Application of the relativistic DV-Xα molecular orbital method to γ-uranium alloys with transition metals

The alloying behavior of 4d and 5d transition metals (TMs) in γ-phase solid uranium (U) has been investigated using the discrete-variational Dirac–Fock–Slater (DV-DFS) method. We examined the d-orbital energy (Md value) of these TMs, the orbital overlap population (OOP) between the d-orbital of these TMs and the 5f or 6d orbital of γ-U, and the effective charge on each atom of the γ-U/TM alloy, and the effect of these parameters on alloying. It was found that the maximum solid solubility (MSS) of TMs into γ-U was exponentially proportional to both the Md and the OOP (U5f–TMd and U6d–TMd), except for Ta and W elements. We found a good correlation between the MSS and Md, the effective charge, or OOP.     

Atomistic modeling of the effects of dose and implant temperature on dopant diffusion and amorphization in Si

We discuss atomistic simulations of ion implantation and annealing of Si over a wide range of ion dose and substrate temperatures. The DADOS Monte Carlo model has been extended to include the formation of amorphous regions, and this allows simulations of dopant diffusion at high doses. As the dose of ions increases, the amorphous regions formed by cascades eventually overlap, and a continuous amorphous layer is formed. In that case, most of the excess interstitials generated by the implantation are swept to the surface as the amorphous layer regrows, and do not diffuse in the crystalline region. This process reduces the amount of transient enhanced diffusion (TED) during annealing. This model also reproduces the dynamic annealing during high temperature implants. In this case, the local amorphous regions regrow as the implant proceeds, without the formation of a continuous amorphous layer. For sufficiently high temperatures, each cascade is annealed out independently; interstitials and vacancies can escape from the cascade and thus increase dopant diffusion.     

Activity level of gross α and gross β in airborne aerosol samples around the Qinshan NPP

The monitoring results of gross α and gross β activity from 2001 to 2005 for environmental airborne aerosol samples around the Qinshan NPP base are presented in this paper. A total of 170 aerosol samples were collected from monitoring sites of Caichenmen village, Qinlian village, Xiajiawan village and Yangliucun village around the Qinshan NPP base. The measured specific activity of gross α and gross β are in the range of 0.02 - 0.38 mBq/m^3 and 0.10 - 1.81 mBq/m^3, respectively, with an average of 0.11 mBq/m^3 and 0.45mBq/m^3, respectively. They are lower than the average of 0.15 mBq/m^3 and 0.52mBq/m^3, of reference site at Hangzhou City. It is indicated that the specific activity of gross α and gross β for environmental aerosol samples around the Qinshan NPP base had not been increased in normal operating conditions of the NPP.     

New code for digital imaging system for track measurements

A code for the numerical analysis of images from a CCD camera, including correction of acquisition system defects, has been written and applied to the visualization of α-particle tracks in the solid state nuclear track detectors CR39 and LR115. A standard mask having different diameter holes permitted the calibration of the imaging system. Comparison of manual scanning results with those given by the automatic system are presented for detectors exposed to α-particles of ²⁴¹Am source. As application, the system was used to measure specific activities of ²³⁸U in the Moroccan phosphates and their phosphogypsums samples by contact autoradiography.     

Quasi-molecular orbital calculation using the DV-Xα method in Ne–Ne collisions

Molecular orbital calculations were performed for Ne–Ne quasi-molecules formed during collisions by changing the internuclear distance between 0.01 and 10 a.u. using the discrete variational (DV)-Xα MO calculational method. The equilibrium number of electrons on the basis atomic orbitals were estimated as a function of internuclear distance from which the critical internuclear distance to form quasi-molecular orbitals were deduced.     

Metal location and thickness in a multilayered sheet by measuring Kα/Kβ, Lα/Lβ and Lα/Lγ X-ray ratios

When a multilayered material is analyzed by means of energy-dispersive X-ray fluorescence analysis, then the X-ray ratios of Kα/Kβ, or Lα/Lβ and Lα/Lγ, for an element in the multilayered material, depend on the composition and thickness of the layer in which the element is situated, and on the composition and thickness of the superimposed layer (or layers).Multilayered samples are common in archaeometry, for example, in the case of pigment layers in paintings, or in the case of gilded or silvered alloys. The latter situation is examined in detail in the present paper, with a specific reference to pre-Columbian alloys from various museums in the north of Peru.     

Theoretical prediction of S Kβ fine structures in PIXE-induced XRF spectra

Sulfur is one of the most important elements found in air pollutants. A PIXE-induced XRF system equipped with a crystal spectrometer is a candidate to analyze chemical states of S in the pollutants. To aid in the design of the spectrometer for this purpose, fundamental data have been collected by calculating S Kβ spectra by use of the discrete variational Xα (DV-Xα) method for molecular orbital calculations. The calculated spectra have very faithfully reproduced XRF spectra observed for mixtures of Na₂SO₄, Na₂SO₃ and ZnS using a Ge (1 1 1) flat crystal spectrometer, which were used as representative chemical species including SO₄²⁻and SO₃²⁻, and as an example of sulfides in the air pollutants.     

N(α,p)O nuclear reaction cross-section at 4.9–6.1 MeV

The ¹⁴N(α,p)¹⁷O nuclear reaction cross-section was measured in the energy range 4.9–6.1 MeV at the laboratory angle θ = 172° in order to apply ion beam analysis to the detection of N in metal oxynitride layers. Comparison between the new calculation and data in literature was performed, highlighting important discrepancies between the new results and old cross-section data. Application of the new calculations to a standard TiN film suggests improved accuracy for the data in the present work.     

Primary study on holdup measurement of ^235U in pipe using γ-ray spectrometry and Monte Carlo simulation

The pipe holdup measurement is very important for decommissioning nuclear facilities and nuclear-material control and accounting. The absolute detection efficiencies （εsp） of full-energy γ rays peak under different source density distribution function have been simulated using the Monte Carlo （MC） software, and the counting rates （no） of the characteristic γ rays have been measured using the γ spectrometer followed by the calculation of the holdup. The holdup is affected by the energy of γ rays, distance at which they are detected, pipe material, thickness, and source distribution of pipe, especially source distribution at a short distance. The comparative test of ^235U reference materials on the inner wall of Fe and A1 pipes （the total mass of ^235U is 44.6 mg and 222.8 mg, respectively） have been accomplished using this method. The determined result of ^235U is 43.2mg （U0.95rel=5.4%） and 216.2mg （U0.95rel= 3.2%）, respectively, which are in accordance with the reference values.     

The Finite Beta Effects on the Toroidal Field Ripple in a Tokamak Plasma

The efficiency of energetic ion confinement is reduced in a tokamak plasma by the non-axisymmetric field, namely the ripple field. The ripple field is produced by a finite number of toroidal field coils. It is affected by the non-axisymmetric finite beta effect. The three-dimensional MHD equilibrium calculation code VMEC is used to analyze the non-axisymmetric finite beta effect in a ripple tokamak. In the VMEC code, the flux coordinates are used, so the calculation region is limited to the area of plasma. To calculate the orbit outside the plasma, we develop a field calculation code, which is based on the Biot-Savart law. The details of the method and results are described in this paper.     

Feedback control of the position of the levitated superconducting magnet in the RT-1 device

The Ring Trap-1 (RT-1) device confines a high- plasma in a magnetospheric configuration which is generated by a high-temperature-superconducting coil levitated in a vacuum chamber. The levitated coil is unstable with respect to the vertical motion when it is attracted from above. The vertical motion has been analyzed from the equation of motion and the flux conservation law and the response of the PD (proportional-derivative) feedback system of RT-1 has been formulated by using a transfer function. The result of the model analysis has shown sufficient agreement with experiments. To meet the various requirements in order to conduct the plasma experiments and measurement, the feedback gains are optimized to suppress a feedback noise in parallel with ensuring the stability of the system.