bluuebunny/crossref_metadata_2025 huggingface dataset:
On the phase transition in a gas of rodlike particles: A modified square-well model
Authors: Brenner Stephen L. , McQuarrie Donald A.
Published: February 2004

A recent calculation by Brenner, McQuarrie, and Olivares on the effect of attractive forces on the order-disorder phase transition in a gas of long hard rods is extended to include a more realistic attractive interaction potential. Rather than use the conventional square-well potential, we modify the attractive part of the potential such that the attractive interaction energy is proportional to area of overlap of the attractive regions. This is meant to reflect the fact that the more two rods are in register, the stronger is their attraction. The effects of well depth and well width on the thermodynamic parameters characterizing the phase transition are re-examined. This modified model yields significantly different results than the previous one for several of the transition parameters.
Interaction potential and reaction dynamics of He(21S, 23S)+Ne, Ar by the crossed molecular beam method
Authors: Chen C. H. , Haberland H. , Lee Y. T.
Published: February 2004

Differential elastic scattering cross sections of metastable He(21S) and He(23S) with Ne and Ar were measured at thermal collision energies by the crossed molecular beam method. The interaction potentials of these systems are found to be similar to those of alkali-rare gas systems. The excitation transfer from He(21S) to Ne and the Penning and associative ionization processes in He(21S,23S) and Ar collisions only occur when interatomic distances are shorter than given critical values and interaction potentials are repulsive. The ratios of associative to Penning ionization cross sections were also measured for collisions of metastable He(21S,23S) and Ar as a function of collision energies. These results combined with the opacity function derived from differential elastic scattering cross sections of He(21S,23S) and Ar provide some information on the long range interaction of He+Ar+.
Chloroethylene photochemical lasers: Vibrational energy content of the HCl molecular elimination products
Authors: Berry Michael J.
Published: February 2004

Chemical laser techniques have been used to determine relative photochemical product yields and HCl† (v′ ≤4) photoelimination product vibronic state distributions resulting from chloroethylene (CH2=CHCl, CH2=CDCl, CH2=CCl2, cis- and trans-CHCl=CHCl, and CHCl=CCl2) photolyses at λ ≥ 1550 Å. The observed highly nonstatistical product vibronic state distributions are successfully matched by a bootstrap reaction dynamics model which considers sudden structural distortion and intramolecular relaxation of HCl as it separates from acetylene or haloacetylene products. Chloroethylene vacuum ultraviolet absorption spectra (λ≥ 1400 Å) are also reported. All available spectroscopic, photochemical, and product energy partitioning data are used to formulate a state-to-state photochemical reaction mechanism for HCl photoelimination from the chloroethylenes.
Hyperfine interactions at a high-spin (5T2) ⇌ low-spin (1A1) transition in bis 2-(2-pyridylamino)-4-(2-pyridyl)thiazolato iron (II)
Authors: König E. , Ritter G. , Zimmermann R. , Goodwin H. A.
Published: February 2004

Hyperfine interactions have been studied at the 5T2⇄1A1 transition in the solid complexes Fe(papt)2, Fe(papt)2 · 4/3CHCl3, and Fe(papt)2 · C6H6 employing an external field Hext=40 kG and temperatures between 4.2° and 180°K [papt=2-(2-pyridyl)thiazolate]. It is shown that the 1A1 ground state may be characterized by Vzz <0, η∼0.7, and Hn=0. For the 5T2 ground state, the result is, within the χ tensor approximation, Vzz>0, η∼0.75, Hnx=Hny=−15 kG, and Hnz=−10 kG. The hyperfine fields at the iron(II) nuclei are identical for the three complexes studied here in the 1A1 and 5T2 ground states separately.
Wavelength-selective bleaching (``burning holes'') in the optical spectra of trapped electrons in organic glasses
Authors: Hager S. L. , Willard J. E.
Published: February 2004

This paper presents experimental evidence confirming that the broad optical absorption spectra of trapped electrons in glassy 3-methylpentane and methyltetrahydrofuran (MTHF) are convolutions of spectra of electrons trapped with different energies. Laser light of wavelengths near or to the red of the et− optical absorption maximum selectively depopulates electrons which absorb at the bleaching wavelength, thus creating a hole in the et− spectrum. Some additional indications as to the spectral properties of the individual electrons are given by the observations that (1) illumination of et− produced in MTHF at 25°K with laser light to the blue of the absorption maximum results in nearly uniform bleaching throughout the spectrum; (2) et− produced in MTHF at 67°K and illuminated at 25°K with 1064 nm are bleached less efficiently then et− produced at 25°K and have a low probability of being shifted to traps typical of mobile electron trapping at 25°K; (3) the spectra of et− in MTHF are progressively red-shifted as the temperature at which they are produced is lowered from 97 to 10°K, and the resolution of the peaks observable in the spectrum produced at 72°K is lower for spectra of et− produced at higher (97°K) or lower (25 and 10°K) temperatures. Some implications of these observations are discussed.
Calculation of normal vibrations and intra- and intermolecular force constants in crystalline imidazole
Authors: Colombo L. , Bleckmann P. , Schrader B. , Schneider R. , Plesser Th.
Published: February 2004

Couplings between molecular and crystal vibrational modes in imidazole have been investigated and the influence of the hydrogen bond on these modes has been studied. In normal-mode calculations a program has been used which allows all possible couplings between vibrations of the molecules and those of the crystal lattice. In this way molecular modes coupled to lattice vibrations and lattice modes describing predominantly hydrogen-bond vibrations have been isolated.
Theoretical studies in photoelectron spectroscopy: Use of angular distribution data to deduce molecular orbital parameters. III. Extraction of effective charge and anisotropy parameters of the molecular orbital from energy dependent measurements of β, the asymmetry parameter of the angular distribution
Authors: Ritchie Burke
Published: February 2004

Formulas are presented for β, the asymmetry parameter of the angular distribution for photoionization, for the ejection of electrons from molecular orbitals of molecules possessing a center of symmetry. Previous studies are indicative that the motion of the ejected electron is dominated by the monopole term of the electron-molecular ion potential expanded about the molecular center of mass when the ratio of the orbital velocity of the bound electron to the velocity of the ejected electron is smaller than about 1:2. Thus the motion of the ejected electron appears to be approaching the limit of motion in a spherically symmetric, screened Coulomb potential. At this limit, β has a form particularly easy to evaluate. We replace the screened Coulomb potential by the Coulomb potential itself, of strength Z, where Z is taken to be an adjustable parameter. We present arguments to justify this approximation based on the condition that at high energies the photoelectric conversion occurs most efficiently in the immediate vicinity of the nuclei such that it can be argued that it is a good approximation to take the zeroth order motion of the ejected electron as motion in the Coulomb potential of strength equal to the full nuclear charge, and to correct for screening effects to first order in the Coulomb-Born series. This procedure provides β in analytic form and thereby facilitates its study as a function of Z, of k, the velocity of the photoelectron, and of the sets {λj} and {ζj}, where these are anisotropy and effective charge parameters, respectively, of the jth-component of the molecular orbital expanded about the center of mass. The theory can be made systematically more accurate by exact numerical or Coulomb-Born solution of the partial wave equations of the ejected electron in the appropriate screened Coulomb potential, eliminating Z as an adjustable parameter.
Model for the effects of a condensed phase on the infrared spectra of hydrogen-bonded systems
Authors: Rösch Notker , Ratner Mark A.
Published: February 2004

A formal scheme is developed for treating the effects of a condensed phase on the vibrational spectrum of hydrogen-bonded systems. A coupling of the moving proton to the bath is assumed responsible for the broadening, and is taken as simply the electrostatic interaction between the protonic dipole and the random local field set up by the internal modes of the bath or solvent. This corresponds to the electrostatic broadening. A strong-coupling treatment is employed. The spectrum is found by a cumulant expansion of the dipole-dipole correlation function. Expressions for the shift and broadening of the individual lines are given. The dynamics, as well as the strength, of the system-bath coupling are important for determining lineshape. The lineshape is thus related to the microscopic dynamic behavior of the hydrogen-bonded system in solution.
Calculations of the second virial coefficients for water and ammonia
Authors: MacRury Thomas B. , Steele William A.
Published: February 2004

General theoretical results obtained in the preceding paper for the ordinary and the dielectric second virial coefficients of polarizable polar molecules were utilized in a calculation of these quantities for water and ammonia. For these molecules the following was found: Rotational quantum effects are appreciable even at 300°K and higher; the dipole-induced dipole energy plays an important role in the calculation; and the available data can be fit using two sharply different potential functions that differ by a factor of roughly 10 in the Lennard-Jones well depth parameters chosen. Excepting the quantum effect, it is argued that the virial coefficients will behave similarly for any strongly polar molecule. It is noted that experimental data are surprisingly sparce for these two important molecules, especially in the case of the dielectric virial coefficients.
Semiclassical treatment of bound state systems. III. A uniform stationary phase integration for the multidimensional problem
Authors: Starkschall George , Light John C.
Published: February 2004

The semiclassical bound state formalism is extended to the multidimensional problem by deriving an expression for the reduced density matrix which remains finite when the charge density is calculated. We derive a uniform stationary phase integration technique by mapping the phase of the semiclassical propagator onto a function which has the same behavior as the phase of the free particle propagator, enabling us to incorporate the singularity at t = 0 into the integration. The resulting rdm has the oscillatory behavior of a Bessel function of order d/2, where d is the dimensionality, rather than that of a simple trigonometric function.
Magnetothermodynamics of Ce2Zn3(NO3)12 · 24H2O. I. Heat capacity, entropy, magnetic moment from 0.5 to 4.2 °K with fields to 90 kG along the a crystal axis
Authors: Giauque W. F. , Fisher R. A. , Hornung E. W. , Brodale G. E.
Published: February 2004

The magnetic moment and heat capacity of a 4.059 cm diam. spherical single crystal of cerium zinc nitrate hydrate (CZN) has been measured with stabilized fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the a crystal axis, from 0.5 to 4.2°K. The zero of electronic entropy was reached at fields of 90, 65, and 40 kG and the lower temperatures. The isoerstedic entropy changes derived from heat capacity series were interconnected by 28 series of temperatures vs fields on isentropes. Analysis of the heat capacity data established that the first excited doublet is (61.0±0.3+7.8×10−10H2) cal/mole (h/2π) above the zero field ground state. H is in gauss. The splitting factor of the ground state doublet was evaluated calorimetrically as gH=1.8175−7.88×10−12H2G −2. Near 0.5°K, and over the range 40–90 kG, the total magnetic moment reaches temperature-independent limits at each field. Subtracting the low temperature limiting value of the temperature-dependent moment, 5075–6.60×10−8 H2G · cm3/mole Ce3+, from the total, enabled the evaluation of the differential temperature-independent susceptibility as 2.632×10−2−7.8×10−14H2 cm3/mole Ce3+. Thus, Mlimit T→0 = (5075+2.632×10−2 H−6.60×10−8H2−2.6×10−14H 3) G · cm3/mole Ce3+, where H is in gauss. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.5–4.2°K. The problem of obtaining crystals of CZN which approximate stoichiometric proportions has been discussed. The principal purpose of the data is to lay a foundation for subsequent measurements needed to establish a temperature scale for CZN to the millidegree region.
Crystal structure of NH4ClO4 at 298, 78, and 10 °K by neutron diffraction
Authors: Choi C. S. , Prask H. J. , Prince E.
Published: February 2004

The crystal structure of ammonium perchlorate has been studied at 298, 78, and 10°K by means of neutron diffraction. The NH4ClO4 crystal has an orthorhombic unit cell, space group Pnma, with four formula units per cell at all three temperatures. The unit cell dimensions at 298°K are a=9.20, b=5.82, c=7.45 Å, as determined previously; at 78°K, a=9.02, b=5.85, c=7.39 Å; and a=8.94, b=5.89, c=7.30 for 10°K. Initial positions of H atoms were determined from a difference Fourier map of the room temperature data. However, a least-square refinement of these data did not converge. The thermal motions and orientations of the ammonium groups at low temperature (10 and 78°K) were determined by means of a constrained refinement which treated the ammonium group as a rigid body; these results are compared with the results obtained by the conventional least-squares method. Both refinements show that the librational motions about one of the three principal axes have particularly large rms amplitudes: 21° for the 10°K structure and 30° for the 78°K structure. Each ammonium group is surrounded by 10 oxygen atoms with short N ⋯ O distances ranging from 2.9 to 3.25 Å. The ClO4− group and NH4+ group each have essentially ideal tetrahedral structure. They are linked together by N–H ⋯ O type hydrogen bonds, one for each hydrogen, to form a three-dimensional network. Examination of the rms amplitudes for libration and the hydrogen bonding of the NH4+ ions indicates that two of the four hydrogens are bound identically, one hydrogen is bound more rigidly, and the fourth more weakly. These results suggest that the rotational motions of the ammoniums are quite complex even at 10°K.
Theoretical study of curve crossing: ab initio calculations on the four lowest 1Σ+ states of LiF
Authors: Kahn Luis R. , Hay P. Jeffrey , Shavitt Isaiah
Published: February 2004

The potential curves of the four lowest 1Σ+ states of LiF have been studied by ab initio configuration interaction methods, using a contracted Gaussian basis set of better than double-ζ quality, augmented with diffuse basis functions on the fluorine atom. The choice of orbitals and selection of configurations were carried out with the objective of obtaining a balanced treatment of the four states and of the different regions of the potential curves. ``Generalized valence-bond'' orbitals, obtained from ground-state MCSCF calculations, together with ``improved virtual orbitals,'' were found suitable for the construction of the configuration functions. The latter were energy selected from all single and double excitations relative to a set of 12 ``reference configurations,'' chosen to include all contributions found important for any of the four states at any internuclear distance. The expected avoided crossing between the lowest covalent and ionic structures is found at an internuclear distance of about 11 bohr, compared to the experimentally deduced value of 14 bohr, due to the considerable difficulty in obtaining a balanced description of the electron correlation of the separated species, particularly the F− ion. A set of diabatic potential curves was generated from the two lowest adiabatic curves by a novel procedure based on the Rittner model of the ionic state. A set of adjusted adiabatic potentials was obtained from the diabatic curves after shifting the ionic diabatic curve downward by 0.42 eV to correct for the error in the computed electron affinity of the fluorine atom, resulting in a shift of the avoided crossing to the correct internuclear distance of 14 bohr. The dipole moments of the four states were computed as a function of internuclear distance and were interpreted in terms of the electronic structure.
Lattice model for a binary mixture of hard rods of different lengths. Application to solute induced nematic→isotropic transitions
Authors: Peterson Henry T. , Martire Daniel E. , Cotter Martha A.
Published: February 2004

A statistical mechanical treatment for two-component mixtures of hard rods placed on a simple cubic lattice is presented. Each mixture is composed of two types of rods of different length-to-breadth ratios; and the pressure-to-temperature ratios are chosen so that the system is anisotropic when only longer rods are present but isotropic when composed of only shorter rods. Such solutions can be induced to undergo a first-order anisotropic-isotropic phase transition, with a small two phase region, by increasing the concentration of the shorter rods. The dependence of this transition on the parameters of the model is described and deviations from ideal solution behavior are discussed. Recent experimental data are cited and compared with the results of the lattice calculation.
Ultraviolet- and x-ray-induced radicals in frozen polar solutions of L-tryptophan
Authors: Moan Johan , Kaalhus Olav
Published: February 2004

Acid, neutral, and alkaline matrices containing the aromatic amino acid L-tryptophan have been uv and x irradiated at 77 K, and the irradiation products examined by ESR and optical absorption spectroscopy. Three types of tryptophan radicals have been detected: (1) T1ox, supposedly the tryptophan cation, which has a characteristic optical absorption band around 600 nm and a singlet ESR spectrum at g=2.004 of width around 25 G, (2) T2ox, probably the radical formed by H abstraction at N1, which absorbs light around 550 nm and has a narrow singlet ESR spectrum (g=2.004, H=13–14 G), and (3) Tred, assumed to be the radical formed by H addition at C7, showing an ESR spectrum which is a triplet of triplets with hfs constants a1=39 G and a2=12 G. T1ox is formed by photoionization of tryptophan or by the reaction of tryptophan molecules with x-ray induced oxidized solvent radicals such as Cl2− in matrices containing LiCl or HCl, O− in alkaline solutions, and sulphuric acid radicals in matrices containing H2SO4. T2ox is formed by radical conversion of T1ox in acid matrices, and is probably the main oxidized tryptophan radical present in alcohol matrices. Tred is formed by the reaction of electrons as well as H atoms with tryptophan molecules.
Electrostatic model for the rotational potential in ammonium halides
Authors: Hüller Alfred , Kane Joseph W.
Published: February 2004

An electrostatic model for the rotational potential of an ammonium tetrahedron in a cubic field is proposed. The rotational potential can be written as a rapidly converging series of kubic rotator functions. The NX4 ion, where X is hydrogen or deuterium, performs small angular motions about the minimum of the potential in both the ordered and disordered states, giving rise to librational energy levels. The anharmonic portion of the energy levels, both from the kinetic and potential energies, accounts for good agreement with infrared absorption data in NH4Cl, ND4Cl, NH4Br, and ND4Br. We use a one parameter fit to these data and then compute the potential barriers for rotations about threefold and fourfold axes of the tetrahedron. The difference between the transition temperatures for ND4Cl and NH4Cl is also explained.
Gas-discharge polymerization
Authors: Carchano H.
Published: February 2004

A synthesis of the study that we undertook on the polymerization of monomer vapors in an alternating luminescent discharge is presented. After a brief description of the deposit apparatus, the experimental study of the deposit parameters has been given. The study relates to the influence of the discharge frequency (50 Hz to 6 MHz), of the discharge duration and its current density, of the substrate temperature, and of the monomer pressure (7×10−2 to 3 torr). Thereby it is demonstrated that the polymerization takes place in the interelectrode space rather than on the electrodes above a frequency of about 105 Hz, that the deposit thickness is a linear function of time (15 s to 10 mn), and that for a given substrate temperature and pressure it is necessary not to exceed a certain current threshold above which there is not any increase of the growth rate but rather a degradation of the forming layer. Finally it is shown that too high a pressure lowers the film growth rate as a result of the cooling of discharge electrons following an increase of the shocks in the discharge. These experimental results permit an explanation of the film formation on the substrate by the association of two phenomena: the monomer-molecule adsorption on the substrate which yields the matter to be polymerized and the electrical discharge which furnishes the necessary active particles to initiate and thereafter maintain the polymerization mechanism. In the second part of this article, an experimental and theoretical verification of this hypothesis has been undertaken. At first, the case of an dc electrical discharge is considered which permits the demonstration that the active particles are the positive ions of the discharges. Next, the multilayer adsorption phenomenon following the BET (Brunauer, Emmet, and Teller) theory is presented, and it is shown that this is in good agreement with the experimental results of the first part. Finally a radical polymerization scheme is proposed enabling the determination of an analytical expression for the polymer formation speed which agrees well with the experimental findings.
Study of the ground state potential curve and dipole moment of OH by the method of optimized valence configurations
Authors: Stevens Walter J. , Das G. , Wahl Arnold C. , Krauss Morris , Neumann David
Published: February 2004

Accurate theoretical potential and dipole moment curves are presented for the X2Πi state of the hydroxyl radical. The theoretically determined dissociation energy is 4.53 eV as compared to the experimental value of 4.63 eV. The computed dipole moment at the experimental equilibrium internuclear separation is 1.674 D, which is in excellent agreement with the most reliable experimental value of 1.66±0.01 D. A detailed, general prescription for constructing optimized valence configuration wavefunctions for diatomic hydrides is presented with OH as a specific example.
Effective pair potentials for the noninteracting spin-1/2 Fermi gas
Authors: Stevens F. A. , Pokrant M. A.
Published: February 2004

The N-particle configurational probability density P(N) of a noninteracting Fermi gas may be approximated as P(N) ≃ Πi<je−u(rij) / ∫d 3NrΠi<je −u(rij), where u(r) is an effective pair potential. Our reason for considering these potentials is that they have been successfully used in computing properties of interacting Fermi systems. We define the best effective potential to be the one whose corresponding two-body distribution function is closest to the exact two-body distribution function. A method for calculating the best u(r) is not known. Lado has calculated u(r) by using the Born-Green-Yvon integrodifferential equation relating u(r) to the two- and three-body distribution functions. Effective potentials may also be calculated using the hypernetted chain and Percus-Yevick integral equations. It is found that potentials computed by the above three methods are in fairly close agreement. The principal purpose of this paper is to present tables of effective potentials approximating both the spin-summed system and parallel spin subsystem probability densities for a system of noninteracting spin-1/2 fermions.
On the master equation approach of vibrational relaxation in condensed media
Authors: Lin S. H.
Published: February 2004

The purpose of this paper has been to examine the validity and limitations of the Pauli master equation and to demonstrate the use of the master equation approach in describing the vibrational relaxation in the condensed phase. The master equations for vibrational relaxation of a number of model systems have been derived. The calculation of rate constants of vibrational relaxation has been discussed. The solution of the master equations of multimode relaxation at low temperatures has been presented. The Brownian motion of an oscillator linearly coupled with the medium has been investigated and a model of the coupling between the vibrational relaxation and other unimolecular processes (like electronic relaxation, etc.) has been developed.
Relaxation of fluorine nuclei by collisions with free radicals
Authors: Poindexter Edward H. , Caplan Philip J. , Wagner Burkhard E. , Bates Richard D.
Published: February 2004

Intermolecular nuclear relaxation during liquid-state collisions has been examined for 16 combinations of four free radicals and four fluorocarbons. The spectra of electron-induced scalar relaxation transitions are resolved into high- and low-frequency components. All samples are found to have a spectral component with a short correlation time of around 1×10−11 sec, corresponding to fast diffusion-controlled collisions. Those samples which show stronger scalar hyperfine coupling show a second component with time up to 44×10−11 sec, corresponding to sluggish stereospecific collisions or transient complexation. Strong scalar coupling is found to occur with a proportionally strong dipolar coupling, which is augmented well beyond that expected from feasible molecular approach distances. Monopoly of spin-rich sites by the fluorocarbon might account for part of the dipolar augmentation but does not satisfactorily account for the entire range of observations. An induced anisotropic hyperfine coupling, after the manner of the scalar coupling, is proposed as an alternative explanation. The existence of an augmented dipolar coupling poses certain new considerations in theoretical interpretation of diffusion-controlled dipolar relaxation, and in computation of atomic distances in spin-labeling studies.
Hydrogen Flash Lamps
Authors: Berlman I. B. , Steingraber O. J. , Benson M. J.
Published: February 2004

Many hydrogen-filled lamps have been tested and the effect of each of several parameters on the intensity and shape of the radiation pulse determined. The parameters were gas pressure, type of gas (hydrogen or deuterium), tube voltage, and electrode gap distance. A flash lamp has been designed and built which is simple, inexpensive, and easily disassembled.

Our results show that deuterium-filled tubes with 2 mm gaps emit about (65±10)% more photons per discharge than hydrogen-filled tubes operated under similar conditions. The parameters favorable for a high intensity discharge are large gap with deuterium gas—for a rapid discharge, high pressure and voltage.
Fast Metallic Contact Solid Dielectric Switch for High Voltage and Current
Authors: Henins Ivars , Marshall John
Published: February 2004

A metallic contact solid dielectric switch with a closing time of 10.13±0.31 μsec is described. An electrically exploded foil is used to drive a 0.317 cm thick aluminum plate through 0.076 cm polyethylene insulation into solid contact with the other switch electrode. The switch has been used as a series switch in a 20 kV circuit with a current of 1.2×106 A rising in 40 μsec. In a ``crowbar'' application it has carried 40 kA with a 1/e decay time of 45 msec.
MOSFET Operation at 4.2 K
Authors: Green Robert R.
Published: February 2004

MOSFETS operate at 4.2 K and act as impedance transformers for high impedance (1010Ω) ir detectors. Several types, both n-channel and p-channel, have operated successfully at this temperature and withstood the thermal shock of repeated cycling from room temperature. Low device power dissipation and relatively low noise can be achieved by optimizing drain current (ID) and drain-to-source voltage (VDS) for the particular device. Power dissipations as low as 0.4 mW have been recognized.
Low Temperature Force Generating Apparatus Using Sylphon Bellows
Authors: McWane J. W. , Bijl D. , Shiffman C. A.
Published: February 2004

An apparatus is described in which a Sylphon bellows is used to generate pressures to 3400 atm or uniaxial forces to 1150 kg in the liquid helium temperature range without the use of mechanical compressors. Correction factors, operating procedures, and practical limitations of the design are discussed. The shift in transition temperature of indium is given as a test of the overall behavior of the apparatus.
Two-Dimensional Evaluation of a Plane of Rotation
Authors: Nypan Lester J.
Published: February 2004

Occasionally problems of instrumentation and measurement will require a very accurately defined plane of rotation. When such a plane or axis of rotation must be defined to within a few arc seconds it is difficult to separate random and determinate errors inherent in the rotational system from errors attributable to measurement techniques and to misalignment of the plane of rotation with a reference plane or axis. A two-dimensional analysis of these errors is presented to permit an estimation of the magnitude of each error component. Two measurements separated by 90° are made at a series of intervals of angular rotation. A least squares analysis is performed to determine a best-fitting plane or axis of rotation, and the standard deviation of the measurements from this axis is compared with the standard deviation of the measuring instrument. An example of the application of the method to the evaluation of a 1.067 m diam azimuth axis bearing is presented.
Energy Distribution of Positive Ions Extracted from a Hot Cathode Gas Discharge Ion Source
Authors: Theard Lowell P.
Published: February 2004

An electrostatic parallel plate energy analyzer was used for measuring the energy distribution of Ar+ ions in a beam extracted from a nonmagnetic, hot cathode, gas discharge ion source under various conditions of source pressure, anode voltage, and anode current. A large number of energy distribution curves were obtained as X-Y recordings. The curve shape depends upon source conditions, though not strongly when the pressure is greater than 3×10−3 Torr with an anode voltage above 50 V (for argon) and an anode current of at least 200 mA. When conditions are optimum, the ion energy distribution curve is a narrow peak with a tail that gradually diminishes towards lower energies over an interval of approximately 30 eV. The actual value of the optimum full width at half maximum was found to be 1.1 eV by extrapolation to zero beam energy. The shape of the curve is such that more than 81% of the beam ions have energies within a 10 eV interval. The source can be used to increase beam currents greatly in certain types of magnetic deflection mass spectrometers without extreme loss of mass resolution due to ion beam energy spread.
Retracting Pedestal Apparatus that Presents a Single Solid Target to a Focused Q-Switched Laser Beam
Authors: Pack John L. , George T. V. , Engelhardt A. G.
Published: February 2004

An electromechanically operated retracting pedestal system has been developed for injection of a single solid target as small as a few tens of microns in radius into a vacuum system. After the pedestal has withdrawn completely from the system, the falling target, which originally was positioned on top of the pedestal, is ionized by a focused, high power, Q-switched laser beam. Since the plasma is produced in a relatively large volume free of mechanical obstructions, it can be easily studied or used as a source of ions. The pedestal is withdrawn with a velocity in excess of 10 m-sec−1, whereas the target falls with a velocity given solely by the acceleration due to gravity. The laser beam which ionizes the target is triggered by an optical tracking system, consisting principally of an He–Ne laser whose beam is collinear with that of the pulsed laser. The device can be loaded rapidly in vacuum from a reservior with a capacity of hundreds of targets, and fired every few minutes. Application to experiments on laser created plasmas is discussed.
Rapid Recording Microspectrophotometer
Authors: Wolken J. J. , Forsberg R. , Gallik G. , Florida R.
Published: February 2004

A microspectrophotometer of increased sensitivity has been constructed to rapidly record absorption spectra in a single sweep at relatively low light levels from the ultraviolet through the visible, from 2500 to 8000 Å. The visible spectrum can be scanned within 2 sec. Absorption spectra from single living cells, cell organelles and particles as small as 0.5 μ diam can be obtained. The design of the optical system, the electronics and properties of the components of the instrument are given. Examples of its performance are presented and its versatility for obtaining spectral data is discussed.
Mass Discrimination in a Time-of-Flight Mass Spectrometer. I. Geometric Mass Discrimination at Magnetic Electron Multiplier
Authors: Hunt W. W. , McGee K. E. , Streeter J. K. , Maughan S. E.
Published: February 2004

The magnetic electron multiplier widely used as the particle detector in time-of-flight (TOF) mass spectrometers can introduce several mass discrimination effects. One, geometric mass discrimination, arises from ions being deflected by the magnetic field so that the multiplier entrance apertures intercept a mass-dependent fraction of the incoming ions and prevent their being detected. A method of correcting for geometric mass discrimination in linear TOF instruments is outlined and used to compute correction factors for the specific geometry and magnetic field configuration that characterize our modified TOF mass spectrometer. The results indicate that, except perhaps for H+ and H2+, geometric mass discrimination is negligible in most commercial TOF instruments when they are operated at the normal 3000 V accelerating potential. Geometric discrimination can become serious, however, if the instrument is operated at accelerating potentials significantly below normal, since the amount that an ion bunch is deflected increases as its kinetic energy, as well as its mass-to-charge ratio, decreases. For this same reason, geometric discrimination against fragment ions formed in the drift tube can be quite serious even when the instrument is operated at accelerating potentials higher than the normal 3000 V.
Helium Cooled Radio Frequency Preamplifier for Use in NMR
Authors: Miyoshi D. S. , Cotts R. M.
Published: February 2004

A low temperature (4.2 K) radio frequency amplifier has been constructed using metal oxide semiconductor field effect transistors (MOSFET). Noise characteristics of the amplifier are compared to a model that includes two noise sources: shot noise and induced gate noise. The model is similar to models used to represent noise in vacuum tubes. Amplifier use for observation of low temperature nuclear magnetic resonance (NMR) signals is considered. Conditions for optimum signal-to-noise (S/N) are expressed in terms of the noise figure and are compared to those for room temperature vacuum tube amplifiers. Improvement of S/N by factors of 3 to 10 are readily obtainable. The S/N improvement with the low temperature MOSFET amplifier is demonstrated by observation of the NMR signal of 205Tl at 4.2 K at a frequency of 20 MHz.
Two ``Whisker'' Straining Devices Suitable for Low Temperatures
Authors: Stillwell E. P. , Skove M. J. , Davis J. H.
Published: February 2004

Two devices for straining ``whiskers'' are described. In the first device, the whisker is mounted on a Mylar film that is stretched by a differential screw. The entire device can be immersed in liquid helium, which eliminates thermal expansion problems in low temperature experiments. In the second device the whisker is mounted between two bimorphs of piezoelectric material. The piezoelectric puller is small enough to fit inside a 2.5 cm i.d. superconducting solenoid and still permit the entire device to be rotated about an axis perpendicular to the solenoid axis.
System Approach to Fast Logic for Counter Experiments in High Energy Physics
Authors: Sippach W. , Sunderland J.
Published: February 2004

A fast counter logic system is described that separates the time correlation and logic questions. A loose trigger generates a set of time windows for gating narrow discriminator pulses into storage elements. The stored signals are then logically combined into event definitions that are strobed to produce system outputs. Special emphasis is placed on use of the system with a data handler. Modules built for a counter hodoscope experiment are also described.
Blanking Circuit for a Magnetic Electron Multiplier in a Time-of-Flight Mass Spectrometer
Authors: Haumann Joseph R. , Studier Martin H.
Published: February 2004

A blanking generator has been developed for use with a magnetic electron multiplier in a time-of-flight mass spectrometer. By blanking out superfluous portions of the mass spectrum, non-linearity in the electron multiplier is minimized, gain is increased, and dirtying of the dynode strip is retarded.
Very Low Frequency Integrating Vibrating Sample Magnetometer (VLFVSM) with High Differential Sensitivity in High dc Fields
Authors: Foner S. , McNiff E. J.
Published: February 2004

A vibrating sample magnetometer is described which is specifically adapted for magnetic moment measurements in high dc fields. The sample is moved at very low frequencies between series opposing detection coils, the induced voltage is integrated, and each cycle is recorded so that the output can be further time-averaged. Two novel aspects make this instrument particularly useful for high field measurements. First, the sample is moved beyond the center of the detection coils so that positioning errors, forces, and other incidental effects are eliminated. Second, a precise reference balance voltage is synchronously applied to the output signal to permit high-resolution differential measurements of magnetic moment. In addition to a detailed description of the basic VLFVSM, a general discussion of flux integration techniques is presented. Operation of the VLFVSM with field modulation superimposed, variable temperature, variable pressure, additional electronic filtering, and under swept-field conditions is discussed. Mechanical and electronic details and typical operating characteristics are included. The entire magnetometer has moderately high sensitivity, is extremely rugged, versatile, and eliminates sources of error present in many sample extraction techniques. All components, excluding the mechanical systems associated with the sample, are available commercially. This magnetometer has been applied to practically all types of high field magnetic moment measurements including differential susceptibility measurements in metals, alloys and insulators, superconductors, and highly anisotropic materials such as the rare earth metals.
cw Microwave Spectrometer for Ultrasonic Paramagnetic Resonance
Authors: Leisure R. G. , Bolef D. I.
Published: February 2004

A description and detailed analysis of an acoustic cw microwave spectrometer is given. The spectrometer, although designed specifically to measure the small changes in acoustic velocity and attenuation characteristic of ultrasonic paramagnetic resonance, can be used also to measure absolute values of acoustic velocity and attenuation over wide ranges of frequency and temperature. The use of a calibrator in producing a known reference signal is described.
Ionization of Fast Neutral Atoms by Passage through a Hot-Cathode Discharge
Authors: Fleischmann H. H. , Kribel R.
Published: February 2004

The possibilities and conditions for ionization of neutral hydrogen atoms in the energy range of 30–300 eV by passage through an auxiliary plasma are investigated. The general requirements for the plasma are determined by the scattering of the fast neutrals and ions to be detected: density, integrated along the path of the fast particles, several ×1012 cm−2; integrated neutral density [less than double sim] 1015 cm−2 electric fields [less than double sim] 1 V cm−1 and magnetic fields not more than a few hundred gauss. In this case, usable conversion ratios of several 10−3 seem possible. Experimentally, the conversion efficiency of a plasma produced by a hot-cathode discharge is compared with the efficiency of a calibrated air stripping cell. At low energies, for the plasma cell, higher efficiencies by about an order of magnitude are found. Expected values for the conversion efficiencies are achieved for particle energies above 250 eV. At lower energies, similar values seem achievable using ion analyzers with wide acceptance angle.
Square and Sine Wave Modulation of the Beam from a 3 MV Van de Graaff Accelerator
Authors: Fraser H. J. , Ritchie A. I. M. , Whittlestone S.
Published: February 2004

Methods of producing square and sine wave beam modulation of a 3 MV Van de Graaff accelerator are described. Square pulses are produced at frequencies from 100 kc to zero with up to a 100% duty cycle and a minimum pulse length of 8 μsec. The ratio of the off-current level to the on-current level is less than 5×10−4 and can be further reduced by a post-acceleration deflection system to less than 10−5. The unit, which is triggered from a command pulse external to the machine, is in the top terminal of the Van de Graaff and has shown itself to be highly reliable over some 1000 h of machine operation. The sine wave modulation unit described here operates in the range 80–1000 cps with a modulation depth of up to 90% and higher harmonic contamination of less than 1%.
Condensable Gases in a McLeod Gauge
Authors: Wear K. B.
Published: February 2004

Condensable gases need not be precluded from a McLeod gauge operated in the mode described. Readings taken with a captured gas sample at different compression ratios may be used to identify the condensables, estimate their concentrations, and determine both the vacuum system pressure and the partial pressure due to noncondensable gases. Theory, vacuum system and gauge manipulation, data, and difficulties encountered are discussed.
Direct Gravimetric Calibration of a Quartz Crystal Microbalance
Authors: Mueller R. M. , White W.
Published: February 2004

A commercial quartz crystal microbalance has been calibrated via simultaneous comparison with a reference vacuum electrobalance. Aluminum, copper, and gold thermally deposited on 10 MHz AT-cut oscillators gave a composite linear calibration to a precision of ±0.2%. For a uniformly distributed deposition, the ratio K of the fractional change of mass Δm/m to the fractional change of frequency Δf/f is shown to be 0.991 with a probable error of 0.6% for a configuration having peripheral contact restraints of the oscillators. The response function δf/δm (sensitivity variation over the face of the crystal) was determined to exhibit asymmetries about the central axes.
Double-Beam Vibrating Mirror Flying Spot Scanning-Integrating Microspectrophotometer
Authors: Engle James L. , Freed Jerome J.
Published: February 2004

Serial measurements of integrated ultraviolet absorbance of individual living cultured animal cells are possible with a double-beam scanning microscope designed to maximize the signal-to-noise ratio obtained for a given radiation flux traversing the sensitive specimen. A 192-line raster (2 sec/frame), scanned in the specimen plane by a focused spot of monochromatized radiation, is reconstructed by video technique to provide an image display and permit manual delineation of photometric fields of arbitrary shape, corresponding to the shape of the specimen. Analog circuits produce a read-out proportional to the integrated absorbance present in the photometric field, unaffected by inhomogeneity in the distribution of absorbing material.
Liquid Helium Field-Ion Microscope for Radiation Damage Investigations
Authors: Petroff Pierre , Washburn Jack
Published: February 2004

A field ion microscope is described which allows in situ irradiation of a metal specimen at a temperature close to 5°K. It has been used with the 88 in. cyclotron at Berkeley which provides 10 MeV protons. The design permits ``field off'' irradiation of the specimen, as well as in situ temperature cycling. Qualitative observations on the surface damage of iridium upon ``field off'' and ``field on'' irradiation are given.
Combined Leak Detector and High Sensitivity Vacuum Gauge
Authors: Perkins George D. , Robinson Charles F.
Published: February 2004

A combined vacuum gauge and leak detector in which background currents are suppressed by an appropriately disposed magnetic field, permitting the measurement of total pressures below the limit of a Bayard-Alpert gauge. In leak detection, negative-ion-forming tracer gases such as Freon-12 can be detected at partial pressures below 10−11 Torr in the presence of common background gases at total pressures as high as 10−4 Torr.
Automatic Constant-Pressure Apparatus for Measuring the Absorption or Evolution of Gases
Authors: Tinker H. Burnham , Craddock John H. , Paulik Frank E.
Published: February 2004

An improved apparatus for automatic measuring and recording of the absorption or evolution of gases at constant pressure has been constructed. The instrument is applicable to kinetic studies over a wide range of operating conditions including (a) pressures up to 20 atm, (b) temperatures up to 120°C, and (c) rates of reaction as fast as 5 ml min−1. A differential-pressure transducer is used and makes the instrument sensitive to pressure changes as small as 0.020 mm Hg. The mechanical and electronic components of the system are described. The apparatus has been evaluated by measurements of the rate of oxygen uptake by Vaska's complex, IrCl(CO) (PPh3)2.
Ten Watt Coaxial Calorimeter for rf Power Measurement
Authors: Clark Richard F. , Jurkus Algirdas
Published: February 2004

This paper describes a dry static calorimeter intended for the measurement of rf power in coaxial lines. The calorimeter is calibrated with dc power. Its maximum input level is 10 W and the highest frequency of operation is 8 GHz. A detailed analysis of the sources of error is presented. The total estimated uncertainty increases from ±0.1% at very low frequencies to ±0.5% at 8 GHz.
Low Temperature ir Cell for Studies Using Anhydrous HF as a Solvent
Authors: Spears Larry G. , Hackerman Norman
Published: February 2004

The ir cell described below was developed to study soluble products formed from the electrolysis of ammonium bifluoride in anhydrous hydrogen fluoride. For these purposes it was necessary that the sample be kept in a liquid state, at atmospheric pressure, both in the sample transfer and during ir analysis. It was also necessary that the materials with which the sample (mainly HF) came in contact during sample transfer and ir analysis be resistant to corrosion. No commercial cells or cells reported in the literature could fulfill these requirements.
Flash X-Ray Actuated Trigger Switch
Authors: Swift H. F. , Strader E.
Published: February 2004

A trigger switch system actuated by high intensity x-ray pulses has been developed and is being used with flash radiography equipment. Ten-kilovolt, low-impedance output pulses are initiated by the trigger system within 10 nsec of x-ray pulse initiation. The switch assembly causes little attenuation or scatter of the x-ray beam since the only material intercepted by the beam is two aluminum sheets, 25 μ thick.