range physics is nuclear-spin independent.

Gross, Noam; Shotan, Zav; Khaykovich, Lev [Department of Physics, Bar-Ilan University, Ramat-Gan, 52900 (Israel); Kokkelmans, Servaas [Eindhoven University of Technology, Post Office Box 513, 5600 MB Eindhoven (Netherlands)

2010-09-03

185

Optimal control of the inversion of two spins in Nuclear Magnetic Resonance  

NASA Astrophysics Data System (ADS)

We investigate the optimal control of the inversion of two spin 1/2 particles in Nuclear Magnetic Resonance. The two spins, which differ by their resonance offset, are controlled by the same radio frequency magnetic field. Using the Pontryagin Maximum Principle, we compute the optimal control sequence which allows to reach the target state in a given time, while minimizing the energy of the magnetic field. A comparison with the time-optimal solution for bounded control amplitude realizing the same control in the same time is made. An experimental illustration is done using techniques of Nuclear Magnetic Resonance.

Assémat, E.; Attar, L.; Penouilh, M.-J.; Picquet, M.; Tabard, A.; Zhang, Y.; Glaser, S. J.; Sugny, D.

2012-09-01

186

Electronic population effect in halogen nuclear spin - lattice relaxation in praseodymium trihalide compounds  

Microsoft Academic Search

Nuclear quadrupole resonance determinations of the spin - lattice relaxation rates of the 0953-8984\\/8\\/42\\/018\\/img7, 0953-8984\\/8\\/42\\/018\\/img8 and 0953-8984\\/8\\/42\\/018\\/img9 nuclei in the praseodymium trihalide crystals 0953-8984\\/8\\/42\\/018\\/img10 and 0953-8984\\/8\\/42\\/018\\/img11 are reported. Data are presented in the temperature range 7 - 297 K. They are shown to be dominated by magnetic dipole interactions between the halogen nuclear spins and the 0953-8984\\/8\\/42\\/018\\/img12 paramagnetic ions. The

Sunyu Su; Pablo Prado; Robin L. Armstrong; Mariano Zuriaga

1996-01-01

187

Studies of nuclear rotational bands with the spin spectrometer  

Microsoft Academic Search

In the last few years increasingly sophisticated gamma-ray spectrometer arrays have been built at a number of laboratories around the world. These instruments, coupled with versatile heavy-ion accelerators, are capable of probing the detailed behaviour of atomic nuclei under extreme conditions of angular momentum and temperature. Characteristics of one such detector array, the Spin Spectrometer at Oak Ridge National Laboratory,

L. L. Riedinger; M. P. Carpenter; L. H. Courtney; V. P. Janzen

1987-01-01

188

Robust few-electron quantum dot devices in nuclear spin engineered Si/SiGe  

NASA Astrophysics Data System (ADS)

Spins in gate-defined quantum dots are currently discussed as one of the most promising scalable qubit architecture. Since the identification of the hyperfine interaction as a dominant spin qubit decoherence mechanism, Si/SiGe heterostructures have been receiving steadily increasing attention for realizing devices almost free of nuclear spin carrying isotopes. Building Si/SiGe heterostructures from material enriched in nuclear spin-free isotopes brings new perspectives of reaching a regime of further improved decoherence times compared to Si/SiGe of natural isotope composition. In such isotopically engineered heterostructures, the decoherence is predicted to no longer be governed by the hyperfine interaction with the nuclear spin bath, but solely by dipolar interactions. In the first part of my presentation I will review the development of two-dimensional electron systems in 28Si for spin qubit applications in my group and discuss few electron double quantum dot devices based on these heterostructures. Being able to avoid hyperfine-induced decoherence then brings a second major limitation for the realization of robust spin qubits into focus. Indeed, the manipulation of such qubits relies on Coulomb interactions, enabling electronic noise to cause decoherence. Charge traps in the heterostructure may contribute to decoherence through a fluctuation of charges or through dipolar interactions of the spin degree of freedom of the trap and the qubit. In the second part of my talk I will present our recent study of charge noise in modulation-doped Si/SiGe heterostructures and discuss device and heterostructure designs which efficiently suppress charge noise.

Bougeard, Dominique

2013-03-01

189

High-resolution spectroscopy of single NV defects coupled with nearby 13C nuclear spins in diamond  

NASA Astrophysics Data System (ADS)

We report a systematic study of the hyperfine interaction between the electron spin of a single nitrogen-vacancy (NV) defect in diamond and nearby 13C nuclear spins, by using pulsed electron-spin resonance spectroscopy. We isolate a set of discrete values of the hyperfine coupling strength ranging from 14 MHz to 400 kHz and corresponding to 13C nuclear spins placed at different lattice sites of the diamond matrix. For each lattice site, the hyperfine interaction is further investigated through nuclear-spin polarization measurements and by studying the magnetic field dependence of the hyperfine splitting. This work provides information that is relevant for the development of nuclear-spin-based quantum register in diamond.

Dréau, A.; Maze, J.-R.; Lesik, M.; Roch, J.-F.; Jacques, V.

2012-04-01

190

Realization of quantum non-demolition measurement of nuclear spin 1\\/2 of cold ytterbium atom  

Microsoft Academic Search

We have demonstrated a quantum non-demolition (QND) measurement with a collective spin of cold ytterbium atoms (171Yb) via Faraday rotation interaction, and have observed 1.8-1.5+2.4 dB spin squeezing. Since 171Yb atoms have only a nuclear spin of one-half in the ground state, the system constitutes the simplest spin ensemble and is thus robust against decoherence. Furthermore, we have considered the

T. Takano; R. Namiki; Y. Takahashi

2009-01-01

191

NMR Investigation of Optical Polarization of Nuclear Spins in GaAs  

NASA Astrophysics Data System (ADS)

Light-induced nuclear spin alignments have been measured in GaAs as a function of photon energy, irradiation time, and sample temperature using NMR spectroscopy at 9.4 Tesla and 10 to 50 K. Significant optical enhancements were observed at a range of photon energies, starting just below the band gap and persisting through 100 meV above the gap. Irradiation above the band gap resulted in thermally activated NMR signal enhancements while sub band gap irradiation did not. Short and long irradiation time dependencies revealed insights into the nature of cross relaxation between electronic nuclear spins, contradicting mechanisms based on either localized electron-nuclear contact at defect sites or cross relaxation between nuclei and free electrons. We propose that the presence of a mobile or delocalized enabling electronic species characterized by a long electron-nuclear correlation time, such as an exciton, is necessary in any mechanism which explains the data.

Paravastu, Anant; Hayes, Sophia; Schwickert, Birgit; Reimer, Jeffrey; Dinh, Long; Balooch, Mehdi

2003-03-01

192

The nuclear spin-isospin response to quasifree nucleon scattering  

SciTech Connect

The Neutron-Time-of-Flight (NTOF) facility at LAMPF has been used to measure complete sets of polarization-transfer coefficients for quasifree ({ital {rvec p}},{ital {rvec n}}) scattering from {sup 2}H, {sup 12}C, and {sup 40}Ca at 494 MeV and scattering angles of 12.5{degree}, 18{degree}, and 27{degree} ({ital q}=1.2, 1.7, 2.5 fm{sup {minus}1}). These measurements yield separated transverse ({sigma}{times}{bold q}) and longitudinal ({sigma}{center_dot}q) isovector spin responses. Comparison of the separated responses to calculations and to electron-scattering responses reveals a strong enhancement in the spin transverse channel. This excess transverse strength masks the effect of pionic correlations in the response ratio.

Taddeucci, T.N. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1995-07-15

193

Korringa-Like Nuclear Spin-Lattice Relaxation in a 2DES at ?= 1/2  

NASA Astrophysics Data System (ADS)

Via a resistively-detected NMR technique, the nuclear spin lattice relaxation time T1 of ^71Ga at low temperatures has been measured in a GaAs/AlGaAs heterostructure containing two weakly-coupled 2D electron systems (2DES), each at Landau level filling ?= 1/2. Incomplete electronic spin polarization, which has been reported previously [1,2] for low density 2DESs at ?= 1/2, should facilitate hyperfine- coupled nuclear spin relaxation owing to the presence of both electron spin states at the Fermi level. Within composite fermion theory, a Korringa law temperature dependence: T1T = constant, is expected for temperatures T<1 K. Our measurements made at temperatures in the range 35 mK nuclear spin relaxation mechanisms in this system.[1] I. V. Kukushkin, K. v. Klitzing, and K. Eberl. Phys. Rev. Lett. 82, 3665 (1999); A. E. Dementyev, et al., Phys. Rev. Lett. 83, 5074 (1999); S. Melinte, et al., Phys. Rev. Lett. 84, 354 (2000).[2] I.B. Spielman, L.A. Tracy, J.P. Eisenstein, L.N. Pfeiffer, K.W. West, condmat/0410092.This work was supported by the DOE, NSF, and NDSEG.

Tracy, L. A.; Pfeiffer, L. N.

2005-03-01

194

Nuclear enhancement of the spin Hall angle in n-InxGa1-xAs  

NASA Astrophysics Data System (ADS)

We present measurements of the inverse spin Hall effect in vertical Fe/InxGa1-xAs heterostructures as identified via a Hanle effect in the local Hall voltage. The spin Hall angle is greatly enhanced in the presence of polarized nuclei, achieving typical values of ?˜5x10-2. Phenomenological modeling of the observed line-shapes shows that the nuclear polarization acts as a linear prefactor to the standard spin Hall conductivity. This enhancement far exceeds expectations based on the energy splitting of the electron or nuclear spin systems. Our samples are doped just above the Mott transition (n˜3nc) where metallic impurity band conduction is dominant. A strong coupling between localized moments and delocalized states is evidenced by the temperature dependence and sensitivity to disorder at higher In concentrations. This leads us to interpret our results using an Anderson-like model of polarized impurities whereby both dynamic nuclear polarization and resonant skew scattering arise as a result of a spin polarized doubly occupied (D^-) impurity band.

Geppert, Chad; Christie, Kevin; Chan, Mun; Hu, Qi; Palmstrøm, Chris; Crowell, Paul

2012-02-01

195

Phase transitions in dissipative quantum transport and mesoscopic nuclear spin pumping  

NASA Astrophysics Data System (ADS)

Topological phase transitions can occur in the dissipative dynamics of a quantum system when the ratio of matrix elements for competing transport channels is varied. Here we establish a relation between such behavior in a class of non-Hermitian quantum walk problems [M. S. Rudner and L. S. Levitov, Phys. Rev. Lett. 102, 065703 (2009)10.1103/PhysRevLett.102.065703] and nuclear spin pumping in double quantum dots, which is mediated by the decay of a spin-blockaded electron triplet state in the presence of spin-orbit and hyperfine interactions. The transition occurs when the strength of spin-orbit coupling exceeds the strength of the net hyperfine coupling and results in the complete suppression of nuclear spin pumping. Below the transition point, nuclear pumping is accompanied by a strong reduction in current due to the presence of nondecaying “dark states” in this regime. Due to its topological character, the transition is expected to be robust against dephasing of the electronic degrees of freedom.

Rudner, M. S.; Levitov, L. S.

2010-10-01

196

Anomalous nuclear spin relaxation of adsorbed helium-3  

Microsoft Academic Search

Within the framework of a general theory of two-dimensional NMR we are able to elucidate certain anomalous features of spin relaxation in adsorbed and porous systems. We explain the linear dependence of relaxation time on applied magnetic field, and this is demonstrated to be related to the relative insensitivity ofT1to temperature. We also show thatT1remains field dependent on the “fast”

Brian P. Cowan

1983-01-01

197

Description of Nuclear Reactions of Particles with Spin  

NASA Astrophysics Data System (ADS)

As for nuclear reactions of spinless particles (this is the only case and the simplest one normally treated in lectures and textbooks) scattering amplitudes between entrance and exit states are a useful tool for the description of two-particle nuclear reactions.

Schieck, Hans Paetz Gen.

198

Photochemically Induced Dynamic Nuclear Polarization (Photo-CIDNP) Magic-Angle Spinning NMR  

Microsoft Academic Search

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is non-Boltzmann nuclear magnetization which can be observed\\u000a by NMR spectroscopy as enhanced absorptive (positive) or emissive (negative) signals. In solids, photo-CIDNP has been observed\\u000a since its discovery in 1994 in various photosynthetic reaction centers (RCs) by magic angle spinning (MAS) solid-state NMR.\\u000a The photo-CIDNP effect in solids can be explained by a combination

Eugenio Daviso; Gunnar Jeschke; Jörg Matysik

199

Muon spin relaxation and hyperfine-enhanced Pr141 nuclear spin dynamics in Pr(Os,Ru)4Sb12 and (Pr,La)Os4Sb12  

NASA Astrophysics Data System (ADS)

Zero- and longitudinal-field muon spin relaxation experiments have been carried out in the alloy series Pr(Os1-xRux)4Sb12 and Pr1-yLayOs4Sb12 to elucidate the anomalous dynamic muon spin relaxation observed in these materials. The damping rate ? associated with this relaxation varies with temperature, applied magnetic field, and dopant concentrations x and y in a manner consistent with the “hyperfine enhancement” of Pr141 nuclear spins first discussed by Bleaney [Physica (Utrecht) 69, 317 (1973)]. This mechanism arises from Van Vleck-like admixture of magnetic Pr3+ crystalline-electric-field-split excited states into the nonmagnetic singlet ground state by the nuclear hyperfine coupling, thereby increasing the strengths of spin-spin interactions between Pr141 and muon spins and within the Pr141 spin system. We find qualitative agreement with this scenario and conclude that electronic spin fluctuations are not directly involved in the dynamic muon spin relaxation.

Shu, Lei; Maclaughlin, D. E.; Aoki, Y.; Tunashima, Y.; Yonezawa, Y.; Sanada, S.; Kikuchi, D.; Sato, H.; Heffner, R. H.; Higemoto, W.; Ohishi, K.; Ito, T. U.; Bernal, O. O.; Hillier, A. D.; Kadono, R.; Koda, A.; Ishida, K.; Sugawara, H.; Frederick, N. A.; Yuhasz, W. M.; Sayles, T. A.; Yanagisawa, T.; Maple, M. B.

2007-07-01

200

Using spin fluctuations to reveal long hole spin lifetimes and hole-nuclear coupling in (In,Ga)As quantum dots  

NASA Astrophysics Data System (ADS)

``Spin noise spectroscopy'' is a recently-developed technique for passively measuring the spin dynamics of electrons and holes via their intrinsic random spin fluctuations. In accord with the fluctuation-dissipation theorem, the frequency spectra of this spin noise alone reveals spin dephasing times and Land'e g-factors. Using these methods we measure hole spins confined in self-assembled (In,Ga)As/GaAs quantum dots (QDs). Owing to their p-type wavefunctions, holes experience much less hyperfine interaction with lattice nuclei as compared with confined electrons, leading in principle to long spin decoherence times which are favorable for potential qubit applications. We observe very long hole spin correlation times (˜400 ns) in zero magnetic field, ultimately limited by dephasing from hole-nuclear hyperfine interactions. Suppressing this dephasing with small longitudinal fields (< 100 G) directly reveals the hyperfine coupling strength, and unveils intrinsic hole spin relaxation times up to ˜5 ?s. Importantly, the lineshape of the noise evolves from a Lorentzian to a power-law as the hole-nuclear dephasing is suppressed.

Li, Yan; Crooker, S. A.; Reuter, D.; Wieck, A. D.; Yakovlev, D. R.; Bayer, M.

2012-02-01

201

Nuclear spin temperatures of hydrogen and water molecules on amorphous solid water  

NASA Astrophysics Data System (ADS)

To clarify the meaning of the nuclear spin temperatures of H2 and H2O molecules associated with various astronomical targets, it is important to understand the mechanisms that could alter these temperatures; i.e., the molecules' ortho/para nuclear-spin ratio (OPR). We have performed a series of experiments to investigate how the OPRs of H2 and H2O behave on the surface of amorphous solid water (ASW), which is analogous to cosmic ice dust. The OPR of H2 initially shows a high temperature limit of 3 upon its formation through H-H recombination at ~10 K and gradually decreases toward lower temperatures on the surface. The spin temperatures of H2O molecules that are thermally desorbed from various types of ASW at ~10 K always return the high-temperature limit.

Watanabe, Naoki; Hama, Tetsuya; Kouchi, Akira

2013-06-01

202

Nuclear Spin Measurements in Some Nuclides of the Alkali Elements Rubidium and Francium.  

National Technical Information Service (NTIS)

The nuclear spins of several nuclides of the alkali elements rubidium and francium have been measured using atomic-beam magnetic resonance techniques. The following results have been obtained: exp 77 Rb I = 3/2, exp 78 Rb I = 0 sup(78m)Rb I = 4, exp 79 Rb...

C. Ekstroem S. Ingleman G. Wannberg M. Skarestad

1977-01-01

203

Angular dependence of nuclear spin echo decay in thin-film yttrium iron garnet  

Microsoft Academic Search

The angular dependence of the nuclear spin echo decay of 57Fe in monocrystalline thin-film Y3Fe5O12 was measured. The experimental results for the octahedral Fe3+ a-ions were explained by the orientation fluctuations of the electron magnetization about the local symmetry axis.

G. N. Abelyashev; S. N. Polulyah; V. N. Berzhanskij; N. A. Sergeev

1995-01-01

204

Nuclear spin dependence of the reaction of H3+ with H2. I. Kinetics and modeling  

NASA Astrophysics Data System (ADS)

The chemical reaction H3+ + H2 --> H2 + H3+ is the simplest bimolecular reaction involving a polyatomic, yet is complex enough that exact quantum mechanical calculations to adequately model its dynamics are still unfeasible. In particular, the branching fractions for the ``identity,'' ``proton hop,'' and ``hydrogen exchange'' reaction pathways are unknown, and to date, experimental measurements of this process have been limited. In this work, the nuclear-spin-dependent steady-state kinetics of the H3+ + H2 reaction is examined in detail, and employed to generate models of the ortho:para ratio of H3+ formed in plasmas of varying ortho:para H2 ratios. One model is based entirely on nuclear spin statistics, and is appropriate for temperatures high enough to populate a large number of H3+ rotational states. Efforts are made to include the influence of three-body collisions in this model by deriving nuclear spin product branching fractions for the H5+ + H2 reaction. Another model, based on rate coefficients calculated using a microcanonical statistical approach, is appropriate for lower-temperature plasmas in which energetic considerations begin to compete with the nuclear spin branching fractions. These models serve as a theoretical framework for interpreting the results of laboratory studies on the reaction of H3+ with H2.

Crabtree, Kyle N.; Tom, Brian A.; McCall, Benjamin J.

2011-05-01

205

Nuclear spin-lattice relaxation of 195Pt between 10 mK and 1 K  

Microsoft Academic Search

The nuclear spin-lattice relaxation time tau1 of 195Pt has been measured between 10 mK and 1 K in a magnetic field of 0.045 T. The data agree with Korringa's relation kappa = tau1T with kappa = 29.6 msK.

M. I. Aalto; H. K. Collan; R. G. Gylling; K. O. Nores

1972-01-01

206

A spin polarizer for radioactive nuclear beams by taking advantage of polarized electron transfer reactions  

Microsoft Academic Search

A versatile spin polarizer for radioactive nuclear beams is proposed for spectroscopic studies of exotic nuclei far from stability. The polarizer takes advantage of the polarized electron transfer process, as in the optically pumped polarized proton ion sources. The feasibility of the polarizer has been experimentally investigated at the test stand. Successful results are reported.

T. Shimoda; S. Shimizu; E. Doumoto; M. Yagi; M. Asai; M. Nakamura; Y. Hirayama; K. Horie; T. Shigematsu; H. Izumi; N. Takahashi

2002-01-01

207

Reanalysis of nuclear spin matrix elements for dark matter spin-dependent scattering  

NASA Astrophysics Data System (ADS)

We show how to include in the existing calculations for nuclei other than Xe129 and Xe131 the corrections to the isovector coupling arising in chiral effective field theory recently found in Menendez et al. [Phys. Rev. D 86, 103511 (2012)PRVDAQ1550-7998]. The dominant, momentum-independent, two-body current effect can be taken into account by formally redefining the static spin matrix elements ?Sp,n?. By further using the normalized form factor at q?0 built with the one-body level structure functions, we show that the weakly interacting massive particles (WIMP)-nucleus cross section and the upper limits on the WIMP-nucleon cross sections coincide with the ones derived by using the exact functions at the two-body level. We explicitly show it in the case of XENON100 limits on the WIMP-neutron cross section, and we recalculate the limits on the WIMP-proton spin-dependent cross section set by COUPP. We also give practical formulas to obtain ?Sp,n? given the structure functions in the various formalisms and notations existing in the literature. We argue that the standard treatment of the spin-dependent cross section in terms of three independent isospin functions, S00(q), S11(q), and S01(q), is redundant in the sense that the interference function S01(q) is the double product |S01(q)|=2S00(q)S11(q) even when including the new effective field theory corrections.

Cannoni, M.

2013-04-01

208

Rabi and Larmor nuclear quadrupole double resonance of spin-1 nuclei  

NASA Astrophysics Data System (ADS)

We demonstrate the creation of two novel double-resonance conditions between spin-1 and spin-1/2 nuclei in a crystalline solid. Using a magnetic field oscillating at the spin-1/2 Larmor frequency, the nuclear quadrupole resonance (NQR) frequency is matched to the Rabi or Rabi plus Larmor frequency, as opposed to the Larmor frequency as is conventionally done. We derive expressions for the cross-polarization rate for all three conditions in terms of the relevant secular dipolar Hamiltonian, and demonstrate with these expressions how to measure the strength of the heterogenous dipolar coupling using only low magnetic fields. In addition, the combination of different resonance conditions permits the measurement of the spin-1/2 angular momentum vector using spin-1 NQR, opening up an alternate modality for the monitoring of low-field nuclear magnetic resonance. We use ammonium nitrate to explore these resonance conditions, and furthermore use the oscillating field to increase the signal-to-noise ratio per time by a factor of 3.5 for NQR detection of this substance.

Prescott, D. W.; Malone, M. W.; Douglass, S. P.; Sauer, K. L.

2012-12-01

209

Nuclear orientation of radon isotopes by spin-exchange optical pumping  

SciTech Connect

This paper reports the first demonstration of nuclear orientation of radon atoms. The method employed was spin exchange with potassium atoms polarized by optical pumping. The radon isotopes were produced at the ISOLDE isotope separator of CERN. The nuclear alignment of /sup 209/Rn and /sup 223/Rn has been measured by observation of ..gamma..-ray anisotropies and the magnetic dipole moment for /sup 209/Rn has been measured by the nuclear-magnetic-resonance method to be chemically bond..mu..chemically bond = 0.838 81(39)..mu../sub N/.

Kitano, M.; Calaprice, F.P.; Pitt, M.L.; Clayhold, J.; Happer, W.; Kadar-Kallen, M.; Musolf, M.; Ulm, G.; Wendt, K.; Chupp, T.

1988-05-23

210

High-Spin Isomeric States in Nuclear Reactions Induced by He Isotopes  

NASA Astrophysics Data System (ADS)

The high-spin states production in nuclear reactions is reviewed. The analysis of various experiments, our estimates and calculations reveal that in different compound nucleus energy regions maximal relative yield of high-spin states can be realized by different projectiles: at low energies -- by neutrons, in ˜ 20 -- 50 MeV region -- by ?-particles, at higher energies -- by heavy ions. It was predicted [1] that there are energy ranges in which neutron-rich radioactive ions (^6,8He, for example) are favorable. ?m/?g (the ratio between the yields of high-spin Jm and low-spin Jg metastable states of a nucleus in one and the same reaction) e.g. the isomeric cross-section ratio is a very good indicator of high-spin states production capability of a nuclear reaction. These experiments demonstrate that maximal values of isomeric cross-section ratios (up to 30) are obtained in ?-particle induced reactions. Experiment with ^6He beam [2] confirms the predictions of the work [1] concerning the prospects of neutron-rich radioactive-ion beams in high-spin states population. The results of calculations of the isomeric cross section ratios using the code EMPIRE-II-18 approach to statistical theory of nuclear reactions demonstrate rather good agreement with the experimental data. Due to that these prediction power of these calculation is confirmed. The results of widespread calculations of the isomeric cross-section ratios of the reactions with ^6,8He are presented. [1] T.V.Chvilskaya et al., AIP-Conference Proceedings ENAM-98 1998. V. 455. P. 482. [2] P.A.DeYoung et al., Phys.Rev.C. 2000. V. 62. P.047601.

Chuvilskaya, Tatjana; Shirokova, Alla

2010-11-01

211

Natural reference for nuclear high-spin states  

SciTech Connect

We suggest two new representations of the data on rotational nuclei. The first is reference-free and the second arises from a natural reference related to the variable moment of inertia model parameters of the ground-state band of the system. As such, neither representation contains any free parameters. By defining a 'configuration spin' we show how a new ground-state band reference can be applied. Its use allows a complete description of the changes associated with the first, and higher, band crossings. We apply these new representations to discuss the nature of the first band crossing along even-even isotopic chains in the erbium and osmium isotopes and to odd-even nuclei in the vicinity of {sup 158}Er.

Rowley, Neil; Ollier, James; Simpson, John [UMR 8608, Universite de Paris Sud/IN2P3, Division de Physique Theorique, Institut de Physique Nucleaire, F-91406 Orsay Cedex (France); STFC Daresbury Laboratory, Daresbury, Warrington WA44AD (United Kingdom)

2009-08-15

212

Relativistic impulse approximation, nuclear currents, and the spin-difference function  

NASA Astrophysics Data System (ADS)

Traditional nonrelativistic impulse-approximation treatments of p-nucleus scattering using a local nucleon-nucleon t matrix neglect nuclear currents which are intrinsic to relativistic approaches also employing a local t matrix. Inclusion of these current terms is essen- tial to understanding the spin-difference function (Dqk+Dkq) +i(P-Ay), as shown by comparison with 12C(p,p')12C*(12.71 MeV, 1+, T=0) spin-difference data at 150 MeV.

Sparrow, D. A.; Piekarewicz, J.; Rost, E.; Shepard, J. R.; McNeil, J. A.; Carey, T. A.; McClelland, J. B.

1985-05-01

213

Magnetic equivalence of terminal nuclei in the azide anion broken by nuclear spin relaxation  

NASA Astrophysics Data System (ADS)

NMR spectra of water solution of sodium azide selectively 15N labelled in the central position were studied using an iterative least-squares method. In agreement with predictions based on Bloch-Wangsness-Redfield nuclear spin relaxation theory, it is demonstrated that quadrupolar relaxation of the magnetically equivalent terminal 14N (spin-1) nuclei in the azide anion renders the J coupling between these nuclei an observable quantity. In isotropic fluids, this seems to be the first experimental evidence of relaxation-broken magnetic equivalence symmetry.

Bernatowicz, P.; Szyma?ski, S.

214

Cell Potassium by K39 Spin Echo Nuclear Magnetic Resonance.  

National Technical Information Service (NTIS)

Pulsed nuclear magnetic resonance (NMR) measurements of K39 in solutions and bacteria were made, by the use of a super-conducting magnet with a field of 50,300 gauss, which provides the necessary increase in sensitivity. Transverse relaxation time (T2) of...

F. W. Cope R. Damadian

1970-01-01

215

Magnetic-field cycling triplet-DNP/NMR system for true quantum computation with hyperpolarized nuclear spins  

NASA Astrophysics Data System (ADS)

Toward NMR quantum computing with hyperpolarization beyond the entanglement threshold, a system has been developed enabling dynamic nuclear polarization (DNP) using photo-excited triplet electron spins with X-band microwave apparatus, followed by solid-state NMR experiments using the polarized nuclear spin system. In order to perform the triplet-DNP and NMR experiments in different magnetic fields, the triplet-DNP system and the NMR system are made to be spatially separated, between which the sample can be shuttled. It is shown that the system developed in this work fulfils the requirements for solid-state NMR quantum computing with hyperpolarized nuclear spin systems.

Kagawa, A.; Negoro, M.; Takeda, K.; Kitagawa, M.

2009-04-01

216

Isovector spin observables in nuclear charge reactions at LAMPF  

SciTech Connect

LAMPF has undertaken a major development program to upgrade facilities for nuclear charge-exchange studies at intermediate energies. The major components of this upgrade are a medium-resolution spectrometer and neutron time-of-flight system for good resolution (delta E < 1 MeV) charge-exchange perograms in (n,p) and (p,n) respectively. Major emphasis is placed on polarization phenomena using polarized beams and analyzing the polarization of the outgoing particle.

McClelland, J.B.

1988-01-01

217

Investigation of a new model of dipolar-coupled nuclear spin relaxation and applications of dynamic nuclear polarization  

NASA Astrophysics Data System (ADS)

This work presents the results of various investigations using various techniques of hyperpolarizing the nuclei of atoms. Hyperpolarization implies magnetic order in excess of the thermal order obtained naturally as described by Curie's law. The main portion of this work presents the results of a detailed experimental exploration of predictions arising from a new model of transverse nuclear spin relaxation in quantum systems, based on possible manifestations of microscopic chaos in quantum systems. Experiments have been carried out on a number of hyperpolarized xenon samples, each differing in its relative percentage of xenon isotopes in order to vary the homonuclear and heteronuclear dipole couplings in the spin system. The experiments were performed under a variety of conditions in an attempt to observe the behaviors predicted by the model. Additionally, much more extensive measurements were made on a number of samples of solid CaF2 in both single crystal and powder forms. These samples, although thermally polarized, were observed with superior signal to noise ratios than even the hyperpolarized xenon solids, allowing for more precise measurements for comparison to the theory. This work thus contains the first experimental evidence for the majority of the model's predictions. Additionally, this work contains the first precise measurements of the frequency-shift enhancement parameters for 129Xe and krypton in the presence of spin-polarized Rb. The determination of these important numbers will be useful to many groups who utilize spin-exchange optical pumping in their labs. This work built on the prior knowledge of a precise number for the frequency-shift enhancement parameter of 3He in Rb vapor. Finally, I detail work using NMR to detect nuclear-spin polarization enhancement in silicon phosphorus by a novel, photo-induced hyperpolarization technique developed by the Boehme research group at the University of Utah. Significant nuclear polarization enhancements were observed by the Boehme group due to electron-photon interactions in semiconductor soilds; these enhancements were observed by their effects on the ambient electrons and measured with electron spin resonance techniques. The work described here details experiments to observe the enhanced nuclear polarization by directly measuring the intensity increase in an NMR measurement. I will conclude this dissertation with a brief appendix giving a summary of one additional project involving the use of high pressure fluorinated gas NMR to measure the internal topology and characteristics of energy-rich oil shales.

Sorte, Eric G.

218

Room-temperature high-speed nuclear-spin quantum memory in diamond  

NASA Astrophysics Data System (ADS)

Quantum memories provide intermediate storage of quantum information until it is needed for the next step of a quantum algorithm or a quantum communication process. Relevant figures of merit are therefore the fidelity with which the information can be written and retrieved, the storage time, and also the speed of the read-write process. Here, we present experimental data on a quantum memory consisting of a single 13C nuclear spin that is strongly coupled to the electron spin of a nitrogen-vacancy (NV) center in diamond. The strong hyperfine interaction of the nearest-neighbor carbon results in transfer times of 300 ns between the register qubit and the memory qubit, with an overall fidelity of 88% for the write-storage-read cycle. The observed storage times of 3.3 ms appear to be limited by the T1 relaxation of the electron spin. We discuss a possible scheme that may extend the storage time beyond this limit.

Shim, J. H.; Niemeyer, I.; Zhang, J.; Suter, D.

2013-01-01

219

Exactly solvable spin dynamics of an electron coupled to a large number of nuclei; the electron-nuclear spin echo in a quantum dot  

SciTech Connect

The model used to describe the spin dynamics in quantum dots after optical excitation is considered. Problems of the electron-spin polarization decay and the dependence of the steady-state polarization on magnetic field are solved on the basis of exact diagonalization of the model Hamiltonian. An important role of the nuclear state is shown and methods of its calculation for different regimes of optical excitation are proposed. The effect of spin echo generation after application of a {pi} pulse of a magnetic field is predicted for the system under consideration.

Kozlov, G. G. [St. Petersburg State University, Institute of Physics (Russian Federation)], E-mail: gkozlov@photonics.phys.spbu.ru

2007-10-15

220

Spectroscopic Measurement of LEAD-204 Isotope Shift and LEAD-205 Nuclear Spin.  

NASA Astrophysics Data System (ADS)

The isotope shift of ('204)Pb and the nuclear spin of 1.4 x 10('7)-y ('205)Pb was determined from a high -resolution optical measurement of the 6p('2) ('3)P(,o) -6p7s('3)P(,1)('o) 283.3-nm resonance line. The value of the shift, relative to ('208)Pb is -140.2(8) x 10('-3)cm(' -1), the negative sign indicating a shift to lower wave numbers. The precision is 3-4 times greater than that of previous measurements. The spin of ('205)Pb l = 5/2 was obtained from the measurement of the relative intensities of its three hyperfine components. This method of absorption spectroscopy determination of ground state nuclear spin is applicable to any stable or longlived isotope. High resolution optical absorption spectra were obtained with a 25.4cm diffraction grating in a 9.1m focal length Czerny-Turner spectrometer. A signal-averaging scanning technique was used to record the spectra. Increased precision in the isotope shift measurement was attained by using separated isotope samples of ('204)Pb and ('207)Pb. A controlled amount of the later was incorporated in the absorption cell to provide internal calibration by its 6p7s ('3)P(,1)('o) hfs separation. Absorption spectra were recorded for several optical thicknesses of the absorber. A single spin value of increased precision was derived from the entire set of combined data.

Schonberger, Peter

221

Electron-nuclear spin coupling in nano-scale devices: self-sustaining resistance oscillations and controlled multiple quantum coherences  

NASA Astrophysics Data System (ADS)

Author: G Yusa, K. Muraki, K. Takashina (NTT BRL), K. Hashimoto (SORST-JST), and Y. Hirayama (NTT BRL and SORST-JST). We studied electron-nuclear spin coupled systems implemented in microscopic fractional quantum Hall devices and found that in a constant voltage measurement, the longitudinal resistance of such devices oscillates self-sustainingly with a period of about 200 sec. Such behavior suggests that the average nuclear spin polarization self-sustainingly oscillates between randomized and polarized states. When the resistance is measured in constant current mode, on the other hand, nuclear spins are polarized and reach a steady state in about 200 sec. Using the polarized state as an initial state, quantum mechanical superpositional states between four nuclear spin states (multiple quantum coherence) are controlled by pulsed radio frequency radiation resonant with nuclear spin transitions (nuclear magnetic resonance, NMR). Any arbitrary multiple quantum coherent state can be detected as change in the longitudinal resistance. Our findings represent a big step closer to practical all-electrical solid state nuclear spin quantum computing and quantum memory devices.

Yusa, Go

2005-03-01

222

Charge order and low frequency spin dynamics in lanthanum cuprates revealed by Nuclear Magnetic Resonance  

NASA Astrophysics Data System (ADS)

We report detailed 17O, 139La, and 63,65Cu Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) measurements in a stripe ordered La1.875Ba0.125CuO4 single crystal and in oriented powder samples of La1.8- x Eu0.2Sr x CuO4. We observe a partial wipeout of the 17O NMR intensity and a simultaneous drop of the 17O electric field gradient (EFG) at low temperatures where the spin stripe order sets in. In contrast, the 63,65Cu intensity is completely wiped out at the same temperature. The drop of the 17O quadrupole frequency is compatible with a charge stripe order. The 17O spin lattice relaxation rate shows a peak similar to that of the 139La, which is of magnetic origin. This peak is doping dependent and is maximal at x ? 1/8.

Grafe, H.-J.; Curro, N. J.; Young, B. L.; Vyalikh, A.; Vavilova, J.; Gu, G. D.; Hücker, M.; Büchner, B.

2010-10-01

223

Fluctuation-Induced Heat Release from Temperature-Quenched Nuclear Spins near a Quantum Critical Point  

NASA Astrophysics Data System (ADS)

The quasi-two-dimensional quantum antiferromagnet Cr(diethylenetriamine)(O2)2.H2O [1] has a magnetic-field-tuned quantum critical point (QCP) at 12.3 T, where a highly polarized antiferromagnetic phase turns into a field-induced ferromagnetic phase. We report a novel relaxation phenomenon near this QCP: quantum-fluctuation-driven annealing of hydrogen nuclear spins frozen in a non-equilibrium high-energy state by temperature quenching. This relaxation phenomenon, with readily detectable heat release from the nuclear spins as they are annealed, reveals the extent of a quantum critical region around the QCP and provides a unique avenue to investigate the dynamics of the divergent quantum fluctuations that underlie quantum criticality. [1] C. M. Ramsey et al., Chem. Mater. 15, 92 (2003).

Kim, Y. H.; Kaur, N.; Atkins, B. M.; Dalal, N. S.; Takano, Y.

2010-03-01

224

Enhancement of the skyrmionic excitations due to the suppression of Zeeman energy by optical orientation of nuclear spins  

Microsoft Academic Search

An effective experimental method for compensation of Zeeman energy of two-dimensional (2D) electrons based on optical pumping of nuclear spins is proposed and used to enhance skyrmionic excitations under conditions of integer and fractional quantum Hall effect. We demonstrate that photoexcitation by circularly polarized light can result in a strong spin orientation of nuclei along (or against) the direction of

I. V. Kukushkin; K. V. Klitzing; K. Eberl

1999-01-01

225

A convenient way of measuring nuclear spin-lattice relaxation times based on the null method  

Microsoft Academic Search

Describes a method for measuring the nuclear spin-lattice relaxation time T1 by the free precession technique, which offers certain practical advantages, particularly in the measurement of relative values of T1. The method is a simple modification of the original signal-growth technique of Carr and Purcell. Instead of measuring the time constant for the signal growth or the time required for

S. K. Ghosh; E. Tettamanti; A. Panatta

1980-01-01

226

The Low-Temperature Nuclear Spin Equilibrium of H_3^+ in Collisions with H_2  

NASA Astrophysics Data System (ADS)

Observations of H_3^+ in diffuse molecular clouds have revealed that the ratio of its ortho and para nuclear spin modifications are not in thermodynamic equilibrium with the environment. This discrepancy could be explained if the reaction H_3^+ + H_2 to H_2 + H_3^+, which interconverts the nuclear spin modifications of H_3^+, has a nonthermal outcome at low temperatures, possibly arising from nuclear spin selection rules on systems of identical fermions. While the nuclear spin dependence of this reaction has previously been investigated experimentally, the prior measurements were limited to temperatures above ˜130 K, well above the 50-70 K typical of diffuse molecular clouds. To investigate whether the outcome of the H_3^+ + H_2 reaction is nonthermal, H_3^+ ions were allowed to interact with H_2 in the temperature-controlled environment of a 22-pole radiofrequency ion trap, and the relative abundances of ortho- and para-H_3^+ at steady state were measured using action spectroscopy. By carefully controlling the ortho:para ratio of the H_2 samples in conjunction with the ion trap temperature, the outcome of the reaction was observed to be close to thermodynamic equilibrium over the temperature range of 45-100 K. Thus, the nonequilibrium ortho:para ratio of H_3^+ observed in diffuse molecular clouds does not arise from a nonthermal outcome of the H_3^+ + H_2 reaction at low temperature. This implies that the origin of the discrepancy lies in the respective formation and destruction mechanisms of H_3^+.

Grussie, Florian; Berg, Max H.; Wolf, Andreas; Kreckel, Holger; Crabtree, Kyle N.; McCall, Benjamin J.; Gartner, Sabrina; Schlemmer, Stephan

2013-06-01

227

Body-fixed relativistic molecular Hamiltonian and its application to nuclear spin-rotation tensor  

NASA Astrophysics Data System (ADS)

A relativistic molecular Hamiltonian that describes electrons fully relativistically and nuclei quasi-relativistically is proposed and transformed from the laboratory to the body-fixed frame of reference. As a first application of the resulting body-fixed relativistic molecular Hamiltonian, the long anticipated relativistic theory of nuclear spin-rotation (NSR) tensor is formulated rigorously. A ``relativistic mapping'' between experimental NSR and NMR is further proposed, which is of great value in establishing high-precision absolute NMR shielding scales.

Xiao, Yunlong; Liu, Wenjian

2013-04-01

228

Spin, Hyperfine Structure, and Nuclear Magnetic Dipole Moment of O15  

Microsoft Academic Search

The nuclear spin and hfs splitting of O15(tau12=124 ) in the 3P2 atomic ground state have been determined by the atomic beam magnetic resonance method. O15 was produced in the reaction N14(d, n)O15 by allowing a 5-MeV deuteron beam from the Columbia Van de Graaff accelerator to impinge upon a gaseous N2 target. The radioactive gas flowed continuously from the

E. D. Commins; H. R. Feldman

1963-01-01

229

Nuclear Ground State Spins of the Francium Isotopes 208-213, 220-222Fr  

Microsoft Academic Search

The nuclear ground state spins of some francium isotopes have been measured using on-line atomic-beam magnetic resonance techniques. The following results have been obtained: 208Fr I = 7, 209Fr I = 9\\/2, 210Fr I = 6, 211Fr I = 9\\/2, 212Fr I = 5, 213Fr I = 9\\/2, 220Fr I = 1, 221Fr I = 5\\/2 and 222Fr I =

C. Ekström; S. Ingelman; G. Wannberg; M. Skarestad

1978-01-01

230

Nuclear-spin relaxation of ²º?Pb in ferroelectric powders  

SciTech Connect

The ²º?Pb nuclear system (nuclear spin I = 1/2; magnetic Moment ? ?0.58 ?N; isotopic abundance ? 22%) in ferroelectric solids has been proposed for a search for a Schiff moment associated with simultaneous violation of parity (P) and time-reversal invariance (T) in fundamental interactions [1] (see also a discussion of the sensitivity of such search in Ref. [2]). The idea is that, due to the Schiff moment, a ferroelectric sample would acquire a P,T-odd magnetic polarization along the direction of its electric polarization. In conclusion, we have presented the first experimental study of relaxation properties of ²º?Pb in PT and PZT below room temperature. We find that above T? 50 K, longitudinal relaxation rate follows the T² dependence characteristic of the two-phonon Raman process. On the other hand, as the temperature is decreased below T? 50 K, the longitudinal relaxation rates drop slower than ?T2 (as opposed to ?T7 expected for the Raman process), and the relaxation is probably due to a direct process associated with paramagnetic impurities and nuclear-spin diffusion. While the longitudinal relaxation times T? vary between several seconds and over an hour in the temperature range between 290 and 10 K, the transverse relaxation time T? is found to be ?1.5 ms for all temperatures and all powder samples studied. D: we never discuss the origin of T? relaxation. Maybe we should. 1.5 ms is only a bit shorter from what would be expected from nuclear spin-spin interactions. Any comments? At some point Sasha asked Oleg to calculate T? exactly for PT and PZT, but I forgot what was the result. If such calculation exists, it would be great to compare with the expt. result. The obtained results provide an important input in the design of the experiments to search for P,T-violating effects in solid ferroelectrics

Bouchard, Louis S.; Sushkov, Alexander O.; Budker, Dmitry; Ford, Joe; Lipton, Andrew S.

2008-02-05

231

Nuclear Spin-Lattice Relaxation in CaF2 Crystals via Paramagnetic Centers  

Microsoft Academic Search

The results of nuclear spin-lattice relaxation-time measurements in the laboratory reference frame (T1) and the rotating reference frame (T1r), made on F19 nuclei in CaF2 crystals doped either with Eu3+, Ce3+, or Mn2+ paramagnetic centers, are reported. From 0.25 to 0.36 of the Debye temperature, values of the correlation time tauc are found from T1r minima for Mn2+ ions. Over

D. Tse; I. J. Lowe

1968-01-01

232

The Statistical Model in Nuclear Fission-Excitation Energy and Spin Population in Fragments  

NASA Astrophysics Data System (ADS)

We apply the statistical model of nuclear physics to the fission process, in particular to calculate excitation energy and spin distributions in fission products. We give the functions for these distributions, and by applying a Monte Carlo procedure we construct the distribution functions for the fragment kinetic energies. The temperature parameter which is needed for the distribution functions is calculated from an empirical law which relates nuclear temperature to the Q-value of the reaction. Results of the calculations are compared with experimental data, and excellent agreement is observed in all cases.

Faust, Herbert

2011-10-01

233

Transverse nuclear spin relaxation in phosphatidylcholine bilayers containing gramicidin.  

PubMed

Deuterium nuclear magnetic resonance has been used to study transverse relaxation in samples of 1,2-dimyristoyl-sn-glycero-3-phosphocholine, perdeuterated and specifically deuterated at the alpha position of the chains, containing the polypeptide gramicidin at concentrations of 0, 1, and 4 mol%. For 4 mol% gramicidin, the bilayer is thought to undergo a continuous phase change rather than a phase transition proceeding via two phase coexistence. Information is obtained regarding lipid dynamics in the continuous phase change region of the phase diagram. In the presence of gramicidin, the transverse relaxation time measured by the quadrupole echo technique, T2e, passes through a minimum in the gel phase. The gramicidin concentration dependence of T2e suggests that the polypeptide reduces the temperature sensitivity of the correlation time responsible for the minimum. The polypeptide also increases the sensitivity of the first spectral moment, M1, to the quadrupole echo pulse separation. This behavior is attributed to a polypeptide-induced enhancement of the spread in T2e along the acyl chains. Quadrupole Carr-Purcell-Meiboom-Gill experiments are used to separate contributions to the observed behavior from fast and slow motions. PMID:1691657

Morrow, M R

1990-04-13

234

Realization of quantum non-demolition measurement of nuclear spin 1/2 of cold ytterbium atom  

NASA Astrophysics Data System (ADS)

We have demonstrated a quantum non-demolition (QND) measurement with a collective spin of cold ytterbium atoms (171Yb) via Faraday rotation interaction, and have observed 1.8-1.5+2.4 dB spin squeezing. Since 171Yb atoms have only a nuclear spin of one-half in the ground state, the system constitutes the simplest spin ensemble and is thus robust against decoherence. Furthermore, we have considered the atomic quantum swapping gate as a quantum information device using multiple Faraday rotation interactions, and have found that we can realize the quantum-domain performance for a realistic experimental condition.

Takano, T.; Namiki, R.; Takahashi, Y.

2009-04-01

235

Nuclear spin dependence of hydrogenic plasmas in the laboratory and the diffuse interstellar medium  

NASA Astrophysics Data System (ADS)

Observations of diffuse molecular clouds have shown that the excitation temperature T(H_3^+) derived from the (J,K) = (1,0) (ortho) and (1,1) (para) rotational levels of H_3^+ does not necessarily agree with the kinetic temperature (T01) inferred from UV measurements of H_2. In four of the five diffuse molecular cloud sight lines for which both H_3^+ and H_2 observations are available, T(H_3^+) is lower than T01 by 30 K. The reaction H_3^+ + H_2 ? H_2 + H_3^+ is expected to thermalize the H_3^+ nuclear spin distribution, but the interplay of nuclear spin selection rules and energetic restrictions at the low temperatures of the diffuse interstellar medium may prevent full thermalization at steady state. Alternatively, the nonthermal distribution could arise if H_3^+ does not experience a sufficient number of thermalizing collisions with H_2 during its lifetime. We have studied the nuclear spin dependence of the reaction of H_3^+ with H_2 in the laboratory by measuring the ortho:para ratio of H_3^+ formed in plasmas of varying ortho:para H_2 ratios. This study was performed in a hollow cathode cell which enabled the first measurements of this reaction at low temperature (130 K). From these measurements, we derived the ratio of the ``proton hop'' and ``hydrogen exchange'' rate coefficients as a function of temperature. The ratio, ?, was found to decrease with temperature, already reaching the statistical limit of 0.5 at a temperature of 130 K. Knowledge of ? enables modeling of the ortho:para ratio of H_3^+ in diffuse molecular clouds. We have modeled the nuclear spin dependence of the formation, thermalization, and destruction processes of H_3^+, and found that the nonthermal distribution is not caused by nuclear spin selection rules or energetic restrictions in the H_3^+ + H_2 reaction. Rather, it is likely caused by incomplete thermalization prior to H_3^+ destruction via electron dissociative recombination.

Crabtree, K. N.; Indriolo, N.; Kreckel, H.; Kauffman, C. A.; Tom, B. A.; Becka, E.; McGuire, B. A.; McCall, B. J.

2011-05-01

236

Nuclear Spin Dependence of Hydrogenic Plasmas in the Laboratory and the Diffuse Interstellar Medium  

NASA Astrophysics Data System (ADS)

Observations of diffuse molecular clouds have shown that the excitation temperature T(H3+) derived from the (J,K) = (1,0) (ortho) and (1,1) (para) rotational levels of H3+ does not necessarily agree with the kinetic temperature (T01) inferred from UV measurements of H2. In four of the five diffuse molecular cloud sight lines for which both H3+ and H2 observations are available, T(H3+) is lower than T01 by 30 K. The reaction H3+ + H2 ? H2 + H3+ is expected to thermalize the H3+ nuclear spin distribution, but the interplay of nuclear spin selection rules and energetic restrictions at the low temperatures of the diffuse interstellar medium may prevent full thermalization at steady state. Alternatively, the nonthermal distribution could arise if H3+ does not experience a sufficient number of thermalizing collisions with H2 during its lifetime. We have studied the nuclear spin dependence of the reaction of H3+ with H2 in the laboratory by measuring the ortho:para ratio of H3+ formed in plasmas of varying ortho:para H2 ratios. This study was performed in a hollow cathode cell which enabled the first measurements of this reaction at low temperature (130 K). From these measurements, we derived the ratio of the "proton hop" and "hydrogen exchange" rate coefficients as a function of temperature. The ratio, ?, was found to decrease with temperature, already reaching the statistical limit of 0.5 at a temperature of 130 K. Knowledge of ? enables modeling of the ortho:para ratio of H3+ in diffuse molecular clouds. We have modeled the nuclear spin dependence of the formation, thermalization, and destruction processes of H3+, and found that the nonthermal distribution is not caused by nuclear spin selection rules or energetic restrictions in the H3+ + H2 reaction. Rather, it is likely caused by incomplete thermalization prior to H3+ destruction via electron dissociative recombination.

Crabtree, Kyle N.; Indriolo, Nick; Kreckel, Holger; Kauffman, Carrie A.; Tom, Brian A.; Beçka, Eftalda; McGuire, Brett A.; McCall, Benjamin J.

2011-10-01

237

Synthesis and carbon-13 NMR studies of liquid crystals  

NASA Astrophysics Data System (ADS)

The orientation of different segments of 4'-cyanophenyl 4-heptylbenzoate (7CPB) has been investigated using 13C NMR. The method of proton encoded local field (PELF) spectroscopy was used in combination with off-magic-angle spinning (OMAS) of the sample. High-resolution 2D spectra were obtained and the order parameters were calculated from the spectra. Linear relationships between the obtained order parameters and anisotropic chemical shifts determined by 1D 13C NMR were established and semi-empirical parameters were obtained. A 1:2 mixture of 7CPB and its chain-perfluorinated analog (7PFCPB) shows interesting phase behavior with changing of temperature. The mixture was studied by the use of 13C NMR and polarizing optical microscopy. The order parameters of 7CPB in the smectic A phase of the mixture were calculated using the semi-empirical parameters obtained by the 2D NMR method. Eight series of liquid crystals containing an electron- donating group at one end of a conjugated system and an electron-withdrawing group at the other end have been synthesized. The electron-donating group is 4- n-alkylpiperazinyl group, the electron- withdrawing group is nitro group and the conjugated system is diphenyldiazene with zero, one or two substituents on the phenyl rings. The substituents are -F, -Cl, and -CH3. Two series of compounds with cyano group as electron-withdrawing group were also synthesized. Most of the compounds synthesized are nematogenic and exhibit rather broad liquid crystalline ranges. The effects of the lateral substituents on the optical absorption and phase transition temperatures are correlated with their nature and position of substitution. Birefringence, dielectric anisotropy, elastic constant ratio and rise time of the liquid crystals were carried out using 10 wt% LC mixtures in E7. It has been found that lateral substituents have subtle effects on the properties. The presence of lateral substituents depresses melting points and clearing points of the liquid crystals. All the liquid crystals synthesized in this work have relatively large values of birefiringence, although the dielectric anisotropy values were not as high as desired. The incorporation of a fluorine atom onto the position neighboring the nitro group enhances the conjugation of the push-pull system and liquid crystals with better physical properties were obtained.

Sun, Hong

2000-08-01

238

Modeling of proton spin relaxation in muscle tissue using nuclear magnetic resonance spin grouping and exchange analysis  

Microsoft Academic Search

NMR spin relaxation experiments performed on healthy mouse muscle tissue at 40 MHz and 293 K are reported. The spin-lattice relaxation experiments were performed using different combinations of selective and nonselective radio frequency pulses. Relaxation experiments in the rotating frame at H⁠= 10, 5 and 1 G are also reported. The experimental results were analyzed using the spin-grouping method,

W. T. Sobol; I. G. Cameron; W. R. Inch; M. M. Pintar

1986-01-01

239

The role of spin-orbit potential in nuclear prolate-shape dominance  

NASA Astrophysics Data System (ADS)

It is confirmed, in terms of the Woods-Saxon-Strutinsky method, that the spin-orbit potential plays a decisive role in the predominance of prolate deformation, which has been a long standing problem in nuclear physics. It is originated from the combined effects of the spin-orbit coupling and the diffused surface of the potential, in agreement with the previous work based on a more schematic Nilsson-Strutinsky method. The degree of prolate-shape dominance exhibits an oscillatory behavior with respect to the strength of spin-orbit potential and, the prolate-shape dominance is realized at the proper strength of the spin-orbit potential together with the standard surface diffuseness; this oscillatory behavior disappears in case of small diffuseness corresponding to ellipsoidal cavity. The calculated energy differences between oblate and prolate minima in this Letter are consistent with those of our extensive self-consistent calculations of the Hartree-Fock + BCS method with the Skyrme interaction.

Takahara, Satoshi; Onishi, Naoki; Shimizu, Yoshifumi R.; Tajima, Naoki

2011-08-01

240

Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization  

NASA Astrophysics Data System (ADS)

One fundamental requirement for quantum computation is to carry out universal manipulations of quantum bits at rates much faster than the qubit's rate of decoherence. Recently, fast gate operations have been demonstrated in logical spin qubits composed of two electron spins where the rapid exchange of the two electrons permits electrically controllable rotations around one axis of the qubit. However, universal control of the qubit requires arbitrary rotations around at least two axes. Here, we show that by subjecting each electron spin to a magnetic field of different magnitude, we achieve full quantum control of the two-electron logical spin qubit with nanosecond operation times. Using a single device, a magnetic-field gradient of several hundred millitesla is generated and sustained using dynamic nuclear polarization of the underlying Ga and As nuclei. Universal control of the two-electron qubit is then demonstrated using quantum state tomography. The presented technique provides the basis for single- and potentially multiple-qubit operations with gate times that approach the threshold required for quantum error correction.

Foletti, Sandra; Bluhm, Hendrik; Mahalu, Diana; Umansky, Vladimir; Yacoby, Amir

2009-12-01

241

Quadrupolar spectra of nuclear spins in strained InxGa1-xAs quantum dots  

NASA Astrophysics Data System (ADS)

Self-assembled quantum dots (QDs) are born out of lattice mismatched ingredients where strain plays an indispensable role. Through the electric quadrupolar coupling, strain affects the magnetic environment as seen by the nuclear spins. To guide prospective single-QD nuclear magnetic resonance (NMR), as well as dynamic nuclear spin polarization experiments, an atomistic insight to the strain and quadrupolar field distributions is presented. A number of implications of the structural and compositional profile of the QD have been identified. A high aspect ratio of the QD geometry enhances the quadrupolar interaction. The inclined interfaces introduce biaxiality and the tilting of the major quadrupolar principal axis away from the growth axis; the alloy mixing of gallium into the QD enhances both of these features while reducing the quadrupolar energy. Regarding the NMR spectra, both Faraday and Voigt geometries are investigated, unraveling in the first place the extend of inhomogeneous broadening and the appearance of the normally forbidden transitions. Moreover, it is shown that from the main extend of the NMR spectra the alloy mole fraction of a single QD can be inferred. By means of the element-resolved NMR intensities it is found that In nuclei has a factor of 5 dominance over those of As. In the presence of an external magnetic field, the borderlines between the quadrupolar and Zeeman regimes are extracted as 1.5 T for In and 1.1 T for As nuclei. At these values the nuclear spin depolarization rates of the respective nuclei get maximized due to the noncollinear secular hyperfine interaction with a resident electron in the QD.

Bulutay, Ceyhun

2012-03-01

242

Ignition conditions for inertial confinement fusion targets with a nuclear spin-polarized DT fuel  

NASA Astrophysics Data System (ADS)

The nuclear fusion cross-section is modified when the spins of the interacting nuclei are polarized. In the case of deuterium-tritium it has been theoretically predicted that the nuclear fusion cross-section could be increased by a factor ? = 1.5 if all the nuclei were polarized. In inertial confinement fusion this would result in a modification of the required ignition conditions. Using numerical simulations it is found that the required hot-spot temperature and areal density can both be reduced by about 15% for a fully polarized nuclear fuel. Moreover, numerical simulations of a directly driven capsule show that the required laser power and energy to achieve a high gain scale as ?-0.6 and ?-0.4 respectively, while the maximum achievable energy gain scales as ?0.9.

Temporal, M.; Brandon, V.; Canaud, B.; Didelez, J. P.; Fedosejevs, R.; Ramis, R.

2012-10-01

243

Spatial gradient of dynamic nuclear spin polarization induced by breakdown of the quantum Hall effect  

NASA Astrophysics Data System (ADS)

We studied spatial distribution of dynamic nuclear polarization (DNP) in a Hall-bar device in a breakdown regime of the quantum Hall effect (QHE). We detected nuclear magnetic resonance (NMR) signals from the polarized nuclear spins by measuring the Hall voltage Vxy using three pairs of voltage probes attached to the conducting channel of the Hall bar. We find that the amplitude of the NMR signal depends on the position of the Hall voltage probes and that the largest NMR signal is obtained from the pair of probes farthest from the electron-injecting electrode. Combined with results on pump-and-probe measurements, we conclude that the DNP induced by QHE breakdown develops along the electron-drift direction.

Kawamura, M.; Kono, K.; Hashimoto, Y.; Katsumoto, S.; Machida, T.

2011-01-01

244

Proton-decoupled, Overhauser-enhanced, spatially localized carbon-13 spectroscopy in humans.  

PubMed

Spatially localized, natural abundance, carbon (13C) NMR spectroscopy has been combined with proton (1H) decoupling and nuclear Overhauser enhancement to improve 13C sensitivity up to five-fold in the human leg, liver, and heart. Broadhand-decoupled 13C spectra were acquired in 1 s to 17 min with a conventional 1.5-T imaging/spectroscopy system, an auxiliary 1H decoupler, an air-cooled dual-coil coplanar surface probe, and both depth-resolved surface coil spectroscopy (DRESS) and one-dimensional phase-encoding gradient NMR pulse sequences. The surface coil probe comprised circular and figure-eight-shaped coils to eliminate problems with mutual coupling of coils at high decoupling power levels applied during 13C reception. Peak decoupler RF power deposition in tissue was computed numerically from electromagnetic theory assuming a semi-infinite plane of uniform biological conductor. Peak values at the surface were calculated at 4 to 6 W/kg in any gram of tissue for each watt of decoupler power input excluding all coil and cable losses, warning of potential local RF heating problems in these and related experiments. The average power deposition was about 9 mW/kg per watt input, which should present no systemic hazard. At 3 W input, human 13C spectra were decoupled to a depth of about 5 cm while some Overhauser enhancement was sustained up to about 3 cm depth, without ill effect. The observation of glycogen in localized natural abundance 13C spectra of heart and muscle suggests that metabolites in the citric acid cycle should be observable noninvasively using 13C-labeled substrates. PMID:2560801

Bottomley, P A; Hardy, C J; Roemer, P B; Mueller, O M

1989-12-01

245

Proton-decoupled, Overhauser-enhanced, spatially localized carbon-13 spectroscopy in humans  

SciTech Connect

Spatially localized, natural abundance, carbon (13C) NMR spectroscopy has been combined with proton (1H) decoupling and nuclear Overhauser enhancement to improve 13C sensitivity up to five-fold in the human leg, liver, and heart. Broadhand-decoupled 13C spectra were acquired in 1 s to 17 min with a conventional 1.5-T imaging/spectroscopy system, an auxiliary 1H decoupler, an air-cooled dual-coil coplanar surface probe, and both depth-resolved surface coil spectroscopy (DRESS) and one-dimensional phase-encoding gradient NMR pulse sequences. The surface coil probe comprised circular and figure-eight-shaped coils to eliminate problems with mutual coupling of coils at high decoupling power levels applied during 13C reception. Peak decoupler RF power deposition in tissue was computed numerically from electromagnetic theory assuming a semi-infinite plane of uniform biological conductor. Peak values at the surface were calculated at 4 to 6 W/kg in any gram of tissue for each watt of decoupler power input excluding all coil and cable losses, warning of potential local RF heating problems in these and related experiments. The average power deposition was about 9 mW/kg per watt input, which should present no systemic hazard. At 3 W input, human 13C spectra were decoupled to a depth of about 5 cm while some Overhauser enhancement was sustained up to about 3 cm depth, without ill effect. The observation of glycogen in localized natural abundance 13C spectra of heart and muscle suggests that metabolites in the citric acid cycle should be observable noninvasively using 13C-labeled substrates.

Bottomley, P.A.; Hardy, C.J.; Roemer, P.B.; Mueller, O.M. (GE Corporate Research and Development Center, Schenectady, NY (USA))

1989-12-01

246

Effects of barrier-induced nuclear spin magnetization inhomogeneities on diffusion-attenuated MR signal.  

PubMed

The spatial distribution of the transverse nuclear spin magnetization, appearing in a single compartment with impermeable boundaries in a Stejskal-Tanner gradient pulse MR experiment, is analyzed in detail. At short diffusion times the presence of diffusion-restrictive barriers (membranes) reduces effective diffusivity near the membranes and leads to an inhomogeneous spin magnetization distribution (the edge-enhancement effect). In this case, the signal reveals a quasi-two-compartment behavior and can be empirically modeled remarkably well by a biexponential function. The current results provide a framework for interpreting experimental MR data on various phenomena, including water diffusion in giant axons, metabolite diffusion in the brain, and hyperpolarized gas diffusion in lung airways. PMID:14523959

Sukstanskii, A L; Ackerman, J J H; Yablonskiy, D A

2003-10-01

247

First complete set of spin 3/2 nuclear scattering analyzing powers  

NASA Astrophysics Data System (ADS)

The first complete set of analyzing powers for any nuclear spin 32 beam is reported. Analyzing powers and elastic cross section are presented for 4He(7Li-->,7Li)4He at the two center of mass energies of 11.5 and 16.5 MeV. An optical model analysis of these data shows the need for spin-orbit and second rank tensor potentials in addition to real and imaginary central potentials. The inclusion of triton transfer improves the description of the large angle elastic scattering cross section but has little impact on the calculated analyzing powers. The description of the third rank analyzing powers iT31 and iT33 is poor at small angles, and no combination of potentials including a large third rank potential is able to describe them. No real evidence for the presence of a third rank potential is found.

Cathers, P. D.; Bartosz, E. E.; Cooper, M. W.; Curtis, N.; Keeley, N.; Kemper, K. W.; Maréchal, F.; Myers, E. G.; Schmidt, B. G.; Rusek, K.; Hnizdo, V.

2001-06-01

248

Nuclear spin-lattice relaxation of 60 Co in ferromagnetic alloys Pt 99 Co 1 and Pd 99 Co 1  

Microsoft Academic Search

Nuclear spin-lattice relaxation (SLR) of60Co in the systems Pt99Co1, Pd99Co1 has been studied by very low temperature nuclear orientation technique. The thermal cycling method has been used. The difference\\u000a of two orders of magnitude of Korringa constant has been found between Pt99Co1 and Pd99Co1.

M. Trhlík; B. Sedlák; M. Rotter; ?. Lešták; V. N. Pavlov; P. ?ížek; M. Finger; A. L. Erzinkyan; V. P. Parfenova; G. M. Gurevich

1987-01-01

249

Finite-temperature calculations for spin-polarized asymmetric nuclear matter with the lowest order constrained variational method  

SciTech Connect

The lowest order constrained variational technique has been used to investigate some of the thermodynamic properties of spin-polarized hot asymmetric nuclear matter, such as the free energy, symmetry energy, susceptibility, and equation of state. We have shown that the symmetry energy of the nuclear matter is substantially sensitive to the value of spin polarization. Our calculations show that the equation of state of the polarized hot asymmetric nuclear matter is stiffer for higher values of the polarization as well as the isospin asymmetry parameter. Our results for the free energy and susceptibility show that spontaneous ferromagnetic phase transition cannot occur for hot asymmetric matter.

Bigdeli, M. [Department of Physics, Zanjan University, Post Office Box 45195-313, Zanjan (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha, Post Office Box 55134-441, Maragha (Iran, Islamic Republic of); Bordbar, G. H. [Department of Physics, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha, Post Office Box 55134-441, Maragha (Iran, Islamic Republic of); Poostforush, A. [Department of Physics, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)

2010-09-15

250

Exploiting level anti-crossings for efficient and selective transfer of hyperpolarization in coupled nuclear spin systems.  

PubMed

Spin hyperpolarization can be coherently transferred to other nuclei in field-cycling NMR experiments. At low magnetic fields spin polarization is redistributed in a strongly coupled network of spins. Polarization transfer is most efficient at fields where level anti-crossings (LACs) occur for the nuclear spin-states. A further condition is that field switching to the LAC positions is non-adiabatic in order to convert the starting population differences into spin coherences that cause time-dependent mixing of states. The power of this method has been demonstrated by studying transfer of photo-Chemically Induced Dynamic Nuclear Polarization (photo-CIDNP) in N-acetyl-tryptophan. We have investigated the magnetic field dependence and time dependence of coherent CIDNP transfer and directly assessed nuclear spin LACs by studying polarization transfer at specific field positions. The proposed approach based on LACs is not limited to CIDNP but is advantageous for enhancing NMR signals by spin order transfer from any type of hyper-polarized nuclei. PMID:23893009

Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Kaptein, Robert; Miesel, Karsten; Vieth, Hans-Martin; Ivanov, Konstantin L

2013-09-21

251

Nuclear spin-lattice relaxation-time reduction in small particles  

NASA Astrophysics Data System (ADS)

A method is described of reducing the nuclear spin-lattice relaxation time in a polycrystalline solid without the introduction of any paramagnetic impurities. It relies on the fact that the relaxation times of nuclei on a surface are usually much shorter than those in the bulk due to greater freedom of movement. Simply reducing the particle size by grinding or other methods is shown to be effective in markedly reducing the spin-lattice relaxation time of all the nuclei in the specimen because of the good thermal contact between like nuclei in the interior and surface of small particles. The nuclear quadrupole resonance (NQR) of 14N, 2D, or 23Na was measured for the same specimens with different particle sizes by nuclear quadrupole double resonance to ensure that the chemical structure of the compound did not alter due to the grinding. In all samples studied, except sodium thiosulphate, the NQR spectrum was unaffected by the grinding except that the time necessary to collect the data was reduced. In the case of sodium thiosulphate a marked change in the NQR spectrum was observed despite the fact that no change in chemical composition could be detected. Data is presented which demonstrates the effectiveness of the technique and a simple model of the underlying mechanism is described.

Rabbani, S. R.; Edmonds, D. T.

1994-09-01

252

Selection rules for nuclear spin modifications in ion-neutral reactions involving H3+  

NASA Astrophysics Data System (ADS)

We present experimental evidence for nuclear spin selection rules in chemical reactions that have been theoretically anticipated by Quack [M. Quack, Mol. Phys. 34, 477 (1997)]. The abundance ratio of ortho-H3+ (I=3/2) and para-H3+ (I=1/2), R=[o-H3+]/[p-H3+], has been measured from relative intensities of their infrared spectral lines in hydrogen plasmas using para-H2 and normal-H2 (75% o-H2 and 25% p-H2). The observed clear differences in the value of R between the p-H2 and n-H2 plasmas demonstrate the spin memory of protons even after ion-neutral reactions, and thus the existence of selection rules for spin modifications. Both positive column discharges and hollow cathode discharges have been used to demonstrate the effect. Experiments using pulsed plasmas have been conducted in the hollow cathode to minimize the uncertainty due to long-term conversion between p-H2 and o-H2 and to study the time dependence of the o-H3+ to p-H3+ ratio. The observed R(t) has been analyzed using simultaneous rate equations assuming the nuclear spin branching ratios calculated from Quack's theory. In p-H2 plasmas, the electron impact ionization followed by the ion-neutral reaction H2++H2-->H3++H produces pure p-H3+, but the subsequent reaction between p-H3+ and p-H2 scrambles protons. While the proton hop reaction (rate constant kH) maintains the purity of p-H3+, the hydrogen exchange reaction (rate constant kE) produces o-H3+ and acts as the gateway for nuclear spin conversion. The value of R(t), therefore, depends critically on the ratio of their reaction rates ?=kH/kE. From observed values of R(t), the ratio has been determined to be ?=2.4. This is in approximate agreement with the value reported by Gerlich using isotopic species.

Cordonnier, M.; Uy, D.; Dickson, R. M.; Kerr, K. E.; Zhang, Y.; Oka, T.

2000-08-01

253

Dephasing time of GaAs electron-spin qubits coupled to a nuclear bath exceeding 200?s  

NASA Astrophysics Data System (ADS)

Qubits, the quantum mechanical bits required for quantum computing, must retain their quantum states for times long enough to allow the information contained in them to be processed. In many types of electron-spin qubits, the primary source of information loss is decoherence due to the interaction with nuclear spins of the host lattice. For electrons in gate-defined GaAs quantum dots, spin-echo measurements have revealed coherence times of about 1?s at magnetic fields below 100mT (refs 1, 2). Here, we show that coherence in such devices can survive much longer, and provide a detailed understanding of the measured nuclear-spin-induced decoherence. At fields above a few hundred millitesla, the coherence time measured using a single-pulse spin echo is 30?s. At lower fields, the echo first collapses, but then revives at times determined by the relative Larmor precession of different nuclear species. This behaviour was recently predicted, and can, as we show, be quantitatively accounted for by a semiclassical model for the dynamics of electron and nuclear spins. Using a multiple-pulse Carr-Purcell-Meiboom-Gillecho sequence, the decoherence time can be extended to more than 200?s, an improvement by two orders of magnitude compared with previous measurements.

Bluhm, Hendrik; Foletti, Sandra; Neder, Izhar; Rudner, Mark; Mahalu, Diana; Umansky, Vladimir; Yacoby, Amir

2011-02-01

254

NUCLEAR SPIN AND HYPERFINE-STRUCTURE MEASUREMENTS ON THE RADIOACTIVE-IODINE AND ASTATINE ISOTOPES (thesis)  

Microsoft Academic Search

Atomic-beam magnetic resonance techniques were used to measure the ; nuclear spins of I¹²³, I¹²⁴, I¹²⁶, I¹³°, I¹³², I\\/; sup 133\\/, I¹³⁵, and At²¹¹. Also, measurements of the magnetic-dipole ; interaction constant, and the electroquadrupole interaction constant, and the ; electroquadrupole interaction constant for I¹³¹ and I¹³² are reported. ; The design of the atomic-beam apparatus is described. Experimental methods

Garvin

1959-01-01

255

Studies of Phospholipid Hydration by High-Resolution Magic-Angle Spinning Nuclear Magnetic Resonance  

Microsoft Academic Search

A sample preparation method using spherical glass ampoules has been used to achieve 1.5-Hz resolution in 1H magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of aqueous multilamellar dispersions of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), serving to differentiate between slowly exchanging interlamellar and bulk water and to reveal new molecular-level information about hydration phenomena in these model biological membranes. The

Zhe Zhou; Brian G. Sayer; Donald W. Hughes; Ruth E. Stark; Richard M. Epand

1999-01-01

256

Body-fixed relativistic molecular Hamiltonian and its application to nuclear spin-rotation tensor.  

PubMed

A relativistic molecular Hamiltonian that describes electrons fully relativistically and nuclei quasi-relativistically is proposed and transformed from the laboratory to the body-fixed frame of reference. As a first application of the resulting body-fixed relativistic molecular Hamiltonian, the long anticipated relativistic theory of nuclear spin-rotation (NSR) tensor is formulated rigorously. A "relativistic mapping" between experimental NSR and NMR is further proposed, which is of great value in establishing high-precision absolute NMR shielding scales. PMID:23574205

Xiao, Yunlong; Liu, Wenjian

2013-04-01

257

The spin chemistry and magnetic resonance of H2@C60. From the Pauli principle to trapping a long lived nuclear excited spin state inside a buckyball.  

PubMed

One of the early triumphs of quantum mechanics was Heisenberg's prediction, based on the Pauli principle and wave function symmetry arguments, that the simplest molecule, H(2), should exist as two distinct species-allotropes of elemental hydrogen. One allotrope, termed para-H(2) (pH(2)), was predicted to be a lower energy species that could be visualized as rotating like a sphere and possessing antiparallel ( upward arrow downward arrow) nuclear spins; the other allotrope, termed ortho-H(2) (oH(2)), was predicted to be a higher energy state that could be visualized as rotating like a cartwheel and possessing parallel ( upward arrow upward arrow) nuclear spins. This remarkable prediction was confirmed by the early 1930s, and pH(2) and oH(2) were not only separated and characterized but were also found to be stable almost indefinitely in the absence of paramagnetic "spin catalysts", such as molecular oxygen, or traces of paramagnetic impurities, such as metal ions. The two allotropes of elemental hydrogen, pH(2) and oH(2), may be quantitatively incarcerated in C(60) to form endofullerene guest@host complexes, symbolized as pH(2)@C(60) and oH(2)@C(60), respectively. How does the subtle difference in nuclear spin manifest itself when hydrogen allotropes are incarcerated in a buckyball? Can the incarcerated "guests" communicate with the outside world and vice versa? Can a paramagnetic spin catalyst in the outside world cause the interconversion of the allotropes and thereby effect a chemical transformation inside a buckyball? How close are the measurable properties of H(2)@C(60) to those computed for the "quantum particle in a spherical box"? Are there any potential practical applications of this fascinating marriage of the simplest molecule, H(2), with one of the most beautiful of all molecules, C(60)? How can one address such questions theoretically and experimentally? A goal of our studies is to produce an understanding of how the H(2) guest molecules incarcerated in the host C(60) can "communicate" with the chemical world surrounding it. This world includes both the "walls" of the incarcerating host (the carbon atom "bricks" that compose the wall) and the "outside" world beyond the atoms of the host walls, namely, the solvent molecules and selected paramagnetic molecules added to the solvent that will have special spin interactions with the H(2) inside the complex. In this Account, we describe the temperature dependence of the equilibrium of the interconversion of oH(2)@C(60) and pH(2)@C(60) and show how elemental dioxygen, O(2), a ground-state triplet, is an excellent paramagnetic spin catalyst for this interconversion. We then describe an exploration of the spin spectroscopy and spin chemistry of H(2)@C(60). We find that H(2)@C(60) and its isotopic analogs, HD@C(60) and D(2)@C(60), provide a rich and fascinating platform on which to investigate spin spectroscopy and spin chemistry. Finally, we consider the potential extension of spin chemistry to another molecule with spin isomers, H(2)O, and the potential applications of the use of pH(2)@C(60) as a source of latent massive nuclear polarization. PMID:19902960

Turro, Nicholas J; Chen, Judy Y-C; Sartori, Elena; Ruzzi, Marco; Marti, Angel; Lawler, Ronald; Jockusch, Steffen; López-Gejo, Juan; Komatsu, Koichi; Murata, Yasujiro

2010-02-16

258

Effect of spin-orbit nuclear charge density corrections due to the anomalous magnetic moment on halonuclei  

SciTech Connect

In this paper we consider the contribution of the anomalous magnetic moments of protons and neutrons to the nuclear charge density. We show that the spin-orbit contribution to the mean-square charge radius, which has been neglected in recent nuclear calculations, can be important in light halonuclei. We estimate the size of the effect in helium, lithium, and beryllium nuclei. It is found that the spin-orbit contribution represents a approx2% correction to the charge density at the center of the {sup 7}Be nucleus. We derive a simple expression for the correction to the mean-square charge radius due to the spin-orbit term and find that in light halonuclei it may be larger than the Darwin-Foldy term and comparable to finite size corrections. A comparison of experimental and theoretical mean-square radii including the spin-orbit contribution is presented.

Ong, A.; Berengut, J. C.; Flambaum, V. V. [School of Physics, University of New South Wales, Sydney 2052 (Australia)

2010-07-15

259

Effect of spin-orbit nuclear charge density corrections due to the anomalous magnetic moment on halonuclei  

NASA Astrophysics Data System (ADS)

In this paper we consider the contribution of the anomalous magnetic moments of protons and neutrons to the nuclear charge density. We show that the spin-orbit contribution to the mean-square charge radius, which has been neglected in recent nuclear calculations, can be important in light halonuclei. We estimate the size of the effect in helium, lithium, and beryllium nuclei. It is found that the spin-orbit contribution represents a ~2% correction to the charge density at the center of the Be7 nucleus. We derive a simple expression for the correction to the mean-square charge radius due to the spin-orbit term and find that in light halonuclei it may be larger than the Darwin-Foldy term and comparable to finite size corrections. A comparison of experimental and theoretical mean-square radii including the spin-orbit contribution is presented.

Ong, A.; Berengut, J. C.; Flambaum, V. V.

2010-07-01

260

Acoustic Techniques in Magnetic Resonance: Acoustic coupling to nuclear and electron spins is a measure of relaxation in paramagnetic systems.  

PubMed

In conclusion, I believe it fair to say that the marriage of ultrasonics and magnetic resonance holds promise of being a productive one. In the application of these disciplines to nuclear spins, little more has been done than to demonstrate the acoustic techniques and to apply them to a particular problem of quadrupolar coupling in the heavy alkali halides. Particularly promising is the extension of acoustic NMR techniques to bulk metals, to ferromagnetic crystals, and to the study of spin-lattice relaxation as a function of temperature. In the technique of phonon coupling to electron spins in paramagnetic materials, also, the reports to date have all been of a preliminary nature. Used in combination with the powerful new hypersonic technique of generating microwave acoustic waves, electron spin-phonon interaction measurements may help to resolve some of the present confusion regarding the mechanisms of spin-lattice relaxation in paramagnetic solids (29). PMID:17798054

Bolef, D I

1962-05-01

261

Frequency-stepped acquisition in nuclear magnetic resonance spectroscopy under magic angle spinning  

NASA Astrophysics Data System (ADS)

The nuclear magnetic resonance of paramagnetic solids is usually characterized by the presence of large chemical shifts and shift anisotropies due to hyperfine interactions. Frequently the resulting spectra cover a frequency range of several megahertz, which is greater than the bandwidth of commercially available radio-frequency (RF) probes, making it impossible to acquire the whole spectrum in a single experiment. In these cases it common to record a series of spectra, in which the probe is tuned to a different frequency for each, and then sum the results to give the ``true'' spectrum. While this method is very widely used on static samples, the application of frequency stepping under magic-angle spinning (MAS) is less common, owing to the increased complexity of the spin dynamics when describing the interplay of the RF irradiation with the mechanical rotation of the shift tensor. In this paper, we present a theoretical description, based on the jolting frame formalism of Caravatti et al. [J. Magn. Reson. 55, 88 (1983)], for describing the spin dynamics of a powder sample under MAS when subjected to a selective pulse of low RF-field amplitude. The formalism is used to describe the frequency stepping method under MAS, and under what circumstances the true spectrum is reproduced. We also present an experimental validation of the methodology under ultra-fast MAS with the paramagnetic materials LiMnPO4 and TbCsDPA.

Pell, Andrew J.; Clément, Raphaële J.; Grey, Clare P.; Emsley, Lyndon; Pintacuda, Guido

2013-03-01

262

Carbon 13 Measurements on Dissolved Inorganic Carbon at the North Pacific (1969) E Secs Statio n.  

National Technical Information Service (NTIS)

Samples from 22 depths at the Geosecs station were measured for carbon 13 independently at Scripps Institution of Oceanography and Woods Hole Institution of Oceanography. The mean deviation between the two sets of data is -0.02 pH scale and the absolute d...

P. Kroopnick W. G. Deuser H. Craig

1970-01-01

263

Analytical theory of the nuclear-spin-induced optical rotation in liquids  

NASA Astrophysics Data System (ADS)

Based on the thought on the antisymmetric polarizability induced by nuclear magnetic moments and theory of the Faraday effect, an analytical theoretical expression is derived for the nuclear-spin-induced optical rotation (NSOR) of diamagnetic saturated molecules in a circular cylinder. That consists of two parts, ? and ?, induced by the intramolecular and intermolecular hyperfine interaction, respectively. By using them and the Verdet constants, NSOR for 1H in water, hexane, cyclohexane and methyl-alcohol in liquid and H 2 gas have been calculated. The calculated NSOR for water agrees with the experiment and for three hydrocarbons predicts the same order of magnitude as water. For the samples studied except H 2 gas, ? and ? are comparable in magnitude.

Yao, Guo-hua; He, Ming; Chen, Dong-ming; He, Tian-jing; Liu, Fan-chen

2011-08-01

264

A Performant Algorithm to Calculate Spin- and Parity-Dependent Nuclear Level Densities  

NASA Astrophysics Data System (ADS)

A new algorithm for calculating the spin- and parity-dependent shell model nuclear level densities using the moments method in the proton-neutron formalism will be presented. A new, parallelized code based on this algorithm was developed and tested using up to 4,000 cores on FRANKLIN/NERSC, for a set of nuclei from the sd-, pf-, and pf+g9/2- model spaces. By comparing the low excitation energy nuclear level densities for a given nucleus calculated in two model spaces, such as pf and pf+g9/2, we could estimated its ground state energy in the larger model space, which is not accessible to direct shell model calculations because of the unmanageable dimension. Examples for the ground state energies of for ^64Ge and ^68Se in the pf+g9/2 model space will be presented. )

Senkov, Roman; Horoi, Mihai

2010-02-01

265

Growth of nuclear spin precession frequency of antiprotons (negative hyperons) under deceleration in matter with polarized nuclei  

NASA Astrophysics Data System (ADS)

The Coulomb interaction leads to an increase of the real part of the amplitude of scattering of negatively charged particles (antiprotons, hyperons) by nuclei. In consequence, when antiprotons (negative hyperons) are decelerated in a medium with polarized nuclei, their effective energy of interaction with the medium and the nuclear spin precession frequency in a pseudomagnetic field grow as the particles decelerate. As a result, spin rotation of negatively charged particles becomes observable despite their rapid deceleration. This provides information about the spin-dependent part of the amplitude of coherent elastic zero-angle scattering in the range of low energies, where scattering experiments are practically impossible to perform.

Baryshevsky, V. G.

2012-05-01

266

Unusual temperature behavior of the entropy of the antiferromagnetic spin state in nuclear matter with an effective finite range interaction  

SciTech Connect

The unusual temperature behavior of the entropy of the antiferromagnetic (AFM) spin state in symmetric nuclear matter with the Gogny D1S interaction, being larger at low temperatures than the entropy of nonpolarized matter, is related to the dependence of the entropy on the effective masses of nucleons in a spin polarized state. The corresponding conditions for comparing the entropies of the AFM and nonpolarized states in terms of the effective masses are formulated, including the low and high temperature limits. It is shown that the unexpected temperature behavior of the entropy of the AFM spin state at low temperatures is caused by the violation of the corresponding low-temperature criterion.

Isayev, A. A. [Kharkov Institute of Physics and Technology, Academicheskaya Street 1, Kharkov 61108 (Ukraine)

2007-10-15

267

WURST-QCPMG sequence and "spin-lock" in ¹?N nuclear quadrupole resonance.  

PubMed

¹?N nuclear quadrupole resonance (NQR) is a promising method for the analysis of pharmaceuticals or for the detection of nitrogen based illicit compounds, but so far, the technique is still not widely used, mostly due to the very low sensitivity. This problem is already acute in the preliminary NQR stage, when a compound is being examined for the first time and the NQR frequencies are being searched for, by scanning a wide frequency range step-by-step. In the present work, we experimentally show how to increase the efficiency of this initial stage by using a combination of a wideband excitation achieved with frequency swept pulses (WURST) and a "spin-lock" state obtained with a quadrupolar-CPMG (QCPMG) sequence. In the first part we show that WURST pulses provide a much larger excitation bandwidth compared to common rectangular pulses. This increased bandwidth allows to increase the frequency step and reduces the total number of steps in a scanning stage. In the second part we show that the "spin-lock" decay time T2eff obtained with the WURST-QCPMG combination is practically identical with the T2eff obtained with the most common "spin-lock" sequence, the SLSE, despite a very different nature and length of excitation pulses. This allows for a substantial S/N increase through echo averaging in every individual step and really allows to exploit all the advantages of the wider excitation in the NQR frequency scanning stage. Our experimental results were obtained on a sample of trinitrotoluene, but identical behavior is expected for all compounds where a "spin-lock" state can be created. PMID:23793057

Gregorovi?, Alan; Apih, Tomaž

2013-06-04

268

Nuclear spin conversion of molecular hydrogen on amorphous solid water in the presence of O2 traces.  

PubMed

Nuclear spin conversion (NSC) of ortho- to para-H(2) and para- to ortho-D(2) has been investigated on an amorphous solid water (ASW) surface at 10 K, in the presence of co-adsorbed O(2). The dynamics of the nuclear spin conversion could be revealed by combination of resonance enhanced multiphoton ionization spectroscopy (REMPI) with temperature programmed desorption (TPD) experiments. The conversion rates are consistent with a diffusion of molecular hydrogen inducing a nuclear spin conversion enhanced in the vicinity of molecular oxygen. The conversion times were found to increase with decreasing O(2) and H(2) coverage. Finally, on oxygen free ASW surface, the extremely long conversion characteristic times measured showed that such surface is not an efficient catalyst for NSC, in contradiction with hypothesis commonly made for interstellar medium. PMID:21113527

Chehrouri, M; Fillion, J-H; Chaabouni, H; Mokrane, H; Congiu, E; Dulieu, F; Matar, E; Michaut, X; Lemaire, J L

2010-11-26

269

A high-performance Fortran code to calculate spin- and parity-dependent nuclear level densities  

NASA Astrophysics Data System (ADS)

A high-performance Fortran code is developed to calculate the spin- and parity-dependent shell model nuclear level densities. The algorithm is based on the extension of methods of statistical spectroscopy and implies exact calculation of the first and second Hamiltonian moments for different configurations at fixed spin and parity. The proton-neutron formalism is used. We have applied the method for calculating the level densities for a set of nuclei in the sd-, pf-, and pf+g- model spaces. Examples of the calculations for 28Si (in the sd-model space) and 64Ge (in the pf+g-model space) are presented. To illustrate the power of the method we estimate the ground state energy of 64Ge in the larger model space pf+g, which is not accessible to direct shell model diagonalization due to the prohibitively large dimension, by comparing with the nuclear level densities at low excitation energy calculated in the smaller model space pf.

Sen'kov, R. A.; Horoi, M.; Zelevinsky, V. G.

2013-01-01

270

Nitrogen nuclear spin flips in nitroxide spin probes of different sizes in glassy o-terphenyl: possible relation with ?- and ?-relaxations.  

PubMed

The pulsed electron-electron double resonance (ELDOR) technique was employed to study nitroxide spin probes of three different sizes dissolved in glassy o-terphenyl. A microwave pulse applied to the central hyperfine structure (hfs) component of the nitroxide electron paramagnetic resonance spectrum was followed by two echo-detecting pulses of different microwave frequency to probe the magnetization transfer (MT) to the low-field hfs component. The MT between hfs components is readily related to flips in the nitrogen nuclear spin, which in turn are induced by molecular motion. The MT on the time scale of tens of microseconds was observed over a wide temperature range, including temperatures near and well below the glass transition. For a bulky nitroxide, it was found that MT rates approach dielectric ? (primary) relaxation frequencies reported for o-terphenyl in the literature. For small nitroxides, MT rates were found to match the frequencies of dielectric ? (secondary) Johari-Goldstein relaxation. The most probable motional mechanism inducing the nitrogen nuclear spin flips is large-angle angular jumps, between some orientations of unequal occupation probabilities. The pulsed ELDOR of nitroxide spin probes may provide additional insight into the nature of Johari-Goldstein relaxation in glassy media and may serve as a tool for studying this relaxation in substances consisting of non-rigid molecules (such as branched polymers) and in heterogeneous and non-polar systems (such as a core of biological membranes). PMID:21913776

Isaev, N P; Dzuba, S A

2011-09-01

271

Muon spin relaxation and hyperfine-enhanced ^141Pr nuclear spin dynamics in (Pr,La)Os4Sb12 and Pr(Os,Ru)4Sb12  

NASA Astrophysics Data System (ADS)

The longitudinal-field muon relaxation experiments have been carried out in the Pr,La)Os4Sb12 and Pr(Os,Ru)4Sb12 alloy systems. At low temperatures, the dynamic fluctuations are involved in muon relaxation in addition to the contribution from a distributions of static muon local fields. The temperature and concentration dependencies of the muon damping rate ? indicate that this dynamic contribution is due to ^141Pr nuclear magnetism, which is enhanced by hyperfine coupling to the Pr^3+ Van Vleck susceptibility. Further evidence comes from the field dependence of ?, which is in reasonable agreement with the modified model for muon spin relaxation by dipole-coupled nuclear spins.

Shu, Lei; Maclaughlin, D. E.; Higemoto, W.; Heffner, R. H.; Ohishi, K.; Ito, T. U.; Aoki, Y.; Tunashima, Y.; Yonezawa, Y.; Sanada, S.; Kikuchi, D.; Sato, H.; Ishida, K.; Kadono, R.; Koda, A.; Bernal, O. O.; Sugawara, H.; Frederick, N. A.; Yuhasz, W. M.; Sayles, T. A.; Yanagisawa, T.; Maple, M. B.

2007-03-01

272

High polarization of nuclear spins mediated by nanoparticles at millikelvin temperatures.  

PubMed

Nuclear magnetic resonance (NMR) techniques are extensively used in many areas of basic and clinical research, as well as in diagnostic medicine. However, NMR signals are intrinsically weak, and this imposes substantial constraints on the amounts and concentrations of materials that can be detected. The signals are weak because of the low energies characteristic of NMR and the resulting very low (typically 0.0001-0.01%) polarization of the nuclear spins. Here, we show that exposure to very low temperatures and high magnetic fields, in conjunction with nanoparticle-mediated relaxation enhancement, can be used to generate extremely high nuclear polarization levels on a realistic timescale; with copper nanoparticles at 15 mK and 14 T, (13)C polarization grew towards its equilibrium level of 23% with an estimated half-time of about 60 hours. This contrasts with a (13)C half-time of at least one year in the presence of aluminium nanoparticles. Cupric oxide nanoparticles were also effective relaxation agents. Our findings lead us to suspect that the relaxation may be mediated, at least in part, by the remarkable magnetic properties that some nanoparticle preparations can display. This methodology offers prospects for achieving polarization levels of 10-50% or more for many nuclear species, with a wide range of potential applications in structural biology and medicine. PMID:23681204

Owers-Bradley, John R; Horsewill, Anthony J; Peat, David T; Goh, Kelvin S K; Gadian, David G

2013-05-17

273

Sub-millisecond dynamic nuclear spin hyperpolarization in a semiconductor: A case study from PIn antisite in InP  

NASA Astrophysics Data System (ADS)

Optically detected magnetic resonance is employed to identify key factors governing dynamic nuclear polarization (DNP) in a semiconductor. We demonstrate that the extent of DNP can be efficiently controlled by varying lifetime of the localized electrons that transfer spin angular momentum to nuclei. The ultimate speed of a DNP process, on the other hand, is determined by the strength of hyperfine interaction that drives DNP. We show that about 50% nuclear spin polarization of a PIn antisite in InP can be achieved by shortening electron lifetime within a remarkably short time (<0.1 ms) due to strong hyperfine coupling.

Wang, X. J.; Buyanova, I. A.; Chen, W. M.

2012-11-01

274

Simultaneous Subsecond Hyperpolarization of the Nuclear and Electron Spins of Phosphorus in Silicon by Optical Pumping of Exciton Transitions  

NASA Astrophysics Data System (ADS)

We demonstrate a method which can hyperpolarize both the electron and nuclear spins of P31 donors in Si at low field, where both would be essentially unpolarized in equilibrium. It is based on the selective ionization of donors in a specific hyperfine state by optically pumping donor bound exciton hyperfine transitions, which can be spectrally resolved in Si28. Electron and nuclear polarizations of 90% and 76%, respectively, are obtained in less than a second, providing an initialization mechanism for qubits based on these spins, and enabling further ESR and NMR studies on dilute P31 in Si28.

Yang, A.; Steger, M.; Sekiguchi, T.; Thewalt, M. L. W.; Ladd, T. D.; Itoh, K. M.; Riemann, H.; Abrosimov, N. V.; Becker, P.; Pohl, H.-J.

2009-06-01

275

Nuclear Scalar Spin-Spin Coupling Reveals Novel Properties of Low-Barrier Hydrogen Bonds in a Polar Environment  

Microsoft Academic Search

The structure of the hydrogen bridge 19 F· ·· 1 H· ··15N in the acid - base complex A ··· H ··· B formed by HF and (15N)2,4,6-trimethylpyridine in CDF3\\/ CDF2Cl has been studied between 112 K and 200 K by low-temperature, multinuclear NMR spectroscopy. For the first time scalar spin - spin coupling between all three nuclei of a

Nikolai S. Golubev; Ilja G. Shenderovich; Sergei N. Smirnov; Gleb S. Denisov; Hans-Heinrich Limbach

1999-01-01

276

Nuclear Spin of H_3^+ and H_2 in Dense Molecular Clouds  

NASA Astrophysics Data System (ADS)

The ortho:para ratio of H_2 is a critical parameter for deuterium fractionation in cold, dense quiescent cores. The dominant reservoir for interstellar deuterium is in the inert molecule HD, but the exothermic reaction H_3^+ + HD ? H_2D^+ + H_2 + 220 K (and H_2D^+ + HD, etc.) can yield highly reactive species capable of distributing deuterium to other molecules. The barrier to the reverse reaction, however, can be overcome even at temperatures below 10 K when ortho-H_2 (o-H_2) reacts with H_2D^+ (or D_2H^+, D_3^+), as ortho-H_2 possesses ˜170 K of internal rotational energy in its ground state. Recent modeling work has demonstrated the importance of o-H_2 in cold, dense, highly depleted cores using a chemical network that includes all nuclear spin modifications of H_3^+, H_2, and their isotopologues, but the initial o-H_2 fraction is taken as a parameter in the model. Observationally or computationally constraining this quantity would aid in understanding deuterium fractionation in dense cores. To learn about the initial o-H_2 fraction in a cold core, we have modeled the chemistry of non-depleted dense interstellar clouds from which cold cores are thought to form. A simplified gas-phase chemical network consisting of 28 species and ˜170 reactions is combined with a physical model of a dense cloud, including time-dependent physical conditions. Included in the network are the nuclear spin modifications of H_2, H_2^+, and H_3^+, as well as nuclear spin dependent rate coefficients for the thermalization reactions H_2 + H^+ and H_3^+ + H_2. By modeling the time-dependent chemistry, we find that the ortho:para ratio of H_2 requires 10^7-10^8 years to reach steady state under ``standard'' dense cloud conditions, which is at least on the order of the cloud lifetime. The timescale depends on the ionization rate, the rate coefficients of the various H_3^+ + H_2 reactions, and the relative abundances of H_3^+ and H^+, but is largely insensitive to the total density and temperature. Even at steady state, the o-H_2 fraction is calculated to be >0.5% at 10 K, which is several orders of magnitude above its value at thermodynamic equilibrium. The prospects for using observations of the ortho:para ratio of H_3^+ as a probe of the H_2 ortho:para ratio will be discussed.

Crabtree, Kyle N.; McCall, Benjamin J.

2012-06-01

277

Treatment of scalar-relativistic effects on nuclear magnetic shieldings using a spin-free exact-two-component approach.  

PubMed

A cost-effective treatment of scalar-relativistic effects on nuclear magnetic shieldings based on the spin-free exact-two-component theory in its one-electron variant (SFX2C-1e) is presented. The SFX2C-1e scheme gains its computational efficiency, in comparison to the four-component approach, from a focus on spin-free contributions and from the elimination of the small component. For the calculation of nuclear magnetic shieldings, the separation of spin-free and spin-dependent terms in the parent four-component theory is carried out here for the matrix representation of the Dirac equation in terms of a restricted-magnetically balanced gauge-including atomic orbital basis. The resulting spin-free four-component matrix elements required to calculate nuclear magnetic shieldings are then used to construct the corresponding SFX2C-1e Hamiltonian and its perturbed counterpart in the context of SFX2C-1e analytic derivative theory. To demonstrate the applicability of the approach, we report coupled-cluster calculations for prototypical problems such as the (17)O shieldings of transition-metal oxo complexes (MO4(2-), M = Cr, Mo, and W) and the (129)Xe shieldings of xenon fluorides (XeF2, XeF4, and XeF6). PMID:23927241

Cheng, Lan; Gauss, Jürgen; Stanton, John F

2013-08-01

278

Ortho–Para Mixing Hyperfine Interaction in the H2O+ Ion and Nuclear Spin Equilibration  

NASA Astrophysics Data System (ADS)

The ortho to para conversion of water ion, H2O+, due to the interaction between the magnetic moments of the unpaired electron and protons has been theoretically studied to calculate the spontaneous emission lifetime between the ortho- and para-levels. The electron spin-nuclear spin interaction term, Tab(Sa-Ib + Sb-Ia) mixes ortho (I = 1) and para (I = 0) levels to cause the -forbidden- ortho to para |-I| = 1 transition. The mixing term with Tab = 72.0 MHz is 4 orders of magnitude higher for H2O+ than for its neutral counterpart H2O where the magnetic field interacting with proton spins is by molecular rotation rather than the free electron. The resultant 108 increase of ortho to para conversion rate possibly makes the effect of conversion in H2O+ measurable in laboratories and possibly explains the anomalous ortho to para ratio recently reported by Herschel heterodyne instrument for the far-infrared (HIFI) observation. Results of our calculations show that the ortho - para mixings involving near-degenerate ortho and para levels are high (-10-3), but they tend to occur at high energy levels, -300 K. Because of the rapid spontaneous emission, such high levels are not populated in diffuse clouds unless the radiative temperature of the environment is very high. The low-lying 101 (para) and 111 (ortho) levels of H2O+ are mixed by -10-4 making the spontaneous emission lifetime for the para 101 - ortho 000 transition 520 years and 5200 years depending on the F value of the hyperfine structure. Thus the ortho - para conversion due to the unpaired electron is not likely to seriously affect thermalization of interstellar H2O+ unless either the radiative temperature is very high or number density of the cloud is very low.

Tanaka, Keiichi; Harada, Kensuke; Oka, Takeshi

2013-10-01

279

Ortho-Para Mixing Hyperfine Interaction in the H2O(+) Ion and Nuclear Spin Equilibration.  

PubMed

The ortho to para conversion of water ion, H2O(+), due to the interaction between the magnetic moments of the unpaired electron and protons has been theoretically studied to calculate the spontaneous emission lifetime between the ortho- and para-levels. The electron spin-nuclear spin interaction term, Tab(Sa?Ib + Sb?Ia) mixes ortho (I = 1) and para (I = 0) levels to cause the "forbidden" ortho to para |?I| = 1 transition. The mixing term with Tab = 72.0 MHz is 4 orders of magnitude higher for H2O(+) than for its neutral counterpart H2O where the magnetic field interacting with proton spins is by molecular rotation rather than the free electron. The resultant 10(8) increase of ortho to para conversion rate possibly makes the effect of conversion in H2O(+) measurable in laboratories and possibly explains the anomalous ortho to para ratio recently reported by Herschel heterodyne instrument for the far-infrared (HIFI) observation. Results of our calculations show that the ortho ? para mixings involving near-degenerate ortho and para levels are high (?10(-3)), but they tend to occur at high energy levels, ?300 K. Because of the rapid spontaneous emission, such high levels are not populated in diffuse clouds unless the radiative temperature of the environment is very high. The low-lying 101 (para) and 111 (ortho) levels of H2O(+) are mixed by ?10(-4) making the spontaneous emission lifetime for the para 101 ? ortho 000 transition 520 years and 5200 years depending on the F value of the hyperfine structure. Thus the ortho ? para conversion due to the unpaired electron is not likely to seriously affect thermalization of interstellar H2O(+) unless either the radiative temperature is very high or number density of the cloud is very low. PMID:23530629

Tanaka, Keiichi; Harada, Kensuke; Oka, Takeshi

2013-04-25

280

Solid state nuclear magnetic resonance with magic-angle spinning and dynamic nuclear polarization below 25 K.  

PubMed

We describe an apparatus for solid state nuclear magnetic resonance (NMR) with dynamic nuclear polarization (DNP) and magic-angle spinning (MAS) at 20-25 K and 9.4 Tesla. The MAS NMR probe uses helium to cool the sample space and nitrogen gas for MAS drive and bearings, as described earlier, but also includes a corrugated waveguide for transmission of microwaves from below the probe to the sample. With a 30 mW circularly polarized microwave source at 264 GHz, MAS at 6.8 kHz, and 21 K sample temperature, greater than 25-fold enhancements of cross-polarized (13)C NMR signals are observed in spectra of frozen glycerol/water solutions containing the triradical dopant DOTOPA-TEMPO when microwaves are applied. As demonstrations, we present DNP-enhanced one-dimensional and two-dimensional (13)C MAS NMR spectra of frozen solutions of uniformly (13)C-labeled l-alanine and melittin, a 26-residue helical peptide that we have synthesized with four uniformly (13)C-labeled amino acids. PMID:23238592

Thurber, Kent R; Potapov, Alexey; Yau, Wai-Ming; Tycko, Robert

2012-11-21

281

Simultaneous quantitative determination of deuterium- and carbon-13-labeled essential fatty acids in rat plasma  

Microsoft Academic Search

This study reports methods for the quantitative determination of stable isotope-labeled essential fatty acids (EFAs) as well as an experiment in which deuterium-labeled linoleic acid (18:2n-6) and ? -linolenic acid (18:3n-3) were compared with those labeled with carbon-13 in rat plasma in vivo. Standard curves were constructed to compensate for concentration and plasma matrix effects. It was observed that endogenous

Yu Hong Lin; Robert J. Pawlosky; Norman Salem

2005-01-01

282

Monitoring of liver glycogen synthesis in diabetic patients using carbon-13 MR spectroscopy  

Microsoft Academic Search

To investigate the relationship between liver glucose, glycogen, and plasma glucose in diabetic patients, in vivo liver carbon-13 magnetic resonance spectroscopy (13C MRS) with a clinical 3.0T MR system was performed. Subjects were healthy male volunteers (n=5) and male type-2 diabetic patients (n=5). Pre- and during oral glucose tolerance tests (OGTT), 13C MR spectra without proton decoupling were acquired in

Moyoko Tomiyasu; Takayuki Obata; Yukio Nishi; Hiromitsu Nakamoto; Hiroi Nonaka; Yukihisa Takayama; Joonas Autio; Hiroo Ikehira; Iwao Kanno

2010-01-01

283

Nuclear spin relaxation of {sup 129}Xe due to persistent xenon dimers  

SciTech Connect

We have measured longitudinal nuclear relaxation rates of {sup 129}Xe in Xe-N{sub 2} mixtures at densities below 0.5 amagats in a magnetic field of 8.0 T. We find that intrinsic spin relaxation in this regime is principally due to fluctuations in the intramolecular spin-rotation (SR) and chemical-shift-anisotropy (CSA) interactions, mediated by the formation of {sup 129}Xe-Xe persistent dimers. Our results are consistent with previous work done in one case at much lower applied fields where the CSA interaction is negligible and in another case at much higher gas densities where transient xenon dimers mediate the interactions. We have verified that a large applied field suppresses the persistent-dimer mechanism, consistent with standard relaxation theory, allowing us to measure room-temperature gas-phase relaxation times T{sub 1} for {sup 129}Xe greater than 25 h at 8.0 T. These data also yield a maximum possible low-field T{sub 1} for pure xenon gas at room temperature of 5.45{+-}0.2 h. The coupling strengths for the SR and CSA interactions that we extract are in fair agreement with estimates based both on previous experimental work and on ab initio calculations. Our results have potential implications for the production and storage of large quantities of hyperpolarized {sup 129}Xe for use in various applications.

Berry-Pusey, B. N.; Anger, B. C.; Laicher, G.; Saam, B. [Department of Physics, University of Utah, Salt Lake City, Utah 84112-0830 (United States)

2006-12-15

284

Features of influence of dc magnetic field pulses on a nuclear spin echo in magnets  

NASA Astrophysics Data System (ADS)

Signal intensities of a two-pulse nuclear spin echo as a function of parameters of dc magnetic field pulses are measured in the series of materials: Li0.5Fe2.5-xZnxO4 (x < 0.25) (enriched in 57Fe isotope to 96.8%), NiMnSb, Co2MnSi, La1-\\khcy \\khcy MnO3 (x = 0.2 0.25) and polycrystalline Co. Two types of dependences of these signals on a supplying time of such pulses with respect to the times of the exciting RF pulses are found. The mechanisms of influence of a domain structure and a dynamic frequency shift on the observed features of the investigated signals are discussed.

Mamniashvili, G. I.; Gegechkori, T. O.; Akhalkatsi, A. M.; Gavasheli, C. A.

2012-06-01

285

Electron spin resonance and its implication on the maximum nuclear polarization of deuterated solid target materials  

SciTech Connect

ESR spectroscopy is an important tool in polarized solid target material research, since it allows us to study the paramagnetic centers, which are used for the dynamic nuclear polarization (DNP). The polarization behavior of the different target materials is strongly affected by the properties of these centers, which are added to the diamagnetic materials by chemical doping or irradiation. In particular, the ESR linewidth of the paramagnetic centers is a very important parameter, especially concerning the deuterated target materials. In this paper, the results of the first precise ESR measurements of the deuterated target materials at a DNP-relevant magnetic field of 2.5 T are presented. Moreover, these results allowed us to experimentally study the correlation between ESR linewidth and maximum deuteron polarization, as given by the spin-temperature theory.

Heckmann, J.; Meyer, W.; Radtke, E.; Reicherz, G.; Goertz, S. [Institute for Experimental Physics AG I, Ruhr-University Bochum, D-44780 Bochum (Germany); Physics Institute, University of Bonn, Nussallee 12, D-53115 Bonn (Germany)

2006-10-01

286

Extended s± scenario for the nuclear spin-lattice relaxation rate in superconducting pnictides  

NASA Astrophysics Data System (ADS)

Recently, several measurements of the nuclear spin-lattice relaxation rate T1-1 in the superconducting Fe pnictides have been reported. These measurements generally show no coherence peak below Tc and indicate a low-temperature power-law behavior, the characteristics commonly taken as evidence of unconventional superconductivity with lines of nodes crossing the Fermi surface. In this work we show that (i) the lack of a coherence peak is fully consistent with the previously proposed nodeless extended s± -wave symmetry of the order parameter (whether in the clean or dirty limit) and (ii) the low-temperature power-law behavior can be also explained in the framework of the same model but requires going beyond the Born limit.

Parker, D.; Dolgov, O. V.; Korshunov, M. M.; Golubov, A. A.; Mazin, I. I.

2008-10-01

287

The Low-temperature Nuclear Spin Equilibrium of H+ 3 in Collisions with H2  

NASA Astrophysics Data System (ADS)

Recent observations of H2 and H+ 3 in diffuse interstellar sightlines revealed a difference in the nuclear spin excitation temperatures of the two species. This discrepancy comes as a surprise, as H+ 3 and H2 should undergo frequent thermalizing collisions in molecular clouds. Non-thermal behavior of the fundamental H+ 3/H2 collision system at low temperatures was considered as a possible cause for the observed irregular populations. Here, we present measurements of the steady-state ortho/para ratio of H+ 3 in collisions with H2 molecules in a temperature-variable radiofrequency ion trap between 45 and 100 K. The experimental results are close to the expected thermal outcome and they agree very well with a previous micro-canonical model. We briefly discuss the implications of the experimental results for the chemistry of the diffuse interstellar medium.

Grussie, F.; Berg, M. H.; Crabtree, K. N.; Gärtner, S.; McCall, B. J.; Schlemmer, S.; Wolf, A.; Kreckel, H.

2012-11-01

288

Optimized basis sets for the calculation of indirect nuclear spin-spin coupling constants involving the atoms B, Al, Si, P, and Cl  

NASA Astrophysics Data System (ADS)

The aug-cc-pVTZ-J series of basis sets for indirect nuclear spin-spin coupling constants has been extended to the atoms B, Al, Si, P, and Cl. The basis sets were obtained according to the scheme previously described by Provasi et al. [J. Chem. Phys. 115, 1324 (2001)]. First, the completely uncontracted correlation consistent aug-cc-pVTZ basis sets were extended with four tight s and three tight d functions. Second, the s and p basis functions were contracted with the molecular orbital coefficients of self-consistent-field calculations performed with the uncontracted basis sets on the simplest hydrides of each atom. As a first illustration, we have calculated the one-bond indirect spin-spin coupling constants in BH4-, BF, AlH, AlF, SiH4, SiF4, PH3, PF3, H2S, SF6, HCl, and ClF at the level of density functional theory using the Becke three parameter Lee-Yang-Parr and the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes.

Provasi, Patricio F.; Sauer, Stephan P. A.

2010-08-01

289

Fractionated Mercury Isotopes in Fish: The Effects of Nuclear Mass, Spin, and Volume  

NASA Astrophysics Data System (ADS)

Mercury is long known as a common environmental contaminant. In methylated form it is even more toxic and the methylation process is facilitated by microbial activities. Methyl mercury easily crosses cell membrane and accumulates in soft tissues of fishes and finally biomagnifies with increasing trophic levels. Natural variations in the isotopic composition of mercury have been reported and such variations have emphasized mass dependent fractionations, while theory and laboratory experiments indicate that mass-independent isotopic fractionation (MIF) effects are likely to be found as well. This study focuses on the MIF of mercury isotopes in the soft tissues of fishes. Samples include both fresh water and marine fish, from different continents and oceans. Approximately 1 gm of fish soft tissue was dissolved in 5 ml of conc. aqua regia for 24 hrs and filtered through a ¬¬¬100 ?m filter paper and diluted with DI water. Hg is measured as a gaseous phase generated by reduction of the sample with SnCl2 in a continuous- flow cold-vapor generator connected to a Thermo-Finnigan Neptune MC-ICPMS. To minimize instrumental fractionation isotope ratios were measured by sample standard bracketing and reported as ?‰ relative to NIST SRM 3133 Hg standard where ?AHg = [(A Hg/202Hg)sample/(A Hg/202Hg)NIST313] -1 ×1000‰. In this study we have measured the isotope ratios 198Hg/202Hg, 199Hg/202Hg, 200Hg/202Hg, 201Hg/202Hg and 204Hg/202Hg. In all the fish samples ?198Hg, ?200Hg, ?202Hg, ?204Hg define a mass- dependent fractionation sequence, where as the ?199Hg and ?201Hg depart from the mass- dependent fractionation line and indicate an excess of the odd-N isotopes. The magnitude of the deviation (?AHg where A=199 or 201) as obtained by difference between the measured ?199Hg and ?201Hg of the samples and the value obtained by linear scaling defined by the even-N isotopes ranges from approximately 0.2 ‰ to 3‰. The ratios of ?199Hg /?201Hg range from 0.8 to 1.3, and thus more than one mass-independent isotope effect is inferred. MIF of mercury can be caused by the nuclear volume effect. Schauble, 2007 has calculated nuclear volume fractionation scaling factors for a number of common mercury chemical species in equilibrium with Hg° vapor. From his calculations the nuclear field shift effect is larger in ?199Hg than in ?201Hg by approximately a factor of two. The predominant mercury chemical species in fish is methylmercury cysteine. From the experimental studies of Buchachenko and others (2004) on the reaction of methylmercury chloride with creatine kinase it seems reasonable to predicted that the thiol functional groups of cysteine gets enriched in 199Hg and 201Hg. Here the magnetic isotope effect (MIE) produces a kinetic partial separation of isotopes with non-zero nuclear spin quantum numbers from the even-N isotopes. The ratio of enrichment of ?201Hg /?199Hg is predicted from theory to be 1.11, which is the ratio of the magnetic moments of 199Hg and 201Hg. Because mercury possesses two odd-N isotopes, it is possible to detect and evaluate the effects of two distinct, mass-independent isotope fractionating processes. From the data obtained on fish samples, we can deconvolute the contributions of the isotope effects of nuclear mass, spin and volume. For these samples the role of spin or the magnetic isotope effect is the most dominant.

Das, R.; Odom, A. L.

2007-12-01

290

Quantitative nuclear magnetic resonance analysis of solid formoterol fumarate and its dihydrate.  

PubMed

Carbon-13 cross-polarization magic-angle spinning nuclear magnetic resonance spectra of anhydrous formoterol fumarate and the dihydrate are presented, together with some relaxation time measurements. The latter enabled quantitation of mixtures of the anhydrate and dihydrate to be made. Quantitative nuclear magnetic resonance measurements were then performed on mixtures of the two forms formulated in lactose. Relative amounts of the forms could be assessed at a total formulation level of 2%, whereas the dihydrate on its own in lactose was detectable at the 0.45% level. The optimum experiment involves dipolar dephasing, because that minimizes the intensity of signals from the lactose. PMID:14603494

Apperley, David C; Harris, Robin K; Larsson, Tomas; Malmstrom, Torsten

2003-12-01

291

Propagation of dynamic nuclear polarization across the xenon cluster boundaries: Elucidation of the spin-diffusion bottleneck  

NASA Astrophysics Data System (ADS)

Earlier Dynamic Nuclear Polarization (DNP) experiments with frozen xenon/1-propanol/trityl mixtures have demonstrated spontaneous formation of pure xenon clusters above 120 K, enabling spectrally-resolved real-time measurements of 129Xe nuclear magnetization in the clusters and in the surrounding radical-rich matrix. A spin-diffusion bottleneck was postulated to explain the peculiar time evolution of 129Xe signals in the clusters as well as the apparent discontinuity of 129Xe polarization across the cluster boundaries. A self-contained ab initio model of nuclear spin diffusion in heterogeneous systems is developed here, incorporating the intrinsic T1 relaxation towards the temperature-dependent equilibrium polarization and the spin-diffusion coefficients based on the measured NMR line widths and the known atomic densities in each compartment. This simple model provides the physical basis for the observed spin-diffusion bottleneck and is in a good quantitative agreement with the earlier measurements. A simultaneous fit of the model to the time-dependent NMR data at two different DNP frequencies provides excellent estimates of the cluster size, the intrinsic sample temperature, and 129Xe T1 constants. The model was also applied to the NMR data acquired during relaxation towards the thermal equilibrium after the microwaves were turned off, to estimate T1 relaxation time constants inside and outside the clusters. Fitting the model to the data during and after DNP provides consistent estimates of the cluster size.

Pourfathi, M.; Kuzma, N. N.; Kara, H.; Ghosh, R. K.; Shaghaghi, H.; Kadlecek, S. J.; Rizi, R. R.

2013-10-01

292

Propagation of dynamic nuclear polarization across the xenon cluster boundaries: Elucidation of the spin-diffusion bottleneck.  

PubMed

Earlier Dynamic Nuclear Polarization (DNP) experiments with frozen xenon/1-propanol/trityl mixtures have demonstrated spontaneous formation of pure xenon clusters above 120K, enabling spectrally-resolved real-time measurements of (129)Xe nuclear magnetization in the clusters and in the surrounding radical-rich matrix. A spin-diffusion bottleneck was postulated to explain the peculiar time evolution of (129)Xe signals in the clusters as well as the apparent discontinuity of (129)Xe polarization across the cluster boundaries. A self-contained ab initio model of nuclear spin diffusion in heterogeneous systems is developed here, incorporating the intrinsic T1 relaxation towards the temperature-dependent equilibrium polarization and the spin-diffusion coefficients based on the measured NMR line widths and the known atomic densities in each compartment. This simple model provides the physical basis for the observed spin-diffusion bottleneck and is in a good quantitative agreement with the earlier measurements. A simultaneous fit of the model to the time-dependent NMR data at two different DNP frequencies provides excellent estimates of the cluster size, the intrinsic sample temperature, and (129)Xe T1 constants. The model was also applied to the NMR data acquired during relaxation towards the thermal equilibrium after the microwaves were turned off, to estimate T1 relaxation time constants inside and outside the clusters. Fitting the model to the data during and after DNP provides consistent estimates of the cluster size. PMID:23981341

Pourfathi, M; Kuzma, N N; Kara, H; Ghosh, R K; Shaghaghi, H; Kadlecek, S J; Rizi, R R

2013-07-27

293

Motions and electrostatic interactions in natural and semisynthetic myoglobins: a carbon-13 nuclear magnetic resonance study  

SciTech Connect

It is expected that the internal motions of amino acid side chains and protein backbone segments influence and are in turn affected by charge-charge and related interactions, steric constraints, hydrophobic forces, and hydrogen bonding. As an initial test of this theory /sup 13/C-enriched glycine, alanine, and isoleucine have been substituted for the amino terminal valine of sperm whale myoglobin using semisynthetic techniques. /sup 13/C-NMR has been used to analyze the motions of the side chain and the protonation state of the alpha amino group as a function of pH. The addition of a single methyl group to the side chain can alter the alpha amino pK value by as much as 0.3 pH units indicating a delicately balanced set of change-charge interactions between the alpha amino group and the rest of the protein. Further evidence in support of the state theory was found upon examination of the internal motions of seven of nine isoleucine vectors. These motions were extracted from natural abundance /sup 13/C-NMR relaxation data. The results suggest a strong possibility that concerted motions are important. Also, an increase in temperature from 32/sup 0/C to 52/sup 0/C leads to an electrostatically driven tightening of the myoglobin structure as evidenced by no significant increase in motion amplitude of most of the vectors.

Maskalick, D.G.

1984-01-01

294

Carbon-13, Nitrogen-14, Oxygen-17 NMR (Nuclear Magnetic Resonance) Spectra of Aromatic Nitro-Compounds.  

National Technical Information Service (NTIS)

exp 13 C, exp 14 N, and exp 17 O NMR spectra of a series of nitrobenzenes, nitrophenols, and nitroanilines were measured. Measurement precision of the chemical shifts was +-0.2 m.d. in exp 13 C and +-0.5 m.d. in exp 14 N. (LK). (ERA citation 03:035764)

M. Magi

1971-01-01

295

Microwave field distribution in a magic angle spinning dynamic nuclear polarization NMR probe  

NASA Astrophysics Data System (ADS)

We present a calculation of the microwave field distribution in a magic angle spinning (MAS) probe utilized in dynamic nuclear polarization (DNP) experiments. The microwave magnetic field (B1S) profile was obtained from simulations performed with the High Frequency Structure Simulator (HFSS) software suite, using a model that includes the launching antenna, the outer Kel-F stator housing coated with Ag, the RF coil, and the 4 mm diameter sapphire rotor containing the sample. The predicted average B1S field is 13 ?T/W1/2, where S denotes the electron spin. For a routinely achievable input power of 5 W the corresponding value is ?SB1S = 0.84 MHz. The calculations provide insights into the coupling of the microwave power to the sample, including reflections from the RF coil and diffraction of the power transmitted through the coil. The variation of enhancement with rotor wall thickness was also successfully simulated. A second, simplified calculation was performed using a single pass model based on Gaussian beam propagation and Fresnel diffraction. This model provided additional physical insight and was in good agreement with the full HFSS simulation. These calculations indicate approaches to increasing the coupling of the microwave power to the sample, including the use of a converging lens and fine adjustment of the spacing of the windings of the RF coil. The present results should prove useful in optimizing the coupling of microwave power to the sample in future DNP experiments. Finally, the results of the simulation were used to predict the cross effect DNP enhancement (?) vs. ?1S/(2?) for a sample of 13C-urea dissolved in a 60:40 glycerol/water mixture containing the polarizing agent TOTAPOL; very good agreement was obtained between theory and experiment.

Nanni, Emilio A.; Barnes, Alexander B.; Matsuki, Yoh; Woskov, Paul P.; Corzilius, Björn; Griffin, Robert G.; Temkin, Richard J.

2011-05-01

296

The Spin Dependence of Nuclear Muon Capture by Laser Polarized HELIUM-3.  

NASA Astrophysics Data System (ADS)

Using the muon beam at TRIUMF, we have made the first measurement of the spin dependence of the reaction: mu^- + ^3He tonu +^3H. This spin dependence is quite sensitive to the induced pseudoscalar form factor, F_{P}, a piece of the weak charged nuclear current of ^3He about which, experimentally, relatively little is known. The ratio of F_{P} to F _{A}, the axial vector form factor, is predicted by the partially conserved axial current hypothesis (PCAC) and the Goldberger-Treiman relation. Thus, a measurement of F_{P} will test our understanding of strong interactions at low energies. The rate of nuclear muon capture in ^3 He is proportional to (1+A_{v }P_{v} {rm cos} theta), where theta is the angle between the muon polarization and the direction of the triton recoil, P_{v} is the muon vector polarization and A_{v } is the vector analyzing power, a preliminary value for which is: A_{v} = .604 +/-.093(stat.)_sp{-142}{+112 }(system.). This value is in agreement with the PCAC prediction of: A_{v}=.524 +/-.006. A measure of the strength of our technique is that the raw forward/backward asymmetry in the triton recoil direction was measured to 11.5% of itself. The design, construction and operation of the device that served both as a polarized target and as a detector for the recoil tritons is the main emphasis of this thesis. The detector, a gridded ion chamber, was incorporated inside a 5 liter target that was filled with 8 atmospheres of ^3He, 100 torr of N_2, and 6 grams of Rb. Muons stopped in the target formed muonic helium atoms and were polarized by collisions with Rb atoms that were optically pumped with lasers. The ion chamber produced clean signals despite operating under the severe conditions required for optical pumping. The direction of the tritons was determined by fitting the shapes of the ionization pulses. Future improvements of our technique appear to provide the most promising avenue to improved understanding of the induced pseudoscalar coupling, F_ {P}, as well as the induced pseudoscalar coupling of the proton, g_{P}. .

Bogorad, Paul Lev

1995-01-01

297

Studies of phospholipid hydration by high-resolution magic-angle spinning nuclear magnetic resonance.  

PubMed Central

A sample preparation method using spherical glass ampoules has been used to achieve 1.5-Hz resolution in 1H magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of aqueous multilamellar dispersions of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), serving to differentiate between slowly exchanging interlamellar and bulk water and to reveal new molecular-level information about hydration phenomena in these model biological membranes. The average numbers of interlamellar water molecules in multilamellar vesicles (MLVs) of DOPC and POPC were found to be 37.5 +/- 1 and 37.2 +/- 1, respectively, at a spinning speed of 3 kHz. Even at speeds as high as 9 kHz, the number of interlamellar waters remained as high as 31, arguing against dehydration effects for DOPC and POPC. Both homonuclear and heteronuclear nuclear Overhauser enhancement spectroscopy (NOESY and HOESY) were used to establish the location of water near the headgroup of a PC bilayer. 1H NMR comparisons of DOPC with a lipid that can hydrogen bond (monomethyldioleoylphosphatidylethanolamine, MeDOPE) showed the following trends: 1) the interlamellar water resonance was shifted to lower frequency for DOPC but to higher frequency for MeDOPE, 2) the chemical shift variation with temperature for interlamellar water was less than that of bulk water for MeDOPE MLVs, 3) water exchange between the two lipids was rapid on the NMR time scale if they were mixed in the same bilayer, 4) water exchange was slow if they were present in separate MLVs, and 5) exchange between bulk and interlamellar water was found by two-dimensional exchange experiments to be slow, and the exchange rate should be less than 157 Hz. These results illustrate the utility of ultra-high-resolution 1H MAS NMR for determining the nature and extent of lipid hydration as well as the arrangement of nuclei at the membrane/water interface.

Zhou, Z; Sayer, B G; Hughes, D W; Stark, R E; Epand, R M

1999-01-01

298

19F and 29Si nuclear magnetic shielding and spin–spin coupling constants in silicon tetrafluoride and hexafluorodisiloxane in the gaseous state  

NASA Astrophysics Data System (ADS)

In this contribution the gas-phase measurements of 19F and 29Si chemical shifts and scalar spin–spin couplings in SiF4 and (SiF3)2O have been reported. The density dependence of silicon and fluorine nuclei chemical shifts is strictly linear for both compounds. An extrapolation of gaseous data to the zero-density limit permitted the measurements of 19F and 29Si absolute nuclear magnetic shielding of isolated molecules at 300 K. They were referenced against general accepted standards and are as follows: ?0(SiF4) = 362.87 ppm, ?0(SiF4) = 488.15 ppm, ?0((SiF3)2O) = 356.50 ppm, and ?0((SiF3)2O) = 487.95 ppm. The direct measurements of shielding constants on the basis of NMR frequencies were also performed. Indeed, we have successfully demonstrated the equivalence of both shielding values refinements. Careful investigation of 19F spectra shows isotope effects connected with the presence of three naturally occurring silicon isotopes: 28Si (92.19%), 29Si (4.70%) and 30Si (3.09%). The isotope effect measured on 19F nuclei does not exceed 0.01 ppm. The 1J(Si, F) indirect spin–spin coupling constants in both molecules were extracted from an experimental spectra of gaseous samples. The intermolecular effects in the gaseous state as well as in coming from gas to organic solutions were also observed. The new experimental results were used for verification of the theoretical evaluations presented earlier.

Makulski, W?odzimierz

2013-03-01

299

Carbon-13 NMR relaxation study of motional dynamics in complex liquids  

NASA Astrophysics Data System (ADS)

The motional behavior of complex liquids of various phthalates and structurally related compounds has been investigated using 13C NMR relaxation measurements. Natural abundance 13C NMR spin- lattice relaxation times (T1), spin-spin relaxation times (T2), and nuclear Overhauser effects of individual carbon nuclei in the complex phthalate liquids were measured as a function of temperature and pressure. In addition, an unambiguous 13C peak assignments were carried out using both 2D hydrogen-carbon chemical shift correlation and specific relaxation of individual carbons in the molecule. The choice of model for the spectral density function was critical for proper analysis of the NMR relaxation data in terms of the molecular motion of these molecules, which have flexible side chains attached to a relatively rigid framework composed of phenyl ring and conjugated ester groups. The temperature and pressure dependencies of the relaxation behavior were successfully interpreted in terms of a theoretical model assuming a Cole-Davidson distribution of correlation times, which in turn provided information on the overall and internal motions. Based on these results, the effects of structural variation, both in a relatively rigid framework and in the flexible alkyl side chains of phthalates, on the change in motional behavior and bulk flow properties have been investigated. The 13C NMR relaxation data of individual nuclei for these molecules analyzed in terms of the Cole-Davidson distribution model have provided detailed information about the effect of structural change on their motional characteristics. The motional behavior of these compounds was significantly affected by both the structural shape of the framework and the branching of the side chain, which could be represented by the parameter ? in the Cole-Davidson distribution model. It was found that the mobility gradient along the alkyl side chains was independent of the relatively rigid framework composed of a ring and carboxyl group. The motional characteristics influenced by the molecular structure for the phthalates could be related to the macroscopic physical property of viscosity and its temperature dependence.

Kim, Yoo Joong

1997-06-01

300

Syntheses of carbon-13 labeled protoporphyrin-IX for spectroscopic studies of heme proteins  

SciTech Connect

The development of various methodologies for synthesis of selectively tailored protoporphyrin-IX dimethyl ester are presented. The iron(II) complex of protoporphyrin-IX is the heme, the prosthetic group for Hb, Mb, cytochromes and peroxidases. The significance of this research is to provide direct means to establish definitive carbon-13 NMR assignments of heme proteins in order to study not only the structure-function relationships, but also protein dynamics of these vital systems. Carbon-13 labeling at the beta-vinyl position was first achieved by ozonolysis of protoporphyrin-IX dimethyl ester. Column LC method were used to first isolate 2,4-diformyldeuteroporphyrin-IX dimethyl ester. Concomitantly, monofomyl-monovinyl porphyrins were obtained as a mixture of two isomers. This mixture was separated by MPLC or prep HPLC to afford the isomerically pure products, Spirographis porphyrin dimethyl ester and Iso-Spirographis porphyrin dimethyl ester. A Wittig reaction to each of these porphyrins with /sup 13/C-methyltriphenylphosphonium iodide gave 2,4-bis(/sup 13/C/sub 2/)-vinyl protoporphyrin-IX dimethyl ester, 2-(/sup 13/C/sub 2/)-vinyl protoporphyrin-IX dimethyl ester, and the 4-(/sup 13/C/sub 2/)-vinyl protoporphyrin-IX dimethyl ester, respectively.

Fujinari, E.M.

1985-01-01

301

Properties of Mixtures of Cholesterol with Phosphatidylcholine or with Phosphatidylserine Studied by 13C Magic Angle Spinning Nuclear Magnetic Resonance  

Microsoft Academic Search

The behavior of cholesterol is different in mixtures with phosphatidylcholine as compared with phosphatidylserine. In 13C cross polarization\\/magic angle spinning nuclear magnetic resonance spectra, resonance peaks of the vinylic carbons of cholesterol are a doublet in samples containing 0.3 or 0.5mol fraction cholesterol with 1-palmitoyl-2-oleoyl phosphatidylserine (POPS) or in cholesterol monohydrate crystals, but a singlet with mixtures of cholesterol and

Richard M. Epand; Alex D. Bain; Brian G. Sayer; Diana Bach; Ellen Wachtel

2002-01-01

302

Nuclear spin dependence of the reaction of H(3)+ with H2. II. Experimental measurements.  

PubMed

The nuclear spin dependence of the chemical reaction H(3)(+)+ H(2) ? H(2)?+ H(3)(+) has been studied in a hollow cathode plasma cell. Multipass infrared direct absorption spectroscopy has been employed to monitor the populations of several low-energy rotational levels of ortho- and para-H(3)(+) (o-H(3)(+) and p-H(3)(+)) in hydrogenic plasmas of varying para-H(2) (p-H(2)) enrichment. The ratio of the rates of the proton hop (k(H)) and hydrogen exchange (k(E)) reactions ? ? k(H)/k(E) is inferred from the observed p-H(3)(+) fraction as a function of p-H(2) fraction using steady-state chemical models. Measurements have been performed both in uncooled (T(kin) ? 350 K) and in liquid-nitrogen-cooled (T(kin) ? 135 K) plasmas, marking the first time this reaction has been studied at low temperature. The value of ? has been found to decrease from 1.6 ± 0.1 at 350 K to 0.5 ± 0.1 at 135 K. PMID:21599063

Crabtree, Kyle N; Kauffman, Carrie A; Tom, Brian A; Beçka, Eftalda; McGuire, Brett A; McCall, Benjamin J

2011-05-21

303

Nuclear spin dependence of the reaction of H3+ with H2. II. Experimental measurements  

NASA Astrophysics Data System (ADS)

The nuclear spin dependence of the chemical reaction H3++ H2 --> H2 + H3+ has been studied in a hollow cathode plasma cell. Multipass infrared direct absorption spectroscopy has been employed to monitor the populations of several low-energy rotational levels of ortho- and para-H3+ (o-H3+ and p-H3+) in hydrogenic plasmas of varying para-H2 (p-H2) enrichment. The ratio of the rates of the proton hop (kH) and hydrogen exchange (kE) reactions ? ? kH/kE is inferred from the observed p-H3+ fraction as a function of p-H2 fraction using steady-state chemical models. Measurements have been performed both in uncooled (Tkin ~ 350 K) and in liquid-nitrogen-cooled (Tkin ~ 135 K) plasmas, marking the first time this reaction has been studied at low temperature. The value of ? has been found to decrease from 1.6 +/- 0.1 at 350 K to 0.5 +/- 0.1 at 135 K.

Crabtree, Kyle N.; Kauffman, Carrie A.; Tom, Brian A.; Beçka, Eftalda; McGuire, Brett A.; McCall, Benjamin J.

2011-05-01

304

Modeling the Influence of Nuclear Spin in the Reaction of H_3^+ with H_2  

NASA Astrophysics Data System (ADS)

The reaction H_3^+ + H_2 ? H_2 + H_3^+ is among the simplest of bimolecular chemical reactions, and may play an important role in determining the ortho:para ratios of H_3^+ and H_2 in interstellar environments. Despite its apparent simplicity, the kinetics of this reaction is not well understood, particularly the branching fractions of the proton hop and hydrogen exchange reaction pathways. In this contribution, we present a series of steady state chemical models that show how this reaction can be studied in the laboratory with spectroscopy. Our first model is based entirely on nuclear spin statistics, appropriate for high temperature, low pressure plasmas. This model is then extended to account for the possibility of a small number of three-body collisions which could influence the interpretation of spectroscopic measurements of the H_3^+ + H_2 binary reaction. Our final model employs rate coefficients calculated using a microcanonical statistical approach which takes into account energetic restrictions on certain reaction pathways, which may become important at lower temperatures. These models are directly aimed at extracting kinetic information about the H_3^+ + H_2 reaction from laboratory spectra of hydrogenic plasmas.

Crabtree, Kyle N.; Tom, Brian A.; McCall, Benjamin J.

2011-06-01

305

Breit interaction effects in relativistic theory of the nuclear spin-rotation tensor  

NASA Astrophysics Data System (ADS)

In this work, relativistic effects on the nuclear spin-rotation (SR) tensor originated in the electron-nucleus and electron-electron Breit interactions are analysed. To this end, four-component numerical calculations were carried out in model systems HX (X=H,F,Cl,Br,I). The electron-nucleus Breit interaction couples the electrons and nuclei dynamics giving rise to a purely relativistic contribution to the SR tensor. Its leading order in 1/c is of the same value as that of relativistic corrections on the usual second order expression of the SR tensor considered in previous work [I. A. Aucar, S. S. Gómez, J. I. Melo, C. G. Giribet, and M. C. Ruiz de Azúa, J. Chem. Phys. 138, 134107 (2013)], and therefore it is absolutely necessary to establish its relative importance. For the sake of completeness, the corresponding effect originating in the electron-electron Breit interaction is also considered. It is verified that in all cases these Breit interactions yield only very small corrections to the SR tensors of both the X and H nuclei in the present series of compounds. Results of the present work strongly suggest that in order to achieve experimental accuracy in the theoretical study of the SR tensor both electron-nucleus and electron-electron Breit effects can be safely neglected.

Aucar, I. Agustín; Gómez, Sergio S.; Giribet, Claudia G.; Ruiz de Azúa, Martín C.

2013-09-01

306

Magic angle sample spinning sup 13 C nuclear magnetic resonance of isotopically labeled bacteriorhodopsin  

SciTech Connect

Bacteriorhodopsin (bR), the light-driven proton pump protein from Halobacterium halobium, was biosynthetically labeled with (4-{sup 13}C)Asp. The incorporation yield was 48%. The magic angle sample spinning (MASS) {sup 13}C nuclear magnetic resonance (NMR) spectrum of this sample revealed six different peaks superimposed on a broad band of naturally abundant peptide-bond {sup 13}C. Two of the six carbonyl signals can be attributed to internal-protonated Asp carboxyl groups, one of which might be Asp115. An additional resonance at 110 ppm can be associated with the C-11 carbon of Trp, indicating an unusual biosynthetic pathway of this amino acid in Halobacterium halobium. Similar measurements performed on papain-treated purple membrane which lacks the C-terminal tail display two new intense signals at 178 and 178.9 ppm. If the same spectrum is taken without cross-polarization, these signals do not decrease or disappear. On the basis of their intensities and their chemical shifts, one can assign in addition to the C-terminal Asp four Asp residues facing the cytoplasmic phase. In native bR, at least two of these form a salt-bridge-like bond which also might include the C-terminal tail. These experiments not only provide data about the chemical environment of the Asp residues within the hydrophobic core of bacteriorhodopsin but also yield information about the interactions between surface components.

Engelhard, M.; Hess, B.; Emeis, D.; Metz, G.; Kreutz, W.; Siebert, F. (Max-Planck-Institut fuer Ernaehrungsphysiologie, Dortmund (Germany, F.R.))

1989-05-02

307

Pump-and-probe measurements of the nuclear spin relaxation time in a two-subband electron system  

NASA Astrophysics Data System (ADS)

Nuclear spin relaxation measurements are emerging as an effective tool to study the low-frequency spin dynamics of two-dimensional electrons in quantum Hall systems. We present such a measurement in a two-dimensional electron system consisting of two filled subbands. A recently developed pump-and-probe technique [1] was used to obtain the nuclear spin relaxation time in a region where the two sets of Landau levels, corresponding to the two subbands, were nearly degenerate. The pump-and-probe technique allowed us to measure the relaxation time over a much broader range of magnetic fields and electron densities than that in an earlier nuclear magnetic resonance study [2]. An array of interesting observations will be reported,including phase space and temperature dependence study. The project is supported by the NSF under Grant No. DMR-0804794. [4pt] [1] N. Kumada, K. Muraki, and Y. Hirayama, Science 313, 329 (2006). [0pt] [2] X. C. Zhang, G. D. Scott and H. W. Jiang, Phys. Rev. Lett. 98,246802 (2007).

Pan, Hong; Jiang, Hongwen

2010-03-01

308

Large-scale nuclear structure calculations for spin-dependent WIMP scattering with chiral effective field theory currents  

NASA Astrophysics Data System (ADS)

We perform state-of-the-art large-scale shell-model calculations of the structure factors for elastic spin-dependent WIMP scattering off Xe129,131, I127, Ge73, F19, Na23, Al27, and Si29. This comprehensive survey covers the nonzero-spin nuclei relevant to direct dark matter detection. We include a pedagogical presentation of the formalism necessary to describe elastic and inelastic WIMP-nucleus scattering. The valence spaces and nuclear interactions employed have been previously used in nuclear structure calculations for these mass regions and yield a good spectroscopic description of these isotopes. We use spin-dependent WIMP-nucleus currents based on chiral effective field theory at the one-body level and including the leading long-range two-body currents due to pion exchange, which are predicted in chiral effective field theory. Results for all structure factors are provided with theoretical error bands due to the nuclear uncertainties of WIMP currents in nuclei.

Klos, P.; Menéndez, J.; Gazit, D.; Schwenk, A.

2013-10-01

309

Coherence time of the nuclear spin of ionized phosphorus donors in ^28Si at liquid He and room temperature  

NASA Astrophysics Data System (ADS)

Remarkable coherence times have recently been reported for the nuclear spin of dilute neutral ^31P in highly enriched ^28Si [1]. For ionized ^31P, the removal of the hyperfine-coupled electron should result in a nuclear spin even more decoupled from the environment, and hence even longer coherence times at cryogenic temperatures. The coherence time of ionized ^31P was recently observed in natural Si, and while the nuclear coherence time was indeed much longer than the electron coherence time measured in the same device, it was limited to 18 ms due to both the presence of ^29Si as well as the readout mechanism being employed [2]. Here we report on coherence time measurements for ionized ^31P in the same ^28Si samples used for the previous [1] neutral donor study. In addition to the promise of longer cryogenic coherence times, the removal of the hyperfine-coupled electron should result in a profound change in the temperature dependence of T2. For the neutral donor, the electron T1 decreases very rapidly with increasing temperature, and even at 4.2 K the nuclear T2 is limited by the electron T1 [1]. This mechanism is absent for the ionized donor, and we will report on nuclear coherence time measurements for ionized ^31P at room temperature.[4pt] [1] M. Steger et al., Science 336, 1280 (2012).[0pt] [2] L. Dreher et al., Phys. Rev. Lett. 108, 027602 (2012).

Thewalt, Michael L. W.; Saeedi, Kamyar; Simmons, Stephanie; Morton, John J. L.

2013-03-01

310

Nuclear Spin Symmetry Conservation and Relaxation in Water (1H216O) Studied by Cavity Ring-Down (CRD) Spectroscopy of Supersonic Jets  

NASA Astrophysics Data System (ADS)

We report high resolution near-infrared laser spectra of water seeded in a supersonic jet expansion of argon probed by cavity ring-down spectroscopy (CRDS) in the R branch of the 2-3 band (above 7500 cm-1) at several effective temperatures T < 30 K. Our goal is to study nuclear spin symmetry conservation and relaxation. For low mole fractions of water in the gas mixture, we obtained the lowest rotational temperatures and observed nuclear spin symmetry conservation, in agreement with theoretical expectation for inelastic collisions of isolated H2O molecules with Ar and similar to a previous series of experiments with other small molecules in supersonic jet expansions. However, for the highest mole fractions of water, which we used (xH2O < 1.6%), we obtained slightly higher rotational temperatures and observed nuclear spin symmetry relaxation, which cannot be explained by the intramolecular quantum relaxation mechanism in the monomer H2O. The nuclear spin symmetry relaxation observed is, indeed, seen to be related to the formation of water clusters at the early stage of the supersonic jet expansion. Under these conditions, two mechanisms can contribute to nuclear spin symmetry relaxation. The results are discussed in relation to claims of the stability of nuclear spin isomers of H2O in the condensed phase and briefly also to astrophysical spectroscopy.

Manca Tanner, Carine; Quack, Martin; Schmidiger, David

2013-10-01

311

Nuclear spin polarization following intermediate-energy heavy-ion reactions  

SciTech Connect

Intermediate-energy heavy-ion collisions can produce a spin polarization of the projectile-like species. Spin polarization has been observed for both nucleon removal and nucleon pickup processes. Qualitative agreement with measured spin polarization as a function of the momentum of the projectile-like fragment is found in a kinematical model that considers conservation of linear and angular momentum and assumes peripheral interactions between the fast projectile and target. Improvements to the kinematical model are discussed that aim to achieve quantitative agreement with spin polarization data from both the nucleon removal and pickup processes.

Mantica, P. F.; Groh, D. E.; Pinter, J. S. [Department of Chemistry, Michigan State University, East Lansing, MI 48824 (United States); NSCL, Michigan State University, East Lansing, MI 48824 (United States); Mertzimekis, T. J. [NSCL, Michigan State University, East Lansing, MI 48824 (United States); Stuchbery, A. E. [Department of Nuclear Physics, Research School for Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200 (Australia)

2007-06-13

312

Spin transition in iron(II) complexes induced by heat, pressure, light, and nuclear decay  

Microsoft Academic Search

The phenomenon of temperature-dependent spin transition will be introduced and the numerous chemical and physical influences\\u000a affecting the spin transition characteristics will be discussed. We shall mainly concentrate on the spin crossover system\\u000a [Fe(2-pic)3]X2Sol (2-pic=2-aminomethylpyridine; X=Cl, Br; Sol=C2H5OH, CH3OH) and demonstrate how the behaviour of the spin transition5T2g(Oh)?1A1g(Oh) is influenced by substituting the metalion, the non-coordinating anions X, the crystal

P. Gütlich

1987-01-01

313

Nuclear Spin-Spin Coupling Involving Heavy Nuclei. The Coupling between Hg199 and H1 Nuclei in CH3HgX and CH3CH2HgX Compounds  

Microsoft Academic Search

Nuclear spin coupling between protons and Hg199 nuclei in CH3HgX and CH3CH2HgX compounds has been investigated. As the X substituent is made more electronegative very large increases in the spin-coupling constant up to 2½-fold were observed. Smaller alterations occur in different solvent media, and alkyl exchange could be observed in several compounds. In the CH3CH2HgX compounds the changes in the

J. V. Hatton; W. G. Schneider; W. Siebrand

1963-01-01

314

CARBON-13 NMR OR SOLID STATE HYDROCARBONS AND RELATED SUBSTANCES-FINAL REPORT  

SciTech Connect

CARBON-13 NMR OR SOLID STATE HYDROCARBONS AND RELATED SUBSTANCES-FINAL REPORT Abstract: During recent years we have been engaged in SSNMR (Solid State NMR) structural studies of unusual tetracyanoethylene compounds with unusually long bonds between four carbons centered on two electrons. The chemical shift tensors reflect these unusual atomic arrangements. Quantum chemistry predicts the strange tensor shifts. The three dimensional molecular structure may be determined in this manner. Despite significant advances in structural determination from powder diffraction data, NMR shift tensors argument the structural accuracy and also suggest initial trial structures. Mixtures of polymorphs are difficult to analyze with diffraction methods whereas the SSNMR methods are able to characterize such mixtures in one another’s presence. Spectroscopic developments in our laboratory include SSNMR INADEQUATE and FIREMAT methods. We have used these methods to study the 13C and 15N NMR explosive CL-20.

Grant, David M.

2007-08-16

315

On the carbon-13 chemical shift tensors of bent-core mesogens  

NASA Astrophysics Data System (ADS)

Solid state NMR techniques are used to study bent-shape achiral molecules which can form a new type of mesophases, known as 'banana' or B phases. In particular, a recent method called SUPER is applied to two solids of this type of polar mesogens, rotating at the magic angle, to extract carbon-13 chemical shift anisotropy tensors. They are useful not only to aid 13C peak assignments in the isotropic state, but are necessary for accounting the observed chemical shifts of various carbon sites, resided on the bent-core aromatic part, in the spectrum of an aligned mesophase. An example to extract ordering information is given for one of the studied mesogens.

Dong, Ronald Y.; Zhang, J.; Fodor-Csorba, K.

2006-01-01

316

Studies of lake environments using stable isotope ratios of nitrogen (?15N) and carbon (?13C)  

NASA Astrophysics Data System (ADS)

Increasing numbers of studies have recently used stable isotopes of nitrogen (?15N) and carbon (?13C) to clarify the source of nutrients in lake water and sediments, the structure and energy flow of food webs, the bioaccumulation and biomagnification of hazardous chemicals in aquatic animals, and temporal trends in lake environments. In lake research in particular, the analysis of ?15N and ?13C is a powerful tool in analyzing the structure of the food web and energy flows, as well as the bioaccumulation and biomagnification of toxic chemicals in aquatic animals. Furthermore, the integration of data on food webs, stable isotope ratios, and environmental geochemistry can be useful in evaluating the risks of exposure to environmental contaminants. It is hoped that further research on lake environments using stable isotopic methods can be performed with the aim of conserving water quality and aquatic ecosystems.

Iizumi, Yoshiko

317

Water, hydrogen, deuterium, carbon, carbon-13, and oxygen-18 content of selected lunar material  

USGS Publications Warehouse

The water content of the breccia is 150 to 455 ppm, with a ??D from -580 to -870 per mil. Hydrogen gas content is 40 to 53 ppm with a ??D of -830 to -970 per mil. The CO2 is 290 to 418 ppm with S 13C = + 2.3 to + 5.1 per mil and ??18O = 14.2 to 19.1 per mil. Non-CO2 carbon is 22 to 100 ppm, ??18C = -6.4 to -23.2 per mil. Lunar dust is 810 ppm H2O (D = 80 ppm) and 188 ppm total carbon (??13C = -17.6 per mil). The 18O analyses of whole rocks range from 5.8 to 6.2 per mil. The temperature of crystallization of type B rocks is 1100?? to 1300??C, based on the oxygen isotope fractionation between coexisting plagioclase and ilmenite.

Friedman, I.; O'Neil, J. R.; Adami, L. H.; Gleason, J. D.; Hardcastle, K.

1970-01-01

318

Molecular orbital calculations of /sup 13/C-/sup 13/C and /sup 1/H-/sup 1/H nuclear spin-spin coupling constants  

SciTech Connect

Theoretical studies are presented for the conformational dependencies of vicinal /sup 13/C-/sup 13/C coupling constants within a variety of saturated and unsaturated molecular frameworks. Using the molecular orbital approach of Blizzard and Santry, it is shown that three distinct patterns of dihedral angle versus /sup 3/H/sub CC/sup contract/ coupling are produced, depending upon the degree of double bonding present within the direct coupling path. By means of calculations that involve modifying the various exchange integrals, two of these coupling patterns are found to depend on sigma-..pi.. exchange. A rationalization of the origin of these coupling patterns is presented. In all systems studied, the orbital and dipolar contributions to the vicinal coupling constant are calculated to be negligible compared to the Fermi contact mechanism except in conjugated systems. The FP/INDO molecular orbital method is employed in the investigation of substitutent effects on /sup 1/H-/sup 1/H coupling constants in substituted ethanes, ethylenes, and benzenes. Substituent effects are simulated by varying the (1/2)(I + A) INDO parameters on two different types of pseudoatoms, one essentially a pseudo-hydrogen and the other involving 2s and 2p orbitals on two centers. A review of the theory of nuclear spin-spin coupling is presented.

Severson, M.L.

1984-01-01

319

Matrix Isolation Spectroscopy and Nuclear Spin Conversion of NH3 and ND3 in Solid Parahydrogen  

NASA Astrophysics Data System (ADS)

We present matrix isolation infrared absorption spectra of NH3 and ND3 trapped in solid parahydrogen (pH2) at temperatures around 1.8 K. We used the relatively slow nuclear spin conversion (NSC) of NH3 and ND3 in freshly deposited pH2 samples as a tool to assign the sparse vibration-inversion-rotation (VIR) spectra of NH3 in the regions of the -2, -4, 2-4, -1, and -3 bands and ND3 in the regions of the -2, -4, -1, and -3 fundamentals. Partial assignments are also presented for various combination bands of NH3. Detailed analysis of the -2 bands of NH3 and ND3 indicates that both isotopomers are nearly free rotors; that the vibrational energy is blue-shifted by 1-2%; and that the rotational constants and inversion tunneling splitting are 91-94% and 67-75%, respectively, of the gas-phase values. The line shapes of the VIR absorptions are narrow (0.2-0.4 cm-1) for upper states that cannot rotationally relax and broad (>1 cm-1) for upper states that can rotationally relax. We report and assign a number of NH3-induced infrared absorption features of the pH2 host near 4150 cm-1, along with a cooperative transition that involves simultaneous vibrational excitation of a pH2 molecule and rotation-inversion excitation of NH3. The NSCs of NH3 and ND3 were found to follow first-order kinetics with rate constants at 1.8 K of k = 1.88(16) - 10-3 s-1 and k = 1.08(8) - 10-3 s-1, respectively. These measured rate constants are compared to previous measurements for NH3 in an Ar matrix and with the rate constants measured for other dopant molecules isolated in solid pH2.

Ruzi, Mahmut; Anderson, David T.

2013-10-01

320

Intermolecular structure determination of amyloid fibrils with magic-angle spinning and dynamic nuclear polarization NMR  

PubMed Central

We describe magic-angle spinning NMR experiments designed to elucidate the interstrand architecture of amyloid fibrils. Three methods are introduced for this purpose, two being based on the analysis of long-range 13C-13C correlation spectra and a third based on the identification of intermolecular interactions in 13C-15N spectra. We show, in studies of fibrils formed by the 86-residue SH3 domain of PI3 kinase (PI3-SH3), that efficient 13C-13C correlation spectra display a resonance degeneracy that establishes a parallel, in-register alignment of the proteins in the amyloid fibrils. In addition, this degeneracy can be circumvented to yield direct intermolecular constraints. The 13C-13C experiments are corroborated by 15N-13C correlation spectrum obtained from a mixed [15N,12C]/[14N,13C] sample which directly quantifies interstrand distances. Furthermore, when the spectra are recorded with signal enhancement provided by dynamic nuclear polarization (DNP) at 100 K, we demonstrate a dramatic increase (from 23 to 52) in the number of intermolecular 15N-13C constraints present in the spectra. The increase in the information content is due to the enhanced signal intensities and to the fact that dynamic processes, leading to spectral intensity losses, are quenched at low temperatures. Thus, acquisition of low temperature spectra addresses a problem that is frequently encountered in MAS spectra of proteins. In total the experiments provide 111 intermolecular 13C-13C and 15N-13C constraints that establish that the PI3-SH3 protein strands are aligned in a parallel, in-register arrangement within the amyloid fibril.

Bayro, Marvin J.; Debelouchina, Galia T.; Eddy, Matthew T.; Birkett, Neil R.; MacPhee, Catherine E.; Rosay, Melanie; Maas, Werner E.; Dobson, Christopher M.

2011-01-01

321

Landau-Zener tunneling of a single Tb3+ magnetic moment allowing the electronic read-out of a nuclear spin  

NASA Astrophysics Data System (ADS)

A multiterminal device based on a carbon nanotube quantum dot was used at very low temperature to probe a single electronic and nuclear spin embedded in a bis-(phthalocyaninato) terbium (III) complex (TbPc2). A spin-valve signature with large conductance jumps was found when two molecules were strongly coupled to the nanotube. The application of a transverse field separated the magnetic signal of both molecules and enabled single-shot read-out of the terbium nuclear spin. The Landau-Zener (LZ) quantum tunneling probability was studied as a function of field sweep rate, establishing a good agreement with the LZ equation and yielding the tunnel splitting ?. It was found that ? increased linearly as a function of the transverse field. These studies are an essential prerequisite for the coherent manipulation of a single nuclear spin in TbPc2.

Urdampilleta, M.; Klyatskaya, S.; Ruben, M.; Wernsdorfer, W.

2013-05-01

322

Growth of semiconductor nanostructures by MBE for the study of electron and nuclear spin enhancement and other physical phenomena  

NASA Astrophysics Data System (ADS)

Molecular beam epitaxy (MBE) is an extremely versatile thin film technique, which can produce single-crystal layers with atomic dimensional controls and thus permit the preparation of novel structures and devices tailored to meet specific needs. Spin relaxation time ts is one of the key features in spin-related phenomena and thus of great importance for spintronics. In this work, we prepare high quality samples, mainly of CdTe epilayers, by MBE, characterize their spin relaxation dynamics, and discuss the results theoretically. First, with the goal of understanding the mechanisms of electron relaxation dynamics and nuclear spin enhancement, we focus on the growth and characterization of CdTe epilayers. By changing the shutter sequences and inserting ZnSe buffer layer, we have reproducibly grown (111) and (100) CdTe epilayers of high crystalline qualities by MBE, despite the large lattice mismatch between CdTe and GaAs substrate. Then we investigate ts for the (111) and (100) CdTe epilayers. It is found that for the (111) CdTe, spin relaxation rate t-1s is significantly enhanced and shows no temperature dependence through 130K to 300K, while t-1s for the (100) CdTe is strongly affected by the temperature. It is also found that t-1s is dependent on material quality for both (111) and (100) CdTe. We theoretically discuss the effect of strain and defect on spin relaxation time of CdTe. It is the first experimental observation of the effect of strain on t-1s in a II-VI semiconductor material. Second, the growth and characterization of ZnTe/ZnSe related type II quantum structures, or quantum dots (QDs), are also presented in this work. The PL of Zn-Se-Te related type II quantum structures show blue shifts with higher intensities of exciting laser, an indication of type II QDs. Besides being an attractive method to p-type dope wide bandgap materials, the resulting material may be a promising structure for spin enhancement properties. Third, we present the study of the enhancement of nuclear spin polarization through pumping laser. We find strong enhancement both in bulk CdTe as well as in CdTe epilayers, independent of the helicity of the laser, which is on the contrary to the prior reports by others. Compared with GaAs crystal, we ascribe this independence to the surface spin-dependent recombination. GaAs/AlAs and GaAs/GaAlAs multiple coupled double quantum wells (QWs), and CdTe/CdMgTe QW have also been grown and explored. The measurements show good quality of the material and are consistent with the designed structures. Last, we summary the work and propose the future directions. Samples are in-situ monitored by reflection high energy electron diffraction (RHEED). Post growth characterization techniques, such as time resolved Kerr rotation (TRKR), X-ray diffraction (XRD), photoluminescence (PL), and optical pumping nuclear magnetic resonance (OPNMR), are introduced and applied to the samples.

Zhang, Qiang

323

Spin density wave and superconductivity in CaFe1-xCoxAsF studied by nuclear magnetic resonance  

NASA Astrophysics Data System (ADS)

We performed nuclear magnetic resonance measurements to investigate the evolution of spin-density-wave (SDW) and superconducting (SC) states upon electron doping in CaFe1-xCoxAsF, which exhibits an intermediate phase diagram between those of LaFeAsO1-xFx and Ba(Fe1-xCox)2As2. We found that homogeneous coexistence of the incommensurate SDW and SC states occurs only in a narrow doping region around the crossover regime, which supports S+--wave symmetry. However, only the structural phase transition survives upon further doping, which agrees with predictions from orbital fluctuation theory. The transitional features upon electron doping imply that both spin and orbital fluctuations are involved in the superconducting mechanism.

Tsutsumi, S.; Fujiwara, N.; Matsuishi, S.; Hosono, H.

2012-08-01

324

Dynamics of exocyclic groups in the Escherichia coli O91 O-antigen polysaccharide in solution studied by carbon-13 NMR relaxation.  

PubMed

Carbon-13 relaxation data are reported for exocyclic groups of hexopyranosyl sugar residues in the repeating unit within the Escherichia coli O91 O-antigen polysaccharide in a dilute D2O solution. The measurements of T 1, T 2 and heteronuclear nuclear Overhauser enhancements were carried out at 310 K at two magnetic fields (16.4 T, 21.1 T). The data were analyzed using the standard and extended Lipari-Szabo models, as well as a conformational jump model. The extended version of the Lipari-Szabo and the two-site jump models were most successful for the hydroxymethyl groups of Gal and GlcNAc sugar residues. Different dynamics was found for the hydroxymethyl groups associated with different configurations (D-gluco, D-galacto) of the sugar residues, the latter being faster than the former. PMID:23897032

Soltesova, Maria; Kowalewski, Jozef; Widmalm, Göran

2013-07-30

325

Relativistic nuclear corrections to the spin structure function of the deuteron in the light-cone variables  

SciTech Connect

The relativistic deuteron has been considered in the light-cone formalism as a system of two strongly interacting nucleons (two-nucleon approximation). The technique for the calculation of the average helicity of the proton in the deuteron has been considered in the light-cone variables. A receipt has been pro-posed for the consistent calculation of relativistic nuclear corrections to the average helicity of the proton in the deuteron and to the spin structure function of the deuteron g{sub 1}{sup D}. Relativistic-correction-induced change in the Bjorken sum rule has been discussed.

Pavlov, F. F., E-mail: f.pavlov@tuexph.stu.neva.ru [St. Petersburg State Polytechnic University (Russian Federation)

2012-06-15

326

Limits for spatial anisotropy by use of nuclear-spin--polarized /sup 9/Be/sup +/ ions  

SciTech Connect

The frequency of a nuclear spin-flip (Vertical Bar..delta..m/sub I/Vertical Bar = 1) transition in /sup 9/Be/sup +/ has been compared to the frequency of a hydrogen maser transition (Vertical Bar..delta..FVertical Bar = 1, ..delta..m/sub F/ = 0) to see if the relative frequencies depend on the orientation of the /sup 9/Be/sup +/ ions in space. The present null result represents a decrease in the limits set by Hughes and Drever on a spatial anisotropy by a factor of about 300.

Prestage, J.D.; Bollinger, J.J.; Itano, W.M.; Wineland, D.J.

1985-06-03

327

Carbon13 NMR distinction between categories of molecular order and disorder in cellulose  

Microsoft Academic Search

Differences between values of proton rotating-frame spin relaxation time constants can be exploited to separate a solid-state13C NMR spectrum of cellulose into subspectra of crystalline and noncrystalline regions. Variations in chemical shifts and13C spin-lattice relaxation time constants can then be used to study variations in molecular order and disorder within each of the two broader categories. Mechanical damage during Wiley

Roger H. Newman; Jacqueline A. Hemmingson

1995-01-01

328

Use of Carbon-13 IN Biosynthetic Studies. Incorporation of Isotopically Labelled Acetate and Formate into the Fungal Tropolone, Sepedonin.  

National Technical Information Service (NTIS)

When carbon-13 is used as the isotopic tracer in biosynthetic studies, the labelled atoms in the metabolite can often be determined by n.m.r. spectrometry, without need for chemical degradation. By this technique the biosynthesis of sepedonin in cultures ...

A. G. McInnes D. G. Smith L. C. Vining J. L. C. Wright

1968-01-01

329

Multi-dimensional 1H NMR nuclear Overhauser spectroscopy under magic angle spinning: theory and application to elastomers  

NASA Astrophysics Data System (ADS)

The process of cross-relaxation between different protons (nuclear Overhauser effect) is investigated in soft solids by 2- and 3-dimensional NMR under the conditions of fast magic-angle spinning. The cross-relaxation rates are found to depend weakly on fast motions in the Larmor frequency range and strongly on slow motions of the order of the spinning frequency omegaR. Explicit expressions for the omegaR dependent cross-relaxation rates are derived for different motional models. These findings were tested experimentally on elastomers, i.e., on a crosslinking series of styrene-butadiene rubbers where the cross-relaxation was studied as a function of omegaR. Short mixing times as are required for extracting the relaxation rates could be realized conveniently using a pulsed magnetic-field gradient for coherence pathway selection. As in solution NMR, relative couplings between chemically resolved spins can be determined from the peak intensities. By combining cross-relaxation measurements with T 1 measurements, the distribution of correlation times can be probed for slow and fast timescales, respectively. Only the former were found to depend on the crosslink density.

Fritzhanns, Tilo; Demco, Dan E.; Hafner, Siegfried; Spiess, Hans W.

330

Eigenmodes in the Long-Time Behavior of a Coupled Spin System Measured with Nuclear Magnetic Resonance  

NASA Astrophysics Data System (ADS)

The many-body quantum dynamics of dipolar coupled nuclear spins I=1/2 on an otherwise isolated cubic lattice are studied with nuclear magnetic resonance. By increasing the signal-to-noise ratio by 2 orders of magnitude compared with previous reports for the free induction decay (FID) of F19 in CaF2 we obtain new insight into its long-time behavior. We confirm that the tail of the FID is an exponentially decaying cosine, but our measurements reveal a second decay mode with comparable frequency but twice the decay constant. This result is in agreement with a recent theoretical prediction for the FID in terms of eigenvalues for the time evolution of chaotic many-body quantum systems.

Meier, Benno; Kohlrautz, Jonas; Haase, Jürgen

2012-04-01

331

Body-fixed relativistic molecular Hamiltonian and its application to nuclear spin-rotation tensor: linear molecules.  

PubMed

The relativistic molecular Hamiltonian written in the body-fixed frame of reference is the basis for high-precision calculations of spectroscopic parameters involving nuclear vibrations and/or rotations. Such a Hamiltonian that describes electrons fully relativistically and nuclei quasi-relativistically is just developed for semi-rigid nonlinear molecules [Y. Xiao and W. Liu, J. Chem. Phys. 138, 134104 (2013)]. Yet, the formulation should somewhat be revised for linear molecules thanks to some unusual features arising from the redundancy of the rotation around the molecular axis. Nonetheless, the resulting isomorphic Hamiltonian is rather similar to that for nonlinear molecules. Consequently, the relativistic formulation of nuclear spin-rotation (NSR) tensor for linear molecules is very much the same as that for nonlinear molecules. So is the relativistic mapping between experimental NSR and NMR. PMID:23883016

Xiao, Yunlong; Liu, Wenjian

2013-07-21

332

Eigenmodes in the long-time behavior of a coupled spin system measured with nuclear magnetic resonance.  

PubMed

The many-body quantum dynamics of dipolar coupled nuclear spins I=1/2 on an otherwise isolated cubic lattice are studied with nuclear magnetic resonance. By increasing the signal-to-noise ratio by 2 orders of magnitude compared with previous reports for the free induction decay (FID) of (19)F in CaF(2) we obtain new insight into its long-time behavior. We confirm that the tail of the FID is an exponentially decaying cosine, but our measurements reveal a second decay mode with comparable frequency but twice the decay constant. This result is in agreement with a recent theoretical prediction for the FID in terms of eigenvalues for the time evolution of chaotic many-body quantum systems. PMID:22680905

Meier, Benno; Kohlrautz, Jonas; Haase, Jürgen

2012-04-25

333

Body-fixed relativistic molecular Hamiltonian and its application to nuclear spin-rotation tensor: Linear molecules  

NASA Astrophysics Data System (ADS)

The relativistic molecular Hamiltonian written in the body-fixed frame of reference is the basis for high-precision calculations of spectroscopic parameters involving nuclear vibrations and/or rotations. Such a Hamiltonian that describes electrons fully relativistically and nuclei quasi-relativistically is just developed for semi-rigid nonlinear molecules [Y. Xiao and W. Liu, J. Chem. Phys. 138, 134104 (2013)]. Yet, the formulation should somewhat be revised for linear molecules thanks to some unusual features arising from the redundancy of the rotation around the molecular axis. Nonetheless, the resulting isomorphic Hamiltonian is rather similar to that for nonlinear molecules. Consequently, the relativistic formulation of nuclear spin-rotation (NSR) tensor for linear molecules is very much the same as that for nonlinear molecules. So is the relativistic mapping between experimental NSR and NMR.

Xiao, Yunlong; Liu, Wenjian

2013-07-01

334

Carbon-13 chemical shielding tensors in polycyclic aromatic compounds. 1. single-crystal study of pyrene  

SciTech Connect

The carbon-13 chemical shielding tensors measured in single-crystal pyrene are reported. The two internal bridgehead carbons have principal values of 197, 191, and -18 ppm and the four peripheral bridgehead carbons 213, 187, and -7 ppm with respect to liquid Me/sub 4/Si. The high field component of every tensor is determined to be perpendicular to the molecular plane, as in benzene. The protonated carbons have principal values similar to benzene, with the low-field components lying approximately along the C-H bonds. The rotation of the principal axes away from the C-H bond direction is measured experimentally and interpreted by quantum chemical calculations. By use of a MNDO wave function and the Pople model of chemical shielding, the magnitudes of the experimental in-plane components are reproduced very well and the calculated orientations of the principal axes are consistent with the experimental data. The results reported here demonstrate that the measurement of /sup 13/C shielding tensors in polycyclic aromatic compounds can be used as a measurement of the aromatic character of bonds adjacent to /sup 13/C nuclei.

Carter, C.M.; Alderman, D.W.; Facelli, J.C.; Grant, D.M.

1987-04-29

335

What Do Nuclear Spin Temperatures Tell Us About The Origin Of Comets? A Multi-molecule Study  

NASA Astrophysics Data System (ADS)

Comets are true remnants of our primordial Solar System, and provide unique clues to its formation and evolution, including the delivery of organics and water to our planet. A key indicator stored in the molecular structure of the nuclear ices is the spin temperature (Tspin), derived from spin-isomeric ratios (Rspin, e.g. ortho/para). At the time when cometary ices formed, the prevailing temperature defined the relative abundance of the different spin-isomeric species, and herewith Rspin and Tspin are normally treated as “remnant thermometers” probing the formation environments. Most of our knowledge of this indicator comes from measurements of ortho-para ratios in water and NH2, suggesting a common Tspin near 30K. This information is based on a restricted sample of comets, and the measurements are particularly sensitive to the molecular modeling technique and adopted spectral database. Here, we present new methodologies for extracting spin temperatures from ethane (C2H6), methane (CH4), and methanol (CH3OH), and describe advanced new models for ortho/para water (H2O) and ammonia (NH3). Our H2O analysis is based on the most complete fluorescence radiative transfer model to date, which incorporates 1,200 million transitions including those originating from high-energy levels that are activated in comets via non-resonance cascade. In a similar fashion, we developed non-resonance fluorescence models for NH3 and HCN, and quantum band models for the ?7 band of C2H6 and ?3 band of CH3OH. All models respect spin symmetry non-conversion radiative rules, and make use of a realistic Solar spectrum for the computation of fluorescence pumps. We applied these new methods to derive spin-isomeric ratios for H2O, CH4, C2H6, CH3OH and NH3 from three high-quality cometary datasets: 1) C/2007 W1 (Boattini), 2) C/2001 A2 (LINEAR), and 3) 8P/Tuttle. We compare our results with the measured organic compositions for these comets, and present possible formation and evolution scenarios.

Villanueva, Geronimo; Mumma, M. J.; Bonev, B. P.; DiSanti, M. A.; Magee-Sauer, K.; Gibb, E. L.; Paganini, L.; Radeva, Y. L.

2012-10-01

336

Analysis of experimental data on nuclear masses within Wigner spin-isospin SU(4) symmetry  

NASA Astrophysics Data System (ADS)

The problem of the realization of Wigner spin-isospin SU(4) symmetry in nuclei is analyzed on the basis of available experimental data on nuclide masses in the mass-number range 1 ? A ? 257. Empirical expressions are obtained for the universal functions in the Wigner mass formula. The experimental values of the energy of spin-orbit interaction are determined for the aforementioned nuclides. An alternative mechanism of the origin of the odd-even effect in nuclei having an even mass number associated with a specific property of the Casimir operator is proposed. The results obtained in this study suggest that SU(4) symmetry is broken predominantly by spin-orbit interaction.

Nurmukhamedov, A. M.

2009-03-01

337

Nuclear spin polarization following intermediate-energy heavy-ion reactions  

SciTech Connect

Intermediate-energy heavy-ion collisions can produce a spin polarization of the projectile-like species. Spin polarization has been observed for both nucleon removal and nucleon pickup processes. Qualitative agreement with measured spin polarization as a function of the momentum of the projectile-like fragment is found in a kinematic model that considers conservation of linear and angular momentum and assumes peripheral interactions between the fast projectile and target. Better quantitative agreement was reached by including more realistic angular distributions and deorientation caused by {gamma}-ray emission and by correcting for the out-of-plane acceptance. The newly introduced corrections were found to apply to both nucleon removal and nucleon pickup processes.

Groh, D. E.; Pinter, J. S.; Mantica, P. F. [Department of Chemistry, Michigan State University, East Lansing, Michigan 48824 (United States); National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 (United States); Mertzimekis, T. J. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 (United States); Stuchbery, A. E. [Department of Nuclear Physics, Research School for Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Khoa, D. T. [Institute for Nuclear Science and Technique, VAEC, P. O. Box 5T-160, Nghia Do, Hanoi, (Viet Nam)

2007-11-15

338

Electron spin resonance and electron nuclear double resonance of photogenerated polarons in polyfluorene and its fullerene composite  

NASA Astrophysics Data System (ADS)

Electron spin resonance (ESR) and electron-nuclear double resonance (ENDOR) of photogenerated polarons in poly(9,9-dioctylfluorene) (PFO) and its composite with fullerene (C60) using variable photoexcitation energy up to 4.1 eV are reported. For PFO, a light-induced ESR (LESR) signal (g=2.003) is observed below 60 K, and its transient response and excitation spectrum indicate that the observed spins are photogenerated polarons on PFO. For the PFO-C60 composite, two LESR signals of photogenerated positive polarons on PFO (g1=2.003) and radical anions on C60 (g2=1.999) , respectively, are observed below 120 K, which are caused by photoinduced electron transfer from PFO to C60 . A remarkable enhancement of the LESR signals in the excitation spectrum at ˜2.8eV is observed compared with the case of pure PFO. The bimolecular-recombination kinetics of photogenerated charge carriers in the composite are confirmed by the dependence of the LESR on excitation-light intensity and by the decay dynamics. Light-induced ENDOR (LENDOR) signals are clearly observed for excitation around 2.8 eV owing to the highly efficient photoinduced electron transfer in the composite. Broad LENDOR shifts directly reflect the spin-density distribution of the polarons in PFO. We have determined its maximum shift using LENDOR-induced ESR, and have evaluated the maximum spin density on the carbon site coupled to the proton as 0.032. This value is consistent with the theoretical result obtained by Pariser-Parr-Pople (PPP) model, where the spatial extent of the polarons is calculated as ˜3 monomer units of PFO. The calculated LESR spectra of PFO based on the PPP model are consistent with the experimental spectra, which confirm the above spatial extension of the polaron in PFO.

Marumoto, K.; Kato, M.; Kondo, H.; Kuroda, S.; Greenham, N. C.; Friend, R. H.; Shimoi, Y.; Abe, S.

2009-06-01

339

The Nuclear Responses for Double Beta Neutrinos and Double Spin Isospin Resonances by Using of Double Charge Exchange Heavey Ion Reaction  

NASA Astrophysics Data System (ADS)

To study double spin-isospin responses in view of the ??? decays, double charge-exchange nuclear reactions have measured at RCNP. We have succeeded to measure the double charge exchange reaction by means of heavy ion reaction. From these experiments, we conclude that the (11B,11Li) reaction at 70 MeV/nucleon is a good spectroscopic tool. We believe that the reaction can be well applied to the study of pure spin-flip nuclear responses in higher-excited regions including DGT and higher ?L excitations.

Takahisa, K.; Akimune, H.; Ejiri, H.; Fujimura, H.; Fujiwara, M.; Hara, K.; Hasimoto, H.; Hatanaka, K.; Itahasi, T.; Kawabata, T.; Kawase, K.; Koreeda, Y.; Maehara, N.; Mordechai, S.; Nagai, Y.; Nakanishi, K.; Ninomiya, S.; Shima, T.; Tanaka, M.; Umehara, S.; Umisedo, S.; Yoshida, H. P.; Yoshida, S.; Yoshimura, M.; Yosoi, M.

2005-12-01

340

Nuclear spin-orbit interaction and T-odd angular correlations in ternary fission  

NASA Astrophysics Data System (ADS)

T-odd angular correlations in ternary fission of 233U and 235U nuclei by slow polarized neutrons are not related to TRI (time reversal invariance) violation, but are caused by an effective spin-orbit interaction in the final state.

Barabanov, A. L.

2013-07-01

341

Dipolar nuclear spin relaxation in liquids and plane fluids undergoing chemical reactions  

NASA Astrophysics Data System (ADS)

We describe the correlated translational and rotational relative brownian motions of two reacting groups of atoms, alternatively bound and free, by the normalized solutions of a set of coupled diffusion equations. Under equilibrium conditions we calculate the spectral densities j(?) characteristic of the fluctuations of the intermolecular dipolar coupling between spins of these diffusing groups of atoms. When ?? << 1, where ? is the translational correlation time, the form of the spectral density j2(?) in three-dimensional liquids is j2(0) - ?3?1/2. The coefficient ?3 is independent of the molecular local order, of the diffusional rotation speed of the spin-carrying groups of atoms and of their association and dissociation rates. In plane fluids, when ?? << 1, the spectral density j(0)(?) may be written as -a2 ln (??) where the dependence of a2 on the average relative distribution of the interacting spins varies with the rate of the chemical reactions. In both three- and two-dimensional fluids spectral densities show an ?-3/2 or ?-2 behaviour for ?? >> 1 according to the magnitude of the association rate of the reacting groups of atoms. In liquid glycerol we analyse the low- and high-frequency limits of the experimental proton relaxation rate 1/T1 and 1/T1? measured by Harmon, Harmon and Burnett, and Lenk. We also discuss the proton spin-lattice relaxation times measured by Kleinberg and Silbernagel in layered intercalation compounds TiS2-NH3 and TaS2-NH3.

Fries, P. H.

342

Carbon-13 NMR relaxation studies of pre-melt structural dynamics in [4-13C-uracil] labeled E. coli transfer RNAIVal.  

PubMed Central

We report 67.8 MHz carbon-13 spin-lattice relaxation studies on [4-13C-uracil] labeled tRNAIVal purified from E. coli SO-187. Following 13C-enriched C4 carbonyl resonances from modified and unsubstituted uridines scattered throughout the polymer backbone enables us to determine dynamical features in both loop and helical stem regions. The experimental results have been analyzed in terms of a model of isotropic overall molecular reorientation. "Anomalous" residues for which the experimental data cannot be accounted for in terms of the model provide an assessment of local and regional properties. Thus, "native" tRNAIVal under physiological conditions of magnesium (10 mM) and temperature (20 degrees - 40 degrees C), exhibits the following characteristics: 1) uridines held rigidly in helical stems and tertiary interactions display correlation times for rotational reorientation of 15-20 nsecs, typical for overall tRNA motion; 2) uridines in loops such as the wobble residue uridine-5-oxyacetic acid (V34) are quite accessible to solvent; moreover V34 and another loop residue, D17, exhibit local mobility; 3) the tertiary interactions involving 4-thio uridine (s4U8) and A14 and ribothymidine (rT54) and A58 are weakened as temperature increases.

Olsen, J I; Schweizer, M P; Walkiw, I J; Hamill, W D; Horton, W J; Grant, D M

1982-01-01

343

Nuclear magnetic resonance of organophosphorus compounds: Signs and magnitudes of long-range 1H-31P spin-spin coupling constants in methyl-substituted trithienylphosphine derivatives  

Microsoft Academic Search

The signs and magnitudes of the long-range spin-spin coupling constants between the methyl protons and ring phosphorus nuclei in the six isomeric methyl-substituted trithienylphosphines and their sulfides have been determined. The signs of the coupling constants were obtained using homonuclear selective decoupling and spin tickling techniques and the double resonance spectra compared with those theoretically calculated. In the phosphines the

H. J. Jakobsen; M. Begtrup

1971-01-01

344

Nuclear magnetic resonance and electron spins: Some history, ancient and in the making  

Microsoft Academic Search

Scaling relationships for Nmr spin-lattice relaxation time T1 and Gaussian transverse relaxation tme T c reviewed and applied to analyse experiments in the normal state of YBa2Cu4O8. Studies of T2G in the superconducting state are analysed using the theory of Pines and Wrobel to show a preference for d-state orbital pairing over anisotropic s-state. Data on C Nmr in the

Charles P. Slighter; R. L. Coreyf; N. J. Curro; S. M. Desoto; K. Ohara; T. Imai; A. M. Kini; H. H. Wang; U. Geiser; J. M. Williams; K. Yoshimura; M. Katoh; K. Kosuge

1996-01-01

345

Spin, Hyperfine Structure, and Nuclear Magnetic Dipole Moment of 7.7Min K38  

Microsoft Academic Search

The spin and hyperfine structure of 7.7-min K38 have been determined by the atomic-beam magnetic-resonance method. In this experiment about 100 mg of K39 was placed in an oven in the resonance apparatus and was bombarded with an 0.3 muA beam of 18-MeV protons. K38 was produced by the reaction K39 (p,d or pn)K38, and the resulting specific activity was

E. A. Phillips; O. Ames; S. S. Glickstein

1965-01-01

346

Progress in spin dynamics solid-state nuclear magnetic resonance with the application of Floquet-Magnus expansion to chemical shift anisotropy.  

PubMed

The purpose of this article is to present an historical overview of theoretical approaches used for describing spin dynamics under static or rotating experiments in solid state nuclear magnetic resonance. The article gives a brief historical overview for major theories in nuclear magnetic resonance and the promising theories. We present the first application of Floquet-Magnus expansion to chemical shift anisotropy when irradiated by BABA pulse sequence. PMID:23711337

Mananga, Eugene Stephane

2013-05-06

347

Identifying and Quantifying Actinide Radiation Damage in Ceramics with Radiological Magic-Angle Spinning Nuclear Magnetic Resonance  

SciTech Connect

In the characterisation of amorphization or local disordering due to actinide radiation damage, nuclear magnetic resonance (NMR) spectroscopy is attractive because it is element specific and equally sensitive to local structure in crystalline and amorphous materials. Here, we have applied high-resolution solid-state NMR spectroscopy (magic-angle spinning) to radiation damaged natural minerals containing {sup 238}U/{sup 232}Th to determine the 'number fraction' of amorphous material (fa) through spin-counting techniques. In samples with a known alpha dose, the number of atoms displaced per alpha decay may be determined from an integration of the spectrum. A protocol for performing similar radiological magic-angle spinning experiments on plutonium containing ceramic samples with an activity of > 5 GBq is described. Results obtained have allowed data from ancient, radiation damaged mineral samples of ZrSiO{sub 4} ({sup 238}U/{sup 232}Th) to be compared with modern {sup 238}/{sup 239}Pu doped ceramic ZrSiO{sub 4} samples. The number of atomic displacements per alpha particle from {sup 239}Pu is similar to that for {sup 238}U/{sup 232}Th (4980 {+-} 300/{alpha}). At lower {alpha}-doses there are significant differences in the amorphous volume fraction (observed by density and X-ray diffraction) and the number fraction of displaced atoms (as measured by NMR) as a function of cumulative dose. These differences arise from local density considerations that manifest themselves in the local structure of the amorphous and crystalline phases. Using ab initio simulations of the damaged crystalline and amorphous regions, the magnetic response of these structures and hence the NMR shifts can be compared with experiment to reveal the nature of radiation induced changes occurring at the local scale. (authors)

Farnan, Ian [Earth Sciences, Cambridge University, Cambridge (United Kingdom); Cho, Herman; Weber, William J. [EMSL, Pacific Northwest National Laboratory, Mail Stop, P.O. Box 999, Richland, WA 99352 (United States)

2007-07-01

348

Applications of carbon-13 and sodium-23 NMR in the study of plants, animal, and human cells  

Microsoft Academic Search

Carbon-13 and sodium-23 NMR have been applied to the study of a variety of plant, animal and human cell types. Sodium NMR, in combination with dysprosium shift reagents, has been used to monitor sodium transport kinetics in salt-adapted, and non-adapted cells of P. milliaceum and whole D. spicata plants. The sodium content of human erythrocytes and leukemic macrophages was measured.

L. O. Sillerud; J. W. Heyser; C. H. Han; M. W. Bitensky

1984-01-01

349

Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for a dipole-coupled spin-1/2 pair.  

PubMed

In complex biological or colloidal samples, magnetic relaxation dispersion (MRD) experiments using the field-cycling technique can characterize molecular motions on time scales ranging from nanoseconds to microseconds, provided that a rigorous theory of nuclear spin relaxation is available. In gels, cross-linked proteins, and biological tissues, where an immobilized macromolecular component coexists with a mobile solvent phase, nuclear spins residing in solvent (or cosolvent) species relax predominantly via exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings. The physical or chemical exchange processes that dominate the MRD typically occur on a time scale of microseconds or longer, where the conventional perturbation theory of spin relaxation breaks down. There is thus a need for a more general relaxation theory. Such a theory, based on the stochastic Liouville equation (SLE) for the EMOR mechanism, is available for a single quadrupolar spin I = 1. Here, we present the corresponding theory for a dipole-coupled spin-1/2 pair. To our knowledge, this is the first treatment of dipolar MRD outside the motional-narrowing regime. Based on an analytical solution of the spatial part of the SLE, we show how the integral longitudinal relaxation rate can be computed efficiently. Both like and unlike spins, with selective or non-selective excitation, are treated. For the experimentally important dilute regime, where only a small fraction of the spin pairs are immobilized, we obtain simple analytical expressions for the auto-relaxation and cross-relaxation rates which generalize the well-known Solomon equations. These generalized results will be useful in biophysical studies, e.g., of intermittent protein dynamics. In addition, they represent a first step towards a rigorous theory of water (1)H relaxation in biological tissues, which is a prerequisite for unravelling the molecular basis of soft-tissue contrast in clinical magnetic resonance imaging. PMID:24116610

Chang, Zhiwei; Halle, Bertil

2013-10-14

350

Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for a dipole-coupled spin-1/2 pair  

NASA Astrophysics Data System (ADS)

In complex biological or colloidal samples, magnetic relaxation dispersion (MRD) experiments using the field-cycling technique can characterize molecular motions on time scales ranging from nanoseconds to microseconds, provided that a rigorous theory of nuclear spin relaxation is available. In gels, cross-linked proteins, and biological tissues, where an immobilized macromolecular component coexists with a mobile solvent phase, nuclear spins residing in solvent (or cosolvent) species relax predominantly via exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings. The physical or chemical exchange processes that dominate the MRD typically occur on a time scale of microseconds or longer, where the conventional perturbation theory of spin relaxation breaks down. There is thus a need for a more general relaxation theory. Such a theory, based on the stochastic Liouville equation (SLE) for the EMOR mechanism, is available for a single quadrupolar spin I = 1. Here, we present the corresponding theory for a dipole-coupled spin-1/2 pair. To our knowledge, this is the first treatment of dipolar MRD outside the motional-narrowing regime. Based on an analytical solution of the spatial part of the SLE, we show how the integral longitudinal relaxation rate can be computed efficiently. Both like and unlike spins, with selective or non-selective excitation, are treated. For the experimentally important dilute regime, where only a small fraction of the spin pairs are immobilized, we obtain simple analytical expressions for the auto-relaxation and cross-relaxation rates which generalize the well-known Solomon equations. These generalized results will be useful in biophysical studies, e.g., of intermittent protein dynamics. In addition, they represent a first step towards a rigorous theory of water 1H relaxation in biological tissues, which is a prerequisite for unravelling the molecular basis of soft-tissue contrast in clinical magnetic resonance imaging.

Chang, Zhiwei; Halle, Bertil

2013-10-01

351

Laser cooling and real-time measurement of the nuclear spin environment of a solid-state qubit.  

PubMed

Control over quantum dynamics of open systems is one of the central challenges in quantum science and engineering. Coherent optical techniques, such as coherent population trapping involving dark resonances, are widely used to control quantum states of isolated atoms and ions. In conjunction with spontaneous emission, they allow for laser cooling of atomic motion, preparation and manipulation of atomic states, and rapid quantum optical measurements that are essential for applications in metrology. Here we show that these techniques can be applied to monitor and control individual atom-like impurities, and their local environment, in the solid state. Using all-optical manipulation of the electronic spin of an individual nitrogen-vacancy colour centre in diamond, we demonstrate optical cooling, real-time measurement and conditional preparation of its nuclear spin environment by post-selection. These methods offer potential applications ranging from all-optical nanomagnetometry to quantum feedback control of solid-state qubits, and may lead to new approaches for quantum information storage and processing. PMID:22031442

Togan, E; Chu, Y; Imamoglu, A; Lukin, M D

2011-10-26

352

Nuclear ground-state spins and magnetic moments of {sup 27}Mg, {sup 29}Mg, and {sup 31}Mg  

SciTech Connect

The ground-state spins and magnetic moments of neutron-rich {sup 27}Mg, {sup 29}Mg, and {sup 31}Mg were measured for the first time with laser and {beta}-NMR spectroscopy at ISOLDE/CERN. The hyperfine structure of {sup 27}Mg--observed in fluorescence--confirms previous assignments of the spin I=1/2 and reveals the magnetic moment {mu}{sub I}({sup 27}Mg)=-0.4107(15){mu}{sub N}. The hyperfine structure and nuclear magnetic resonance of optically polarized {sup 29}Mg--observed in the asymmetry of its {beta} decay after implantation in a cubic crystal--give I=3/2 and {mu}{sub I}({sup 29}Mg)=+0.9780(6){mu}{sub N}. For {sup 31}Mg they yield together I=1/2 and {mu}{sub I}({sup 31}Mg)=-0.88355(15){mu}{sub N}, where the negative magnetic moment provides evidence for a positive parity. The results for {sup 27}Mg and {sup 29}Mg agree well with shell-model calculations confined only to the sd model space, whereas the ground state of {sup 31}Mg involves large contributions from neutrons in the pf shell, which places this nucleus inside the ''island of inversion.''.

Kowalska, M.; Neugart, R. [Institut fuer Physik, Universitaet Mainz, D-55099 Mainz (Germany); Yordanov, D. T.; Himpe, P.; Mallion, S.; Neyens, G.; Vermeulen, N. [Instituut voor Kern-en Stralingsfysica, Katholieke Universiteit Leuven, B-3001 Leuven (Belgium); Blaum, K. [Institut fuer Physik, Universitaet Mainz, D-55099 Mainz (Germany); GSI, D-64291 Darmstadt (Germany); Lievens, P. [Laboratorium voor Vaste-Stoffysica en Magnetisme, Katholieke Universiteit Leuven, B-3001 Leuven (Belgium)

2008-03-15

353

Anti-symmetric spin-orbit force in the effective interaction for the shell model and its effect on nuclear structure  

SciTech Connect

Anti-symmetric spin-orbit force (ALS) in the effective interaction for the shell model and its effect on nuclear structure is discussed. We investigate possible origins of the ALS and the effects on the level schemes of several nuclei.

Tsunoda, N.; Shimizu, N. [Department of Science, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, I-80126 (Japan); Otsuka, T. [Department of Science, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, I-80126 (Japan); Center for Nuclear Study, University of Tokyo, Hongo, Bunkyo-ku Tokyo, 113-0033 (Japan) and National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI (United States); Suzuki, T. [Department of Physics, College of Humanities and Sciences, Nihon University, Sakurajosui 3, Tokyo 156-8550 (Japan)

2011-05-06

354

Frequency characteristics of a nuclear spin maser for the search for the electric dipole moment of 129Xe atom  

NASA Astrophysics Data System (ADS)

Frequency characteristics of a 129Xe nuclear spin maser was studied, which is under development at Tokyo Institute of Technology for the search for a permanent electric dipole moment in diamagnetic 129Xe atom. Drifts in the solenoid current and cell temperature were found to be the most influential factors on the maser frequency. From correlation coefficient analysis, there seem to exist other origins of frequency fluctuation, such as phase drifts in the maser oscillation. In order to improve the stability of the maser frequency, the intensity of the pumping laser required to fully polarize 129Xe nuclei was evaluated. Construction of a polarization assessment system for 129Xe gas cells and development of a new scheme of current stabilization are also remarked.

Inoue, T.; Tsuchiya, M.; Furukawa, T.; Hayashi, H.; Nanao, T.; Yoshimi, A.; Uchida, M.; Matsuo, Y.; Asahi, K.

2011-01-01

355

Direct observation of low energy nuclear spin excitations in HoCrO3 by high resolution neutron spectroscopy.  

PubMed

We have investigated low energy nuclear spin excitations in the strongly correlated electron compound HoCrO3. We observe clear inelastic peaks at E = 22.18 ± 0.04 ?eV in both energy loss and gain sides. The energy of the inelastic peaks remains constant in the temperature range 1.5-40 K at which they are observed. The intensity of the inelastic peak increases at first with increasing temperature and then decreases at higher temperatures. The temperature dependence of the energy and intensity of the inelastic peaks is very unusual compared to that observed in other Nd, Co, V and also simple Ho compounds. Huge quasielastic scattering appears at higher temperatures presumably due to the fluctuating electronic moments of the Ho ions that get increasingly disordered at higher temperatures. The strong quasielastic scattering may also originate in the first Ho crystal-field excitations at about 1.5 meV. PMID:23779198

Chatterji, T; Jalarvo, N; Kumar, C M N; Xiao, Y; Brückel, Th

2013-06-19

356

Nuclear spin driven quantum tunneling of magnetization in a new lanthanide single-molecule magnet: bis(phthalocyaninato)holmium anion.  

PubMed

The first measurements of magnetization hysteresis loops on a diluted single crystal of [(Pc)2Ho]-.TBA+ (Pc = phthalocyaninato, TBA = tetrabutylammonium) in the subkelvin temperature range are reported. Characteristic staircase-like structure was observed, indicating the occurrence of the quantum tunneling of magnetization (QTM), which is a characteristic feature of SMMs. The quantum process in the new lanthanide SMMs is due to resonant quantum tunneling between entangled states of the electronic and nuclear spin systems, which is an essentially different mechanism from those of the known transition-metal-cluster SMMs. Evidence of the two-body quantum process was also observed for the first time in lanthanide complex systems. PMID:15771471

Ishikawa, Naoto; Sugita, Miki; Wernsdorfer, Wolfgang

2005-03-23

357

Theory of nuclear spin relaxation in disordered systems: comparison of Bloembergen-Purcell-Pound models and Monte Carlo simulations  

NASA Astrophysics Data System (ADS)

Two Bloembergen-Purcell-Pound (BPP) models for analysing nuclear spin relaxation data for translational diffusion in disordered systems are compared with Monte Carlo simulations. One model (the a-BPP model, 'a' standing for average) is commonly used for disordered systems and the other (the Cameron-Sholl BPP model) is more rigorously based and can distinguish between site-and barrier-energy disorder. Simulated relaxation data produced using Gaussian distributions of energy disorder are analysed using the models, and the parameters obtained from the fits are compared with the values used for the simulations. It is found that both models can give reasonable fits to the data. Both models also give reasonable agreement with the simulation parameters provided that the standard deviation of the energy distribution for the a-BPP model is interpreted as the average of the site-and barrier-energy standard deviations. Quantitative estimates are given of the accuracy of the parameters from the fits.

Luo, Xinjun; Sholl, C. A.

2002-07-01

358

Nuclear Spin-Lattice Relaxation in the La1-cGdcAl2 Intermetallic Compounds  

Microsoft Academic Search

The contribution of Gd impurities to the spin-lattice relaxation of La139 and Al27 nuclei in the compound La1-cGdcAl2 is studied for values of c from 0.0013 to 0.10, applied magnetic fields between 3.6 and 24.4 kOe, and temperatures from 1.2 to 300 K. The impurity component of the magnetization recovery for Al27 is characterized by an exp[-(ttau1)12] time dependence, indicating

M. R. McHenry; B. G. Silbernagel; J. H. Wernick

1972-01-01

359

Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: longitudinal relaxation dispersion for spin I = 1.  

PubMed

The frequency dependence of the longitudinal relaxation rate, known as the magnetic relaxation dispersion (MRD), can provide a frequency-resolved characterization of molecular motions in complex biological and colloidal systems on time scales ranging from 1 ns to 100 ?s. The conformational dynamics of immobilized proteins and other biopolymers can thus be probed in vitro or in vivo by exploiting internal water molecules or labile hydrogens that exchange with a dominant bulk water pool. Numerous water (1)H and (2)H MRD studies of such systems have been reported, but the widely different theoretical models currently used to analyze the MRD data have resulted in divergent views of the underlying molecular motions. We have argued that the essential mechanism responsible for the main dispersion is the exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings when internal water molecules or labile hydrogens escape from orientationally confining macromolecular sites. In the EMOR model, the exchange process is thus not just a means of mixing spin populations but it is also the direct cause of spin relaxation. Although the EMOR theory has been used in several studies to analyze water (2)H MRD data from immobilized biopolymers, the fully developed theory has not been described. Here, we present a comprehensive account of a generalized version of the EMOR theory for spin I = 1 nuclides like (2)H. As compared to a previously described version of the EMOR theory, the present version incorporates three generalizations that are all essential in applications to experimental data: (i) a biaxial (residual) electric field gradient tensor, (ii) direct and indirect effects of internal motions, and (iii) multiple sites with different exchange rates. In addition, we describe and assess different approximations to the exact EMOR theory that are useful in various regimes. In particular, we consider the experimentally important dilute regime, for which approximate analytical results are derived. As shown by the analytical expressions, and confirmed by exact numerical calculations, the dispersion is governed by the pure nuclear quadrupole resonance frequencies in the ultraslow-motion regime, where the relaxation rate also exhibits a much stronger dependence on the electric field gradient asymmetry than in the motional-narrowing regime. PMID:22894360

Nilsson, Tomas; Halle, Bertil

2012-08-01

360

Nuclear-acoustic-resonance determination of the gradient-elastic tensor and indirect nuclear-spin interactions in niobium  

Microsoft Academic Search

Nuclear-acoustic-resonance studies of the absolute intensity of the signals and of the angular dependence of their second moments have been made in single crystals of niobium for the electric quadrupole transitions Deltam=+\\/-1 and Deltam=+\\/-2 as well as for the Deltam=+\\/-1 magnetic dipole transition. From the intensity measurements we find the two independent coefficients of the electric field gradient-elastic strain tensor

J. Pellisson; J. Buttet

1975-01-01

361

Nuclear structure of {sup 94,95}Mo at high spins  

SciTech Connect

The high-spin level structures of {sup 94,95}Mo (N=52,53) have been investigated via the {sup 65}Cu({sup 36}S, {alpha}p2n){sup 94}Mo and {sup 65}Cu({sup 36}S, {alpha}pn){sup 95}Mo reactions at 142 MeV. The level schemes have been extended up to spin J{approx}19{h_bar} and excitation energies E{sub x}{approx}12 MeV. Spherical shell-model calculations have been performed and compared with the experimental energy levels. The level structure of {sup 94}Mo exhibits a single-particle nature and the higher-angular-momentum states are dominated by the excitation of a g{sub 9/2} neutron across the N=50 shell gap. The level sequences observed in {sup 95}Mo have been interpreted on the basis of the spherical shell model and weak coupling of a d{sub 5/2} or a g{sub 7/2} neutron to the {sup 94}Mo core. {copyright} {ital 1998} {ital The American Physical Society}

Kharraja, B.; Ghugre, S.S.; Garg, U. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Janssens, R.V.; Carpenter, M.P.; Crowell, B.; Khoo, T.L.; Lauritsen, T.; Nisius, D. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Reviol, W.; Mueller, W.F.; Riedinger, L.L. [Department of Physics, University of Tennessee, Knoxville, Tennessee 37996 (United States); Kaczarowski, R. [Soltan Institute for Nuclear Studies, 05-400 Swierk (Poland)

1998-06-01

362

Element-sensitive measurement of the hole-nuclear spin interaction in quantum dots  

NASA Astrophysics Data System (ADS)

It has been proposed that valence-band holes can form robust spin qubits owing to their weaker hyperfine coupling compared with electrons. However, it was demonstrated recently that the hole hyperfine interaction is not negligible, although a consistent picture of the mechanism controlling its magnitude is still lacking. Here we address this problem by measuring the hole hyperfine constant independently for each chemical element in InGaAs/GaAs, InP/GaInP and GaAs/AlGaAs quantum dots. Contrary to existing models we find that the hole hyperfine constant has opposite signs for cations and anions and ranges from -15% to +15% relative to that for electrons. We attribute such changes to the competing positive contributions of p-symmetry atomic orbitals and the negative contributions of d-orbitals. These findings yield information on the orbital composition of the valence band and enable a fundamentally new approach for verification of computed Bloch wavefunctions in semiconductor nanostructures. Furthermore, we show that the contribution of cationic d-orbitals leads to a new mechanism of hole spin decoherence.

Chekhovich, E. A.; Glazov, M. M.; Krysa, A. B.; Hopkinson, M.; Senellart, P.; Lemaître, A.; Skolnick, M. S.; Tartakovskii, A. I.

2013-02-01

363

Intermolecular potentials from nuclear spin lattice relaxation in pure gases with octahedral symmetry  

NASA Astrophysics Data System (ADS)

Fluorine spin lattice relaxation times per unit density T1/? in pure SF6, MoF6, WF6 and UF6 gases are experimentally found to be proportional to T-1·5 where T is the temperature. These data can be analysed to obtain information on the anisotropic part of the intermolecular potential in these systems. Hard sphere, Lennard-Jones (6-12) and modified Buckingham (exp-6) potentials were used for the isotropic part of the intermolecular interaction. The analysis is made using the Bloom-Oppenheim theory, assuming that the correlation time of the spin rotation interaction can be approximated by the average lifetime of a molecule in the given J state. We have obtained the strengths of the repulsive and attractive terms in the anisotropic potential. From the strength of the attractive term in the anisotropic potential, the hexadecapole moments of all the four molecules are obtained. The hexadecapole moment of SF6 obtained by us using the Lennard-Jones model is in good agreement with the values reported earlier, based on other techniques, while the values for MoF6, WF6 and UF6 are reported for the first time.

Ursu, I.; Bogdan, M.; Balibanu, F.; Fitori, P.; Mihailescu, G.; Demco, D. E.

364

Nuclear spin relaxation and magnetic shielding tensors of atoms constituting cyanogen bromide molecule  

NASA Astrophysics Data System (ADS)

The temperature dependence of the correlation time describing reorientation kinetics of cyanogen bromide in CDCl 3 solution has been determined on the basis of the linewidths of the 14 N NMR signal. It has been found that the longitudinal spin relaxation of the 15 N nucleus occurs by shielding anisotropy and spin-rotation mechanisms, whereas for the 13 C nucleus these mechanisms are of lesser importance. In the latter case the scalar relaxation of the second kind due to carbon-bromine coupling is the predominant relaxation mechanism. The parameter values: 1 J ( 13 C - 79 Br) = 349 ±10Hz, T 1 ( 79 Br,303K) = 2.31 ±0.22 ×10 -7 s, ??( 15 N) = 13 565 ±16ppm and ??( 13 C) = 276 ±120ppm have been determined from the relaxation data analysis. The shielding anisotropy parameters ??( 15 N) = 580 ±50ppm and Delta ?( 13 C) = 274 ±9ppm have been independently determined using 13 C and 15 N NMR in liquid crystalline solvent. The experimentally determined shielding tensors for sp -hybridized atoms in the investigated compound and in a series of bromoacetylenes have been compared with the results of quantum mechanical calculations [GIAO, DFT B3LYP/6-311++G(2d,p)]. The 'heavy atom effect' shielding bromine-bonded carbons is of the order of-25ppm and concerns mainly the ? ?? component.

Molchanov, Sergey; Gryff-Keller, Adam

365

Intermediate energy neutrons at WNR. Spin-isospin and energy dependence of the NN interaction and the nuclear response  

SciTech Connect

This report summarizes results of nuclear physics studies using intermediate energy (50-800 MeV) neutron probes carried out over the past five years using the Neutron Time-of-Flight (NTOF) Facility and Optically-Pumped Ion Source (OPPIS) at LAMPF and the `white` neutron source at the Weapons Neutron Research (WNR) facility. LAMPF did significant work in polarization transfer, while WNR took advantage of the wide neutron energy spectrum available to study energy dependent effects. The major focus of experiments with intermediate energy neutron probes for the next five years will be to explore fundamental details of the spin-isospin and energy dependence of the NN interaction and the nuclear response. To achieve this goal, the WNR white neutron source will be used for nucleon-nucleon and nucleon-nucleus interaction studies over a broad continuous range of incident neutron energy. Measurement of polarization observables using polarized targets or polarized beam should be possible, and will add an important extra dimension to these studies.

Taddeucci, T.N.

1995-02-01

366

Nuclear spin-spin coupling constants from regular approximate relativistic density functional calculations. I. Formalism and scalar relativistic results for heavy metal compounds  

Microsoft Academic Search

We present a relativistic formulation of the spin-spin coupling hyperfine terms based on the two component zeroth-order regular approximate Hamiltonian. The scalar relativistic parts of the resulting operators were used for an implementation into the Amsterdam density functional program. Application of the code for the calculation of one-bond metal-ligand couplings of systems containing 183W, 195Pt, 199Hg, and 207Pb shows that

Jochen Autschbach; Tom Ziegler

2000-01-01

367

Very long nuclear relaxation times of spin polarized helium 3 in metal coated cells  

Microsoft Academic Search

We obtained very long relaxation times T1 of up to 120 h for the nuclear polarization of an optically pumped helium 3 gas. The glass containers were internally coated with metallic films such as bismuth or cesium. These findings will have applications in the field of helium magnetometers and polarized targets.

Werner Heil; Hubert Humblot; Ernst Otten; Matthias Schafer; Reinhard Sarkau; Michèle Leduc

1995-01-01

368

Methyl Zeeman-tunnel resonance and nuclear spin relaxation in copper acetate  

Microsoft Academic Search

The methyl tunnel spectrum of copper acetate is studied at low temperatures by means of nuclear magnetic resonance level-crossing spectroscopy employing a field-cycling technique. The recovery of the proton magnetisation following saturation is measured as a function of magnetic field. Changing the magnetic field causes energy levels to cross when the methyl tunnel frequency is equal to one or two

P. Coppens; L. Van Gerven; S. Clough; A. J. Horsewill

1983-01-01

369

Mineral Carbonation in Wet Supercritical CO2: An in situ High-Pressure Magic Angle Spinning Nuclear Magnetic Resonance Study  

NASA Astrophysics Data System (ADS)

Understanding the mechanisms and kinetics of mineral carbonation reactions relevant to sequestering carbon dioxide as a supercritical fluid (scCO2) in geologic formations is crucial for accurately predicting long-term storage risks. In situ probes that provide molecular-level information at geologically relevant temperatures and pressures are highly desirable and challenging to develop. Magic angle spinning nuclear magnetic resonance (MAS NMR) is a powerful tool for obtaining detailed molecular structure and dynamics information of a system regardless whether the system is in a solid, a liquid, a gaseous, a supercritical state, or a mixture thereof. However, MAS NMR under scCO2 conditions has never been realized due to the tremendous technical difficulties of achieving and maintaining high pressure within a fast spinning MAS sample rotor. In this work, we report development of a unique high pressure MAS NMR capability capable of handling fluid pressure exceeding 170 bars and temperatures up to 80°C, and its application to mineral carbonation in scCO2 under geologically relevant temperatures and pressures. Mineral carbonation reactions of the magnesium silicate mineral forsterite and the magnesium hydroxide brucite reacted with scCO2 (up to 170 bar) and containing variable content of H2O (at, below, and above saturation in scCO2) were investigated at 50 to 70°C. In situ 13C MAS NMR spectra show peaks corresponding to the reactants, intermediates, and the magnesium carbonation products in a single spectrum. For example, Figure 1 shows the reaction dynamics, i.e., the formation and conversion of reaction intermediates, i.e., HCO3- and nesquehonite, to magnesite as a function of time at 70°C. This capability offers a significant advantage over traditional ex situ 13C MAS experiments on similar systems, where, for example, CO2 and HCO3- are not directly observable.

Turcu, R. V.; Hoyt, D. H.; Sears, J. A.; Rosso, K. M.; Felmy, A. R.; Hu, J. Z.

2011-12-01

370

Influence of Intramolecular f-f Interactions on Nuclear Spin Driven Quantum Tunneling of Magnetizations in Quadruple-Decker Phthalocyanine Complexes Containing Two Terbium or Dysprosium Magnetic Centers.  

PubMed

Nuclear spin driven quantum tunneling of magnetization (QTM) phenomena, which arise from admixture of more than two orthogonal electronic spin wave functions through the couplings with those of the nuclear spins, are one of the important magnetic relaxation processes in lanthanide single molecule magnets (SMMs) in the low temperature range. Although recent experimental studies have indicated that the presence of the intramolecular f-f interactions affects their magnetic relaxation processes, little attention has been given to their mechanisms and, to the best of our knowledge, no rational theoretical models have been proposed for the interpretations of how the nuclear spin driven QTMs are influenced by the f-f interactions. Since quadruple-decker phthalocyanine complexes with two terbium or dysprosium ions as the magnetic centers show moderate f-f interactions, these are appropriate to investigate the influence of the f-f interactions on the dynamic magnetic relaxation processes. In the present paper, a theoretical model including ligand field (LF) potentials, hyperfine, nuclear quadrupole, magnetic dipolar, and the Zeeman interactions has been constructed to understand the roles of the nuclear spins for the QTM processes, and the resultant Zeeman plots are obtained. The ac susceptibility measurements of the magnetically diluted quadruple-decker monoterbium and diterbium phthalocyanine complexes, [Tb-Y] and [Tb-Tb], have indicated that the presence of the f-f interactions suppresses the QTMs in the absence of the external magnetic field (Hdc) being consistent with previous reports. On the contrary, the faster magnetic relaxation processes are observed for [Tb-Tb] than [Tb-Y] at Hdc = 1000 Oe, clearly demonstrating that the QTMs are rather enhanced in the presence of the external magnetic field. Based on the calculated Zeeman diagrams, these observations can be attributed to the enhanced nuclear spin driven QTMs for [Tb-Tb]. At the Hdc higher than 2000 Oe, the magnetic relaxations become faster with increasing Hdc for both complexes, which are possibly ascribed to the enhanced direct processes. The results on the dysprosium complexes are also discussed as the example of a Kramers system. PMID:24003906

Fukuda, Takamitsu; Matsumura, Kazuya; Ishikawa, Naoto

2013-09-19

371

Long-time behavior of nuclear spin decays in various lattices  

SciTech Connect

The transverse NMR decays of {sup 129}Xe in polycrystalline xenon were recently shown to have a universal property: in the long-time regime these decays all converge to the same sinusoidally modulated exponential function irrespective of the initial transverse spin configuration prepared by a sequence of one or more radio frequency pulses. The present work constitutes a more comprehensive survey of this phenomenon. It examines transverse decays for several different isotopic concentrations of {sup 129}Xe, employs additional pulse sequences, and performs similar measurements in a different material: {sup 19}F in single-crystal and polycrystalline CaF{sub 2}. With the possible exception of polycrystalline CaF{sub 2} where the observation of the long-time behavior is limited by the experimental resolution, all these systems display the long-time universal behavior characterized by particular values of the exponential decay coefficient and beat frequency that were unique for each lattice. This behavior has been theoretically predicted based on the notion of microscopic chaos.

Sorte, E. G.; Saam, B. [Department of Physics, University of Utah, 115 South 1400 East, Salt Lake City, UT 84112-0830 (United States); Fine, B. V. [Institute of Theoretical Physics, University of Heidelberg, Philosophenweg 19, 69120 Heidelberg (Germany)

2011-02-01

372

Long-time behavior of nuclear spin decays in various lattices  

NASA Astrophysics Data System (ADS)

The transverse NMR decays of Xe129 in polycrystalline xenon were recently shown to have a universal property: in the long-time regime these decays all converge to the same sinusoidally modulated exponential function irrespective of the initial transverse spin configuration prepared by a sequence of one or more radio frequency pulses. The present work constitutes a more comprehensive survey of this phenomenon. It examines transverse decays for several different isotopic concentrations of Xe129, employs additional pulse sequences, and performs similar measurements in a different material: F19 in single-crystal and polycrystalline CaF2. With the possible exception of polycrystalline CaF2 where the observation of the long-time behavior is limited by the experimental resolution, all these systems display the long-time universal behavior characterized by particular values of the exponential decay coefficient and beat frequency that were unique for each lattice. This behavior has been theoretically predicted based on the notion of microscopic chaos.

Sorte, E. G.; Fine, B. V.; Saam, B.

2011-02-01

373

Observable effects of mechanical stress induced by sample spinning in solid state nuclear magnetic resonance.  

PubMed

The stress-induced change in chemical shielding induced by sample spinning is measured and interpreted theoretically. By considering the rotating sample as an elastic body in the plane-strain approximation, the internal stress field as a function of sample size, rotation frequency, and elastic constants is determined. This stress field and the dependence of chemical shielding on strain, as determined by first-principles calculations, are combined to predict the shielding dependence on rotation frequency under isothermal conditions in single crystal gallium phosphide. The prediction is in good qualitative agreement with the experiment. Little to no effect is detected in powder samples of both gallium phosphide and copper iodide, and it is argued that this follows from the stress distribution in granular material, as opposed to bulk crystals. Finally, the temperature and pressure dependence of the chemical shielding is estimated from these considerations and found consistently to underestimate the experimental values, indicating the importance of finite-temperature anharmonic effects even in very simple solids. PMID:18266421

Jochum, M; Werner-Zwanziger, U; Zwanziger, J W

2008-02-01

374

Parallel implementation of the MAGPACK package for the analysis of high-nuclearity spin clusters  

NASA Astrophysics Data System (ADS)

Molecular clusters are formed by a finite number of exchange-coupled paramagnetic centers and they are model systems between molecules and extended solids. In order to simulate their properties and extrapolate to solids, the size of the systems to be treated should be as large as possible. In this context, the use of efficient parallel codes is essential. We present the parallel programs PARANI and PARISO, for anisotropic and isotropic models, that enable the calculation of large energy matrices in parallel and the subsequent computation of the relevant spectral information. The evaluation of the matrix elements is based on the serial package MAGPACK that uses the irreducible tensor operators technique and takes into account all kinds of anisotropic and isotropic magnetic interactions. To obtain the eigenvalues, the energy matrix is partially diagonalized by means of the SLEPc library. The calculation of eigenvalues and eigenvectors of these spin clusters enables us to evaluate the bulk magnetic properties (magnetic susceptibility and magnetization) as well as the spectroscopic properties (inelastic neutron scattering spectra). The results are encouraging in terms of parallel efficiency and open the way to address very challenging problems.

Ramos, E.; Roman, J. E.; Cardona-Serra, S.; Clemente-Juan, J. M.

2010-12-01

375

Evaluation of nitrogen nuclear hyperfine and quadrupole coupling parameters for the proximal imidazole in myoglobin-azide, -cyanide, and -mercaptoethanol complexes by electron spin echo envelope modulation spectroscopy.  

PubMed

Electron spin echo envelope modulation (ESEEM) spectroscopy and computer simulation of spectra has been used to evaluate the nitrogen nuclear hyperfine and quadrupole coupling parameters for the proximal imidazole nitrogen directly coordinated to iron in three low-spin heme complexes, myoglobin-azide, -cyanide, and -mercaptoethanol (MbN3, MbCN, and MbRS). The variability in the weak electron-nuclear coupling parameters reveals the electronic flexibility within the heme group that depends on properties of the exogenous ligands. For example, the isotropic component of the nitrogen nuclear hyperfine coupling ranges from 4.4 MHz for MbN3 to 2.2 MHz for both MbCN and MbRS. The weaker coupling in MbCN and MbRS is taken as evidence for delocalization of unpaired electron spin from iron into the exogenous anionic ligands. The value of e2Qq, the nuclear quadrupole coupling constant for the axial imidazole nitrogen in MbCN and MbRS, was 2.5 MHz but was significantly larger, 3.2 MHz, in MbN3. This large value is considered evidence for a weakened sigma bond between the proximal imidazole and ferric iron in this form, and for a feature contributing to the origin of the high spin-low spin equilibrium exhibited by MbN3 [Beetlestone, J., & George, P. (1964) Biochemistry 5, 707-714]. The ESEEM results have allowed a correlation to be made between the orientation of the g tensor axes, the orientation of the p-pi orbital of the proximal imidazole nitrogen, and sigma- and pi-bonding features of the axial ligands. Furthermore, the proximal imidazole is suggested to act as a pi-acceptor in low-spin heme complexes in order to support strong sigma electron donation from the lone pair orbital to iron. An evaluation of the nitrogen nuclear hyperfine coupling parameters for the porphyrin pyrrole sites in MbRS reveals a large inequivalence in isotropic components consistent with an orientation of rhombic axes (and g tensor axes) that eclipses the Fe-Npyrrole vector directions. PMID:8395204

Magliozzo, R S; Peisach, J

1993-08-24

376

Intermediate energy spin physics. Appendix 6  

SciTech Connect

Topics include nuclear information from proton spin observables in elastic scattering, nuclear information from proton spin observables in inelastic scattering, recent measurements at the HRS utilizing a focal plane polarimeter, proton spin observables in natural parity transitions, and proton spin transfer observables in unnatural parity transitions. 47 references.

Igo, G.

1983-01-01

377

Cadmium 113 and carbon 13 NMR studies of ligand binding to pig heart NADP-dependent isocitrate dehydrogenase  

SciTech Connect

Isocitrate dehydrogenase catalyzes the conversion of isocitrate to ..cap alpha..-ketoglutarate. The reaction requires a divalent metal. NMR studies using cadmium 113 reveal a resonance in the enzyme-metal-isocitrate complex at 8 ppm relative to Cd(ClO/sub 4/)/sub 2/; whereas, in the absence of enzyme, the Cd-isocitrate complex has a resonance at approx.18 ppm. The resonance of enzyme-bound cadmium is typical of cadmium in a complex containing 6 oxygen ligands. Carbon 13 studies were done using specific enrichments at the 1, 2, or 5 positions of ..cap alpha..-ketoglutarate and isocitrate, synthesized by enzymatic conversion from glutamate. The carbon 13 resonances of the 1 and 5 carboxyl of ..cap alpha..-ketoglutarate are identical in free and enzyme-bound forms over the pH range 5.5-7.5, implying the absence of alterations in geometry of the enzyme-bound form. The 2-carbonyl resonance could not be located in the bound form, suggesting either significant perturbation or immobilization of this group. While the resonances of the carboxyls of free isocitrate shift over the pH range 5-8 reflecting a pK of 5.37, the positions of enzyme-bound resonances remain constant over this pH range. This indicates that isocitrate remains ionized in the enzyme-bound form.

Ehrlich, R.S.; Colman, R.F.

1986-05-01

378

Nuclear magnetic resonance spectra for l > 1 spins in dynamically heterogeneous systems with chemical exchange among environments.  

PubMed Central

Nuclear magnetic resonance spectra for nuclei with spin l > 1 are considered in cases in which the observed nucleus may sample a rotationally immobilized and an isotropic environment that are coupled by a chemical exchange process. Spectra are simulated for the central (1/2, -1/2) transition for a 3/2 nucleus as a function of the concentrations of the two environments and as a function of the exchange rate between them. It is shown that a crucial feature determining the shape of the observable spectra is the spatial extent or the local order in the immobilized phase. In the case for which all rotationally immobilized sites sampled by the exchanging nucleus are identically oriented but where there is a distribution of these microdomain orientations with respect to the magnetic field direction, a powder pattern for the central transition is observed that carries whatever dynamic information may be derived from it. In the fast exchange limit, the width of the powder pattern scales inversely with the concentration of the isotropic environment as usual. In the intermediate exchange regimes, a complex line shape results that may mask the anisotropic character of the spectrum. In the slow exchange limit, superposition of the spectral contributions results; however, if the isotropic environment concentration is significantly larger than the anisotropic environment concentration, the anisotropic contribution is very difficult to detect because of the dynamic range problem and the possibly large difference in the effective line widths. In the case for which the exchanging nucleus samples a considerable distribution of rotationally immobilized site orientations, the anisotropic character of the spectrum is lost and a super-Lorentzian line shape results. These effects are demonstrated experimentally by 35Cl nuclear magnetic resonance spectra obtained on a lamellar liquid crystal that is modified with the addition of a thiolmercurate to provide a site of large quadrupole coupling constant and with cross-linked bovine serum albumin gels.

Zhang, H; Bryant, R G

1995-01-01

379

Solid State CARBON-13 NMR Studies of the Morphology and Orientational Order of Polymer Fibers  

NASA Astrophysics Data System (ADS)

A fundamental understanding of the mechanism of fiber formation requires a detailed knowledge of fiber morphology. However due to the limitation of current techniques, the crystallization behavior is still not fully understood. Modern solid state NMR techniques enable one to approach this subject from different aspects. In this work we conducted detailed studies of the morphology of as-spun PET (poly (ethylene terephthalate)) and gel-spun PE (poly (ethylene)) fibers by ^{13}C CP/MAS (Cross Polarization/Magic Angle Spinning) NMR technique. The presence of multiple-component resonance lineshapes allows one to calculate the true population of various morphological components, after correcting for pin relaxation effects. From these NMR measurements, two different models for PET and PE polymer systems have been proposed. We have also employed and further developed the advanced two-dimensional rotor synchronized MAS (2D ROSMAS) technique to study the orientational order of various morphological components. A wide range of orientational order is clearly displayed on 2D spectra for samples under different fabrication conditions. A regression simulation program has been used to deduce the order parameter used in computing the orientational distribution function (ODF) for each component. Our results for the first time provide unique information about orientational order and morphology at the molecular level, thereby providing a much more complete basis for theoretical modeling of polymer system.

Tzou, Der-Lii Mike

380

The nuclear modulation effect in electron spin echoes for complexes of Cu2 + and imidazole with 14N and 15N  

Microsoft Academic Search

We have studied the nuclear modulation effect in the electron spin echo decay envelope for the complexes Cu2+–ethylenediamine–imidazole and Cu2+– (imidazole)4 with specific attention to the prominent low frequency patterns due to coupling between Cu2+ and the remote nitrogen nucleus of bound imidazole. (Nitrogen nuclei directly coordinated with Cu2+ do not contribute to the effect.) Some experiments were also made

W. B. Mims; J. Peisach

1978-01-01

381

Paramagnetic Resonance Absorption in Uranium (III) Chloride and the Nuclear Spin, Magnetic Dipole Moment, and Electric Quadrupole Moment of Uranium233  

Microsoft Academic Search

Paramagnetic resonance absorption in single crystals of U233Cl3 diluted with LaCl3 has been investigated. The values of the parameters in the appropriate Hamiltonian are given. The values of the nuclear spin, magnetic dipole moment, and electric quadrupole moment obtained from these studies are discussed. The ratios of the mo ments of U235 and U233, which can be obtained with much

Paul B. Dorain; Clyde A. Hutchison; Eugene Wong

1957-01-01

382

Nuclear spin dependence of the reaction of H{sub 3}{sup +} with H{sub 2}. I. Kinetics and modeling  

SciTech Connect

The chemical reaction H{sub 3}{sup +}+ H{sub 2}{yields} H{sub 2}+H{sub 3}{sup +} is the simplest bimolecular reaction involving a polyatomic, yet is complex enough that exact quantum mechanical calculations to adequately model its dynamics are still unfeasible. In particular, the branching fractions for the ''identity,''''proton hop,'' and ''hydrogen exchange'' reaction pathways are unknown, and to date, experimental measurements of this process have been limited. In this work, the nuclear-spin-dependent steady-state kinetics of the H{sub 3}{sup +}+ H{sub 2} reaction is examined in detail, and employed to generate models of the ortho:para ratio of H{sub 3}{sup +} formed in plasmas of varying ortho:para H{sub 2} ratios. One model is based entirely on nuclear spin statistics, and is appropriate for temperatures high enough to populate a large number of H{sub 3}{sup +} rotational states. Efforts are made to include the influence of three-body collisions in this model by deriving nuclear spin product branching fractions for the H{sub 5}{sup +}+ H{sub 2} reaction. Another model, based on rate coefficients calculated using a microcanonical statistical approach, is appropriate for lower-temperature plasmas in which energetic considerations begin to compete with the nuclear spin branching fractions. These models serve as a theoretical framework for interpreting the results of laboratory studies on the reaction of H{sub 3}{sup +} with H{sub 2}.

Crabtree, Kyle N.; Tom, Brian A. [Department of Chemistry, University of Illinois, Urbana, Illinois 61801 (United States); McCall, Benjamin J. [Departments of Chemistry, Astronomy, and Physics, University of Illinois, Urbana, Illinois 61801 (United States)

2011-05-21

383

Knight Shift and Nuclear Spin Relaxation Rate in a Charge-Ordered State of the One-Dimensional Extended Hubbard Model at Quarter Filling  

Microsoft Academic Search

We investigate Knight shift and nuclear spin relaxation rate in a charge-ordered state of the one-dimensional extended Hubbard model with a quarter-filled band by using RPA around the mean-field solution. It is shown that both quantities show splitting below the critical temperature of the charge order, as is experimentally observed. The relationships between the amount of the splitting in the

Hideo Yoshioka

2006-01-01

384

Nuclear spin dependence of the reaction of H{sub 3}{sup +} with H{sub 2}. II. Experimental measurements  

SciTech Connect

The nuclear spin dependence of the chemical reaction H{sub 3}{sup +}+ H{sub 2}{yields} H{sub 2} +H{sub 3}{sup +} has been studied in a hollow cathode plasma cell. Multipass infrared direct absorption spectroscopy has been employed to monitor the populations of several low-energy rotational levels of ortho- and para-H{sub 3}{sup +} (o-H{sub 3}{sup +} and p-H{sub 3}{sup +}) in hydrogenic plasmas of varying para-H{sub 2} (p-H{sub 2}) enrichment. The ratio of the rates of the proton hop (k{sup H}) and hydrogen exchange (k{sup E}) reactions {alpha}{identical_to}k{sup H}/k{sup E} is inferred from the observed p-H{sub 3}{sup +} fraction as a function of p-H{sub 2} fraction using steady-state chemical models. Measurements have been performed both in uncooled (T{sub kin}{approx} 350 K) and in liquid-nitrogen-cooled (T{sub kin}{approx} 135 K) plasmas, marking the first time this reaction has been studied at low temperature. The value of {alpha} has been found to decrease from 1.6 {+-} 0.1 at 350 K to 0.5 {+-} 0.1 at 135 K.

Crabtree, Kyle N.; Kauffman, Carrie A.; Tom, Brian A.; Becka, Eftalda; McGuire, Brett A. [Department of Chemistry, University of Illinois, Urbana, Illinois 61801 (United States); McCall, Benjamin J. [Departments of Chemistry, Astronomy, and Physics, University of Illinois, Urbana, Illinois 61801 (United States)

2011-05-21

385

Nuclear Spin Temperature and Deuterium-to-Hydrogen Ratio of Methane in Comet C/2001 Q4 (NEAT)  

NASA Astrophysics Data System (ADS)

We carried out high-dispersion, spectroscopic observations of comet C/2001 Q4 (NEAT) in the near-infrared with the 8 m Subaru telescope and detected the R-branch emission series of the ?3 vibrational band of methane. The signal-to-noise ratio of the observed spectrum was sufficient to make the first determination of the nuclear spin temperature of methane, derived to be 33 K, which reflects the temperature of formation or condensation of molecules on cold grains. The upper limit of the CH3D/CH4 ratio was determined to be 0.04 (95% confidence limit), indicating the formation of methane in a dense molecular cloud at temperatures higher than about 30 K. On the basis of these observational results, we conclude that the Sun was born in a warm molecular cloud near 30 K, not in a cold dark cloud near 10 K, as is usually assumed. This article is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Kawakita, Hideyo; Watanabe, Jun-ichi; Furusho, Reiko; Fuse, Tetsuharu; Boice, Daniel C.

2005-04-01

386

(1)H and (13)C magic-angle spinning nuclear magnetic resonance studies of the chicken eggshell.  

PubMed

The chicken eggshell, a product of biomineralization, contains inorganic and organic substances whose content changes during the incubation process. Bloch-decay (BD) (1)H, (13)C, and cross-polarization (CP) (13)C nuclear magnetic resonance (NMR) spectra of chicken eggshells were acquired under magic-angle spinning (MAS). Variable contact time (13)C CP MAS NMR experiments revealed the signals of carbonyl groups from organic and inorganic compounds. In the (13)C BD NMR spectra, a single peak at 168.1 ppm was detected, whereas in the (1)H BD spectra, the signals from water and the bicarbonate ion were assigned. A simultaneous decrease of the water signal in the (1)H MAS NMR spectra and an increase of the carbonate ion signal in the (13)C CP MAS NMR spectra of eggshells collected during the incubation period indicate the substitution of calcium ions by hydrogen ions in the calcium carbonate crystalline phase during the incubation of an egg. PMID:23157303

Pisklak, Dariusz Maciej; Szeleszczuk, Lukasz; Wawer, Iwona

2012-12-05

387

Spin-orbit coupled particle in a spin bath  

NASA Astrophysics Data System (ADS)

We consider a spin-orbit coupled particle confined in a quantum dot in a bath of impurity spins. We investigate the consequences of spin-orbit coupling on the interactions that the particle mediates in the spin bath. We show that in the presence of spin-orbit coupling, the impurity-impurity interactions are no longer spin conserving. We quantify the degree of this symmetry breaking and show how it relates to the spin-orbit coupling strength. We identify several ways how the impurity ensemble can in this way relax its spin by coupling to phonons. A typical resulting relaxation rate for a self-assembled Mn-doped ZnTe quantum dot populated by a hole is 1 ?s. We also show that decoherence arising from nuclear spins in lateral quantum dots is still removable by a spin echo protocol, even if the confined electron is spin-orbit coupled.

Stano, Peter; Fabian, Jaroslav; Žuti?, Igor

2013-04-01

388

Finite-Perturbation Intermediate - Neglect - of - Differential - Overlap Molecular Orbital Calculations of Nuclear Magnetic Resonance Spin-Spin Coupling Constants for Polycyclic Aromatic Hydrocarbons and Aromatic Nitrogen Heterocyclics  

NASA Astrophysics Data System (ADS)

The H-H, C-H, and C-C spin-spin coupling constants were calculated by the finite-perturbation, intermediate -neglect-of-differential-overlap method using the Fermi contact interaction for benzene, naphthalene, biphenyl, anthracene, phenanthrene, and pyrene. The calculations were made using both the actual and the average molecular geometries. For all six of these molecules, the agreements between the calculated and the experimental coupling constants were comparable to those previously reported for other, predominantly smaller, molecules. The actual molecular geometries always gave the correct relative order of values for the H-H coupling constants, whereas the average molecular geometries did not always do so. The magnitudes, but not the signs, of the calculated coupling constants were sensitive to small changes in molecular geometry. The results were the best (next best) for the H-H (C-H) coupling constants. In addition the H-H, C-H, N-H, C-C, and N-C spin -spin coupling constants were calculated in a similar manner for pyridine, pyridazine, pyrimidine, pyrazine, s-triazine, quinoline, quinoxaline, phthalazine, benzo g quinoxaline, and benzo b phenazine. The agreements between the theoretical and the experimental values were comparable to those for the polycyclic aromatic hydrocarbons.

Long, Sheila Ann Thibeault

389

STRUCTURES OF SOME KEPONE PHOTOPRODUCTS AND RELATED CHLORINATED PENTACYCLODECANES BY CARBON-13 AND PROTON NUCLEAR MAGNETIC RESONANCE  

EPA Science Inventory

The pesticide Kepone, 1,1a,3,3a,4,5,5a,5b,6-decachlorooctahydro-1,3,4-metheno-2H-cyclobuta(cd)pentalen-2-one, the related compounds mirex, kelevan, a monohydro photoproduct of kelevan, kepone alcohol, kepone hydrate, and the mono- and dihydro photoproducts of Kepone hydrate and t...

390

CARBON-13 NUCLEAR MAGNETIC RESONANCE. 13C CHEMICAL SHIFTS AND 13C-199HG COUPLING CONSTANTS FOR SOME ORGANOMERCURY COMPOUNDS  

EPA Science Inventory

The (13)C shieldings and (13)C-(199)Hg coupling constants of fourteen phenyl- and seven alkyl- and alkenyl-mercury compounds have been obtained. Substituent effects on the (13)C shieldings are similar to those in nonmercurated phenyl compounds, with a similar relationship between...

391

Nuclear magnetic resonance data of CHF3Se  

NASA Astrophysics Data System (ADS)

This document is part of Part 6 `Organic Metalloid Compounds' of Subvolume D 'Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 'Nuclear Magnetic Resonance Data', Group III 'Condensed Matter'.

Mikhova, B. M.

392

Nuclear magnetic resonance data of C9H11NSe  

NASA Astrophysics Data System (ADS)

This document is part of Part 6 `Organic Metalloid Compounds' of Subvolume D 'Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 'Nuclear Magnetic Resonance Data', Group III 'Condensed Matter'.

Mikhova, B. M.

393

Nuclear magnetic resonance data of C9H11NO  

NASA Astrophysics Data System (ADS)

This document is part of Part 1 `Aliphatic Compounds' of Subvolume D `Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 `Nuclear Magnetic Resonance Data', Group III `Condensed Matter'.

Kalinowski, H.-O.; Kumar, M.; Gupta, V.; Gupta, R.

394

Nuclear magnetic resonance data of C9H11NS  

NASA Astrophysics Data System (ADS)

This document is part of Part 6 `Organic Metalloid Compounds' of Subvolume D 'Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 'Nuclear Magnetic Resonance Data', Group III 'Condensed Matter'.

Mikhova, B. M.

395

Nuclear magnetic resonance data of C9H11ITe  

NASA Astrophysics Data System (ADS)

This document is part of Part 6 `Organic Metalloid Compounds' of Subvolume D 'Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 'Nuclear Magnetic Resonance Data', Group III 'Condensed Matter'.

Mikhova, B. M.

396

Nuclear magnetic resonance data of CH3NSSi  

NASA Astrophysics Data System (ADS)

This document is part of Part 6 `Organic Metalloid Compounds' of Subvolume D 'Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 'Nuclear Magnetic Resonance Data', Group III 'Condensed Matter'.

Mikhova, B. M.

397

Nuclear magnetic resonance data of C9H12INSe  

NASA Astrophysics Data System (ADS)

This document is part of Part 6 `Organic Metalloid Compounds' of Subvolume D 'Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 'Nuclear Magnetic Resonance Data', Group III 'Condensed Matter'.

Mikhova, B. M.

398

Nuclear Spin Effects in the Reactions of H3^+ with H2 and Electrons  

NASA Astrophysics Data System (ADS)

H3^+ is the simplest polyatomic molecule. It is widely used as a benchmark for theoretical calculations of molecular spectroscopy and reaction dynamics, and also plays a pivotal role as the cornerstone of interstellar chemistry. In Urbana, we have investigated the proton hop/exchange reaction H3^+ + H2 -> (H5^+)^* -> H2 + H3^+ for the first time at low temperatures. This reaction is the simplest bimolecular reaction involving a polyatomic, and is also the most common bimolecular reaction in the universe. Our experiments have revealed the branching ratio between proton hop and exchange, and appear to explain the observed ortho:para ratio of H3^+ in diffuse interstellar clouds. At the TSR storage ring of the Max Planck Institute for Nuclear Physics in Heidelberg, we have performed high-resolution measurements of the dissociative recombination (DR) cross sections of cold H3^+ in different mixtures of its lowest ortho and para quantum states. These measurements represent an important step towards the first state-selected DR measurements.

Kreckel, Holger; Crabtree, Kyle; Kauffman, Carrie; Tom, Brian; Novotny, Oldrich; Berg, Max; Bing, Dennis; Buhr, Henrik; Krantz, Claude; Lestinsky, Michael; Mendes, Mario; Nordhorn, Christian; Stutzel, Julia; Wolf, Andreas; Thomas, Richard; McCall, Benjamin

2010-03-01

399

Morphology of the poly(vinyl alcohol)–poly(vinyl acetate) copolymer in macrodefect-free composites: a 13C magic-angle-spinning nuclear magnetic resonance and 1H spin-diffusion study  

Microsoft Academic Search

A study was made of the macrodefect-free (MDF) composite based on aluminate cement and a poly(vinyl alcohol)–poly(vinyl acetate)\\u000a (PVAc) copolymer by 13C cross-polarization magic-angle-spinning nuclear magnetic resonance. The spectra were run on both the copolymer and the MDF\\u000a composite in order to observe the atomic environments of the carbon nuclei. An analysis of the intramolecular hydrogen bonds\\u000a showed a stronger

ANGIOLINA COMOTTI; ROBERTO SIMONUTTI; PIERO SOZZANI

1997-01-01

400

A new method of nuclear spin cooling in the mK region, applied to 54Mn NMR\\/ON in antiferromagnetic MnCl2.4H2O  

Microsoft Academic Search

A new method of cooling nuclear spins in the mK region, using antiferromagnetic magnons, is described. The method is based on dramatic reduction in the spin-lattice relaxation time T1 at the antiferromagnetic-spin-flop and spin-flop-paramagnetic phase transitions, induced respectively by fields 0.71 and 2.0 T applied along the easy axis (at 7 degrees to the c axis) of the hexagonal-shaped MnCl2.4H2O

A. L. Allsop; M. de Araujo; G. J. Bowden; R. G. Clark; N. J. Stone

1984-01-01

401

Finite-perturbation intermediate neglect of differential overlap molecular orbital calculations of nuclear magnetic resonance spin-spin coupling constants for polycyclic aromatic hydrocarbons and aromatic nitrogen heterocyclics  

NASA Astrophysics Data System (ADS)

The H-H, C-H, and C-C spin-spin coupling constants were calculated by the finite-perturbation, intermediate neglect of differential overlap method using the Fermi contat interaction for benzene, naphthalene, biphenyl, anthracene, phenanthrene, and pyrene. The calculations were made using both the actual and the average molecular geometries. For all six of these molecules, the agreements between the calculated and the experimental coupling constants were comparable to those previously reported for other, predominantly smaller, molecules. The actual molecular geometries always gave the correct relative order of values for the H-H coupling constants, whereas the average molecular geometries did not always do so. The magnitudes, but not the signs, of the calculated coupling constants were sensitive to small changes in molecular geometry. The results were the best (next best) for the H-H (C-H) coupling constants.

Long, S. A. T.

402

Effect of small concentrations of Gd spins on the knight shift and nuclear spin relaxation of 27Al in the heavy fermion system CeAl3  

Microsoft Academic Search

The spin-lattice relaxation rate and Knight shift of 27Al at 9.5 kOe in Ce1-xGdxAl3 with x<=0.02 are reported. The relaxation rate and Knight shift of several samples were investigated over the range 1.5-4.2 K and the Knight shift measurements of the x = 0 sample covered 1.5-300 K. The low temperature relaxation rates indicate a resonance in the conduction electron

J. M. Moore; W. G. Clark; J. Sanny; W. H. Wong; W. A. Hines; D. P. Yang; M. Schlott

1990-01-01

403

Detailed analysis of the S-RESPDOR solid-state NMR method for inter-nuclear distance measurement between spin-1/2 and quadrupolar nuclei  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of the Symmetry-based Resonance-Echo Saturation-Pulse DOuble-Resonance (S-RESPDOR) method in order to measure the inter-nuclear distances between spin-1/2 and quadrupolar nuclei. This recently introduced sequence employs a symmetry-based recoupling scheme on the observed spin-1/2 channel and a saturation pulse on the quadrupolar channel. This method requires a low radio-frequency (rf) field, is compatible with high MAS frequency and allows a rapid determination of inter-nuclear distances by fitting the experimental signal fraction to an analytical expression. Here, we analyze in detail the influence of the various experimental and spin-interaction parameters on the S-RESPDOR signal fraction and the measured distance. We show that the S-RESPDOR signal fraction only depends on the quadrupole interaction and the inter-nuclear distance. We demonstrate that the required rf-field on the quadrupolar channel is smaller than that required for an adiabatic-passage pulse in REAPDOR-type experiments. The only limitation of the method is the requirement of accurate rotor synchronization between the two parts of the dipolar recoupling sequences. Using S-RESPDOR, we have quantitatively measured a 31P-51V distance of 357 pm in a mono-vanadium-substituted polyoxo-tungstate, K4PVW11O40, from the Keggin family and a 13C-67Zn distance of 286 pm in [80%-67Zn]zinc [1 - 13C]acetate. These results show that S-RESPDOR can be employed in the challenging cases of quadrupolar nuclei exhibiting a high spin number and either large chemical-shift anisotropy (51V) or low gyromagnetic ratio (67Zn).

Lu, Xingyu; Lafon, Olivier; Trébosc, Julien; Amoureux, Jean-Paul

2012-02-01

404

Nuclear magnetic resonance in [N(CH3)4]2CoCl4 single crystals: transferred hyperfine interaction and spin-lattice relaxation rate  

NASA Astrophysics Data System (ADS)

The molecular susceptibility and paramagnetic shift of [N(CH3)4]2CoCl4 single crystals were measured, and from these experimental results we obtained the transferred hyperfine interaction, Hhf, due to the transfer of spin density from Co2+ ions to [N(CH3)4]+ ions. The transferred hyperfine interaction can be expressed as a linear equation, with Hhf increasing with increasing temperature. The remarkable change in Hhf near Tc5 (=192 K) corresponds to a phase transition. The proton spin-lattice relaxation times of [N(CH3)4]2CoCl4 single crystals were also investigated, and it was found that the relaxation process can be described by a single exponential function. The variation of the relaxation time with temperature undergoes a remarkable change near Tc5, confirming the presence of a phase transition at that temperature. From the above results, we conclude that the increase in Hhf with increasing temperature is large enough to allow the transfer of spin density between Co2+ ions and the nuclear spins of the nonmagnetic [N(CH3)4]+ ions in the lattice, and thus the increase in the relaxation time with temperature is attributed to an increase in the transferred hyperfine field.

Lim, Ae Ran

2005-06-01

405

Slow Magic Angle Sample Spinning: A Non- or Minimally Invasive Method for High- Resolution 1H Nuclear Magnetic Resonance (NMR) Metabolic Profiling  

SciTech Connect

High resolution 1H magic angle spinning nuclear magnetic resonance (NMR), using a sample spinning rate of several kHz or more (i.e., high resolution-magic angle spinning (hr-MAS)), is a well established method for metabolic profiling in intact tissues without the need for sample extraction. The only shortcoming with hr-MAS is that it is invasive and is thus unusable for non-destructive detections. Recently, a method called slow-MAS, using the concept of two dimensional NMR spectroscopy, has emerged as an alternative method for non- or minimal invasive metabolomics in intact tissues, including live animals, due to the slow or ultra-slow-sample spinning used. Although slow-MAS is a powerful method, its applications are hindered by experimental challenges. Correctly designing the experiment and choosing the appropriate slow-MAS method both require a fundamental understanding of the operation principles, in particular the details of line narrowing due to the presence of molecular diffusion. However, these fundamental principles have not yet been fully disclosed in previous publications. The goal of this chapter is to provide an in depth evaluation of the principles associated with slow-MAS techniques by emphasizing the challenges associated with a phantom sample consisting of glass beads and H2O, where an unusually large magnetic susceptibility field gradient is obtained.

Hu, Jian Z.

2011-05-01

406

A nuclear magnetic resonance spectrometer concept for hermetically sealed magic angle spinning investigations on highly toxic, radiotoxic, or air sensitive materials  

NASA Astrophysics Data System (ADS)

A concept to integrate a commercial high-resolution, magic angle spinning nuclear magnetic resonance (MAS-NMR) probe capable of very rapid rotation rates (70 kHz) in a hermetically sealed enclosure for the study of highly radiotoxic materials has been developed and successfully demonstrated. The concept centres on a conventional wide bore (89 mm) solid-state NMR magnet operating with industry standard 54 mm diameter probes designed for narrow bore magnets. Rotor insertion and probe tuning take place within a hermetically enclosed glovebox, which extends into the bore of the magnet, in the space between the probe and the magnet shim system. Oxygen-17 MAS-NMR measurements demonstrate the possibility of obtaining high quality spectra from small sample masses (~10 mg) of highly radiotoxic material and the need for high spinning speeds to improve the spectral resolution when working with actinides. The large paramagnetic susceptibility arising from actinide paramagnetism in (Th1-xUx)O2 solid solutions gives rise to extensive spinning sidebands and poor resolution at 15 kHz, which is dramatically improved at 55 kHz. The first 17O MAS-NMR measurements on NpO2+x samples spinning at 55 kHz are also reported. The glovebox approach developed here for radiotoxic materials can be easily adapted to work with other hazardous or even air sensitive materials.

Martel, L.; Somers, J.; Berkmann, C.; Koepp, F.; Rothermel, A.; Pauvert, O.; Selfslag, C.; Farnan, I.

2013-05-01

407

A nuclear magnetic resonance spectrometer concept for hermetically sealed magic angle spinning investigations on highly toxic, radiotoxic, or air sensitive materials.  

PubMed

A concept to integrate a commercial high-resolution, magic angle spinning nuclear magnetic resonance (MAS-NMR) probe capable of very rapid rotation rates (70 kHz) in a hermetically sealed enclosure for the study of highly radiotoxic materials has been developed and successfully demonstrated. The concept centres on a conventional wide bore (89 mm) solid-state NMR magnet operating with industry standard 54 mm diameter probes designed for narrow bore magnets. Rotor insertion and probe tuning take place within a hermetically enclosed glovebox, which extends into the bore of the magnet, in the space between the probe and the magnet shim system. Oxygen-17 MAS-NMR measurements demonstrate the possibility of obtaining high quality spectra from small sample masses (~10 mg) of highly radiotoxic material and the need for high spinning speeds to improve the spectral resolution when working with actinides. The large paramagnetic susceptibility arising from actinide paramagnetism in (Th(1-x)U(x))O2 solid solutions gives rise to extensive spinning sidebands and poor resolution at 15 kHz, which is dramatically improved at 55 kHz. The first (17)O MAS-NMR measurements on NpO(2+x) samples spinning at 55 kHz are also reported. The glovebox approach developed here for radiotoxic materials can be easily adapted to work with other hazardous or even air sensitive materials. PMID:23742594

Martel, L; Somers, J; Berkmann, C; Koepp, F; Rothermel, A; Pauvert, O; Selfslag, C; Farnan, I

2013-05-01

408

Weak Spin Fluctuation with Finite Wave Vector and Superconducting Gap Symmetry in KxFe2-ySe2: 77Se Nuclear Magnetic Resonance  

NASA Astrophysics Data System (ADS)

We report 77Se-nuclear magnetic resonance (NMR) results down to sufficiently low temperatures under magnetic fields parallel to both the ab-plane and the c-axis in a paramagnetic/superconducting (PM/SC) phase of KxFe2-ySe2. The observation of anisotropy in the orbital part of the Knight shift results in the anisotropy of its spin part increasing on approaching the transition temperature. The anisotropy of the Korringa relation suggests the presence of the weak spin fluctuations with a finite wave vector \\mbi{q}, which induce the magnetic fluctuations along the ab-plane at the Se site. Such fluctuations do not correspond to the stripe (?,0) correlation of the Fe moment observed in many Fe-based superconductors, and are not contradictory to weak (?,?) correlations. The nuclear spin--lattice relaxation rate 1/T1 shows a field-independent T1 T˜ const. behavior at low temperatures for H\\parallel ab, which is attributed to the nonzero density of states at the Fermi level and can be explained by the sign-changing order parameter even for nodeless gaps. The temperature dependence of 1/T1 is reproduced well by nodeless models with two isotropic gaps or a single anisotropic gap. The obtained gap magnitude in the isotropic two-gap model is comparable to those obtained in the angle-resolved photoemission spectroscopy experiments.

Kotegawa, Hisashi; Tomita, Yusuke; Tou, Hideki; Mizuguchi, Yoshikazu; Takeya, Hiroyuki; Takano, Yoshihiko

2012-10-01

409

Isotopic multiplets in the carbon-13 NMR spectra of aniline derivatives and nucleosides with partially deuterated amino groups: effects of intra- and intermolecular hydrogen bonding  

SciTech Connect

In aniline derivatives, the carbon-13 resonances of atoms bearing partially deuterated amino groups, as well as the resonances of vicinal carbon atoms, appear as multiplets. This phenomenon, which is due to upfield deuterium isotope effects on carbon-13 chemical shifts, is observed under conditions of slow hydrogen exchange (e.g., in Me/sub 2/SO solutions). The effects are larger for groups engaged in intramolecular hydrogen bonds. Empirical expressions are presented that relate isotope effects with amino proton chemical shifts and hydrogen bond energies. Isotopic multiplets are also observed in the carbon-13 NMR spectra of partially deuterated nucleosides. The multiplet structure is altered upon formation of base pairs. These results are interpreted in terms of hydrogen exchange reactions involving uridine (or thymidine) hydrogen-bonded dimers or changes in hydrogen bond energies upon formation of guanosine-cytidine complexes. Estimates are given for the energies of individual hydrogen bonds in Watson-Crick base pairs.

Reuben, J.

1987-01-21

410

Twelve-spin ``Schrödinger cat''  

NASA Astrophysics Data System (ADS)

Pseudopure ``cat'' state, a superposition of quantum states with all spins up and all spins down, is experimentally demonstrated for a system of 12 dipolar-coupled nuclear spins of fully 13C-labeled benzene molecule oriented in a liquid-crystalline matrix.

Lee, Jae-Seung; Khitrin, A. K.

2005-11-01

411

Homogeneous coexistence of superconducting and spin-density-wave states in CaFe1-xCoxAsF as seen via nuclear magnetic resonance  

NASA Astrophysics Data System (ADS)

We investigated the homogeneous coexistence of spin-density-wave (SDW) and superconducting (SC) states via As75-nuclear magnetic resonance (NMR) in CaFe1-xCoxAsF and found that the electronic and magnetic properties of this compound are intermediate between those of LaFeAsO1-xFx and Ba(Fe1-xCox)2As2. For 6% Co-doped samples, the paramagnetic spectral weight completely disappears in the crossover regime between the SDW and SC phases followed by anomalous behavior of relaxation rate (1/T1), implying that the two phases are not segregated. Co59-NMR spectra show that spin moments are not commensurate but spatially modulated. These experimental results suggest that incommensurate SDW (IC-SDW) and SC states are compatible in this compound.

Nakano, T.; Tsutsumi, S.; Fujiwara, N.; Matsuishi, S.; Hosono, H.

2011-05-01

412

Formation Conditions of Icy Materials in Comet C/2004 Q2 (Machholz). II. Diagnostics Using Nuclear Spin Temperatures and Deuterium-to-Hydrogen Ratios in Cometary Molecules  

NASA Astrophysics Data System (ADS)

We report the nuclear spin temperatures (T spin) of H2O and CH4 in comet C/2004 Q2 (Machholz) based on high-dispersion spectroscopic observations of the comet in the L band taken by the Keck II telescope with the NIRSPEC spectrograph on 2005 January 30.2 UT. The ortho-to-para abundance ratio of H2O was determined to be 3.13+0.56 -0.42, which is consistent with the high-temperature limit of H2O (3.0). The lower limit of T spin is 27 K (95% confidence limit (c.l.)) for H2O. In the case of CH4, the abundance ratios of A:E:F are consistent with 5:2:9 (high-temperature limit) and the lower limit of T spin is 36 K (95%-c.l.). We also report the result of our sensitive search for mono-deuterated methane (CH3D) in C/2004 Q2 (Machholz). A candidate for the emission line from the CH3D ?4 RR(3, 3) transition was found in our spectra. Although the D/H ratio in methane could be determined as (3.8 ± 1.3) × 10-3 based on a tentative detection of CH3D, this emission line also might be assigned to other molecules, e.g., CH3OH. Therefore, we conclude that the D/H ratio in methane is lower than 6.4 × 10-3 (95%-c.l.) in the comet. Both the lower limits of T spin of H2O and CH4 and the upper limit of the D/H ratio in methane indicate the formation of molecules frozen in C/2004 Q2 (Machholz) at relatively higher temperatures compared with the typical Oort Cloud comets.

Kawakita, Hideyo; Kobayashi, Hitomi

2009-03-01

413

Effective Spin Spin Interactions in the Damped Ferromagnets.  

National Technical Information Service (NTIS)

Simanek's theory is extended by taking into account the nuclear spin excitations due to the motion of the electronic system. Damping of the magnons is found to be an extra criteria for having a finite interaction range for the nuclear spin system. The res...

H. N. Tin

1972-01-01

414

High-resolution magic-angle spinning 1H nuclear magnetic resonance studies of lipid dispersions using spherical glass ampoules  

Microsoft Academic Search

A very useful high-resolution magic-angle spinning (MAS) 1H NMR method for studying lipid dispersions is presented. The sample can be loaded into the spherical glass ampoule very easily, and a spinning speed of more than 10 kHz can be achieved without the problems of sample leakage or water loss. The line width at half height for the HDO peak is

Zhe Zhou; Brian G Sayer; Ruth E Stark; Richard M Epand

1997-01-01

415

THE EFFECTS OF PARAMAGNETIC RELAXATION REAGENTS ON 15N SPIN RELAXATION AND THE USE OF GD(DPM)3 AS A NITROGEN-15 NUCLEAR MAGNETIC RESONANCE SPIN LABEL  

EPA Science Inventory

Electron-nuclear relaxation times (T(1) sup e's) for (15)N and (13)C in natural abundance are measured for a series of amines of a wide range of pK(a)s using four paramagnetic relaxation reagents that are soluable in organic solutions. Cr(acac)3 and Cr(dpm)3 are seen to affect th...

416

13C-13C Homonuclear Recoupling in Solid-State Nuclear Magnetic Resonance at a Moderately High Magic-Angle-Spinning Frequency  

PubMed Central

Two-dimensional 13C-13C correlation experiments are widely employed in structure determination of protein assemblies using solid-state nuclear magnetic resonance. Here, we investigate the process of 13C-13C magnetisation transfer at a moderate magic-angle-spinning frequency of 30 kHz using some of the prominent second-order dipolar recoupling schemes. The effect of isotropic chemical-shift difference and spatial distance between two carbons and amplitude of radio frequency on 1H channel on the magnetisation transfer efficiency of these schemes is discussed in detail.

Mithu, Venus Singh; Bakthavatsalam, Subha; Madhu, Perunthiruthy K.

2013-01-01

417

Analysis of the A3(X3)3 nuclear spin system and pi-electron coupled hyperfine splitting constants in aromatic hydrocarbons  

Microsoft Academic Search

The nuclear spin functions for the A3(X3)3 system have been developed and used to analyse the NMR spectra of (CH3)3C6H3 and (CF3)3C6H3. The pi-electron coupled hyperfine splitting constants, obtained from the Ramsey theory with simple Hückel M.O.'s for benzene and without the assumption of an average energy of excitation for the virtual processes which give rise to the coupling, are

Juana Vivó Acrivos

1962-01-01

418

PREFACE: SPIN2010 - Preface for Conference Proceedings  

Microsoft Academic Search

SPIN2010, the 19th International Spin Physics Symposium, took place between 27 September and 2 October, 2010 on the campus of Forschungszentrum Jülich GmbH (FZJ) in Jülich, Germany. The scientific program of this Symposium included many topics related to spin phenomena in particle and nuclear physics as well as those in related fields. The International Spin Physics Symposium series has combined

Hans Ströher; Frank Rathmann

2011-01-01

419

Electron spin resonance, electron spin echo, and electron nuclear double resonance studies of the photoreduction yield of a series of alkylmethylviologens in sodium dodecyl sulfate and dodecyltrimethylammonium chloride micelles: Effect of the alkyl chain length of the viologen  

SciTech Connect

An electron spin resonance (ESR), electron spin echo (ESR), and proton matrix electron nuclear double resonance (ENDOR) study was carried out on a series of photoreduced alkylmethylviologens solubilized in frozen sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (DTAC) micelles. Photoreduction yields were measured with ESR, while ESE and ENDOR were used to probe the location of the viologen cation with respect to the polar and nonpolar phases of the micellar suspensions. The ESE and ENDOR results show that the location of the viologen moiety within a DTAC micelle is determined by the length of the pendent alkyl chain. In SDS micelles, the ESE and ENDOR results indicate that the viologen cation radical appears to be bound to the anionic surface of the micelle. The ENDOR data show that SDS micelles have a more ordered interface compared to DTAC micelles. A secondary alkyl radical observed in DTAC is formed by radical conversion from the photoreduced alkylmethylviologen. The location of this alkyl radical was probed using ESE and proton matrix ENDOR spectroscopy, and the data support a micelle model with negligible water penetration into the hydrocarbon interior. 62 refs., 8 figs., 2 tabs.

McManus, H.J.D.; Kang, Young Soo; Kevan, L. [Univ. of Houston, TX (United States)

1992-06-25

420

Electron spin resonance, electron spin echo, and electron nuclear double resonance investigations of the photoreduction yield of a series of alkylmethylviologens in dihexadecyl phosphate vesicles: Effect of added cholesterol  

SciTech Connect

The initial event in photosynthesis, photoinduced charge separation, takes place in a membrane bound proton/chlorophyll complex - the photosynthetic reaction center. An electron spin resonance (ESR), electron spin echo (ESE), and electron nuclear double resonance (ENDOR) investigation was performed on a series of alkylmethylviolgens which were solubilized in dihexadecyl phosphate (DHP) vesicles and rapidly frozen at 77 K. Photoreduction yields were measured by ESR, while ESE and matrix ENDOR were used to determine the location of the viologen radical in the lipid bilayer with respect to the water interface and the hydrocarbon interior, respectively. The effect of various concentrations on cholesterol on both the photoreduction yield and the location of the viologen probe within the DHP vesicle was measured. The ESE and ENDOR results indicate that the increased lipophilicity of the longer chained viologens effects deeper solubilization into the bilayer. This increased lipophilicity correlates with an enhancement of the photoreduction yield due to a reduced back electron transfer rate. Addition of cholesterol results in a disruption of the integrity of the vesicle interface and some increase in the photoreduction yield. This increase is mostly probably due to a decrease in effective interface charge density of the vesicle as a result of the intercalation of cholesterol molecules into the bilayer.

McManus, H.J.D.; Kevan, L. (Univ. of Houston, TX (United States))

1991-11-28