Thermodynamics of ternary Fe-Ni-N-austenites

Measurements, in the range 1140–1548 K, of the temperature variation of the solubility of nitrogen at constant pressure (1.04 × 10⁵ Pa) in Fe-Ni fee solid solutions in equilibrium with N₂ gas, show that the partial molar enthalpy $\text{H}$_i of the nitrogen atoms is invariant to the nickel concentration up to 15 atm % Ni. In the same temperature range the partial molar excess entropy $\text{S}$^xs_i exhibits a slight decrease with increasing nickel concentration.The thermodynamic data are consistent with the cell model for ternary solid solutions in which the nickel atoms create shallow trapping sites for N-atoms, deeper by only 4.9 kJ/mol than interstitial sites in binary Fe-N solutions.The variation in H_i with nickel content due to the distribution of N atoms in energetically differing cells is of about the same size, but opposite in sign, to the contribution to $\text{H}$_i ascribable to the change in specific density of the substitutional lattice with varying Ni content.     

Formation energies of point defects in rutile (TiO2)

The formation energies for the point defect species Ti⁴⁺ interstitials, Ti_i⁴⁺, and oxygen vacancies with an effective charge of + 2e, Vo²⁺, have been calculated using the polarisable point ion shell model. The formation energy of Ti_i⁴⁺ was found to be a 10.8 eV for occupation of the (0, $\text{1}\text{2}$, $\text{1}\text{2}$) site. The energy of Ti_i⁴⁺ at other sites is somewhat higher than this figure, and allowed the migration energy of Ti_i⁴⁺ parallel to the c axis to be estimated as 2.9 eV. The formation energy of Vo²⁺ was found to be 10.1eV. The variation of these formation energies with dielectric constant was also calculated. It was found that the energy of formation of Ti_i⁴⁺ varied considerably with dielectric constant, while the formation energy of Vo²⁺ was almost independent of dielectric constant. The relevance of these results to the presence of crystallographic shear planes in reduced rutile is considered.     

A light scattering investigation of the incommensurate transition in BaMnF4

The results of a Brillouin scattering investigation of BaMnF₄ near its incommensurate structural phase transition at T_i=247 K are reported. We have observed an anomalous dynamic central peak in the polarized (bb) spectrum, with $\text{q}\text{6}\text{c}$. This feature is visible only very near T_i, and possesses a width which is strongly wavevector dependent. The indicated behavior is Λ=D_tq², with D_t=0.14 ± 0.02 cm²sec^-1. It is identified as the result of a coupling between the LA phonon and the soft mode, where the latter contains a relaxing self energy due to a linear coupling to a diffusive process, possibly entropy fluctuations. The narrow central peak is not visible for $\text{q}\text{6}\text{a}$. In addition, we report an anomalous dispersion (～4%), in the LA mode propagating along $\text{c}$ (V_cc) near T_i.     

High-resolution study of E0 internal pair decay of excited 0+ states in 58,60,62Ni

The recently developed magnetic plus Si(Li)-Si(Li) sum-coincidence technique is employed to measure E0 internal-pair-formation (IPF) branching ratios of excited 0⁺ states in ^58,60,62Ni. The $\text{X(}\text{E}\text{0}\text{E}\text{2}\text{)}$ values are obtained for a new 0⁺₄ state in ⁶⁰Ni at 3588.0 keV, for the 0⁺₂ and 0⁺₃ states at 2942.3 keV and 3530.9 keV in ⁵⁸Ni, for the corresponding states at 2284.8 keV and 3318.3 keV in ⁶⁰Ni, and for the 0⁺₂ state in ⁶²Ni at 2048.4 keV. The results are combined with the available lifetimes of these states to extract the monopole strengths ?²(0⁺_i ? 0⁺₁). The results and the nature of the 0⁺ states are discussed.     

Nuclear g-factor of the 172+ isomeric state in 63Cu

The nuclear g-factor of the 4498 keV $\text{17}\text{2}$⁺ isomeric state in ⁶³Cu was measured with the in-bearn perturbed angular distribution method, through the ⁶²Ni(α, p2nγ)⁶³Cu reaction, to be g_exp = 0.184 ± 0.012. This value is in good agreement with a semiempirical g-factor for the three-quasiparticle configuration [π2p_{$\text{3}\text{2}$}(v1f_{$\text{5}\text{2}$}, 1g_{$\text{9}\text{2}$})₇]_{$\text{17}\text{2}$⁺} calculated using the experimental single-particle g-factors of neighbouring nuclei. At the same time the internal magnetic field at the Cu nuclei in Ni metal was obtained to be B_int = ?46.6 ± 1.3 kG.     

Multiple meron solutions of the classical Yang-Mills equation

We give a construction for multiple meron-antimeron solutions to the classical SU(2) Yang-Mills field equations. The corresponding charge density is $\text{Q(x) =}\text{1}\text{2}\text{∑ ± γ(x?x}{}_{\mathrm{i}}\text{)}$, with the x_i distinct points on a line. The problem is reduced to the solution of a scalar φ⁴ equation. We obtain a model with merons connected in pairs.     

Energies of the n2S12 and n2D32,52 states of Cs

Using the technique of Doppler-free two-photon spectroscopy the energies of the n²S_{$\text{1}\text{2}$} (12 ? n ? 35) and n²D_{$\text{3}\text{2}$,$\text{5}\text{2}$} (11 ? n ? 48) states of CsI have been measured with a thermionic detector. The absorption spectrum of molecular iodine was used as a reference giving us a total estimated accuracy of about 2 × 10^-7. Taking also into account the energies of the 7–11 ²S_{$\text{1}\text{2}$} and 5 and 6 ²D_{$\text{3}\text{2}$,$\text{5}\text{2}$} states measured by other authors and using an extended Ritz-formula we found the ionization limit to be E_i = 31406.468 ± 0.006 cm^-1.     

Solving the linearized Φ4 equation in external driving fields

The Φ⁴ equation, linearized about a kink at rest, is solved for external driving fields F(t) = Σ_i=n^∞f_itⁱ. The x-dependent part of the solution $\text{u}\text{?}\text{(x, t)}$ is proportional to the translation mode. This implies that also for large times the kink's dynamics is adiabatic, if the external field is sufficiently weak and $\text{|}\text{u}\text{?}\text{|? z1}$|ν| ? 1.     

Experimental studies of two-photon absorption of sodium perturbed by collisions with noble gas atoms

This study was performed with sodium vapor at about 300°C perturbed by noble gases at densities between 0.5 x 10¹⁹ and 6 x 10¹⁹ atoms/cm³. We have measured the rate of two-photon absorption for step-wise processes, which occur if the exciting frequency is resonant with one of the transition frequencies ω_ri or ω_fr with i, r, and f referring, respectively, to the initial, the relay and the final state. By varying the exciting frequency, we obtain collision profiles which may be difficult to obtain by other methods. The shifts and widths for the transitions 3S-3P_{$\text{3}\text{2}$}, 3S-3P_{$\text{1}\text{2}$}, and 3P_{$\text{3}\text{2}$}-5S have been measured for several noble gases. The observed variation of the profiles with perturber gas pressure suggests possible quenching of the relay state by noble gas molecules present in the mixture.     

Magnetic moments of the 12+ isomeric states in 194, 196, 198Pb

The g-factor of the 12⁺ isomeric state in lead isotopes with A = 194, 196, 198 was measured using the time-differential perturbed angular distribution method (TDPAD). The values obtained are respectively g(194) = ?0.158(6); g(196) = ?0.157(7); g(198) = ?0.144(11). A more precise determination of the 12⁺ level half-life is also made. The g-factprs of these nuclear states, which are described with v(i_{$\text{13}\text{2}$})^?2 as the main configuration, are surprisingly constant over a large mass range (between A = 206 and 194). A core polarization analysis explains this trend: the polarization induced on neutrons in i_{$\text{13}\text{2}$} orbit decreases with the mass number A (blocking effect), but a compensation is provided by the other spin-orbit partners f_{$\text{7}\text{2}$}-f_{$\text{5}\text{2}$} and P_{$\text{3}\text{2}$}-P_{$\text{1}\text{2}$}.     

Decoupled bands in odd-mass mercury isotopes

The schemes of the low-lying high-spin states in mercury isotopes with A = 195, 197, and 199 have been studied by γ-ray spectroscopy following (α, xn) reactions on separated platinum targets. Two bands have been excited in each Hg nucleus, one with positive parity based on the isomeric i$\text{13}\text{2}$. state and one, probably with negative parity, starting at spin $\text{case21}\text{2}$. The positive-parity states are interpreted with the rotation-aligned coupling scheme as decoupled bands; this implies oblate deformation in these three Hg isotopes. The negative-parity states are discussed as a decoupled i$\text{13}\text{2}$ neutron state coupled to the 5^?, 7^?, 9^?,…states, recently discovered in doubly even mercury isotopes.     

Angular distributions of auger electron emission: Clean and gas-adsorbed polycrystalline Ni surfaces

The excitation angle (β) and emission angle (θ) dependences of the Ni M₂,₃VV (61 eV) and Ni L₃VV (850 eV) Auger emissions from clean polycrystalline Ni surfaces, and the S L₂, ₃ M₂, ₃M₂, ₃ (150 eV) Auger emission from S-adsorbed poly-Ni surfaces have been investigated. In the case of Ni (61 eV) and S Auger emissions, the β-dependence shows the $\text{1}\text{cos β}$ distribution, while a significant deviation from $\text{1}\text{cos β}$ is observed for Ni (850 eV) Auger emission. The cosθ distribution and the intermediate between isotropic and cosθ distributions are observed for Ni (61 eV), and for Ni (850 eV) and S Auger emissions, respectively. Those results have been found to be in fairly good agreement with the calculations based on the simple continuum model without consideration of the diffraction effect and the inherent anisotropic emission.     

Polarization transfer in the deuteron break-up reaction at 56 MeV

The polarization transfer coefficients K^yy′ of the break-up spectra in the reactions ¹²C, ⁵⁸Ni, ²⁰⁹Bi($\text{d}$, $\text{p}$X) were measured at 56 MeV. In the forwardd angles (13.5° and 20.0°), the K_y^y′ data at the break-up peak are nearly equal to $\text{2}\text{3}$ (the spectator model prediction) and they decrease at both sides of the peak. The deviation due to the deuteron D-state is estimated, using PWBA and DWBA.     

A study of the low-lying levels in 61Ni

Electromagnetic decay properties for seventeen states in ⁶¹Ni have been examined by means of the ⁵⁸Fe(α,nγ)⁶¹Ni reaction with E_α = 8 MeV and the ⁶⁰Ni(d, pγ)⁶¹Ni reaction at E_d = 6 MeV. Mean lifetimes were obtained with the Doppler-shift attenuation method. Spins, parities, and mixing ratios were determined from angular correlation studies and linear polarization measurements. The combined results permit new J^π assignments of $\text{7}\text{2}{}^{\mathrm{?}}\text{,}\text{5}\text{2}{}^{\mathrm{?}}\text{,}\text{7}\text{2}{}^{\mathrm{?}}\text{,}\text{and}\text{9}\text{2}{}^{\mathrm{+}}$ for the levels at 1016, 1611, 2020 and 2123 keV, respectively. Experimental results, including transition strengths, are compared to shell model predictions.     

Effect of pressure on the Curie temperature of PdFe,PdCo, PtFe and PtCo alloys

The Curie temperatures of $\text{Pd}$Fe, $\text{Pd}$Co, $\text{Pt}$Fe and $\text{Pt}$Co alloys with Fe or Co concentrations between 1 and 10 at. % have been measured by thermal scanning of the ⁵⁷Fe Mössbauer resonance under pressures up to 170 kbar. Systematically, the largest (positive) values of the logarithmic derivative, dlnT_e/dlnV, are found in the most dilute alloys. The data are compared with models, which relate the variation of T_c under pressure to changes in the impurity spin-conduction electron coupling parameter, J_i, and to changes of the pure host metal susceptibility, χ_h. The discrepancies between the experimental data and these models are discussed.     

Valence band parameters of cubic zinc selenide derived from magnetoreflectance of the Γ6 − Γ8 exciton

Magnetoreflectance measurements on the Γ₆ ? Γ₈ free exciton ground state in cubic ZnSe in magnetic fields up to 18 Tesla are reported. The diamagnetic shift rate of the ground state components: $\text{|}\text{3}\text{2}\text{>β}$, $\text{|?}\text{3}\text{2}\text{>α}$, $\text{|}\text{1}\text{2}\text{>β}$ and $\text{|?}\text{1}\text{2}\text{>α}$ yield γ₂ = 0.53 ± 0.07 and an exciton reduced mass μ₀ = 0.117 ± 0.003, corresponding to γ₁ = 2.30 ± 0.45 for m_e¹ = 0.16 m₀. γ₁, γ₂ and an effective hole g-value $\text{κ}\text{tilde}\text{= -0.21}$ yield γ₃ = 0.82 ± 0.16 in the parabolic approximation and in agreement with the observed splitting of the $\text{|?}\text{3}\text{2}\text{>α}$, $\text{|?}\text{1}\text{2}\text{>β}$ states for B ∥ [110]. Taking into account polaron effects we derive bare valence band parameters γ₁^L = 2.71 ± 0.60, γ₂^L = 0.63 ± 0.09 and γ₃^L = 0.97 ± 0.21 from the renormalized parameters γ_i. The present results are considerably smaller than earlier theoretical calculations suggest, however they are in good agreement with a recent detailed analysis of two-photon absorption data for 2P exciton states.     

Operator formulation of Regge asymptotic behavior

If the appropriate high-energy limits of the amplitudes $\text{W ≡ ?}\text{d}\text{x}\text{e}{}^{\mathrm{<mtext>i</mtext><mtext>q\; ·\; x</mtext>}}\text{<b|j(x)j′(0)|b′ >}$ are Regge pole dominated, then the large distance (x₀ → ∞, x²fixed) behavior of the current product is completely characterized by an operator expression $\text{R}\text{(x : 0)}$, involving only local operators at 0, which is such that $\text{R ≡ ?}\text{d}\text{x}\text{e}{}^{\mathrm{<mtext>i</mtext><mtext>q\; ·\; x</mtext>}}\text{<b|}\text{R}\text{|b′ >}$ and W have the same high-energy behavior. In the only case (|b> a single particle stateand |b′> the vacuum) where W is not Regge behaved, it is shown that R is identical to W, and so the relation $\text{jj′ →}\text{R}$ is established as a large distance operator expansion, valid between all states. $\text{R}$ is expressed as a differential operation B(□_x, ?_x · ?₀, □₀) on the light-cone expansion and some of its properties are deduced by carrying out the differentiations. A second form of $\text{R}$ is given in terms of non-local “reggeon” field operators R_αm(0) (α is a (fixed) spin index and m is a (variable) helicity index) which might be useful coordinate in reggeon field theories. These operators can be used to define reggeon-particle amplitudes and if conventional double-Regge and triple-Regge behaviors are further assumed, the large distance behaviors of the current-reggeon and reggeon-reggeon field products are specified in terms of other reggeon fields.     

(II) Infrared and X-ray photoelectron spectroscopy of some transition metal dithiocarbamates and xanthates

Measurements are presented for the binding energy variations of (a) (Ni, Cu) 2p_{$\text{3}\text{2}$}, S 2p and N 1s core levels in a series of Ni and Cu disubstituted dithiocarbamates and (b) (Ni, Cu) 2p_{$\text{3}\text{2}$}, and S 2p core levels in a series of Ni xanthates. These shifts, which are observed to be negative and quite large for the S 2p levels, are then correlated with the infrared absorption frequency variations for the associated intramolecular stretching vibrations of the same series. The results are interpreted in terms of a model based on atomic charges and their potential effects on both variations. The functional relationships between the binding energy and infrared frequency variations are shown to be in good agreement with the experimental results.     

Mean residence time of potassium ions on tungsten as measured with reference to ionization efficiency

The mean residence time, τ_i, of potassium ions on “clean” and oxygenated tungsten has been measured, together with the ionization efficiency, as a function of surface temperature T by using incident K beams of low intensity (10⁹–10¹² atoms cm^?2 s^?1). For T higher than ~900 K the observed τ_i followed Frenkel's equation $\text{τ}{}_{\mathrm{<mtext>i</mtext>}}\text{= τ}{}_{\mathrm{<mtext>i</mtext>}}{}^0\text{exp}\text{(}\text{Q}{}_{\mathrm{<mtext>i</mtext>}}\text{kT}\text{)}$ as usual and the agreement of the ionic desorption energy Q_i and of the pre-exponential factor τ_i⁰ with the corresponding values of previous experiments was quite satisfactory. Below 830 ~ 910 K, where a steep drop of ionization efficiency began to be noticeable, Arrhenius plots of τ_i deviated considerably from linearity. The apparent increment of the desorption energy was shown to be nearly equal to the decrement of thermionic work function of tungsten as obtained from the ionization efficiency and Saha-Langmuir equation. The increase of surface coverage by potassium was accordingly taken as the main cause of the departure of Arrhenius plots from linearity. Under certain conditions of incident beam intensity and surface temperature τ_i was observed to make an abrupt change from a higher to a lower value — a difference expressed as 100–140 meV in terms of the difference in ionic desorption energy. This peculiar phenomenon was attributed to the phase change of adsorbed potassium on tungsten.