bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoluminescence in Quartz
Authors: Medlin W. L. 
Published: January 2005

X-ray- and uv-excited thermoluminescence in natural quartz has been investigated by studying the properties of synthetic samples. The results for a large number of natural samples, including single crystals, outcrop specimens, and core-hole samples showed that most of them had four prominent glow peaks in common. One of these is due to the presence of Ti and the others are apparently associated with a defect center. The effects of annealing at temperatures up to 900°C were found to be important in well-crystallized samples but unimportant in others.
The emission spectrum of the Ti glow peak shows that a number of levels are involved in the luminescent transitions. All of the defect-center glow peaks have the same emission spectrum which consists of a single maximum with a long wavelength tail. Direct-current electrical measurements on single crystals showed that the trap-emptying processes for the defect center were nonlocalized. Optical absorption measurements at room temperature indicated that none of the common absorption bands are associated with peaks in the glow curve. From phosphorescent-decay measurements it was determined that the trapping levels associated with the defect center have very narrow energy distributions whereas the trapping level due to Ti is discrete.
The glow peaks for ordinary quartz are not excitable by uv irradiation, but in samples annealed at 900°C all of the glow peaks due to the defect center are excited by uv. The annealed samples show absorption in the uv region which is not present in unannealed specimens. The results suggest changes in the trap-filling mechanism, but the effects can also be explained by alterations in the luminescent levels.
Luminescence can be excited in all of the samples at fixed temperatures by x rays but not by uv. At low temperatures the effects of transitions through trapping levels are unimportant, and the emission is due only to x-ray excitation of the luminescent centers. The spectral response of the emission is the same as that for the Ti glow peak. The intensity is about the same in all samples and is not affected by impurity content. This indicates that the luminescent levels involved are due to a crystal defect center and that the same center is involved in the thermoluminescence due to Ti.
Sequence Selection Problem in the Crystallization of Polymers
Authors: Gornick F. , Jackson J. L. 
Published: January 2005

The crystallization of linear polymer chains is considered as a process involving the selection of crystallizable sequences from the melt. If, owing to the requirements of thermodynamic stability, such sequences must exceed in length some critical value less than the chain length, and if the selection process is random, then the melt will be increasingly subdivided into uncrystallized sequences of varying length. Some of these may be expected to be less than the critical length, so that the segments comprising them are ``wasted'' insofar as participation in further crystallization is concerned.
An approximate sequence length distribution function for the uncrystallized sequences in the system is derived and utilized in connection with the problem of retardation in crystallization kinetics.
Self-Diffusion of Lead 210 in Single Crystals of Lead Sulfide as a Function of Stoichiometry and Doping Additions
Authors: Simkovich George , Wagner J. Bruce 
Published: January 2005

Self-diffusion of lead 210 in single crystals of lead sulfide has been studied in the temperature range of 500° to 800°C. Measurements were made on undoped crystals and on crystals doped with Bi2S3 or Ag2S under well-defined sulfur pressures and under an inert gas. Results show that increasing the cation vacancy concentration by means of excess sulfur or by bismuth additions increases the diffusion coefficient, whereas decreasing the concentration of cation vacancies by means of excess lead or by silver additions also increases the diffusion coefficient over those of stoichiometric PbS. In all cases the electron concentration is accounted for according to: [interstitial lead atoms]∝pPb/[excess electrons],and [cation vacancies]∝[excess electrons]/pPb,assuming singly ionized interstitial lead atoms and singly ionized cation vacancies. The activation energies decrease in the order, stoichiometric PbS, lead excess PbS and sulfur excess PbS.
Results support a Frenkel disorder of the cation type.
Identification of Color Centers in Lithium Fluoride
Authors: Kaufman J. V. R. , Clark C. D. 
Published: January 2005

The optical absorption spectra induced in LiF by 2.0-MeV electron irradiation at a number of doses and at temperatures of 120° and 293°K have been measured. The effects resulting from thermal and optical bleaching experiments on such specimens are described.
A determined effort to color LiF additively was made. No induced absorption was observed between 1.0 and 6.0 eV.
Anisotropic absorption was induced in the 4500-Å (2.76-eV) band by plane polarized 4047- and 4358-Å (3.06- and 2.84-eV) light at 293°K. The anisotropy was not affected by standing in the dark at 293°K. Results indicate that at least two absorption bands constitute the 4500-Å band, and it is suggested that one of these is the M band.
It seems to have been generally accepted that the 2500-Å (4.948-eV) band in LiF is the F band, by analogy with the other alkali halides. However, the present results show that analogies between results on LiF and the other alkali halides cannot be carried very far.
Radiation Decomposition of Aqueous Azide Solution Containing Mercuric Salts
Authors: Shinohara Kenichi , Shida Tadamasa , Saito Nobufusa 
Published: January 2005

The addition of mercuric salts causes a marked change in the radiolytic reactions of aqueous azide ion solution. Hydroxyl radicals and hydrogen atoms are scavenged by the azide ion and mercuric salt, respectively.
In order to explain the high yields of nitrogen and mercurous azide in terms of the current theory of water radiolysis, it is suggested that the excited water molecule which might be formed by primary recombination between the H2O+ ion and the ejected electron, and by slow electron collision in spur, may be involved. The excited water molecule is assumed tentatively to be a triplet and to behave like a diradical, which with an azide ion gives a comparatively long-lived complex (N3–H2O)(triplet)*.
The previous results of the radiolysis of pure azide ion solution have been rediscussed in terms of this new assumption.
Energy Levels of Tb3+ in LaCl3 and Other Chlorides
Authors: Thomas K. S. , Singh S. , Dieke G. H. 
Published: January 2005

The absorption and fluorescence spectra of Tb3+ in LaCl3 have been used to find the levels of Tb3+. All Stark components of 7F and 5D4 were unambiguously established. The classification of the higher levels is still doubtful.
The analysis was helped by Zeeman effects and particularly crystal field calculations. The latter gave as crystal field parameters: B20=92,B40=−40,B60=−30,B66=290 cm−1.
Tb3+ in YCl3 has a similar spectrum but, because of different crystal symmetry, with different fine structure. A third type of spectrum is obtained from pure TbCl3.
Integral Equations between Distribution Functions of Molecules
Authors: Mayer Joseph E. 
Published: January 2005

Integral equations are derived that relate variations in the potentials of average force between molecules of a system at two different densities or activities. These permit the calculation of the change in thermodynamic properties, or of the change in the distribution of molecules in space, in a liquid or crystalline phase, if either the temperature is varied, or if the the mutual potentials between the molecules is assumed to change. The equations are in a somewhat complex, but still distinguishable, matrix form. A matrix operates on the variations in potential occurring at one activity and transforms them into those occurring at a second activity. The matrix elements are combinations of the distribution functions at the second activity, to which the transformation is made, multiplied by powers of the difference of the two activities. The matrix approaches the unit matrix in value as this activity difference approaches zero. The product of the two matrices, one which transforms from activity α to activity β, with that which transforms from activity β to α, is the unit matrix. This leads to an integral (matrix) equation between the distribution functions at any two activities.
The calculation of one element of this matrix product leads to a cell type equation for the computation of the activity, or free energy, of a system in terms of the potential between a single molecule and the molecules that immediately surround it in the system.
The transformation matrices have solutions, at certain values of the activity difference y, corresponding to variations in the potentials of average force, which are transformed into zero variations at the new activity. The activities at which such variations can occur are those of the phase transitions in the systems. The solutions at these special values of the activity are differences of combinations of the distribution functions in the two pure phases that can coexist at these activities.
Thermodynamics of Crystallization in High Polymers. I. Crystallization Induced by Stretching
Authors: Flory Paul J. 
Published: January 2005

A theory of oriented crystallization in elongated polymers having network structures (e.g., in vulcanized rubber) is developed through the application of statistical mechanical procedures similar to those employed in rubber elasticity theory. Expressions are derived which, within the limitation imposed by the simplifying assumptions, relate the incipient crystallization temperature with the elongation, the degree of crystallinity with the elongation and temperature, and the retractive force at crystallization equilibrium with the elongation at constant temperature. The reciprocal of the absolute temperature for incipient crystallization is predicted to decrease linearly with a simple function of the elongation and the average number of chain segments between cross linkages. Only moderate degrees of crystallinity are predicted at equilibrium. In conformity with requirements of the second law of thermodynamics, equilibrium crystallization decreases the tension in the stretched specimen.
Apparent discrepancies between some of these predictions and various observations are attributed to severe departure from equilibrium crystallization when the polymer undergoes crystallization during the stretching process. A better approach to equilibrium should be achieved by stretching under conditions which prevent crystallization (e.g., at elevated temperature), then allowing crystallization to proceed at fixed elongation. Few experiments have been performed in this manner, but such results as are available confirm qualitatively the predictions of the theory.
Reasons for the rapid increase in tension which is observed when crystallization occurs during ordinary stretching of rubber are discussed. It is pointed out that crystalline and amorphous regions preferably should not be regarded as separate phases. Likewise, the conversion of amorphous to crystalline polymer does not conform to the definition of a phase transition.
Photo-Conductivity in Photographic Systems I. Dye-Sensitization of Photo-Conductivity
Authors: West W. , Carroll B. H. 
Published: January 2005

Gelatino-silver halide photographic films increase in electrical conductivity on exposure to light at intensities corresponding to exposures within the normal photographic range, and above. The spectral distribution of this change in conductivity in films containing, respectively, photographic sensitizing dyes, and no dye, is found to be parallel with the spectral distribution of photographic sensitivity— the wave-lengths of maximum and minimum sensitivity in the two effects are identical and coincide with absorption maxima and minima, and there is a general parallelism in the efficiency of a dye in sensitizing the two effects to light not absorbed by the silver halide. The conclusion is drawn that the observed changes in conductivity represent a photo-conductivity originating in the photo-liberation of electrons within the silver halide, the primary act of the photographic process.
The photo-currents are proportional to the applied field up to strengths of at least 140 volts per millimeter, and at intensities of illumination within the normal photographic range and somewhat above, are proportional to the intensity. At still higher light intensities, the photo-currents verge towards a dependence on the square root of the intensity. The change in the intensity relation is interpreted as representing the passage from a situation, at low intensities, in which most of the electrons are captured by foreign traps to that, at high intensities, in which recombination with bromine atoms predominates.
It is shown that a sensitizing dye acts by causing the liberation of an electron within the conduction band of the silver halide under the stimulus of light absorbed by the dye but whether the process involves direct electron-transfer or energy-transfer is left open.
Polymorphism and Anion Rotational Disorder in the Alkaline Earth Carbonates
Authors: Lander J. J. 
Published: January 2005

X-ray diffraction methods have been developed for the study of materials at high temperatures under controlled atmospheres, and an investigation of the high temperature phases of the alkaline earth carbonates has been made. BaCO3 was found to change from orthorhombic (aragonite type) to hexagonal (calcite type) at 803°C, and to cubic (sodium chloride type) at 976°C. SrCO3 was found to change from orthorhombic (aragonite type) to hexagonal (calcite type) at 912°C. A few experiments with mixtures, which go through similar transitions, are described.
These transitions are related to the rotational activity of the carbonate ions and consideration of the nature of the transitions leads to a description of the probable rotational behavior of these ions in the various phases.
Macroscopic Space Charge in Electrolytes during Electrolysis
Authors: Reed Charles Albert , Schriever William 
Published: January 2005

Since the publication of Hittorf's famous paper in 1853 it has been assumed, in general, that macroscopic space charge does not exist in an electrolyte during electrolysis. An apparatus and procedures were developed which made possible reproducible data on potential distribution in an electrolyte. In a uniform column of electrolyte the potential rise was found to be a non-linear function of the distance from the cathode, and it was shown that this non-linearity could not have been due to concentration changes caused by the electrolysis, but must have been due to macroscopic space charges in the electrolyte. Calculations showed the space charge to be positive very close to the cathode, negative in the next quarter of the column, positive for the next nearly three-quarters of the column and negative very close to the anode.
The eight electrolytes studied were 0.0024N solutions of CuSo4, CuCl2, ZnSO4, ZnCl2, Zn(C2H3O2)2, NiSO4, NiCl2 and Al2(SO4)3. The pure metal was used for the electrodes in each case. Each column of electrolyte was 8 cm×8 cm×40 cm long, and the constant potential difference was 8.000 volts. The largest observed space charge at the end of 15 minutes was in CuSO4 at 2 mm from the anode; it was an excess of 2×106 Cu++ ions over SO4−— ions per cm3, which is an excess of only 3 Cu++ ions for every 1012 Cu++ ions originally present.
Although the space charges were all very small, they had very appreciable effects on the potential gradients, which also were calculated. The potential gradients in the different electrolytes were not constant, but had maximum deviations from constancy of from 5 to 20 percent in the explorable part of the column (to within 1 mm of each electrode). The average potential gradients in the explorable part were from 1.1 to 23 percent less than the 8/40 volt/cm. Thus Ohm's law was found not to hold even over the explorable part of the column.
Isothermal Compositional Order-Disorder. I. Superstructure Solid Solutions in a Salt System
Authors: Grenall Alexander 
Published: January 2005

Solid solutions in the system, NH4Cl–MnCl2–H2O, exhibit properties characteristic of order-disorder in alloys. Disordered solid solutions are indistinguishable in structure from that of ammonium chloride. Order is revealed by superstructure formation. The familiar compositions A3B and AB appear as end-members of the ordered solid solution series. Crystal symmetry alteration from cubic to tetragonal results from ordering. Tetragonality is intimately related to the state of order. Though increase in ``solute'' content produces significant lattice distortion, superstructure unit cell volumes are constant.
Despite their unusual properties, the ordered salt solid solutions exhibit a normal Vegard's law relationship.
The salt system's features resemble those of a low temperature isotherm across Shockley's theoretical phase diagram for alloy order-disorder transformation and are regarded as experimental verification of Shockley's qualitative predictions. A concept of isothermal, compositional order-disorder is used in presenting the results.
Demonstration of a two-phase region, wherein ordered and disordered solid solutions coexist in equilibrium, provides a basis for resolving the controversy over whether the phase rule governs order-disorder transformations.
Identity of the order-disorder phenomenon in metal and salt systems was further shown by producing the disordered state of salt solutions from the ordered by thermal and cold-working methods. In both instances, order was spontaneously restored with aging at room temperature.
The Infra-Red Absorption Spectra of Some Metal Borohydrides
Authors: Price W. C. 
Published: January 2005

The absorption spectra of aluminum, lithium, and sodium borohydride have been obtained in the region from 1–25μ. The aluminum borohydride was investigated as gas and an analysis of the infra-red and Raman bands fits a bridge-type structure of symmetry D3 (probably D3h). The spectra of lithium and sodium borohydrides were obtained from finely ground slurries of these materials. Their spectra indicate how the bridge structure of the H2BH2 metal groups passes over to the tetrahedral structure in a completely ionic lattic.
Using certain bond-distance force-constant relationships in conjunction with data from the diatomic hydrides and accepting electron and x-ray diffraction data for bond distances between the heavier atoms, values for the geometrical parameters are calculated for beryllium, aluminum, and sodium borohydride. These seem more plausible than any so far suggested. Observations on the electronic spectrum of aluminum borohydride have also been made down to 1000A. The diffuseness of the absorption obtained at short wave-lengths prevented any detailed interpretation.
The spectrum of a compound formed between beryllium borohydride and sodium chloride has also been obtained and a consideration of its absorption bands has given information concerning the nature of this material. A spectrum of a slurry of the methyl derivative of lithium borohydride (LiBH3CH3) indicates considerable change in the structure relative to that of lithium borohydride.
A table of frequencies of related bands in the metal and other borohydrides is given which illustrates the changes referred to above. It includes a number of boron-nitrogen hydrides and shows that the BH frequency, when it is associated with analogous electronic groups, behaves in much the same way as that of CH when it is attached to saturated, olefinic or aromatic groups.
Molecular Rotation in Sodium Cyanide and Sodium Nitrate
Authors: Siegel L. A. 
Published: January 2005

An attempt has been made to decide between the Pauling and Frenkel hypotheses for group disorder in crystals on the basis of x-ray diffraction data.
Measurements of the line intensities of sodium cyanide showed that no decision could be reached between two models involving complete spherical rotation and a tetrahedral distribution of equilibrium positions. The 220 line was found to possess an anomalously large variation of intensity with temperature. A new rhombohedral form of sodium cyanide was found which can be produced only by quenching the cubic form from the vicinity of 300°C. The cubic and rhombohedral forms coexist from 20°C to 80°C. An ordered structure has been proposed for the rhombohedral phase.
The diffuse scattering from a single crystal of sodium nitrate has been studied, and a diffuse maximum has been found which is believed to be a result of group disorder. This maximum shows a strong angular dependence which is incompatible with the predictions of the rotation theory. The data fit a twofold disorder model for the nitrate groups, provided that the positions have an aragonite-type of coordination with the surrounding sodium atoms, rather than the calcite coordination found in the ordered structure.
Refractive Indices and Dielectric Constants of Liquids and Gases under Pressure
Authors: Rosen Joseph S. 
Published: January 2005

Several interpolation formulas are given which reproduce refractive index and dielectric constant data for liquids and gases at high pressures. These formulas involve functions of the refractive indices and dielectric constants which appear in the formulas of Lorentz-Lorenz, Clausius-Mosotti, Gladstone and Dale, the empirical Eykman formula, etc. One formula shows the reciprocals of these functions to be linear in the specific volumes at various pressures. Another interpolation formula, involving the reciprocals of the same functions, contains a logarithmic term which is similar to that appearing in the Tait equation for compressibilities of liquids. The parameters involved in the Tait equations for compressibilities and in the analogous interpolation formula for refractive indices and dielectric constants are discussed.
The article also shows that the Tait equation which has been so successfully adapted to compressibility data of liquids can also be applied to gases.
A Kinetic Study of the Thermoluminescence of Lithium Fluoride
Authors: Boyd Charles A. 
Published: January 2005

The isothermal decay of the thermoluminescence of single crystals of lithium fluoride activated by x-rays has been determined at various temperatures. The results are interpreted in terms of a simple reaction rate mechanism based on a picture of the thermoluminescent process similar to that of Johnson. The analysis of the isothermal decay studies is in agreement with the results of ``glow curve'' experiments on similar lithium fluoride samples where the intensity of luminescence is measured as the temperature of the crystal is heated at a constant rate.
Two principal types of electron traps in lithium fluoride are found to have trapping energies of 19,800 cal./mole and 45,300 cal./mole respectively.