Z31 effect on the stopping powers of several metallic elements for 28.8 MeV alpha particles: Deviations of experimental data from theories

Stopping powers of several metallic elements for 28.8 MeV alpha particles have been measured. One fourth of the stopping power for alpha particles is larger than the stopping power for protons of the same velocity. But the differences do not agree with Z³₁ correction theories.     

Z1 and Z2 variations in the stopping powers of Z1=10 to 18 ions deduced from Dsam lifetime measurements

From lifetime measurements of the ²²Ne(3.26 MeV), ¹³P(2.23 MeV) levels and published data, deviations from theory of the stopping powers for Ne and other ions in many materials have been deduced; they correlate strongly with electron densities deduced from positron lifetimes. The data also indicate that Z₁ deviations for s-d shell nuclei are Z₂ dependent.     

On-line Time Differential Perturbed Angular Correlation with Light Probe Nucleus 19F

An on-line time differential perturbed angular correlation technique has been developed with the light probe nucleus ¹⁹F. The first on-line TDPAC measurement was carried out to determine the field gradient in Cd and quadrupole moment of ¹⁹F (0.197 MeV: I ^π = 5/2⁺, T_1/2 = 89 ns). This revised version was published online in September 2006 with corrections to the Cover Date.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH₂)₃]₂HgBr₄ has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH₂)₃]⁺ and distorted tetrahedral [HgBr₄]^2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr₄]^2? ion. In accordance with the crystal structure, two ⁸¹Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH₂)₃]₂HgI₄ yielded four ¹²⁷I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The ¹H NMR T ₁ measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C₃ reorientations of the planar [C(NH₂)₃]⁺ ions gave the activation energies of 29.8 kJ mol^?1 for the bromide, and 30.2 and 40.0 kJ mol^?1 for the iodide.     

Thermonuclear reaction rates from (p,n) reactions

Thermonuclear reaction rates for the temperature range 1≤T ₉≤5 have been extracted from experimentally measured (p, n) cross sections for⁴⁵Sc⁵⁰Ti,⁵¹V,⁵⁴Cr,⁵⁵Mn and⁵⁹Co nuclides below 5 MeV bombarding energy. These reaction rates are important in the build-up of medium and heavy nuclides in the stellar evolution process and nucleosynthesis. To enhance the usefulness of these reaction rates in astrophysical calculations, they have been fitted to an analytic function of temperature, valid throughout the temperature range considered here.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]3Sb2Br9

The crystal structure of [C(NH₂)₃]₃Sb₂Br₉ was determined at 143 K: monoclinic, space group C2/c, Z = 4, a = 15.695 (3), b = 9.039(2), c = 18.364(3) Å, β = 96.94(1)°. The structure consists of two crystallographically independent guanidinium ions and two-dimensional corrugated sheets of (Sb₂Br₉ ^3?) _n , in which SbBr₆ octahedra are connected through three bridging Br atoms each other. One of the cations situates in a cavity of the (Sb₂Br₉ ^3?) _n layer with statistical disorder, while the other situates between the layers without disorder. Three ⁸¹Br NQR resonance lines were assignable to terminal Br atoms, while only one line was found for two inequivalent bridging Br atoms. All the ⁸¹Br NQR resonance lines were subjected to fade-out at low temperatures. The temperature dependence curve of ¹H NMR T ₁ showed well defined two minima, which were explained by postulating the C₃ reorientations of two types of cations with very different activation energies. The DTA (DSC) measurement revealed a phase transition of a first-order type at 444 K.     

Investigation of the passage of 100–1000-MeV/nucleon superheavy ions through homogeneous media

This work is a continuation of the experimental and theoretical investigations of the effect of the Z ₁ ³ correction to the stopping power of ions on the passage of heavy ions ⁴⁰Ar, ⁵⁶Fe, ¹⁹⁷Au, ¹³¹Xe, and ²³⁸U with energies of about 1 GeV/nucleon through a homogeneous medium. The previously observed systematic deviations of the calculations based on the first Born approximation to the scattering of a particle by the atomic electrons in the medium from the experimental values of the total ionization ranges of the nuclei and their stopping powers is confirmed. The discrepancy increases with the atomic number of the projectile nucleus. It is shown that the Z ₁ ³ correction in the form proposed by Jackson and McCarthy eliminates, especially for ions with Z ₁>50, the systematic discrepancy between the computed and experimental values. For the experimental energy range relativistic Mott scattering of a particle by the atomic electrons in the target makes the dominant contribution to the observed Z ₁ ³ effect. Zh. éksp. Teor. Fiz. 115, 404–415 (February 1999)     

Cross-sections for the formation of isomeric pair Ge through (n, 2n), (n, p) and (n, α) reactions measured over 13.73 MeV to 14.77 MeV and calculated from near threshold to 20 MeV neutron energies

The cross-sections for formation of isomeric pair, ⁷⁵Ge^m(σ_m) and ⁷⁵Ge^g(σ_g), through ⁷⁶Ge(n, 2n), ⁷⁵As(n, p) and ⁷⁸Se(n, α) reactions were measured at 13.73 MeV, 14.42 MeV and 14.77 MeV neutrons and also estimated using EMPIRE-II and TALYS codes over neutron energies from near threshold to 20 MeV. For each (n, 2n), (n, p) and (n, α) reaction, the cross-section initially increases with neutron energy, but starts decreasing as the neutron energy exceeds the respective threshold of (n, 3n), (n, pn) and (n, αn) reactions. The higher values of σ_m relative to σ_g reveal that the transitions of the excited ⁷⁵Ge from higher energy levels to metastable state (7⁺/2) are favored as compared to unstable ground state (1⁻/2). The present values of cross sections for formation of ⁷⁵Ge^m,g through (n, 2n) and (n, α) reactions are lower, and that of (n, p) reaction are higher compared to most of the corresponding literature cross-sections.     

Electron paramagnetic resonance parameters and local structure for Gd3+ in KY3F10

The electron paramagnetic resonance parameters, zero-field splittings (ZFSs) b₂⁰, b₄⁰, b₄⁴, b₆⁰, b₆⁴ and the g factors for Gd³⁺ on the tetragonal Y³⁺ site in KY₃F₁₀ are theoretically studied from the superposition model for the ZFSs and the approximation formula for the g factor containing the admixture of the ground ⁸S_7/2 and the excited ⁶L_7/2 (L=P, D, F, G) states via the spin-orbit coupling interactions, respectively. By analysing the above ZFSs, the local structure information for the impurity Gd³⁺ is obtained, i.e., the impurity-ligand bonding angles related to the four-fold (C₄) axis for the impurity Gd³⁺ center are found to be about 0.6° larger than those for the host Y³⁺ site in KY₃F₁₀. The calculated ZFSs based on the above angular distortion as well as the g factors are in reasonable agreement with the observed values. The present studies on the ZFSs and the local structure would be helpful to understand the optical and magnetic properties of this material with Gd dopants.      

中子物质中的3PF2态超流性和微观三体核力效应

利用Brueckner-Hartree-Fock(BHF)和BCS理论方法，计算了纯中子物质中处于³PF₂态的中子对关联能隙，特别是研究并讨论了微观三体核力对³PF₂态中子超流性强弱的影响. 结果表明：三体核力显著地增强了中子物质中³PF₂态中子超流性；当采用BHF单粒子能谱时，三体核力导致相应的对关联能隙峰值由0.22MeV增大到0.50MeV. 关键词： 中子物质 3PF₂超流性')" href="#">³PF₂超流性 三体核力 BCS理论     

New observation of the , 1Δg, and 2Πg states and molecular constants with all Li2, Li2, and LiLi data

This paper reports our new observation of the , 1³Δ_g (v = 2–4), and 2³Π_g (v = 2–8) states of ⁶Li⁷Li by continuous wave perturbation facilitated optical–optical double resonance spectroscopy. Combining our new experimental term values of ⁶Li⁷Li with the available experimental data of ⁶Li₂ and ⁷Li₂, molecular constants and potential energy curves by Rydberg–Klein–Rees and direct-potential-fit techniques have been determined. Born-Oppenheimer breakdown parameters of the Li₂ 1³Δ_g and 2³Π_g states are calculated.     

Analysis of fission excitation functions and the determination of shell effects at the saddle point

A method is proposed to deduce the shell correction energy corresponding to the fission transition state shape of nuclei in the mass region around 200, from an analysis of the first chance fission values of the ratio of fission to neutron widths, (Γ _f /Γ _n )₁. The method is applied to the typical case of the fissioning nucleus²¹²Po, formed by alpha bombardment of²⁰⁸Pb. For the calculation of the neutron width, the level densities of the daughter nucleus after neutron emission were obtained from a numerical calculation starting from shell model single particle energy level scheme. It is shown that with the use of standard Fermi gas expression for the level densities of the fission transition state nucleus in the calculation of the fission width, an apparent energy dependence of the fission barrier height is required to fit the experimental data. This energy dependence, which arises from the excitation energy dependence of shell effects on level densities, can be used to deduce the shell correction energy at the fission transition state point. It is found that in the case of²¹²Po, the energy of the actual transition state point is higher than the energy of the liquid drop model (LDM) saddle point by (3 ± 1) MeV, implying significant positive shell correction energy at the fission transition state. Further, the liquid drop model value of level density parametera is found to be a few per cent smaller for the saddle point shape as compared to its spherical shape.     

Applications of the three points analysis method for obtaining the trap parameters and the separation of thermoluminescence glow curve into its components

Here, we apply a recently developed technique to separate a composite thermoluminescence (TL) glow curve into its individual components and to evaluate the trap parameters of the individual TL glow peaks. These parameters include the order of kinetics b, the activation energy E (eV) and the frequency factor S (s^?1) or the pre-exponential factor S″ (s^?1). Recently, a general equation was developed to estimate the order of kinetics b. The characteristic point of this equation is that any set of three data points in a TL glow curve can yield b. Using this characteristic, an improved procedure was suggested to separate a composite glow curve, which includes several overlapping peaks, into its individual components and to obtain the trap parameters of the individual glow peaks. The method was applied here to analyze and determine the trap parameters of the TL glow curve of the promising TL dosimetric material, double potassium yttrium fluoride (K₂YF₅) doped with praseodymium ions (Pr³⁺), in response to γ-irradiation.     

On the liquid drop model mass formulae and charge radii

An adjustment to 782 ground-state nuclear charge radii for nuclei with N, Z 3 \ge8 leads to R₀ = 1.2257 A^1/3\ensuremath R_0 = 1.2257 A^{1/3} fm and s \sigma = 0.124 fm for the charge radius. Assuming such a Coulomb energy E_c = \frac35 e²Z²/1.2257 A^\frac13\ensuremath E_c = \frac{3}{5} e^2Z^2/1.2257 A^{\frac{1}{3}} , the coefficients of different possible mass formulae derived from the liquid drop model and including the shell and pairing energies have been determined from 2027 masses verifying N, Z 3 \ge8 and a mass uncertainty ￡ \le150 keV. These formulae take into account or do not the diffuseness correction ( Z²/A\ensuremath Z^2/A term), the charge exchange correction term ( Z^4/3/A^1/3\ensuremath Z^{4/3}/A^{1/3} term), the curvature energy, the Wigner terms and different powers of I = (N - Z)/A . The Coulomb diffuseness correction or the charge exchange correction term play the main role to improve the accuracy of the mass formulae. The different fits lead to a surface energy coefficient of around 17-18MeV. A possible more precise formula for the Coulomb radius is R₀ = 1.2332A^1/3 + 2.8961/A^2/3 - 0.18688A^1/3I\ensuremath R_0 = 1.2332A^{1/3} + 2.8961/A^{2/3} - 0.18688A^{1/3}I fm with s \sigma = 0.052 fm.     

具有D4h对称性构型的C2+4分子的Jahn-Teller效应与能级分裂

依据量子理论与配位场理论,利用群论和对称性分析的方法探讨了C²⁺₄分子在具有D_4h对称性构型时,E×(b_1g+b_2g)系统的Jahn-Teller效应中的相关问题.研究了C²⁺₄分子的电子态与声子态的对称性及其活跃声子态,讨论了系统声子间的耦合与CG系数,构建了E×(b_1g+b_{2g 关键词： 2+4分子')" href="#">C²⁺4分子 对称性 能级分裂 Jahn-Teller畸变}     

The collective bands of positive parity states in odd-A (fp) shell nuclei

The low-lying collective bands of positive parity states in (fp) shell nuclei are described in the deformed Hartree-Fock method by projecting states of definite angular momenta from ‘the lowest energy intrinsic states in (sd)⁻¹ (fp) ⁿ⁺¹ configurations. The modified Kuo-Brown effective interaction for (fp) shell and modified surface delta interaction (MSDI) for a hole in (sd) shell with a particle in (fp) shell have been used. The collective bands of states are in general well reproduced by the effective interactions. The excitation energies of the band head states are however off by about one MeV. The calculated magnetic moments of the band headj=3/2⁺ states are in reasonable agreement with experiment. Using effective chargese _p=1.33e ande _n=0.64e we get fairly good agreement forE(2) transitions. The hinderedM(1) transition strengths are reproduced to the correct order however they are slightly higher compared to experiment.     

共沉淀法制备Y2SiO5∶Er3+ ,Yb3+ ,Tm3+及其上转换发光性能研究

采用化学共沉淀法制备了系列Y_1.98-2xYb_2x Er_0.02SiO₅(0.00≤x≤0.15)以及Y_1.736Yb_0.24Er_0.02Tm_0.004SiO₅上转换发光材料,比较了室温下Y_1.98-2xYb_2x Er_0.02 SiO₅ (x=0.00,0.08)样品在400—1600 nm范围内的吸收光谱,测量了所有样品在976 nm OPO激光器激发下的上转换发射光谱,以及Er³⁺离子⁴S_3/2(⁴F_9/2)→⁴I_15/2,Tm³⁺离子¹G₄→³H₆荧光衰减曲线和不同激发功率下的上转换蓝光发射强度,从而分析讨论了Er³⁺,Tm³⁺在Y₂SiO₅中的上转换发光机理.研究结果表明:在1250 ℃相对较低的温度下合成了X2型单斜晶系Y₂SiO₅ ∶Ln³⁺(Ln³⁺=Er³⁺,Yb³⁺,Tm³⁺),Yb³⁺的敏化显著增强了样品在976 nm附近的吸收能力,并大幅度加宽了该处的吸收带.分析上转换发射光谱发现:上转换绿光和红光强度都随着Yb³⁺浓度的增加先增强后减弱,但红光的猝灭浓度较高,归因于Er³⁺→Yb³⁺反向能量传递ETU4和Yb³⁺→Er³⁺正向能量传递ETU3过程的发生;上转换蓝光发射是三光子吸收过程,是通过Yb³⁺,Tm³⁺之间三次声子辅助的能量转移方式实现的. 关键词： 上转换 共沉淀 2SiO₅∶Er³⁺')" href="#">Y₂SiO₅∶Er³⁺ 3+')" href="#">Yb³⁺ 3+')" href="#">Tm³⁺     

High spin states in 63Cu

Excited states of ⁶³Cu were populated via the ⁵²Cr+¹⁰O (65 MeV) reaction using the gamma detector array equipped with charged particle detector array for reaction channel separation. On the basis of γ-γ coincidence relations and angular distribution ratios, a level scheme was constructed up to E _n=7 MeV and J ^π=23/2⁽⁺⁾. The decay scheme deduced was interpreted in terms of shell model calculations, with a restricted basis of the f _5/2, p _3/2, p _1/2, g _9/2 orbitals outside a ⁵⁶ ₂₈Ni core.     

Torsion-rotation far-infrared spectrum of O-18 methanol

High-resolution Fourier transform spectra have been recorded from 15–470 cm^–1 for the far-infrared trosion-rotation band of O-18 methanol in the vibrational ground state. So far, 57 subbands have been assigned in the 15–220 cm^–1 region for a wide range of rotational and torsional states, and their J-independent origins have been determined to an estimated accuracy of ±0.01 cm^–1. The observed origins were found to deviate in many cases by several tenths of a cm^–1 from the values calculated with the previous molecular parameters. Together with 4 known microwave origins, the new data have been fitted to a model torsion-rotation Hamiltonian in order to refine the set ofb-type molecular constants for the ground state. With the new parameter set, the experimental subband origins are reproduced with an rms error of ±0.02 cm^–1, representing a substantial improvement over the earlier situation. The spectroscopic results have also been of great assistance with our assignments of optically-pumped FIR laser emission in CH₃ ¹⁸OH, in providing FIR data for checking the identification of the IR-pump/FIR-laser transition systems through combination loop relations.