bluuebunny/crossref_metadata_2025 huggingface dataset:
A HIGH RESOLUTION FLAT CRYSTAL SPECTROMETER FOR NEUTRON CAPTURE γ-RAY STUDIES
Authors: Knowles J. W.
Published: April 2011

A flat crystal diffraction spectrometer, constructed for the measurement of γ-rays resulting from neutron capture, is discussed both experimentally and theoretically. The spectrometer is used either as a single crystal or a double crystal instrument. In the single crystal arrangement a Laue diffracted γ-ray beam from a broad source proceeds through a Soller slit which gives it a 45-second angular divergence, to a sodium iodide scintillation detector. The energy is determined by the angle between the Soller slit and the crystal. The resolution is determined by the Soller slit, and is 4% at 1 Mev when diffracting from the (440) planes of a single germanium crystal. In the two-crystal configuration a γ-ray which is Laue diffracted from the first crystal is further diffracted from a second crystal set in the antiparallel position. The angle between the reflecting planes of the two crystals determines the γ-ray energy. The Soller slit serves only as shielding for the detector in this arrangement. The resolution depends upon the mosaics and thicknesses of the crystals; it is 0.4% at 1 Mev for diffraction from the (211) planes of two calcite crystals, each 23 mm thick and of 1.7- and 0.9-second mosaics respectively. The range of measurement extends from 80 kev to greater than 5 Mev. Where other values of γ-ray energies exist, agreement to within the expected precision, ± 0.2% is obtained. The counting efficiency as a function of energy depends on the integrated reflectivities of the crystals which may be determined at the time of a γ-ray measurement by means of the double crystal arrangement. The integrated reflectivity as a function of energy has been calculated for a number of crystals of known mosaic and throughout the range of measurement, from 0.2 to 5 Mev, good agreement is obtained.
A PROPOSED MECHANISM FOR ICE FRICTION
Authors: Niven C. D.
Published: April 2011

The collapsible structure of ice is stressed. The adhesion bond is visualized as being associated with a readjustment of a partially collapsed or distorted molecular structure when cooling sets in after plastic flow has occurred in the asperity. With this general idea in view the friction mechanism on ice is compared in detail with that on a non-collapsible material, and explanations for observations are suggested.
ABSOLUTE STANDARDIZATION OF RADIOACTIVE NEUTRON SOURCES: I. ACTIVATION OF MANGANESE BATH
Authors: Geiger K. W. , Whyte G. N.
Published: April 2011

The neutron emission rate of a Ra-α-Be source of the National Research Council has been measured by moderating the neutrons in manganese sulphate solution surrounding the source. Some of the thermal neutrons captured in the bath produce manganese-56, and the neutron emission rate is found from an absolute determination of the resulting activity. A number of corrections are discussed in detail. The value of (3.22 ± 0.05) × 106 neutrons per second found for the neutron emission rate shows satisfactory agreement with the results of our intercomparison with the primary neutron standard of the National Bureau of Standards, and allows a tie-in with a series of international comparisons of primary neutron sources.
AN EXPERIMENTAL STUDY OF INTERCEPTION NOISE IN ELECTRON STREAMS AT MICROWAVE FREQUENCIES
Authors: McIntosh B. A.
Published: April 2011

The noise added to an electron stream by the interception of a fraction of the current has been studied experimentally at a frequency of 3 kMc/s. The electron beam was produced in a demountable vacuum system by a parallel-flow Pierce gun in a confining magnetic field. A series of circular apertures and mesh grids on a plate capable of being moved within the vacuum chamber allowed the interception of various fractions of the total beam current. The excess noise caused by interception was measured at the anode of the electron gun and at various points in a drift region.Interception noise caused by mesh grids was found to be of much greater magnitude than that caused by circular apertures. The absolute level of the excess noise and its variation with the strength of the confining magnetic field were found to be in reasonable agreement with existing theory as modified by the author.It was shown that current interception excites a standing wave of noise along the electron beam in the drift region. Measurements made on a temperature-limited electron beam have shown that interception noise can arise in a region where noise smoothing is a consequence of processes external to the electron gun.
FIRST ADSORBED LAYER OF HELIUM AT 4.2° K
Authors: Hobson J. P.
Published: April 2011

An attempt has been made to measure the helium adsorption isotherm on pyrex (Corning 7740) at 4.2° K for pressures above the adsorbed layer ranging from 10−4 to 10−12 mm Hg. New ultrahigh vacuum techniques were used for the pressure measurements with geometric adsorbing areas from 10 to 70 cm2. Above 10−9 mm Hg the results give a true measurement. Below 10−9 mm Hg the results give an upper limit on the pressure above the adsorbed layer. The form of the isotherm indicates that the first adsorbed layer is complete at a pressure [Formula: see text]. A comparison of the present" results with previous measurements of the helium adsorption isotherm at 4.2° K, which extend down to 10−6 mm Hg, suggests that all such measurements with solid adsorbents have been made on helium layers thicker than one monolayer. This conclusion supports similar conclusions drawn from heats of adsorption data at higher temperatures. An extrapolation of the results suggests that total gaseous densities approaching those of interstellar space (1.0 × 10−24 g/cm3) should be possible in the laboratory, with liquid helium trapping.
PROLONGED SIGNAL FADE-OUT ON A SHORT MICROWAVE PATH
Authors: Hay D. R. , Poaps G. E.
Published: April 2011

During a period of 1 year, the incidence of signal fade-out has been observed in 2000 Mc/s transmissions over a 21-mile path near Ottawa. Fade-out durations varied from a few minutes to several hours, with the most frequent occurrence in summer and during the night. The cause of signal fade-out has been studied qualitatively through a ray analysis of the air refractivity profiles at the center of the radio path. This analysis indicates that fade-out is associated with a shallow, horizontal transition zone in air vapor pressure at a level near the antenna heights. Here, the vapor pressure changes through 1 millibar or more in a height interval of 100 ft. The signal fade-out is weak if the transition is from dry air below to moist air above, but is strong if the inverse transition occurs. Weak fade-out (a 'radio hole') is due to ray divergence, and strong fade-out (a 'radio antihole') is due to ray interference at the receiver.
THE TRANSPORT OF HEAT BETWEEN DISSIMILAR SOLIDS AT LOW TEMPERATURES
Authors: Little W. A.
Published: April 2011

The resistance offered to the flow of heat by the mismatch of the elastic constants at the interface between two materials has been calculated. It is shown that for a perfectly joined interface the heat flow is proportional to the difference of the fourth powers of the temperature on each side of the interface. Deviations from this temperature dependence are to be expected for rough surfaces and for surfaces pressed into contact with one another. The calculated contact resistance between some common solids is given, and graphs are presented from which the heat flow between any two materials may be computed. It is shown too that the spin–phonon, phonon–electron, and phonon–phonon relaxation processes give rise to additional resistive processes in some solids, some of which restrict the heat flow at the surface. The theoretical results compare well with the available experimental data. However, the problem of the contact resistance between helium and metals is still unresolved. A tentative explanation of this is presented which predicts that there should be an appreciable difference between the contact resistance of a metal in the normal and in the superconducting state.
THE PRESSURE-INDUCED ROTATIONAL ABSORPTION SPECTRUM OF HYDROGEN: I. A STUDY OF THE ABSORPTION INTENSITIES
Authors: Kiss Z. J. , Gush H. P. , Welsh H. L.
Published: April 2011

The pressure-induced infrared spectrum of H2 and mixtures of H2 with N2, He, Ne, A, Kr, and Xe was measured in the region 300–1400 cm−1 at total gas pressures up to 250 atm at 300° K and, where possible, at 195° K and 85° K. The spectrum shows greatly broadened S lines (ΔJ = + 2) with half widths which decrease as the temperature is lowered. The integrated absorption coefficient of the band is of the form [Formula: see text], where ρƒ is the density of the perturbing gas, except in the case of Xe for which a cubic term, [Formula: see text], is also necessary. The binary coefficient α1 increases by a factor of 28 in going from He to Xe. The theoretical band intensity, calculated on the basis of quadrupole interaction alone, is in good agreement with the experimental value only for Xe as perturbing gas; in other cases the calculated value is appreciably less than the observed value. The shape of the absorption contours suggests that the S lines are overlaid by a continuum increasing in intensity towards lower frequencies. This continuum is interpreted as the counterpart of the QR component in the vibrational band, that is, a collision-induced absorption due to overlap interaction in which the relative kinetic energy of the collision partners changes in the absorption process.
MEASUREMENT OF THE ENERGIES OF NUCLEAR STATES EXCITED BY INELASTIC NEUTRON SCATTERING, AND A SEARCH FOR ELECTRIC MONOPOLE TRANSITIONS IN Pb
Authors: Evans J. E. , Whitmore B. G. , Kinsey B. B.
Published: April 2011

A method of measuring the energies of nuclear states excited by inelastic neutron scattering is described, in which an energy-selective detector is used. The neutron source was Li or H3 bombarded by protons from a Van de Graaff generator. The ratio of the counting rate produced in this detector by the material under study to that produced by a long counter was plotted against the proton energy. Peaks in this curve occur when the energy of the scattered neutrons is equal to the resonance energy of the selective detector (255 kev). The energies of the excited states responsible for these neutrons were determined with some precision by a step-by-step comparison with those produced by a standard material for which the energies of the excited states are already well known (e.g. Fe56). A weak peak, not corresponding to any known state, was found in Zr. Two states in Fe56 were used to determine the energies of peaks obtained from Pb. One of these was that due to the well-known state at 2.62 Mev. However, peaks were observed corresponding to both lower and higher energies, none of which agree with those of known excited states. Except for that caused by the 803-kev state of Pb206, no other peaks were observed from a target of Pb206. Th232 produced strong peaks corresponding to excited states at 760 and 1080 kev; U238 produced a peak at 710 kev and another (unresolved from higher energy peaks) at 940 kev. Both peaks near 700 kev from these two nuclei showed unresolved structure.A peak was found from natural Pb corresponding to an excited state at 3.185 Mev. Reasons are given for believing that this state is 0+. An unsuccessful search was made for annihilation radiation using coincident NaI crystals in a rectilinear arrangement. This apparatus detected readily the pair production from the 0+ state in Zr90, but was apparently responsible for a spurious effect in Pb. If pairs are emitted by a 3.185-Mev state in Pb208, the cross section for this process for neutrons with energy 0.5 Mev above threshold is probably less than one half of that from Zr90 for an equal energy excess above threshold.
WATER VAPOR PERMEABILITY OF POROUS MEDIA
Authors: Woodside William
Published: April 2011

Following the analogy between the laws of heat conduction and vapor diffusion, two theoretical expressions for the thermal conductivity of a composite medium are applied to the water vapor permeability coefficient of certain porous media. It is shown that both expressions reduce to a form very similar to the empirical relationships found by Penman and Edenholm for soils, glass spheres, charcoal, and cellular concrete. The calculation of the variation of water vapor permeability with density for a cellular lightweight concrete is illustrated.
SOLUTION OF THE HUND GRAVITATIONAL EQUATIONS
Authors: Chambers Ll. G.
Published: April 2011

Solutions are indicated for the Maxwell type gravitational field equations developed by Hund in the realization of Mach's program. These solutions are of interest in connection with recent work by Kaempffer.
NORMAL GRAIN GROWTH IN ZONE-REFINED HIGH-PURITY METALS
Authors: Holmes E. L. , Winegard W. C.
Published: April 2011

Comparisons are made between theoretical and experimental rates of boundary migration during grain growth in zone-refined metals; these indicate that a single-atom process is involved. A model is proposed for the mechanism of grain-boundary migration based on the assumption of a single-atom process and the fact that the energies of activation for grain growth, both in zone-refined lead and tin, are similar to the energy barrier to be overcome by an atom in transferring from the solid to the liquid state during melting.
THERMAL NEUTRON ABSORPTION CROSS SECTION OF Xe135
Authors: Fickel H. R. , Tomlinson R. H.
Published: April 2011

The effective neutron absorption cross section of Xe135 has been measured with a mass spectrometer by observing the variation in the Cs135/Cs137 fission yield ratio obtained at various thermal neutron fluxes. Values of 3.15 ± 0.06 megabarns and 3.27 ± 0.11 megabarns have been determined for neutron temperatures of 120 °C and 137 °C respectively.
SIZE OF IRREGULARITIES IN THE E REGION OF THE IONOSPHERE
Authors: Rao M. Srirama
Published: April 2011

Three-station fading records taken at Ottawa on frequencies ranging between 2.0 and 2.6 Mc/s have been analyzed to determine the E region wind velocities (V) and frequencies of fading (N) for the period June 1953 to April 1955. An empirical relation V = 2.41 Nλ has been deduced, on a statistical basis, to represent the above observations. In this equation, λ represents the wavelength of operation. The constant of proportionality (K) in this relation has been studied comparatively for three different locations in the northern hemisphere. This constant has been related to a characteristic length L which specifies the horizontal size of the irregularities in the E region of the ionosphere by the equation: L = (1/2)Kλ. Variation of this size with latitude is discussed.
TRANSIENT DECREASES IN COSMIC RAY INTENSITY DURING THE PERIOD OCTOBER 1956 TO JANUARY 1958
Authors: Fenton A. G. , Rose D. C. , McCracken K. G. , Wilson B. G.
Published: April 2011

Recent nucleon intensity data obtained from high counting rate recorders at Ottawa and Hobart, and subsidiary stations, have been examined for evidence for the superposition of transient decreases. It is concluded that, with the statistical accuracy now available due to the high counting rates, it is possible to distinguish two types of transient decreases in the observed variations, superimposed upon the slower 11-year intensity changes. One of these is an almost symmetrical event lasting up to 2 weeks and exhibiting a recurrence tendency of about 27 days, while the other is the more abrupt Forbush decrease which recovers over a period of several days. The evidence indicates that the intensity-controlling mechanism responsible for these short-term transient changes is able to influence the cosmic ray flux at the earth independently of other events that may be in progress at the time. There is also evidence that the physical process controlling the Forbush type of decrease operates over a volume large compared with the earth because the intensity changes at places as far apart as Ottawa, Canada, and Hobart, Tasmania, show changes that are the same within the accuracy of the measurements.
INVESTIGATION OF DEFORMATION PROCESSES IN ARMCO IRON BY MEANS OF INTERNAL FRICTION AT MEGACYCLE FREQUENCIES
Authors: Bratina W. J.
Published: April 2011

Internal friction, employing frequencies in the megacycle range, has been used in order to study the characteristics of elastic and plastic deformation in Armco iron. Tensile stresses only were applied in the present investigation.Among the characteristic features observed three were investigated in detail. (1) A decrease in ultrasonic attenuation at external static stresses within the elastic range, which appears to be related to the ordering effect of the stress on magnetic domains, was investigated. (2) An initial increase in attenuation values regularly observed in cold-worked specimens upon the application of an external load was shown to be associated with the internal stresses. (3) The changes in attenuation resulting from plastic deformation were found to be insignificant in some instances and large in others. An explanation employing the magnetic domain theory and dislocation mechanisms is suggested.
THE SCATTERING OF ELECTROMAGNETIC WAVES BY A CORRUGATED SHEET
Authors: Senior T. B. A.
Published: April 2011

The physical optics method is used to determine the scattering of a plane wave by a perfectly conducting sheet having sinusoidal corrugations. The only approximation concerns the current distribution on the sheet and the scattered field then appears as a spectrum of plane waves whose amplitudes are given by a simple integral expression.
A SIMPLE GAMMA-RAY INSENSITIVE FAST-NEUTRON COUNTER
Authors: Griffiths G. M. , Singh P. P. , Ssu Y. I. , Warren J. B.
Published: April 2011

A gamma-ray insensitive fast-neutron counter is described which consists of a number of thin rectangular sheets of lucite coated with zinc sulphide and sandwiched together to form a rectangular block which is mounted on a photo-multiplier. Pulse height spectra and absolute efficiency curves are presented for neutrons from 300 kev to 15 Mev.
MAGNETIC CONTROL ON THE VARIATIONS OF THE CRITICAL FREQUENCY OF THE F2 LAYER OF THE IONOSPHERE
Authors: Rastogi R. G.
Published: April 2011

The paper discusses the comparative influence of the true magnetic and smooth geomagnetic latitudes on the diurnal and latitudinal variations of the critical frequency of the F2 layer (f0F2) at low latitudes. The diurnal variations of f0F2 are shown to differ considerably at stations having the same geomagnetic latitude, but the discrepancies disappear when the true magnetic latitude is taken into consideration. The latitudinal variation of noon values of f0F2 is also shown to present discrepancies for low latitude stations in the geomagnetic latitudes plot, but on true magnetic latitude plots the points fall regularly along a smooth curve.
SCATTERING FACTORS FOR SOME OF THE HEAVIER ATOMS
Authors: Worsley Beatrice H.
Published: April 2011

A program for calculating X-ray atomic scattering factors from the radial wave functions has been written for the IBM 650 installation at the University of Toronto. It has been applied to the results of self-consistent field calculations previously performed at this University on the FERUT computer. Results are given for Ne, V++, Kr, Ag+, and Pb+++. The results for Ne and V++ are compared with those calculated by Freeman using Allen's wave functions for Ne and Hartree's approximate wave functions for V++.
APPROXIMATE WAVE FUNCTIONS OF Pb+++ BY THE METHOD OF SELF-CONSISTENT FIELD WITHOUT EXCHANGE
Authors: Hart J. F. , Worsley Beatrice H.
Published: April 2011

The FERUT program previously described for calculating Hartree–Fock wave functions by the method of the self-consistent field has been adapted to the configuration Pb+++. Although the exchange factors were omitted, the program was extended beyond its original scope in other respects, and an assessment of the difficulties so encountered is made. It might be noted, however, that, except in the case of the 4ƒ wave function, it was possible to begin all the integrations at a common point. Initial estimates were made from the Douglas, Hartree, and Runciman results for thallium. The estimates for the core functions were not assumed to be satisfactory. The errors in the final wave functions are considered to be no more than one or two units in the second decimal digit.
A CRYOSTAT FOR MEASURING SPECIFIC HEATS BETWEEN 1 AND 4.2° K USING A MECHANICAL THERMAL SWITCH
Authors: Manchester F. D.
Published: April 2011

A design for a low temperature cryostat using a mechanical thermal switch is described and its performance and some general features of interest in its operation, such as the importance of vibration, are discussed. Sample measurements on pure copper and a cupro–nickel alloy are presented.
ORBITAL FOLLOWING IN TETRAHEDRAL MOLECULES
Authors: Blum Lesser , Cohan Norah V.
Published: April 2011

On the basis of Heath and Linnett's formulas, the "orbital following" force constants of NH3- and [Formula: see text]-like molecules are calculated. The anomalous results are interpreted as a consequence of orbital deformation during the vibratory movement.
THE HUND GRAVITATIONAL EQUATIONS AND GEONS
Authors: Chambers Ll. G.
Published: April 2011

Certain solutions of the Hund gravitational equations which represent geons are derived, and the stability of steady solutions is discussed.
ULTRASONIC ATTENUATION IN SUPERCONDUCTING AND NORMAL MERCURY
Authors: Chopra K. L. , Hutchison T. S.
Published: April 2011

Ultrasonic attenuation in superconducting and normal mercury has been studied with 20, 34, and 60 Mc/s longitudinal waves. The difference in attenuation between the superconducting and normal states below the transition temperature is greatly increased at the higher frequencies. The attenuation in the normal state is the same for both longitudinal and transverse critical magnetic fields and is independent of field strength between the critical value and 880 oersteds. The results disagree in some respects with those of MacKinnon and Myers. The experimental limitations of the method as a critical test of the Bardeen–Cooper–Schrieffer theory of superconductivity are discussed.
FIRST ADSORBED LAYER OF NITROGEN ON PYREX AT 77.4° K
Authors: Hobson J. P.
Published: April 2011

A measure of the nitrogen adsorption isotherm on pyrex (Corning 7740) at 77.4° K has been made for pressures above the adsorbed layer ranging from 10−3 to 10−9 mm Hg. Ultrahigh-vacuum techniques were used. Geometric adsorbing areas were 60 and 32 cm2. Coverages ranged approximately from 0.001 to 0.3 monolayer. Full equilibrium was probably not achieved but the data could be represented by the Dubinin–Radushkevich equation,[Formula: see text]for P/P0 from 10−6 to 10−11, where σ is the amount adsorbed.
DESIGN OF GRADIENTLESS FURNACES
Authors: Laubitz M. J.
Published: April 2011

Temperature distributions in cylindrical furnaces are discussed, and design data are given which permit the construction of short furnaces in which the temperature varies less than 0.5% along the central half of the length of the heater. Formulae are also given for the calculation of temperature distributions in conventional furnaces with uniformly wound heaters.
RADIO STAR SCINTILLATIONS AND IONOSPHERIC DISTURBANCES
Authors: Hartz T. R.
Published: April 2011

The generation mechanism for the ionization irregularities in the upper atmosphere which are responsible for radio star scintillations is considered. The general belief that scintillations are related to the spread-F phenomenon observed on ionosonde recordings is found to be an inadequate explanation for the scintillations at 53 Mc/s recorded at Ottawa. An examination of the Ottawa recordings shows that there is a definite association, both in time of occurrence and geographical location, with those ionospheric disturbances that are usually considered to be due to incoming solar particles. Since other workers at more southerly geomagnetic latitudes have associated their scintillation observations with the spread-F phenomenon which they consider to be independent of auroral activity, it would appear that two mechanisms, at least, are responsible for the radio star fluctuations: namely, the precipitation of solar corpuscles and a mechanism linked with the spread-F phenomenon. The former seems to predominate at high latitudes, the latter is probably predominant at low latitudes, while both mechanisms probably are operative in middle latitudes.
THE 0–0 AND 1–0 BANDS OF THE A(3Πi)–X(3Σ−) SYSTEM OF NH
Authors: Dixon R. N.
Published: April 2011

NH molecules have been produced during the flash photolysis of HNCO, and the 0–0 and 1–0 bands of the A(3Πi) ← X(3Σ−) system have been photographed in absorption in the third order of a 21-foot concave grating spectrograph. The intensity distribution in the bands showed that the molecules were approximately at room temperature. The lines of lowest J value are identified for 25 branches of the 0–0 band and 19 branches of the 1–0 band. The analysis of the 0–0 band leads to a correction of the published line assignments for this band. The spin splittings in both the A and X electronic states, and the A-doubling in the A state, are considered in detail. Wavelengths in air are given for lines of astrophysical interest.
THE SUN AS A SOURCE OF COSMIC RAYS OF INTERMEDIATE ENERGIES
Authors: Katzman J.
Published: April 2011

The cosmic ray intensity as measured with an extremely narrow-angle telescope, 1.2 × 10−3 steradians, and with 96 inches of lead as absorber for the period 1 January 1955 to 31 December 1958 shows an increase of 20%. This increase is attributed to particles coming from the sun. It is shown that the change in hour of maximum of the first and second harmonics can be explained by a change in the relative importance of the impact zones. This phenomenon is attributed to a change in the number and polarity of sunspots.
RESOLVING POWER OF THREE ANTENNA PATTERNS DERIVED FROM THE SAME APERTURE
Authors: Covington E. , Harvey Gladys A.
Published: April 2011

Three antenna patterns are derived from the same linear aperture and may be described in terms of an angular spectrum of spatial frequencies ranging from zero to a common cutoff frequency. The band passes according to the shape of the spectrum are rectangular, triangular, and cosinusoidal for the three patterns, and give resolving powers respectively of 1.33, 1.00, and 1.05, in terms of the cutoff period. The rectangular band pass gives rise to the optimum antenna pattern and allows the Fourier components of a source from zero to cutoff frequency to be received with equal intensity and zero phase shift. Scanning curves of two equally intense point sources and a uniformly bright line are investigated.
THE PRESSURE-INDUCED ROTATIONAL ABSORPTION SPECTRUM OF HYDROGEN: II. ANALYSIS OF THE ABSORPTION PROFILES
Authors: Kiss Z. J. , Welsh H. L.
Published: April 2011

The experimental profiles obtained in Part I for the pressure-induced absorption of H2 and H2 – foreign gas mixtures in the region 300–1400 cm−1 are separated by a semiempirical method into rotational and translational parts. The pressure-induced rotational lines of H2 are shown to have a dispersion line shape, modified by the Boltzmann law. The intensities of the rotational parts of the spectra are, on the average, 13% greater than those calculated in Part I on the assumption of quadrupole interaction alone; the residual experimental intensity probably represents the effect of overlap interaction. The intensities of the translational parts of the spectra are of the same order of magnitude as the translational intensities in mixtures of the rare gases. Some additional experimental data on double rotational transitions and on the anomalous density variation of the absorption in H2–Xe mixtures are given.
FRONTAL PERTURBATION OF A TROPOSPHERIG SCATTER PATH
Authors: Hay D. R. , Poaps G. E.
Published: April 2011

A 2-year study of 500 Mc/s radio transmissions over an 85-mile path near Ottawa has shown that the signal fading rate rises well above the diurnal maximum when the transmission path is perturbed by a weather front. The fading rate reaches a maximum when the upper boundary of the frontal zone is 3000 feet above the center of the radio path, and the fading rate remains high as long as any part of the frontal zone is between the surface and 3000 feet. A similar relationship between frontal position and signal fading rate is found for Arctic, Maritime, or Polar fronts in the Ottawa area, but the Arctic fronts provide the clearest definition. There is some indication that high fading rate also may be associated with horizontal layers of contrasting humidity at low levels in the troposphere.
LIMITING PRECISION IN OPTICAL INTERFEROMETRY
Authors: Hanes G. R.
Published: April 2011

The fundamental limit to the precision of setting on a fringe peak due to photon noise is evaluated for a certain class of interferometric methods in terms of parameters characterizing the source, the interferometer, and the detector. It is shown that changes in path difference of 10−10 should be detectable with an observing time of 1 second, using only modest equipment. Some of the experimental conditions required to attain this precision are discussed.
THE PHOTODISINTEGRATION OF MANGANESE AND RHODIUM
Authors: Parsons R. W.
Published: April 2011

The cross section for the production of photoneutrons from Mn55 and Rh103 has been found by irradiating these elements in the X-ray beam of a 24-Mev betatron. For Mn55, the giant resonance shows two distinct peaks and the intrinsic quadrupole moment is estimated to be 0.73 ± 0.14 barn; for Rh103, two peaks cannot be resolved, but the shape of the giant resonance curve is consistent with an intrinsic quadrupole moment of approximately 2.1 barns.
EBULLIOMETRY AND THE DETERMINATION OF THE MOLECULAR WEIGHTS OF POLYMERS: PART III. CONSIDERATIONS ON THERMISTOR WHEATSTONE BRIDGES
Authors: Blackmore W. R.
Published: April 2011

It is shown that a d-c. thermistor Wheatstone bridge may be used in ebulliometry to measure the small temperature differences which are observed between the boiling points of polymer solutions and the pure solvent. A relationship is derived between the thermistor bridge unbalance voltage and the solute molecular weight, which it is desired to measure. It is shown that a bridge composed of suitably matched thermistors may be made independent of the gross changes in boiling point of both solution and solvent produced by changes in atmospheric pressure. The possibility of the current flowing through the thermistors disturbing the measurements is discussed and in situ measurements of thermistor dissipation and time constants are given. The sensitivity attainable with various thermistor bridges and modern amplifiers at full gain is calculated and shown to be much greater than may be employed with the usual type of ebulliometer. The reason for this is the relatively large background noise (random temperature fluctuations) produced in the ebulliometer by the boiling process itself.
LUMINESCENCE AND CONDUCTIVITY INDUCED BY FIELD IONIZATION OF TRAPS
Authors: Haering Rudolph R.
Published: April 2011

When a photoconductor is illuminated at low temperatures, trapping states may be populated by electrons. If the light is then removed and an electric field is applied to the sample, these traps may be emptied by field ionization. For an electric field which increases linearly with time, the conductivity and the luminescent brightness display a sharp maximum at some field strength. It is shown that this maximum may be used to obtain the trap energy. The analysis of such field-ionization-induced maxima is very similar to the analysis of glow curves in thermoluminescence.
SPECTRAL DISTRIBUTION OF BREMSSTRAHLUNG FROM AN IONIZED GAS
Authors: Sodha Mahendra Singh
Published: April 2011

Using Heitler's and Sommerfeld's cross section the spectral distribution of bremsstrahlung from an ionized gas has been calculated, neglecting self-absorption and stimulated emission. These results can be used to calculate the spectral distribution of bremsstrahlung from a mass of ionized gas, considering self-absorption and stimulated emission if one utilizes the expression obtained by Allen and Hindmarsh.
ON THE DIFFRACTION OF ELECTROMAGNETIC PULSES BY CURVED CONDUCTING SURFACES
Authors: Wait James R. , Conda Alyce M.
Published: April 2011

Starting with the known steady-state solutions for diffraction by a perfectly conducting convex surface, the corresponding transient responses are derived using Fourier–Laplace inversion. Explicit results are given for an incident wave which varies with time as a step function.
SOME PHYSICAL PROPERTIES OF SEA ICE. II
Authors: Langleben M. P.
Published: April 2011

Some properties of annual sea ice at mid-temperate latitudes are investigated. It is found that the salinity is comparable to, and the density much lower than, annual arctic sea ice. Permeability to air flow compares favorably to calculations based on the model of sea ice of Anderson and Weeks (1958). Small sample ring tests of ultimate tensile strength yield values ranging from 9.5 to 24.8 kg cm−2 at test temperatures of −3.6 °C to −17.2 °C. Tensile strength appears to depend on crystal size rather than on brine content.
BETATRON ENERGY CALIBRATION
Authors: Katz L.
Published: April 2011

A new betatron energy controlling circuit is described which has many advantages over those previously used. It is shown that there is a linear relationship between the helipot control on this circuit and the momentum of the electrons in the betatron just prior to striking the X-ray producing target. It is also shown that photoneutron thresholds can be used to calibrate the betatron energy scale with good internal consistency.
STUDIES OF (p,n) REACTIONS IN THE PROTON ENERGY RANGE FROM 2 TO 10 MEV
Authors: Bromley D. A. , Ferguson A. J. , Gove H. E. , Kuehner J. A. , Litherland A. E. , Almqvist E. , Batchelor R.
Published: April 2011

Reaction thresholds have been studied for (p,n) reactions on B11, F19, Al27, Si30, P31, K39, Ni58, and Ni60. Using the C13(p,n)N13 and Cu65(p,n)Zn66 thresholds, which have previously been measured with precision, to calibrate the magnetic beam analyzer of the tandem accelerator, and the H2(O16,n)F17 threshold to establish the linearity of this calibration to an equivalent proton energy of 14.57 Mev, threshold energies of 3.019±0.004, 4.229±0.006, 5.800±0.008, 5.174±0.030, 6.456±0.020, 7.227±0.070, 9.480±0.025, and 7.016±0.015 Mev, respectively, have been established. These data are in reasonable agreement with the available positron decay data except in the case of Ca39 where an unexplained discrepancy exists. Resonances of total width less than 20 kev have been observed in the neutron-excitation curves of the Al27(p,n)Si27 and Si30(p,n)P30 reactions corresponding to excitations of approximately 17 Mev and 13 Mev in the compound systems Si28 and P31, respectively. In the latter case isolated resonances are found without overlapping broad resonances. The reaction threshold falls between resonances and is not directly observable; the counter-ratio technique was calibrated for use in such situations. Neutron yield measurements have been made on thick targets of C, Al, Ni60O, Ni58O, Ni58, W, Pb, Au, Th, and U as functions of the incident proton energy in the energy range from 4 to 10 Mev.
A 2Π-2Π ELECTRONIC BAND SYSTEM OF THE FREE NCO RADICAL
Authors: Dixon R. N.
Published: April 2011

A series of red-degraded absorption bands has been observed between 2650 Å and 3200 Å and is attributed to a 2Π-2Π transition of the NCO radical. The bands probably represent a progression of the upper-state stretching vibration [Formula: see text]. The rotational structure of one band has been analyzed. Diffuseness in some of the bands indicates predissociation of the upper state, and is discussed in terms of the dissociation energy of NCO.
THE SPECIFIC HEAT OF COPPER FROM 20° TO 300 deg;K
Authors: Martin Douglas L.
Published: April 2011

The specific heats of commercially pure cold-rolled copper and of annealed and heavily cold-worked 99.999% pure copper have been measured in the temperature range 20° to 300 deg;K. When results are averaged over the whole temperature range of measurement the specific heat of the pure cold-worked copper is about 0.15% above that of the pure annealed sample while results for the commercially pure cold-rolled material lie in an intermediate position. Results on a given sample are reproducible within 0.05%. The entropy of pure annealed copper at 298.15 deg;K is 7.92 ± 0.04 cal/°K g-atom.
COMPARISON OF FLOW LINES IN VARIOUS TYPES OF RHEOLOGICAL BODIES
Authors: Das Sisir Chandra
Published: April 2011

An attempt has been made to investigate the nature of flow in Bingham bodies compressed by means of parallel rigid approaching plates. The results have been compared with those of plastic and viscous flow under the same conditions. It is shown that the flow lines in all three cases are very similar.
DIFFRACTION BY A SPHEROID
Authors: Levy Bertram R. , Keller Joseph B.
Published: April 2011

The diffraction of a spherical scalar wave by a hard or soft spheroid is investigated theoretically. First the diffracted field is determined by the geometrical theory of diffraction. Then for comparison the corresponding boundary value problem is solved exactly in terms of a series of products of spheroidal functions. The series involves the "radial" eigenfunctions which correspond to appropriate complex eigenvalues. Asymptotic expansions are derived for these functions for large values of the variable and the parameter. When used in the series solution, these expansions yield the asymptotic form of the diffracted field for incident wavelengths small compared to the spheroid dimensions. This result coincides precisely with that given by the geometrical theory. This agreement provides another verification of that theory. The expression for the field is used to calculate the backscattering and the field on the spheroid. The electromagnetic backscattering is finally computed with the aid of a theorem which relates it to the two scalar results.
ON THE STABILITY OF DISPLACEMENT FRONTS IN POROUS MEDIA: A DISCUSSION OF THE MUSKAT–ARONOFSKY MODEL
Authors: Scheidegger A. E.
Published: April 2011

It is well known that, during the displacement of a fluid contained in a porous medium by another less viscous one, the displacement front may become unstable: Fingers occur which proceed rapidly through the system.The Muskat–Aronofsky model of displacement in porous media, in which it is assumed that a sharp front exists with maximum saturation by the respective fluid being present on either side of the front, is analyzed in the light of the phenomenon of fingering. It is shown that the Muskat–Aronofsky model, in fact, demands that fingering occurs for mobility ratios (displaced/displacing fluid) smaller than one. This model should, therefore, not be used for the calculation of the steady progress of a front for such mobility ratios. The Muskat–Aronofsky model also yields some conditions regarding the geometry of fingers; the latter are deduced. It does not, however, describe the fingering process completely. In this connection, one would have to take recourse to the statistical geometry of porous media. This will be done in a separate paper.
DIFFRACTION BY A UNIDIRECTIONALLY CONDUCTING HALF-PLANE
Authors: Hurd R. A.
Published: April 2011

The problem of the diffraction of a plane electromagnetic wave by a unidirectionally conducting half-plane is solved by transform techniques. A comparison is made with the results previously obtained by Karp.
THE INFRARED FUNDAMENTAL BAND OF LIQUID AND SOLID HYDROGEN
Authors: Gush H. P. , Allin E. J. , Welsh H. L. , Hare W. F. J.
Published: April 2011

The infrared fundamental band of liquid and solid hydrogen was investigated over a range of para-concentrations from 25% to 100% with a prism spectrometer and, in part, with a grating spectrometer at a resolution of ~0.2 cm−1. The spectrum of the solid shows (a) comparatively sharp Q, S(0), and S(1) lines due to quadrupolar interaction, (b) broad bands interpreted as combination tones of the molecular frequencies with the lattice frequencies (phonon spectra), and (c) weak double transitions of the type S1(0) + S0(0). At high resolution the quadrupolar S(0) and S(1) groups show weak single transitions, S1(0) and S1(1), and much stronger double transitions of the type Q1(J) + S0(J), J = 0,1. In solid parahydrogen the lines become very sharp and the double transition, Q1(0) + S0(0), shows a complex structure; the observations are in good agreement with the theory of the rotational and vibrational levels of solid parahydrogen by Van Kranendonk. The quadrupolar Q branch shows a structure which is interpreted as double transitions of the type Q ± δi where the δi are the small changes in energy due to the orientational transitions of two ortho-molecules. The phonon spectra show a maximum at the Debye temperature of the solid, and, at higher resolution, a structure indicative of the various branches of the lattice frequencies. A long extension of the phonon spectrum towards high frequencies is probably due to multiple phonon creation. Double transitions, for which the cancellation principle in induced absorption does not apply, account for at least 98% of the intensity of the spectrum of the solid.
THE GAMMA-NEUTRON CROSS SECTION FOR N14
Authors: King J. D. , Haslam R. N. H. , Parsons R. W.
Published: April 2011

The reaction N14(γ,n)N13 has been studied by irradiating dicyandiamide in the X-ray beam of a 25-Mev betatron and measuring the residual activity with a sodium iodide crystal system. The photoneutron cross section shows maxima at 11.7, 13.2, 15.2, 19.5, and 22.8 Mev, the last two being in the giant resonance region. The integrated cross section from threshold to the beginning of the giant resonance region is 1.8 Mev-mb, and this is compared with a recent theoretical prediction. During the course of the experiment, accurate measurements were made of the half-life of N13 and it was found to be 9.93 ± 0.05 minutes.
THEORY OF THE INFRARED AND RAMAN SPECTRA OF SOLID PARAHYDROGEN
Authors: Kranendonk J. Van
Published: April 2011

The theory of the rotational and vibrational energy bands in solid hydrogen, developed previously, is applied to the interpretation of the infrared and Raman spectra of solid parahydrogen. A comparison of the theory with the experimental results yields information about the nature of the rotational and vibrational motions of the molecules in the solid, and about the anisotropic intermolecular forces. A calculation of the intensity of the infrared rotational and vibrational lines is given, which is based on the induction mechanisms introduced previously to explain the induced absorption in gaseous hydrogen. Satisfactory agreement with the experimental values is obtained. The importance of the interaction between other than nearest neighboring molecules, and of the interference effects affecting the single transitions, is pointed out. A frequency analysis is given of the infrared and Raman rotational and vibrational lines in the solid, and a consistent theory of the shifts and splittings of the various lines is obtained. Empirical values of the rotational and vibrational coupling constants are derived and compared with the theoretical values.
TRANSITION INTENSITIES AND CONVERSION COEFFICIENTS IN Dy160
Authors: Clark M. A.
Published: April 2011

K-conversion coefficients for gamma transitions in Dy160 have been measured and the transition multipolarities determined as follows (Eγ, αK, multipolarity): 86.7 kev, 1.5 (E2); 197 kev, 1.6 × 10−1 (E2); 216 kev, 4.0 × 10−2 (E1); 299 kev, 1.3 × 10−2 (E1); 880 kev, 3.1 × 10−3 (E2); (962 + 966) kev, 2.5 × 10−3 (E2); 1179 kev, 6.6 × 10−4 (E1); 1205 kev, 4.6 × 10−4 (E1); 1273 kev, 6.1 × 10−4 (E1); 1315 kev, 3.9 × 10−4 (E1), Relative transition intensities are compared with the predictions of the Unified Model of Bohr and Mottelson and the asymmetric rotor theory of Davydov and Filippov. Transition intensities from the 966-kev level to members of the ground state rotational band suggest the asymmetric rotor interpretation.
ALPHA DECAY AND FISSION OF ALIGNED NUCLEI
Authors: Steenberg N. R. , Sharma R. C.
Published: April 2011

The theory of the angular distribution of alpha particles and of fission fragments from nuclei aligned at low temperatures is presented. Very explicit results are obtained in the high temperature approximation. These are directly dependent upon the branching which takes place to the various allowed partial waves. This branching is influenced by the nuclear shape, but it is shown that for this problem the effect of penetrating a spheroidal barrier is not critical. An application is made to the experimental work so far available and the result is reasonably satisfactory.
CONDENSATION OF SUPERSATURATED He4 VAPOR IN A CLOUD CHAMBER
Authors: Edwards M. H. , Woodbury W. C.
Published: April 2011

The critical supercooling, ΔTc, required to produce visible condensation in pressure-limited adiabatic expansions of presumably ion-free saturated He4 vapor has been measured in a small glass cloud chamber. The transient gas temperatures were measured during expansions by using a carbon resistance thermometer in a Wheatstone bridge. An oscilloscope was used in place of a galvanometer, and its trace was photographed during expansions. Low-amplitude temperature oscillations in the gas, which might not normally have been detected, were frequently observed in the early stages of this work. These oscillations either appeared spontaneously ("Taconis Resonances"), or could be shock-excited by an expansion. These oscillations were subsequently eliminated. Condensation thresholds were then measured using starting temperatures from 4.2 to 1.7 °K. ΔTc dropped from about 50 to 60 mdeg above the λ point to less than 20 mdeg below the λ point. The critical supersaturations required to produce condensation were thus always less than 105%. The supersaturations were calculated without making the usual, but highly implausible, assumption that the expanding gas is ideal. Assuming that the condensation nuclei are embryonic droplets arising accidentally from density fluctuations in the supersaturated vapor, the critical droplet radius is found to be about 10−6 cm above 2.5 °K, although the theoretical treatment here is not rigorous.
A CONDENSER MEMORY UNIT FOR IMPROVING SIGNAL-TO-NOISE RATIOS
Authors: Hunten D. M.
Published: April 2011

The unit contains 30 low-leakage condensers which can store a signal for several hours if necessary. If the signal is repeated over and over, the successive scans can be added in and the signal-to-noise ratio builds up as the square root of the number of repetitions. In principle, the final signal-to-noise ratio is only slightly better than would be obtained from a single scan stretched out to fill the same total time, but in practice the result may be considerably better, especially if the signal fluctuates slowly. It has been used successfully in several investigations of twilight spectra with photoelectric and photoconductive spectrometers. The original version took 1 minute per scan and was rather bulky; a recent modification can scan 32 channels in 10 seconds if required.
THE ELECTRICAL RESISTANCE OF DILUTE MAGNESIUM AND ALUMINUM ALLOYS AT LOW TEMPERATURES
Authors: Hedgcock F. T. , Muir W. B. , Wallingford E.
Published: April 2011

Experimental data on the influence of type and concentration of impurity on the low-temperature resistance of the metals, magnesium and aluminum, is presented. In particular, comparison is made of the electrical behavior of alloys formed using transition element impurities in the divalent metal magnesium, and in the trivalent metal aluminum with the behavior of similar impurities in some of the noble metals.
THE ASSOCIATION OF VISIBLE AURORAL FORMS WITH RADAR ECHOES
Authors: Lyon G. F.
Published: April 2011

A peak in 48.2-Mc/sec echo occurrence is observed at Saskatoon corresponding in time to the period of breakup of quiet arcs into active rayed structures. This is also the time of most frequent occurrence of characteristic "curl" forms in the aurora. If, as Gartlein suggests, the "curl" forms are formed by instabilities in a sheet beam then the primary particles are positively charged.