A monte-carlo/molecular dynamics study of the diffusional recombination kinetics of C(a) + O(a) → CO(g) on Pt(111)

The diffusion constants for C and O adsorbates on Pt(111) surfaces have been calculated with Monte-Carlo/Molecular Dynamics techniques. The diffusion constants are determined to be D_C(T)=(3.4 × 10^?3e^{$\text{?13156}\text{T}$})cm²s^?1 for carbon and D_O(T) = (1.5×10^?3 e^{$\text{?9089}\text{T}$}) cm² s^?1 for oxygen. Using a recently developed diffusion model for surface recombination kinetics an approximate upper bound to the recombination rate constant of C and O on Pt(111) to produce CO_(g) is found to be (9.4×10^?3 e^{$\text{?9089}\text{T}$}) cm² s^?1.     

On the QCD perturbative predictions for the signal ofW± production in hadronic collisions

Evidence for the intermediate bosons in high energy pp and p?p collisions as signal in the cross section of large p_T charged lepton pp, $\text{p}\text{p}\text{→}\text{W}{}^{\mathrm{\pm }}\text{+}\text{X}$, W^±→?^±ν_? is considered for CM energy range $\text{s}\text{=100?800}\text{GeV}$. Besides the usual Drell-Yan term which gives a very sharp peak in the lepton p_T distribution, the first order QCD contribution is included thus producing the intermediate boson with transverse momentum and smearing the lepton distribution. Scaling violation of the structure functions is incorporated and compared with the case when it is absent.     

Determination of some atomic-state densities in an Xe-Br2 mixture

The atomic-state densities of the 6s[1 $\text{1}\text{2}$]⁰ metastable Xe energy level and of the 5s⁴P_{$\text{1}\text{2}$}, 5s⁴P_{$\text{3}\text{2}$} and 5s⁴P_{$\text{5}\text{2}$}Br energy levels in an Xe-Br₂ mixture have been determined as a function of current strength.     

Large-pT protons from constituent diquark scattering

Recent data from the CERN ISR on the fractional proton yield in pp collisions are explained within the Stockholm diquark model. Describing the proton as a u(ud)₀ system, the observed high magnitude and fall-off _pT, θ and $\text{s}$ of the proton yield are natural consequences of constituent diquark elastic scattering. The _pT and θ dependence favour a value of around 10 GeV²/c² for the size parameter in the diquark form factor, corresponding to a diquark rms radius of around 0.2 fm. This is consistent with earlier results of the model applied to deep inelastic lepton-nucleon scattering and e⁺e^? annihilation.     

Inclusive π0 production at very large pT at the ISR

Inclusive π⁰ production at 90° has been studied at the ISR at $\text{s}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 52.7}\text{and}\text{62.4}\text{GeV}$ over the p_T range from 7 to 15 GeV/c. The two photons from π⁰ decay yielded overlapping electromagnetic showers in the liquid-argon-Pb plate calorimeter detector system. Any direct photon production is included in these measurements. For large values of p_T, the cross section is observed to decrease with p_T more slowly than the p_T^?8 behaviour which has been observed at lower values of p_T.     

Determination of the atomic-state population in A Kr-Br2 mixture

The atomic-state populations of the 5s[1$\text{1}\text{2}$]° metastable level of Kr and of the 5s²P_{$\text{3}\text{2}$} resonant level of Br in a Kr-Br₂ mixture have been determined as functions of current strength. Occurrence of energy transfer from the Kr-level to the Br-level has been verified.     

Comparison of direct photon production in pp collisions at s= 30.6 GeV and 53.2 GeV

We present data obtained at the ISR, on the determination of the ratio $\text{R =}\text{γ}\text{π}{}^0\text{at}\text{s}\text{= 30.6}$ GeV and we compare the results with our previous measurement at $\text{s}\text{= 53.2}$ GeV. The ratio $\text{R =}\text{γ}\text{π}{}^0$ integrated over the interval 0.1 ? χ_T ? 0.2 is (1.6 ± 0.5) × 10^?2 and we obtain an indication of a universal χ_T dependence.     

The Grüneisen parameter γ of KBr,RbCl and Bi through high pressure phase transitions

High pressure values for the adiabatic pressure derivative of temperature $\text{(}\text{?T}\text{?P}\text{)}{}_{\mathrm{s}}$ have been obtained by measuring the temperature change caused by a small rapid increase in pressure. Values for KBr and RbCl in phases B1 and B2 and for Bi in phases I, II and III are given for T = 295 K. The Grüneisen parameter γ is given by $\text{γ =}\text{B}{}_{\mathrm{s}}\text{(}\text{?T}\text{?P}\text{)}{}_{\mathrm{s}}\text{T}$ where B_s is the adiabatic bulk modulus. Ultrasonic and statk compressibility data are used to estimate the pressure and phase dependence of B_s. Dramatic increases in both γ and (?T/?P)_s are observed as the pressure increases through a phase transition. Values for the logarithmic derivate $\text{q ≡ (? ln}\text{γ}\text{?}\text{ln V}{}_{\mathrm{T}}$ are given.     

The cosmic microwave background and the hadron era of the early universe: A possible connection

A cosmological model is constructed which is a Friedman model, but with a finite ultimate temperature (T_F). A plausible argument is presented which suggests that the existence of T_F and the cosmic microwave background restricts the form of the hadronic level density:

, where A, B = constants. In our model, $\text{B =}\text{7}\text{2}\text{?}\text{3}\text{s}\text{,}\text{where}\text{s =}\text{positive}$ integer. The case $\text{s = 3 (B =}\text{5}\text{2}\text{)}$ is the well-known Hagedorn model; the Frautschi model corresponds to s = 6 (B = 3); the cases $\text{s = 1 (B =}\text{1}\text{2}\text{)}$ and s = 2 (B = 2) have not been considered before now. For each value of $\text{B <}\text{7}\text{2}$, the model gives the temperature (T_γ0) of the microwave background as a function of A, T_F and ?₀ (the present energy density of the universe). Two fascinating results then emerge: first, all estimates of T_γ0 favor a low density Friedman universe (?0 = 10^?31g/cm³), which rules out a universe with positive curvature; second, for ?₀ = 10^?31gr/cm³ the best estimate of T_γ0 (?3K) occurs for the Hagedorn model.     

Study on vacancy motion in Y2O3-doped CeO2 by 17O NMR technique

The ¹⁷O NMR measurement was made to elucidate the microscopic nature of vacancy motion in Y₂O₃-doped CeO₂. Spin-lattice relaxation rate, T^?1₁, spin-spin relaxation rate, T^?1₂, and resonance intensity were measured at v₀ = 8.13 MHz as a function of temperature [385 < T (K) < 1110] and composition [$\text{0.06 <}\text{Y}{}_2\text{O}{}_3\text{(}\text{m}\text{o}\text{) < 6}$]. The static electric field gradient associated with lattice defects resulted in the composition dependences of the line width and the intensity. In low dopant concentrations, doubly peaked temperature dependence of T^?1₁ was found, while a single and asymmetric peak was observed in high concentrations. T^?1₁ of 4.0 and 6.0 $\text{m}\text{o}$ doped samples were analyzed using a barrier height distribution model for the oxygen vacancy jump. The mean value of the activation energy was found to increase with the Y₂O₃ concentration.     

High pT π0 production from αα and αp collisions at the CERN ISR

The invariant cross sections for π⁰ meson production in alpha—alpha and alpha—proton collisions at the ISR were meas- ured up to transverse momenta of $\text{7}\text{GeV}\text{c}$ and $\text{8}\text{GeV}\text{c}$, respectively. These measurements are compared with π⁰ production in pp collisions at the same values of $\text{s}\text{/}$nucleon, and the variation of the nuclear A-dependence with p_T is determined.     

Excitation of bromine by means of krypton in Kr-Br2 mixtures

The atomic-state populations of the 5s⁴P_{$\text{3}\text{2}$} and 5s⁴P_{$\text{1}\text{2}$} resonant levels of Br in a Kr-Br₂ mixture have been determined as functions of current strength. An increase in flux of Br emission lines passing into 5s levels has been observed.     

Crystal growth,structure, electron paramagnetic resonance and magnetic properties of (NH4)2V3O8

A method to grow single crystals of ammonium vanadate (IV, V) (NH₄)₂V₃O₈ has been devised. The crystal structure is tetragonal P4bm; residual factor is R = 0.030. Cell parameters are $\text{a = 8.891 ± 0.004}\text{A}\text{?}$ and $\text{c = 5.582 + 0.002}\text{A}\text{?}$. The V⁵⁺ atom lies at the center of a triangular pyramide (VO₄ tetrahedron) while the V⁴⁺ atom is on A 4-fold rotation axis at the center of a square-based pyramide VO₅ whose symmetry point group is almost C_4v with the short V = O bond lying along the 4-fold axis parallel to the c edge of the tetragonal cell. Crystals are thin platlets with (001) cleavage planes. The platlets have very often a square or rectangular shape limited by {100} or {110} planes. Each single crystal was not large enough to record a good e.p.r. spectrum, but by sticking on the same quartz plate a score of them it was possible to gather enough crystals so to record correct spectra and by orienting the plate to obtain resonance lines separately for g_∥ = 1.9263 et g_τ = 1.9755. Measurements at 283 K on powder samples gave times for spin-spin relaxation T₂ = 0.4 × 10^?7s and for spin-lattice relaxation T₁ = 1.6 × 10^?7s. The magnetic structure is characterized by an exchange narrowing ω_e = 3 × 10¹⁰rad/s which corresponds to a transition temperature of about 0.5 K. Static susceptibility measurements at high magnetic field show a paramagnetic behaviour with an antiferromagnetic interaction which is interpreted in the magnetic space group P_2c4bm as the interaction between V⁴⁺ ions from consecutive planes parallel to (001).     

87Rb NMR lineshape study of the incommensurate phase in Rb2ZnBr4

On going from the paraelectric (P) to the incommensurate (I) phase the ⁸⁷Rb $\text{1}\text{2}$ → $\text{1}\text{2}$ NMR lines in Rb₂ZnBr₄ broaden into a continuum which is limited by two edge singularities. The observed line shape and its temperature dependence are well described by the frequency distribution function predicted by the “plane wave” modulation model of the I phase. The anomalous temperature dependence of T₁ shows the presence of the phason branch in the I phase.     

Temperature and pressure dependence of the elastic property of GeS2 glass

The sound velocities in GeS₂ glass have been measured by means of ultrasonic interferometry as a function of temperature or pressure up to 1.8 kbar. The bulk modulus K_s = 117.6 kbar and shear modulus G = 60.60 kbar were obtained for GeS₂ glass at 15°C and 1 atm. The temperature derivatives of both sound velocities and elastic moduli are negative :

$\text{(}\text{?ν}{}_1\text{?T}\text{)}$

_p =

$\text{?1.54 × 10}{}^{\mathrm{?4}}\text{km}\text{sec}$

°C,

$\text{(}\text{?ν}{}_1\text{?T}\text{)}$

_p =

$\text{?1.27× 10}{}^{\mathrm{?4}}\text{km}\text{sec}$

°C and

$\text{(}\text{?K}{}_{\mathrm{s}}\text{?T}\text{)}$

_p =

$\text{?1.27 × 10}{}^{\mathrm{?2}}\text{kbar}\text{°C}$

,

$\text{(}\text{?G}\text{?T}\text{)}$

_p = ?1.23 × 10^?2 kbar/°C,

$\text{(}\text{?Y}\text{?T}\text{)}$

_p = ?2.93 × 10^?2 their pressure derivatives are positive:

$\text{(}\text{?ν}{}_1\text{?P}\text{)}$

_T = 4.43× 10^?2km/kbar,

$\text{(}\text{?ν}{}_1\text{?P}\text{)}$

_T =

$\text{0.633 × 10}{}^{\mathrm{?2}}\text{km}\text{kbar}$

and (?K_s?P0)_T=6.81,

$\text{(}\text{?G}\text{?P)}{}_{\mathrm{T}}$

= 1.03, (?Y?T_T= 3.57. The Grüneisen parameter, γ_th= 0.298, and the second Grüneisen parameter, δ_s = 3.27, have also been calculated from these data. The elastic behavior of GeS₂ glass has proved to be normal despite the structural similarity among the tetrahedrally coordinated SiO₂, GeO₂ and GeS₂ glasses.     

Tensor interaction in heavy-ion scattering: (I). The turning-point model

The Heidelberg shape-effect model for heavy-ion tensor interactions is reformulated and generalized using the Hooton-Johnson formulation. The generalized semiclassical model (the turning-point model) predicts that the components of the tensor analysing power $\text{T}{}_{\mathrm{2q}}$ have certain relations with each other for each type of tensor interaction (T_R, T_P and T_L types). The predicted relations between the $\text{T}{}_{\mathrm{2q}}$ are very simple and have a direct connection with the properties of the tensor interaction at the turning point. The model predictions are satisfied in quantum-mechanical calculations for ⁷Li and ²³Na elastic scattering from ⁵⁸Ni in the Fresnel-diffraction energy region. As a consequence of this model, it becomes possible to single out effects from a T_P? or T_L-type tensor interaction in polarized heavy-ion scattering. The presence of a T_P-type tensor interaction is suggested by measured $\text{T}{}_{20}\text{/}\text{T}{}_{22}$ ratios for ⁷Li+⁵⁸Ni scattering. In the turning-point model the three types of tensor operator are not independent, and this is found to be true also in a quantum-mechanical calculation. The model also predicts relations between the components of higher-rank tensor analysing power in the presence of a higher-rank tensor interaction. The rank-3 tensor case is discussed in detail.     

Thermal changes in the optical properties of SnSxSe2−x crystals

Optical measurements on crystals in the series SnS_xSe_2?x for 0 ? x ? 2, have yielded information on the changes in the ordinary refractive index $\text{Δn}\text{ΔT}$ and the energy gap $\text{ΔEg}\text{ΔT}$ in the temperature range 125–425 K. The coefficient $\text{Δn}\text{ΔT}$ has values +40 to +160 × 10^?6K^?1 and this confirms that covalent bonding predominantly exists in these materials. The coefficient $\text{ΔEg}\text{ΔT}$ remains fairly consistent for all values of x with an average value of -8.0×10^-4eV K^-1.     

Decays of 185m + gHg: Low-spin levels of 185Au as a test of nuclear models

The decay of ^{185m + g}Hg has been studied on-line with mass-separated sources from the ISOCELE facility. Precise conversion-electron measurements were performed with a 180° spectrograph. The $\text{13}\text{2}{}^{\mathrm{+}}$ isomeric state of ¹⁸⁵Hg ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 28 ± 5 s}$) was located with respect to the $\text{1}\text{2}$^? ground state ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 55 ± 10 s}$). A level scheme of ¹⁸⁵Au has been established. Two abnormally converted M1 transitions de-excite a state local at 330.2 keV. Excited states of ¹⁸⁵Au have been discussed in the framework of a “quasi-particle + axial rotor” approach, quasi-particle states being issued from Hartree-Fock plus BCS calculations using the SIII Skyrme force. Most of the low-spin negative-parity levels have been identified as h_{$\text{9}\text{2}$} + f _{$\text{5}\text{2}$} or p_{$\text{3}\text{2}$} + f_{$\text{7}\text{2}$} mixed states. The h_{$\text{11}\text{2}$} system has also been discussed using a model of asingle-j quasi-particle coupled to a triaxial rotor.     

Semi-inclusive scaling for largepT events

We consider semi-inclusive reactions of the type p + p → (particle with large p_T) + n charged particles + neutrals, and propose the following scaling law

$\text{E}\text{d}{}^3\text{σ}{}_{\mathrm{n}}\text{d}{}^3\text{p}\text{=}\text{1}\text{(}\text{s}\text{)}{}^{\mathrm{k+1}}\text{H}{}^{\mathrm{2p}}\text{T}\text{s}\text{,}\text{n}\text{s}$

for the distribution function of the large-p_T particle produced in association with n charged particles. This scaling rule is shown to be consistent with present information on single-particle spectra and average associated multiplicities at large p_T. Also, we show that if the associated multiplicity were to continue to increase linearly with p_T, then moments of the multiplicity distribution would increase like powers of s.     

Lambda polarization in inclusive K−p interactions at 10 and 16 GeV/c

A strong negative transverse polarization P_z is found for forward produced lambdas observed in 10 and 16 GeV/c K^?p interactions. This indicates that exchanges of natural spin-parity are dominant in the production process. Using the polarization results, the $\text{d}\text{σ}\text{d}\text{u′}$ distributions for natural and unnatural spin-parity exchanges are derived. For unnatural exchanges, a dip is observed at u′?0.3 GeV², which can be explained as a nonsense-wrong-signature zero of the N_β trajectory. The value of P_z for forward producted lambdas is constant with energy. This is in agreement with the triple-Regge model prediction, as is the fact that P_z is constant as a function of $\text{M}{}^2\text{s}$. The two non-transverse polarization components, P_x and P_y, have been measured and are found to be consistent with zero for all x values, unlike P_z.