Systematics of charge distribution studies in low-energy fission of actinides

Charge distribution studies were carried out in the thermal neutron-induced fission of ²²⁹Th, ²⁴¹Pu and ²⁴⁵Cm as well as in the spontaneous fission of ²⁵²Cf. The width parameter (σ_z/σ_A), the most probable charge/mass (Z_p/A_p) and the charge polarization (ΔZ) as a function of fragment mass were deduced. The slope of charge polarization as a function of fragment mass [δ(ΔZ)/δA′], average charge dispersion parameter (〈σ_z〉) and proton odd-even effect (δ_p) were also obtained for these fissioning systems. These data along with the literature data for even-Z fissioning systems such as ²³³Th¹, ²³³U¹, ²³⁴U¹, ²³⁶U¹, ²³⁹U¹, ²³⁹Pu¹, ²⁴⁰Pu¹ and ²⁵⁰Cf¹ are discussed in terms of nuclear-structure effects and dynamics of descent from saddle point to the point of neck formation and from the formation of the neck to the scission point.     

The electronic structure of the low lying sextet and quartet states of CrF and CrCl

The electronic structure of CrF and CrCl in X ⁶Σ⁺, ⁶Π, ⁶Δ, A⁶Σ⁺, ⁴Σ⁺, ⁴Π, and ⁴Δ states that correlate with the low lying ⁶S, ⁶D, and ⁴D states of Cr⁺ have been studied, using large atomic natural orbital (ANO) basis sets and a variety of ab initio methods, including multi-reference configuration interaction (MRCI) and coupled cluster with perturbative triples (RCCSD(T)). We include scalar relativistic effects perturbatively and also explore the consequence of correlating the 3s and 3p electrons on the transition metal. We report T _e, R _e,ω_e, as well as dipole moments, bond energies, and charge distributions and compare with the available experimental data as well as previous theoretical results.     

Multireference configuration interaction study of ground and low-lying excited states of the AlC radical

This work explored the spectroscopic parameters and vibrational properties of the 21 Λ–S and 42 Ω states of the AlC radical. The PECs were calculated with the CASSCF method, which was followed by the icMRCI+Q approach. The A⁴Π, a²Π, 5²Π, 2²Δ, and 1²Φ states as well as the first well of B⁴Σ^? state were inverted with the spin–orbit coupling (SOC) effect included; the 1⁴Δ, 1⁴Σ⁺, and 2²Σ^? states as well as the second wells of the B⁴Σ^?, 2²Σ⁺, 3²Σ⁺, 4²Π and 5²Π states were weakly bound, which well depths were less than 650 cm^?1; the B⁴Σ^?, 2²Σ⁺, 3²Σ⁺, 4²Π, 5²Π, and 2²Δ states had double wells and the second wells of these states except for B⁴Σ^? had only several vibrational states; the avoided crossings existed between the 2²Σ⁺ and 3²Σ⁺ states, the 3²Σ⁺ and 4²Σ⁺ states, the B⁴Σ^? and 3⁴Σ^? states, the 2²Δ and 3²Δ states, the 4²Π and 5²Π states, the 5²Π and 6²Π states, as well as the 2⁴Π and 3⁴Π states. The extrapolation scheme, core–valence correlation and scalar relativistic corrections were included. The spectroscopic parameters and vibrational properties were determined. The TDM curves between two different Λ–S states were calculated and Franck–Condon factors of some transitions were evaluated. The SOC effect on the spectroscopic and vibrational properties was evaluated.     

Investigation of cosmogenic radionuclide carriers in the atmosphere

Speciation of ⁷Be, ³²P, ³³P, ³⁵S and stable S carriers and their changes in the atmosphere were investigated. It has been determined that aerosol-carriers of ⁷Be, ³²P and ³³P radionuclides can have different properties, and after several days their transformation was observed. The amount of water-soluble carriers in aerosol samples differed widely (from 11 to 95%). The dependence of radionuclide carrier solubility on pH was obtained for ⁷Be, ³²P and ³³P. It has been found that ⁷Be carriers can be soluble compounds such as mixed chlorides, sulphates and nitrates as well as insoluble carbonates and insoluble hydrous Fe(III) oxides. High percentage of ³²P and ³³P was found in exchangeable fraction. The ³⁵S carriers were found to be more soluble than those of ⁷Be, ³²P and ³³P and exhibited a lower or the same solubility as stable sulphur.     

Electrical conditioning of diamond-like carbon films for the formation of coated field emission cathodes

Diamond-like carbon (DLC) films deposited on different substrates by plasma enhanced chemical vapour deposition were investigated. Bonding states and film quality were characterized by FT-IR spectroscopy. The influence of the power of plasma and the deposition time on the sp²/sp³ ratio as well as the concentration of CH_n bonds was studied. The influence of sp²/sp³ ratio on the formation process of conducting channels in diamond-like carbon films as a result of electrical breakdown was determined. Reproducible increase of diamond-like carbon film conductivity, with initial sp²/sp³ ratio larger than 0.16, was observed after electrical breakdown.     

The competition between different degrees of freedom in the structure of the quintet states of negative parity of some even-even Sn isotopes

Levels 2⁺, 3⁻, 1⁻, 2⁻, 3⁻¹, 5⁻ are interpreted as eigenvalues of a boson expanded Hamiltonian containing a shell model term, pairing, and quadrupole-quadrupole and octupole-octupole interaction. The expansion is performed in terms of standard RPA noncollective phonons and the so-called correlated phonons which are related to the RPA collective phonons by a canonical transformation whose parameters are determined so that the energy of the ground state is minimum. The noncollective degrees of freedom are included via an effective Hamiltonian depending on energy. Formalism is applied to ¹¹⁴Sn, ¹¹⁶Sn, and ¹¹⁸Sn. Also, transition probabilities and quadrupole moments are calculated. Results are compared with experimental data as well as with the previous theoretical calculations.     

Isotope-selective trapping of rare calcium ions using high-power incoherent light sources for the second step of photo-ionization

Rare calcium isotope ⁴⁸Ca⁺ (0.187%) has been selectively loaded in a linear Paul trap using two ultraviolet light emitting diodes with the output power of 85 mW for the second excitation in a two-step photo-ionization process. Isotope selectivity has been achieved by utilizing the isotope shifts for the 4s^{2 1} S ₀–4s4p¹ P ₁ transition of neutral calcium atom. Sympathetic cooling of ⁴⁸Ca⁺ ions has been demonstrated using ⁴⁰Ca⁺ ions as refrigerant ions. Purification of rare isotope ⁴²Ca⁺ ions (0.647%) from a mixture of ⁴⁰Ca⁺ (96.9%) and ⁴²Ca⁺ ions has been performed by adjusting the detuning of the cooling laser frequency, which overcomes the imperfect selectivity for some rare isotopes having close resonance frequencies to that of ⁴⁰Ca in the 4s^{2 1} S ₀–4s4p¹ P ₁ transition. The methods can be applied to ⁴³Ca⁺ ion (0.135%) that has been considered as one of the attractive candidates for quantum information processing as well as for an optical frequency standard. PACS 32.80.Fb; 32.80.Pj; 32.80.Rm     

Computer simulation of high-energy proton-nucleus fragmentation cross-section

A computer simulation code is designed to imitate the mass yield fragmentation cross-section as a result of high energy P-N interaction, as well as other effective distributions influencing it. The Monte-Carlo fragmentation is discussed in the framework of an equilibrium macrocanonical statistical model. The code is used to investigate the mass yield cross-section of U²³⁸ as well as the Coulomb potential distributions of U²³⁸, Au¹⁹⁰, Ta¹⁸¹, Xe¹²⁷, Cu⁶⁴ nuclei. The comparison of predicted yield cross-section with experimental measurements exhibited tolerable agreement, furthermore, the binary fisson cross-section is formulated in terms of target and fragment mass numbers as well as the expectation values of Coulomb potential are formulated in terms of target and fragment atomic numbers,Z _t andZ _f, respectively.     

Photodisintegration of 11Li and Radiation Capture of Two Neutrons by 9Li

Photodisintegration of ¹¹Li and radiation capture of two neutrons by ⁹Li are studied in the frame of algebraic version of resonating group method and in asymptotic potential approximation. The behavior of the scattering phases shows on the existence of J ^π=3/2⁺ and J ^π=5/2⁺ resonances in continuum above the three-body decay threshold ¹¹Li→⁹Li+n + n. The cross-section of photodisintegration as well as the cross-section of radiation capture have been received. Energetic dependence of the first one is in good correspondence with the experimental data.     

Characterization of clay and pillared clay catalysts

High-resolution solid-state NMR (²⁹Si and ²⁷Al), as well as Fourier transform IR and X-ray diffraction are shown to be of considerable value in characterizing pillared clays and various un-pillared clays consisting of one or other of the following interlamellar ions: Li⁺, Na⁺, Cs⁺, NH⁺₄ and Al³⁺. The catalytic activities of clays prior to and after pillaring are briefly discussed.     

Annealing behaviour of iron implanted zirconia

A zirconia film was implanted at room temperature with 100 keV⁵⁷Fe⁺ to a fluence of 8×10¹⁶ ions/cm². The analysis of the Conversion Electron Mössbauer spectra shows that iron is distributed among different charge states: Fe⁰ (in a form of small and large metallic iron aggregates) Fe²⁺ and Fe⁴⁺. The evolution of the iron depth profile deduced from Rutherford backscattering measurements as well as the change in the charge states of iron as a function of annealing under argon atmosphere are presented.     

Dose assessment of bremsstrahlung induced by beta-emitting radioisotopes of uranium-238 series and lead in human tissues

In the natural uranium-238 decay series, pure beta isotopes such as ²³⁴Th, ²³⁴Pa, ²¹⁴Pb, ²¹⁴Bi, ²¹⁰Pb and ²¹⁰Bi are released. The few lead isotopes such as ²¹¹Pb, ²¹²Pb, ²¹³Pb and ²¹⁵Pb are good beta emitters. In certain nuclear reactions of reactor these isotopes are released. These beta isotopes have maximum beta energies, which induce the bremsstrahlung radiation. The bremsstrahlung component of these beta isotopes has been traditionally ignored in dosimetry calculations. The shapes of bremsstrahlung spectra are a basic ingredient in the understanding and quantification of beta-ray dosimetry. The bremsstrahlung spectra produced by these high-energy isotopes such as ²³⁴Th, ²³⁴Pa, ²¹⁴Pb, ²¹⁴Bi, ²¹⁰Pb, ²¹⁰Bi, ²¹¹Pb, ²¹²Pb, ²¹³Pb and ²¹⁵Pb in bone, muscle and teeth are studied, and the computed spectral distributions are presented. The spectral shapes are primarily responsible for variations in the shapes of depth–dose distributions. They are intended to provide a quick and convenient reference for spectral shapes and to give an indication of the wide variation in these shapes. The evaluated beta bremsstrahlung dose as a function distance for the studied nuclides is also presented. The efficiency, intensity and dose rate of bremsstrahlung induced by beta isotopes of natural uranium-238 decay series and beta-emitting lead isotopes in human tissues such as brain, breast, heart, kidney, liver, muscle, pancreas and bone have also been studied in the present investigation. The values of bremsstrahlung dosimetric parameters are low for pancreas, but they are high for bone. For all studied tissues these parameters are high for ²³⁴Pa, but low for ²¹⁰Pb.     

Fluorescence Sensors for Selective Detection of Hg2+ Ion Using a Water-Soluble Poly(vinyl alcohol) Bearing Rhodamine B Moieties

The novel water-soluble poly(vinyl alcohol) with pendant rhodamine B moiety as colorimetric and fluorescene chemosensor for Hg²⁺ ions was prepared by grafting poly(vinyl alcohol) using rhodamine B hydrazide and hexamethylenediisocyanate as fluorescent dye and coupling agent, respectively. Because of their good water-solubility, the polymers binding rhodamine B can be used as chemosensors in aqueous media. With the addition of Hg²⁺ ions into the aqueous solution, visual color changes and fluorescence enhancements were detected. In addition, we also noticed that other metal ions such as Ag⁺, Cd²⁺, Co²⁺, Cu²⁺, K⁺, Mg²⁺, Ba²⁺, Fe²⁺, Ni²⁺, Pb²⁺, Cr³⁺, Fe³⁺ and Zn²⁺ cannot induce obvious changes to the fluorescence spectra of the polymer chemosensors. The combination of water solubility and positive fluorescence response as well as color change are hence particularly promising for the practical utility of the sensors.     

Partial photoionization cross-sections and branching ratios of CO from 750 to 304 Å

The absolute values of the partial photoionization cross-sections and branching ratios for producing carbon monoxide ions in their X²Σ⁺, A²Π, B²Σ⁺ and ²Σ⁺(σ2s) states have been obtained as a function of wavelength from the A²Π ionization threshold to 304 Å. Results have been obtained within autoionizing resonances as well as within the photoionization continuum.     

Theoretical study of fusion reactions 32S + 94,96Zr and 40Ca + 94,96Zr and quadrupole deformation of 94Zr

The dynamic coupling effects on fusion cross sections for reactions~(32)S + ~(94,96)Zr and ~(40)Ca + ~(94,96)Zr are studied with the universal fusion function formalism and an empirical coupled channel(ECC) model. An examination of the reduced fusion functions shows that the total effect of couplings to inelastic excitations and neutron transfer channels on fusion in ~(32)S +~(94)Zr(~(40)Ca +~(94)Zr) is almost the same as that in ~(32)S +~(96)Zr(~(40)Ca +~(96)Zr). The enhancements of the fusion cross section at sub-barrier energies due to inelastic channel coupling and neutron transfer channel coupling are evaluated separately by using the ECC model. The results show that effect of couplings to inelastic excitations channels in the reactions with94 Zr as target should be similar as that in the reactions with ~(96) Zr as target. This implies that the quadrupole deformation parameters β_2of ~(94)Zr and~(96) Zr should be similar to each other.However, β_2 's predicted from the finite-range droplet model, which are used in the ECC model, are quite different. Experiments on~(48) Ca +~(94)Zr or~(36) S +~(94)Zr are suggested to solve the puzzling issue concerning β_2for~(94)Zr.     

Assessment of the nature of interactions of cations with cycloheptatriene derivatives using change in the aromaticity: Comparison with electron density and NBO results

ABSTRACT

Interactions of cycloheptatriene derivatives, C₇H₆X, (X?=?NH, PH, AsH, O, S, Se) with the cations H⁺, CH₃⁺, Cu⁺, Al⁺, Li⁺, Na⁺, and K⁺ are studied using B3LYP functional and 6-311++G(d,p) basis set. The calculated gas-phase cation affinities (CA) and cation basicities (CB) for all molecules decrease as H⁺ > CH₃⁺ > Cu⁺ > Al⁺ > Li⁺ > Na⁺ > K⁺. We used the induced aromaticity in the 7-membered ring of C₇H₆X upon interaction with the cations, M⁺, as a measure of C₇H₆X/M⁺ interaction. Nucleus-independent chemical shift (NICS) and harmonic oscillator model of aromaticity (HOMA) were used as two indices of aromaticity. The highest and lowest induced aromaticities were observed for interactions of H⁺ and K⁺, respectively. Also, the aromaticity induced by interaction with a cation in C₇H₆AsH and C₇H₆PH was larger than that in C₇H₆NH and C₇H₆O. Hence, the aromaticity was considered as a measure of covalency for the C₇H₆X/M⁺ interactions showing a rational dependence on both the molecule and cation. The nature of the interactions was also assessed using electron density, charge distribution analysis and NBO calculations. The results of the aromaticity indices, NICS and HOMA, were compared with the electron density and NBO results.     

Investigation of theβ +-decay of105,106,109In and of100,102Ag

Isomers in the nuclei¹⁰⁰Ag (I=5⁺),¹⁰²Ag (I=5⁺),¹⁰⁵In (I=9/2⁺),¹⁰⁶In (I=6⁺),¹⁰⁸In (I=6⁺) were selectively populated by the reactions⁹⁰Zr(¹⁹F,xnγ),⁹²Mo(¹⁹F, 2pnγ),⁹²Mo(¹²C,pxnγ),⁹⁰Zr(¹⁹F,α3nγ) atE _lab=72 and 66MeV, and their (β ⁺+EC)-decay was studied with an Anticomptonγ-spectrometer. Spins of the beta-decaying isomers are determined. The results obtained for the beta strength functions are discussed as well as new information on the structure of the neutron-deficient even-even daughter nuclei nearZ=50.     

A solid-state NMR study of the formation of molecular sieve SAPO-34

This work examined the formation of a catalytically important microporous material, SAPO-34, in the presence of HF under hydrothermal synthesis conditions. The local environments of P, Al, F and Si atoms in several solid phases obtained at different stages of crystallization were characterized by several solid-state NMR techniques including ³¹P, ²⁷Al, ¹⁹F and ²⁹Si MAS, ²⁷Al triple-quantum MAS, ³¹P{²⁷Al} transfer of populations in double-resonance, ²⁷Al{³¹P} rotational-echo double-resonance (REDOR), ²⁷Al→³¹P heteronuclear correlation spectroscopy, ³¹P{¹⁹F} and ²⁷Al{¹⁹F} REDOR as well as ¹H→³¹P cross polarization. The NMR results provide the new insights into the formation of SAPO-34.     

Stabilization of elements in unusual oxidation states and temperature-reversible dynamics of electron pairs in oxide glasses. EPR-investigation

Binary, three-component and multi-component borate, phosphate, germanate and silicate glasses, as well as barium-aluminophosphate glasses containing oxide of metals of (I–V) B groups, metals of the first transition series from titanium to nickel, niobium, tantalum, molybdenum and tungsten are investigated by EPR and optical spectroscopy at 77 and 300 K. The formation of metal ions in unusual oxidation states, such as Ag⁰, Zn¹⁺, Cd¹⁺, Hg¹⁺, Ga²⁺, Tl²⁺, Ge³⁺, Sn³⁺, Pb³⁺, Sb⁴⁺, Bi⁴⁺, Nb⁴⁺, Ti³⁺, Ni¹⁺, Mo⁵⁺, Cr³⁺, and Cr⁵⁺ was established. They were stabilized in the aforementioned glasses at specific compositions of components for an unlimited time at 300 K. It is shown that the reversible low temperature effect of disproportionation on atoms such as Nb, Ti, V, Mo, and W proves that in glass under ionizing gamma-radiation and temperature the reactions of disproportionation occur together with the reconstruction of conformation, the electron density transfer, the atomic displacement and the change (reversible or not) of a local structure of glass. It is shown that the formation of metal clusters in glass is connected with reaction of disproportionation.