Experimental study of photon beam polarimeter based on nuclear e+e- pair production in an amorphous target

The experimental method of the linearly polarized photons polarimetry,using incoherent e+e- pair production process has been investigated on the beam of coherent bremsstrahlung (CB) photons in the energy range of 0.9-1.1 GeV at the Yerevan synchrotron.Comment: 6 pages (text),10 figure

Model Independent Form Factors for Spin Independent Neutralino-Nucleon Scattering from Elastic Electron Scattering Data

Theoretical calculations of neutralino-nucleon interaction rates with various nuclei are of great interest to direct dark matter searches such as CDMS, EDELWEISS, ZEPLIN, and other experiments since they are used to establish upper bounds on the WIMP-proton cross section. These interaction rates and cross sections are generally computed with standard, one or two parameter model-dependent nuclear form factors, which may not exactly mirror the actual form factor for the particular nucleus in question. As is well known, elastic electron scattering can allow for very precise determinations of nuclear form factors and hence nuclear charge densities for spherical or near-spherical nuclei. We use charge densities derived from elastic electron scattering data to calculate model independent, analytic form factors for various target nuclei important in dark matter searches, such as Si, Ge, S, Ca and others. We have found that for nuclear recoils in the range of 1-100 keV significant differences in cross sections and rates exist when the model independent form factors are used: at 30 keV nuclear recoil the form factors squared differ by a factor of 1.06 for $^{28}$Si, 1.11 for $^{40}$Ca, 1.27 for $^{70}$Ge, and 1.92 for $^{129}$Xe. We show the effect of different form factors on the upper limit on the WIMP-proton cross section obtained with a hypothetical $^{70}$Ge detector during a 100 kg-day effective exposure. Helm form factors with various parameter choices differ at most by 10--20% from the best (Fourier Bessel) form factor, and can approach it to better than 1% if the parameters are chosen to mimic the actual nuclear density.Comment: 20 pages, 8 figure

On X-Ray Waveguiding in Nanochannels: Channeling Formalism

The question on X-ray extreme focusing (smallest reachable spot size) brings us to the idea for using the wave features of X-ray propagation in media. As known, wave features are revealed at propagation in ultra-narrow collimators as well as at glancing reflection from smooth flat and/or strongly curved surfaces. All these phenomena can be described within the general formalism of X-ray channeling.Comment: by the invited lecture at ISRP-1

Neutrino-nucleus reactions on ^{12}C and ^{16}O

Exclusive and inclusive $(\nu_\mu, \mu^-), (\nu_e, e^-)$ cross-sections and $\mu^-$-capture rates are calculated for ^{12}C and ^{16}O using the consistent random phase approximation (RPA) and pairing model. After a pairing correction is introduced to the RPA results the flux-averaged theoretical $(\nu_\mu, \mu^-), (\nu_e, e^-)$ cross-sections and $\mu^-$-capture rates in $^{12}$C are in good agreement with experiment. In particular when one takes into account the experimental error bars, the recently measured range of values for the $(\nu_\mu, \mu^-)$ cross-section is in agreement with the present theoretical results. Predictions of $(\nu_\mu, \mu^-)$ and $(\nu_e, e^-)$ cross-sections in ^{16}O are also presented.Comment: 13 pages, Revte

Dynamics of viscous amphiphilic films supported by elastic solid substrates

The dynamics of amphiphilic films deposited on a solid surface is analyzed for the case when shear oscillations of the solid surface are excited. The two cases of surface- and bulk shear waves are studied with film exposed to gas or to a liquid. By solving the corresponding dispersion equation and the wave equation while maintaining the energy balance we are able to connect the surface density and the shear viscocity of a fluid amphiphilic overlayer with experimentally accessible damping coefficients, phase velocity, dissipation factor and resonant frequency shifts of shear waves.Comment: 19 pages, latex, 3 figures in eps-forma

Muon capture by 3He nuclei followed by proton and deuteron production

The paper describes an experiment aimed at studying muon capture by ${}^{3}\mathrm{He}$ nuclei in pure ${}^{3}\mathrm{He}$ and $\mathrm{D}_2 + {}^{3}\mathrm{He}$ mixtures at various densities. Energy distributions of protons and deuterons produced via $\mu^-+{}^{3}\mathrm{He}\to p+n+n + \nu_{\mu }$ and $\mu^-+{}^{3} \mathrm{He} \to d+n + \nu_{\mu}$ are measured for the energy intervals $10 - 49$ MeV and $13 - 31$ MeV, respectively. Muon capture rates, $\lambda_\mathrm{cap}^p (\Delta E_p)$ and $\lambda_\mathrm{cap}^d (\Delta E_d)$ are obtained using two different analysis methods. The least--squares methods gives $\lambda_\mathrm{cap}^p = (36.7\pm 1.2) {s}^{- 1}$, $\lambda_\mathrm{cap}^d = (21.3 \pm 1.6) {s}^{- 1}$. The Bayes theorem gives $\lambda_\mathrm{cap}^p = (36.8 \pm 0.8) {s}^{- 1}$, $\lambda_\mathrm{cap}^d = (21.9 \pm 0.6) {s}^{- 1}$. The experimental differential capture rates, $d\lambda_\mathrm{cap}^p (E_p) / dE_p$ and $d\lambda_\mathrm{cap}^d (E_d) / dE_d$, are compared with theoretical calculations performed using the plane--wave impulse approximation (PWIA) with the realistic NN interaction Bonn B potential. Extrapolation to the full energy range yields total proton and deuteron capture rates in good agreement with former results.Comment: 17 pages, 13 figures, accepted for publication in PR

RESONANT SCATTERING

Acoustic resonant scattering has become of great interest ever since the Resonance Scattering Theory (RST) was published in 1978 (L. Flax, L. R. Dragonette, and H. Uberall), having been first presented to the public in the preceding year (H. Uberall, IUTAM Symposium at Northwestern University, Evanston, IL, Sept. 12-15, 1977). A large amount of experimental activity followed in the United States, and especially in France where acoustic resonance scattering was first studied on submerged solid objects using the method of long pulses, or MIIR (G. Maze and J. Ripoche, 19831, and later by the method of short pulses (S. K. Numrich et al., 1984; M. de Billy, 1986). The resonances of submerged shells have been studied by M. Talmant and G. Quentin (1988) by this method. The RST also furnishes a physical interpretation of the resonances in terms of the phase matching of surface waves. Recent experimental advances on these topics are reported here.La diffusion acoustique résonnante a evoqué beaucoup d'intérêt depuis la publication de la Théorie de la Diffusion Résonnante (RST) en 1978 (L. Flax, L. R. Dragonette, et H. Uberall), ayant été presentee au public pour la première fois dans l'année précédente (H. Uberall, IUTAM Symposium à Northwestern University, Evanston, IL, 12-15 Sept. 1977). Beaucoup d'activité expérimentale suivit aux Etats Unis, et surtout en France où la diffusion acoustique résonnante était étudié d'abord aux objets solides immergés utilisant la méthode des impulsions de longue durée, ou MIIR (G. Maze et J. Ripoche, 19831, et plus tard la méthode des impulsions de courte durée (s. K. Numrich et al., 1984; M. de Billy, 1986). Les résonances des tubes immergés étaient étudiées par M. Talmant et G. Quentin (1988) utilisant cette méthode. La RST offre ggalement une interpre'tation physique des rgsonances base'e sur l'accordement de phase des ondes de surface. Quelques avancements expérimentaux sur ces sujets sont mentionnés de suite

THE EXCITATION OF WATER-BORNE WAVES AT THE INTERFACE OF EVACUATED ELASTIC SPHERICAL SHELLS AND PSEUDO-STONELEY RESONANCES

Plane monochromatic waves are known to excite resonances on submerged elastic spherical evacuated shells. The resonances are related to symmetric and antisymmetric Lamb modes found in free vibrations and can be observed by examining the backscattered echo's (form functions) which lead to characteristic "tell-talenr esonance signatures. Partial wave analysis of the individual modes can reveal the nature of the resonances provided one is able to subtract the correct deal back ground of the shell. We take advantage of the recent development of the correct acoustical background to analyze the partial wave componenu of shell resonances. It is easy to distinguish between the Lamb modes which are also apparent in the the form functions. However, an additional resonance is observed at high frequencies which correspond to waves which are broad in partial wave space and which propagate in the fluid at the fluid-shell interface at about the speed of sound of the ambient fluid. It may be assumed that they are related to StoneJey waves observed at the interface of a flat plate evacuated on one side and with a fluid on the other and may therefore be referred to as pseudo-Stoneley resonances. The significance of these waves at wincidarce frequency will be disasssed.Il est bien connu que les ondes planes peuvent exciter des résonances sur des coques Bastique spheriques évacués et immergés. Les résonances sont liés aux modes symétriques et antisymétriques de Lamb des vibrations libtres, et elles peuvent etre observées en examinant les rétrodiffusés (fonctions de forme). indiquet des signatures caractéristiques des résonances. L'analyse des modes individuelles au moyen des ondes partielles peut révéler la nature des résonances, pourvu qu'on puisse soustraire le fond accoustique correct de la coque. Nous utilisons le fond correct comme récent développement, afin d'analyser les composants d'ondes partielles des résonances de la coque. I1 est facile de distinguer les modes de Lamb, qui apparaissant aussi dans les fonctions de forme. De plus, nous observons aux fréquences élevées une résonance correspondante aux ondes qui sont larges dans l'espace d'ondes partielles, et qui se propagent dans le fluide adjacent a l'interface fluide-coque, ayant à peu près la vitesse du son dans le fluide. On peut assumer qu'elles sons liés aux ondes de Stoneley, observés à l'interface d'une plaque plane évacué d'un coté et avec du fluide à l'autre, et qu'on puisse appeller donc les résonances pseudo-Stoneney. La signification de ces ondes à la fnéquence de coincidence sera egalement considérée

Influence of bottom refractions on the propagation of underwater sound

Des expériences [ J. S. Hanna, J. Acoust. Soc. Am. 53, 1686 (1973); R. E. Christensen et al., J. Acoust. Soc. Am. 57, 1421 (1975)] faites sur la perte d'énergie du son sous-marin, se propageant sur un fond sédimentaire non-consolidé, ont demontré la présence d'énergie sonore refringée par le fond et retournée dans l'eau. Les champs sonores refringés se marquent ou par le tempsd'arrivée d'impulsions sonores (indiquant des parcours refringés à travers du fond), ou par leurs interférences avec des signaux stationnaires correspondant seulement à des réfléchissements par le fond. L'interprétation théorique de ces expériences était faite jusqu'ici en forme d'éstimations basées sur l'étendue des rayons. Dans une étude antérieure [A. Nagl et al., J. Acoust. Soc. Am. 63, 739 (1978)] nous avons developpé un formalisme de modes normaux de la propagation du son sous-marin contenant de couches d'eau avec des gradients linéaires de vitesse du son. Ce formalisme a été généralisé' ici en introduisant un fond contenant des couches sédimentaires non-consolidés avec des densités et gradients de vitesse du son différents, et nous obtenons de cette façon des champs sonores refringés par le fond et interférant avec des champs réfléchis. Les effets d'interférence peuvent être utilisés pour déterminer la vitesse du son et son gradient dans les couches du fond. [Recherche assistée par l'Office of Naval Research]