Sorption characteristics of Am(III), Sr(II) and Cs(I) on bentonite and granite

The ability of the back-fill and the host rock materials to take up radioisotopes like ²⁴¹Am, ^85,89Sr and ¹³⁷Cs has been examined as a function of contact time, pH, amount of sorbent, sorbate concentration, and the presence of complementary cations. A batch technique using actual borehole water from the granite formation has been utilized. In general, the uptake of nuclides by bentonite is much higher than that with granite. The sorption order of nuclides on bentonite is Am>Cs>Sr. The presence of complementary cations, Na⁺, K⁺, Ca²⁺ and Mg²⁺ depresses the sorption of Cs and Sr on bentonite. The sorption data have been interpreted in terms of Freundlich and Langmuir isotherm equations. Utilizing the Langmuir isotherm equation, the monolayer capacity, V _m ,and the binding constant, K, have been evaluated. The change in free energy for the sorption of nuclides on bentonite has also been calculated.     

Synthesis,structure, dehydration transformations and ion exchange characteristics of iron-silicate with various Si and Fe contents as mixed oxides

The synthesis of a new series of impregnated metal oxides with different Fe/Si ratios (0.5, 1 and 2) was obtained by the direct precipitation method. Physico-chemical properties and molecular formula of the obtained products were identified with different analytical techniques, such as chemical stability, XRD, IR, elemental and thermal analyses. Thermal kinetic parameters, such as order (n) and activation energy (E_a), of the solid-state phase transformations of the first dehydration process have been studied for the obtained materials from DTA thermograms. The ion exchange applications and the sorption properties of the materials with some radioactive nuclides have been studied, depending on the Fe/Si molar ratios. These investigations indicated that the ion exchange capacities as well as the selectivities of different materials towards the studied nuclides show the order Co²⁺ > Cs⁺ > Na⁺ at a certain pH.     

The Hartree–Fock ground state of atomic two-electron systems and the Wilson–Silverstone 1s orbital

For the Hartree–Fock ground state of atomic two-electron systems, the variational function of Wilson and Silverstone, ?(r) = (a + kr)^?1 exp(-kr) / (4π)^1/2, can be optimized in two complementary ways. For small values of the atomic number Z, all intergrals have been calculated numerically and optimization can be performed accurately. However, as Z increases, loss of significant figures is increasingly detrimental to the optimization process. For sufficiently large values of Z, the integrals may be replaced by asymptotic expansions in terms of (2a)^?. As a result of optimization, the parameters and expectation values can be given as expansions in terms of (32Z)^?1/2. Both methods yield good results for Z ≈ 25, so that the whole range of Z can be treated accurately. The results have been compared with those derived from other analytical two-parameter functions. It is found that ?(r) is indeed the outstanding two-parameter function, at least for small and intermediate values of Z.     

Studies of viscous antagonism,excess molar volume and isentropic compressibility in aqueous mixed solvent systems at different temperatures

Using experimental data for the melting temperature T _m for four Li halides (F to I), it is demonstrated that T _m Z ^1/3 is close to constant, ? (2530 ± 250) K, where Z is the atomic number of the halogen. This formula is not appropriate for what sometimes is considered the simplest halide, LiH, and therefore alternatives are investigated which involve a characteristic electrostatic energy e ²/εs, with s the internuclear separation and ε the static dielectric constant.     

An iterative method for obtaining accurate atomic inner shell binding energies

A new method based on an iterative procedure for obtaining accurate atomic inner shell binding energies is described. The method makes use of the doubly modi-fied Moseley plot as the starting point. As an illustration accurate binding energies for the M ₁ shell in the atomic number range 57 ≤ Z ≤ 71 have been obtained. This has also resulted in the removal of the anomaly in the M ₁ binding energy of Z = 68. Our calculations point to a need for a fresh look at the theoretical calculations of inner shell binding energies for Z = 57 to 71 in which some unsuspected effects appear to occur when the 4f shell is opened, half filled and closed.     

Expansion coefficients and moments of electron momentum densities for singly charged ions

Numerical Hartree–Fock calculations of the first three coefficients of the MacLaurin expansion and the leading coefficient of the large-p asymptotic expansion of the electron momentum densities Π(p) are reported for 54 singly charged atomic cations from He⁺ (atomic number Z = 2) to Cs⁺ (Z = 55) and 43 anions from H⁻ (Z = 1) to I⁻ (Z = 53) in their experimental ground states. We also report all the finite moments <p ^k > (−2≤k≤+4) of the momentum densities Π(p) for the above-mentioned 97 ionic species. The results are compared with the previous ones for neutral atoms [Koga and Thakkar (1996) J Phys B 29: 2973], and the dependence of the expansion coefficients and moments on nuclear charge is discussed among isoelectronic species. Received: 20 November 1998 / Accepted: 15 January 1999 / Published online: 7 June 1999     

Boron-Made N2: Realization of a B≡B Triple Bond in the B2Al3− Cluster

Until now, all B≡B triple bonds have been achieved by adopting two ligands in the L→B≡B←L manner. Herein, we report an alternative route of designing the B≡B bonds based on the assumption that by acquiring two extra electrons, an element with the atomic number Z can have properties similar to those of the element with the atomic number Z+2. Specifically, we show that due to the electron donation from Al to B, the negatively charged B≡B kernel in the B₂Al₃⁻ cluster mimics a triple N≡N bond. Comprehensive computational searches reveal that the global minimum structure of B₂Al₃⁻ exhibits a direct B–B distance of 1.553 Å, and its calculated electron vertical detachment energies are in excellent agreement with the corresponding values of the experimental photoelectron spectrum. Chemical bonding analysis revealed one σ and two π bonds between the two B atoms, thus confirming a classical textbook B≡B triple bond, similar to that of N₂.     

Photochemical reactions. 137th communication. Preparation and photolysis of (E/Z)-7-methyl-β-ionone

The title compounds (E/Z)- 7 were prepared in 66% overall yield by reaction of β-ionone ((E)-( 1 ) with lithium dimethylcuprate, trapping of the intermediate enolate with benzeneselenenyl bromide and oxidation with H₂O₂. Analogously, (E/Z)-7-methyl-α-inone ((E/Z)- 12 ) was obtained in 65% yield from α-ionone ((E)- 11 ). ¹n, π^*- Excitation (λ > 347 nm, pentane) of (E)-7 causes rapid (E/Z)-isomerization and subsequent reaction of (Z)- 7 to 15 (66%). The formation of 15 is explained by twisting of the dienone chromophore due to repulsive interaction of the 7-CH₃-group with the CH₃-groups of the cyclohexene ring. On the other hand, irradiation λ > 347 nm, Et₂O) of (E)- 7 in the presence of acid leads to (Z)- 7 (5%) and to the novel compound 16 (88%).     

Electron affinities of the lanthanides

The electron affinities (EA's) of the lanthanides (La through Tm) have been determined from the expression EA = IP₁ ? C)r^?1)_n1, where IP₁ is the first ionization potential and (r^?1)_n1 is the relativistic radial integral of an electron in the unfilled shell, the constant C includes the quantum numbers n, 1 of the partly filled shells and the atomic number Z of each element. The EA's vary from +0.5 eV (La) to –0.2eV (Tm) which is consistent with other semi-empirical estimates for certain lanthanide elements.     

Comment on a perturbation treatment of the ground state of two-electron atoms using the coordinates r< and r>

A perturbation variation treatment of two-electron atoms using exp (–αr_< – βr_>) as the zeroth order wave function is presented. The parameters α and β are variationally determined and the results are compared with the “physical” choice α = Z, β = Z – 1, and with Z^?1 theory. The energy is given through fifth order in the perturbation.     

Generalized exponential functions applied to atomic calculations

The use of a generalized exponential function r ^v?1 exp(?ζr ^μ ) as a radial basis function in atomic calculations is studied with our special interest in the variationally optimum value of the parameter μ, since special cases of μ = 1 and μ = 2 correspond respectively to the radial parts of commonly-used Slater-type and Gaussian-type functions. Roothaan-Hartree-Fock calculations are performed for ground-state neutral atoms with atomic number Z = 2–54, singly-charged cations with Z = 3–55, and anions with Z = 1–53 within the single-zeta (or minimal basis) framework. For all the species examined, the optimtum μ values are found to be smaller than unity and increase towards unity as the atomic number increases. The present results support the use of Slater-type functions when μ is restricted to be an integer, but suggest from the variational point of view that even the exponential decay of Slater-type functions is too “strong” within the single-zeta approximation.     

Thin-layer chromatographic behavior of rare earths on silica gel with aqueous alkaline earth metal nitrate solutions as mobile phases

The TLC behavior of all the rare earths except Pm has been surveyed on silica gel (pH 7.0) pretreated with 0.1 mol L^–1 tris(hydroxymethyl)aminomethane and 0.1 mol L^–1 HCl with aqueous nitrate solutions of alkaline earth metals as mobile phases. The R_F values of the lanthanides varied in a regular and characteristic way accompanied by the tetrad effect with increasing atomic number, and when the mobile phases were changed the R_F values of each metal decreased in the order Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺, as the crystal ionic radii of the alkaline earth metals increased. This adsorption sequence was not observed with alkali metal nitrate and alkali metal chloride mobile phases. A brief discussion concerning the effect on R_F values of the solvent cations and the adsorption mechanism is included; also presented are typical chromatograms for the separation of multi-component mixtures containing adjacent lanthanides. Received: 9 October 2000 / Revised: 20 February 2001 / Accepted: 26 February 2001     

Periodic table of the elements and the Thomas–Fermi atom

How the monotonic trend on which the periodicity of the periodic system is superposed is well described by Thomas–Fermi theory is explained. The mathematical structure of the periodicity is elucidated and explained. Algebraic formulas for the key atomic numbers are derived, e.g., the atomic number at which l electrons first appear is given by Z_f(??) = 4 (∑ n²)+1.     

利用基于Gouy-Chapman模型的离子有效电荷定量表征离子特异性效应

离子特异性效应在固-液界面反应中是普遍存在的. 近期研究指出, 在较低电解质浓度的某些体系中, 离子特异性效应可能并非来源于色散力、经典诱导力、离子半径或水合半径的大小等, 而是界面附近强电场中的离子极化作用. 这种作用可使界面附近的吸附态反号离子被强烈极化(高达经典极化的10⁴倍). 强烈极化的结果将导致离子在界面附近受到的库仑力远远超过离子电荷所能产生的库仑力, 这体现在离子的有效电荷将远大于离子的实际电荷. 因此胶体体系中基于这种强极化的离子有效电荷可以用来定量表征离子特异性效应的强度. 本研究在蒙脱石-胡敏酸混合悬液凝聚过程中发现了Na⁺、K⁺、Ca²⁺、Cu²⁺四种离子的离子特异性效应, 提出了基于激光散射技术测定离子有效电荷的方法, 并成功获得了被强烈极化后的离子有效电荷数值. 实验测得的Na⁺、K⁺、Ca²⁺、Cu²⁺四种离子的有效电荷值分别为: Z_{Na(effective)}=1.46, Z_K(effective)=1.86, Z_{Ca(effective)}=3.92, Z_{Cu(effective)}=6.48.该结果表明: (1) 离子在强电场中的极化将大大提高离子的有效电荷, 从而极大地增强离子所受的库仑作用力;(2) 离子的电子层数越多, 离子极化越强烈, 离子的有效电荷增加越多.     

Reactor neutron activation analysis by using multi-elemental comparators: Problems of nuclear constants of128I,175Yb and several other nuclides

A simple method has been developed for evaluating the neutron spectrum and the temperature by using U, Sb, Cr, Co and Lu as monitors and successfully applied to the routine analysis. For most of nuclides, amounts determined by the method showed reasonable agreements with those added. However, there have been found several nuclides which gave erroneous results beyond the permissible limits. In the case of¹²⁸I, the reason for the deviation was found to lie on the normalization factor of -ray abundances that are in common use. This was confirmed by using I₂ doped polyacethylene which is a material highly resistant to ionizing radiations.⁴⁶Sc,¹⁷⁵Yb and several other rare earth nuclides are discussed as well.     

Sterospecific Syntheses and Spectroscopic Properties of Isomeric 2,4,6,8-Undecatetraenes. New Hydrocarbons from the Marine Brown Alga Giffordia mitchellae. Part IV.

Giffordene (=(2Z,4Z,6E,8Z)-2,4,6,8-undecatetraene; 9f ) and five steroisomers are new C₁₁H₁₆ hydrocarbons from the marine brown alga Giffordia mitchellae. Their synthesis is based on non-stereoselective Wittig reactions of (E)-2-alkenals with appropriate acetylenic phosphoranes and subsequent chromatographic separation of the resulting (E/Z)-pairs. The uniform enynes (>98% purity) are then stereospecifically reduced to (Z)-alkenes with Zn(Cu/Ag) in aq. MeOH at r.t. ¹³C- and ¹ H-NMR data of the new tetraenes are presented. Biosynthetically, giffordene ( 9f ) originates from dodeca-3,6,9-trienoic acid via an unstable (3Z,5Z,8Z)-1,3,5,8,-undecatetraene followed by a thermally allowed antarafacial 1,7-sigmatropic hydrogen shift to the (2Z,4Z,6E,8Z)-isomer 9f .     

Generalized 1/Z expansion for heteronuclear molecules

We have first studied empirical regularities in various series of heteronuclear diatomic molecules between the energy E, the total number of electrons N, the equilibrium distance R_e and Z? = (Z₁Z₂)^1/2 where Z₁e and Z₂e are the nuclear charges in the diatom. In particular, for various alkali halide series, R_e²|E|/N^5/3 is shown to correlate rather simply with Z?R_e³. Some theoretical basis is afforded by generalizing the 1/Z expansion used early by the writers in work on homonuclear diatomics. Finally, when Z₂/Z₁ → ∞, a model is presented which predicts a finite asymptotic bond length and this prediction is confronted with available experimental data for both heteronuclear diatoms and for the polyatomic series CH₄ to SnH₄.     

Rotational relaxation in the Ar—N2 system

The first (Z⁽¹⁾) and second (Z⁽²⁾) approximations to the rotational number of the Ar—N₂ system are compared for a range of temperatures. Although Z⁽¹⁾ and Z⁽²⁾ differ by a significant amount their difference remains nearly constant as a function of temperature. The effects of mass and potential parameter variations on the rotational relaxation time are also studied. When the mass of the incoming atom is decreased Z⁽²⁾ goes through a minimum while Z⁽¹⁾ steadily increases.     

Gamma-spectrometry and residual nuclide analysis of pion irradiated PbWO4 crystals

The electromagnetic calorimeter of the CMS detector at CERN, Geneva will consist of PbWO₄ crystals and be exposed to a hadron flux of 10⁶ cm^-2·s^-1, mostly pions, during its operation. We have used FLUKA and DETRA codes for advance prediction of the activation of the detector. To assess the accuracy of these calculations, a small PbWO₄ crystal was irradiated in a 345 MeV/c pion beam of the PSI to a fluence of 1.6·10¹² cm^-2. The resulting activation was measured using an HPGe-detector after cooling times varying from a few minutes to 14 months. The spectra were analyzed using the SAMPO 90 code for peak search and area determination and the SHAMAN code for radionuclide identification and quantification. The spectra were extremely complex and the first ones measured not useful due to violent peak overlap and pile-up. The number of found peaks in the spectra we analyzed varied between 841 and 128 peaks depending on the cooling time. The corresponding number of nuclides identified per spectrum varied between 116 and 15. The comparisons between the predicted time-development of the nuclide composition by FLUKA/DETRA and the analyzed results show that the activities of nuclides agree excellently for the most important nuclides and very well even for the less abundant ones. The total dose rate in the vicinity of the activated crystals, including its time dependence, is very well reproduced by the FLUKA/DETRA calculations.