bluuebunny/crossref_metadata_2025 huggingface dataset:
On temperature-dependent frequency factor in thermoluminescence measured with a hyperbolic heating profile
Authors: Singh W S , Bhattacharya M , Singh S D , Mazumdar P S
Published: April 2011

In this paper, we investigate the consequences of the temperature dependence of the frequency factor on thermoluminescence peaks recorded in a hyperbolic heating profile. The temperature dependence of the frequency factor leads to nonuniqueness in the symmetry factor for a particular order of kinetics (b) and causes an error of the order of 5% in the determination of b and an error of the order of 10% in the determination of activation energy (E).

PACS No.: 78.60Kn
Magnetohydrodynamic compressible laminar boundary-layer adiabatic flow with adverse pressure gradient and continuous or localized mass transfer
Authors: Xenos M , Kafoussias N , Karahalios G
Published: April 2011

The problem of magnetohydrodynamic compressible boundary-layer flow over a flat plate, in the presence of an adverse pressure gradient, is studied numerically. The fluid is assumed to be Newtonian, electrically conducting and the magnetic field is constant and applied transversely to the direction of the flow. The fluid flow is subjected to a constant velocity of suction and (or) injection, continuous or localized, and there is no heat transfer between the plate and the fluid (adiabatic flow). The system of partial differential equations, describing the problem under consideration, is solved numerically by applying a modification of the Keller box technique. Numerical calculations are carried out for different values of the free-stream Mach number and the magnetic parameter for continuous or localized suction and (or) injection imposed at the wall. The results obtained are shown in the figures and their analysis shows that the flow field can be controlled by the application of a magnetic field as well as by continuous or localized suction and (or) injection.

PACS Nos.: 51.00, 52.00
Chiral bosonic field theories and the quantum Hall effect
Authors: Bracken P
Published: April 2011

The gauge-transformation properties of the actions of certain scalar and ChernSimons theories are investigated, including contributions from the boundary. By imposing chirality constraints on the fields, these types of theories can be used to describe the quantum Hall effect. It is shown that the corresponding equation of motion for the associated current for the theory generates an anomaly, which can be related directly to the Hall conductivity.

PACS Nos.: 73.43, 03.70, 11.10, 11.30R
Polarizabilities and other properties of the tdµ molecular ion
Authors: Bhatia A K , Drachman R J
Published: April 2011

Wave functions of the Hylleraas type were used earlier to calculate energy levels of muonic systems. Recently, we found in the case of the molecular ions H2+, D2+, and HD+ that it was necessary to include high powers of the internuclear distance in the Hylleraas functions to localize the nuclear motion when treating the ions as three-body systems without invoking the BornOppenheimer approximation. We tried the same approach in a muonic system, tdµ (triton, deuteron, and muon). Improved convergence was obtained for J = 0 and 1 states for shorter expansions when we used this type of generalized Hylleraas function, but as the expansion length increased the high powers were no longer useful. We obtained good energy values for the two lowest J = 0 and 1 states and compared them with the best earlier calculations. Expectation values were obtained for various operators, the Fermi contact parameters, and the permanent quadrupole moment. The cusp conditions were also calculated. The polarizability of the ground state was then calculated using second-order perturbation theory with intermediate J = 1 pseudostates. (It should be possible to measure the polarizability by observing Rydberg states of atoms with tdµ acting as the nucleus.) In addition, the initial sticking probability (an essential quantity in the analysis of muon catalyzed fusion) was calculated and compared with earlier results.

PACS Nos.: 30.00, 36.10-k, 02.70-c
κ(BEDTTTF)2X organic crystals: Superconducting versus anti-ferromagnetic instabilities in the Hubbard model on an anisotropic triangular lattice
Authors: Tsai S -W , Marston J B
Published: April 2011

A Hubbard model at half-filling on an anisotropic triangular lattice has been proposed as the minimal model to describe conducting layers of κ(BEDTTTF)2X organic materials. The model interpolates between the square lattice and decoupled chains. The κ(BEDTTTF)2X materials have many similarities with cuprates, such as the presence of unconventional metallic properties and the close proximity of superconducting and anti-ferromagnetic phases. As in cuprates, spin fluctuations are expected to play a crucial role in the onset of superconductivity. We perform a weak-coupling renormalization-group analysis to show that a superconducting instability occurs. Frustration in the anti-ferromagnetic couplings, which arises from the underlying geometrical arrangement of the lattice, breaks the perfect nesting of the square lattice at half-filling. The spin-wave instability is suppressed and a superconducting instability predominates. For the isotropic triangular lattice, there are again signs of long-range magnetic order, in agreement with studies at strong-coupling.

PACS Nos.: 74.30G, 76.50
Analog to the 4He melting curve in a model geometrically frustrated magnet
Authors: Tsui Y K , Snyder J , Schiffer P
Published: April 2011

Gadolinium gallium garnet, Gd3Ga5O12 (GGG) has an extraordinary low-temperature phase diagram. Although the CurieWeiss temperature of GGG is ~2 K, GGG shows no long-range order down to T ~ 0.4 K. At low temperatures GGG has a spin-glass phase at low fields ([Formula: see text] 0.08 T), a field-induced long-range-ordered anti-ferromagnetic (AFM) phase at fields of between 0.7 and 1.3 T, and, at intermediate fields, an apparent spin-liquid (SL) phase without long-range order. We have performed specific heat, magnetocaloric, and static magnetization measurements near the SL/AFM phase boundary. Our results show that the lower field boundary of the AFM phase has a distinct minimum at T ~ 0.2 K, in analogy to the minimum in the melting curve of 4He.

PACS Nos.: 75.30Kz, 75.50Ee
Lanczos study of the S = 1/2 frustrated square-lattice anti-ferromagnet in a magnetic field
Authors: Honecker A
Published: April 2011

We study the zero-temperature phase diagram of the frustrated square-lattice S = 1/2 anti-ferromagnet in an external magnetic field numerically with the Lanczos algorithm. For strong frustration, we find disordered phases at high (and low) magnetic fields. Between these two disordered phases, we find a plateau in the magnetization curve at half of the saturation magnetization, which corresponds to a state with up-up-up-down (uuud) spin order. This and other considerations (M.E. Zhitomirsky, A. Honecker, and O.A. Petrenko. Phys. Rev. Lett. 85, 3269 (2000).) suggest an unusual ordering scenario. There is an ordered phase with a spin gap (the plateau) and disordered magnetically gapless phases above and below. The transition to saturation is studied in further detail and problematic conclusions in earlier investigations of this region are pointed out.

PACS Nos.: 75.50Ee, 75.40Mg, 75.45+j
Chiral-ordered phases in a frustrated S = 1 chain with uniaxial single-ion-type anisotropy
Authors: Hikihara T
Published: April 2011

The ground-state phase transitions of a frustrated S = 1 Heisenberg chain with the uniaxial single-ion-type anisotropy and the frustrating next-nearest-neighbor coupling are studied. For the system, it has been shown that there are gapless and gapped chiral phases in which the chirality κl = Slx Syl+1  Sly Sxl+1 exhibits a finite long-range order (LRO) and the spin correlation decays either algebraically or exponentially. In this study, the transitions between the Haldane and chiral phases and between the large-D (LD) and chiral phases are investigated using the infinite-system density-matrix renormalization group method. It is found that there exist two types of gapped chiral phases, "chiral Haldane" and "chiral LD" phases, in which the string LRO coexists with the chiral LRO and the string correlation decays exponentially, respectively.

PACS No.: 75.30
Search for spin liquid state in sub-monolayer 3He adsorbed on HD-preplated graphite
Authors: Ikegami H , Masutomi R , Obara K , Ishimoto H
Published: April 2011

NMR studies of sub-monolayer solid 3He adsorbed on a bilayer of HD-preplated graphite have been made down to 100 µK, which is more than one order of magnitude smaller than the exchange energy (J). In the highly frustrated anti-ferromagnetic region, the magnetization obeys a CurieWeiss law even at temperatures around J and then increases gradually down to 100 µK. Nevertheless, it does not show any anomalous behavior corresponding to the existence of the spin gap. The normalized magnetization versus the reduced temperature (T/J) is independent of the density just after solidification. This fact is consistent with the result in the high-temperature region where the main multiple spin exchanges have a similar density dependence in the present density region.

PACS Nos.: 67.80Jd, 67.70+n, 75.10Jm
Exact diagonalization studies of two-dimensional frustrated anti-ferromagnet models
Authors: Lhuillier C , Sindzingre P , Fouet J -B
Published: April 2011

We describe the four kinds of behavior found in two-dimensional isotropic quantum anti-ferromagnets. Two of them display long-range order at T = 0: the Néel state and the valence bond crystal. The last two are spin liquids. Properties of these different states are briefly described and open questions are underlined.

PACS Nos.: 75.10Jm, 75.50Ee, 75.40-s
Recent developments in X-ray tests of quantum electrodynamicsThis paper was presented at the International Conference on Precision Physics of Simple Atomic Systems, held at University of Windsor, Windsor, Ontario, Canada on 21–26 July 2008.
Authors: Chantler C. T. , Kimpton J. A.
Published: April 2011

Experimental tests of quantum electrodynamics (QED) have developed dramatically for simple systems of hydrogen and helium, but there has also been significant progress for medium-Z hydrogenic and helium-like atoms over the last few years. In this area, tests are often based on X-ray spectroscopic measurements, and here we review some key developments. Of particular interest is the status of few-electron QED in the medium-Z regime, the fine-structure Lamb shift from X-ray measurements, tests of two-electron QED, and of np subshell and excited state QED. We discuss some recent secondary tests of the data to confirm the quality and different approaches to experimental development to address the dominant systematics in this area.
PHOTOELECTRIC METEOR OBSERVATIONS
Authors: McKinley Barbara M. , McKinley D. W. R.
Published: April 2011

The photoelectric meteor detector consists of 19 type 931-A photomultiplier tubes arranged to cover the entire sky. Signals from the photocells are repeatedly sampled in time sequence and displayed on a cathode ray tube. Photoelectric meteor signals, radar meteor echoes, and a marker light operated by visual observers are photographed by a continuous-film camera.Preliminary tests indicated that the average sensitivity of the photoelectric detector to meteors was about one visual magnitude inferior to that of the human eye. Approximate meteor positions and qualitative light intensities could be obtained from the photoelectric record. Timing comparisons between the photoelectric and the radar records could be made to 0.05 sec. Methods of improving the sensitivity and other operational characteristics are discussed.
STUDY OF IONIC CRYSTALS UNDER ELECTRON BOMBARDMENT
Authors: McLennan D. E.
Published: April 2011

Electron bombardment experiments have been carried out on small crystals of the alkali halides within the electron microscope. Crystals of two size ranges were bombarded at high intensity, and evidence of a generalized photographic effect within the ionic group of solids is presented. The first group of crystal specimens ranged in size from 0.2 to 0.002 cm., the bombardment causing the formation of F-centers and entrapped metal colloids in the crystal lattice. Ionization pulses were observed to occur in the region of the specimen during bombardment. The second group ranged in size from 10 to 0.01 μ, observations on the effects of bombardment being carried out with electron diffraction techniques. A process has been suggested to explain the phenomenon of ionic crystals which appear to lose their centers under high electron beam intensity in the electron microscope.
ON THE STATIC DIELECTRIC CONSTANT OF DIPOLAR SOLIDS
Authors: Simpson J. H.
Published: April 2011

An application of Fröhlich's general formula for the static dielectric constant is made to a material having a cubic arrangement of dipolar molecules, each of which has two equilibrium positions 180° apart and ordering forces of the short range type which tend to make nearest neighbors antiparallel. It is shown that such a model cannot lead to a sharp transition in dielectric constant unless changes in lattice dimensions occur. Qualitative comparison with certain experimental results is made.
THE HALF-LIFE OF IRIDIUM 192
Authors: Kastner J.
Published: April 2011

A Lauritsen electroscope was used to compare the intensity of an Ir192 source with a radium standard. The result of a least squares fitting of the decay curve was a half-life of Ir192 of 74.37 ± 0.07 days.
SOME QUANTITATIVE MEASUREMENTS OF THREE-CENTIMETER RADAR ECHOES FROM FALLING SNOW
Authors: Langille R. C. , Thain R. S.
Published: April 2011

In the winter of 1948–49 a series of measurements was made at Ottawa in an attempt to verify, by experiment, the theoretical computations of J. W. Ryde for the intensity of backscattering of 3 cm. radio waves by snowflakes. The radiation backscattered from falling snow was measured, together with the actual mass of snow per cubic meter of atmosphere. Whenever possible the size distribution of the snowflakes was determined. Owing to the small number of snow-storms studied, firm conclusions cannot be drawn. However, the results obtained are in agreement with those predicted by Ryde, and provide useful practical information.
SHADOW-CASTING WITH HALIDES IN THE ELECTRON MICROSCOPE
Authors: Barnes William H. , Lambe Margaret S.
Published: April 2011

Experiments on the behavior of halides as shadow-casting agents in electron microscopy are described. The use of calcium fluoride, placed directly on the specimen screen, is suggested as a convenient method for routine qualitative shadowing of preparations in the preliminary stages of an electron microscopic study. No vacuum coating equipment is required.
IONIZING POWER OF COSMIC RAY PARTICLES AT SEA LEVEL
Authors: Chatterjee S. D.
Published: April 2011

Using a proportional counter telescope arrangement, experiments have been carried out at sea level to explore the nature and ionizing power of particles in the soft component of cosmic radiation and those produced under 1.8 cm. and 20 cm. of lead. The results indicate a preponderance of relativistic electrons in the soft component and under 20 cm. of lead. Under 1.8 cm. of lead there is some disagreement with the calculated pulse height distribution curve but this can be attributed to the production of showers in the lead. These showers would obscure the presence of a small number of particles of unusually high ionizing power, if such exist.
DISTRIBUTION ZENITHALE DU RAYONNEMENT COSMIQUE
Authors: Voisin André G.
Published: April 2011

not available
THE SOLUTION OF X-RAY ACTIVATION CURVES FOR PHOTONUCLEAR CROSS SECTIONS
Authors: Katz L. , Cameron A. G. W.
Published: April 2011

A method is presented for the computation of photonuclear cross sections from their X-ray activation or yield curves. It is based on the photon differences between successive Schiff representations of bremsstrahlung spectra and assumes that the activation curves have smooth first and second derivatives. Artificially prepared activation curves have been satisfactorily solved by this method, and the published photonuclear activation curves determined in this laboratory have been reanalyzed. The resulting cross section curves are in essential agreement with those originally determined; however the new values are believed to be more reliable. New constants for two proposed relationships between (γ, n) "resonance" peak energies and atomic mass number have been determined. Appended to the paper are tables of the Schiff bremsstrahlung spectra for maximum photon energies between 8 and 28 Mev. and also of special functions for cross section computations between the same energies.
SOME STUDIES IN ANGULAR CORRELATION
Authors: Darby E. K.
Published: April 2011

The beta-gamma-angular correlation in Sb124 has been measured as a function of beta energy using a 12 channel kicksorter and a thick crystal counter as beta-detector. The differential correlation coefficient a(E) has been found to change from −0.17 at 1 Mev. to −0.44 at the end of the beta spectrum. When integrated numerically over all beta energies greater than 1 Mev. the integrated angular correlation coefficient so obtained agrees with the value measured directly. Experiments on the gamma-gamma-angular correlation in Co60 and Sc46 performed with the same apparatus are in agreement with previous results of other workers.
THE QUANTIZATION OF THE CLASSICAL THEORY OF SPINNING PARTICLES
Authors: Shanmugadhasan S.
Published: April 2011

The classical theory of particles, possessing charge and dipole moment, and moving in an electromagnetic field, is considered on the assumptions that there is no constraint connection between the rotational variables and the velocity of the particle, and that the two invariant squares of the dipole moment six–vector are constants of the motion. Two different schemes are obtained according as the two invariant scalar products of the dipole moment and total spin angular momentum six–vectors are or are not constants of the motion. The Bhabha–Corben theory fits into the former scheme. The classical schemes are put into canonical form by using for each particle the relativistic connection between the momenta and the rest-mass, modified to include the effect of the kinetic and potential energies due to spin and dipole moment, as the Hamilton–Jacobi equation and the usual Poisson brackets for the translational and total spin variables. The Wentzel field and the λ-limiting process are used mainly in dealing with the field. The variational principle for the Bhabha–Corben equations is given with the field treated according to the limiting process of Dirac or the relativistic cutoff method of Feynman. The quantization is completed by using the analogy rules. The changes required when the interacting field is a vector meson field are discussed.
ALPHA PARTICLES FROM THE PHOTODISINTEGRATION OF SILVER AND BROMINE
Authors: Haslam R. N. H. , Cameron A. G. W. , Cooke J. A. , Crosby E. H.
Published: April 2011

Ilford E1 nuclear emulsions were exposed behind 4 cm. of lucite to the X-ray beam of the University of Saskatchewan betatron operating at energies from 12 Mev. to 26.6 Mev. They were developed by a "grain-gradation" process in order to suppress proton tracks and γ-ray fog. The variation in yield with energy of the double-peaked single α-particle energy spectrum resulting from the photodisintegration of silver and bromine was studied. Preliminary results are given concerning the cross-section curves corresponding to various portions of this α-particle spectrum. The energy distributions and cross-section curves have been interpreted in terms of the statistical theory of nuclear reactions.
FURTHER OBSERVATIONS ON THE MACROMOSAIC STRUCTURE OF TIN SINGLE CRYSTALS
Authors: Teghtsoonian E. , Chalmers Bruce
Published: April 2011

Further studies are reported on the bands, or striations, into which single crystals of high purity tin, grown by a modified Bridgman method, are partitioned. This striation structure is shown to exist throughout the whole volume of the crystal. The direction in which the boundaries of the striations form relative to the specimen axis is shown to be a compromise between thermal and crystallographic conditions, in which the orientation of the (110) planes is the determining factor. When new striations are formed, they are found to have an incubation period which is longer the slower the rate of growth of the crystal. A qualitative mechanism is developed, based on the formation of dislocations into transition surfaces constituting the striation boundaries, which is consistent with all the experimental observations.
EFFICIENCY OF THE LONG BORON COUNTER FOR FAST NEUTRONS
Authors: Kushneriuk S. A.
Published: April 2011

The efficiency of the long boron counter is calculated as a function of the incident neutron energy using the two-group model of neutron diffusion in conjunction with the age and exponential approximations for the slowing down of neutrons. The neutron energies considered are [Formula: see text]. Results are summarized graphically for several counter geometries.
SEARCH FOR ANOMALOUS ABSORPTION OF Ra(B + G) γ RAYS
Authors: Dixon W. R. , Whyte G. N.
Published: April 2011

The absorption of Ra(B + C) γ rays in lead from 13 to 26 cm. has been investigated in a search for the anomalies reported-by Sen Chaudhary. No such anomalies were found.
ON THE γ-RAY SPECTRUM OF Ra(B + C)
Authors: Whyte G. N.
Published: April 2011

Measurements of the transmission of Ra(B + C) γ rays through lead between 0 and 26 cm. are described and compared with the transmissions predicted on the basis of a modified version of the γ-ray spectrum of Ellis and Aston and on the basis of the spectrum of Latyshev et al. Ellis and Aston's spectrum gives the better agreement. Both the relative and absolute values of the γ-ray intensities given by Ellis and Aston are revised in the light of more recent information. This revised spectrum leads to a predicted value of 0.84 roentgens per hour at a meter for the γ-ray output of a gram of radium and its equilibrium products in 0.5 mm. of platinum, in good agreement with experiment.
MUTUAL INDUCTANCE OF CIRCUITS ON A TWO LAYER EARTH
Authors: Wait James R.
Published: April 2011

A general formula is derived for the mutual inductance of ungrounded insulated wires lying on the surface of a two layer earth with a small conductivity contrast between the layers.
SIZE DISTRIBUTION OF COSMIC RAY STARS IN PHOTOGRAPHIC EMULSIONS
Authors: Mei J. Y.
Published: April 2011

In an analysis of cosmic ray stars found in Ilford G5 emulsions exposed at about 85,000 ft. the star-size distribution curve shows a change in slope at a prong number of about 8.5. A similar effect is shown for emulsions exposed at airplane altitudes, and it is assumed that the effect is mainly due to the composition of the emulsions. While the primary particles producing the stars at about 85,000 ft. are mostly protons, about 50% of the low energy stars are produced by nonionizing radiation, presumably neutrons. a-Particles and heavier nuclei produce about 30% of the larger energetic stars. The absolute frequency of star production is given.
THE DISINTEGRATION OF Tm170
Authors: Graham R. L. , Wolfson J. L. , Bell R. E.
Published: April 2011

The radiations from the decay of Tm170 (127 day) have been studied by means of a lens type β-ray spectrometer, a scintillation spectrometer, short resolving time (2τ0 = 2 × 10−9 sec.) coincidence counting techniques, and a pair of lens type β-ray spectrometers placed end to end with coincidence counting of the focused radiations from a single source. A disintegration scheme is proposed which is consistent with the experimental results. Decay is found to be by negative β-ray emission; the spectrum consists of two components, one of maximum energy 968 ± 4 kev. (76%) proceeding to the ground state of Yb170 and one of maximum energy 884 ± 4 kev. (24%) to an excited state in Yb170 followed by emission of a γ ray or conversion electron to the ground state. The γ-ray transition in Yb170 is found to have an energy of 84.1 ± 0.1 kev., a half-life of (1.57 ± 0.05) × 10−9 sec, and conversion coefficients aK = 1.60 ± 0.15, aL = 4.1 ± 0.5, aM = 1.2 ± 0.2 which show that it is electric quadrupole in character. Upper limits are given for decay by K capture, 0.3%, or positive β-ray emission, 0.01%, and also for the occurrence of other γ rays.
ELECTROMAGNETIC FIELDS OF CURRENT-CARRYING WIRES IN A CONDUCTING MEDIUM
Authors: Wait James R.
Published: April 2011

The fields of a finite wire carrying a harmonically time varying current are calculated for the case of the wire contained in an infinite conducting medium. The insulation of current-carrying wires in a conducting medium is discussed. It is concluded that the insulation characteristics need not usually be considered.The fields of a finite current-carrying vertical wire within a horizontal slab are calculated. The mutual impedance between two finite circuits, one being vertical and within the slab and one horizontal and on the surface of the slab, is calculated for limiting values of the lower medium conductivity. The results are thought to be applicable to electrical methods of well logging in geophysical exploration.
INITIAL DISTRIBUTION OF COMPTON ELECTRONS
Authors: Johns H. E. , Cormack D. V. , Denesuk S. A. , Whitmore G. F.
Published: April 2011

Modifications of the Klein-Nishina formula for the Compton effect are presented which give the energy distribution and the angular distribution of the recoil electrons. Electron distributions have been calculated for photon energies from 10 kev. to 30 Mev. The distributions of the electrons produced by Co60 γ rays have been determined.
THE THEORY OF NEUTRON DIFFRACTION BY GASES. I
Authors: Pope N. K.
Published: April 2011

An expression for the total, elastic and inelastic, differential cross section for scattering of thermal neutrons by a rigid polyatomic molecule is derived. In summing over the final rotational states of the molecule the change in energy of the neutron is assumed negligibly small compared to the neutron's initial energy. The validity of this approximation is discussed. The rigidity of the molecule is then relaxed and the expression obtained for the cross section amended to take account of the vibrational motion of the nuclei. It is shown that the elastic scattering from a vibrating molecule is equivalent to that from a set of uncoupled anisotropic oscillators placed at the mean nuclear sites. Detailed results are given for spherical top molecules of the type YX4. Good agreement is found with the experimental pattern of carbon tetrafluoride but not with that of methane.
THE QUANTIZATION OF CLASSICAL SPIN THEORY
Authors: Shanmugadhasan S.
Published: April 2011

The antisymmetric spin tensor of rank two used to describe the rotational motion of a particle is assumed to satisfy the constraint condition that the velocity 4-vector is orthogonal to it. Since the dipole moment is proportional to the spin tensor, this condition leads always to a purely magnetic dipole in the rest system of the particle. Frenkel has indicated how the action principle for the classical equations of motion can be set up treating the above constraint condition as a supplementary condition. The Hamiltonian dynamics of a system having supplementary conditions and Lagrange undetermined multipliers has been discussed recently by Dirac. Dirac's method and results previously obtained give the required Hamilton–Jacobi equations and Poisson Brackets of the dynamical variables. The cases where the particle behaves like a pure gyroscope and a symmetrical top are treated. When there is an interacting field, it is assumed that the action of the Held is given by the effective 4-vector potential without further specification. The orthogonality of the velocity to the tensor dual to the spin tensor can be imposed as an alternative constraint condition. This possibility is discussed briefly. The quantum formulation is completed with the help of the standard analogy rules.
INTERFERENCE EFFECTS IN THE SMALL ANGLE SCATTERING OF X RAYS BY SMALL PARTICLES
Authors: Noakes G. E. , Allin Elizabeth J.
Published: April 2011

Interparticle interference effects have been observed in the small angle X-ray-scattering from 30 samples prepared by the evaporation of gold colloids containing spherical particles of uniform size. The position of the interference maximum was found not to be the same for all samples containing particles of the same size. Calculation verifies that the position of this maximum is dependent on the radial distribution of the particles. It cannot be used for size determinations unless this distribution is known. The predicted variation of the slope at small angles of the In I vs. k2 curve with particle distribution was confirmed experimentally. This method of size determination is unsatisfactory whenever interference effects are present. It is suggested that size determinations based on the positions of the form function maxima are almost independent of particle distribution even in concentrated samples. A unique determination of the particle distribution from the position and shape of the interference maximum would appear to be impossible even if the size were known.
FURTHER MEASUREMENTS ON THE γ RAYS PRODUCED BY NEUTRON CAPTURE IN BERYLLIUM AND CARBON
Authors: Bartholomew G. A. , Kinsey B. B.
Published: April 2011

New measurements have been made of the neutron capture radiation from beryllium and carbon using a more sensitive pair spectrometer. From beryllium, γ rays with energies of 6.81 and 3.41 ± 0.06 Mev. were detected. The former is the ground state γ ray previously reported. The 3.41 Mev. γ ray, which has an intensity of about 0.25 photon per capture, seems to be due to the excitation of the first excited state in Be10. From carbon, in addition to the 4.95 Mev. ground state γ ray previously reported, a γ ray was found with an energy of 3.68 ± 0.05 Mev. and with an intensity of about 0.3 photon per capture. No γ rays were observed which could be associated with the excitation of the level at 3.9 Mev. in C13.
SECOND-ORDER BEAMS OF SLOTTED WAVE GUIDE ARRAYS
Authors: Gruenberg H.
Published: April 2011

It is shown that the radiation pattern of slotted wave guide arrays may contain small second-order beams even for slot spacings less than a free-space wave length. These beams are usually split with a minimum or even a null in the plane containing the array and main beam. Since patterns are normally taken in this plane, the second-order beams have until now escaped attention, as far as the writer is aware. Methods of suppressing these beams are discussed.
PHOTONEUTRON CROSS SECTIONS IN SILICON AND CALCIUM
Authors: Summers-Gill R. G. , Haslam R. N. H. , Katz L.
Published: April 2011

Using the dropping apparatus and dose monitoring method previously reported, the cross sections for the reactions Si28(γ, n)Si27 and Ca40(γ, n)Ca39 have been measured by detecting positron activities in the residual nuclei. The Si28(γ, n)Si27 cross section has a peak value of 21 mbarns at 20.9 Mev. and an integrated cross section to 24 Mev. of 0.070 Mev-barns. The threshold energy is 16.9 ± 0.1 Mev. The Ca40(γ, n)Ca39 cross section has a peak value of 15 mbarns at 19.3 Mev. and an integrated cross section to 24 Mev. of 0.065 Mev-barns. The threshold is 15.8 ± 0.1 Mev.A comparison of our results with the neutron yield measurement of Price and Kerst at 18 and 22 Mev. gives good agreement. A further comparison with the neutron yield work of Baldwin and Elder is made.The sharp discontinuity in (γ, n) yields using lithium γ rays observed by Wäffler and Hirzel is explained as a threshold effect. Integrated cross sections increase more or less smoothly with Z.In addition, improved values for the half-lives of the residual nuclei Si27 and Ca39 have been measured. These are 4.45 ± 0.05 and 1.00 ± 0.03 sec. respectively.
ENERGY LOSS OF HIGHLY CHARGED PARTICLES PRODUCED BY FISSION AND BY COSMIC RAYS: SECTION II. PHOTOMETRIC MEASUREMENTS ON FISSION FRAGMENTS
Authors: Mathieu Roger , Demers Pierre
Published: April 2011

A sensitive and accurate photometer is described, which is designed to measure directly the light intensity transmitted through very small objects placed under the microscope at the highest resolving powers. Tracks of mesons, protons, α rays, and fission fragments were examined with it, characteristic curves relating optical density D and ionizing power I were obtained and show the feature, unusual for light sensitivity, of two sensitive regions separated by a region of very low gamma. The variation of optical density and of width with ionizing power is discussed for three types of emulsion. Measurements on fission tracks are analyzed to derive a single range ionization relation I = 1.22 + 0.738 R, in Mev. and microns, applicable to both heavy and light fragments, in agreement with Section I. The controversial literature on this matter is discussed.
A STUDY OF WINDS IN THE IONOSPHERE BY RADIO METHODS
Authors: Chapman John H.
Published: April 2011

Winds in the ionosphere have been studied by a method described by S. N. Mitra using the fading of radio echoes at spaced receivers. A mean daily wind variation of nearly semidiurnal period and about 40 meters per second amplitude has been observed at a nominal height of 110 km. (Region E). The wind variation is consistent with the explanation that it is due to tidal oscillations of the atmosphere. A wind variation consistent with that expected from lunar atmospheric tides has also been detected at this level.The winds in the F region appear to increase in velocity with an increase of magnetic activity. A similar effect is not observed in the E region except during severe ionospheric disturbances.
THE PREPARATION OF SINGLE CRYSTALS AND BICRYSTALS BY THE CONTROLLED SOLIDIFICATION OF MOLTEN METALS
Authors: Chalmers Bruce
Published: April 2011

An account is given of the methods that have been developed for the production of single crystals and bicrystals of a wide variety of metals by controlled freezing of the molten metal in a horizontal "boat". Orientations are controlled by a "seeding" technique. A detailed qualitative analysis is given of the factors associated with the presence of "stray" crystals. Their formation is discussed in terms of nucleation and in terms of their subsequent survival, and attention is drawn to the significance of purity, of speed of growth, and of the temperature gradient in the liquid.
ON θ VALUES IN METALS
Authors: Kelly V. M. , MacDonald D. K. C.
Published: April 2011

Following a discussion of specific heat theories, it is suggested that, despite its limitations, the Debye theory is the most useful representation for general analysis. Four methods of calculating θD, the Debye characteristic temperature, are presented; specific heat data of lithium, sodium, and potassium are then analyzed and also compared with similar calculations of θR from resistance measurements made over a wide temperature range. It is shown that more realistic values of θ are obtained when θ is recognized as a temperature-dependent parameter in the mathematical derivation of the relevant equations. It appears that a considerable amount of useful information may be obtained from data analysis in this way.
A DETERMINATION OF THE HALF LIVES OF SOME MAGNETIC DIPOLE γ-RAY TRANSITIONS
Authors: Graham R. L. , Bell R. E.
Published: April 2011

A number of magnetic dipole γ-ray transitions have been studied using a coincidence circuit of short resolving time (2τ0 = 2 × 10−9 sec), a two lens single β-ray spectrometer, a pair of lens spectrometers placed end to end with coincidence counting of the focused radiations from a single source, and a scintillation spectrometer. Lifetimes have been measured using the delayed coincidence method and where feasible conversion coefficients and K/L ratios obtained. Comparison is made with theoretical estimates of the lifetime–energy relation for M1 γ-ray transitions.The new results are as follows:[Formula: see text]
THE MAXIMUM AGE OF THE ELEMENTS AND THE AGE OF THE EARTH'S CRUST
Authors: Collins C. B. , Russell R. D. , Farquhar R. M.
Published: April 2011

Estimates are given of a maximum time of formation of the elements of 5.5 billion years and of the time of formation of the earth's crust at 3.5 billion years. These estimates were based on the isotopic constitution of lead ores dated from isotopic analyses of radiogenic leads from uranium minerals. Methods of calculation are described.Experimental measurements of the isotopic constitution of lead from mass spectrograms of lead tetramethyl are reported with examples.
RESONANT SCATTERING OF SLOW NEUTRONS
Authors: Brockhouse B. N.
Published: April 2011

A method is described for measurement, as a function of neutron energy, of the scattering cross section for slow neutrons of materials having high absorption. The necessary corrections are discussed. The results are normalized to a vanadium scattering cross section of 5.07 barns inferred from the measured total cross section, [Formula: see text]. Measurements are presented for the low energy neutron resonances in cadmium, samarium, gadolinium, dysprosium, europium, rhodium, and indium. The single level Breit-Wigner formula is accurately obeyed for cadmium and samarium but not for gadolinium in which two resonances contribute. The scattering results indicate that the absorption cross sections of cadmium and samarium at resonance are higher than the values previously accepted. This has been confirmed by total cross section measurements on cadmium for which the Breit-Wigner parameters are E0 = 0.180 (±.003) ev., Γ = 0.113 ev., σa0 = 7750 barns, σP = 4.7 barns, aR = 7 × 10−3 cm. The spin of the compound nucleus is unity. For Sm149 the spin of the compound nucleus (0.096 ev. resonance) is [Formula: see text]. The scattering cross section of europium for neutrons of energy 0.03 ev. to 0.15 ev. is 8 barns, almost independent of the energy. The scattering cross section of dysprosium is 100 barns at 0.03 ev. and decreases slowly with increasing energy, thus confirming the existence of a level at negative neutron energy. The spin of the compound nucleus for the 1.26 ev. resonance in Rh103 is found to be unity and that for the 1.45 ev. resonance in In115 is found to be four.
ENERGY SELECTION OF CHARGED PARTICLES BY A MAGNET FIELD
Authors: Gardner J. W.
Published: April 2011

We examine the problem of obtaining a sharply defined mono-energetic beam of particles from an omnidirectional, poly-energetic source without the use of slits. A magnetic field is suggested which will achieve this in the idealized case when the source and counter are of vanishingly small dimensions and the particles are confined to the median plane. We then investigate the proportional spread in energy (ΔE/E) of particles arriving at the counter due to the finite dimensions of the source and counter and a small component of particle velocity out of the median plane. Finally some numerical estimates are made of ΔE/E and of the magnetic fields required in particular cases.
RADIAL-AXIAL HEAT FLOW IN REGIONS BOUNDED INTERNALLY BY CIRCULAR CYLINDERS
Authors: Blackwell J. H.
Published: April 2011

Two radial–axial transient heat flow problems have been solved for regions bounded internally by circular cylinders. They are not of the simple "product-solution" type and it is considered that they may have application in other fields of physics where the Diffusion Equation applies. The problems arose during investigation into "end-effect" in cylindrical thermal-conductivity probes. The solutions are obtained by integral-transform methods, two different types of transform being used in each solution.
THE ABSORPTION DUE TO CARBON MONOXIDE IN THE INFRARED SOLAR SPECTRUM
Authors: Locke J. L. , Herzberg L.
Published: April 2011

New tracings of the absorption bands due to carbon monoxide in the 4.7 μ and 2.4 μ regions of the solar spectrum were obtained with a spectrometer of high resolving power. From the observed absorption intensity at 4.7 μ the abundance of carbon monoxide in the earth's atmosphere over Ottawa was found, during spring and fall 1952, to vary between 0.1 and 0.2 cm-atm. Similar observations, made at other stations, were re-evaluated with the laboratory data used at Ottawa. The values for the carbon monoxide abundance in the earth's atmosphere at different geographical locations, determined in this way, were found to be within the limits of the values obtained at Ottawa. Absorption lines due to solar carbon monoxide in the 4.7 μ region of the spectrum were resolved. Their intensity relative to the intensity of the solar carbon monoxide absorption in the 2.4 μ region of the spectrum was found to be in agreement with expectations based on the theoretical curves of growth for solar absorption lines.
THE MASS SPECTROMETER DETERMINATION OF THE HALF-LIFE OF Kr85
Authors: Wanless R. K. , Thode H. G.
Published: April 2011

The half-life of Kr85 has been redetermined using the high precision mass spectrometer method. Several samples of krypton gas extracted from fission product material have been investigated over a period of seven years. The half-life of Kr85 has been found to be 10.27 ± 0.18 years.
THE MEASUREMENT OF ENERGIES AND INTENSITIES OF γ-RAYS WITH A PAIR SPECTROMETER
Authors: Kinsey B. B. , Bartholomew G. A.
Published: April 2011

The performance of a pair spectrometer of the Walker and McDaniel type is discussed from both a theoretical and an experimental point of view. It is shown that the energy of the γ-ray may be measured to a first approximation by the product of the distance between the inner edges of the slits which define the coincidence counters and the highest value of the magnetic field at which coincidences are found. A more accurate value of the energy of the γ-ray may be obtained by adding a small correction, called the "toe" correction, to the result so obtained. The magnitude of this correction is dependent on the γ-ray energy and on the width of the slits and is obtained from calculations of the shape of the coincidence peak based on the Bethe–Heitler formula. The correction depends very little on the length of the slits or on the thickness of the radiator. The relation between the calculated correction and the slit width has been examined experimentally. It is shown that the ultimate accuracy in energy measurement depends on the homogeneity of the magnetic field and on the error involved in the calculated toe correction. The latter error can be minimized by using very narrow slits and may be eliminated by plotting the value of magnetic field at the upper limit of the coincidence spectrum against the slit width and extrapolating the curve so obtained to zero slit width. The uncertainty in the magnetic field of the present instrument introduces a possible systematic error of about 0.05%. Measured values of the energies of a number of neutron capture γ-rays are compared with the values derived from the energy balance in (d, p) reactions. The results are in good agreement (within 0.1%).The relative counting efficiency as a function of energy is calculated theoretically and found to be in good agreement with experiment from 2.75 to 7.4 Mev. Above 7.4 Mev. no good method of checking the theoretical efficiency has been found. The absolute value of the counting efficiency at 2.75 and 7.38 Mev. has been measured by an ionization chamber method and is found to be in rough agreement with theoretical estimates.
AN ISOLATING POTENTIAL COMPARATOR
Authors: Dauphinee T. M.
Published: April 2011

A circuit is described by which electromotive forces can be compared accurately without making any direct electrical connection between them. A double-pole, double-throw chopper, having a condenser connected between the vibrating contacts, is used with a galvanometer or electronic amplifier to indicate any inequality between the e.m.f.'s without allowing any net flow of current between the circuits. Polystyrene condensers and mechanically driven choppers are used to minimize leakage and pickup problems.Potentiometric measurements may be made through this "isolating potential comparator" to ± 0.1 μv. The error due to potential difference between the circuits is about 10−6 of the difference for 100 ohm circuits. An analysis of the method is given and optimum condenser and galvanometer characteristics determined. Magnitude and elimination of errors are discussed.The comparator is suitable for measurement or control of e.m.f. differences between thermocouples which are electrically connected through the tips. It also has many applications in resistance measurement and resistance thermometry.
COMPTON ELECTRON SUPPRESSION IN THE GAMMA-RAY SPECTRA OF Ra (B + C), Co60, AND Ta182
Authors: Pearce R. M. , Mann K. C.
Published: April 2011

A method of suppression of the Compton electron background present in photoelectron spectra is described. The method employs an anticoincidence element which eliminates Compton electron pulses in the spectrometer detector counter and leaves photoelectron pulses unaffected. The technique has been applied to the photoelectron spectra of Co60, Ta182, and Ra (B + C). Evidence is presented for a previously unreported 1.01 Mev. gamma-ray transition in Ta182. The spectrum of Ra (B + C) is compared with the spectra reported by Ellis and by Latyshev. Some of the new transitions found by Latyshev are confirmed. Other gamma-rays not reported by other workers are presented here.
THE DETERMINATION OF URANIUM AND THORIUM IN ORES
Authors: Eichholz G. G. , Hilborn J. W. , McMahon C.
Published: April 2011

The application of various physical methods to the assay of uranium and thorium in ores is discussed. It is shown how it is possible to determine their uranium and thorium content by means of simultaneous measurement of their beta and gamma activities. Simple working equations are derived which permit this determination to be carried out irrespective of the equilibrium condition of the uranium in the sample. Suitable experimental equipment is described briefly and some typical experimental results are presented.
THEORY OF THE ELECTROMAGNETIC VACUUM. I
Authors: Kaempffer F. A.
Published: April 2011

The reasons are restated and amended which make it possible to consider the electromagnetic vacuum as a nonviscous fluid in which excitations of the motion appear as observable particles. It is shown, in close formal analogy to Dirac's new electrodynamics, that the electromagnetic vacuum can be characterized at each point in space time by a scalar function κ, representing the ratio (energy density)/(charge density) of the medium, and by a four-vector vμ, representing the state of motion of the medium at that point. As a first step towards quantization of this theory a spinor formulation of electrodynamics is set up which allows possible excitations of the vacuum to be classified. The program for full quantization of this theory is outlined.
MEASUREMENT OF NUCLEAR GAMMA-RAY ABSORPTION IN CARBON
Authors: Haslam R. N. H. , Horsley R. J. , Johns H. E. , Robinson L. B.
Published: April 2011

The cross section for the absorption of γ rays by carbon has been determined as a function of photon energy by means of "nuclear detectors". The electronic absorption coefficients in the energy range 12 to 20 Mev. are found to be about 1% lower than the theoretical values. The nuclear absorption is shown to exhibit a resonance behavior. The integrated cross section in carbon is considerably lower than predicted. The contribution of nuclear scattering is found to be negligible. Differences in results as determined by three different detecting reactions, C12(γ, n)C11, O16(γ, d)P15, and S32(γ, d)P30, are discussed on the basis of detector sensitivity. It is suggested that the absorption mechanism can be represented by a continuous absorption on which is superimposed absorption peaks.
A RAPID-SCANNING AURORAL SPECTROMETER
Authors: Hunten D. M.
Published: April 2011

A spectrometer is described which is capable of obtaining an auroral spectrum in 10 sec. with 10 Å resolution. It uses a 4 by 4 in., 6000 lines/cm. grating and parabolic mirrors for focusing. The detector is a 1P21 photomultiplier cooled by dry ice, and the spectrum is recorded by a high-speed magnetic oscillograph. The amplifiers are described and a few sample spectra shown. Some relevant optical equations are collected in an appendix.