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1.
Combined fit of the energy spectrum and mass composition across the ankle with the data measured at the Pierre Auger Observatory
E. Guido, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, objavljeni znanstveni prispevek na konferenci

Opis: The combined fit of the energy spectrum and mass composition data above 5 EeV suggested the presence of extragalactic sources ejecting ultra-high-energy cosmic rays with relatively low maximum energies, hard spectral indices and mixed chemical compositions, dominated by the contribution of intermediate mass groups. Here we present an extension of the fit to lower energies, to include the feature observed near 5 EeV in the all-particle energy spectrum, the so-called ankle. We show that it is possible to generate such a change of slope assuming that the flux below the ankle is provided by the superposition of different contributions. The simplest extension of this sort consists of introducing a supplemental extragalactic component at low energy, characterised by different physical parameters with respect to the one being dominant above the ankle: such a component may originate from a different population of sources or be provided by interactions occurring in the acceleration sites. In this framework we also explore the possibility of including the end of a Galactic contribution at low energies. The fit suggests that these scenarios provide a reasonable description of the measurements across the ankle, without significantly affecting the interpretation obtained for the above-ankle region. In order to evaluate our capability to constrain the source models, we finally discuss the impact of the main experimental systematic uncertainties and of the theoretical models choice on the fit results.
Ključne besede: Pierre Auger Observatory, indirect detection, fluorescence detection, hybrid detection, surface detection, ultra-high energy, cosmic rays, composition, energy spectrum, combined fit
Objavljeno v RUNG: 03.10.2023; Ogledov: 688; Prenosov: 4
.pdf Celotno besedilo (1,09 MB)
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2.
Telescope Array Combined Fit to Cosmic Ray Spectrum and Composition
D. Bergman, Jon Paul Lundquist, 2022, objavljeni znanstveni prispevek na konferenci

Opis: We present the result of fits of an astrophysical model of UHECR sources to the energy spectrum measured using the Telescope Array (TA) surface detectors and the composition data measured by TA fluorescence detectors in stereo mode. The astrophysical model consists of identical sources, uniformly distributed with a density which evolves with age, where groups of nuclei with varying fractions are accelerated producing a power law source with a rigidity-dependent cutoff. The model includes the propagation effects of photo-pion production, photo-nuclear disintegration and general energy loss from universal expansion. Comparison of model data with detector data in both the energy and the Xmax distributions is done via a forward-folding description of detector effects. A prediction of the cosmogenic neutrino flux at Earth resulting from the cosmic rays produced in the model with these fit values is also presented. The predicted flux is considerably higher than other similar fits to Auger data have previously predicted.
Ključne besede: Telescope Array, indirect detection, stereo detection, fluorescence detection, ultra-high energy, cosmic rays, energy spectrum, composition, combined fit, cosmogenic neutrinos, multimessenger
Objavljeno v RUNG: 02.10.2023; Ogledov: 813; Prenosov: 5
.pdf Celotno besedilo (1,48 MB)
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3.
THE ROLE OF SPECT/CT SCINTIGRAPHY IN LOCALIZATION OF PARATHYROID ADENOMAS
Sebastijan Rep, 2016, magistrsko delo

Opis: Parathyroid scintigraphy is based on the different accumulation and distribution of radiopharmaceutical 99mTc-MIBI (MIBI) in parathyroid and adjacent tissues. Different scintigraphic techniques can be used: subtraction scintigraphy is a combination of MIBI and 99mTc-pertehnetate (pertehnetate) scintigraphy; SPECT can be performed after intravenous injection of MIBI or in the combination with low-dose computerized tomography (SPECT/CT) which allows precise anatomical localization of enlarged parathyroid glands (EPG). The objectives of our study were: to assess diagnostic performance of preoperative localization of EPG (adenomas and hyperplasia) of the early, delayed and combined SPECT/CT and of subtraction scintigraphy in patients with biochemically proven primary hyperparathyroidism (PHP); to determine whether size of EPG, serum parathyroid hormone (PTH), calcium (Ca) and phosphate (P) correlate with successful localization; to assess radiation exposure of patients with early and late SPECT/CT and subtraction scintigraphy The study included 41 patients in whom early, delay SPECT/CT and subtraction scintigraphy were performed. For all scintigraphic methods sensitivity, specificity, positive predictive value, negative predictive value and accuracy were calculated. Receiver Operating Characteristic analysis was used to express relationship between scintigraphy results and size of the EPG and serum Ca, P and PTH levels. ImPACT CT Patient Dosimetry Calculator and weighting factors for radiopharmaceuticals (MIBI and pertechnetate) were used for calculating patient expose dose. Sensitivity and specificity were 51.1% and 98.3 for subtraction scintigraphy, 65.1% and 97.5% for early SPECT/CT and 65.1% and 95.5% for delay SPECT/CT. In combined early and delay SPECT/CT sensitivity and specificity were 74.4% and 95.1%.Only size of the EPG correlated with successful localization in our study (AUC of 0.791-0.810). The highest average ED per patient had subtraction scintigraphy (7.37±0.40 mSv), which was statistically significant higher in comparison to combined early and delayed SPECT/CT (6.81±0.44 mSv). The most sensitive and most accurate method of preoperative localization of EPG in patients with PHP is combined early and delayed SPECT/CT. Only size of the EPG correlates with successful localization. The highest radiation exposure is after subtraction scintigraphy.
Ključne besede: Enlarged parathyroid glands, early SPECT/CT, delayed SPECT/CT, combined SPECT/CT, subtraction scintigraphy, 99mTc-MIBI, 99mTc-pertechnetate, effective dose, serum parathyroid hormone, calcium, phosphate
Objavljeno v RUNG: 03.10.2016; Ogledov: 6626; Prenosov: 252
.pdf Celotno besedilo (1,03 MB)

4.
Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory
Andrea Di Matteo, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, objavljeni znanstveni prispevek na konferenci

Opis: We present a combined fit of both flux and composition of ultra-high energy cosmic rays as measured by the Pierre Auger Observatory. The fit has been performed for energies above 5 × 10[sup]18 eV, i.e. the region of the all-particle spectrum above the so-called “ankle” feature. A simple astrophysical model consisting of identical sources has been adopted, where nuclei are injected with a rigidity dependent mechanism and the sources are uniformly distributed in a comoving volume. The fit results suggest a source model characterized by relatively low maximum injection energies and hard spectral indices. The impact of different sources of systematic uncertainties in the above result is discussed.
Ključne besede: Pierre Auger Observatory, ultra-high energy cosmic rays, energy spectrum, elemental composition, combined data fit
Objavljeno v RUNG: 03.03.2016; Ogledov: 4672; Prenosov: 231
.pdf Celotno besedilo (704,98 KB)

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