Browsing by Author "Hannon, James P."
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Item A Monte Carlo study of high transverse energy triggers in PP collisions at Plab=400 Gev/c(1983) Naudet, Charles Joseph.; Mietinen, Hannu E.; Duck, Ian M.; Hannon, James P.We have studied the properties of typical inelastic final states in pp collisions at =4 Gev/c under triggering conditions similar to those used in actual jet experiments . The events were generated by a Monte Carlo method 'which employed experimentally observed multiplicity and inclusive momentum distributions and constrained all the events to conserve momentum and energy. We find that a requirement of high transverse energy in a given solid angle selects mostly very high multiplicity events. Some experimentally observed momentum correlations seem to be of kinematical orgin and the triggered events have a similar transverse energy spectrum, but a less coplanar event structure than what is observed in experimental data.Item Muon spin relaxation in a random ferromagnet: PdMn(1983) Gist, Grant Alan; Dodds, Stanley A.; Hannon, James P.; Corcoran, Marjorie D.Muon spin relaxation (ySR) experiments have been performed in transverse, longitudinal and zero applied field on the disordered ferromagnet PdMn (2.3 at.%). Muon relaxation rates in the paramagnetic phase are in good agreement with predictions of the Walstedt-Walker formula, and appear to have no contribution from muon coupling to the giant moment polarization cloud. The transverse field relaxation rate (yT) and the width of x the zero field quasistatic field distribution (a(T)) in the ferromagnetic phase are less than calculated from a uniform mean field model. This "shortfall" is found to be qualitatively consistent with the Sherrington-Kirkpatrick disordered mean field theory. Spin-lattice relaxation rates in zero applied field give clear evidence for critical slowing down of Mn spin fluctuations over a wide temperature range, and are consistent at low temperatures with a two magnon Raman scattering mechanism.Item NMR measurement of diffusion in liquids by the pulsed field gradient technique(1983) Egan, Thomas F.; Rorschach, Harold E.; Hannon, James P.; Estle, Thomas L.The diffusion coefficient is an important parameter for characterizing the state of water in biological systems. A nuclear magnetic resonance method of diffusion measurement by the pulsed field gradient, technique is described. A 9-T-18 spin-echo sequence is used with one gradient pulse located on each side of the 18 rf pulse. Information on restricted diffusion is obtained by varying the measuring time, which is determined by the separation of the gradient pulse pair. Measuring times greater than 2 msec are possible with the present apparatus. Maximum magnetic field gradients of 11 gauss/cm are applied to cylindrical sample volumes of 1 cm diameter and .5 cm in height. This permits the measurement of diffusion coefficients as low as 1 cm /sec. Details of the electronic hardware and gradient coil construction and calibration are given. The measurement process is software supported and includes digital data acquisition.Item Nuclear superradiance into anomalous emission channels(1978) Hung, Nguyen V.; Hannon, James P.This thesis investigates the coherent spontaneous emission, or superradiance, of initial nuclear excitations into anomalous emission (Borrmann modes) for a perfect needle-shaped crystal sample. The anomalous emission effect, which suppresses the nonresonant photoelectric absorption of gamma rays emitted in the Borrmann modes without destroying the coupling of these modes with the nuclei, allows emission of gamma rays from Mossbauer emitters within a Borrmann depth from the crystal surface, greatly enhanced over the ordinary photoelectric absorption length. Two approaches are discussed. First we treat the superradiance emission semiclassically, solving Lamb's selfconsistent field equations for the emitted intensity in the superradiance limits rather than in the usual rate equation approximation in laser theory. Next we apply the quantum statistical theory developed by R. Bonifacio et al., after incorporating necessary modifications to allow for various multipole emission into Borrmann modes. Finally we attempt to determine criteria that would characterize a good isotope for superradiance.Item On the number of bound states of the Schroedinger Hamiltonian--a review(1981) Swartz, Eric T.; Wells, R. O.; Stanton, Robert J.; Hannon, James P.We consider a non-relativistic, time independent quantum mechanical system consisting of a finite number of particles interacting via a potential, V. A sufficient condition on V that the system have an infinite number of bound states is that the particles must cluster near the continuum limit into two spatially separated clusters, and the sum of the inter-cluster two-body potentials must decay no faster than the inverse square of the inter-cluster separation. This result is proven following the work of B. Simon and W. Hunziker by showing the system reduces to a variant of the two-body problem. Many bounds for the number of bound states N(V) of the two-body system are reviewed. Most depend on integrals of V. These bounds are used to derive conditions on V so that N(V) =. If we introduce a coupling parameter, s, so that H(s)-A + sV is the two-body Hamiltonian, then we find, following the work of B. Simon [18] that N(sV) grows as s^3/2.Item QNS measurement of translational and notational water motion in polynox-water gels and hydrated artemia cysts(1983) Heidorn, Douglas; Rorschach, Harold E.; Hannon, James P.; Roberts, Jabus B.Quasielastic Neutron Scattering is a useful technique for obtaining information about the self-diffusion of water molecules in heterogeneous systems. Quasielastic neutron spectra have been obtained for hydrated brine shrimp (Artemia) cysts (1.2 g water/g solid) and water-polyox (1.67 g/g and 4 g/g) and deuterium-polyox (4 g/g) gels as a function of momentum transfer, Q. A triple axis spectrometer at the Oak Ridge research reactor, HFIR, was used to measure linewidths in the range .33-.1 THz at Q-values ranging from .5 to 1.9 A. A jump-diffusion model was used to describe the translational motion of the water molecules in both the brine shrimp and the polyox systems. The fitting routine employs Marquardt's algorithm which minimizes chi-squared in parameter space and determines parameters such as the Lorentzian linewidth as a function of Q . Results for the brine shrimp indicate that translational as well as rotational motion contributes to the linewidth. The measured linewidth is .329 THz at Q=.5 A, which is about twice the linewidth for pure water at the same O-value. Data for the 2% ployox in DgO mixture shows a large Lorentzian component. The magnitude of this component introduces large errors in the measurement of the motion of the water molecules in the water-polyox gels, due to the subtraction method used to determine the water spectra.Item Quasi-elastic resonant x-ray scattering(1997) Hu, Xiaomin; Hannon, James P.In the fast collision approximation, the scattering amplitude operator of the quasi-elastic scattering is expressed as the summation of multipole moment operators $M\sp{(k)}(l\sb{i},s\sb{i})$ of the valence shell involved in the resonance$\sp1$ with distinct polarization factors. Each multipole moment operator is expressed as the sum of an orbital moment operator and two spin-orbital moment operators with unique coefficients. The explicit form of these coefficients is obtained and the numerical values are calculated. For the transitions to continuous bands, the explicit forms of $M\sp{(k)}(l\sb{i},s\sb{i})$ are extended from electric dipole transitions to any electric multipole transitions. Within the manifolds of good total L and good total S, the $k\sp{\rm th}$ rank multipole moment operator $M\sp{(k)}(l\sb{i},s\sb{i})$ can be expressed in terms of the $k\sp{\rm th}$ rank spin-orbital moments $M\sp{(k)}({\bf L,S})$ of the total L- and total ${\bf S}$-operators of the valence shell involved in the resonance. Furthermore, within the manifolds of good total J, $M\sp{(k)}(l\sb{i},s\sb{i})$ can be further simplified in terms of the spherical tensor operators of the total J of the resonance valence shell. For Hund's rule ground states, the corresponding proportionality coefficients for both cases were obtained. For rare earths, we obtained the thermal expectation value of $M\sp{(k)}(l\sb{i},s\sb{i})$ at T = 0 for coherent elastic scattering. These results are inconsistent with Hamrick's single electron method$\sp2$ for the second half of the rare earth series. For the first half of the rare earth series, we showed that the single electron method is an approximation of our theory. In spiral antiferromagnets, such as holmium, the magnetic sensitivity results in a series of magnetic satellites distributed at each side of Bragg peak. This behavior can be understood on the basis of the XRES electric multipole transition theory we developed. As temperature increases, the higher order harmonics decrease more rapidly than the lower order harmonics, which can be qualitatively explained by mean-field theory. Just above the Neel temperature, there is weak magnetic scattering which can be understood as the short range moment-moment correlations of different spin-orbital multipole moment operators. ftn $\sp1$J. Luo, J. P. Hannon, G. T. Trammell, Phys. Rev. Lett., 71 287 (1993). $\sp2$M. Hamrick, M.A. Thesis, Physics Department, Rice University, 1991.Item Scattering operator for elastic and inelastic resonant x-ray scattering(1994) Luo, Jin; Trammell, George T.; Hannon, James P.I have shown that in the fast collision approximation, the scattering operator for resonant x-ray scattering can be expressed in terms of simple spin-orbital moment operators M$\sp{(k)}$(l,s) of the valence shell involved in the resonance. Using these operators, one not only can determine the thermal expectation values of the various spin-orbit multipole moments in the valence shell through the coherent elastic scattering and absorption, but also can obtain the moment-moment correlation functions (Van Hove scattering function S(q,$\omega$)) among the various atoms of the scattering sample from the coherent elastic and inelastic scattering. We have applied the effective scattering operators to the x-ray magnetic scattering in ${La\sb{2-x}Sr\sb{x}CuO\sb4}$ high temperature superconductors, and obtained the relations between the scattering cross-section and the Van Hove scattering function, and the instantaneous correlation function of the spins in these materials. This theory is applicable to the analysis of a broad range of resonant x-ray elastic and inelastic scattering and absorption experiments involving rare earth, actinide and transition elements.Item Structure of valinomycin-K+ complex and cryptate-k+ complex in solution by extended x-ray absorption fine structure(1981) Williams, Craig; Wang, C. C.; Rorschach, Harold E.; Hannon, James P.A new tool used to study the structure of molecules is Extended X-ray Absorption Fine Structure (EXAFS). EXAFS is small oscillatory signals added on to the smooth x-ray absorption structure curve produced from the excitation of an inner electron out of its bound inner shell into a free electron state. The oscillations are produced from scattering of the excited electron from surrounding atoms. These oscillations, EXAFS, contain molecular structure information, such as the distances between atoms. Since EXAFS can be used for crystals, amorphous solids, solutions and gases it has a strong advantage over x-ray crystallography in many cases for determining local structural information. I used EXAFS to determine what structural changes occur between the known crystalline states and the unknown solution states of K+ complexed with the ionophores cryptate and valinomycin. Ionophores are organic molecules which have a polar oxygen and nitrogen cage in the center of the molecule and a hydrophobic organic exterior. These ionophores are capable of trapping a potassium ion within the cage. The hydrophobic exterior allows the ionophore to dissolve in organic solvents. For the K+-cryptate complex I found no differences in the structure between the crystalline and acetone solution states. For the K+-valinomycin complex I found the K+- distances increased by .3 ± .2 A in the solutions as compared to the crystalline state.Item Superconducting studies of large-scale structure in granular aluminum films(1981) Harrington, Scott Nelson; Dodds, Stanley A.; Estle, Thomas L.; Hannon, James P.Critical field measurements have been performed on granular aluminum films with normal state resistivities ranging from 9x1^-3 Q-cm to 6x1^-5 Q-cm. These experiments indicate the presence of thin internal layers within the films. The layer thickness generally decreases as Pjj decreases, but there is no evidence of layering in the cleanest film. From the angular dependence of the critical field, it has been determined that the layers are essentially decoupled. The perpendicular critical field, H(T), has an anomalous upward curvature, which we are unable to explain. The fluctuation conductivity of the granular films was also measured. Using the layer thickness determined from critical field data, there is good agreement with the two-dimensional Aslamazov-Larkin theory for a moderately dirty film. There is also agreement with the magnitude at intermediate reduced temperatures in very dirty films, but a marked deviation from the theoretical prediction at high t is noted, possibly due to a continuous decoupling of grains within a layer. For the cleanest film, there is fair agreement with the theory if the Maki-Thompson term is included.Item Superradiance and subradiance in systems of excited nuclei(1991) Shen, Tian-Xiang; Hannon, James P.This thesis studies superradiance and subradiance in the normal modes of excitation of systems of resonant nuclei. The nuclei are treated as classical electric dipole oscillators interacting through their radiation fields. This coupling radically alters the radiative decay of the system relative to the decay of an isolated nucleus, and leads to both superradiant and subradiant states with strongly enhanced or suppressed radiative decay rates, and with normal mode frequencies which can be strongly shifted from the natural resonance frequency. This issue is of considerable current interest because it is now possible to create spatially coherent single exciton nuclear states by illuminating crystals containing resonant Mossbauer nuclei with synchrotron radiation pulses. The purpose of this thesis is to solve for the radiative eigenmodes in a system of nuclei and to investigate superradiance and subradiance both in the eigenmode solutions and in the synchrotron radiation produced nuclear exciton state.Item Two photon parametric conversion of Moessbauer gamma rays(1975) Crofton, Bouldin Pat; Hannon, James P.This thesis considers aspects of parametric conversion of Mossbauer gamma rays. This process is important because it could be used to tune the output of a gamma ray laser; but, furthermore, it is a process of fundamental intrinsic interest in quantum electrodynamics. We first calculate the S matrix for the parametric process and obtain from this the differential cross section. We then discuss the signal sharpening which occurs for coherent parametric conversion near a Bragg angle and, finally, make a specific calculation of the expected counting rate from a crystal of Ytterbium 171.