Resonant excitations of fast nuclei in crystals

Resonant excitations of nuclear levels are predicted when relativistic nuclei are directed along a crystal axis. The process is analogous to photo-excitation because the crystal's periodic Coulomb field is equivalent to a flux of photons. A resonance occurs when the periodicity of the lattice leads to a field at the nucleus whose frequency corresponds to a nuclear excitation frequency. The resonant nuclear excitation rate is not large. However, at very high projectile energies its observation is possible. In principle, such resonant excitation could yield new information on both nuclear photo-excitation rates and the electric fields in solids. Numerical results for a favorable example, electric dipole excitation of the ¹⁹F nucleus, are presented.     

HPuO分子激发态的外场效应

采用密度泛函(DFT)方法B3LYP/Gen,在Pu为相对论有效原子实势(RECP)基组水平上,优化计算得到了分子轴方向不同电偶极场（－0.005～0.005a.u.）作用下的HPuO的基态几何结构、偶极矩和分子总能量。在优化构型下,用同样的基组,采用含时密度泛函(TDDFT)方法(TD-B3LYP),研究了同样外电场条件下对HPuO的激发能的影响。计算结果表明,在外场作用下,对HPuO的前5个激发态电子跃迁光谱属于红外 远红外光谱,波长为1046.0～3038.7nm,这是钚原子的奇异特征。激发能与外电场的关系近似满足Grozema等提出的关系。     

Theoretical energy level spectra and transition data for 4p4d, 4p4d4f,and 4p4d configurations of W

The ab initio   quasirelativistic Hartree–Fock method developed specifically for the calculation of spectral parameters of heavy atoms and highly charged ions is used to derive transition data for a multicharged tungsten ion. The configuration interaction method is applied to include electron correlation effects. The relativistic effects are taken into account in the Breit–Pauli approximation for quasirelativistic Hartree–Fock radial orbitals. The energy level spectra, radiative lifetimes and Lande g$g$-factors are calculated for the 4p⁶4d², 4p⁶4d4f, and 4p⁵4d³ configurations of the ion W³⁶⁺. The transition wavelengths, spontaneous transition probabilities, oscillator strengths, and line strengths for the electric dipole, electric quadrupole, electric octupole, and magnetic dipole transitions among the levels of these configurations are tabulated.     

Theoretical energy level spectra and transition data for 4p4d, 4p4f and 4p4d configurations of W ion

The ab initio quasirelativistic Hartree-Fock method developed specifically for the calculation of spectral parameters of heavy atoms and highly charged ions was applied to determine atomic data for tungsten ions. The correlation effects were included by adopting the configuration interaction method. The Breit-Pauli approximation for quasirelativistic Hartree-Fock radial orbitals was employed to take into account relativistic effects. The energy level spectra, radiative lifetimes, Lande factors g were calculated for the 4p⁶4d, 4p⁶4f and 4p⁵4d² configurations of W³⁷⁺ ion. The atomic data, namely, the transition wavelengths, spontaneous emission rates and oscillator strengths for the electric dipole, electric quadrupole and magnetic dipole transitions among and within the levels of these configurations are tabulated.     

Adsorption and solution of hydrogen in single crystal niobium

Hydrogen adsorbs on the (100) face of niobium at 90 K into at least two states sequentially. The first state, which appears to be molecular, has a dipole moment of ?0.022 Debye/molecule, an inittial sticking coefficient of 0.23, and a saturation coverage of 3.2 × 10¹⁴molecules/cm² reached after an exposure of about 1 L (1 L = 10^?6torr·rec). The first state may be a precursor for adsorption into the second state. The second state is atomic and has a dipole moment of ?0.141 Debye/atom, an initial sticking coefficient of 0.056, and a saturation coverage of 9 × 10¹⁴atoms/cm², which is reached after an exposure of about 12 L. The heat of adsorption for state 2 was found to be 26.5 ± 3 kcal/mol.     

Elasto-plastic behavior of pipe subjected to steady axial load and cyclic bending

The elasto-plastic behavior of a pipe subjected to a steady axial force and a cyclic bending moment is studied. By using two parameters c and d, which describe the elasto-plastic interfaces of beam cross-section, the boundary curve equations between various types of elasto-plastic behavior, such as shakedown, plastic fatigue, ratcheting, and plastic collapse, are derived. The results are applicable for beams of any cross-section with two orthogonal axes of symmetry. As a result, the load regime diagram for a pipe is obtained, which gives an intuitive picture of the elasto-plastic behavior of the pipe under a given combination of constant axial load and cyclic bending moment.     

Research of Radioisotope Production with Fast Neutrons, (V)

The preparation of carrier-free ⁶⁵Ni was studied using the reaction ⁶⁵CU(n,/p)⁶⁵.Ni in a nuclear reactor. High purity copper metal was irradiated for 20 min in the JRR-2 reactor. Nickel-65 formed in the copper target was separated by anion exchange method. About 1 μ ⁶⁵Ni per gram of copper was obtained by irradiation with a fast neutron flux of 9×10¹¹ n/cm=²/sec and thermal neutron flux of 3.6 ×10¹³ n/cm²/sec. The specific activity was greater than 3 mc/mg Ni which was over 600 times more than that produced by n, γ) reaction on nickel irradiated at the same time. However, the reaction yield of ⁶⁵Ni per gram of target by the (n, p) reaction was only 1/5,000 of that by the (n, γ) reaction, so that it proved that the method would be unsuitable for practical application.

The cross section for the reaction ⁶⁵Cu(n/p)⁶⁵Ni has been estimated semi-theoretically to be 0.6 mb, an experimental value of 0.2 mb was calculated from the results of the present work.     

Evaluation of Photonuclear Reaction Data on Tantalum-181 up to 140MeV

Photonuclear cross sections of ¹⁸¹Ta are evaluated up to an incident photon energy of 140MeV which is the threshold energy for pion production. Re-analyses were performed on the (γ, n) and (γ, 2n) data measured at Saclay and Livermore, and reference data were reconstructed. The absorption cross sections were evaluated with the giant electric dipole resonance (GDR) model below 40MeV. The calculation by the statistical model with preequilibrium correction reproduced the reference data of all the photoneutron cross sections consistently. From 40 to 140 MeV, the quasideuteron model (QDM) was adopted to evaluate photoabsorption cross sections and the results are compared with the measurements. The decaying processes including n, p, d, t, ³He, and α particle emission up to 140MeV were theoretically evaluated by the ALICE-F code.     

Utilizing RF Electric Field for Injection-Trapping High Energy Molecular Ions in Mirror Field, (I)

A method of using rf electric field in a device for high-energy injection is described, and the behavior of the molecular ions injected into a system combining rf and DC magnetic fields is investigated by calculation and observation.

In this method, some of the injected molecular ions are decelerated by the rf field, and trapped in a small region between the mirror fields, where they are dissociated by collision with the background gas or with the plasma particles, and are thus trapped in the form of atomic ion. The relation between the rf frequency ω and the Larmor frequencies ΩN⁺ ₂, ΩN⁺ ₁ is given by ω=N/2· ΩN⁺ ₂=N/4· ΩN⁺ ₁, where N is the number of rf electrodes. The number N is chosen so that N/2 is an integer and N/4 a non-integer.

Calculation shows that the ions injected in a certain favorable phase are stably decelerated despite their initially possessing a precessional motion. This is proven by observation of actual electron behavior.     

An L2 representation of the continuum in collisions between alpha particles and lithium atoms

We report new theoretical results obtained in close-coupling calculations within the impact parameter method, using two-centred AO expansions with an extended L² basis for charge transfer, target excitation, and ionisation in collisions between H²⁺ and Li. The basis is chosen by demanding a good representation of oscillator strengths for dipole transitions both to excited and to ionised levels. The calculations bring the theoretical and experimental total cross sections for single-electron capture between 40 and 200 keV lab. close together. They also reproduce accurately the Li(2p) excitation cross sections over a wide energy range. The first close-coupling estimate of ion-impact ionisation of Li is also given. Preliminary results suggest that an important contribution to the ionisation cross sections at intermediate energies may come from transitions to d- and f-states of the target continuum.     

Energy levels,lifetimes, and transition probabilities for Mn XII and Ge XIX

Energy levels, transition probabilities, oscillator strengths, line strengths, and lifetimes have been calculated for silicon-like manganese and germanium, Mn XII and Ge XIX. The configurations 3s²3p², 3s3p³, 3s²3p3d, 3s3p²3d, and 3p⁴ were used in the calculations and 88 fine-structure levels were obtained. The fully relativistic GRASP code has been adopted, and results are reported for all electric dipole, electric quadrupole, magnetic dipole, and magnetic quadrupole transitions among levels of Mn XII and Ge XIX. Comparisons have been made with available theoretical and experimental results.     

CROSS SECTIONS AND RATE COEFFICIENTS FOR EXCITATION OF THE 1s2s2pPJ→ 1s2s2pPJ′FINE-STRUCTURE TRANSITIONS IN BERYLLIUM-LIKE IONS BY HEAVY PARTICLE IMPACT

Cross sections for excitation of the 1s²2s2p³P^o_J→ 1s²2s2p³P^o_J′fine-structure transitions in beryllium-like ions by proton, deuteron, triton, and α-particle impact have been calculated using a close-coupled impact-parameter method. This technique includes the effects of dipole coupling to the nearby triplet 2p², 2s3s, and 2s3dconfigurations by means of a polarization potential. We consider the ions C III, N IV, O V, Ne VII, Mg IX, Al X, Si XI, S XIII, Ar XV, Ca XVII, Ti XIX, Cr XXI, Fe XXIII, and Ni XXV. Excitation rate coefficients have also been calculated from the cross sections for a range of temperatures.     

Analytical expression for the Mössbauer line shape of 57Fe in the presence of mixed hyperfine interactions

A new method is presented for the calculation of Mössbauer line shapes of hyperfine split nuclei. Instead of solving explicitly the hyperfine Hamiltonian for its eigenvalues and eigenvectors this method uses a superoperator formalism to yield closed form expressions for the Mössbauer line shape in the presence of magnetic dipole and electric quadrupole hyperfine interactions. The advantage of this method over the conventional one lies in the fact that averages over hyperfine field orientations may be calculated analytically. This is demonstrated for the case of ⁵⁷Fe with randomly oriented electric field gradients in a uniform oriented magnetic field.     

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral of the Reaction 133Cs(n, γ)134m,134gCs

The measurements of the thermal neutron (2,200 m/s neutron) cross section (σ₀) and the resonance integral (I ₀) of the ¹³³Cs(n, γ;) reaction were performed by an activation method to obtain fundamental data for research on the transmutation of nuclear wastes. The cross sections for the formations of the isomeric state ^134mCs and the ground state ^134mCs were measured respectively by following the behavior of the γ-ray counting rate after the irradiation.

The thermal neutron capture cross sections and the resonance integrals of the ¹³³Cs(n, γ) reaction were determined to be 2.70±0.13 b and 23.2±1.8 b for the formation of the isomeric state ^134mCs, and 26.3±1.0 b and 275±16 b for the formation of the ground state of ^134gCs. The results for the reaction ¹³³Cs(n, γ)^134m+gCs were 29.0±l.0 b and 298±16 b, respectively. As for the thermal neutron capture cross section for the formation of ^134m+gCs, the evaluated value (29.00 b) of JENDL-3.2 agreed with the present result. The reported value by Baerg et al. was in good agreement with the present result within the limits of error on the thermal neutron capture cross section for ^134mCs. On the other hand, the resonance integral for ^134m+g Cs was 32% smaller than the experimental value by Steinnes et al.     

Energy levels and radiative rates for transitions in Ga XXIV

Energy levels, transition probabilities, oscillator strengths, line strengths, and lifetimes have been calculated for Oxygen-like Gallium, Ga XXIV. The configurations 2s²2p⁴, 2s2p⁵, 2p⁶, 2s2p⁴3?, 2s²2p³3?, and 2p⁵3? were used in calculations and 226 fine-structure levels were obtained. The fully relativistic GRASP code has been adopted, and results are reported for all electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2) transitions among the lowest 226 levels of Ga XXIV, belonging to the n≤3 configurations. Comparisons have been made with earlier available theoretical and experimental results.     

Calculation of Gamma-Ray Production Cross Sections at Neutron Energies of 1–20 MeV

In order to prepare the p-ray data library requested in a design of fission and fusion reactors, γ-ray production cross sections and spectra of Al, Si, Ca, Fe, Ni, Cu, Nb, Ta, Au and Pb have been obtained at the neutron energies of 1–20 MeV, using a spin-dependent multi-step evaporation model. Calculations include dipole and quadrupole transition without the distinction between electric and magnetic process, and take explicit account of the role of yrast levels. The effects of the yrast levels and γ-ray strength function upon γ-ray production are also investigated in relation to particle emission. At the incident neutron energies where (n,n^γ ) and/or (n,2^nγ ) reactions are dominant, the present model is shown to be able to predict the production of secondary γ-rays (<9.0 MeV) from medium-heavy to heavy nuclei with reasonable accuracy.     

A Theoretical Study of MHD Power Generation, (I)

This paper deals with an analysis of the current and electric field distributions in the entrance and exit regions of a linear MHD power generator, for the case where the working fluid (gas) exhibits the Hall effect. For simplicity, the following assumptions are adopted:

1. The MHD power generator is of constant-velocity-type.

2. The problem is two dimensional.

3. The electrical conductivity and the Hall parameter of the fluid and the magnetic field are constant and uniform in the region of interest.

4. The seeding material is injected uniformly at the entrance plane.

Solutions are presented in closed form for several values of the Hall parameter, ωπ. They show that the electric potential in the entrance plane assumes an extreme value between the electrodes, and that the length of the “entrance region” is of the same order as the distance between the electrodes. The influence of electric field distortion at the entrance on the current and electric field distributions is negligible beyond this region. The electric field distortion occurs in the exit region also, resulting in “end loss” which is approximately proportional to σ ^eff ωτ.     

Fission neutron spectrum of Cf

Average cross sections for the unmoderated spontaneous fission neutron spectrum of ²⁵²Cf have been measured for 10 different threshold reactions by activation method. On the basis of the measured data and of the excitation functions the Maxwellian temperature for ²⁵²Cf neutron spectrum has been deduced and a value of T = 1.41 ± 0.02 MeV was found between 2.5 and 15 MeV. The temperature has been determined also from the average energy which was deduced from the age of epithermal neutrons in water measured by gold foil. The high σ values obtained by the low threshold reactions and the age method confirm the assumption on the excess of neutrons in the low energy region of the spectrum.     

Simulations of turbulence, heat transfer and mixing across narrow gaps between rod-bundle subchannels

Turbulent flow and temperature fields were determined numerically in a rectangular duct containing a heated rod. As the spacing δ between the rod and the duct wall decreased from 0.10D (D is the rod diameter) to 0.03D, coherent turbulent kinetic energy and temperature fluctuations dramatically increased in the gap region, but, for δ = 0.01D, coherent fluctuations essentially disappeared. As δ/D → 0, the frequency of coherent fluctuations decreased and cross-gap mixing weakened, contrary to predictions based on extrapolated available empirical correlations.     

Effect of loading rate upon fracture behavior of ferritic steel under large scaled yielding

Dynamic loading to ferromagnetic materials and large scaled yielding result in peak or valley and non-linear curve, respectively, on the Direct Current Potential Drop (DCPD) versus Crack Opening Displacement (COD) plots, which make it difficult to determine the crack initiation point. In this work high intensity of current up to 100 A was applied to the specimens of SA106Gr.C ferritic steel and the crack growth behavior was directly monitored by a high speed camera to obtain the crack initiation point. The effects of loading rate up to 1200 mm min⁻¹ upon the fracture resistance were explored. As the results, it has been shown that, although no substantial difference was seen in the load–COD plots, the crack initiation and then J_i and J–R curve were quite sensitive to the loading rate. That is, under the loading rate of 300 mm min⁻¹ the material showed the worst fracture resistance than under static loading and even under the higher loading rates of 600 and 1200 mm min⁻¹. Also applying the high speed camera and high current source have been proved to be an effective way to find out the accurate crack initiation point and to compensate the pulse of DCPD due to the ferromagnetic effect.