Electronics for A SiCsI(Tl)-photodiode multidetector system

Preamplifiers, computer-controlled main amplifiers and trigger electronics have been designed and built for our charged particle multidetector system (MDS). These electronic process signals from the individual detection elements of the MDS, each consisting of a silicon surface-barrier detector and a CsI(Tl) scintillator with photodiode readout. Our design is compact, reliable, cheap, and well-suited for the multidetector system.     

A method for measuring the neutron flux from an AmBe source using a Nal(Tl) scintillator

We present a simple method for measuring the neutron flux from an ²⁴¹Am-Be radioactive source. The yield determination is based on counting (n,p) + (n,d) and (n,α) events in a NaI(Tl) scintillator. This technique offers the advantages of two independent measurement of the flux rather than one, insensitivity to the threshold setting used for counting, and low sensitivity to edge effects.     

Comparison of the BGO and CsI(Tl) energy resolutions for p and α

Energy resolution and linearity of a BGO-photodiode have been measured for 20–40 MeV p and 14–25 MeV α. Comparisons are made to BGO and CsI(Tl) read by photomultipliers.     

An optimized C6D6 detector for studies of resonance-dominated (n,γ) cross-sections

Hydrogen-free scintillators are indispensable for determining the small, resonance-dominated neutron capture cross-sections of light and neutron magic nuclei, data which are needed for advanced reactor concepts, for transmutation of radioactive wastes as well as for astrophysical scenarios of neutron capture nucleosynthesis. A critical comparison of the existing detector concepts by means of detailed GEANT simulations revealed large differences in neutron sensitivity. Based on these simulations, an optimized detector was developed and successfully tested. Compared to a commercial detector, the neutron sensitivity of this solution is more than an order of magnitude lower, thus allowing even extremely small capture/scattering ratios to be measured reliably.     

Photoabsorption properties of β-FeSi2 nanoislands grown on Si(111) and Si(001): Dependence on substrate orientation studied by nano-spectroscopic measurements

Photoabsorption properties of β-FeSi₂ nanoislands epitaxially grown on Si(111) and Si(001) have been discussed using photoabsorption nano-spectroscopy based on scanning tunneling microscope. The obtained spectra exhibit clear features around 0.86-0.91 eV and around 0.71-0.74 eV, which are explained as a direct and an indirect photoabsorption edge of β-FeSi₂, respectively. We also observed a blue shift of spectrum obtained from β-FeSi₂ nanoislands on Si(111) substrates, compared to those on Si(001) substrates. We attributed the dependence on Si-substrate orientation not to a quantum confinement effect but to an effect of elastic strain in the? β-FeSi₂ nanoislands epitaxially grown on the substrate.     

Formation of zeolite from the system Na20-Al2O3-SiO2-H2O in alkaline medium (pH > 10)

The hydrothermal reactions of three aluminosilicates, i.e., kaolinite, metakaolinite, and sodium aluminosilicate gel, with aqueous sodium hydroxide have been reexamined. The molar composition of the quaternary system Na₂O-Al₂O₃-SiO₂-H₂O was maintained constant in the three systems. Kaolinite gave a partially rehydrated nonbasic hydroxysodalite, whereas zeolite 4A is the product from metakaolinite and gel. The kinetics of the reaction and the crystal habit of the zeolite formed in the metakaolinite-alkali system appear to be different from that of conventional gel route of synthesis. The metakaolinite slowly dissolves in alkali to form a gel that is the direct precursor of zeolite 4A. However, the crystallization seems to start even before the metakaolinite gel conversion is completed. The ion-exchange and water-adsorption capacity and the chemical assay of the precursors and products have been used to substantiate the XRD and spectroscopic (i.r. and MAS n.m.r.) data in establishing the mechanism of the reaction.     

Location of different phases in oxidized ultrafine FeCr (70:30) alloy particles

Slow or fast oxidation of ultrafine FeCr alloy particles leads to a core/shell like microstructure (1). A slowly oxidized sample revealed FeO (wüstite) and spinel oxide FeCr₂O₄ to be located at the shell, which is built up of very small crystals (3–5 nm). The FeO phase is observed to be very stable, being still present 360 days after the oxidation. The core consists usually of a bcc FeCr alloy, however, some particles contain the σ-FeCr phase, which is the expected form during slow cooling of FeCr particles.A fast oxidized sample contains only two phases, namely °-Fe₂O₃ and CrO₃, which coexist at the shell, leaving the core empty or filled with a lightly scattering substance, e.g. a gas. The outer surface of the shell is CrO₃ free but consists of °-Fe₂O₃. However, CrO₃ is located at the core/shell interface and forms a homogeneous layer around the core and is therefore not mixed with °-Fe₂O₃, which is built up of 10–20 nm crystals.     

Neutral N,N′-bis(2-pyridinecarboxamide)-1,2-ethane as sensing material for determination of lutetium(III) ions in biological and environmental samples

The biological properties of the lutetium as well as other lanthanide ions, primarily based on their similarity to calcium, have been the bases for research into potential therapeutic applications of lanthanide series since the early part of the twentieth century. In this research, a Lu(III) potentiometric membrane sensor based on N,N′-bis(2-pyridinecarboxamide)-1,2-ethane (PCAE) is described. The sensor exhibits a Nernstian response over a concentration range of 1.0 × 10^? 6 mol L^? 1–1.0 × 10^? 1 mol L^? 1, with a detection limit of 6.0 × 10^? 7 mol L^? 1. The best performance was achieved with a membrane composition, consisting of 30% PVC, 63% o-nitrophenyl octyl ether (NPOE), 5% PCAE and 2% sodium tetraphenylborate (NaTPB). It was found that at the pH range of 4.0–9.0, the potential response of the sensor was not affected by the pH. Furthermore, the electrode presents satisfactory reproducibility, very fast response time (5 s) and relatively good discriminating ability for Lu(III) ions with respect to many common cations and other lanthanide ions. The sensor has been applied to the determination of Lu(III) in human serum and in some soil samples where domestic devices were stored.     

Realization of 1 × 10(6) theoretical plates in liquid chromatography using very long pillar array columns

We report on the possibility to achieve ultra high efficiencies (order of 1 million theoretical plates) in liquid chromatography in a relatively short time of 20 min (elution time of unretained marker). This was achieved using a micropillar array column with optimized pillar diameter (5 μm) and interpillar distance (2.5 μm) to operate close to the Knox and Saleem limit of micropillar array columns in the region of the 1 million theoretical plate mark under the prevailing pressure restriction (350 bar in the present study). The obtained efficiency was slightly affected (some 15 to 20% around the optimal flow rate) by the turns that were inevitably needed to arrange a 3 m long column on a 4 in. silicon wafer.     

Variation of Electronic Structure with C Content in Si_(1-x-y)Ge_xC_y/Si(001) System

1.IntroductionInrecentyears,smallam0unts0fis0electronicCaddedt0aSi1-.Ge.layerhavebeenactivelystudied[1~l5].ThelatticestraininducedbyCandGeisofoppositesign.Itisf0undthatlat.pctCc0n-tentcanrelievethestrainintr0ducedbyar0und9at.pctGe11].TheSi1-.-.Ge.C.alloyIayersgrown0naSisubstratecanhaveatetragonaldistorti0nn0t0nlyofcompressivebutals0oftensilecharacteristicl2~4]inc0mparis0nwiththeSi1-.Ge.all0ylayers.Thevalence-bandoffsetandbandgapareimportantpa-rametersfordevicedesign,andp1ayaleadingr0lein…     

Comparison of Li+ conductivity in Li3−xNb1−xMxO4 (M = W,Mo) with that in Li3−2xNixNbO4

The performance at 300 °C of Li_2.9Nb_0.9M_0.lO₄, M = W or Mo, as a solid electrolyte is compared to that reported in 2004 by McLaren et al. for Li_2.9Ni_0.05NbO₄. The Li⁺ conductivity and activation energy were found to be nearly identical for M = W. Ni in the Li array does not impede Li⁺ mobility more than aliovalent substitution for Nb, and W(VI) is not reduced before Nb(V). Substitution of Nb(V) by Mo(VI) was not as advantageous.     

New high dielectric constant materials: Micro/nanocomposites of suspended Au clusters in SiO2/SiO2Al2O3Li2O gels and relevant theory for high capacitance applications

We have materials-designed, synthesized, processed, tested, and interpreted a micro/nanocomposite material consisting of a suspension of gold clusters in an insulating matrix, aimed at producing a high-dielectric constant (>200) high-breakdown-voltage capacitor. The resulting suspension utilizes SiO₂ or a reacted form of SiO₂Al₂O₃Li₂O as the insulating matrix, and was prepared by the sol-gel technique. The scientific approach employs the percolation theory expectation that at a critical topology of small metal elongated clusters amidst a ceramic or other insulating matrix, the dielectric constant of the resulting materials will reach a peak value as a function of spatial geometric loci. Our theoretical work indicates that the metal clusters should be optimally of atomic dimensions and approximately 100–300 A apart. The metal islands must be ellipsoidal-like (or elongated globules or flocculates) to establish a dipole moment (that will be summed over the sample volume). High resolution microscope studies reveal that the gold clusters are observed to take on the general shape of truncated octahedra, which indeed are appropriate for having a polarization vector (charge separation) due to an impressed electric field. From electron spectroscopy chemical analysis there exists indication that some of the clusters appear to be in a charged state. Dielectric constant measurements from 1 to 10 kHz have shown an average dielectric constant of 5000 in the AuSiO₂ gel sample over a wide temperature range of −100 to +100 °C, and a dielectric constant of 364–986 (with consideration for porosity) in the AuSiO₂/Al₂O₃/Li₂O produced from Eucryptite (LiAlSiO₄).     

Early hydration of quick cements in the system C11A7 · CaF2C2SC2(A,F)

To explain the initial hydration of quick cements of the system C₁₁A₇ · CaF₂C₂SC₂(A,F), their SO₃/Al₂O₃ ratio was varied, Portland cement was added to increase the alcalinity of the pore solution in the cement stone, and setting retarded was used during the tests. The process of hydration was investigated with the help of X-ray diffraction and scanning electron microscopy as well as via the determination of the chemically bound water. The quantity of rapidly growing ettringite crystals increases with a rising SO₃/ Al₂O₃ value. The optimal SO₃/Al₂O₃ value of the system C₁₁A₇ · CaF₂C₂SC₂(A,F) is found between 0.26 and 0.38. The sole addition of setting retarder or Portland cement can distinctly reduce the formation of monocarbonate or even stop it completely. However, the simultaneous addition of both additives (setting retarded and a Portland cement) supports the formation of ettringite and monocarbonate crystals and through this also supports the increase of initial strength of quick cement.