The decay of Sc and V

The decays of ⁴⁸Sc and ⁴⁸V have been studied with Ge(Li) diodes, scintillation spectrometers and a double focussing beta-ray spectrometer. The 3507 keV level, from which originates the quadruple cascade (9.4±0.5)% in the ⁴⁸Sc decay, is also de-excited by a 1212 keV cross-over transition to the 2295 keV (4⁺) level and supports the assumption, that the 3507 keV level has a spin 6⁺. The first member of the reported triple cascade in the ⁴⁸V decay is shown to be a doublet of 928.9±0.7 (1.2±0.2)% and 944.3±0.5 keV (8.0±0.5)% gamma rays, both followed by the 1311.4–983.3 keV cascade. Evidence was found, that the 2421 keV (2⁺) level is excited by weak gamma rays from high-energy levels. The K/β⁺ ration in the ⁴⁸V decay is 0.69±0.05 The Q-values of ⁴⁸Sc and ⁴⁸V are calculated to be 3986±7 keV and if 4015±4 keV, respectively. The energy of the gamma ray of ⁴⁷Sc, which is present as an impurity, is 159.2±0.5 keV.     

The g-factor of the 3/2 153 keV state in V

The g-factor of the 3/2⁻ state at 153 keV in ⁴⁹V was measured with the ⁴⁸Ti(p, γ)⁴⁹V reaction and the differential spin-precession method. The g value and the remeasured mean life are g = 1.58 ± 0.08 and τ = 28.7 ± 0.5 ns. The result is compared with some theoretical predictions.     

杂多阴离子的NMR和ESR研究——P-V-W Keggin阴离子的31P、51V、17O-NMR谱

本文合成了六种含有P-V-W和V-V-W Keggin结构的杂多阴离子,并研究了它们的³¹P、⁵¹V、¹⁷O-NMR谱,对于PV_xW_12-xO₄₀^(x+3)-(x=1~4)阴离子,当x=1时,³¹P和⁵¹V-NMR谱只有一条线,并且此线化学位移和pH无关。当x ≥ 2时,谱线数目随着x迅速增加,其原因是几何异构体的数目和类型迅速增加。它们的化学位移δ_p,和δ_v。依赖于溶液的酸性和x,即δ_p,随pH值和x增加而减少,而δ_v,却随pH和x的增加而增加。最后简短讨论了桥氧上质子化的影响。     

Double resonance experiments in a single resonance probe: detecting Na–V dipolar interactions in sodium vanadates

²³Na-{⁵¹V} double resonance TRAPDOR experiments are presented on two different sodium vanadates. This is the first time that the heteronuclear dipolar interaction between nuclei, whose Larmor frequencies lie within a range of 0 to 3 MHz is detected in order to monitor connectivity and internuclear distance information in these systems.     

A study of the Ti(He, t) and Ni(He, t) reactions to isobaric analogue states

The (³He, t) reaction populating 0⁺ and 2⁺ states in ^{58, 60}Cu and ^{46, 48}V which are isobaric analogue states (IAS) of the 0⁺ ground states and 2⁺ first excited states in ^{58, 60}Ni and ^{46, 48}Ti have been studied at an incident ³He energy of 24.6 MeV. Triton spectra were measured for the targets ^46,48Ti, ^natNi and ⁵⁸Ni and angular distributions for the 0⁺ and 2⁺ IAS of ^{46, 48}Ti and ^{58, 60}Ni determined. The data were obtained using a magnetic spectrometer and position-sensitive detectors. The results have been analysed using DWBA theory. The 0⁺ → 0⁺ transitions to analogue states are described quite well using a microscopic form factor derived from a nucleon-nucleon interaction. However, with a Gaussian form, the m.s. radius of this interaction is only limited to the region 0–9 fm². Comparisons with data at other incident energies indicate that the strength of the effective interaction is strongly energy dependent. The Coulomb energies and (³He, t) angular distributions of the states assigned as the 2⁺ analogues in ⁴⁸V and ^58,60Cu are not described well by the models investigated. The ⁴⁶V 2⁺ IAS angular distribution is reproduced by a microscopic calculation, however. The ratios of the 0⁺ → 2⁺ IAS to the 0⁺ → 0⁺ IAS transitions are used to deduce a quadrupole deformation for the valence neutrons. The difference in the quadrupole deformations of the matter and proton distributions, as determined by other means, is found to be correlated with those of the valence neutrons. Several transitions to non-analogue states are also investigated.     

Exchange current effects in magnetic electron scattering from Ti, V, Co, Sr, and Wb

Recent high-multipolarity elastic magnetic electron-scattering experiments on ⁴⁹Ti, ⁵¹V, ⁵⁹Co, ⁸⁷Sr, and ⁹³Nb yield information about the radial distribution of single proton and neutron orbits in the f_7/2 and g_9/2 shells. We examine the effects of exchange currents on the analysis of these measurements by presenting a series of fits to the data both excluding and including exchange currents. The exchange currents are shown to be a significant effect that may alter previous conclusions from these experiments.     

The g-factor of the 320 keV state of V measured by Coulomb excitation in Fe-V alloy

The g-factor of the 320 keV first excited state of ⁵¹V measured by Coulomb excitation in Fe-V alloy was found to be g = 1.54±0.13.     

Nuclear spin-lattice relaxation of V in TIxV5S8 and TIxV6S8

Temperature dependence of the nuclear spin-lattice relaxation rate of ⁵¹V has been studied in metallic vanadium sulfides with quasi-one-dimensional structures. The ternary sulfide TI_0.54V₅S₈ is suggested to be an exchange-enhanced Pauli-parammagnet with antiferromagnetic correlation.     

Statistical theory versus shell model in a large pf configuration space

Spectral distribution method and exact shell-model predictions for the strength sums of different transition operators are compared in detail for the J=0, T−T_z=0 states of ⁴⁶V and ⁵⁰Sc using the full pf shell. Good agreement of both models is observed in the high level density region of the energy spectrum, where chaotic motion is dominant, and larger discrepancies are observed in the ground state region, where nuclear motion is more regular. The agreement in the chaotic region becomes especially good in the 5986 dimensional space of ⁵⁰Sc, illustrating the quality of the statistical theory in large configuration spaces.     

New evidence for a subshell gap at N=32

An 879.9(2) keV γ-ray transition has been identified following the β decay of ⁵⁸V and assigned as the 2⁺₁→0⁺₁ transition in ⁵⁸Cr₃₄. A peak in the energies of the first excited 2⁺ states for the even–even chromium isotopes is now evident at ⁵⁶Cr₃₂, providing empirical evidence for a significant subshell gap at N=32. The appearance of this neutron subshell closure for neutron-rich nuclides may be attributed to the diminished π1f_7/2–ν1f_5/2 monopole proton–neutron interaction as protons are removed from the 1f_7/2 single-particle orbital.     

Vanadium-51 solid-state NMR electric field gradient tensors: a DFT-embedded ion and isolated cluster study of crystalline vanadium oxides

Density functional theory (DFT) calculations (6–311+G(2d,p)/B3LYP level of theory) of ⁵¹V electric field gradient (EFG) tensor elements are performed for embedded and isolated cluster models of orthovanadates. The structural models used to calculate the EFGs of ⁵¹V are (I) an isolated H₄VO₄⁺ cluster, (II) an isolated H_nVO₄ⁿ⁻³ cluster (n=number of next-neighbor cations) (III) an isolated orthovanadate anion, VO₄^−x, and (IV) a VO₄^−x ion embedded in a finite point-charge array whose electrostatic potential, at the embedded ion, is equivalent to that of the infinite lattice. For models III and IV, a charge x is assigned estimating the covalence of the system. Models III and IV provide results in good agreement with the experiment. Calculations, employing the embedded and isolated VO₄^−x models, are used to discuss site assignments for AlVO₄. Correlations between quadrupole coupling parameters and deviations of the orthovanadate structure from ideal tetrahedral symmetry are shown.     

A solid-state V NMR characterization of vanadium sites in LiCoxNi1−xVO4

LiCo_xNi_1−xVO₄ compounds (x=0, 0.2, 0.5, 0.8, 1.0) have been prepared for lithium ion batteries by different preparation methods, namely, wet-chemistry (WC) and solid-state (SS) routes. ⁵¹V nuclear magnetic resonance (NMR) has been employed to accurately assess the vanadium environments in these materials and results show that vanadium atoms are distributed in octahedral and tetrahedral sites. The fractions of vanadium atoms in tetrahedral/octahedral sites depends on composition and sample preparation conditions. The tetrahedral site, which is particularly dominant in samples produced via the WC route, is more affected by paramagnetic interactions and its ⁵¹V NMR spectrum is essentially Gaussian in shape. The octahedral site, on the other hand, exhibits first-order quadrupolar broadened satellites. Even though tetrahedral sites for a given x are comparable for WC and SS materials, there are some differences amongst octahedral environments, namely in the distributions of quadrupolar broadened satellites. The larger satellite distribution observed for WC materials is indicative of a larger distribution of structural defects for these as compared to SS materials.     

Spin-dependent reaction mechanism in Ti(d, p)Ti from proton-γ correlation

The γ-decays of the states in ⁴⁷Ti at 157 keV and 1547 keV have been studied following the ⁴⁶Ti(d, p)⁴⁷Ti reaction at 5.0 MeV incident energy. Protons were detected at 0° with a semiconductor detector. The angular correlations of the γ-rays with the reaction protons were measured. The E2/M1 mixing ratios of the γ-decays and the population ratios of the to the substates were deduced. From the non-zero population of the substate it was concluded that a spin-flip mechanism exists in the ⁴⁶Ti(d, p)⁴⁷Ti stripping reaction.     

H, V and N nuclear magnetic resonance studies of structure and properties of vanadia supported on TiOx/SiO2

¹H magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of TiO_x/SiO₂ catalysts suggest the interaction of surface TiO_x. species with Si-OH groups of the silica. Simultaneously, Ti-OH groups from surface titania species appear. The distribution of TiO_x species over SiO₂ is non-uniform, since a considerable part of surface OH groups remains unreacted with supported titania. Supported vanadia species interact both with Si-OH and Ti-OH groups. ⁵¹V NMR spectra suggest the interaction of vanadia with supported titania species and show the non-uniform distribution of titania over the SiO₂ surface. Deposition of titania as well as vanadia produces strong electron-accepting (Lewis) sites which interact with the terminal N atom of adsorbed N₂O molecules, resulting in a downfield shift of the resonance in ¹⁵N NMR spectra. The acid strength of electron-accepting sites is similar in both cases. Only about 10% of the total amount of supported titania and vanadia create Lewis sites.     

Isomerism in Ag and non-yrast levels in Pd and Rh, studied in β decay

The β decay of ⁹⁶Ag (Z=47,N=49) was investigated by measuring positrons, X rays as well as β-delayed protons and γ rays. The γ radiation was studied by means of germanium detectors and a NaI total-absorption spectrometer. Two β-decaying isomers in ⁹⁶Ag were established with half-lives of 4.40(6) and 6.9(6) s and tentative spin–parity assignments of (8⁺) and (2⁺), respectively. For both isomers, the intensities of β transitions to low-lying levels of ⁹⁶Pd (Z=46,N=50) and β-delayed proton decays to levels in ⁹⁵Rh (Z=45,N=50) were measured. Several new ⁹⁶Pd levels were firmly established. The level energies, their γ decays and the Gamow–Teller decay of ⁹⁶Ag are compared to shell-model predictions. A new low-lying level in ⁹⁵Rh was found at 680 keV excitation energy. Through a comparison with low-lying states of N=50 isotones, this level is interpreted as the first excited 7/2⁺ state built on the proton 9/2⁺ ground state. The assignments of further excited states in ⁹⁵Rh are discussed.     

YNbO4：Tm3+/Yb3+上转换发光特性研究

按照50Nb₂O₅-（46-x）Y₂O₃-4Yb₂O₃-xTm₂O₃（x=0.1,0.2,0.5,1,2）的配比方式,采用高温固相法制备出了掺杂Tm³⁺/Yb³⁺的YNbO₄晶体粉末。在980 nm红外光激发下,观测到波长为478,645,707 nm的上转换荧光,分别对应于Tm³⁺离子的¹G₄→³H₆、¹G₄→³F₄、³F₃→³H₆能级跃迁过程。利用上转换发射功率与980 nm激光器工作电流关系估算出跃迁过程吸收光子数目为2.72,2.69,2.01,从而确定出前两者为三光子吸收过程,最后一个对应于双光子吸收过程。运用Judd-Ofelt理论研究样品光谱特性,根据样品的吸收谱得到样品的谱线强度参数Ω_t（t=2,4,6）,进而得出理论振子强度及实验振子强度,二者均方根偏差δ_rms=1.299×10^-7。计算了Tm³⁺离子向下能级跃迁的跃迁几率、跃迁分支比等参数。最后得出结论：（1）³F₄能级寿命较长,适合作为上转换中间能级;（2）³H₅能级寿命较长,且³H₅→³H₆跃迁分支比（96.46%）接近100%,可用于产生1 216 nm激光。     

Stray-field imaging of quadrupolar nuclei of half integer spin in solids

A report is presented on the observation of Hahn echoes from the following quadrupolar nuclei of half integer spin (I) in polycrystalline solids in the large static magnetic field gradient (37.5 T/m) which exists in the fringe field of a superconducting solenoid: ⁷Li, ²³Na, ¹¹B, ⁶⁵Cu (I = 3/2); ²⁷Al (I = 5/2); ⁵¹V, ⁵⁹Co (I = 7/2); and ¹¹⁵In (I = 9/2). ²³Na echo-trains from NaCl (with non-selective excitation) and from Na₂SO₄ (with selective excitation) are compared quantitatively for two different RF pulse sequences: 90_x-(τ-90_y-τ-echo-)_n and 90_x-(τ-90_x-τ-echo-)_n. The signals obtained from RF pulses corresponding to non-selective 90 ° pulses were shown to be quantitative, whereas in the selective case smaller signals were obtained since only the central transition contributed. The loss of signal from this cause can be distinguished from small signals resulting from low density of nuclei by use of the second sequence. A ⁷Li image obtained from LiF in a cylindrical glass-vial is shown.     

基质对Tb3+单掺荧光玻璃发光性质的影响

采用高温熔融法制备了Tb³⁺单掺硼酸盐、硅酸盐和磷酸盐荧光玻璃和相应的玻璃基质。根据紫外-可见透射光谱计算了Tb³⁺在不同基质中从⁷F₆ 到⁵D₃和 ⁵D₄能级的实验振子强度,解释了不同基质中Tb³⁺发射光谱的变化原因。结果表明：因为对称性差,在磷酸盐玻璃基质中,Tb³⁺在542 nm和585 nm处的发射峰有劈裂现象。在硼酸盐和硅酸盐基质中,Tb³⁺ 的⁵D₃能级上的粒子通过交叉弛豫过程被倒空并转移到⁵D₄能级,故⁵D₃能级发光（413 nm和436 nm）不明显;在磷酸盐基质中,Tb³⁺的⁵D₃能级上的粒子数较少,没有交叉弛豫产生,故⁵D₃能级发光最强。在3种基质中,Tb³⁺从⁵D₄能级发射的特征峰489,542,585,620 nm的强度顺序是硼酸盐>硅酸盐>磷酸盐,与Tb³⁺在不同基质中从⁷F₆ 到 ⁵D₄能级的实验振子强度顺序一致。     

Homonuclear vanadium-51 dipolar couplings in inorganic solids obtained via hahn spin echo decay NMR spectroscopy

Dipolar dephasing of the magnetization following a Hahn spin echo pulse sequence potentially provides a quantitative means for determining the dipolar second moment in solids. In this work, the possibility of employing Hahn spin echo decay spectroscopy to obtain quantitative ⁵¹V–⁵¹V dipolar second moments is explored. Theoretical spin echo response curves are compared to experimental ones for a collection of crystalline vanadium-containing compounds. This work suggests that ⁵¹V dipolar second moments can be obtained by selectively exciting the central m = 1/2 → −1/2 by a Hahn echo sequence for vanadate compounds with line broadening no greater than approximately 220 ppm. For vanadates with greater broadening of the central transition due to chemical shift, second-order quadrupolar, and dipolar interactions, off-resonance effects lead to an oscillatory time dependence of the spin echo. Experimentally determined second moments of the normalized echo decay intensities lie within 10–33% of the calculated values if the second moments are extrapolated to zero evolution time due to the time scale dependence of spin exchange among neighboring vanadium nuclei. Alternatively, the second moments can be obtained to within 10–25% of the calculated values if the broadening of the central transition due to chemical shift and second-order quadrupolar effects can be estimated.     

Gd3+,Yb3+和Tm3+共掺杂氟化物纳米晶中Yb3+-Tm3+-Gd3+间的能量传递

用水热法合成了Y_0.8-x-yF₃∶Gd_x³⁺,Yb_0.2³⁺,Tm_y³⁺纳米晶的上转换发光材料。在典型的Y_0.595F₃∶Gd_0.200³⁺,Yb_0.200³⁺, Tm_0.005³⁺纳米微晶中,在980 nm激光激发下,观察到了Tm³⁺的紫外、紫色上转换发射明显增强和来自于Gd³⁺的⁶D_9/2、⁶I_J、⁶P_5/2及⁶P_7/2能级到基态⁸S_7/2能级的紫外发射。通过比较Y_0.8-x-yF₃∶Gd_x³⁺ ,Yb_0.2³⁺,Tm_y³⁺纳米晶样品的上转换发光性质以及Tm³⁺和Gd³⁺中一些激发态的能级寿命,借助于能级图描述了Yb³⁺-Tm³⁺-Ga³⁺之间的有效的能量传递过程。