Liquid argon as active shielding and coolant for bare germanium detectors:A novel background suppression method for the Gerda 0(nu/beta/beta) experiment

Zwei der wichtigsten offenen Fragen in der Teilchenphysik sind die, ob Neutrinos ihre eigenen Antiteilchen sind, wie die meisten Erweiterungen des Standardmodells vorhersagen und was die absolute Masse der Neutrinos ist. Die höchste Sensitivität um dies zu untersuchen bietet der neutrinolose Doppelbetazerfall (0ν β β) der mittels des ββ Isotops 76Ge untersucht werden kann. Ein Teil der Kollaboration des 76Ge Experiments Heidelberg-Moskau (HdM) hat eine Evidenz für die Entdeckung des 0νββ-Zerfalls veröffentlicht. Das neue 0νββ-Experiment Gerda wird 76Ge-angereicherte Germaniumdetektoren in Flüssigargon (LAr) betreiben um diese Evidenz innerhalb eines Jahres (Phase I) mit 15 kg·y Statistik bei einem Untergrund von ≤10−2 cts/(kg·keV·y) zu überprüfen. Das LAr dient dabei als Kühlflüssigkeit und hochreine Abschirmung. Phase II wird mit 100 kg·y und einem Untergrund von ≤10−3 cts/(kg·keV·y) in höhere Sensitivitätsbereiche vorstoßen. Dafür sind neue Methoden zur Unterdrückung des kosmogenen Untergrunds der Dioden erforderlich, welcher für 60Co ∼2.5·10−3 cts/(kg·keV·y) beträgt. Flüssigargon ist ein Szintillator im UV Bereich (λ=128 nm) und ein neuartiges Konzept ist es, das Szintillationslicht als Anti-Koinzidenzsignal für die Untergrundunterdrückung zu nutzen. In dieser Arbeit wurde die Effizienz eines solchen Anti-Koinzidenz-Vetos mittels LAr-Szintillation erstmalig untersucht. Mit einem Testaufbau (aktive LAr Masse 19 kg) wurde ein Faktor 3 Unterdrückung für 60Co und ein Faktor 17 für 232Th im Bereich um Q(beta/beta)=2039 keV erreicht. Ein größeres aktives Volumen wird die Unterdrückung weiter verbessern (Faktor O(100) für 1t LAr für 232Th und 60Co). Darüber hinaus kann die LAr Szintillation zur Untergrunddiagnose eingesetzt werden. Dazu wurde eine neue, sehr stabile Wellenlängenschieber/Reflektor Kombination für den LAr-Szintillationslichtnachweis entwickelt, mit dem eine Lichtausbeute von 1.2 Photoelektronen pro keV erreicht wurde. Damit wurde durch Pulsformanalyse ein Diskriminationsfaktor von 2 · 106 zwischen α-s und γ-s und von 3 · 103 zwischen γ-s und Neutronen erreicht

Operation of a high purity germanium crystal in liquid argon as a Compton suppressed radiation spectrometer

A high purity germanium crystal was operated in liquid argon as a Compton suppressed radiation spectrometer. Spectroscopic quality resolution of less than 1% of the full-width half maximum of full energy deposition peaks was demonstrated. The construction of the small apparatus used to obtain these results is reported. The design concept is to use the liquid argon bath to both cool the germanium crystal to operating temperatures and act as a scintillating veto. The scintillation light from the liquid argon can veto cosmic-rays, external primordial radiation, and gamma radiation that does not fully deposit within the germanium crystal. This technique was investigated for its potential impact on ultra-low background gamma-ray spectroscopy. This work is based on a concept initially developed for future germanium-based neutrinoless double-beta decay experiments.Comment: Paper presented at the SORMA XI Conference, Ann Arbor, MI, May 200

Radiation emitted by transverse-gradient undulators

Conventional undulators are used in synchrotron light sources to produce radiation with a narrow relative spectral width as compared to bending magnets or wigglers. The spectral width of the radiation produced by conventional undulators is determined by the number of undulator periods and by the energy spread and emittance of the electron beam. In more compact electron sources like for instance laser plasma accelerators the energy spread becomes the dominating factor. Due to this effect these electron sources cannot in general be used for high-gain free electron lasers (FELs). In order to overcome this limitation, modified undulator schemes, so-called transverse gradient undulators (TGUs), were proposed and a first superconducting TGU was built at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. In this paper simulations of the expected synchrotron radiation spectral distribution are presented. An experimental test with that device is under preparation at the laser wakefield accelerator at the JETI laser at the University of Jena, Germany

Arsenic and chromium partitioning in a podzolic soil contaminated by chromated copper arsenate

This research combined the use of selective extractions and x-ray spectroscopy to examine the fate of As and Cr in a podzolic soil contaminated by chromated copper arsenate (CCA). Iron was enriched in the upper 30 cm due to a previous one-time treatment of the soil with Fe(II). High oxalate-soluble Al concentrations in the Bs horizon of the soil and micro-XRD data indicated the presence of short-range ordered aluminosilicates (i.e. proto-imogolite allophane, PIA). In the surface layers, Cr, as Cr(III), was partitioned between a mixed Fe(III)/Cr(III) solid phase that formed upon the Fe(II) application (25-50%) and a recalcitrant phase (50-75%) likely consisting of organic material such as residual CCA-treated wood. Deeper in the profile Cr appeared to be largely in the form of extractable (hydr)oxides. Throughout the soil, As was present as As(V). In the surface layers a considerable fraction of As was also associated with a recalcitrant phase, probably CCA-treated woody debris, and the remainder was associated with (hydr)oxide-like solid phases. In the Bs horizon, however, XAS and XRF findings strongly pointed to the presence of PIA acting as an effective adsorbent for As. This research shows for the first time the relevance of PIA for the adsorption of As in natural soils

A role of SCN9A in human epilepsies, as a cause of febrile seizures and as a potential modifier of Dravet syndrome

A follow-up study of a large Utah family with significant linkage to chromosome 2q24 led us to identify a new febrile seizure (FS) gene, SCN9A encoding Na(v)1.7. In 21 affected members, we uncovered a potential mutation in a highly conserved amino acid, p.N641Y, in the large cytoplasmic loop between transmembrane domains I and II that was absent from 586 ethnically matched population control chromosomes. To establish a functional role for this mutation in seizure susceptibility, we introduced the orthologous mutation into the murine Scn9a ortholog using targeted homologous recombination. Compared to wild-type mice, homozygous Scn9a(N641Y/N641Y) knockin mice exhibit significantly reduced thresholds to electrically induced clonic and tonic-clonic seizures, and increased corneal kindling acquisition rates. Together, these data strongly support the SCN9A p.N641Y mutation as disease-causing in this family. To confirm the role of SCN9A in FS, we analyzed a collection of 92 unrelated FS patients and identified additional highly conserved Na(v)1.7 missense variants in 5% of the patients. After one of these children with FS later developed Dravet syndrome (severe myoclonic epilepsy of infancy), we sequenced the SCN1A gene, a gene known to be associated with Dravet syndrome, and identified a heterozygous frameshift mutation. Subsequent analysis of 109 Dravet syndrome patients yielded nine Na(v)1.7 missense variants (8% of the patients), all in highly conserved amino acids. Six of these Dravet syndrome patients with SCN9A missense variants also harbored either missense or splice site SCN1A mutations and three had no SCN1A mutations. This study provides evidence for a role of SCN9A in human epilepsies, both as a cause of FS and as a partner with SCN1A mutations

Does low and oscillatory wall shear stress correlate spatially with early atherosclerosis? A systematic review

Low and oscillatory wall shear stress is widely assumed to play a key role in the initiation and development of atherosclerosis. Indeed, some studies have relied on the low shear theory when developing diagnostic and treatment strategies for cardiovascular disease. We wished to ascertain if this consensus is justified by published data. We performed a systematic review of papers that compare the localization of atherosclerotic lesions with the distribution of haemodynamic indicators calculated using computational fluid dynamics. The review showed that although many articles claim their results conform to the theory, it has been interpreted in different ways: a range of metrics has been used to characterize the distribution of disease, and they have been compared with a range of haemodynamic factors. Several studies, including all of those making systematic point-by-point comparisons of shear and disease, failed to find the expected relation. The various pre- and post-processing techniques used by different groups have reduced the range of shears over which correlations were sought, and in some cases are mutually incompatible. Finally, only a subset of the known patterns of disease has been investigated. The evidence for the low/oscillatory shear theory is less robust than commonly assumed. Longitudinal studies starting from the healthy state, or the collection of average flow metrics derived from large numbers of healthy vessels, both in conjunction with point-by-point comparisons using appropriate statistical techniques, will be necessary to improve our understanding of the relation between blood flow and atherogenesis

Copy-number-variation and copy-number-alteration region detection by cumulative plots

Background: Regions with copy number variations (in germline cells) or copy number alteration (in somatic cells) are of great interest for human disease gene mapping and cancer studies. They represent a new type of mutation and are larger-scaled than the single nucleotide polymorphisms. Using genotyping microarray for copy number variation detection has become standard, and there is a need for improving analysis methods. Results: We apply the cumulative plot to the detection of regions with copy number variation/alteration, on samples taken from a chronic lymphocytic leukemia patient. Two sets of whole-genome genotyping of 317k single nucleotide polymorphisms, one from the normal cell and another from the cancer cell, are analyzed. We demonstrate the utility of cumulative plot in detecting a 9Mb (9 x 10^6 bases) hemizygous deletion and 1Mb homozygous deletion on chromosome 13. We also show the possibility to detect smaller copy number variation/alteration regions below the 100kb range. Conclusions: As a graphic tool, the cumulative plot is an intuitive and a scale-free (window-less) way for detecting copy number variation/alteration regions, especially when such regions are small