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Trabalho completo: acesso restrito, p. 239–246 Submitted by Bruna Lessa (lessbruna@gmail.com) on 2012-05-14T20:20:09Z No. of bitstreams: 1 (20)1-s2.0-S0370269310001875-main.pdf: 501159 bytes, checksum: 2ef6e672f42baaf0b492895ab50b1402 (MD5) Made available in DSpace on 2012-05-14T20:20:09Z (GMT). No. of bitstreams: 1 (20)1-s2.0-S0370269310001875-main.pdf: 501159 bytes, checksum: 2ef6e672f42baaf0b492895ab50b1402 (MD5) Previous issue date: 2010-03-08 We report a measurement of the flux of cosmic rays with unprecedented precision and statistics using the Pierre Auger Observatory. Based on fluorescence observations in coincidence with at least one surface detector we derive a spectrum for energies above 1018 eV. We also update the previously published energy spectrum obtained with the surface detector array. The two spectra are combined addressing the systematic uncertainties and, in particular, the influence of the energy resolution on the spectral shape. The spectrum can be described by a broken power law E−γ with index γ=3.3 below the ankle which is measured at log10(Eankle/eV)=18.6. Above the ankle the spectrum is described by a power law with index 2.6 followed by a flux suppression, above about log10(E/eV)=19.5, detected with high statistical significance.

Trabalho completo: acesso restrito, p. 29–39 Submitted by Bruna Lessa (lessbruna@gmail.com) on 2012-06-01T19:47:20Z No. of bitstreams: 1 (51)1-s2.0-S0168900209021688-main.pdf: 605452 bytes, checksum: a24e23f098494f571e9e854b4763cef2 (MD5) Made available in DSpace on 2012-06-01T19:47:20Z (GMT). No. of bitstreams: 1 (51)1-s2.0-S0168900209021688-main.pdf: 605452 bytes, checksum: a24e23f098494f571e9e854b4763cef2 (MD5) Previous issue date: 2010-01-21 The surface detector array of the Pierre Auger Observatory consists of 1600 water-Cherenkov detectors, for the study of extensive air showers (EAS) generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy, from the identification of candidate showers at the level of a single detector, amongst a large background (mainly random single cosmic ray muons), up to the selection of real events and the rejection of random coincidences. Such trigger makes the surface detector array fully efficient for the detection of EAS with energy above View the MathML source, for all zenith angles between 0∘ and 60∘, independently of the position of the impact point and of the mass of the primary particle. In these range of energies and angles, the exposure of the surface array can be determined purely on the basis of the geometrical acceptance.

Trabalho completo: acesso restrito, p.89–99 Submitted by Bruna Lessa (lessbruna@gmail.com) on 2012-07-03T13:44:58Z No. of bitstreams: 1 (101)1-s2.0-S0927650509001017-main.pdf: 1294501 bytes, checksum: ce51757e826af91cc03867d15ace5e9a (MD5) Made available in DSpace on 2012-07-03T13:44:59Z (GMT). No. of bitstreams: 1 (101)1-s2.0-S0927650509001017-main.pdf: 1294501 bytes, checksum: ce51757e826af91cc03867d15ace5e9a (MD5) Previous issue date: 2009-09 Atmospheric parameters, such as pressure (P), temperature (T) and density (ρ∝P/T), affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ∼10% seasonal modulation and ∼2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of P and ρ. The former affects the longitudinal development of air showers while the latter influences the Molière radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.

Trabalho completo: acesso restrito, p. 654–658 Submitted by Bruna Lessa (lessbruna@gmail.com) on 2012-07-13T18:42:43Z No. of bitstreams: 1 (117)1-s2.0-S0925838809005143-main.pdf: 524932 bytes, checksum: 33fab11280e63b762ad713d7d328eed3 (MD5) Made available in DSpace on 2012-07-13T18:42:43Z (GMT). No. of bitstreams: 1 (117)1-s2.0-S0925838809005143-main.pdf: 524932 bytes, checksum: 33fab11280e63b762ad713d7d328eed3 (MD5) Previous issue date: 2009-07-29 This paper reports the composition and optical characterization of Sn(IV)–Sn(II) colloidal particles formed in sulfuric acid solution containing Sn(II) and Cu(II) in the presence of sulfur dioxide and Rhodamine B. Precipitated particles from Sn(IV)–Sn(II) colloids were characterized by FTIR, XRD and EPR. Optical properties were evaluated using a homemade transmission spectrometer in the energy range of 1.0–4.0 eV. The colloidal particles consist of copper-doped amorphous SnO2 as the predominant base material with Sn(OH)2(SO4)22− species attached on the surface. The EPR spectra of these materials are typical of Cu2+ ions in axial symmetry, suggesting that some Sn4+ ions in tin dioxide are replaced with Cu2+. Rhodamine B dramatically influences the spectra profile of these materials and also enhances the doping of Cu (Cu2+ and Cu0) in SnO2. An increase in the band gap energy is observed with increasing volume of RhB solution in the reactant media. This demonstrates the possibility of engineering optoelectronic devices with adjustable absorption profiles for a specific application.

Trabalho completo: acesso restrito, p.399–406 Submitted by Bruna Lessa (lessbruna@gmail.com) on 2012-07-13T19:00:59Z No. of bitstreams: 1 (118)1-s2.0-S0927650509000693-main.pdf: 734652 bytes, checksum: 94223680f717afa2613dbc4b90d41da8 (MD5) Made available in DSpace on 2012-07-13T19:00:59Z (GMT). No. of bitstreams: 1 (118)1-s2.0-S0927650509000693-main.pdf: 734652 bytes, checksum: 94223680f717afa2613dbc4b90d41da8 (MD5) Previous issue date: 2009 From direct observations of the longitudinal development of ultra-high energy air showers performed with the Pierre Auger Observatory, upper limits of 3.8%, 2.4%, 3.5% and 11.7% (at 95% c.l.) are obtained on the fraction of cosmic-ray photons above 2, 3, 5 and 10 EeV View the MathML source, respectively. These are the first experimental limits on ultra-high energy photons at energies below 10 EeV. The results complement previous constraints on top–down models from array data and they reduce systematic uncertainties in the interpretation of shower data in terms of primary flux, nuclear composition and proton-air cross-section.