3 resultados para 195-1201A

em CaltechTHESIS


Relevância:

20.00% 20.00%

Publicador:

Resumo:

The Mössbauer technique has been used to study the nuclear hyperfine interactions and lifetimes in W182 (2+ state) and W183 (3/2- and 5/2- states) with the following results: g(5/2-)/g(2+) = 1.40 ± 0.04; g(3/2- = -0.07 ± 0.07; Q(5/2-)/Q(2+) = 0.94 ± 0.04; T1/2(3/2-) = 0.184 ± 0.005 nsec; T1/2(5/2-) >̰ 0.7 nsec. These quantities are discussed in terms of a rotation-particle interaction in W183 due to Coriolis coupling. From the measured quantities and additional information on γ-ray transition intensities magnetic single-particle matrix elements are derived. It is inferred from these that the two effective g-factors, resulting from the Nilsson-model calculation of the single-particle matrix elements for the spin operators ŝz and ŝ+, are not equal, consistent with a proposal of Bochnacki and Ogaza.

The internal magnetic fields at the tungsten nucleus were determined for substitutional solid solutions of tungsten in iron, cobalt, and nickel. With g(2+) = 0.24 the results are: |Heff(W-Fe)| = 715 ± 10 kG; |Heff(W-Co)| = 360 ± 10 kG; |Heff(W-Ni)| = 90 ± 25 kG. The electric field gradients at the tungsten nucleus were determined for WS2 and WO3. With Q(2+) = -1.81b the results are: for WS2, eq = -(1.86 ± 0.05) 1018 V/cm2; for WO3, eq = (1.54 ± 0.04) 1018 V/cm2 and ƞ = 0.63 ± 0.02.

The 5/2- state of Pt195 has also been studied with the Mössbauer technique, and the g-factor of this state has been determined to be -0.41 ± 0.03. The following magnetic fields at the Pt nucleus were found: in an Fe lattice, 1.19 ± 0.04 MG; in a Co lattice, 0.86 ± 0.03 MG; and in a Ni lattice, 0.36 ± 0.04 MG. Isomeric shifts have been detected in a number of compounds and alloys and have been interpreted to imply that the mean square radius of the Pt195 nucleus in the first-excited state is smaller than in the ground state.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

This thesis presents experimental measurements of the rheological behavior of liquid-solid mixtures at moderate Reynolds (defined by the shear rate and particle diameter) and Stokes numbers, ranging from 3 ≤ Re ≤ 1.6 × 103 and 0.4 ≤ St ≤ 195. The experiments use a specifically designed Couette cylindrical rheometer that allows for probing the transition from transporting a pure liquid to transporting a dense suspension of particles. Measurements of the shear stress are presented for a wide range of particle concentration (10 to 60% in volume) and for particle to fluid density ratio between 1 and 1.05. The effective relative viscosity exhibits a strong dependence on the solid fraction for all density ratios tested. For density ratio of 1 the effective viscosity increases with Stokes number (St) for volume fractions (φ) lower than 40% and becomes constant for higher φ. When the particles are denser than the liquid, the effective viscosity shows a stronger dependance on St. An analysis of the particle resuspension for the case with a density ratio of 1.05 is presented and used to predict the local volume fraction where the shear stress measurements take place. When the local volume fraction is considered, the effective viscosity for settling and no settling particles is consistent, indicating that the effective viscosity is independent of differences in density between the solid and liquid phase. Shear stress measurements of pure fluids (no particles) were performed using the same rheometer, and a deviation from laminar behavior is observed for gap Reynolds numbers above 4× 103, indicating the presence of hydrodynamic instabilities associated with the rotation of the outer cylinder. The increase on the effective viscosity with Stokes numbers observed for mixtures with φ ≤ 30% appears to be affected by such hydrodynamic instabilities. The effective viscosity for the current experiments is considerably higher than the one reported in non-inertial suspensions.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The (He3, n) reactions on B11, N15, O16, and O18 targets have been studied using a pulsed-beam time-of-flight spectrometer. Special emphasis was placed upon the determination of the excitation energies and properties of states with T = 1 (in Ne18), T = 3/2 (in N13 and F17) and T = 2 (in Ne20). The identification of the T = 3/2 and T = 2 levels is based on the structure of these states as revealed by intensities and shapes of angular distributions. The reactions are interpreted in terms of double stripping theory. Angular distributions have been compared with plane and distorted wave stripping theories. Results for the four reactions are summarized below:

1) O16 (He3, n). The reaction has been studied at incident energies up to 13.5 MeV and two previously unreported levels in Ne18 were observed at Ex = 4.55 ± .015 MeV (Γ = 70 ± 30 keV) and Ex = 5.14 ± .018 MeV (Γ = 100 ± 40 keV).

2) B11 (He3, n). The reaction has been studied at incident energies up to 13.5 MeV. Three T = 3/2 levels in N13 have been identified at Ex = 15.068 ± .008 MeV (Γ ˂ 15 keV), Ex = 18.44 ± .04, and Ex 18.98 ± .02 MeV (Γ = 40 ± 20 keV).

3) N15 (He3, n). The reaction has been studied at incident energies up to 11.88 MeV. T = 3/2 levels in F17 have been identified at Ex = 11.195 ± .007 MeV (Γ ˂ 20 keV), Ex = 12.540 ± .010 MeV (Γ ˂ 25 keV), and Ex = 13.095 ± .009 MeV (Γ ˂ 25 keV).

4) O18 (He3, n). The reaction has been studied at incident energies up to 9.0 MeV. The excitation energy of the lowest T = 2 level in Ne20 has been found to be 16.730 ± .006 MeV (Γ ˂ 20 keV).

Angular distributions of the transitions leading to the above higher isospin states are well described by double stripping theory. Analog correspondences are established by comparing the present results with recent studies (t, p) and (He3, p) reactions on the same targets.