Results 1 - 10 of 2521
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[en] We present the optical observations of the Near Earth Object 107P/(4015) Wilson-Harrington during the 2009/2010 apparition taken in search of low-level comet activity. Our photometric and spectroscopic data were collected 28-86 days after the perihelion passage on 2009 October 22 in a wide range of solar phase angles of 39 deg. - 68 deg. A disk-integrated phase function was constructed, giving a geometric albedo of 0.055 ± 0.012, phase integral of q = 0.34, and Bond albedo of AB = 0.019. The photometric property shows a profile similar to low albedo asteroids and comet nuclei. No emission lines were found in our spectrum, giving a flat reflectance similar to low albedo asteroids. Although we could not find any evidence for cometary activity in our photometric and spectroscopic data, we found an upper limit of 0.001% on the fractional active area. We derived the upper limit of the optical depth of the dust trail and tail, 7 x 10-10. We conclude that 107P/(4015) Wilson-Harrington was completely dormant or inactive in the 2009/2010 return.
[en] A neutron survey was made inside the containment of the Farley Nuclear Plant, Alabama Power and Light Company, Dothan, Alabama, in November 1977. The survey was made to determine the spectra of leakage neutrons and to evaluate the accuracy of albedo neutron dosimeters and a 9-in.-diameter sphere rem meter. The survey also covered variations in the neutron spectra, the ratio of gamma-to-neutron dose rates, and the thermal neutron component of the neutron dose
[en] IRD has worked in the development of an albedo individual monitor with two-components (albedo and incident). As desired characteristics, this monitor should have a lower detection limit smaller than 0.2 mSv for unmoderated 241 Am Be source and an optimum design project. For its development, several factors had to be analyzed in order to satisfy the requirements and characteristics desired. The monitor developed consists of the following parts: monitor support (badge), incident neutron shielding, moderator body and LiF:Mg,Ti thermoluminescent detectors (TLDs). This work presents a discussion on the factors evaluated, such as: albedo shape, moderator type, among others. (author)
[en] An individual dosimeter for albedo neutrons is simulated with the Geant4 tool kit. Results of the simulation are benchmarked against an intercomparison reference for Monte Carlo codes. Doses are obtained for thermoluminescent dosemeters irradiated free in air and also on the surface of a water phantom for different vales of neutron energies. (author)
[en] The review of the current state in albedo dosimetry shows that only dosimeters of the discriminating type fulfill the requirements for routine application in personnel monitoring. Above all, the properties of the recently developed Karlsruhe albedo neutron dosimeter will be discussed and compared to other dosimeter designs. (Auth.)
[en] Cosmic ray fluxes in the energy range above 13 MeV have been measured by means of a detector of high geometrical factor on a polar orbiting satellite. From the observed altitude dependence in the polar regions, a value of 31 +- 0.3% for the contribution due to splash albedo particles to the total cosmic ray flux at the top of atmosphere, is derived. The experimentally observed cosmic ray flux leads to a value of 2.858 +- 0.008 particles (cm-2sec-1) for the cosmic ray flux in space. A comparison of this value with the Pioneer VI measurement of cosmic ray flux in the same energy range, leads to a value of 6.92 +- 2.0% A.U. for the radial cosmic ray density gradient. (author)
[en] Hot Jupiters are expected to be dark from both observations (albedo upper limits) and theory (alkali metals and/or TiO and VO absorption). However, only a handful of hot Jupiters have been observed with high enough photometric precision at visible wavelengths to investigate these expectations. The NASA Kepler mission provides a means to widen the sample and to assess the extent to which hot Jupiter albedos are low. We present a global analysis of Kepler-7 b based on Q0-Q4 data, published radial velocities, and asteroseismology constraints. We measure an occultation depth in the Kepler bandpass of 44 ± 5 ppm. If directly related to the albedo, this translates to a Kepler geometric albedo of 0.32 ± 0.03, the most precise value measured so far for an exoplanet. We also characterize the planetary orbital phase light curve with an amplitude of 42 ± 4 ppm. Using atmospheric models, we find it unlikely that the high albedo is due to a dominant thermal component and propose two solutions to explain the observed planetary flux. First, we interpret the Kepler-7 b albedo as resulting from an excess reflection over what can be explained solely by Rayleigh scattering, along with a nominal thermal component. This excess reflection might indicate the presence of a cloud or haze layer in the atmosphere, motivating new modeling and observational efforts. Alternatively, the albedo can be explained by Rayleigh scattering alone if Na and K are depleted in the atmosphere by a factor of 10-100 below solar abundances.
[en] A new official albedo dosemeter based on thermoluminescent detectors has been introduced in 2015 by the individual monitoring service of the Helmholtz Zentrum Muenchen for monitoring persons who are exposed occupationally against photon and neutron radiation. To enhance the sensitivity for fast neutrons, a new badge with an enlarged albedo window has been developed at TU Dresden. The properties of the new albedo dosemeter are discussed, and the results of official intercomparisons and field calibrations are shown. (authors)