Crystal Counter Research Articles

Temperature and pressure investigation of Hf x Ta1–x C and Zr x Nb1–x C carbide alloys

Structural mechanical and thermal properties of refractory carbides have been investigated using the Realistic Interaction Potential Approach (RIPA) model. The study has been extended to mixed crystals of Hf x Ta1–x C (0 ≤ x ≤ 1) and Zr x Nb1–x C (0 ≤ x ≤ 1) alloys and the effect of composition on structural and elastic properties are investigated. Phase transition pressure and associated volume collapses (ΔV(P t )/V(0)) calculated from this approach are in good agreement with available literature for the parent compounds (x = 0 and x = 1). The results for the mixed crystal counter parts are also in fair agreement with experimental data generated from the application of Vegard’s law to data for the parent compounds.

On the U–Cu–Al and U–Cu–Ga systems at 600 °C

The phase relations in the U–Cu–Al and U–Cu–Ga systems have been studied at 600 °C in concentration region of 0–45/75 at.% Al and 0–40/75 at.% Ga, respectively. X-ray diffraction techniques, optical microscopy and scanning electronic microscopy, complemented with energy dispersive X-ray spectroscopy (EDS), were used to identify the phases and characterize their crystal structures and compositions. Five new ternary phases have been identified for the first time: UCu6+xAl5−x (x ∼ 0–0.2) (TbCu6.4Al4.6 structure type), UCu6+xAl5−x (x ∼ 0.38–0.68) (BaCd11 structure type), U2−ɛ(Cu7+xGa10−x)1+δ (ɛ ∼ 0.5, δ ∼ 0.03, x ∼ 0.5–1) (related to Th2Ni17 structure type), UCu5+xGa1−x (x ∼ 0–0.7) (CeCu6 structure type) and U14Cu44+xGa7−x (x ∼ 0.5–2.5) (related to Gd14Ag51 structure type). The crystal structure of the UCu5+xGa1−x and U14Cu44+xGa7−x intermetallics has been determined from X-ray single crystal counter data.

Ternary systems Sr–{Ni,Cu}–Si: Phase equilibria and crystal structure of ternary phases

Phase relations were established in the Sr-poor part of the ternary systems Sr–Ni–Si (900 °C) and Sr–Cu–Si (800 °C) by light optical microscopy, electron probe microanalysis and X-ray diffraction on as cast and annealed alloys. Two new ternary compounds SrNiSi 3 (BaNiSn 3-type) and SrNi 9− x Si 4+ x (own-type) were found in the Sr–Ni–Si system along with previously reported Sr(Ni x Si 1− x ) 2 (AlB 2-type). The crystal structure of SrNi 9− x Si 4+ x (own-type, x=2.7, a=0.78998(3), c=1.1337(2) nm; space group P4/ nbm) was determined from X-ray single crystal counter to be a low symmetry derivative of the cubic, parent NaZn 13-type. At higher Si-content X-ray Rietveld refinements reveal the formation of a vacant site (□) corresponding to a formula SrNi 5.5Si 6.5□ 1.0. Phase equilibria in the Sr–Cu–Si system are characterized by the compounds SrCu 2− x Si 2+ x (ThCr 2Si 2-type), Sr(Cu x Si 1− x ) 2 (AlB 2-type), SrCu 9− x Si 4+ x (0≤ x≤1.0; CeNi 8.5Si 4.5-type) and SrCu 13− x Si x (4≤ x≤1.8; NaZn 13-type). The latter two structure types appear within a continuous solid solution. Neither a type-I nor a type-IX clathrate compound was encountered in the Sr–{Cu,Ni}–Si systems. Structural details are furthermore given for about 14 new ternary compounds from related alloy systems with Ba.

The ternary system Yb–Cu–Mg: Isothermal section at 400 °C in the range from 0 to 67 at.% Cu

Phase relations in the ternary system Yb–Cu–Mg have been established for the isothermal section at 400 °C based on X-ray powder diffraction, metallography, SEM and EPMA techniques on about 30 alloys, which were prepared in sealed Ta-crucibles followed by a homogenisation treatment. Phase equilibria in Yb–Cu–Mg are characterized by the absence of Yb solubility in CuMg 2 and of Mg solubility in YbCu 2. In the compositional range 0–67 at.% Cu five ternary compounds were observed in addition to the Cu-rich ternary phase that is already reported in the literature (τ 1-YbCu 9Mg 2). The section Cu 2Mg–YbCu 2 shows an extended homogeneity range for binary Cu 2Mg up to 8 at.% Yb where Mg atoms are substituted by Yb. At increasing Yb-content τ 2-(Yb 1− x Mg x )Cu 2 (ordered variant of the Cu 2Mg-type) forms with a homogeneity region extending from x = 0.45 to x = 0.63. A ternary phase of stoichiometry Yb 2Cu 2Mg (τ 3) was detected, whose crystal structure is still unknown. Three compounds were found to form near the concentration line with 66.7 at.% Yb: τ 4-Yb 4Cu 1− x Mg 1+ x (0 ≤ x ≤ 0.25, Gd 4RhIn-type), τ 5-Yb 23Cu 7Mg 4 (almost stoichiometric, with a unique structure type) and τ 6-Yb 2Cu x Mg 1− x ( x = 0.2, structure still unknown). Atom order in the crystal structures of YbMg 2 and τ 5-Yb 23Cu 7Mg 4 (Yb 23Cu 7Mg 4-type; P6 3/ mmc; a = 1.1866(2); c = 2.34371(5) nm) was determined by direct methods from X-ray single crystal counter data.

Measurements of the photon detection inefficiency of calorimeters between 185 and 505 MeV

Abstract The detection inefficiencies for photons of total-absorption-type electromagnetic calorimeters, an undoped CsI crystal counter and a lead-scintillator sandwich counter, have been measured at photon energies ( E γ ) between 185 and 505 MeV with the tagged photon beam from the INS-ES. The effect of punch-through is estimated by an EGS calculation. The other source of inefficiency, the photonuclear interaction effect, is examined after the interaction is identified by neutron signals observed with liquid scintillation counters surrounding the sample calorimeter. The inefficiency due to the photonuclear interaction in the case of the CsI calorimeter at 1-MeV threshold is found to be 10 −5 –10 −6 and shows a monotonic decrease with E γ . The detection inefficiency of the sandwich calorimeter is found to be dominated by the sampling effect after photonuclear interactions.

Crystal structure and valence behavior of YbPd xGa 11− x

The ternary phase YbPd x Ga 11− x has been synthesized from the elements by high frequency argon melting. An extended homogeneous region at 600 °C has been established from X-ray powder data for 2.3≤ ×≤3.4. The crystal structure of YbPd 3Ga 8 has been derived from X-ray single crystal counter data: partially ordered BaHg 11-type, space group Pm 3 ̄ m (O 1 h , No. 221), a=8.4346(5) Å: R F=0.054 for 176 independent reflections with I>2 σ. YbPd x Ga 11− x samples are temperature independent Pauli-type paramagnets for x≤3. Increasing the palladium content to x>3 leads to an enhanced f–d electron interaction, and a variation of the magnetic moment due to valence instabilities (4f 14→4f 13) is established using X-ray absorption spectroscopy.

Refinement of the crystal structure of scandium diiron disilicide, ScFe2Si2

Atom Site χ y ζ The synthesis and X-ray structure of ScFe2Si2 was reported before (see ref. 3). The compound was found to crystallize with the HfFe2Si2 structure type (see ref. 5). Both structures were established on single crystals from photographic data. Here we report the first single crystal counter data on that structure type. As shown in the figure, the structure of ScFe2Si2 can be described in terms of nets which connect Sc, Fei and Sil atoms at z=l/4 (dashed lines), and at z=3/4 (full lines), and of additional Fe2 and Si2 atoms which are both situated at the heights z=0 and z=0.5. Scandium is the only rare earth element which participates in the formation of that structure type for which the two above compounds are the only known members to date.

Ternary Compounds REAgSb 2, RE = Y, La, Ce, Pr, Ndr Sm, Gd, Tb, Dy, Ho, Er, Tm: Magnetism and Crystal Structure

Ternary compounds REA gSb 2, RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, have been synthesized by are melting followed by a heat treatment at 600 or 800°C for 300 hr. The novel phases were all found to be isotypic with the structure type of ZrCuSi 2. Precise atom parameters have been derived for CeAgSb 2 from X-ray single crystal counter data: space group P4/ nmm, a = 0.43641(9) nm, c = 1.0722(4) nm, and Z = 2. For 274 reflections (| F o| > 3σ) the residual values are R F = Σ|Δ|/Σ| F o| = 0.024 and R w = 0.028. A standardized set of atom parameters is provided. Magnetism of the REAgSb 2 phases in the temperature range 2.5 to 300 K is characterized by tripositive paramagnetic behavior of the rare-earth atoms. REAgSb 2 with RE = Y, La are weakly temperature-dependent paramagnets. In contrast, RE AgSb 2 compounds with RE = Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm are weak antiferromagnets with ordering temperatures lower than T N ∼ 13 K, and CeAgSb 2 is a noncolinear antiferromagnet ( T M ∼ 12 K) with a remanent magnetization μ = 0.15 μ B per Ce atom.

Crystal Chemistry and Magnetic Properties of the Ternary Compounds RE3AgxGa11-x (RE = Y, Gd, Tb, Dy, Ho, Er, Tm, and Yb)

Ternary samples with the composition RE3 AgxGa11-x, RE = Y, Gd, Tb, Dy, Ho, Er, Tm, and Yb, have been synthesized from the elements by arc- or HF-melting and annealing at 600°C. In all cases isotypy with the La3Al11-type has been confirmed from X-ray powder data. The homogeneity region of the Yb3AgxGa11-x phase has been established by X-ray powder diffraction analysis and ranges at 600°C from x = 2.6 to x = 3.8. Unit cell parameters in this region reveal a remarkable positive deviation from Vegard's rule corresponding with a partial composition-dependent atomic ordering in the various sites of the La3Al11-type structure. The occupation mode in the Yb-containing alloys has been studied in detail by full profile X-ray powder analysis for compositions x = 2.55 and 3.65 and by X-ray single crystal counter data refinement for the alloy with x = 3.0, confirming in all cases full consistency with the La3Al11-type structure with the space group Immm. Throughout the homogeneous range Ag was observed to preferentially occupy the (2c) sites. The relative increase of the Ag occupancy in (2c) with increasing content of silver, however, decreases and for compositions x > 3.0, Ag was found to enter the (81) positions. In correspondence with magnetic susceptibility measurements the peculiar lattice parameter variation observed is due to this complicated mode of Ga/Ag-substitution rather than to a valence change on the ytterbium atom. Magnetic susceptibilities were determined over a temperature range from 4 to 550 K. Above LNT, magnetic behavior of Gd (x = 2.8), Tb, Dy, Ho, Er, and Tm compounds (x = 3.8) corresponds to the paramagnetism of ideal tripositive rare earth elements. Below T = 25 K antiferromagnetic ordering of the RE-moments is encountered for the Yb3AgxG11-x alloys. The Yb-atom was found to be in a nonmagnetic Yb2+ ground state throughout the entire homogeneous range. The susceptibilities are practically temperature independent paramagnetic down to 20 K. Y3Ag3Ga8 is a diamagnet.

Structural chemistry and magnetic behavior of binary uranium silicides

Binary uranium silicides have been thoroughly reinvestigated with respect to crystal chemistry and magnetic properties; for most compounds, magnetic studies have been carried out at low temperatures for the first time (2 to 300 K, 0 to 5 T). Formation of all known binary silicides has been confirmed: U 3Si, U 3Si 2 (U 3Si 2-type), USi (USi-type), U 3Si 5 (defect AlB 2-type), USi 1.88 (defect ThSi 2-type) and USi 3 (Cu 3Au-type). At the composition U 3Si ∼5 three different phases have been observed: the defect AlB 2-type as well as a phase separation into two orthorhombically distorted Alb 2-type related phases. USi 2− x with the tetragonal defect ThSi 2-type structure at its silicon poor phase boundary was found to be in equilibrium with USi 2− x of the orthorhombic defect GdSi 2 type. Precise U-U distances have been derived from X-ray single crystal counter data for U 3Si 2, USi, for the AlB 2-type subcell of U 3Si 5, and for USi 1.84 (defect ThSi 2-type). From susceptibility measurements, a band type paramagnetism was observed for U 3Si 2, whereas a temperature independent paramagnetism was confirmed for USi 3. Curie-Weiss paramagnetism was encountered within the investigated temperature range for U 3Si 5 and USi 1.88. A modified Curie-Weiss law was revealed for USi with the USi-type, whereas ferromagnetic ordering at T c = 125 K was observed for the oxygen stabilized “USi” with the FeB-type. Magnetism of the uranium silicides is discussed as a function of the distant dependent 5 f-5 f electron overlap and d- f electron hybridization. No superconductivity was observed above 2 K.

Structural chemistry and magnetic properties of ternary germanides Ce 3Rh 4Ge 4 and Ce 3Rh 3IrGe 4

New compounds Ce 3Rh 4Ge 4 and Ce 3Rh 3IrGe 4 as part of an extended solid-solution range of Ce 3Rh 4− x Ir x Ge 4 have been synthesized by the arc melting technique starting from the pure elements. The crystal structures of Ce 3Rh 4Ge 4 and Ce 3Rh 3IrGe 4 have been refined from single crystal counter data. Both compounds were found to be isotypic with the U 3Ni 4Si 4-type (space group Immm-D 25 2 h , No. 71; Z = 2). The following lattice parameters were obtained: a = 0.40915(5), b = 0.42400(19), c = 2.50673(82) nm for Ce 3Rh 4Ge 4 and a = 0.40839(7), b = 0.42437(6), c = 2.50403(39) nm for isotypic Ce 3Rh 3IrGe 4. For 721 (495) reflections (| F o| > 3 σ) the obtained reliability factors R = Σ |ΔF| Σ F o | were R = 0.08 for Ce 3Rh 4Ge 4 and R = 0.07 for Ce 3Rh 3IrGe 4. According to the topochemical description 2Ce(Rh 0.5Ge 0.5) 2 + CeRh 2Ge 2 = Ce 3Rh 4Ge 4 the structure type of U 3Ni 4Si 4 is a combination of structural units of the AlB 2-type and of the BaAl 4-type (ThCr 2Si 2-type) with a complete statistical distribution of the Rh and Ir atoms. Both compounds, Ce 3Rh 4Ge 4 and Ce 3Rh 3IrGe 4, have been investigated at low temperatures by means of dc electrical resistivity and magnetic susceptibility measurements. No magnetic ordering has been detected above 2 K.

TUNNELLING JUNCTIONS OF SINGLE CRYSTAL BCSCO/SN FILM

The single particle tunnelling junctions consisting of single crystal BCSCO and Sn film counter electrode have been prepared. The I-V and dI/dV-V characteristics have been measured. Observed value of the energy gap is 23 meV which corresponds to 2Δ/kT c of 6.0, much larger than the BCS weak-coupling limit of 3.52.

Dietary treatment for decreasing 141Ce body burden in immature rats.

The purpose of this work was to evaluate the effect of prolonged (immediate or delayed) administration of dietary additives to suckling rats on the absorption and retention of radioactive cerium in the body. The experiment was performed on 6-day-old suckling rats. According to dietary treatment the animals were divided into three groups. Each group was artificially fed over 8 h for 6 or 12 days on one of the diets: the first group of animals was fed milk, the second group was given ingredients of rat diet and the third received milk during the first 2 days of the experiment and the ingredients of rat diet afterwards. At the end of the artificial feeding period the pups returned to their mothers and suckled overnight. On the 1st day of the experiment the food was labelled with 141Ce. Whole body radioactivity was determined in a double crystal scintillation counter every 48 h over a 12-day period. Half of the animals from each group were killed 6 days after 141Ce administration and the other half after 12 days. At these intervals retention was determined in the gut, liver, kidneys and femur. The early and delayed administration of rat diet ingredients--fish meal, sunflower meal, alfalfa, cane molasses and premix--greatly reduced whole body retention. The early treatment was more efficacious than the delayed one. The reduction was mostly due to decreased gut retention but organ retentions were also lower. The results obtained indicate that by prolonged (immediate or delayed) administration of some dietary means the retention of radioactive cerium in sucklings can be significantly decreased.

The crystal structure of U 4Ni 11Ga 20 and of isotypic U 4Pd 11Ga 20 and U 4Pt 11Ga 20 compounds

The crystal structure of U 4Ni 11Ga 20 was derived from single crystal counter data. It has a monoclinic symmetry with space group C2/m, Z = 2, and the lattice parameters a = 2.0734(4), b = 0.4119(1), c = 1.5338(4) and β = 124.71(1)°. For a total number of 1494 independent reflections ( | F 0 | > 3 σ) using anisotropic thermal factors and weights according to the counting statistics w i = 1 (σ(F i)) 2 , the obtained reliability factor was R w = ∑| ΔF|/∑| F 0| = 0.056. The crystal structure of U 4Ni 11Ga 20 is an occupation variant of the Ho 4Ni 10Ga 21-type of structure with nickel-atoms replacing the gallium atoms in the 2d-sites at the centerpoints of distorted icosahedra. From X-ray powder diffraction analysis the compounds U 4Pd 11Ga 20 and U 4Pt 11Ga 20 were found to be isotypic with U 4Ni 11Ga 20, and practically no homogeneous region was revealed for U 4Ni, Pd, Pt 11Ga 20 at 600°C. The crystal chemistry of the new phases is discussed.

Electron transport in solid argon

Electronic transport in solid argon doped with oxygen and nitrogen has been studied by a crystal counter technique as a function of applied electric field and dopant concentration. The experimental data provide evidence that molecular doping levels of less than 1% in solid argon increase the free electron velocity over that measured in undoped solid argon. Molecular oxygen, either as a dopant itself or as an impurity in another dopant gas is believed to cause the observed trapping effects in solid argon.

Nouveau phosphure ternaire NiNbP 2 a liaison nickel-nickel et nickel-niobium et compose isotype NiTaP 2

The phosphides NiNbP 2 and NiTaP 2 crystallize in an orthorhombic unit-cell, space group Pnma and Z = 4. The X-ray structure of NiNbP 2 was determined from four-dimensional single crystal counter data and was refined to a final R value of 0.031 for 475 independent reflections. It shows square-pyramidal and 7-prismatic phosphorus coordination for Ni and Nb atoms respectively, and moreover exhibits zigzag and regular Ni-Ni chains bonded together by means of mixed irregular and almost linear Ni-Nb-Ni chains. The structure is derived from MoP 2 type and may be also considered as a mixture of MnP and WC type structures. Magnetic and electrical measurements indicate a metallic behavior of these new phosphides.

Etude structurale d'un thiohalogenure supra conducteur derivant du Mo(II) : Mo 6S 6Br 2

The X-ray structure of Mo 6S 6Br 2, isostructural with Mo 6Se 8 (space group R 3 ), has been determined from three dimensional single crystal counter data and refined to a final R value of 0.044 for 482 independent reflections. Six sulfur atoms are located on the 6f site, whereas the bromine atoms are located on the 2c site, this later one being slightly deficient. The structural data are compared with M xMo 6S 8 ones, related to the high thermal stability of this compound and correlated with the high superconducting critical temperature.

Effect of the structure and chemical composition of polymers on the concentration and type of motion of excess charge carriers, formed by exposure to ionizing radiation

A crystal counter was used to determine values of ʌμτ (ʌ is the radiation yield of charge carriers, μ, microscopic mobility; τ, life time of the quasi-free charge carrier) for PE with different degrees of crystallinity and PMMA. Relations between ʌμτ and temperature were also examined for PE. It was established that the degree of crystallinity and temperature have a slight effect on the value of ʌμτ. On transition from PE to PMMA the value of ʌμτ decreases by one order of magnitude. It was shown using PS that molecular weight M υ has a slight effect on radiation electrical conductivity σ r while increasing it from 10 5 to 10 7. A correlation was derived between the variation of material density (as a result of pre-treatment and compression) and the variation of the value of σ r.

The crystal structure of Mg 2EDTA·9H 2O

The crystal structure of Mg 2EDTA·9H 2O has been determined using 2102 independent reflections measured by a single crystal counter diffractometer (CuKα radiation). The general conclusions are similar to those of an independent determination using film data [2] but the present investigation is very much more accurate, and all the hydrogen atoms have been located. The crystals are orthorhombic, space group Pbcn, with a = 11.617(1) Å, b = 9.495(1) Å, c = 19.238(2) Å. The structure was refined to a conventional R of 0.048 and wR of 0.037. Standard deviations in bond distances are 0.002–0.003 Å for CC and CO bonds and 0.03–0.04Å for CHand OH bonds. The structure consists of a cation, Mg(H 2O) 2+ 6, which is very close to regular octahedral geometry, and an anion, (MgEDTA OH 2) 2− in which the Mg atom is heptacoordinated by four O and 2 N atoms of the EDTA and one water molecule. The anion coordination sphere is close to pentagonal bipyramidal geometry and the details of the structure are discussed in comparison with other heptacoordinated EDTA complexes. One water molecule is not included in either the cation or the anion, and the whole structure is linked by a tight network of hydrogen bonds, utilizing every proton of the water molecules.

Quantitative immunoautoradiography at the cellular level. II. absolute measurements using labeled standard cells as a source of reference

A quantitative autoradiographic method is presented for determining absolute amounts of 125I-labeled compounds on the surface of individual cells. Autoradiographic evaluation of single cell radioactivity is accomplished by comparing the silver grain densities over the specimen and a radioactive standard being exposed simultaneously. In order to obtain a reference source of comparable physical properties, surface-radioiodinated human erythrocytes are used, the radioactivity of which is determined in a crystal counter. A simple enzymatic method for preparing such standard erythrocytes of very uniform label density is described. Numerous experimental advantages derived from the use of the standard are discussed and demonstrated by examples employing various exposure times and different radioactive standards. Hereby, very similar results were obtained when the number of A-antigenic sites was quantified on single erythrocytes in different experiments. The quantification of membrane-bound IgM on single human lymphocytes is shown as another application of this scheme.