Low-Afterglow, High-Refractive-Index Liquid Scintillators for Fast-Neutron Spectrometry and Imaging Applications

For ion and neutron spectrometry and imaging applications at a high intensity pulsed laser facility, fast liquid scintillators with very low afterglow are required. Furthermore, neutron imaging with fiber (or liquid-core) capillary arrays calls for scintillation materials with high refractive index. To this end, we have examined various combinations of established mixtures of fluors and solvents, that were enriched alternatively with nitrogen or oxygen. Dissolved molecular oxygen is known to be a highly effective quenching agent, that efficiently suppresses the population of the triplet states in the fluor, which are primarily responsible for the afterglow. For measuring the glow curves of scintillators, we have employed the time-correlated single photon counting (TCSPC) technique, characterized by high dynamic range of several orders of magnitude in light intensity. In this paper we outline the application for the fast scintillators, briefly present the scintillation mechanism in liquids, describe our specific TCSPC method and discuss the results.Comment: 5 pages, Contribution to SORMA WEST 2008. To be published in IEEE TNS, 200

Erzeugung und Charakterisierung eines gepulsten, intensiven Neutronen- und Gamma-Strahls zur Anwendung in der Luftfrachtdurchleuchtung

Die vorliegende Arbeit ist Teil eines Forschungsprojekts zur Entwicklung eines neuartigen Systems zur zerstörungsfreien und bildgebenden Untersuchung von Luftfracht mittels Neutronen- und Gammastrahlung. Im Rahmen dieser Arbeit wurde eine Strahlungsquelle entwickelt, die optimal auf die Anwendung angepasst ist: Ein gepulster Deuteronenstrahl wird in einer Ionenquelle erzeugt und mittels eines niederenergetischen Strahltransportsystems zum Hauptbeschleuniger geführt. Dieser besteht aus einem Radiofrequenz Quadrupol (RFQ) mit einer finalen Energie von 6 MeV. Da für die Anwendung sehr kurze Pulse der Strahlung in der Größenordnung einiger Nanosekunden unabdingbar sind, musste eine neuartige Lösung zur Pulsung des Deuteronenstrahls gefunden werden. Eine große Herausforderung bestand hierbei im Zusammenspiel der kurzen Pulsdauer und hohen Pulsladung in Kombination mit der hohen Wiederholrate. Dieses wurde erreicht, indem ein spezielles Pulsungssystem innerhalb des Strahlentransportes zwischen Ionenquelle und RFQ eingefügt wurde. Dieses System enthält neben einem strahlablenkenden auch ein strahlbündelndes Element. Der Deuteronenstrahl wird hinter dem RFQ auf ein Target geführt, welches aus Borcarbid besteht. In dieser Arbeit wird das komplette physikalische Design der Strahlungsquelle diskutiert sowie Simulationen zum Pulsungssystem bzw. dem RFQ-Beschleuniger präsentiert. Weiterhin werden Proof-of-Principle Experimente beschrieben, die mithilfe eines Prototypen-Pulsungssystems entwickelt im Rahmen dieser Arbeit und gefertigt von der RI Research Instruments GmbH an einem speziell für diesen Zweck errichteten Teststands durchgeführt wurden. Außerdem wurden mehrere Experimente sowohl an der Beschleunigeranlage der Physikalisch- Technischen Bundesanstalt (PTB) Braunschweig als auch am RFQ Beschleuniger der Nuclear Energy Corporation of South Africa (NECSA) in Pelindaba durchgeführt, um das Target zu optimieren und das erzeugte Strahlungsfeld zu charakterisieren.This thesis is part of a research project whose goal is to develop a novel, non-destructive imaging system to be employed for air freight security. The screening will be performed employing neutron- and gamma-radiation based techniques. One of the critical issues in this project was the absence of an adequate particle source. Thus, a new type of source was developed during this work. The new source consists of four main parts: A pulsed deuteron beam is formed in an ion source (IS) and is fed, via a matching low energy beam transport system (LEBT), into the main accelerator. The latter comprises a radio frequency quadrupole (RFQ) that produces a deuteron beam with a final energy of 6 MeV. Since pulsing of this beam in the regime of several nanoseconds is mandatory for the application, a novel solution had to be found to apply the required pulsing scheme, without undershoot the required beam charge per pulse. A major challenge in doing so was the combination of pulse length, high bunch charge as well as high repetition rate. This could be achieved by adding a pulsing system in between the LEBT section and RFQ: it consists of a beam-deflection, as well as a beam-bunching element. The deuteron beam is ultimately directed to a wobbling, plasma sprayed boron carbide (B4C) target. This work focuses on an entire physical design as well as simulation work of the pulsing system and RFQ. Furthermore, proof-of-principle experiments concerning a prototype of the pulsing system developed in the framework of this thesis and manufactured by RI Research Instruments GmbH could be performed at a test bench dedicated to this project. To round up the study, the suitability of the target and target reaction was demonstrated during multiple experiments performed at Physikalisch- Technische Bundesanstalt (PTB) at Braunschweig as well as the Nuclear Energy Corporation of South Africa (NECSA) in Pelindaba

Changes in Painting Styles of Two Artists With Alzheimer's Disease

A substantial body of literature supports the idea that systematic changes can occur in artists' painting styles after the onset of degenerating neurological illnesses like Alzheimer's disease or Fronto-temporal dementia. However, these studies have typically been descriptive and qualitative in their analyses. Our study was motivated to show that quantitative methods can be applied to the neuropsychology of art production and to determine whether there are systematic changes in the art produced by two individuals with Alzheimer's disease (AD). Using the Assessment of Art Attributes which probes 6 formal characteristics (depth, color temperature, color saturation, balance, stroke, and simplicity) and 6 conceptual characteristics (depictive accuracy, abstractness, emotion, symbolism, realism, and animacy), we found that both AD patients produced paintings with more abstraction and use of symbolism and with less depictive accuracy and realism. Their paintings did not change in the use of depth, or balance or in the quality of their stroke. When these observations are combined with those made recently in 3 artists with focal brain damage, we find that conceptual more than formal perceptual attributes are susceptible to change after neurological illness. © 2013 American Psychological Association.status: publishe

Investigations toward a Non-Aqueous Hybrid Redox-Flow Battery with a Manganese-Based Anolyte and Catholyte

A new all-Manganese flow battery (all-MFB) as a non-aqueous hybrid redox-flow battery is reported. The discharged active material [Cat]2[MnIICl4] (Cat = organic cation) utilized in both half-cells supports a long cycle life. The reversible oxidation of [MnIICl4]2− to [MnIIICl5]2− at the positive electrode and manganese metal deposition from [MnIICl4]2− at the negative electrode give a cell voltage of 2.59 V. Suitable electrolytes are prepared and optimized, followed by a characterization in static battery cells and in a pumped flow-cell. Several electrode materials, solvents, and membranes are tested for their feasibility in the all-MFB. An electrolyte consisting of [EMP]2[MnCl4] and some solvent γ-butyrolactone is cycled 500 times, both in a static as well as a flow-cell, over a period of two months, with coulombic efficiencies up to 83%. With the electrolytes prepared in this work, energy densities up to 74 Wh L−1 are possible, exceeding the VRFB benchmark system, using solely the cheap and abundant element manganese as the active material. Although further optimizations are necessary, this system represents a new and promising setup toward sustainable stationary energy storage