Rotational bands in 169Re

Based on the systematic investigation of the data available for nuclei with A≥ 40, a Z ^1/3-dependence for the nuclear charge radii is shown to be superior to the generally accepted A ^1/3 law. A delicate scattering of data around R _c/Z ^1/3 is inferred as owing to the isospin effect and a linear dependence of R _c/Z ^1/3 on N/Z (or (N - Z)/2) is found. This inference is well supported by the microscopic Relativistic Continuum Hartree-Bogoliubov (RCHB) calculation conducted for the proton magic Ca, Ni, Zr, Sn and Pb isotopes including the exotic nuclei close to the neutron drip line. With the linear isospin dependence provided by the data and RCHB theory, a new isospin-dependent Z ^1/3 formula for the nuclear charge radii is proposed. Received: 23 September 2001 / Accepted: 21 January 2002     

有机薄膜晶体管中接触效应的研究

研究了接触效应对有机薄膜晶体管性能的影响.首先在n型重掺杂Si片上制备了以M_OO₃修饰的Al电极为源漏电极的Pentacene基OTFTs(organic thin film transistors),器件场效应迁移率μ_ef达到0.42 cm²/V ·s,阈值电压V_T为-9.16 V,开关比4.7×10³.通过中间探针法,对器件电势分布做了定性判断 关键词： 有机薄膜晶体管 场效应迁移率 接触效应 电荷漂移     

Atomic orbitals with angularly dependent Z eff to be used in molecular orbitals calculations

A new type of atomic orbital is proposed for use in molecular problems of quantum mechanics. This orbital is formally similar to Slater's orbitals but is characterized by an effective nuclear charge Z _eff which is an explicit function of the angles ? and φ. The fundamental state of the molecule H₂ ⁺ is studied using such an orbital.     

Effect of the nuclear charge of a fast structural ion on its internal effective stopping in collisions with atoms

The energy losses of fast structural ions in collisions with atoms have been considered in the eikonal approximation. The structural ions are ions consisting of a nucleus and a certain number of electrons bound to it. The effect of nuclear charge Z of the ion on its effective deceleration κ^(p) (energy losses associated with excitation of only intrinsic ion shells) has been analyzed. It is shown that the allowance for the interaction of an atom with the ion nucleus for Z _a Z/v > 1, where Z _a is the charge of the atomic nucleus and v is the velocity of collisions in atomic units, considerably affects the value of κ^(p), which generally necessitates taking into account nonperturbatively the effect of both charges Z _a and Z on κ^(p).     

Scott Correction for Large Atoms and Molecules in a Self-Generated Magnetic Field

We consider a large neutral molecule with total nuclear charge Z in non-relativistic quantum mechanics with a self-generated classical electromagnetic field. To ensure stability, we assume that Z α ² ≤ κ ₀ for a sufficiently small κ ₀, where α denotes the fine structure constant. We show that, in the simultaneous limit Z → ∞, α → 0 such that κ = Z α ² is fixed, the ground state energy of the system is given by a two term expansion c ₁ Z ^7/3 + c ₂(κ) Z ² + o(Z ²). The leading term is given by the non-magnetic Thomas-Fermi theory. Our result shows that the magnetic field affects only the second (so-called Scott) term in the expansion.     

Finite size scaling for critical parameters of simple diatomic molecules

We use the finite size scaling method to study the critical points, points of non-analyticity, of the ground state energy as a function of the coupling parameters in the Hamiltonian. In this approach, the finite size corresponds to the number of elements in a complete basis set used to expand the exact eigenfunction of a given molecular Hamiltonian. To illustrate this approach, we give detailed calculations for systems of one electron and two nuclear centres, Z ⁺ e ^?Z⁺. Within the Born-Oppenheimer approximation, there is no critical point, but without the approximation the system exhibits a critical point at Z = Z_c = 1.228279 when the nuclear charge, Z, varies. We show also that the dissociation occurs in a first-order phase transition and calculate the various related critical exponents. The possibility of generalizing this approach to larger molecular systems using Gaussian basis sets is discussed.     

Preparation, Luminescence Properties, and Application of Scintillators Based on Lu3Al5O12:Ce Single‐Crystal Films

The possibility of obtaining scintillators with a high effective atomic number of the element Z _ef based on Lu₃Al₅O₁₂:Ce³⁺ singlecrystal films (SCF) on doping with La³⁺ and Sc³⁺ ions on Y₃Al₅O₁₂ substrates has been investigated. It is established that the SCF of (LuLaY)₃Al₅O₁₂:Ce³⁺ (Z _ef = 58.9 and = 6.67 g/cm²) does not rank below those of Y₃Al₅O₁₂:Ce³⁺ (Z _ef = 29 and = 4.52 g/cm²) in the conversion efficiency of radiation at the band with _max = 515 nm. This allows their use as screens of xray images with a space resolution of 0.75–1.00 m. It is suggested that in the SCF of Lu₃Al₅O₁₂ the isoelectronic impurities of lanthanum and scandium form radiative recombination centers of the type La_Lu, Sc_Lu, and ScAl as well as the centers Lu as a consequence of the effect of replacement of some Lu³⁺ ions by the La³⁺ ions to octanodes of the garnet lattice. The low efficiency of Ce³⁺ radiation in the SCF of (LuSc)₃(AlSc)₅O₁₂:Ce is explained by substantial losses due to excitation of the recombination luminescence in the UV region of the centers formed by the isoelectronic impurities of scandium and to the possible existence of the channel of energy excitation dissipation related to the transitions between extrema of the allowed energy bands and activator levels.     

Microscopic calculations of ferroelectric instability in perovskite crystals

First-principles calculations are performed relating to the stability of a series of perovskite crystals with respect to transition to the ferroelectric and the antiferroelectric state. The calculations employ the generalized Gordon-Kim method, in which the total charge density of an ionic crystal is represented as a superposition of the densities of the individual ions. In the spirit of the nonequilibrium thermodynamics of Leontovich the charge density of an individual ion is calculated in the presence of external auxiliary fields which deform this density. Multipole deformations up to quadrupole are taken into account. The actual magnitude of the deformation is found by minimizing the total energy of the crystal in the Thomas-Fermi-Dirac approximation. The calculated values of the ion shifts in the ferroelectric phase for BaTiO₃, and also the electron contribution to the dielectric constant ε _∞ and the dynamic Born effective charges Z ^eff are found to be in good agreement with the experimental data. The proposed method allows one to obtain an analytical expression for ε _∞, Z ^eff, and the dynamic vibration matrix. It is shown that these expressions formally coincide with the expressions arising in the phenomenological models of the polarized and deformed ion. Analysis of the expressions obtained confirms the validity of the classical theory of ferroelectrics of displacement type for perovskite crystals. Zh. éksp. Teor. Fiz. 114, 333–358 (July 1998)     

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.     

Scaling of cross-sections for asymmetric (e, 3e) process on helium-like ions by fast electrons

An approximate simple scaling law is obtained for asymmetric (e, 3e) process on helium-like ions for double ionization by fast electrons. It is based on the equation (Z ^′3π) exp[-Z(r₁ + r₂)],Z′ = Z – (5/16) for ground state wave function of helium-like ions and Z^′2 scaling of energies. The scaling law is found to work very well if the lower energy electron is ejected along the momentum transfer direction and the other one is ejected in the opposite direction. It also works quite well if this electron is ejected within about 90° of the momentum transfer direction with the other electron going in the opposite direction. The scaling law becomes increasingly accurate as the target nuclear charge and the energy increase.     

Effect of density on the equilibrium charge distribution of carbon and oxygen ions

Theoretical estimation of the equilibrium charge distribution of carbon and oxygen ions passed through a matter is obtained. The coefficient considering the effect of density on the charge distribution of these ions is calculated for an amorphous medium consisting of atoms with the nuclear charge Z _t (Z _t ≤ 54). An oscillating dependence of the average ion charge on the nuclear charge of the target atom is obtained which cannot be described by empirical relations.     

X ray spectroscopic intercomparison between hydrogenic ions of different Z as a method for determining Lamb shifts

Novel methods for determining the 1s Lamb shift of hydrogenic ions are outlined. In one method the energy of a 2–1 transition in the hydrogenic ion of nuclear charge Z is compared to a 4–2 transition in the hydrogenic ion of charge 2Z. A second method exploits close coincidences between Lyman series transitions in ions of similar Z. This revised version was published online in August 2006 with corrections to the Cover Date.     

Asymptotics of the cross section for the electron loss by atoms and ions in light media

The dependence of the cross section of electron loss on the nuclear charge Z of a bombarding ion and on the nuclear charge Z _t of a target atom for fast collisions is studied theoretically using the plane-wave Born approximation and the sum rule. The results of calculations show that the cross section of electron loss for fast collisions increases monotonically as Z and Z _t increase, which can be used to interpolate cross sections for the processes for which there are no experimental data.     

Polymer–ion–clay interaction based model for ion conduction in intercalation-type polymer nanocomposite

A series of polymer nanocomposite films based on intercalation of (PAN)₈LiCF₃SO₃ into the nanometric clay channels of an organomodified clay has been prepared using the standard solution-casting technique. The role of organoclay concentration on polymer–ion interaction, ion–ion interaction, and ion–clay interaction in clay-based nanocomposite films has been analyzed using Fourier transform infrared (FTIR) analysis. Substantial ion dissociation is observed even at a very low clay loading (1–2 wt.%) in the nanocomposites. FTIR results suggest the presence of both uncoordinated CF₃SO₃ ⁻ (free-anions) and ion pairs in the nanocomposite evidenced by changes in CF₃SO₃ ⁻ symmetry from C3ν to Cs and marked asymmetry in the profile of degenerate δ_d(CF₃ ⁻) mode. The experimental results suggest a direct correlation of clay-assisted ion dissociation process with variation in conductivity (σ _dc) and glass transition temperature (T _g) as a function of clay concentration. A model has been proposed to explain the observed correlation on the basis of polymer–ion–clay interaction. The proposed scheme of ion transport mechanism appears to be consistent with the experimental observation.     

Investigation of cross sections for the formation and destruction of negative boron ions

The electron loss and electron capture cross sections σ _i,i+m and σ _i,i−m for boron ions and atoms traveling at the velocities V=1.19 and 1.83 a.u. in H₂, He, N₂, Ne, Ar, and Xe are measured. The known experimental data on these cross sections at velocities near the cross-section maximum are analyzed. It is found that the electron loss cross sections can be described by a formula which was previously derived in the free-collision approximation and takes into account features of both the ions and the ambient atoms. As the nuclear charge Z _t of the ambient atoms increases, the cross sections vary nonmonotonically, increasing on average as Zt _t ^1/2 . A formula based on the model of independent electrons is proposed for electron capture by ions with small values of the charge i. It describes the dependence of the electron capture cross section σ _i,i−1 on the mean binding energy of an electron in an ion with the charge i−1. The total electron capture cross section σ _i,i−1 is proportional to the number of vacancies in the unfilled electron shell nearest the nucleus. The cross sections 0σ _i,i−1 exhibit substantially nonmonotonic variation with Z _t, increasing on average as Z _t ^1/3 . Zh. éksp. Teor. Fiz. 116, 1539–1550 (November 1999)     

Charge distribution studies in the fast-neutron-induced fission of <Superscript>232</Superscript>Th, <Superscript>238</Superscript>U, <Superscript>240</Superscript>Pu and <Superscript>244</Superscript>Cm

Charge distribution studies for heavy-mass fission products were carried out in the fast-neutron-induced fission of ²³²Th, ²³⁸U, ²⁴⁰Pu and ²⁴⁴Cm using radiochemical and gamma-ray spectrometric techniques. The width parameter( σ_Z/σ_A), the most probable charge/mass ( Z _P/A _P), the charge polarization (ΔZ) and the slope of charge polarization [ δ(ΔZ)/δA ^′] as a function of the fragment mass (A ^′) were deduced. The average charge dispersion parameter ( 〈σ_Z〉) and proton odd-even effect ( δ_p) were also obtained for these fissioning systems. The 〈σ_Z〉 and δ_p values in the fissioning systems ²⁴¹Pu ^* and ²⁴⁵Cm ^* were determined for the first time. The δ(ΔZ)/δA ^′ value is also determined for the first time in the fissioning systems ²³⁹U ^* , ²⁴¹Pu ^* and ²⁴⁵Cm ^* . These data along with the literature data for even-Z fissioning systems such as ²³⁰Th ^* , ²³²Th ^* , ²³³U ^* , ²³⁴U ^* , ²³⁶U ^* , ²³⁸U ^* , ²³⁹Pu ^* , ²⁴⁰Pu*, ²⁴²Pu ^* , ²⁴⁶Cm ^* , ²⁵⁰Cf ^* and ²⁵²Cf(SF) are discussed in terms of nuclear structure effect and dynamics of descent from the saddle to the scission point. The role of the excitation energy in low-energy fission is also discussed. Received: 26 July 2002 / Accepted: 3 December 2002 / Published online: 3 April 2003 RID="a" ID="a"Present address: Emeritus Scientist (CSIR) Bhabha Atomic Research Centre, Nuclear Recycle Group, WIP Building, Trombay, Mumbai-400085, India; e-mail: rhiyer@magnum. barc.ernet.in Communicated by D. Schwalm     

Multiphoton ionization of iodine atoms and CF<Subscript> 3</Subscript>I molecules by XeCl laser radiation

We report about effective ionization of iodine atoms and CF₃I molecules under the action of intense XeCl laser radiation (308 nm). The only ion fragment resulting from the irradiation of the CF₃I molecules is the I⁺ ion. We have studied the influence of the intensity, spectral composition, and polarization of the laser radiation used on the intensity of the ion signal and the shape of its time-of-flight peak. Based on the analysis of the results obtained, we have suggested the mechanism of this effect. The conclusion drawn is that the ionization of the iodine atoms by the ordinary XeCl laser with a nonselective cavity results from a three- (2 + 1)-photon REMPI process. This process is in turn due to the presence of accidental two-photon resonances between various spectral components of the laser radiation and the corresponding intermediate excited states of the iodine atom. The probability of ionization of the atoms from their ground state I(²P_3/2) by the radiation of the ordinary XeCl laser is more than two orders of magnitude higher than the probability of their ionization from the metastable state I^*(²P_1/2). The ionization of the CF₃I molecules by the XeCl laser radiation occurs as a result of a four-photon process involving the preliminary one-photon dissociation of these molecules and the subsequent (2 + 1)-photon REMPI of the resultant neutral iodine atoms.     

e + e − pair production in ultrarelativistic heavy-ion collisions at intermediate impact parameters

Using the semiclassical Green’s function in the Coulomb field, we analyze the probabilities of single and multiple e ⁺ e ⁻ pair production at a fixed impact parameter b between colliding ultrarelativistic heavy nuclei. We perform calculations in the Born approximation with respect to the parameter Z _Bα and exactly in Z _Aα, where Z _A and Z _B are the charge numbers of the corresponding nuclei. We also obtain the approximate formulas for the probabilities valid for Z _Aα, Z _Bα ≲ 1. The text was submitted by the authors in English.     

Fragmentation cross sections of16O at 60 and 200 GeV/nucleon

We used CR39 plastic nuclear track detectors (C₁₂H₁₈O₇) in combination with automatic track measurement to determine total charge changing and partial cross sections for the production of fragments of chargeZ=6 andZ=7 in collisions of¹⁶O beam nuclei at energies of 60 GeV/nucleon and 200 GeV/nucleon in targets H, C, CR39, CH₂, Al, Cu, Ag and Pb. Total charge changing cross sections due to the process of electromagnetic dissociation are calculated based on a theoretical model and found to be consistent with total and partial electromagnetic dissociation cross sections derived from this experiment. The energy dependence of pure nuclear fragmentation is investigated.     

Interaction of <Superscript>12</Superscript>C ions with nuclei of enriched tin isotopes at an energy of 2.2 GeV per nucleon

The formation cross sections for about 110 products of interaction between a ¹²C ion beam of energy 2.2 GeV per nucleon and tin targets from the isotopes ^{112,118,120,124}Sn were calculated. Massyield and charge distributions were obtained for ^112,118,124Sn targets. An analysis of these charge distributions reveals that the positions of their maxima, Z _p , are different for targets having different nucleon compositions. The formation cross sections for neutron-rich products originating from neutron-rich targets are found to increase in all product-mass regions considered in our study. Mass distributions are compared for proton-, deuteron- and ion-nucleus reactions.