New transitions in the β-decay of 36Ca

The β-decay of the T _z = - 2 nucleus ³⁶Ca was studied at the LISE3 magnetic spectrometer at GANIL. Two new proton-emitting states have been detected and the other nine known βp and βγ transitions have been remeasured with improved resolution. A simulation with the GEANT code has been applied to this experimental setup. A comparison with shell model calculations is given. Received: 19 September 2000 / Accepted: 28 February 2001     

Phonon Dispersion in Ca70Mg30 Metallic Glass

The phonon dispersion curves （PDC） of Ca70Mg30 metallic glass has been studied at room temperature in terms of phonon eigen frequencies of longitudinal and transverse modes employing three different approaches proposed by Hubbard and Beeby （J. Phys. C： Solid State Phys. 13 （1969） 556）, Takeno and Goda （Prog. Theor. Phys. 45 （1971） 331; 47 （1972） 790） and Bhatia and Singh （Phys. Rev. B 31 （1985） 4751）. The well recognized model potential of Gajjar et al. is employed successfully to explain electron-ion interaction in the metallic glass. The effective pair potential is used to generate the pair correlation function g（r）. The local field correction function （Int. J. Mod. Phys. B 17 （2003） 6001） is used for the first time to introduce the exchange and correlation effects on the aforesaid properties. The present findings of PDCs are found to be in agreement with the available theoretical as well as experimental data. The thermodynamic and elastic properties, i.e. longitudinal and transverse sound velocities, isothermal bulk modulus, modulus of rigidity, Poisson＇s ratio, Young＇s modulus and Debye temperature, are also investigated successfully.     

Novel Superconducting Electrides in Ca–S System under High Pressures

Due to their unique structure properties,most of the electrides that possess extra electrons locating in interstitial regions as anions are insulators.Metallic and superconducting electrides are very rare under ambient conditions.We systematically search possible compounds in Ca-S systems stabilized under various pressures up to 200 GPa,and investigate their crystal structures and properties using first-principles calculations.We predict a series of novel stoichiometries in Ca-S systems as potential superconductors,including P2_1/m Ca_3S, Pnma C_a3S,Pnma Ca_2S,Cmcm Ca_2S,Fddd CaS_2,Immm CaS_3 and C2/c CaS_4.The P4mbm Ca_3S phase exhibits a maximum T_c value of ～20K.It is interesting to notice that the P2_1/m Ca_3S and Pnma Ca_2S stabilized at 60 and 50 GPa behave as superconducting electrides with critical temperatures T_c of 7.04 K and 0.26 K,respectively.More importantly,our results demonstrate that P2_1/m Ca_3S and Pnma Ca_2S are dynamically stable at 5 GPa and 0 GPa,respectively,indicating a high possibility to be quenched to ambient condition or synthesized using the large volume press.     

Application of ^41Ca Tracer and Its AMS Measurement in CIAE

The man-made calcium isotope ^41Ca is an ideal tracer for the study of calcium metabolism. We represent the first application of accelerator mass spectrometry (AMS) measurement of ^41Ca tracer in China. The technique is being applied to the research field of cell messenger at the China Institute of Atomic Energy (CLAE). The sample preparation methods and the AMS measurements are discussed and some interesting results are presented.     

中能Ca+Ca反应中的对称能效应

采用把重离子碰撞的动力学和统计衰变过程相结合的一个两步模型,再现了INDRA Collaborations 对入射能为35 AMeV40Ca+40Ca 和48Ca+48Ca 反应的实验结果。进而得到了反应碎块同位素分布的Isoscaling 参数α(Z) 和β(N),约化对称能系数ζ(Z) 及与平均场中的对称能强度系数Cs 之间的关系。结果表明,Isoscaling 参数强烈依赖于系统的丰中子程度。随着质子数的增大,ζ(Z) 在动力学阶段呈现平缓趋势但在衰变之后呈现上升趋势,且该结果不依赖于所选取的反应系统。对称能效应在统计衰变过程之后的末级碎块分布中有明显表现。A two-step model for combining the dynamical and statistical decay processes in heavy-ion collisions is used to reproduce the experimental results of the INDRA Collaborations on 40Ca+40Ca and 48Ca+48Ca reactions at 35 AMeV. We obtain the isoscaling parameters α(Z) and β(N) of isotopic distributions of the fragments, the reduced symmetry energy coefficient ζ(Z) and its dependence on the symmetry energy strength coefficient Cs in the mean field. Our results suggest that Isoscaling parameters strongly depend on the degree of neutron-rich. With the increasing atomic number, ζ(Z) represents a smoothly flat tendency during the dynamical process but shows the increasing tendency after decay, and such results are independent on the selected reaction systems. The effect of symmetry energy shows evidently in the isotopic distributions of fragments after statistical decay process.     

Phenomenological Scaling of Rapidity Dependence for Anisotropic Flows in 25 MeV/nucleon Ca＋Ca by Quantum Molecular Dynamics Model

Anisotropic flows （v1, v2, v3 and v4） of light fragments up to the mass number 4 as a function of rapidity are studied for 25 MeV/nucleon ^40Ca ＋ ^40Ca at large impact parameters by a quantum molecular dynamics model. A phenomenological scaling behaviour of rapidity dependent flow parameters vn （n = 1, 2, 3 and 4） is found as a function of mass number plus a constant term, which may arise from the interplay of collective and random motions. In addition, v4/v2^2 keeps to be almost independent of rapidity and remains a rough constant of 1/2 for all light fragments.     

Pico-second photoelectric characteristic in manganite oxide La0.67Ca0.33MnO3 films

Ultrafast photoelectric characteristic has been observed in La_0.67Ca_0.33MnO₃ films on tilted SrTiO₃ substrates. A pico-second (ps) open-circuit photovoltage of the perovskite manganese oxide films has been obtained when the films were irradiated by a 1.064μm laser pulse of 25 ps duration. The rise time and full width at half-maximum of the photovoltage pulse are ～300 ps and ～700 ps, respectively. The photovoltaic sensitivity was as large as ～500 mV/mJ.     

Lu-induced spin entropy enhancement in Ca3Co4O9+δ system

The magnetothermopower have been studied in Lu-doped Ca_3?xLu_xCo₄O_9+δ. A strong magnetic field suppression of thermopower indicates large spin entropy contribution. The magnetothermopower for doped samples are overall enhanced compared with that for undoped Ca₃Co₄O_9+δ, providing an experimental evidence for the enhancement of spin entropy. Magnetic results confirm that Co⁴⁺ concentration is reduced by Lu doping. We suggest that the reduction in Co⁴⁺ concentration results in the enhanced spin entropy.     

Development of the Neck in Fusion Reactions ^40Ca＋^90,96Zr

The neck dynamics and nucleon transfer through the neck in fusion reactions ^40Ca ^90,96Zr are studied by applyingthe improved quantum molecular dynamics model. A special attention is paid to the dynamic behaviour of the neck development at touching point and to the contribution of excess neutrons in a neutron-rich target (or projectile) to neck formation and nucleon transfer.     

EPR study of the [H−Ca+]0 defect in Tcr CaO

Abstract

A new hydrogen related low-temperature trap for the electrons released during the photoconversion of F→F⁺ centers is studied by EPR. The defects are stable up to 80 K. Below 20 K the spectrum corresponds to the static situation showing tetragonal symmetry. Above this temperature the spectrum is isotropic a consequence of the hopping among the six equivalent orientations. A model for the defect and the study of its reorientational motion are given.     

Charge disproportionation induced exchange bias in La0.5Ca0.5FeO3-δ

We observed an exchange bias effect in La0.5Ca0.5FeO3 perovskite compound.The exchange bias is associated with the charge disproportionation transition from Fe4+ions to Fe3+and Fe5+ions below 175 K.The competition between the ferromagnetic interaction of Fe3+and Fe5+ions and the antiferromagnetic one of Fe3+and Fe3+ions results in a unidirectional anisotropy in the cluster-glass system.An antiferromagnetically interfacial exchange coupling constant Ji1.95 meV at the cluster-glass region was yielded by fitting the cooling field-dependence of the exchange bias field.     

Enhancement of the colossal magnetoresistance in Eu1 − x Ca x B6

The transport and magnetic properties of single crystal samples of substitutional solid solutions Eu_{1 ? x} Ca _x B₆ (0 ≤ x ≤ 0.26) have been studied at temperatures 1.8–300 K in magnetic fields up to 80 kOe. It has been shown that an increase in the calcium concentration results in the suppression of the charge transport accompanied by an increase in the amplitude of the colossal magnetoresistance (CMR) up to the value (ρ(0) ? ρ(H))/ρ(H) ≈ 7 × 10⁵ detected for x = 0.26 at liquid-helium temperature in a field of 80 kOe. The transition from the hole-like conductivity to the electron-like conductivity has been observed in the Eu_0.74Ca_0.26B₆ solid solution in the CMR regime at T < 40 K. The Hall mobility values μH = 200?350 cm²/(V s) estimated for charge carriers in the strongly disordered matrix of the Eu_0.74Ca_0.26B₆ solid solution are comparable with the charge carrier mobility μH = 400?600 cm²/(V s) for the undoped EuB₆ compound. The anomalous behavior of the transport and magnetic parameters of the Eu_{1 ? x} Ca _x B₆ solid solutions is discussed in terms of a metal-insulator transition predicted within the double exchange model for this system with low carrier density.     

同位素对Ca+HCl，Ca+DCl，Ca+TCl反应立体动力学性质的影响

基于准经典轨线方法和Verbockhaven等人通过多参考组态相互作用计算建立的势能面研究了Ca+HCl/Ca+DCl/Ca+TCl反应中的矢量相关效应. 计算和分析了 P(θr)和 P(Φr)以及(2π/σ)(dσ₀₀/dω_t), (2π/σ)(dσ₂₀/dω_t), (2π/σ)(dσ₂₂₊/dω_t), (2π/σ)(dσ_21-/dω_{t相似文献}   

Fine structure of the isoscalar giant quadrupole resonance in Ca due to Landau damping?

The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in ⁴⁰Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at Ep=200 MeV$E_{\mathrm{p}}=200\text{MeV}$. Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon–nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for ⁴⁰Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle–two-hole (2p–2h) states.     

Phase separation region in the phase diagram of polycrystalline Pr0.65Ca0.35−xSrxMnO3

We have performed measurements of thermoelectric power, electrical resistivity and DC magnetization in polycrystalline samples of Pr_0.65Ca_0.35−xSr_xMnO₃ with x=0, 0.02, 0.05, 0.10 and 0.20. The system presents an evolution from a charge-ordered manganite at x=0, with an insulating-like resistivity and low magnetization values, towards a ferromagnetic (FM) metallic state for x=0.20. We show that in the intermediate region a strong competition between the FM double-exchange and the localized charge-ordering occurs, inducing the phase segregation of the two competing states in a wide temperature range. We estimate the temperature (T) evolution of the FM phase fraction of the x=0.10 sample and construct a complete T−x phase diagram.     

Change of membrane fluidity and protein conformation involved in [Ca2+]i overload in neuronal cells induced by ONOO−

Considerable evidence indicates that the formation of peroxynitrite (ONOO⁻) with superoxide anion (O₂^−⊙ot) may be involved in the neuronal toxicity of NO. Here, the effects of ONOO⁻ on intracellular free calcium concentration ([Ca²⁺]_i) in single MN9D cells was studied by the Fura-2 microfluorometric technique. The results showed that [Ca²⁺]_i was increased dose-dependently with the addition of ONOO⁻ (0–40 μmol/l) after 5 s and then decreased rapidly back to the basal level after ONOO⁻ was removed. [Ca²⁺]_i response to ONOO⁻ can be blocked by removing Ca²⁺ from the bath or adding L-type calcium channel antagonist nifedipine (10 μmol/l) to the bath. [Ca²⁺]_i transients by ONOO⁻ were substantially inhibited by dithiothreitol (DTT), which indicated ONOO⁻ may alter the L-type calcium channel on neuronal cell by thiol oxidation. To elucidate the mechanism of ONOO⁻ on [Ca²⁺]_i, the electron spin resonance spin-labeling technique was used to study the effects of ONOO⁻ on the membrane fluidity and the membrane protein conformation on freshly dissociated neurons. The results indicate that ONOO⁻ decreases membrane fluidity both near the surface and deep in the membrane and affects protein conformation. The fact that DTT effectively inhibits the deterioration supports the conclusion that the change of membrane fluidity and protein conformation is involved in [Ca²⁺]_i overload in neuronal cells induced by ONOO⁻.     

А∧Ca和А∧∧Ca超核中的巨中子晕现象

利用密度相关零程对力的相对论连续谱Hartree—Bogolubov方法，对偶中子数的Ca同位素从质子滴线到中子滴线范围内的单∧超核和双∧超核基态性质进行了系统研究。与通常的原子核相比，单∧超核和双∧超核中起子提供的吸引力会相应地降低中子费米面。所预言的中子滴线超核分别为А∧Ca和А∧∧Ca，比原来预测的通常滴线核^74Ca多两个中子。基于对双中子分离能、中子密度分布、半径、单粒子能谱、轨道占据数和连续谱贡献的分析，预言了超核中的巨中子晕现象。     

AΛCa和 AΛΛCa超核中的巨中子晕现象

利用密度相关零程对力的相对论连续谱Hartree-Bogoliubov方法,对偶中子数的Ca同位素从质子滴线到中子滴线范围内的单Λ超核和双Λ超核基态性质进行了系统研究. 与通常的原子核相比,单Λ超核和双Λ超核中超子提供的吸引力会相应地降低中子费米面. 所预言的中子滴线超核分别为77ΛCa和78ΛΛCa,比原来预测的通常滴线核74Ca多两个中子. 基于对双中子分离能、中子密度分布、半径、单粒子能谱、轨道占据数和连续谱贡献的分析,预言了超核中的巨中子晕现象.     

New investigation for Tc depression by Ca in Y1−xCax:123 superconducting systems

Two similar sets of the series Y_1?xCa_xBa₂Cu₃O_Y (0.00 ? x ? 0.50) are prepared by two different heat treatments at the final process of calcinations. The first set is quenched in air down to room temperature (ssq); while the second is left in the furnace and slowly cooled to room temperature (sss). After that, the samples are separately sintered in two different oxygen purity (99.99% Hp and 93% Lp, respectively) to obtain four different sets called ssqHp, sssHp, ssqLp and sssLp. Then, the considered samples are tested by XRD, SEM, resistivity and microhardness (VHN) techniques. It is found that c-parameter for ssqHP and sssLP samples increases slightly with Ca doping; while orthorhombic distortion remains nearly invariant. Interestingly, unlike for ssqHp and sssLp samples, the OD decreases continuously with Ca doping in sssHp and ssqLp samples; while c-parameter increases. SEM micrographs indicate that Ca generally improve the link between superconducting grains for all set of samples. The oxygen content is gradually decreased by Ca for all set of samples and generally follow the relation, y = 6.93 ? 0.5x. The effective Cu valence slightly decreases, as compared to pure samples, but stays nearly independent of Ca content for all the series. The relative decrease in critical temperature T_c by Ca is more in ssqHp and sssLp samples, when compared with those of sssHp and ssqLp samples. Although, an approximately linear increase in VHN with various Ca is obtained, the relative increase is more in ssqHp and sssLp samples with respect to sssHp and ssqLp samples. These results indicate that substitution of Ca at Y site leads towards oxygen vacancies predominantly created in CuO₂ planes (CuO chains) of ssqHp and sssLp (sssHp and ssqLp) based samples, and far from overdoping.