Measurement of Isotopic Abundance Ratio of Argon-36, −38 and −40 by General-Purpose Double-Focused Mass Spectrometer

Atomic fractions of each isotope in ³⁶Ar-³⁸Ar-⁴⁰Ar gas mixture near natural abundance were measured by using a general-purpose double-focused mass spectrometer HITACHI M-80. Because an amount of gas in a sample bulb and consequently a height of output peak decreases while taking measurements. 30 sets of peak height and time elapsed for each isotope were measured for calculation of atomic fractions through a least squares method under the assumptions (1) the reduction in heights follows an exponential function of time and (2) the rates of reduction are the same among argon isotopes. Application of this method to argon gas samples extracted from the top and bottom of a thermal diffusion column for isotope separation have proved that the method gives data with small dispersion even for ³⁸Ar, and is satisfactory for studying separative performances of thermal diffusion column.     

Use of the alloy Na−K−Cs as a coolant in a fast reactor: Preliminary results of safety characteristics optimization

A possible variant of a safe reactor operating on fast neutrons and cooled by the alloy Na−K−Cs is examined. The results of optimization investigations of the layout of a fast reactor with constraints on the functionals characterizing the internal self-shielding from ATWS-type accidents are presented. 2 tables, 5 references. Moscow Engineering-Physics Institute. Translated from Atomnaya énergiya. Vol. 88, No. 3, pp. 169–176, March, 2000.     

Investigation of H− production in a pulsed power diode at 10 GW

Several experimental runs on the investigation of H⁻ production in various types of pulsed power diodes (reflex and magnetically insulated) at a power level of 10 GW and electron cathode surface current density in the (0.5-) KA/cm range with different prepulse conditions in the anode-cathode (A-C) gap were carried out. The scheme with intermediate ion charge exchange (H⁻ → H⁺) and two stage acceleration was used to identify the H⁻ (or D⁻) ions and estimate their relative concentration in the plasma formed at the cathode surface. The measured activation yield of ¹³N in the ¹²C(p, γ)¹³N reaction gave values of H⁻ current densities equal to (0.25 ± 0.15) A/cm², which corresponded to (0.5–2)% of H⁻ percentage in the cathode plasma in our experimental conditions.     

Molecular-dynamics simulation of Si1−xGex epitaxial growth on Si(100)

Molecular dynamics study of the Si_1−xGe_x epitaxial growth on Si(1 0 0) substrate utilizing the Stillinger–Weber two- and three-body interaction potentials was carried out. The Stranski–Krastanov growth mechanism of the Si_1−xGe_x strain layers on Si(1 0 0) was studied and compared with experiment results. The influence of different x on the epitaxial growth layers morphology was investigated. The structure properties of the Si_1−xGe_x layers were evaluated.     

Thermophysical properties of Th1−xUxO2 pellets prepared by spark plasma sintering technique

Th_1?x U _x O₂ solid solutions were synthesized by solid-state reaction and pelletized using the spark plasma sintering (SPS) technique. Pellets with >90% theoretical density were easily obtained within 40 min of sintering without any additive. The thermal conductivity, Young's modulus, Debye temperature, Vickers hardness, and heat capacity were systematically investigated, and the values for ThO₂ agree with the literature data. The thermal conductivity of Th_1?x U _x O₂ decreased with increasing U content up to x =～0.5. This tendency corresponds to phonon-point defect scattering theory. The Young's modulus and Debye temperature linearly decreased with increasing U content. The Debye temperature and standard molar entropy derived from the low-temperature heat capacity agree with the reported values.     

Pn-values of 94Rb and 95Rb measured by a β−γ spectroscopic method

The delayed-neutron emission probabilities (P_n-values) of ⁹⁴Rb and ⁹⁵Rb have been measured as 9.73 ± 0.62 and 8.60 ± 0.57%, respectively, by a β−γ spectroscopic method utilizing the on-line isotope separator KUR-ISOL. This method can be usefully applied if a pure isotopic and mass-separated ion beam is available and the absolute emission probabilities per decay of main γ-rays emitted from relevant nuclides are well-established.     

Sound speeds in and mechanical properties of (U,Pu)O2−x

The sound speeds of longitudinal and transverse waves in the uranium–plutonium mixed oxide pellets were measured as functions of porosity, oxygen-to-metal ratio, and plutonium content. The effect of each parameter was well fitted by a linear function and the equations were obtained to calculate the sound speeds. Mechanical properties were evaluated with the sound speeds and the result of Young's modulus showed that porosity was the most important factor to decrease Young's modulus. Temperature dependence on Young's modulus was also evaluated with previously reported thermal expansion. Decrease of Young's modulus with increasing temperature was in good agreement with available literature.     

Numerical Calculation of H2-HT Separative Performances up to −0.3 MPa of Thermal Diffusion Column with Fairly Higher Hot-Wire Temperature

By using the two-dimensional rigorous numerical solution of flow and convection-diffusion equations, the H₂-HT separative performances of thermal diffusion column with 15 mm-radius and 288.15K cold-wall was analyzed up to ?0.3 MPa for higher hot-wire temperature (up to ?1,700K). Flow analysis has revealed: (1) The magnitude of the free convection is almost proportional to the pressure, and laminar solution of free convection could not be obtained at the pressure more than ?0.32 MPa. (2) The magnitude of the free convection increases gradually with ΔT (the temperature difference between hot and cold surfaces), when ΔT<–800 K. In the range of larger ΔT, the magnitude is almost constant or rather decreases gradually with ΔT. As a result, the laminar solution could always be obtained at the pressure less than ?0.32 MPa, no matter how large ΔT may be. Separative analysis for H₂-HT isotope separation has made clear that the thermal diffusion column with 288.15 K cold-wall should be operated at (1) 0.15–0.2 MPa, (2) ΔT that is as large as technically possible, and (3) the feed rate F of 50–100 cm³ (288.15 K, 0.1 MPa)/min.     

A UHV-compatible ΔE−E gas telescope for depth profiling and surface analysis of light elements

We have developed a compact ΔE−E gas telescope that can easily be incorporated into a standard ultrahigh vacuum ion scattering chamber. If energetic, heavy ions are available as a primary beam, the gas telescope can be used to detect light elastic recoils scattered from the surface region of a sample. The detector consists of a gas ionization chamber in front of a surface-barrier detector. The energy loss signal in the gas (ΔE) is taken in coincidence with the energy signal in the surface-barrier detector (E) to identify both the atomic number and the total energy of the elastic recoil. The design parameters of the detector have been chosen to allow detection of elements from H to O with good depth resolution ( < 100 Å) and submonolayer sensitivity. The mass resolution is adequate to easily separate all elements from H to O.     

RBS and ion channeling studies of Ag-doped YBa2Cu3O7−δ targets and films

The location of Ag in Ag-doped YBa₂Cu₃O_7−δ (YBCO) films and other high-T_c materials (such as Ag-doped BiSrCaCuO films and Ag-sheathed textured BiSrCaCuO wires) is a very important issue for improving high-T_c materials. In this work, laser ablated and DC magnetron sputtered YBCO films on (1 0 0) LaAlO₃ and (1 0 0) SrTiO₃ were prepared from sintered Ag-YBCO composite targets (nominally containing 5 wt% Ag) and studied by Rutherford Backscattering Spectrometry (RBS) and ion channeling techniques using 2.0 MeV⁴He⁺ and ⁷Li⁺ beams. We have found that the Ag-YBCO targets contain about 3 wt% Ag and most of the retained Ag atoms form some small size Ag precipitates with a typical size smaller than a few microns. We have demonstrated that in very good single crystalline YBCO films, the percentage of retained Ag in substitutional sites can be estimated by ion channeling technique. For example, we have found that about 1.2 wt% Ag atoms remain in the laser ablated Ag-doped films prepared from the Ag-YBCO target and about two-thirds of the retained Ag atoms occupy substitutional sites. The sputtered films contain less retained Ag atoms since the deposition temperature is higher and deposition time is longer than those for laser ablated films.     

Influence of pre-irradiation annealing and Lix–Co(1−x)–O thin film deposition on the TL response of soda lime glass

Effects of pre-irradiation annealing and deposition of a thin film of Li_x–Co_(1−x)–O on soda lime glass substrate are studied using the thermoluminescence technique, at low gamma radiation doses. Simple but similar glow curves were obtained with a single glow peak in all cases. Glow peaks occurred within the temperature range of 266 and 288 °C depending on sample treatment and gamma dosage. Within the studied gamma radiation dose range of 0.86–4.29 mGy, the heated soda lime glass consistently showed the highest TL response, while that from the film deposited sample was the least. At a dose of 0.86 mGy, a 41.8% enhancement and a 56.7% loss in signal over those from ordinary soda lime glass were recorded for annealed and film deposited samples respectively. Peak shift to higher temperatures were also observed in the two treated samples, relative to blank. These we have attributed to the increased diffusion of alkali ions in the annealed glass and exchange of impurity ions between the Li_x–Co_(1−x)–O thin film and the soda lime glass substrate, at high temperatures, resulting in increased formation of points and complex defects that could be either killer or radiative traps.