Experimental determination of Q 0 factors and effective resonance energies with a multi-channel approach: the α-vector method

Some of the Q ₀ and ē _r factors from the 2003 to 2012 recommended k ₀-datasets were adopted from older literature (Lit; before 1984), at the time of the launch of the k ₀-method and have associated uncertainties of 10 %. The ē _r factors on the other hand, were derived analytically in 1979 and 1987 by employing the Breit–Wigner resonance representation, but in 1984 a multi-channel method was proposed for simultaneous Q ₀ and ē _r experimental determination. In this work we assumed the α-dependence of the ē _r parameter proposed later in 1987 for a generalization of this method, which was then employed in the experimental determination of Q ₀ and ē _r factors for 17 (n,γ) target isotopes on up to three channels of the BR1 reactor at the SCK-CEN (Mol, Belgium). Retrospectively, this “α-vector method” can be employed for α-calibration and it provides a practical way of averaging the experimental Q ₀ (and ē _r) results from several laboratories. Our Q ₀ results have 2–3 % uncertainty and are compared with the Lit elsewhere.     

Analysis of selected fertilizers imported to Libya for major, minor, trace and toxic elements using ICP-OES and INAA

The concentration of 35 elements (Al, As, B, Ba, Be, Ca, Cd, Co, Cl, Cr, Cu, Fe, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Sb, Sc, Si, Sr, Tb, Th, Ti, U, V, Yb, Zn and Zr) in six different imported, NPK, NP and K fertilizers were determined by ICP-OES in two different laboratories and by INAA. The fertilizers were labeled as 24/12 (Belgium), 46/18 (Morocco), 50% ammonium sulfate 50% K₂O (Belgium), New 24/12 (Belgium), 16.8.24 (France) and 17.17.17 (France). It is clear that these fertilizers vary widely in their heavy metals and uranium content, and the accumulation of certain elements in vitally important media such as water, soil and food is undesirable from the medical point of view. The results obtained were acceptable and intercomparison between various methods was carried out.     

The impact of polyethylene vials on reactor channel characterization in k 0 -NAA

Reactor channel characterization is commonly performed by irradiating bare and cadmium-covered “fluence rate monitors”, avoiding as much as possible the use of irradiation vials and spacers to position the monitors inside the channel. However, in routine k ₀ -Neutron Activation Analysis often samples are packed in small polyethylene vials prior to irradiation. This work aims at studying the impact of typical NAA polyethylene vials (~1 mm wall thickness) on the determination of the f and α channel-specific parameters through the “Bare”, “Cadmium-Covered” and “Cadmium-Ratio” methods. The impact of these vials on each method was studied for 3 irradiation channels of the Belgian Reactor 1 at SCK·CEN (Mol, Belgium) with low to high f and α-values. The net impact was 1% on each parameter. Inconsistencies between the different methods were found when the impact of the polyethylene was neglected, implying that all determination methods must be pooled and thin monitors should be used for an accurate channel characterization.     

Experimental determination of k 0, Q 0 factors,effective resonance energies and neutron cross-sections for 37 isotopes of interest in NAA

The recommended k ₀ nuclear data from 2003 has been re-investigated by some authors during the last decade, motivated by some discrepancies that were systematically observed during the analysis of reference materials. Their significant findings have not been included (yet) on a newer compilation, as it is difficult to draw conclusions on the accuracy of k ₀ and Q ₀ factors when the statistical population of independent experimental values are quite scarce. In some cases, a strong correlation to the adopted Q ₀ factor means that a direct comparison between the results of different authors is not possible if the data required for a proper renormalization was not provided. At the SCK-CEN and UGent (Belgium) we would like to continue with the experimental k ₀ determination exercises performed during the last years and to supply to the k ₀-community with the nuclear data of 37 additional target isotopes, for a total of 77 isotopes investigated since 2012. The isotopes were investigated on up to 4 channels of the BR1 reactor at the SCK-CEN, obtaining values with <2.6 % uncertainty. Our results are discussed and compared to the literature elsewhere.     

Determination of k 0-factors and validation of k 0-INAA for short-lived nuclides

For standardization of k ₀-based instrumental neutron activation analysis, k ₀-factors for short-lived nuclides (half-lives—11 s to 37 min) of elements F, Se, Sc, Al, V, Ti, Cu, Ca, Mg, I, and Cl with respect to gold (¹⁹⁷Au) were determined using pneumatic carrier facility (PCF) at CIRUS reactor of BARC, Mumbai. Characterization of PCF was carried out by cadmium-ratio method using Au and Zr. The experimental k ₀-factors of the isotopes were found to be in good agreement with the recommended k ₀-factors in most of the cases, as evident from the values of % error and U-score at 95% confidence level. The method was validated by determining concentrations of elements through their short-lived nuclides in one type of the synthetic multielement standards (SMELS-I) obtained from SCK-CEN, Belgium. The method was also applied for determination of concentrations of some of the elements in two reference materials of IAEA, SL-3, and SL-1.     

Measurement of k 0 and Q 0 values for iridium isotopes

There is an increasing demand for the chemical analysis of new materials containing iridium. The k ₀-method is an excellent method for the analysis of new materials but measured k ₀-values and Q ₀-values have been lacking for ¹⁹¹Ir(n,γ)¹⁹²Ir, which offers greater sensitivity than ¹⁹³Ir(n,γ)¹⁹⁴Ir. In this work, the Q ₀-values were determined for the two reactions by the two-channel method, using five irradiation channels in two research reactors in Belgium and Canada. These measured Q ₀-values enabled the first determination of the resonance neutron Cd transmission factors for these two capture reactions, confirming suspicions that they are much less than unity. At the two laboratories, k ₀-values were measured for ¹⁹²Ir and ¹⁹⁴Ir and there was good agreement between the two laboratories. The k ₀-values for ¹⁹²Ir are original measurements, while those for ¹⁹⁴Ir are in good agreement with previously published values.     

Seven new rare-earth transition-metal oxychalcogenides: Syntheses and characterization of Ln4MnOSe6 (Ln=La, Ce, Nd), Ln4FeOSe6 (Ln=La, Ce, Sm), and La4MnOS6

The quaternary oxychalcogenides Ln₄MnOSe₆ (Ln=La, Ce, Nd), Ln₄FeOSe₆ (Ln=La, Ce, Sm), and La₄MnOS₆ have been synthesized by the reactions of Ln (Ln=La, Ce, Nd, Sm), M (M=Mn, Fe), Se, and SeO₂ at 1173 K for the selenides or by the reaction of La₂S₃ and MnO at 1173 K for the sulfide. Warning: These reactions frequently end in explosions. These isostructural compounds crystallize with two formula units in space group of the hexagonal system. The cell constants (a, c in Å) at 153 K are: La₄MnOSe₆, 9.7596(3), 7.0722(4); La₄FeOSe₆, 9.7388(4), 7.0512(5); Ce₄MnOSe₆, 9.6795(4), 7.0235(5); Ce₄FeOSe₆, 9.6405(6), 6.9888(4); Nd₄MnOSe₆, 9.5553(5), 6.9516(5); Sm₄FeOSe₆, 9.4489(5), 6.8784(5); and La₄MnOS₆, 9.4766(6), 6.8246(6). The structure of these Ln₄MOQ₆ compounds comprises a three-dimensional framework of interconnected LnOQ₇ bicapped trigonal prisms, MQ₆ octahedra, and the unusual LnOQ₆ tricapped tetrahedra.     

Rare-earth-rich tellurides: Gd4NiTe2 and Er5M2Te2 (M=Co, Ni)

Three new rare earth metal-rich compounds, Gd₄NiTe₂, and Er₅M₂Te₂ (M=Ni, Co), were synthesized in direct reactions using R, R₃M, and R₂Te₃ (R=Gd, Er; M=Co, Ni) and single-crystal structures were determined. Gd₄NiTe₂ is orthorhombic and crystallizes in space group Pnma with four formula units per cell. Lattice parameters at 110(2) K are a=15.548(9), b=4.113(2), . Er₅Ni₂Te₂ and Er₅Co₂Te₂ are isostructural and crystallize in the orthorhombic space group Cmcm with two formula units per cell. Lattice parameters at 110(2) K are a=3.934(1), b=14.811(4), , and a=3.898(1), b=14.920(3), , respectively. Metal-metal bonding correlations were analyzed using the empirical Pauling bond order concept.     

Structures and syntheses of four Np sulfate chain structures: Divergence from U crystal chemistry

Four Np⁵⁺ sulfates, X₄[(NpO₂)(SO₄)₂]Cl (X=K, Rb) (KS1, RbS1), Na₃[(NpO₂)(SO₄)₂](H₂O)_2.5 (NaS1), and CaZn₂[(NpO₂)₂(SO₄)₄](H₂O)₁₀ (CaZnS1) were synthesized by evaporation of solutions derived from hydrothermal treatment. Their structures were solved by direct methods and refined on the basis of F² for all unique data collected with MoKα radiation and a CCD-based detector to agreement indices (KS1, RbS1, NaS1, CaZnS1) R₁=0.0237, 0.0593, 0.0363, 0.0265 calculated for 2617, 2944, 2635, 2572 unique observed reflections, respectively. KS1 crystallizes in space group P2/n, a=10.0873(4), b=4.5354(2), c=14.3518(6), β=103.383(1)°, , Z=2. RbS1 is also monoclinic, P2/n, with a=10.5375(8), b=4.6151(3), c=16.0680(12), β=103.184(1)°, , Z=2. NaS1 is monoclinic, P2₁/m, with a=7.6615(5), b=7.0184(4), c=11.0070(7), β=90.787(1)°, , Z=4. CaZnS1 is monoclinic, P2₁/m, with a=8.321(2), b=7.0520(2), c=10.743(3), β=91.758(5)°, , Z=2. The structures of KS1 and RbS1 contain chains of edge-sharing neptunyl hexagonal bipyramids, with sulfate tetrahedra attached to either side of the chain by sharing edges with the bipyramids. NaS1 and CaZnS1 both contain chains of neptunyl pentagonal bipyramids and sulfate tetrahedra in which each bipyramid is linked to four tetrahedra, three by sharing vertices and one by sharing an edge. Bipyramids are bridged by sharing vertices with sulfate tetrahedra. Each of these structures exhibits significant departures from those of uranyl sulfates.     

Crystal and molecular structures of the olefin complexes trichloro(π-allylammonium)platinum(II), trichloro(π-but-3-enylammonium)platinum(II) and trichloro(π-hex-5-enylammonium)platinum(II)

The crystal and molecular structures of the title compounds, [PtCl₃(C₃H₈N)] (I), [PtCl₃(C₄H₁₀N)] (II), and [PtCl₃(C₆H₁₄N)] (III) have been determined by single-crystal X-ray methods. I crystallizes in the orthorombic system (Pbca) with a 10.444(3), b 8.782(2), c 17.036(5)Å, Z 8; II is monoclinic (P2₁/n) with a 7.953(5), b 11.254(6), c 10.722(6)Å, β 111.07(4)°, Z 4; III is orthorombic (P2₁2₁2₁) with a 17.080(6), b 6.768(2), c 9.541(4)Å, Z 4. Full-matrix least-squares refinements have given final R-factors of 0.051 (1077 reflections for I), 0.043 (1325 reflections for II) and 0.041 (1123 reflections for III). The reflections were collected by counter methods and only those having I τ 3σ(I) were used in the analyses.In all three complexes platinum is four-coordinate, having as ligands the three chlorine atoms and the double bond of the

(n=1, 2 or 4) cationic species. The structures are discussed, and compared with that of the analogous complex containing the pent-4-enylammonium cation,

.     

Liquid-liquid phase equilibria for some polystyrene-methylcyclohexane mixtures

Liquid-liquid cloud point diagrams of solutions of nearly monodisperse samples of polystyrene (PS), and binary mixtures of nearly monodisperse PS’s, both in methylcyclohexane (MCH), were determined for several polymer molecular weights (M_w) at 0.1 MPa. The bimodal mixtures (PS[M_w(1),ρ(1)] + PS[M_w(2),ρ(2)], M_w(1)=90×10³ g/mol, M_w(2)=13×10³ g/mol, 5.78 × 10³ g/mol, and 2.2 × 10³ g/mol, ρ=1.06) were prepared constraining 〈M_w〉=38.6×10³ g/mol, ρ=M_w/M_n is the polydispersity index. In each case the cloud point curves (CPC’s) for the bimodal mixtures are strongly skewed, lying well above CPC for 〈M_w〉 when φ<φ_CRITICAL, and below CPC for 〈M_w〉 when φ>φ_CRITICAL; φ is volume fraction polymer in the polymer/solvent mixture. The experimental results are discussed in the context of empirical and mean-field representations.     

The crystal structure determinations and refinements of K2S2O7, KNaS2O7 and Na2S2O7 from X-ray powder and single crystal diffraction data

The crystal structures of K₂S₂O₇, KNaS₂O₇ and Na₂S₂O₇ have been solved and/or refined from X-ray synchrotron powder diffraction data and conventional single-crystal data. K₂S₂O₇: From powder diffraction data, monoclinic C2/c, Z=4, a=12.3653(2), b=7.3122(1), , β=93.0792(7)°, R_Bragg=0.096. KNaS₂O₇: From powder diffraction data; triclinic , Z=2, a=5.90476(9), b=7.2008(1), , α=101.7074(9), β=90.6960(7), γ=94.2403(9)°, R_Bragg=0.075. Na₂S₂O₇: From single-crystal data; triclinic , Z=2, a=6.7702(9), b=6.7975(10), , α=116.779(2), β=96.089(3), γ=84.000(3)°, R_F=0.033. The disulphate anions are essentially eclipsed. All three structures can be described as dichromate-like, where the alkali cations coordinate oxygens of the isolated disulphate groups in three-dimensional networks. The K-O and Na-O coordinations were determined from electron density topology and coordination geometry. The three structures have a cation-disulphate chain in common. In K₂S₂O₇ and Na₂S₂O₇ the neighbouring chains are antiparallel, while in KNaS₂O₇ the chains are parallel. The differences between the K₂S₂O₇ and Na₂S₂O₇ structures, with double-, respectively single-sided chain connections and straight, respectively, corrugated structural layers can be understood in terms of the differences in size and coordinating ability of the cations.     

Rh3B2−x, new structure type of binary borides with triclinic symmetry

New binary compound Rh₃B_2−x, x=0.167 crystallizing with its own structure type has been observed from the as cast alloys. The compound has a limited thermal stability range: it was found to decompose after annealing at 800 °C for 20 days. The crystal structure was investigated by X-ray diffraction from two single crystals using different techniques: CAD-4 automatic diffractometer, a=5.470(2), b=6.816(3), c=9.068(4), α=110.74(3), β=94.81(3), γ=90.44(2), 107 refined parameters, R₁=0.0418, wR₂=0.1087 for 1223 reflections with I>2σ(I_o), and BRUKER SMART AXS, a=5.483(4), b=6.818(6), c=9.072 (7), a=110.78(1), b=94.73(1), g=90.46(1), 107 refined parameters, R₁=0.0401, wR₂=0.0959 for 943 reflections with I>2σ(I_o). The Rh₃B_2−x, structure (space group , Pearson symbol aP30-1) is the first representative of structures with triclinic symmetry among binary borides and contains three different types of boron-boron aggregation: isolated boron atoms, B-B pairs and B₆ chain fragments.     

Some reduced ternary and quaternary oxides of molybdenum. A family of compounds with strong metal-metal bonds

Several new, reduced ternary and quaternary oxides of molybdenum are reported, each containing molybdenum in an average oxidation state <4.0. All are prepared by reactions between a molybdate salt; metal oxide, if needed; and MoO₂ sealed in Mo tubes held at 1100°C for ca. 7 days. Refinement of the substructure of the new compound Ba_0.62Mo₄O₆ was based on an orthorhombic cell, witha = 9.509(2), b = 9.825(2), c = 2.853(1)Å, Z = 2 in space groupPbam; weak supercell reflections indicate the true structure hasc = 8(2.853) Å. The chief structural feature is closely related to that of NaMo₄O₆ (C. C. Torardi, R. E. McCarley,J. Amer. Chem. Soc.101, 3963 (1979)), which consists of infinite chains of Mo₆ octahedral clusters fused on opposite edges, bridged on the outer edges by O atoms and crosslinked by MoOMo bonding to create four-sided tunnels in which the Ba²⁺ ions are located. The structure of Ba_1.13Mo₈O₁₆ is triclinic,a = 7.311(1), b = 7.453(1), c = 5.726(1)Å, α = 101.49(2), β = 99.60(2), γ = 89.31(2)°,Z = 1, space groupP1¯. It is a low-symmetry, metal-metal bonded variant of the hollandite structure, in which two different infinite chains, built up from Mo₄O^2?₈ and Mo₄O^0.26?₈ cluster units, respectively, are interlinked via MoOMo bridge bonding to create again four-sided tunnels in which the Ba²⁺ ions reside. Other compounds prepared and characterized by analyses and X-ray powder diffraction data arePb_xMo₄O₆(x ～ 0.6), LiZn₂Mo₃O₈, CaMo₅O₈, K₂Mo₁₂O₁₉, and Na₂Mo₁₂O₁₉.     

Structural studies on bulky phosphines: X-ray crystal structures of [2,4,6-(t-Bu)3C6H2P(SiMe3)2] and

The crystal and molecular structures of two bulky phosphines containing the 2,4,6-(t-Bu)₃C₆H₂ group are reported. Compound1, [2,4,6-(t-Bu)₃C₆H₂P(SiMe₃)₂], crystallizes in the monoclinic space group P2₁/c; a = 9.450(8), b = 17.154(6), c = 17.790(5)Å, β = 101.19(5)°. Compound2,

, also crystallizes in the monoclinic space group P2₁/c: a = 18.224(5), b = 9.394(2), c = 12.321(2)Å, β = 107.28(2)°. Structural features resulting as a consequence of the bulky 2,4,6-(tBu)₃C₆H₂ group, in particular the geometry at phosphorus, are discussed.     

A phase-analytical study of the TlCuSe system

High-temperature silica-tube syntheses and room-temperature copper extraction experiments of the single phases found with the former technique have established five new ternary phases in the TlCuSe system. The compositions were determined by microprobe analysis. The new phases have been crystallographically characterized by means of single-crystal and powder diffraction: TlCu₃Se₂ (CsAg₃S₂ type),a = 15.2128(7)Å,b = 4.0115(2)Å,c = 8.3944(4)Å, β = 111.700°(4); Tl₅Cu₁₄Se₁₀ (new type),C2/m?)a = 18.097(2)Å,b = 3.9582(2)Å,c = 18.118(2)Å, β = 116.089°(7); TlCu₅Se₃ (new type,P4¯n2?),a = 12.9023(2)Å,c = 3.9905(1)Å; TlCu_5−xSe₃ (new type,Pnn2?),a = 12.43(1)Å,b = 12.80(1)Å,c = 3.93(1)Å; TlCu₇Se₄ (NH₄Cu₇S₄ type),a = 10.4524(2)Å,c = 3.9736(1)Å. The latter phase may be considered as stoichiometric crookesite.     

Syntheses, structure, and magnetic properties of several LnYbQ3 chalcogenides, Q=S, Se

The six LnYbQ₃ compounds β-LaYbS₃, LaYbSe₃, CeYbSe₃, PrYbSe₃, NdYbSe₃, and SmYbSe₃ have been synthesized from high-temperature solid-state reactions of the constituent elements at 1223 K. The compounds are isostructural to UFeS₃ and crystallize in the space group Cmcm of the orthorhombic system with four formula units in a cell. Cell constants (Å) at 153 K are: β-LaYbS₃, 3.9238(8), 12.632(3), 9.514(2); LaYbSe₃, 4.0616(8), 13.094(3), 9.932(2); CeYbSe₃, 4.0234(5), 13.065(2), 9.885(1); PrYbSe₃, 4.0152(5), 13.053(2), 9.868(1); NdYbSe₃, 4.0015(6), 13.047(2), 9.859(1); SmYbSe₃, 3.9780(9), 13.040(3), 9.860(2). The structure is composed of layers of YbQ₆ (Q=S or Se) octahedra that alternate with layers of LnQ₈ bicapped trigonal prisms along the b-axis. Because there are no Q-Q bonds in the structure the formal oxidation states of Ln/Yb/Q are 3+/3+/2−. Magnetic susceptibility measurements indicate that CeYbSe₃ and SmYbSe₃ are Curie-Weiss paramagnets over the temperature range 5-300 K.     

New three-dimensional inorganic frameworks based on the uranophane-type sheet in monoamine templated uranyl-vanadates

Seven new uranyl vanadates with mono-protonated amine or tetramethylammonium used as structure directing cations, (C₂NH₈)₂{[(UO₂)(H₂O)][(UO₂)(VO₄)]₄}·H₂O (DMetU5V4) (C₂NH₈){[(UO₂)(H₂O)₂][(UO₂)(VO₄)]₃}·H₂O (DMetU4V3), (C₅NH₆)₂{[(UO₂)(H₂O)][(UO₂)(VO₄)]₄}·H₂O (PyrU5V4), (C₃NH₁₀){[(UO₂)(H₂O)₂][(UO₂)(VO₄)]₃}·H₂O (isoPrU4V3), (N(CH₃)₄){[(UO₂)(H₂O)₂][(UO₂)(VO₄)]₃}·H₂O (TMetU4V3), (C₆NH₁₄){[(UO₂)(H₂O)₂][(UO₂)(VO₄)]₃}·H₂O (CHexU4V3), and (C₄NH₁₂){[(UO₂)(H₂O)][(UO₂)(VO₄)]₃} (TButU4V3) were prepared from mild-hydrothermal reactions using dimethylamine, pyridine, isopropylamine, tetramethylammonium hydroxide, cyclohexylamine and tertiobutylamine, respectively, with uranyl nitrate and vanadium oxide in acidic medium. The structures were solved using single-crystal X-ray diffraction data. The compounds exhibit three-dimensional uranyl-vanadate inorganic frameworks built from uranophane-type uranyl-vanadate layers pillared by uranyl polyhedra with cavities in between occupied by protonated organic moieties. In the uranyl-vanadate layers the orientations of the vanadate tetrahedra give new geometrical isomers leading to unprecedented pillared systems and new inorganic frameworks with U/V=4/3. Crystallographic data: (DMetU5V4) orthorhombic, Cmc2₁ space group, a=15.6276(4), b=14.1341(4), c=13.6040(4) Å; (DMetU4V3) monoclinic, P2₁/n space group, a=10.2312(4), b=13.5661(7), c=17.5291(7) Å, β=96.966(2); (PyrU5V4), triclinic, P1 space group, a=9.6981(3), b=9.9966(2), c=10.5523(2) Å, α=117.194(1), β=113.551(1), γ=92.216(1)°; (isoPrU4V3) monoclinic, P2₁/n space group, a=10.3507(1), b=13.6500(2), c=17.3035(2) Å, β=97.551(1)°; (TMetU4V3) orthorhombic, Pbca space group, a=17.1819(2), b=13.6931(1), c=21.4826(2) Å; (CHexU4V3), triclinic P−1 space group, a=9.8273(6), b=11.0294(7), c=12.7506(8) Å, α=98.461(3), β=96.437(3), γ=105.955(3)°; (TButU4V3), monoclinic, P2₁/m space group, a=9.8048(4), b=17.4567(8), c=15.4820(6) Å, β=106.103(2).