Canadian Journal of Physics
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FISSION YIELDS OF THE STABLE AND LONG-LIVED ISOTOPES OF CESIUM, RUBIDIUM, AND STRONTIUM AND NUCLEAR SHELL STRUCTURE The relative yields of the isotopes of cesium, rubidium, and strontium from thermal neutron fission of U235 have been determined mass spectrometrically. The cesium isotope yields are combined with those obtained previously for the xenon isotopes to give high precision yields for mass chains from 131 to 137. In this work neutron capture reactions have been considered and corrections made where these take place to an appreciable extent. The results give further evidence of abnormal yields in the 82 neutron shell region. The half-life of Cs137 was determined and found to be 33 ± 2 years.
Canadian Journal of Physics - Tập 31 Số 3 - Trang 419-431 - 1953
Self-organization in freezing soils: from microscopic ice lenses to patterned ground Freezing in moist fine-grained soils is a highly nonhomogeneous process. It involves transport of water to freezing sites and growth of distinct ice bodies separated by soil domains free of ice. On a much larger scale, recurrent ice growth and thawing of cold regions produce a rich diversity of patterns in soils; these patterns can be defined by local relief, soil cracks, or segregation of mineral material according to size. This paper reviews the principal spatial structures characteristic of freezing soils and discusses the underlying processes in the broader context of geomorphic self-organization.
Canadian Journal of Physics - Tập 68 Số 9 - Trang 842-852 - 1990
NUCLEAR LEVEL SPACINGS T. D. Newton's shell-dependent level spacing formula [Formula: see text] depends upon the densities of single-particle orbits near the Fermi level in the nucleon gas. It has been found that these densities can be computed by taking appropriate averages of the second differences between adjacent atomic masses, using the writer's semiempirical mass formula from which electrostatic and pairing energy terms have been omitted. With this procedure, observed nuclear level spacings have been fitted with a root mean square error factor of 1.74. This fit shows that the level spacings are proportional to (2J + 1)−1 to a good approximation. Since the average density of single-particle orbits depends on the nuclear excitation energy, and since its computation takes a long time even with an electronic computer, an approximation formula with five coefficients has been fitted to the computed orbit densities for each Z and N in the ranges [Formula: see text] and [Formula: see text]. These coefficients are tabulated.
Canadian Journal of Physics - Tập 36 Số 8 - Trang 1040-1057 - 1958
SHELL EFFECTS ON THE SPACING OF NUCLEAR LEVELS Recent measurements of resonances in slow neutron total cross sections yield good estimates of the average level spacing, D, in medium and heavy nuclei. These spacings show large variations, by factors of 103 to 105 , in the region of magic numbers of nucleons. There are also variations by smaller factors between nuclei with even and odd numbers of protons or neutrons. The even–odd effect is a co-operative phenomenon; it can be approximately treated by redefining the ground state to be used for a Fermi gas model. After this correction the gas model should predict D with reasonable accuracy since it is required only to define the density of a complete set of states. The magic number variations are shown to be fitted by an improved approximation to the single-nucleon level density. This is obtained from the observed sequence of single-particle spins and the assumption that the energy interval between spin subshells is constant. Fifty-two observed spacings are fitted by a two-parameter formula with an average uncertainty factor 3. Many of the larger remaining differences between observation and the predictions of the model are qualitatively explicable as expected departures from this uniform spacing hypothesis.
Canadian Journal of Physics - Tập 34 Số 8 - Trang 804-829 - 1956
Radiative Mean-Life Measurements in Neon below 1000 Å Neon spectra between 379 and 914 Å were studied by the beam-foil technique. Mean lives have been obtained for 21 levels in Ne I – Ne VII. In addition, mean lives are reported for upper levels of 12 unassigned lines.
Canadian Journal of Physics - Tập 51 Số 18 - Trang 1948-1955 - 1973
Spectroscopie atomique à l'aide d'un accélérateur Van de Graaff: Applications à l'hélium et à l'azote not available
Canadian Journal of Physics - Tập 47 Số 8 - Trang 859-863 - 1969
Beam–Foil Studies of Oxygen Below 2000 Å Oxygen spectra between 1050 and 1800 Å were studied by the beam–foil technique. Mean lives were obtained for 22 levels in OI–OV. Some amended mean lives from studies below 650 Å are also given.
Canadian Journal of Physics - Tập 50 Số 20 - Trang 2496-2501 - 1972
ON VOLTERRA'S DISLOCATIONS IN A SEMI-INFINITE ELASTIC MEDIUM In this paper a Green's function method is developed to deal with the problem of a Volterra dislocation in a semi-infinite elastic medium in such a way that the boundary surface of the medium remains free from stresses. (A Volterra dislocation is here defined as a surface across which the displacement components show a discontinuity of the type Δu = U + Ω ×r, where U and Ω are constant vectors.) It is found that the general problem requires the construction of six sets of Green's functions. The method for the construction is outlined and applied to one of the six sets, which is of the type of two double forces with moments in a plane parallel with the boundary. The displacement field thus generated is computed. Several of the results obtained are believed to be of geophysical interest, but a more detailed discussion of these applications is postponed to a further communication which is being prepared.
Canadian Journal of Physics - Tập 36 Số 2 - Trang 192-205 - 1958
Boundary layer flow of an Oldroyd-B fluid in the region of a stagnation point over a stretching sheet In this paper, the mathematical model for the two-dimensional boundary layer flow of an Oldroyd-B fluid is presented. The developed equations are used to discuss the problem of two-dimensional flow in the region of a stagnation point over a stretching sheet. The obtained partial differential equations are reduced to an ordinary differential equation by a suitable transformation. The obtained equation is then solved using a finite difference method. The influence of the pertinent fluid parameters on the velocity is discussed through graphs. The behaviour of f ″(0) is also investigated with changes in parameter values. It is observed that an increase in the relaxation time constant causes a reduction in the boundary layer thickness. To the best of our knowledge, this type of solution for an Oldroyd-B fluid is presented for the first time in the literature.
Canadian Journal of Physics - Tập 88 Số 9 - Trang 635-640 - 2010
Studies of Ionospheric Inhomogeneities using Phase Interferometry of Satellite Beacon Transmissions at 136.410 MHz A newly developed sensitive phase interferometer, based on a North–South and East–West antenna system, situated at London, Ontario, was used to record fast angle-of-arrival variations of the satellites ISIS-1 and ISIS-2 beacon transmissions at 136.410 MHz.The relative phase and corresponding amplitude scintillations indicate the presence of two distinct types of ionospheric irregularities which were classified as A-type and B-type. A-type predominantly occurred in a time interval centered on local midnight, and the major disturbance areas were south of the station. A number of them showed a near-field effect, which indicated the presence of F region field-aligned irregularities with large axial ratios.The B-type events, associated in publications with the sporadic E region, occurred at high elevation angles northwest and northeast of the station. Tentative results indicate that these events, predominantly recorded during daytime, are due to ionospheric irregularities occurring at altitudes considerably higher than those of the sporadic E region.
Canadian Journal of Physics - Tập 50 Số 4 - Trang 336-344 - 1972
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