A new level at 192.5 keV in Ge

In the experiments on ⁷⁴Ge(d, pγ)⁷⁵Ge, a 52.5±0.1 keV γ-ray was found in ⁷⁵Ge with a half-life of 216±5 ns. From the analysis of the γ-ray spectra the conversion coefficient of the 52.5 keV γ-ray was determined. Then, a new level of is confirmed to exist at 192.5 keV. The reduced transition probabilities of the 52.5 keV transition are deduced to be (6.9^+5.6 _−2.1) × 10⁻⁵ for B(M1) and 31⁺³ ₋₂ for B(E2) in Weisskopf units.     

Structural and dielectric anomaly in Na1−XKxNbO3, at x = 0.315

Structural and dielectric properties of sodium-potassium niobate (Na_1?x K_xNbO₃) (0.250?≤?x?≤?0.350) ceramics, prepared by the solid-state reaction method were investigated. Observed dielectric properties show a strong compositional dependence, at all the measured temperatures (from room temperature to 150°C) and frequencies (from 1 to 1000?kHz). In the prepared compositions, the lowest values of dielectric permittivity, loss tangent and electrical conductivity were found, and an anomaly in the shifting pattern of X-ray diffraction (XRD) peaks and change in the slope of a/c vs. x plot were observed at x?=?0.315. The observed structural and dielectric anomaly gives a morphotropic phase boundary-like indication, in Na_1?xK_xNbO₃ system, at x?=?0.315.     

Exact solution of two-species ballistic annihilation with general pair-reaction probability

The reaction processA + B → ∅ is modeled for ballistic reactants on an infinite line with particle velocitiesυ _A =c andυ _B = -c and initially segregated conditions, i.e., allA particles to the left and allB particles to the right of the origin. Previous models of ballistic annihilation have particles that always react on contact, i.e., pair-reaction probabilityp = 1. The evolutions of such systems are wholly determined by the initial distributions of particles and therefore do not have a stochastic dynamics. However, in this paper the generalization is made to p< 1, allowing particles to pass through each other without necessarily reacting. In this way, theA andB particle domains overlap to form a fluctuating, finitesized reaction zone where the product ∅ is created. Fluctuations are also included in the currents ofA andB particles entering the overlap region, thereby inducing a stochastic motion of the reaction zone as a whole. These two types of fluctuations, in the reactions and particle currents, are characterised by theintrinsic reaction rate, seen in a single system, and theextrinsic reaction rate, seen in an average over many systems. The intrinsic and extrinsic behaviors are examined and compared to the case of isotropically diffusing reactants     

Lifetimes and branching ratios of excited states of Na

The decay of ²⁴Na levels below 4.3 MeV excitation was studied by means of the ²³Na(d, pγ)²⁴Na reaction at E_d = 2.45 MeV. Gamma-ray spectra were measured at three angles, in coincidence with proton groups detected around 180°. Excitation energies, branching ratios and Doppler shifts were determined. Mean lives were obtained for the levels at 1341 keV (62±15 fs), and 1846 keV (200±50 fs). The 1347 keV level has τ >3 ps. For other levels above 1 MeV upper limits of ≈ 60 fs are set. In some cases spin restrictions follow. In particular J = 2 is assigned to the 1341 keV level.     

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). III. Rheological Kinetics of Cross‐Linking Reaction

Abstract

The kinetics of the thermally activated cross‐linking reaction of poly(vinyl methyl ether) (PVME) were investigated rheologically by evaluating the viscoelastic material functions such as elastic storage modulus, G′, viscous loss modulus, G″ and complex dynamic viscosity, η*, during the curing process, both isothermally and nonisothermally. The isothermal kinetics reaction was described using a phenomenological equation based on the Malkin and Kulichikhin model, which was predicated originally for the isothermal curing kinetics of thermosetting polymers followed by differential scanning calorimetery (DSC) and was found to be applicable for rheokinetic reactions as well. An excellent representation of the data was obtained using this model; the rate of the reaction was found to be second order regardless of the temperature, which is in good agreement with literature data. The temperature dependence of the cross‐linking rate constant was described by an Arrhenius plot with an apparent activation energy equal to 60–62 kJ mol^?1, in reasonable agreement with the value obtained previously from the temperature dependence of gel time, t _gel. The nonisothermal kinetics reaction rate was described by a model that included the classical rate equation, the Arrhenius equation, and the time–temperature relationships. The apparent activation energy obtained nonisothermally was found to be frequency independent and equal to 72 kJ mol^?1, in very good agreement with the value obtained isothermally from the temperature dependence of t _gel in part II.     

Solid-state photodimerization of 9-methylanthracene as studied by solid-state NMR

The locus of the photodimerization reaction of 9-methylanthracene in the crystal was examined by high-resolution solid-state NMR techniques. Examination of the spectra of the products showed that only the trans dimer is formed by the solid state photodimerization, while both trans and cis dimers are formed by the photodimerization in benzene solution. The T₁ relaxation curves for the monomer and the dimer at various exposure times were separately observed via well-resolved peaks. The two T₁ curves exhibit characteristic features for relaxation of a weakly coupled two-spin system. By analyzing the T₁ curves, the spin diffusion rates between the monomer and the dimer and the fraction of the dimer were obtained for various exposure times. From the result, the maximum domain size of the minor component during the photodimerization process was estimated to be ca. 0.3 μm. The heterogeneous domain structure generated by the photodimerization indicates that the reaction takes place at defects of the crystal in the monomer.     

Isoscalar quadrupole strength in Ca from the (p,p′α0) reaction at Ep = 100 MeV

The ⁴⁰Ca(p,p′ α) reaction has been studied at an incident proton energy E_p = 99.5 MeV for proton laboratory scattering angles Θ_p^lab = 17°, 23° and 27°. Emission of α particles coincident with the scattered proton has been measured for an angular range Θ_α 0° − 180° relative to the recoil axis. A multipole decomposition for the α₀-decay channel to the ³⁶Ar ground state has been performed from the angular-correlation functions. The energy distribution of the dominating E2 strength deduced in the excitation energy range E_x = 11–21 MeV agrees reasonably well with the results from electron and α-induced α₀-decay investigations. The exhaustion of the E2 energy-weighted sum rule in this channel up to an energy of 17 MeV is 16.1(4.0)%, in accord with the study of the (α, α′ α₀) reaction. However, this value is twice what is found in the (e,e′ α₀) experiment in the same energy region. Thus, the puzzling discrepancy in the E2 strengths derived from electromagnetic and hadronic probes remains unsolved.     

Surface reaction kinetics in oxygen nonstoichiometry re-equilibration of BaTiO3−δ

We report the (bare) surface redox-reaction rate constant that was determined, along with the chemical diffusivity , by a conductivity relaxation technique on Al-doped single crystal and undoped polycrystal BaTiO_3−δ as a function of oxygen activity in its range of −16≤log a_O2≤0 at elevated temperatures of 800–1100 °C. It takes a value in the range of −4<log( /cm s⁻¹)≤−1, which is even larger than that of the oxides that are considered best as oxygen membranes. It has been found that the surface reaction step grows more rate controlling as the electronic transference number gets smaller or the electronic stoichiometric composition (δ≈0) is approached. The oxygen potential drop due to the surface reaction was estimated by an oxygen concentration cell technique. The oxygen potential drop grows larger as the stoichiometric composition is approached, that is in accord with the variation of against oxygen activity.     

Peritectic phase growth in directionally solidified Cu-70% Sn alloy

The growth mechanism of the peritectic η phase involving the peritectic reaction and peritectic transformation in Cu-70%Sn alloy was investigated under directional solidification. The results show that a major growth mechanism in thickening of the peritectic η-layer is not the peritectic reaction but the peritectic transformation. The transformation temperature and isothermal time play crucial roles in determining the volume fraction and the thickness of the peritectic η phase. With the increase of the temperature and isothermal time, the volume fraction of the peritectic η phase increases. The regressed data show that the relationship between the thickness of η phase (Δx) and the transformation temperature (T) meets the following equation In Δx=6.5−1673 1 / T. Additionally, there exists a relationship between the thickness of the η phase (Δx) and the isothermal time (t) at the 9 mm solidification distance below the peritectic reaction interface, Δx=0.72t ^1/2, which is consistent with the theoretical model. Supported by the National Science Foundation of China (Grant No. 50395102)     

Molecular dynamics simulation of the vapour → liquid transition of argon and the reaction coordinate of condensation

We have investigated the n-dependences of the rate constants of absorption and emission of monomers that are attached to and detached from the cluster of n monomers, and have determined n*, the number of monomers that form the critical nucleus of the homogeneous condensation of the Lennard-Jones?Ar vapour. The dynamics was clearly separated into two regions at the critical nucleus; n* did not, however, give the unique dividing point. The observed strong dependences of both the nucleus size and the barrier height of the nucleation on the induction time of the condensation suggest that a slowly changing variable instead of the cluster size is necessary as the reaction coordinate of the nucleation. Although the slow variable is not well characterised at the present stage of the investigation, it seems to be related to the local density of the gas atoms around the liquid-like clusters. Both the slow evolution of the radial distribution function of the gas atoms around the liquid-like atoms, and the correlation between n* and the onset of the condensation indicate that Gibbs energy curves represented in n-space change significantly with the activation of the slow variable.     

Pseudo five-component synthesis of bis-α-acyloxy-β-diketo amides from diimide-dicarboxylic acids

Diimide-dicaboxylic acids derived from condensation of α-amino acids with the 2,3,5,6-bicyclo[2.2.2] oct-2-enetetracarboxylic-2,3:5,6-dianhydride or 1,2,4,5- bezenetetracarboxylic-1,2:4,5-dianhydride react with ninhydrin and isocyanides to produce some novel interesting bis-α-acyloxy-β-diketo amides.     

Renormalization group study of theA+B→⊘ diffusion-limited reaction

TheA+B diffusion-limited reaction, with equal initial densitiesa(0)=b(0)=n ₀, is studied by means of a field-theoretic renormalization group formulation of the problem. For dimensiond>2 an effective theory is derived, from which the density and correlation functions call be calculated. We find the density decays in time as ford<4, with =n ₀ –Cn ₀ ^d/2 +..., whereC is a universal constant andC is nonuniversal. The calculation is extended to the case of unequal diffusion constantsD _A D _B , resulting in a new amplitude but the same exponent. Ford2 a controlled calculation is not possible, but a heuristic argument is presented that the results above give at least the leading term in an =2–d expansion. Finally, we address reaction zones formed in the steady state by opposing currents ofA andB particles, and derive scaling properties.     

Cross sections and asymmetries for the reaction from threshold to 1 GeV

Total cross sections, differential cross sections and asymmetries for the reaction from threshold to 1 GeV have been measured. The outgoing π⁰ was detected by a 4π neutral meson spectrometer. Our data are compared with the corresponding np→NNπ^± reactions. The isoscalar partial cross sections are extracted from the relevant total cross sections. They are significant throughout the whole energy range. Below the Δ-region, energy-integrated differential cross sections show a large anisotropy difference between the neutral and charged pion channels, respectively. A partial-wave fit shows that the initial T = 0 state is dominated by the ³D₁ wave in this energy region. Finally, predictions of phenomenological models give reasonable good account of the measured observables but cannot reproduce the sign of the asymmetries.     

Synthesis of NaxMoO3 crystals through high pressure solid-state reaction

We report growth of high-purity single crystals of the sodium molybdenum bronzes Na_xMoO₃ through high pressure solid-state reaction routes. Our results demonstrate that the crystallite sizes of Na_xMoO₃ can rapidly grow to ～25?μm under a moderate pressure of 4.0?GPa in just 10?min. This discovery provides a starting point for the growth of large single crystals of alkali metal molybdenum bronzes under high pressure.     

Chromatic Spatial Summation at Equiluminance

The effect of spatial summation on chromatic detection at suprathreshold levels for the red-green and yellow-blue chromatic opponent mechanisms has been studied using simple reaction time (RT) as a measurement of the response. We varied the target size in the experiments from 8 min of arc in diameter to 10 deg, and the hue-substitution paradigm was adopted to generate only chromatic changes in the cone input. Equiluminant stimuli were distributed along three tritan and three red-green confusion lines. Three reference stimuli were chosen as both reference and adapting stimuli, in this case to determine whether the chromatic adaptation affected the spatial summation. The results showed that the mean value of RT at a constant cone-input variation, either of the L #x2212; 2M channel or of the S #x2212; (L #x002B; M) channel, against the target size decreased until a stimulus size was reached, the RT being constant for greater sizes. The spatial summation was fulfilled for a maximum target size which was less for the L #x2212; 2M channel than for the S #x2212; (L #x002B; M) channel, this size decreasing as the cone-input variation rose. Furthermore, there was no spatial summation for high-enough variations in the cone input. In addition, the chromatic mechanisms appear to organize their spatial integration with the adapting level.     

Modeling complex networks of nuclear reaction data for probing their discovery processes

Hundreds of thousands of experimental data sets of nuclear reactions have been systematically collected, and their number is still growing rapidly. The data and their correlations compose a complex system, which underpins nuclear science and technology. We model the nuclear reaction data as weighted evolving networks for the purpose of data verification and validation. The networks are employed to study the growing cross-section data of a neutron induced threshold reaction (n,2n) and photoneutron reaction. In the networks, the nodes are the historical data, and the weights of the links are the relative deviation between the data points. It is found that the networks exhibit small-world behavior, and their discovery processes are well described by the Heaps law. What makes the networks novel is the mapping relation between the network properties and the salient features of the database: the Heaps exponent corresponds to the exploration efficiency of the specific data set, the distribution of the edge-weights corresponds to the global uncertainty of the data set, and the mean node weight corresponds to the uncertainty of the individual data point. This new perspective to understand the database will be helpful for nuclear data analysis and compilation.     

Dependence on collision energy of the stereodynamical properties of the 18O + 32O2 exchange reaction

We report a quantum stereodynamical study of the ¹⁸O + ¹⁶O¹⁶O(v = 0, j = 1) → ¹⁸O¹⁶O(v′ = 0, j′) + ¹⁶O oxygen exchange reaction at four different collision energies. We calculated the polarisation moments and generated stereodynamical portraits related to the key vectors involved in this collision process. Ozone complex-forming approaches of reactants are then deduced. The results indicate that different approaches are possible but strongly depend on the collision energy and other parameters of the collision. We also conclude that the reaction globally tends to favour a perpendicular approach with increasing energy.     

Damage spreading in a single-component irreversible reaction process: Dependence of the system's immunity on the Euclidean dimension

The spreading of a globally distributed damage, created in the stationary regime, is studied in a single-component irreversible reaction process, i.e., the BK model [Browne and Kleban,Phys. Rev. A 40, 1615 (1989)]. The BK model describes one variant of the A+AA₂ reaction process on a lattice in contact with a reservoir of A species. The BK model has a single parameter, namely the rate of arrival of A species to the lattice (Y). The model, exhibits an irreversible phase transition between a stationary reactive state with production of A₂ species and a poisoned state with the lattice fully covered by A species. The transition takes place at critical points (Y _C ) which solely depend on the Euclidean dimensiond. It is found that the system is immune ford=1 andd=2, in the sense that even 100% of initial damage is healed within a finite healing period (T _H ). Within the reactive regime,T _H diverges when approachingY _C according toT _H (Y _C –Y)^–, with 1.62 and 1.08 ford=1 andd=2, respectively. Ford=3 a frozen-chaotic transition is found close toY _s 0.4125, i.e., well inside the reactive regime 0YY _C 0.4985. Just atY _S the damageD(t) heals according toD(t) t ^–, with 0.71. For the frozen-chaotic transition atd=3 the order parameter critical exponent 0.997 is determined.