290 research outputs found
Low-energy solar neutrino spectroscopy with Borexino : Towards the detection of the solar pep and CNO neutrino flux
No full textBorexino ist ein großvolumiger Detektor, der mit organischem Flüssigszintillator von einer bisher noch nie erreichten geringen Eigenradioaktivität gefüllt ist und für die Echtzeitspektroskopie niederenergetischer Neutrinos konzipiert wurde. Neben dem Hauptziel des Experiments, der Messung des solaren 7Be Neutrinoflusses, wird auch der Nachweis von Sonnenneutrinos aus dem pep-Fusionsprozess und dem CNO-Zyklus angestrebt. Die Nachweisbarkeit dieser Neutrinos hängt von der erfolgreichen Unterdrückung aller relevanten Untergrundkomponenten ab. Die Identifizierung und Reduktion verschiedener Untergrundsignale ist das Hauptthema dieser Dissertation. Im ersten Teil der Arbeit werden myon-induzierte Untergründe analysiert. Der dominierende Untergrund ist das kosmogene Radioisotop 11C, dessen Rate ~10 mal höher ist als die erwartete pep- und CNO-Neutrinorate im bevorzugten Beobachtungsfenster von [0.8,1.3] MeV. Da 11C meistens unter Emission eines Neutrons entsteht, kann 11C über eine Dreifachkoinzidenz (DFK), bestehend aus dem Myon-Signal, dem Neutroneinfang und dem 11C-Zerfall identifiziert werden. Die DFK-Methode und weitere Techniken zur Unterdrückung von 11C wurden optimiert, dadurch wurde eine 11C-Unterdrückungseffizienz von 80% und ein Neutrino-zu-Untergrund-Verhältnis von 1:1.7 erreicht. Dabei geht 61% der Statistik verloren. Der zweite Teil der Arbeit beschäftigt sich mit der Untersuchung des externen Untergrundes. Vorwiegend langreichweitige 2.6 MeV Photonen, die durch 208Tl Zerfälle in den äußeren Detektorkomponenten emittiert werden, können den Szintillator im inneren Bereich des Detektor erreichen. Um die spektrale Form des externen Untergrundes zu bestimmen, wurde eine ~5 MBq 228Th-Quelle eigens angefertigt und damit erstmals eine externe Kalibration durchgeführt. Die gewonnenen Kalibrationsdaten werden zusammen mit den optimierten 11C-Unterdrückungsmethoden den direkten Nachweis solarer pep- und womöglich auch CNO-Neutrinos in Borexino ermöglichen
Low-Level-Gammaspektroskopie im Rahmen des GERDA-Experiments zur Suche nach dem neutrinolosen Doppel-Betazerfall in <sup>76</sup>Ge
No full text
Present status of neutrinoless double beta decay searches
No full textSeveral new generation experiments searching for neutrinoless double beta decay (0vbb) have become operational over the last five years. This report summarizes the present status of the experimental search and discusses peculiarities, challenges and reached half-life limits/sensitivities in these experiments. So far, no evidence for 0vbb has been found. Starting from the current situation, the paper addresses the question whether an experiment alone will be able to proof unambiguously 0vbb decay and which would be the key-requirements to succeed in this
Identification of radiopure tungsten for low background applications
No full textIn this article we explore the availability of radiopure tungsten and its
potential as high density shield material for low background applications. For
compact shield designs, conventionally, lead is used. Metallic tungsten and
tungsten pseudo-alloys reach higher densities up to 19.3 gcm and do not
exhibit a significant Pb activity, which is a typical intrinsic
contamination in lead. Within several -ray screening campaigns we were
able to identify tungsten samples with activities similar or better than 1
mBqkg in Th, K, Co and the second part of the
U decay chain. In cooperation with a manufacturer we further reduced a
persisting contamination in the first part of the U decay chain by a
factor of 2.5 down to (30530) mBqkg. With Monte Carlo
simulations, the construction of prototype tungsten-based setups and dedicated
measurements, the shield capability of tungsten in comparison to lead was
extensively studied. Specifically, the impact of cosmogenic radiation on the
background at shallow depth was investigated. We showed that a 6-40% reduction
(depending on the exact shield configuration) in the muon-induced neutron
fluence is achievable by replacing lead with an equivalent amount of tungsten
regarding the suppression of external -radiation. Overall, many
benefits using tungsten especially for low energy applications below a few 100
keV are found. The pseudo-tungsten alloy presented in this work paves the way
for several applications especially regarding background suppression in
particle and astroparticle physics search programs.Comment: 17 pages, 15 figure
Optimisation of the MC-model of a p-type Ge-spectrometer for the purpose of efficiency determination
No full textProduction and characterization of a custom-made 228Th source with reduced neutron source strength for the Borexino experiment
No full textA custom-made 228Th source of several MBq activities was produced for the Borexino experiment to study the external background of the detector. The aim was to reduce the unwanted neutron emission produced via (α,n) reactions in ceramics typically used for commercial 228Th sources. For this purpose a ThCl4 solution was chemically converted into ThO2 and embedded in a gold foil.
The paper describes the production of the custom-made source and its characterization by means of γ-activity, dose rate and neutron source strength measurements. From γ-spectroscopic measurements it was deduced that activity transfer from the initial solution to the final source was >91% (at 68% C.L.) and the final activity was (5.41±0.30) MBq. The dose rate was measured with two dosimeters yielding 12.1 mSv/h and 14.3 mSv/h in 1 cm distance. The neutron source strength of the 5.41 MBq 228Th source was determined to be (6.59±0.85) s−1
Measurements of extremely low radioactivity levels in stainless steel for GERDA
No full textThe radioisotope concentrations in stainless steel for the cryostat of the GERDA experiment at the Laboratori Nazionali del Gran Sasso (LNGS) have been measured. A total of 13 different stainless steel form batches have been screened by low-level gamma-ray spectrometry with germanium detectors located at two underground laboratories. The article reports the discovery of commonly available stainless steel with very low concentrations of primordial and cosmogenic radionuclides. The concentrations are in the range of 1 mBq/kg and below. Only the manmade 60Co-isotope is present in all samples with a higher concentration of around 19 mBq/kg. Further, deviations from secular equilibrium in the natural decay chains of U and Th have been observed in some cases
Ophthalmic Aspects of Stevens–Johnson Syndrome and Toxic Epidermal Necrolysis: A Narrative Review
No full textAbstract The aim of our review article was to summarize the current literature on Stevens–Johnson syndrome (SJS) and its severe form, toxic epidermal necrolysis (TEN). SJS/TEN is a serious, rare multi-system, immune-mediated, mucocutaneous disease with a significant mortality rate that can lead to severe ocular surface sequelae and even to bilateral blindness. Restoration of the ocular surface in acute and chronic SJS/TEN is challenging. There are only limited local or systemic treatment options for SJS/TEN. Early diagnosis, timely amniotic membrane transplantation and aggressive topical management in acute SJS/TEN are necessary to prevent long-term, chronic ocular complications. Although the primary aim of acute care is to save the life of the patient, ophthalmologists should regularly examine patients already in the acute phase, which should also be followed by systematic ophthalmic examination in the chronic phase. Herein, we summarize actual knowledge on the epidemiology, aetiology, pathology, clinical appearance and treatment of SJS/TEN
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