Experimental study of the neutron emission mechanisms in a Filippov-type plasma focus device

The results of an experimental investigation of neutron emission characteristics in the Filippov-type plasma focus facility Dena (90 kJ, 25 kV, 288 µF) with D₂ + %1 Kr as working gas are presented. From the experimental results, one can conclude that both thermonuclear and nonthermonuclear mechanisms are always present in neutron production, but their contributions to the total neutron yield are strongly dependent on the initial pressure and discharge voltage. It has been found that at constant discharge voltages and low pressures the beam—target interaction mechanism plays an important role in the neutron production and with increasing the pressure, its role decreases and the importance of thermonuclear mechanism increases. Also at constant pressures, the contribution of beam—target interaction mechanism in neutron production decreases with increasing the discharge energy. The value of the index in the empirical neutron yield scaling law Y_n I E^/2 was found to be about 3.82.     

Sensitivity ofn-p scattering observables to charge-independence breaking of the3 P N-N phase shifts

The sensitivity of neutron-proton scattering observables to the recently reported charge-independence breaking of the isospinT=1³ P nucleon-nucleon interaction has been calculated. It is shown that only the analyzing powerA _y () at extreme forward angles and at =90° c.m. and the spin-correlation coefficientA _zx () at 90° c.m. exhibit a measurable sensitivity. It is concluded that the determination ofA _y at 90° c.m. is currently the most accurate approach to verify independently charge-independence breaking in the³ P nucleon-nucleon phase shifts, considering the status of present experimental techniques.     

Discovery of a <Emphasis Type="Italic">P</Emphasis>-odd effect in triton emission from the reaction <Superscript>6</Superscript>Li(<Emphasis Type="Italic">n</Emphasis>, α)<Superscript>3</Superscript>H

The results of measuring the P-odd asymmetry (S_n · P_t) for triton emission from the reaction ⁶Li(n, α)³H are presented. Here, S_n is the neutron spin and P_t is the triton momentum. Three series of measurements were performed, one at the Petersburg Nuclear Physics Institute (Gatchina, Russia) in a vertical neutron beam from the PWR reactor and two in the PF1B beam from the reactor at the Institute Laue-Langevin (Grenoble, France). On the basis of all three experiments, the P-odd asymmetry coefficient was found to be α_PN = ?(8.6 ± 2.0) × 10^?8. The results of zero experiments and calculations give every reason to believe that the above P-odd asymmetry is due to the reaction being studied.     

A study of frequency and temperature dependence of ionic conductance

An approach to study the frequency and temperature dependence of the bulk ionic conductivity, based on the log-log representation of the frequency response, is described. Experimental results obtained on -PbF₂ thin-film samples are used to illustrate this approach. The analysis of these results permits to separate the different physical mechanisms involved and to model the cells. Using CPE (Constant Phase Element) Y=Y ₀(j) ⁿ for the interfaces, but also for the bulk ionic conductance, permits to fit the experimental results. A progressive increase of the slope n of the admittance which corresponds to the bulk ionic conductivity is observed when the temperature decreases. A graphical method is described which can be used to determine the activation energy in this case of a CPE behavior of the conductance. It is based on the obtention of a unique curye which describes the frequency and temperature dependence of the reduced conductance G=Y _r T plotted versus the reduced radial frequency u=. This curve shows the whole conductance variation which starts from pure transport with n=0 at low frequencies and high temperature, and tends for high frequencies or low temperatures toward the dielectric response (n1), corresponding to ion displacements limited to only one jump. The observed CPE behavior of the conductance at constant temperature thus appears to be the result of the very slow variation rate of the slope n of the reduced conductance versus the radial frequency.     

Influence of crystallisation on the photoluminescence properties of Y2-xErxTi2O7 sol-gel thin films

Optically active Er₂Ti₂O₇ (ETO) and Y_2-xEr_xTi₂O₇ (YETO) films have been successfully deposited using the aerosol-gel process. Several heat-treatment procedures are investigated in the 600–850 °C range. ETO and YETO films start to crystallise in the pyrochlore phase at about 750 °C, depending on the heat-treatment time. Crystalline YETO films form a solid solution where the erbium ions are well diluted. Up-conversion emission (UPE) in the visible wavelength range and infrared photoluminescence (PL) at 1.53 m are investigated. PL spectra are composed of several sharp peaks. Stark splitting of the ⁴I_13/2 and ⁴I_15/2 erbium levels is analysed. A clear correlation between spectroscopic properties and film microstructure is evidenced. YETO films exhibit strong PL compared to ETO films. PL lifetimes of up to 8.6 ms were measured on YETO films at an erbium concentration of 2×10²⁰ ions/cm³. The YETO compound is found to be a suitable material, improving the erbium active properties. PACS 81.20.Fw; 78.55; 78.66     

Sol–gel deposition and luminescence properties of lanthanide ion-doped Y2(1-x)Gd2xSiWO8 (0≤x ≤1) phosphor films

Y_2(1-x)Gd_2xSiWO₈:A (0x1; A=Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺) phosphor films have been prepared on silica glass substrates through the sol–gel dip-coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscope (AFM), scanning electron microscopy (SEM) and photoluminescence spectra as well as lifetimes were used to characterize the resulting films. The results of the XRD indicated that the films began to crystallize at 800 °C and crystallized completely at 1000 °C. The AFM and SEM study revealed that the phosphor films, which mainly consisted of closely packed grains with an average size of 90–120 nm with a thickness of 660 nm, were uniform and crack free. Owing to an efficient energy transfer from the WO₄^2- groups to the activators, the doped lanthanide ion (A) showed its characteristic f–f transition emissions in crystalline Y_2(1-x)Gd_2xSiWO₈ (0x1) films. The optimum concentrations for Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺ were determined to be 21, 5, 3 and 7 mol % of Y³⁺ in Y₂SiWO₈ films, respectively. The above lanthanide ions showed higher emission intensity for 02(1-x)Gd_2xSiWO₈ films. PACS 73.63.Bd; 78.55.Hx; 78.66.Nk; 81.15.Lm; 81.20.Fw     

Single \mathrm{\ensuremath{\pi^{-}}} production in np collisions for excess energies up to 90 MeV

The quasifree reaction was studied in a kinematically complete experiment by bombarding a liquid-hydrogen target with a deuteron beam of momentum 1.85GeV/c and analyzing the data along the lines of the spectator model. In addition to the three charged ejectiles the spectator proton was also detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was identified by its momentum and flight direction thus yielding access to the Fermi motion of the bound neutron and to the effective neutron 4-momentum vector _n which differed from event to event. A range of almost 90MeV excess energy above threshold was covered. Energy-dependent angular distributions, invariant-mass spectra as well as fully covered Dalitz plots were deduced. Sizeable pp FSI effects were found as were contributions of p and d partial waves. In comparison with existing literature data the results provide a sensitive test of the spectator model. The behavior of the elementary cross-section σ₀₁ close to threshold is discussed in view of new cross-section data.     

Bifurcation in a coupled logistic map. Some analytic and numerical results

We study the bifurcation pattern, two- and four-cycle generation, and supertrack functions in the case of the coupled logistic system given byX _n+1=x _n (1–2y _n ) +y _n ,Y _n+1=y _n(1-y _n ), which is of immense importance in various biophysical processes. We deduce analytic formulas for the two -and four-cycle fixed points and cross-check them numerically. The agreement is quite good. Next the bifurcation pattern is explained with the help of analytically derived supertrack functions. To discuss the stability of the system in the various zones defined by the parameter values (, ), the Lyapunov exponents are evaluated, showing a nice transition from the stable to the unstable region. An interesting phenomena occurs at=4, where the logistic itself is chaotic. We then show that near the fixed point an analytic solution can be obtained for the renormalization group equation. In the special case=1,=4 a neat analytic formula can be deduced for then-times iterated values of (x _i ,y _i ).     

Combinatorial thin film synthesis of Gd-doped Y3Al5O12 ultraviolet emitting materials

Multi-layer Y₃Al₅O₁₂:Gd thin films were deposited in a combinatorial fashion using radio-frequency magnetron sputtering. Initially, Y₃Al₅O₁₂ (yttrium aluminum garnet or YAG) films were deposited in a combinatorial fashion to optimize the Y and Al sputtering conditions. Subsequently, alternating layers of uniform Y₃Al₅O₁₂ and graded Gd were deposited and the film composition was homogenized by post-deposition 1000 °C 10-h thermal treatment. A composition range of 1–12 at% Gd was produced in two films. Ultraviolet emission with a peak wavelength at 312 nm was observed from the gadolinium ⁸S_7/2-⁶P_7/2 transition via cathodoluminescence (CL) excitation. The CL-induced intensity was found to be maximum at 5.5 at% Gd. PACS 81.15.Cd, 78.60.Hf, 02.10.Ox, 78.66.-w, 81.15.-z, 78.67.Pt     

On neutron charge structure

The aim of the present work is to investigate the charge structure of neutron by calculating its root mean square charge radius r _n ^{2 1/2} and the corresponding charge form factor,G _n(q), within the general framework of quark-parton model. The neutron (the nucleon in general) is considered to be disc-like in conformity with the idea of Lorentz invariance. Using the proton charge radius, r _p ² =0·707 fm² as input, our calculations not only reproduce the observed negative sign correctly but also give reasonable value for the magnitude of r _n ² when compared with the experimental limits. –0·16r _n ² –0·11 (fm²). Predictiona are also made for the proton and the neutron charge form factors and the results compared with the data.One of us (D. P.) would like to express his gratitude to Professor A. N. Mitra for his interest and advice in the work, and to Dr. S. M. Mustafa for the warm hospitality at the University of Mosul.     

Excitation functions of the analyzing power in elastic proton-proton scattering from 0.45 to 2.5 GeV

Excitation functions A_N(p_lab,_c.m.) of the analyzing power in elastic proton-proton scattering have been measured in an internal target experiment at the Cooler Synchrotron COSY with an unpolarized proton beam and a polarized atomic hydrogen target. Data were taken continuously during the acceleration and deceleration for proton kinetic energies T_lab (momenta p_lab) between 0.45 and 2.5 GeV (1.0 and 3.3 GeV/c) and scattering angles 30 ^° _c.m. 90^°. The results provide excitation functions and angular distributions of high precision and internal consistency. The data can be used as calibration standard between 0.45 and 2.5 GeV. They have significant impact on phase shift solutions, in particular on the spin triplet phase shifts between 1.0 and 1.8 GeV.     

Phases and phase transitions in the mixed molecular system (NaCN)1−x(KCN)x

The phase diagram of (NaCN)_1–x(KCN)_x was examined by neutron powder diffraction in the temperature range 5K T300 K. Several non-cubic low-temperature phases were identified for concentrationsx<x _c1=0.15 andxx _c2=0.89. Lattice parameters and ferroelastic deformations were determined from the observed powder patterns. The phase transformations were characterized following the temperature dependence of the appropriate order parameters.     

Superconductivity above 100 K in multi-phase Y−Ba−Cu−O

We report the synthesis, characterization and superconducting temperature of high-temperature superconducting Y_0.3Ba_0.7CuO₃, Y_0.4Ba_0.6CuO₃ and Y_1.2Ba_0.8CuO₄. The volume fraction of the superconducting phase is estimated to be of the order of 10%.HighT _c superconductivity withT _c -onsets up to 125 K (midpoint 102 K, zero resistance: 90 K) is observed in multi-phase Y–Ba–Cu–O oxygen defect compounds with the nominal composition of Y_1.2Ba_0.8CuO_4–y (0y0.4).     

Thorium fission by 4.8 and 14 MeV neutrons

The fission of natural Thorium byE _n =4.8 and 14.0 MeV neutrons has been investigated by measuring the kinetic energies of both fragments in surface barrier detectors. The fragments were detected forE _n =14.0 MeV neutron energy at 90 ° to the neutron beam, forE _n =4.8 MeV at 0 ° and 90 °. The results given are the distributions of mass and of energy correlative to the fragment mass, and the correlation between anisotropy and fragment mass atE _n =4.8 MeV. The average total kinetic energy before prompt neutron emission atE _n =4.8 and 14.0 MeV neutron energy has been found to be \(\overline {E_K^* } \) =170.47±0.03 and 168.1 ± 0.05 MeV respectively. Within the limits of statistical error the anisotropy atE _n =4.8 MeV is independent of the fragment mass. The results are analysed in the framework of the Two-Mode-Fission-Hypothesis. It appears, that the behaviour of the kinetic energy is too complicated as to be well described by the Two-Mode-Fission-Hypothesis. Both the Cluster Model of fission and the Fragment Shell Theory are suited to reproduce qualitatively the observed energetics of fission.     

Measurement of the2H(d, γ)4He reaction at intermediate excitation energies

The²H(d, )⁴He differential cross section was measured at deuteron laboratory energies of 20, 24, and 28 MeV between _cm=45° and _cm=135°. AtE _d =28 MeV a complete angular distribution was determined and fitted with Legendre polynomials. The ratioR=d/d (_cm=90°)/d/d (_cm=135°) was measured for each deuteron energy.     

Assessment of persistent-photoconductivity centers in MBE grown Al x Ga1-x as using capacitance spectroscopy measurements

Deep-level transient spectroscopy and thermally stimulated capacitance measurements were used to investigate the properties of deep traps in Si-dopedn-Al _x Ga_1–xAl layers grown by molecular beam epitaxy. Two electron traps at electron emission activation energies of 0.44 and 0.57 eV have been detected. Both traps were studied in detail and found to be the origin of the persistent-photo-conductivity phenomenon in this material. The nature of both traps is the same as of the DX center in liquid phase epitaxial material reported by Lang et al. The electron capture cross-sections are _n 1 = _n 2=8.3×10^–22cm² atT=205K. Activation energies ofE 1= 0.33eV andE 2=0.37eV at temperatures higher than 125 K were determined by DLTS measurements and by direct measurements of the capture transient. In order to allow for the variation of the free-electron concentration during the capture process, a new method for the evaluation of the electron capture crosssection was developed.     

A remark on neutron slowing down

Using the integral representation of Dirac-function the densityW _n(U) of the neutron lethargy probability distribution after then ^th collision with nuclei of a moderator has been found. The assumption has been made that the collisions are elastic and lethargy increments in individual collisions are independent. This procedure leads to expression ofW _n(U) by an improper integral which is in turn converted to a finite sum. Further the asymptotic behaviour ofW _n(U) for great number of collisionsn has been determined.Ronov pod Radhotm, Czechoslovakia.     

Copper and Copper Oxide Nanoparticle Formation by Chemical Vapor Nucleation From Copper (II) Acetylacetonate

Crystalline nanometer-size copper and copper (I) oxide particle formation was studied by thermal decomposition of copper acetylacetonate Cu(acac)₂ vapor using a vertical flow reactor at ambient nitrogen pressure. The experiments were performed in the precursor vapor pressure range of P _prec = 0.06 to 44 Pa at furnace temperatures of 431.5°C, 596.0°C, and 705.0°C. Agglomerates of primary particles were formed at P _prec0.1 Pa at all temperatures. At 431.5°C the number mean size of the primary particles increased from D _p = 3.7 nm (with geometric standard deviation _g = 1.42) to D _p = 7.2 nm (_g = 1.33) with the increasing precursor vapor particle pressure from 1.8 to 16 Pa. At 705.0°C the primary particle size decreased from D _p = 24.0 nm (_g=1.57) to D _p = 7.6 nm (_g = 1.54), respectively.At furnace temperatures of 431.5°C and 596.0°C only crystalline copper particles were produced. At 705.0°C the crystalline product of the decomposition depended on the precursor vapor pressure: copper particles were formed at P _prec>10 Pa, copper (I) oxide at P _precleq 1 Pa, and a mixture of the metal and its oxide at intermediate vapor pressures. A kinetic restriction on copper particle growth was shown, which leads to the main role of Cu₂ molecule participation in the particle formation. The formation of copper (I) oxide particles occurs due to the surface reaction of the decomposition products (mainly carbon dioxide). For the explanation of the experimental results, a model is proposed to build a semiempirical phase diagram of the precursor decomposition products.     

Photon scattering on quasi-free neutrons in the reaction γd→γ′np and neutron polarizabilities

The possibility to obtain information on n scattering at intermediate energies from the reaction dnp is analyzed. To this aim, the differential cross sectiond ³ /d ,d _n dE _n and the scattering asymmetry with linearly polarized photons are calculated at photon energies 100 to 400 MeV in the diagrammatic approach. The pole diagrams of the impulse approximation are evaluated with realistic n and p scattering amplitudes. One-loop diagrams withnp rescattering in the final state and with meson-exchange and isobar currents are taken into account as well. The main contribution to the differential cross sectiond ³ /d ,d _n dE _n in the kinematics of quasi-free n scattering arises from the neutron pole diagram. The correction due to other diagrams is typically –30% to –10% and decreases with increasing photon energy and momentum transfer. The sensitivity of the cross sections to the magnitude of the neutron electric polarizability and to the sign of the ⁰2 decay constant is demonstrated.     

EXAFS and thermal studies on zinc polymeric electrolytes

(PEO) _n :ZnX ₂ (X = I, Br) complexes were formed at room temperature with values ofn ranging from 8 to 30. Differential scanning calorimetry (DSC) results indicate that none of them contained any crystalline phases that can be associated with the formation of a complex (i.e. it can be assumed that all the salt is in the amorphous phase). EXAFS studies carried out on these samples suggest that the zinc cation is co-ordinated to two of the halide ions and, in addition, to 4 oxygen atoms whereX = I and 6 oxygen atoms whereX = Br. The DSC results confirm that the zinc cation is in an environment independent of overall stoichiometry, as the glass transition temperatures of the samples were found to be similar throughout. By comparing these with those of annealed samples (made by heating the above samples to 150°C and cooling to –80°C at 320°C min^–1) it was found that the stoichiometry of the amorphous phase was roughly 61 forX=I and 81 forX = Br.