Low temperature structural distortion in the high Tc Chevrel-phase superconductors PbMo6S8 and SnMo6S8

High-resolution powder neutron diffraction data reveal that, at temperatures below 100 K, oxygen-free, high-T_c samples of PbMo₆S₈ and SnMo₆S₈ exhibit a small structural distortion from the R$\text{3}$ rhombohedral space group. The data cannot be refined in a simple P$\text{1}$ triclinic space group as previously reported for EuMo₆S₈ and BaMo₆S₈. Thus, a supercell ordering is suggested.     

Positive cones in enveloping algebras

The concept of strong ordering on enveloping algebras of finite-dimensional Lie algebras is introduced and studied as a generalization of the corresponding notion for the commutative polynomial algebra. A linear functional f on an enveloping algebra $\text{E}$ (G) is called strongly positive if f(x) ? 0 for all x ? $\text{E}$(G) which are mapped on positive operators for all G-integrable irreducible representations of $\text{E}$(G). We prove that for each real connected Lie group G ≠ R₁ there are positive, not strongly positive, linear functionals on $\text{E}$(G). A non-commutative problem of moments is defined. It has a solution iff the corresponding linear functional is strongly positive.     

Nuclear orientation of 160Tb in Tb metal

The decay of ¹⁶⁰Tb oriented at low temperatures in Tb metal has been investigated, and angular distributions of 19 γ-rays have been determined. The reduction in anisotropy in polycrystalline metal samples is discussed. Multipole mixing ratios have been determined for many of the γ-rays. A critical discussion is given of the previously reported $\text{M2}\text{E1}$ mixing ratios, and previous nuclear orientation studies are re-analyzed in a consistent manner so that their results can be compared. It is shown that the nuclear orientation and angular correlation results for the 1178 keV transition are consistent only if E3/E1 mixing is present. The El branching ratios and $\text{M2}\text{E1}$ mixing ratios are analyzed on the basis of Coriolis-mixed K = 0, 1 and 2 character for the negative-parity levels of ¹⁶⁰Dy.     

Coulomb effects in the organic charge transfer salt TTT2I3

Madelung energy and simple band structure calculations on different models of the TTT₂I₃ complex indicate, that the iodine chains do not play an active role in the conduction process. The relatively small Coulomb coupling of the iodine chains to the crystal obtained by the Madelung calculations rationalizes the structural findings about the ordering of these chains at low temperatures. The Madelung energy difference between the localized model (with TTT^o and TTT⁺ ions) and delocalized model (with partly charged $\text{TTT}{}^{\mathrm{<mtext>1</mtext><mtext>2+</mtext>}}$ stacks) is large enough to stabilize the former.     

The decay process 11ΛB → π− + 11C

The branching ratios are calculated for ¹¹_ΛB decay to the ¹¹C ground and excited states below 8 MeV for two possible spin values of ¹¹_ΛB. It is found that the decay rate to the ¹¹C^★ state at E^★ = 6.48 MeV is comparable in magnitude to that leading to the ¹¹C ground state if $\text{J(}{}^{11}{}_{\mathrm{\Lambda }}\text{B}\text{) =}\text{5}\text{2}$ is assumed. This result, unlike the branching ratios calculated for the $\text{J(}{}^{11}{}_{\mathrm{\Lambda }}\text{B}\text{) =}\text{7}\text{2}$ case, is in accord with experiment and lends support to the assumption that $\text{J =}\text{5}\text{2}$ holds for ¹¹_ΛB. The necessity of the reinterpretation of some of the so-called ¹³_ΛC events in terms of ${}^{11}{}_{\mathrm{\Lambda }}\text{B}\text{→ π}{}^{\mathrm{?}}\text{+}{}^{11}\text{C}{}^1$ is indicated.     

Resonance production in the reaction π±p→Ks0K±p at 30 and 50 GeV/c

The mass and momentum transfer spectra of the charged $\text{K}\text{K}$ system produced in the reaction π^±p→K_s⁰K^±p are analyzed. The data have been collected at the CERN SPS with the Geneva-Lausanne two-arm, non-magnetic spectrometer at 30 and 50 GeV/c incident momenta. The general features of the reactions at these energies and the results of partial-wave analyses of the two kaon system are presented.The channel is dominated by the diffractive production of even spin resonances. The spin 4 recurrence of the A₂(1320) is clearly observed at 2040 MeV (Γ=380 MeV. A new resonance is observed with a mass M=2450MeV and a width Γ=400 MeV; the quantum numbers of this state are found to be I^G(J^PC)=1^?(6++). The analysis also shows the decay of the decay of the meson ?′(1600) through the $\text{K}\text{K}$ channel at both energies.The production amplitudes are determined both as a function of the $\text{K}\text{K}$ effective mass and of the momentum transfer. Isoscalar natural parity exchange is dominant. The energy dependence between 10 and 50 GeV/c is shown to be well described by a Regge pole model based on the f-dominated pomeron hypothesis. We compare the production mechanisms of the 2⁺ resonances A₂(1320) and K¹(1430). Finally, we estimate the $\text{K}\text{K}$ branching ratios of the spin 4 A₂(2040) and spin 6 A₂(2450) resonances.     

Study of ππ → KK and Kπ reactions

We provide the partial-wave solution of the $\text{ππ →}\text{K}\text{K}$ reaction in the f-meson region. By the use of the unitarity constraint given by our $\text{ππ →}\text{K}\text{K}$ solution and the smoothness condition of the amplitude zeros in various charge configurations, we show that the (???) type solution seems the correct one among the four types of ππ partial-wave solutions. Other possibilities, especially the (+??) type, are also discussed briefly. The study of the behaviour of poles and zeros of the $\text{ππ →}\text{K}\text{K}$ and Kπ amplitudes gives corroborative evidence of the dual resonance model satisfying the gauge condition.     

Magnetic ordering of a d1 compound: VF4

Magnetic susceptibility and nuclear magnetic resonance above and below the ordering temperature show that VF₄ is an $\text{S =}\text{1}\text{2}$, 3d¹ canted antiferromagnet with a transition temperature near 28°K and a canting angle of ～ .02 rad. The compound is not an example of a proposed nonmagnetic singlet ground state of resonating covalent bonds.     

Relative Cl 2p:P 2s photoionization intensities in transition metal complexes

X-ray photoelectron spectra of the Cl 2p_{$\text{1}\text{2}$, $\text{3}\text{2}$}, P 2s region were obtained for nine transition metal complexes. The Cl:P atom ratios ranged from 1:3 to 3:2 and exhibited a linear relationship with the Cl 2p_{$\text{1}\text{2}$, $\text{3}\text{2}$} : P 2s intensities. Using AlKα radiation, the ratio of the Cl 2p: P 2s photoionization intensities was found to be 2.5: 1.0 with the McPherson ESCA-36 Photoelectron Spectrometer operated in its standard configuration.     

Proton states in the N = 88 nuclei 149Pm, 151Eu and 153Tb populated in the (τ, d) and (α, t) reactions

The (τ, d) and (α, t) reaction on targets of ¹⁴⁸Nd, ¹⁵⁰Sm and ¹⁵²Gd have been studied, using beams of 24 MeV ³He and 27 MeV ⁴He from the McMaster University FN tandem Van de Graaff accelerator. The reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions. The (α, t) spectra were measured at two angles for each target, and the (τ, d) reactions were studied at 8 or 9 angles. The l-values for a number of low-spin states were determined from the (τ, d) angular distributions, and ratios of the (α, t) and (τ, d) cross sections were used to obtain l-values for several other states. There are some striking similarities in the observed structures of the three final nuclei, ¹⁴⁹Pm, ¹⁵¹Eu and ¹⁵³Tb. In each case there are low-lying strongly populated $\text{11}\text{2}$^? states and a higher lying l = 5 level somewhat below 1 MeV of excitation energy. Several states (10 in ¹⁴⁹Pm, 17 in ¹⁵¹Eu and 8 in ¹⁵³Tb) appear to be populated via l = 2 transitions, and there are strongly excited $\text{1}\text{2}$⁺ levels at $\text{≧ 1}\text{MeV}$ of excitation energy in each case. Of particular interest is a $\text{7}\text{2}$^? state located ≦ 50 keV above the lowest $\text{11}\text{2}$^? state in each nuclide. The relatively strong populations of these $\text{7}\text{2}$^? levels in the present experiments are contrary to expectations based on the simple shell model as there are no f_{$\text{7}\text{2}$} states in the 50 < Z < 82 shell.     

Etude de 17N par la reaction 18O(t, αγ)17N

The first six excited states of ¹⁷N have been studied by using the ¹⁸Ot, αγ)¹⁷N reaction at a bombarding energy of E_t = 3.5 MeV. Alpha-gamma angular correlation measurements (method II) were used to determine spins, mixing ratios and branching ratios. The 1.37, 1.85, 1.91, 2.53, 3.13 and 3.20 MeV levels have been assigned the spins $\text{3}\text{2}$, $\text{1}\text{2}$, $\text{5}\text{2}$^?, $\text{5}\text{2}$⁺, $\text{7}\text{2}$ and $\text{3}\text{2}$ respectively. Excitation energies are also given. Most of the results are in good agreement with previous data or suggested values. Mixing ratios have been obtained for the first time. The level scheme of ¹⁷N is compared with some $\text{T =}\text{3}\text{2}$ analogue states in ¹⁷O and ¹⁷F and with results of recent shell-model calculations.     

Proton 1h112 excitations in odd-mass N = 82 nuclei

The structure of negative-parity states in odd-mass N= 82 isotones (135 ≦ A ≦ 145) is investigated in the framework of a model which is based on coupling one $\text{1h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ proton to π = + 1 states of the appropriate doubly-even isotonic core. It is shown that an effective model-space truncation can be achieved if only core states in the vicinity of the yrast line are taken into account. These have been selected from the several hundreds or even thousands of states obtained from shell-model calculations, where the $\text{1g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$, $\text{2d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$, $\text{2d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{3s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ single- are assumed to be occupied. Spectroscopic data are calculated and predictions on the structure of low-lying π = ? 1 states are discussed and compared as far as possible to experimental findings. Thereby, the particle-core coupling approach is shown to be capable of describing essential properties of negative-parity levels in the N = 82 nuclei considered.     

Radiative decays of the Jψ and evidence for a new heavy resonance

The three photon final state produced in e⁺e^? collisions has been measured at the mass of the $\text{J}\text{ψ}$ resonance using the nonmagnetic part of the double arm spectrometer DASP. The decays $\text{J}\text{ψ}\text{→ ηγ, η'γ}$ and π^oγ were observed and their branching ratios are given. A four standard deviation signal was observed in the γγ mass spectrum at a mass of (2.83 ± 0.03) GeV. An upper limit is given for the direct decay $\text{J}\text{ψ}\text{→ 3γ}$.     

Study of inclusive neutral current interactions of neutrinos and antineutrinos

We report on results from a study of hadron-energy distributions for ν and $\text{ν}$ inclusive neutral current interactions. There is no significant variation of the neutral to charged current total cross-section ratios R_ν and $\text{R}\text{ν}$ with neutrino energy. The space-time structure of neutral currents is dominated by V?A, with a significant admixture of V+A. The Weinberg-Salam model is in agreement with all data if sin²θ_w=0.24±0.02.     

Jψ and ψ′ decays into two hadrons

Branching ratios have been determined for the decays of $\text{J}\text{ψ}$ and ψ ′ into π⁺π^?, K⁺K^?, $\text{p}\text{p}$, π^±?^? and $\text{K}{}^{\mathrm{\pm }}\text{K}{}^1\text{(892)}{}^{\mathrm{?}}$. Results on a search for other two body decays of $\text{J}\text{ψ}$ and ψ′ are given. Also presented are values for the π and K from factors at $\text{s}\text{= 3.1}\text{and}\text{3.7}\text{GeV}$.     

Liquid-crystalline ordering in the solution of partially flexible macromolecules

The liquid-crystalline ordering in the solution of persistent chains which length, L, is comparable with the length of the effective Kuhn segment, l, is considered by means of a generalization of the Onsager method. The orientational entropy for this case is calculated using the method proposed by I.M. Lifshitz (for another problem) in 1968. It is shown that a slight flexibility of the persistent chain is sufficient for the complete change in the properties of the liquid-crystalline transition: for example, at $\text{L}\text{l}$～0.1 these properties are more similar to those which are characteristic for the semi-flexible limit ($\text{L}\text{l}$?1), than for the rigid rod limit ($\text{L}\text{l}$?1), although at such $\text{L}\text{l}$ the geometric form of the macromolecule is much closer to the rodlike one.     

239PuN powder neutron diffraction study

A powder neutron diffraction study has been carried out on ²³⁹PuN, which was reported to be antiferromagnetic below T = 13 K. No magnetic ordering has been detected at 4K, the limit of the magnetic ordering which could be detected being μ_ord = 0.25μ_B per Pu atom. Moreover a neutron scattering length determination of ²³⁹Pu was performed which gave a value of b_²³⁹Pu = (0.81 ± 0.05) × 10^-12 cm at neutron wavelength $\text{λ = 1.219}\text{A}\text{?}$.     

νμp and νμn charged-current interactions unfolded from high energy νμ interactions in neon

We have developed a method to separate $\text{ν}$n and $\text{ν}$p interactions from antineutrino-neon interactions by using the final state electric charge. We present the distributions of the scaling variables x and y for $\text{ν}$n and $\text{ν}$p interactions separately , along with the $\text{ν}$n and $\text{ν}$p cross section ratios as a function of x and y. We obtain a total $\text{ν}$n to $\text{ν}$p cross section ratio of 0.45± 0.08. Our results are consistent with the predictions of the simple quark parton model.     

Ferromagnetic ordering in the MMnF6 series (M = Ni,Cu, Zn,Pd)

Neutron diffraction experiments performed on MMnF₆ compounds (M = Ni, Cu, Zn, Pd) have shown that both NiMnF₆ and ZnMnF₆ crystallize in the rhombohedral R$\text{3}$ space group with a cationic ordering, whereas PdMnF₆ shows cationic disordering (R$\text{3}$c, a = 5.46 Å, α = 54.45°). CuMnF₆ has a monoclinic distortion derived from the MnF₃ structural type (a = 8.57 Å, b = 4.85 Å, c = 13.46 Å, β = 92.12°). The magnetic properties can be correlated with the structure: the R$\text{3}$ ordered compounds show a ferromagnetic behavior (T_C(NiMnF₆) = 39 K; T_C(ZnMnF₆) = 9.5 K; T_C(CdMnF₆) = 8 K), while the other two have an antiferromagnetic ordering.     

Specific heat of (C6H11NH3) CuCl3 (CHAC), a system of ferromagnetic chains

The heat capacity of (C₆H₁₁NH₃) CuCl₃ (CHAC) has been measured for 0.45 < T < 60 K. Three-dimensional ordering is observed at T = 2.214 K. The data in the paramagnetic region can be described by a ferromagnetic $\text{S =}\text{1}\text{2}$ Heisenberg linear chain model system with J/k = +45 ± 5K.