Analyzing powers in the 12C( \vec d ,p)13C reaction at the energy T d = 270 MeV

The preliminary results on the tensor T₂₀ analyzing power for the ¹²C(,p)¹³C* reaction with the excitation of ¹³C levels and the d(,p)X reaction at the energies T _d = 140, 200 and 270 MeV at the emission angle Θ _cm = 0° are presented. The data on the tensor A _yy and vector A _y analyzing powers for the ¹²C(,p)¹³C* reaction at the energy T _d = 270 MeV in the angular range from 4° to 18° in the laboratory are also obtained.     

Analyzing powers Ayy , Axx , Axz and Ay in the dd → 3Hen reaction at 270 MeV

The data on the tensor A_yy, A_xx, A_xz and vector A_y analyzing powers in the dd → ^3Hen obtained at T _d = 270 MeV in the angular range 0^° - 110^° in the c.m. are presented. The observed negative sign of the tensor analyzing powers A_yy, A_xx and A_xz at small angles clearly demonstrate the sensitivity to the ratio of the D - and S -wave component of the ³He wave function. However, the one-nucleon exchange calculations by using the standard ³He wave functions have failed to reproduce the strong variation of the tensor analyzing powers as a function of the angle in the c.m.     

Transverse beam asymmetries measured from <Superscript>4</Superscript>He and hydrogen targets

The HAPPEX Collaboration at Jefferson Lab has measured the transverse beam spin asymmetries (A_T) for elastic electron scattering from proton and ⁴He targets. The experiment was conducted using a vertically polarized electron beam of energy ∼ 3 GeV, at a Q ² ∼ 0.1 GeV^2 and a scattering angle θ_lab ∼ 6^° . The preliminary results are reported here. The ⁴He measurement is the first measurement of A_T from a nucleus. A_T for ⁴He is non-negligible; therefore, it will be necessary to make measurements of A_T for future parity-violating experiments using nuclear targets.     

New results from the HAPPEX Experiments at Q<Superscript>2</Superscript> = 0.1GeV/c<Superscript>2</Superscript>

The nucleon's strange electric and magnetic form factors G _E ^s and G _M ^s can be probed via parity-violating electron scattering. The HAPPEX Collaboration has made new measurements of the parity-violating asymmetry A _PV in elastic scattering of 3GeV electrons off hydrogen and ⁴He targets with 〈θ_lab〉 ≈ 6.0^° . For ⁴He the preliminary result is A _PV = (+ 6.43±0.23(stat)±0.22(syst))×10^-6 . For hydrogen the preliminary result is A _PV = (- 1.60±0.12(stat)±0.05(syst))×10^-6 . From these values we extract G ^s _E = 0.004±0.014±0.013 at 〈Q ²〉 = 0.077 GeV/c^2 , and G ^s _E +0.09G ^s _M = 0.004±0.011±0.005 at 〈Q ²〉 = 0.109 GeV/c^2 , both consistent with zero, providing stringent new limits on the role of strange quarks in the vector structure of the nucleon.     

Synthesis and characterization of the new high pressure phases ACu3 V4O12(A=Gd,Tb, Er)

New ACu₃V₄O₁₂ (A=Gd, Tb, Er) phases have been prepared at high pressure and high-temperature conditions (P～8–9 GPa, T～1000°C) in a toroid-type high pressure cell. These compounds crystallize in the cubic symmetry with a perovskite-like structure. At ambient pressure, they are paramagnetic and have activation-type conductivity. The effect of high pressure (10–50 GPa) on the electrical properties of the materials was analyzed in the temperature range from 78 to 300 K. Pressure ranges of the transition from activation type to metallic conductivity have been determined. The crystal structure of ACu₃V₄O₁₂ (A=Gd, Tb, Er) was found to be stable up to 50 GPa.     

Optically detected E.P.R. and low-field ENDOR of triplet benzophenone

The ENDOR spectrum of ¹³C substituted (carbonyl carbon) triplet excited benzophenone was studied at ca. 100 G applied magnetic field by means of optical detection. The benzophenone was substitutionally dissolved in dibromodiphenylether (DDE). The ENDOR transitions and the E.P.R. transitions were studied as a function of applied field direction in the ab and bc crystal planes. The angle ? between the line joining the phenyl group centres and a principal axis of the fine structure tensor was found to be 23·6° ± 0·02° (standard deviation limited to one set of measurements). The principal axes of the ¹³C hyperfine tensor were within experimental error (±10°) coincident with the fine structure axes. The principal values of the hyperfine tensor were found to be : |A_xx /h| = 43·16 ± 1·84, |A_yy /th| = 22·66 ± 2·50, |A_zz /h| = 10·25 ± 1·30 MHz. The low-field ENDOR does not provide an indication of the signs of these tensor elements, so the value of the isotropic coupling constant cannot be measured. Two values of the anisotropic (dipole) hyperfine tensor elements were deduced on the assumption that the transitions frequencies are mainly determined by interactions between the nuclear spin and electron density on the carbonyl carbon atom. These values were (i) A _xx / ^d /h = 17·82, A_yy /h = -22·68, A_zz /h = -15·14 MHz and (ii) A_xx /h = 39·73, A_yy /h = -26·09, A_zz /h = -13·63 MHz. Set (ii) is consistent with recent calculations of the spin density distribution in triplet benzophenone in which the orbital spin densities are 0·64 for the carbonyl carbon π-orbital, 0·17 for the oxygen π-orbital, and 0·88 for the non-bonding orbital on oxygen (all expressed as fractions of one electron).

Isotope effects on the fine structure constants of triplet benzophenone were measured and found to be consistent with the changes occurring in the spin-orbit coupling with the ground state.

The kinetic parameters for the excitation and de-excitation of the triplet substates were deduced from transient ODMR studies of benzophenone in DDE. The T_z spin state is mainly populated (85–88 per cent) and this is also the most strongly radiative state (k_z ^r = 0·88). The steady-state populations of the three triplet levels are similar.     

High resolution gamma-ray spectroscopy of the27Al(p,γ)28Si resonance reaction

High resolution gamma-ray spectra have been measured from the²⁷Al (p,γ)²⁸Si reaction for the resonances atE _p=2·482, 2·511 and 2·735 MeV at ϑ _pγ=0°, 30°, 55° and 90° using a Ge (Li) gamma spectrometer. From the spectra and the angular distributions the properties of the resonance states have been obtained. These states are the isobaric analogues of the levels at 4·69, 4·75 and 4·93MeV levels respectively in the parent nucleus A²⁸l.     

Further study on the influence of thermal treatments on the glow curve structure in LiF:Mg,Cu,P (GR-200A)

The influence of various annealing treatments with heating temperatures (T_A) from 240 to 700 °C, with re-annealing at 240 °C, and with a combined re-annealing procedure of 20 min at 270 °C followed by 10 min at 240 °C on LiF:Mg,Cu,P (GR-200A) was investigated. As the T_A increased, the intensity decreased rapidly to almost no signal at 340–380 °C then increased clearly and achieved a maximum at 540 °C. The position of the maximum intensity of the glow curve shifted basically in the direction of higher temperatures with an increase at T_A and achieved a maximum of 279 °C when annealed at 460 °C. The re-annealing influenced both the intensity and the glow curve structure at certain degree. The effect of re-annealing on the glow curve depended markedly on the T_A. With re-annealing at 240 °C, the intensity decreased as T_A increased up to 360 °C then increased and achieved a maximum at 540 °C. The intensity could be restored fully when annealed at above 500 °C, however, the glow curve couldn't be restored fully. With a combined annealing, the shape of glow curve of a sample annealed at above 540 °C or below 320 °C was similar to that of the standard glow curve of LiF:Mg,Cu,P and the intensity and glow curve could be restored completely when annealed in the range 620–660 °C. It seems that the main roles of the re-annealing at 240 °C are to restore partially the intensity of peak 4 and peak shape for LiF:Mg,Cu,P when annealed at above 260 °C, and restore fully the total TL intensity of LiF:Mg,Cu,P when annealed at above 500 °C and the main roles of the combined re-annealing are to reduce the intensity of peak 5 and the total TL intensity, increase the intensity of peak 4 and restore the glow curve shape.     

Broad-line NMR investigation of the amorphous component of poly(trans-1,4-butadiene) and poly(4-methyl pentene-1) crystals wetted by carbon disulfide

Broad-line (proton) NMR measurements were made at temperatures from -15 to -96°C on crystals of poly(4-methyl pentene-1) wetted with a nonprotonated solvent, CS₂. The mobile fraction, A_n, is found to depend on the crystal morphology and subsequent annealing treatments of dried crystals. A_n varies with temperature in the -30 to -70°C region; changes in the slope of the A_n vs temperature plot in this region with annealing treatment are interpreted in terms of changes in the amorphous portions of the lamellae. Previous NMR results for poly(trans-1, 4-butadiene) have been reanalyzed and the new A_n values obtained are given; annealing dry PTBD crystals at 80°C is shown to bring about a significant decrease in A_n.     

Enthalpy Relaxation Study of Poly(Vinyl Chloride) Films Based on the Time-Temperature Superposition Principle

Abstract

In the enthalpy relaxation of poly(vinyl chloride), a decrease in enthalpy upon the isothermal ageing was measured using the differential scanning calorimetry method as a function of ageing time (t_A) and ageing temperature. The range of the ageing temperature was from 56?°C (T_g ? 25?°C) to 72?°C (T_g ? 9?°C) where T_g denotes the glass transition temperature. The limiting value of the decrease in enthalpy was determined by applying a stretched exponential function to the measured enthalpy data. The relaxation function (?) was derived from the measured enthalpy and the construction of a master curve was tried by shifting the ? ? t_A curves of the respective ageing temperatures horizontally. Although there was no agreement between the shift factors (a_T) and the relaxation times of the ? ? t_A curves, the superposition was successfully constructed and the a_T values obtained for the poly(vinyl chloride) sample were found to be comparable to those reported for viscoelastic experiments over a broad temperature range above and below T_g carried out for different polymers. The origin of the decrease in enthalpy was briefly discussed in terms of the chain dynamics in the isothermal condition.     

Study on the local structure and EPR spectroscopy of compressed CuX4 (X = N,S, Cl and Br) tetrahedral cluster

The spin Hamiltonian parameters g and A for copper(II) in CuX₄ (X = N, S, Cl and Br) tetrahedrons are theoretically investigated within a uniform model by utilizing the perturbation method and cluster approach for 3d⁹ ions suffering D_2d symmetry in view of host structures and angular distortions in terms of a single parameter β. For all the studied polymers, the isotropy of g tensors g_av and the hyperfine structure constant component A_‖ are found, respectively, to undergo an increasing and decreasing trend with the enlarging average X–Cu–X angle β, while the obtained cubic crystal field parameter D_q and isotropic Fermi contact constant κ are experiencing a declining and growing tendency with the rising Cu–X bond length, respectively. The critical angle β_c is concluded locating in the range of 109.471°–120° in which the g-isotropy value would reach the maximum, while the hyperfine structure factor might vanish that needs to be verified in future X-ray and EPR experiments. This work would be beneficial to the establishment of complete EPR and structure diagram for CuX₄ complexes and the synthesis of new compounds possessing novel physical and chemical properties.     

Photopolymerization in the Fullerene Layers of the Molecular Donor–Acceptor Complex {Pt(nPr2dtc)2} · (C60)2

We measured Raman spectra in crystals of molecular donor–acceptor fullerene complexes {Me(nPr₂dtc)₂} · (C₆₀)₂ (Me = Ni, Cu, Pt). In the spectra of the {Pt(nPr₂dtc)₂} · (C₆₀)₂ complex under prolonged irradiation with a laser with λ = 532 nm, characteristic changes in the photopolymerization of fullerene are observed, associated with the splitting of degenerate phonon Hg modes and softening of Ag modes of the C₆₀ molecule. The kinetics of photopolymerization under conditions of weak irradiation at room temperature is studied. It was found that thermal destruction of the photopolymer with increasing temperature leads to a decrease in its concentration in the final photopolymerization product. The kinetics of thermal destruction is described by the Arrhenius equation, with the activation energy E_A of (0.68 ± 0.03) eV; the dimers are destructed to a concentration of 1% within 15 min at ~114°C.

     

The analyzing power Aγ(θ) for the elastic scattering of 12 MeV neutrons from deuterons

The analyzing power A_γ(θ) was obtained at 10° intervals between 30° (lab) to 120° (lab) for ²H(n, n)²H at 12.0 MeV. The polarized neutron beam employed in the measurement was obtained by using neutrons emitted at 0° from the polarization transfer reaction ${}^2\text{H}\text{(}\text{d}\text{,}\text{n}\text{)}{}^3\text{He}$. The accuracy in the A_γ(θ) values that was achieved ranged from ± 0.006 to ± 0.013. Comparison of the data to A_γ(θ) results obtained at 12 MeV for the charge symmetric reaction ²H(p, p)²H shows that the two A_γ(θ) distributions are equal to within the above accuracy.     

Synthesis and Raman characterization of mono-sized single-wall carbon nanotubes in one-dimensional channels of AlPO4-5 crystals

Mono-sized single-wall carbon nanotubes were formed in one-dimensional channels of AlPO₄-5 single crystal (AFI) by pyrolysis of tripropylamine (TPA). Raman spectra have been measured for the TPA-AFI crystals thermally processed at different conditions. TPA molecules are carbonized at 400 °C, and carbon nanotubes were formed at 500 °C or above. The radial-breathing mode, which is special for carbon nanotube geometry, was observed. Three Raman-active modes with symmetry A _1g, E _1g, and E _2g were identified by detailed symmetrical analysis for the polarized-Raman spectra. Received: 29 October 1998 / Accepted: 29 March 1999 / Published online: 24 June 1999     

The permittivities of PVDF/PMMA blends at hydrostatic pressure

The complex permittivities of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends have been measured under variation of temperature T(20°-60°C), frequency v(5 Hz-300 kHz), and hydrostatic pressure p (0-260 MPa). The values can be represented by a master curve with the shift factors △p/△ log (v/Hz) = ?140 MPa at room temperature and △ (1 /T) /△ log (v/Hz) = ?2. 10^?4 K^?1 at atmospheric pressure. The dependence of the activation energy △E _A on pressure p is then given by △E _A=(100 + 0.02 MPa^?1 p) kJ/mol. Furthermore, the results indicate that the β-relaxation of PVDF is due to motions in the crystal-amorphous interphase. The interactions between the two polymers, which are miscible at all compositions, disturb the correlations between the PVDF monomer units at that location as well as the mobility of the PMMA side group.     

Measurement of the differential cross section and of the tensor and vector analyzing powers for the fragmentation of 4.5-GeV/c deuterons on beryllium in the reaction involving proton emission at an angle of 80 mrad

The invariant differential cross section, the tensor analyzing power A _yy , and the vector analyzing power A _y for the reaction ⁹Be(d, p)X are measured at an initial deuteron momentum of 4.5 GeV/c and a proton detection angle of about 80 mrad. The data obtained for the differential cross section are consistent with the results of measurements at 3.5 and 5.78 GeV/c and a proton emission angle of 2.5°. The values found for the tensor analyzing power A _yy are compared with similar data obtained previously for the deuteron-fragmentation process occurring on a carbon target at various values of the initial deuteron momentum and leading to proton emission at zero angle. The data on the differential cross section for the reaction ⁹Be(d, p)X can be satisfactorily described within the relativistic impulse approximation by using standard deuteron wave functions; however, the approach based on this conceptual framework proves to be inadequate in dealing with data on the tensor analyzing power. These results indicate that it is necessary either to change the method for describing the relativistic deuteron or to take into account additional mechanisms.     

Nonleptonic Interactions of Kaons in the Quark Confinement Model

Nonleptonic, electromagnetic decays of K-mesons and K°–K̄° transition are treated with the effective Hamiltonians with ΔS = 1, 2. Matrix elements of four-quark operators are calculated in the framework of Quark Confinement Model. The account of the intermediate scalar mesons turns out to allow to explain ΔI = 1/2 rule. The account of intermediate scalar and pseudo-scalar states leads to experimental value of mass difference of K_L°–K_S° mesons. The obtained values for nonleptonic and electromagnetic decay widths as well as mass difference Δm_LS are in good agreement with experimental data.     

Measurement of the spin correlation Aookk in pp elastic scattering from 0.88 to 2.7 GeV

The spin correlation parameter A_ookk in pp elastic scattering was measured using the SATURNE II polarized proton beam and the Saclay frozen spin polarized target. The measurements at 0.88 and 1.1 GeV were carried out in the angular region θ_CM from 28° to ⋍ 50° and complete our previous measurements from 45° to 90°. Above 1.1 GeV the measurements presented here cover both regions, extending from θ_CM = 28° (at the lower energies) or θ_CM = 18° (at the higher energies) to θ_CM > 90°. The shape of the angular distribution A_ookk (pp) = f(θ_CM) changes considerably between in our energy region.     

Electron spin resonance studies of chlorine centres in irradiated chlorine-doped Na2SO4 single crystals

The nature of paramagnetic centres trapped in X-irradiated Na₂SO₄ single crystals containing chlorine as impurity has been determined from E.S.R. measurements both at room and liquid nitrogen temperatures. ClO₃, ClO₂, SO₄ ^- and O₃ ^- are the paramagnetic centres identified. The g and A parameters of ClO₃ change considerably between 298 K and 77 K. Thus the parameters of ClO₃ obtained at 298 K are g_xx = 2·0123, g_yy = 2·0143, g_zz = 2·0206 G and those of the A-tensor are A_xx = 97, A_yy = 100 and A_zz = 112 G. The parameters obtained for the same centre at 77 K are g_xx = 2·0132, g_yy = 2·0173, g_zz = 2·0073 G and those of the A-tensor are A_xx = 130·6, A_yy = 146·3 and A_zz = 181·2 G. The temperature variation of the principal values are determined in the temperature range between 298 K and 77 K. These data can be interpreted on the assumption that ClO₃ undergoes libration at room temperature, which is frozen out reversibly on cooling. The structure and mechanism of these defects are discussed further.     

Ferroelectric elastance of sodium niobate-lithium niobate solid solutions in relation to A-O bond covalence

The ferroelectric elastance of (Na, Li, A _0.5 ^′ )NbO₃ solid solutions was found to vary directly with the total electronegativity of elements A (EN _{∑ A} ), that is, with the A-O bond covalence at B=const. Using EN _{∑ A} values and the position on the phase diagram, one can determine the solid solution parameters optimum for use in high-frequency (A′=Sr, Pb), medium-frequency (A′=Cd), and elevated-temperature (A′=Cd) devices.