Using X-ray diffraction (XRD) and small angle X-ray scattering (SAXS), we probed the nanostructural features of several PECVD grown nc-Si:H thin films with varying crystalline volume fraction. XRD ...results of a mixed phase film, 70% a-Si:H and 30% c-Si:H, show these crystallites have a preferred 220 orientation in the growth direction. Another film with approximately 90% c-Si also shows elongated grains, but with a preferred 111 orientation. The SAXS results also show an increase in scattering intensity when compared to the mixed phase material. In the mixed phase material, models show that the electron density fluctuations between the amorphous and crystalline phases are not enough to explain the measured SAXS scattering. Hydrogen clustered at the crystallite boundaries and in void regions of the a-Si phase must be included as well.
► Increasing the number of crystallites creates a distinct change in nanostructure. ► XRD shows crystallite preferred orientation changes from 220 to 111. ► SAXS intensity increases with increasing crystallinity.
Detecting the Radiative Decay Mode of the Neutron Fisher, B M; Wietfeldt, F E; Dewey, M S ...
Journal of research of the National Institute of Standards and Technology,
07/2005, Volume:
110, Issue:
4
Journal Article
Open access
Beta decay of the neutron into a proton, electron, and electron antineutrino is occasionally accompanied by the emission of a photon. Despite decades of detailed experimental studies of neutron ...beta-decay, this rare branch of a fundamental weak decay has never been observed. An experiment to study the radiative beta-decay of the neutron is currently being developed for the NG-6 fundamental physics endstation at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). The experiment will make use of the existing apparatus for the NIST proton-trap lifetime experiment, which can provide substantial background reduction by providing an electron-proton coincidence trigger. Tests and design of a detector for gamma-rays in the 10 keV to 200 keV range are under development. The need for a large solid-angle gamma-ray detector that can operate in a strong magnetic field and at low temperature has led us to consider scintillating crystals in conjunction with avalanche photodiodes. The motivation and experimental technique will be discussed.
We present measurements of J/{psi} yields in d+Au collisions at {radical}(s{sub NN})=200 GeV recorded by the PHENIX experiment and compare them with yields in p+p collisions at the same energy per ...nucleon-nucleon collision. The measurements cover a large kinematic range in J/{psi} rapidity (-2.2<y<2.4) with high statistical precision and are compared with two theoretical models: one with nuclear shadowing combined with final state breakup and one with coherent gluon saturation effects. In order to remove model dependent systematic uncertainties we also compare the data to a simple geometric model. The forward rapidity data are inconsistent with nuclear modifications that are linear or exponential in the density weighted longitudinal thickness, such as those from the final state breakup of the bound state.
We have measured the azimuthal anisotropy of {pi}{sup 0} production for 1<p{sub T}<18 GeV/c for Au+Au collisions at {radical}(s{sub NN})=200 GeV. The observed anisotropy shows a gradual decrease for ...3 < or approx. p{sub T} < or approx.l 7-10 GeV/c, but remains positive beyond 10 GeV/c. The magnitude of this anisotropy is underpredicted, up to at least {approx}10 GeV/c, by current perturbative QCD (PQCD) energy-loss model calculations. An estimate of the increase in anisotropy expected from initial-geometry modification due to gluon saturation effects and fluctuations is insufficient to account for this discrepancy. Calculations that implement a path-length dependence steeper than what is implied by current PQCD energy-loss models show reasonable agreement with the data.
Differential measurements of the elliptic (v{sub 2}) and hexadecapole (v{sub 4}) Fourier flow coefficients are reported for charged hadrons as a function of transverse momentum (p{sub T}) and ...collision centrality or number of participant nucleons (N{sub part}) for Au+Au collisions at {radical}(s{sub NN})=200 GeV. The v{sub 2,4} measurements at pseudorapidity |{eta}|{<=}0.35, obtained with four separate reaction-plane detectors positioned in the range 1.0<|{eta}|<3.9, show good agreement, indicating the absence of significant {Delta}{eta}-dependent nonflow correlations. Sizable values for v{sub 4}(p{sub T}) are observed with a ratio v{sub 4}(p{sub T},N{sub part})/v{sub 2}{sup 2}(p{sub T},N{sub part}){approx_equal}0.8 for 50 < or approx. IN{sub part} < or approx. 200, which is compatible with the combined effects of a finite viscosity and initial eccentricity fluctuations. For N{sub part} > or approx. 200 this ratio increases up to 1.7 in the most central collisions.
Particle and photon detection for a neutron radiative decay experiment Gentile, T.R.; Dewey, M.S.; Mumm, H.P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2007, Volume:
579, Issue:
1
Journal Article
Peer reviewed
We present the particle and photon detection methods employed in a program to observe neutron radiative beta-decay. The experiment is located at the NG-6 beam line at the National Institute of ...Standards and Technology Center for Neutron Research. Electrons and protons are guided by a 4.6
T magnetic field and detected by a silicon surface barrier detector. Photons with energies between 15 and 750
keV are registered by a detector consisting of a bismuth germanate scintillator coupled to a large area avalanche photodiode. The photon detector operates at a temperature near 80
K in the bore of a superconducting magnet. We discuss CsI as an alternative scintillator, and avalanche photodiodes for direct detection of photons in the 0.1–10
keV range.
The momentum distribution of electrons from semileptonic decays of charm and bottom quarks for midrapidity |y|<0.35 in p+p collisions at sq root(s)=200 GeV is measured by the PHENIX experiment at the ...Relativistic Heavy Ion Collider over the transverse momentum range 2<p{sub T}<7 GeV/c. The ratio of the yield of electrons from bottom to that from charm is presented. The ratio is determined using partial D/D->e{sup +}-K{sup +}-X (K unidentified) reconstruction. It is found that the yield of electrons from bottom becomes significant above 4 GeV/c in p{sub T}. A fixed-order-plus-next-to-leading-log perturbative quantum chromodynamics calculation agrees with the data within the theoretical and experimental uncertainties. The extracted total bottom production cross section at this energy is sigma{sub bb}=3.2{sub -1.1}{sup +1.2}(stat){sub -1.3}{sup +1.4}(syst)mub.
The double helicity asymmetry in neutral pion production for p{sub T}=1 to 12 GeV/c was measured with the PHENIX experiment to access the gluon-spin contribution, DELTAG, to the proton spin. Measured ...asymmetries are consistent with zero, and at a theory scale of mu{sup 2}=4 GeV{sup 2} a next to leading order QCD analysis gives DELTAG{sup 0.02,0.3}=0.2, with a constraint of -0.7<DELTAG{sup 0.02,0.3}<0.5 at DELTAchi{sup 2}=9 (approx3sigma) for the sampled gluon momentum fraction (x) range, 0.02 to 0.3. The results are obtained using predictions for the measured asymmetries generated from four representative fits to polarized deep inelastic scattering data. We also consider the dependence of the DELTAG constraint on the choice of the theoretical scale, a dominant uncertainty in these predictions.
Deep oxygen related defects form in hydrogenated nanocrystalline silicon (nc-Si:H) as a consequence of thermal annealing, but their microscopic origins and formation mechanisms are not well ...understood. To gain insight to this behavior we intentionally drive-out hydrogen from nc-Si:H films by thermal annealing and monitor accompanying changes in the electronic and vibrational structure of the films with photoluminescence (PL) and Fourier transform infrared (FTIR) absorption spectroscopy. Hydrogen effusion (HE) data provide additional insight, because the annealing temperature range shown to induce a defect band, centered at ~0.7 eV in PL studies, and that corresponding to the onset of thermally activated hydrogen desorption from grain boundaries, coincide. This coincidence suggests a probable link between the two processes. The activation energy obtained from correlated annealing-PL experiments, of ~0.6 eV, for defect formation with thermal exposure, provides substantial insight regarding the mechanism.
Neutral pion transverse momentum (p{sub T}) spectra at midrapidity (|y| < or approx. 0.35) were measured in Cu+Cu collisions at {radical}(s{sub NN})=22.4, 62.4, and 200 GeV. Relative to {pi}{sup 0} ...yields in p+p collisions scaled by the number of inelastic nucleon-nucleon collisions (N{sub coll}) the {pi}{sup 0} yields for p{sub T}(> or approx. 2 GeV/c in central Cu+Cu collisions are suppressed at 62.4 and 200 GeV whereas an enhancement is observed at 22.4 GeV. A comparison with a jet-quenching model suggests that final state parton energy loss dominates in central Cu+Cu collisions at 62.4 and 200 GeV, while the enhancement at 22.4 GeV is consistent with nuclear modifications in the initial state alone.
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