同位旋效应对F同位素s-d能级间隙的影响

在单粒子势模型的框架下, 计算了O同位素和F同位素的基态和某些低激发态的能级值、均方根半径值及密度分布。通过在伍兹 萨克逊势中引入同位旋依赖项, 研究了同位旋效应对F同位素s-d能级间隙的影响。理论计算得到的均方根半径值和自旋宇称值与实验结果一致。尤其是, 理论计算能够实现16F, 15F和14F中2s_1/2与1d_5/2质子能级间的反转, 且F同位素中s-d质子能级间隙及其整体变化趋势与已知实验结果符合较好。此外, 理论结果表明17F的(1/2)+第一激发态为单质子晕态。 The level structures of O and F isotopes are investigated in the framework of the single particle potential model. The isospin effect on the s d level spacing in F isotopes is studied by introducing an isospin dependent term in the depth of the Woods Saxon potential. The theoretical results of RMS radii and spin parity values are in agreement with the experimental data. In particular, the level inversion between proton levels of 2s_1/2 and 1d_5/2 in 16F, 15F and 14F is reproduced. The global tendency of the s-d level spacing agrees with the observed fact. In addition, the study confirms the one proton halo structure in 17F(2s_1/2).     

中子中子碰撞产生超高能中子问题模拟

ICF的聚变靶丸中,高能中子相互之间发生碰撞将导致超高能中子的产生,推导中子中子碰撞与超高能中子产生的关系,研究利用蒙特卡罗方法确定碰撞后中子速度的方法,通过求解非线性中子输运方程及对DT聚变小球中的中子输运问题进行数值模拟,研究中子与中子碰撞产生超高能中子及其与聚变中子源强的关系问题.     

CoFe/TiZr多层膜材料界面结构与性能的极化中子反射研究

利用极化中子反射技术较系统地研究了CoFe/TiZr复合多层膜材料界面结构,结果表明.1)从多层膜超镜传输特性角度考虑,等厚对层不如非等厚对层膜结构好.2)等厚对层的最佳退火温度约250℃,非等厚对层退火温度低于250℃影响不明显,等厚和非等厚对层经350℃退火后膜层变化严重.3)从布拉格峰位变化看,随着退火温度的升高,等厚对层膜的厚度先变小后变大;非等厚对层与之相反. 关键词： CoFe/TiZr多层膜 退火影响 膜层结构 极化中子反射     

超强超短脉冲激光诱发大尺度氘团簇聚变

 利用低温脉冲气阀获得了平均含有3×103氘原子的氘团簇。在飞秒激光装置上实现了氘团簇聚变,每发中子产额为1×10³。中子产额对激光功率密度敏感,保持激光能量不变,随着激光焦斑的变大,DD聚变中子产额逐渐增加,最大值出现在激光焦斑为470 mm时;继续增大激光焦斑,没有观察到中子信号。实验结果还表明激光氘团簇聚变发生的区域主要是激光辐照的等离子体热区,此区域内邻近氘团簇库仑爆炸发射的高能氘离子碰撞引发聚变反应。     

塑料闪烁光纤在高能中子辐照下质子分布特性的数值模拟

 利用Geant4系统模拟了在高能中子照射下,塑料闪烁光纤中产生的反冲质子的分布特性,分析了入射中子能量分别为2,4,6,8 MeV时,产生的反冲质子能量和方向分布,给出了反冲质子在不同方向上的能量分布。结果表明:向前和向后出射的质子分布不对称;反冲质子的能量在零与入射中子能量之间连续地分布;接近垂直入射方向产生的质子数较多;入射中子能量越高,产生质子数越少;反冲质子的出射角度越小,其能量越大,即沿着入射中子方向的反冲质子能量较大,垂直入射方向的反冲质子能量较小。     

Influence of octahedral tilting and composition on electrical properties of the Li0.2 − xNaxLa0.6TiO3 (0 ≤ x ≤ 0.2) series

The Rietveld analysis of ND patterns of polycrystalline Li_0.2 − xNa_xLa_0.6TiO₃ (0 ≤ x < 0.2) samples, recorded between 300 and 1075 K, shows an orthorhombic–tetragonal transformation, in which the octahedral tilting along the b axis is eliminated at ~ 773 K, but the vacancy ordering along the c axis remains. In Li rich samples, conductivity (10^− 3 Ω^− 1 cm^− 1 at 300 K) departs from the Arrhenius behaviour, decreasing activation energies from 0.37 to 0.14 eV when octahedral tilting is eliminated. Successive Maxwell–Wagner blocking processes, detected in the real part of dielectric constant plots, have been ascribed to the Li blocking at interior domains, grain-boundary and electrode–electrolyte interfaces. The substitution of Li⁺ by Na⁺ decreases the amount of vacant A-sites, decreasing several orders of magnitude the conductivity when the amount of vacancies approaches the vacancy percolation threshold (n_p = 0.27). Below the percolation threshold, Li ions only display local mobility, remaining confined into small domains of perovskites.     

Steady state investigation on neutronics of a molten salt reactor considering the flow effect of fuel salt

The Molten Salt Reactor (MSR), one of the `Generation IV' concepts, is a liquid-fuel reactor, which is different from the conventional reactors using solid fissile materials due to the flow effect of fuel salt. The study on its neutronics considering the fuel salt flow, which is the base of the thermal-hydraulic calculation and safety analysis, must be done. In this paper, the theoretical model on neutronics under steady condition for a single-liquid-fueled MSR is conducted and calculated by numerical method. The neutronics model consists of two group neutron diffusion equations for fast and thermal neutron fluxes, and balance equations for six-group delayed neutron precursors considering the flow effect of fuel salt. The spatial discretization of the above models is based on the finite volume method, and the discretization equations are computed by the source iteration method. The distributions of neutron fluxes and the distributions of the delayed neutron precursors in the core are obtained. The numerical calculated results show that, the fuel salt flow has little effect on the distribution of fast and thermal neutron fluxes and the effective multiplication factor; however, it affects the distribution of the delayed neutron precursors significantly, especially the long-lived one. In addition, it could be found that the delayed neutron precursors influence the neutronics slightly under the steady condition.     

Thiourea-doped ammonium dihydrogen phosphate: A single crystal neutron diffraction investigation

Thiourea-doped ammonium dihydrogen phosphate (TADP) exhibits nonlinear optical property and the second harmonic generation efficiency of these crystals is three times that of pure ammonium dihydrogen phosphate (ADP) crystal. In this context, the study of structural distortion in the thiourea-doped ADP crystal is significant, hence single neutron diffraction investigations were undertaken. The final R-factors are: R[F ² > 2σ(F ²)] = 0.11, Goodness of fit(S) = 1.15. Though the dopant could not be located from the difference Fourier map, the cell parameters (a = b = 7.531(3) A, c = 7.544(5) Å) were found to be significantly greater than that of pure ADP at RT (a = b = 7.502(1) Å, c = 7.546(1) Å). This indicates that the dopant concentration in the crystals is small but enough to bring changes in the overall average structure.     

SMARTer for magnetic structure studies

SMARTer, a 36-meter small angle neutron scattering (SANS) spectrometer was installed at the Neutron Scattering Laboratory (NSL), National Nuclear Energy Agency of Indonesia — BATAN in Serpong, Indonesia and has performed the experiment for studying the magnetic structures of Cu(NiFe), CuCo and FeSiBNbCu metal alloys. The experiments were conducted at room temperature and up to 1 T (10 kOe) of external magnetic field. At zero fields, isotropic scattering identified as nuclear scattering is dominant. When a magnetic field is applied in a horizontal direction perpendicular to the neutron beam, the response of the magnetic scattering permits extraction of the field-induced re-arrangement of the magnetic moment. With increasing field the distortion is more pronounced and the magnetic scattering dominates the intensity and affects the peak position. Radial and angular averaging from experimental data are given to show the details of magnetic structures.      

Magnetization in permalloy thin films

Thin films of permalloy (Ni₈₀Fe₂₀) were prepared using an Ar+N₂ mixture with magnetron sputtering technique at ambient temperature. The film prepared with only Ar gas shows reflections corresponding to the permalloy phase in X-ray diffraction (XRD) pattern. The addition of nitrogen during sputtering results in broadening of the peaks in XRD pattern, which finally leads to an amorphous phase. The M-H loop for the sample prepared with only Ar gas is matching well with the values obtained for the permalloy. For the samples prepared with increased nitrogen partial pressure the magnetic moment decreased rapidly and the values of coercivity increased. The polarized neutron reflectivity measurements (PNR) were performed in the sample prepared with only Ar gas and with nitrogen partial pressure of 5 and 10%. It was found that the spin-up and spin-down reflectivities show exactly similar reflectivity for the sample prepared with Ar gas alone, while PNR measurements on 5 and 10% sample show splitting in the spin-up and spin-down reflectivity.