I discuss current issues in hadron spectroscopy and their connection to Quantum Chromodynamics and to more general issues of hadron physics. The discussion is in elementary terms and is directed to non‐experts.
I discuss current issues in hadron spectroscopy and their connection to Quantum Chromodynamics and to more general issues of hadron physics. The discussion is in elementary terms and is directed to non‐experts.
Accurate measurements of the x-ray intensity ratio I(Kβ)/I(Kα) from electron-capture radionuclides, using Si(Li) detectors of calibrated line shape, eliminate an existing large discrepancy between experiment and rel...
Accurate measurements of the x-ray intensity ratio I(Kβ)/I(Kα) from electron-capture radionuclides, using Si(Li) detectors of calibrated line shape, eliminate an existing large discrepancy between experiment and relativistic Hartree-Fock predictions. Small systematic discrepancies in the literature ratios for the mechanisms of photoionization, and electron and proton excitation, are attributed to omission of radiative Auger (RA) satellites in spectrum analysis. With the inclusion of RA peaks in the spectrum fitting, the present data support Scofield’s predictions of I(Kβ)/I(Kα) at the 1% accuracy level, an important conclusion for elemental analysis techniques such as proton-induced x-ray emission and x-ray fluorescence. The resulting radiative Auger intensities also agree quite well with calculations.
Series of submerged arc welds of HSLA steel made with three different fluxes and metallic additions of Ti, Mo, and Cr have been examined to study the inclusions and their role in the nucleation of acicular ferrite. In...
Spectra in the wavelength range of 300–600 nm have been acquired during proton‐beam irradiation of samples of solid hydrogen and deuterium at 4.2 K. Emission spectra from the transitions A′?3Δ u →X? 3Σ? g of O...
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Spectra in the wavelength range of 300–600 nm have been acquired during proton‐beam irradiation of samples of solid hydrogen and deuterium at 4.2 K. Emission spectra from the transitions A′?3Δ u →X? 3Σ? g of O2, 4S–2 D of N?i, and 1 D–1 S of O?i have been measured and attributed to an air impurity in the sample. Comparison is made of the vibrational constants derived from the molecular bands, the spectral shifts of all features, and the lifetime of the 2p 32 D multiplet of N?i obtained in the solid hydrogens with those obtained by matrix isolation studies using N2 and rare gas hosts.
The problem of chemisorbing a hydrogen atom on a Cu-Ni or Au-Pt disordered binary alloy (DBA) is addressed. The DBA is modeled by a semi-infinite linear array of atomic sites each of which is randomly occupied by an a...
The problem of chemisorbing a hydrogen atom on a Cu-Ni or Au-Pt disordered binary alloy (DBA) is addressed. The DBA is modeled by a semi-infinite linear array of atomic sites each of which is randomly occupied by an atom of either component. The electronic properties of such a DBA are obtained via a Green’s-function technique based on the coherent-potential (CP) approximation. The chemisorption process is described by the Anderson-Newns approach, which takes account of the intra-atomic electron interaction on the adatom. The chemisorption energy and the adatom charge transfer are then computed as a function of the alloy concentration. The calculations at the surface involve the solution of two coupled self-consistent equations, one being concerned with the CP on the surface atom and the other with the adatom occupancy. In the case of the Cu-Ni system, the effect of surface segregation is also investigated.
High‐density polyethylene has good spectral transmission characteristics in the range from 20–500 cm? 1. This, coupled with its ease of fabrication and low cost, make it an excellent choice for far‐infrared absorpt...
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High‐density polyethylene has good spectral transmission characteristics in the range from 20–500 cm?1. This, coupled with its ease of fabrication and low cost, make it an excellent choice for far‐infrared absorption cell windows which operate at room temperature. However, because of its relatively large thermal coefficient of expansion and its brittleness (at low temperatures), the usual type of polyethylene absorption cell windows are difficult to make leaktight at low temperatures, especially if there is a moderately high pressure inside the absorption cell. In this article the problems associated with the use of such windows at low temperatures and moderately high pressures are discussed and a successful window design which overcomes these problems is described. These windows have been incorporated in a cell which has been used to measure the collision‐induced absorption of various nonpolar gases at low temperatures. In these experiments the cell was cycled hundreds of times at pressures up to 96.5 bar and at temperatures down to 126 K.
Brillouin frequency shifts from light scattering are used to measure the variation with pressure of the zero‐frequency glass transition temperature T g in atactic polystyrene (PS) at pressures up to 3 kbar. These r...
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Brillouin frequency shifts from light scattering are used to measure the variation with pressure of the zero‐frequency glass transition temperature T g in atactic polystyrene (PS) at pressures up to 3 kbar. These results are extrapolated to high pressures and compared with theoretical predictions. Experimentally it is found that T g asymptotically approaches a critical value at high pressures. The equilibrium lattice model of DiMarzio, Gibbs, Fleming, and Sanchez which approximates the residual entropy of a polymeric glass correctly predicts the experimentally observed trends. The molecular theory of Bengtzelius, G?tze, and Sj?lander is also qualitatively correct at high pressures even though it deals with the glass transition of a classical monatomic fluid. Neither theory is quantitatively in agreement with our results.
Spatially resolved carrier lifetimes have been measured at the same grain boundary using a series of adjacent samples doped to different levels by neutron transmutation. The samples had dopant concentration levels bet...
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Spatially resolved carrier lifetimes have been measured at the same grain boundary using a series of adjacent samples doped to different levels by neutron transmutation. The samples had dopant concentration levels between 1013 and 1017 atoms/cm3. The carrier lifetime was measured using a contactless microwave absorption technique to monitor the decay of photoconductivity which allowed us to perform either isothermal or isochronal annealing to remove the damage caused by irradiation. An optimum anneal of 30 min at 700?°C resulted in almost full recovery to the lifetime before irradiation. A short laser pulse of wavelength 900 nm was focused to a 0.3‐mm‐diam spot on the samples. Lifetimes of two different sets of carriers were measured, the bulk carrier lifetime at the center of a grain and the carrier lifetime at a grain boundary. This latter carrier lifetime involves both fast and slow recombination mechanisms. The slow decay mechanism is due to interface states at the grain boundary. The fast recombination lifetime was found to be of the same order as the bulk recombination lifetime (of the order of 1 μs) and the slow one was of the order of 1 ms. Doping levels up to 1016 atoms/cm3 show no significant effect on the measured bulk carrier lifetime.
作者：
M. SteslickaM. RadnyS. G. DavisonQuantum Theory Group
Department of Applied Mathematics and Department of Physics University of Waterloo Waterloo Ontario Canada N2L?1 and Guelph-Waterloo Program for Graduate Work in Physics University of Guelph Guelph Ontario Canada N1G?1
The effective-range approximation is adopted to study surface states of a linear array of scattering centers. It is shown that, depending on the values of the scattering length and effective range for the surface atom...
The effective-range approximation is adopted to study surface states of a linear array of scattering centers. It is shown that, depending on the values of the scattering length and effective range for the surface atom, two, one, or zero surface states can exist in the forbidden energy gap. The possibility of a smooth transition from true (stationary) surface states to virtual (decaying) states is discussed. A comparison is also made with the crystal-potential approach.
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