Spektrale messungen der gamma-zahlrate an einer neutronen bestrahlten salicyli-chinin-lithium-komnination

Eine Salieyl-Chinin-Lithium-Kombination wurde im Siemens Unterriehtsreaktor SUR 100 BE des Instituts fur Kernteehnik der Teehnisehen UniversiUit Berlin mit Neutronen aktiviert. AnsehlieBend erfolgte die Messung der spektralen Verteilung der Gamma-Zahlrate zu zwei versehiedenen Zeitpunkten naeh der Aktivierung. Es wird festgestellt, daB diese Salieyl-Chinin-Lithium-Kombination nur sehwaeh im SUR-Reaktor aktivierbar ist, vergliehen mit einer Goldsonde etwa 200 mal sehwaeher. Trotzdem konnten mit Hilfe eines 400-Kanal-Analysators die spektralen Verteilungen der Gamma-Energien dieses Praparates noch sehr genau bestimmt werden. Ein ausgepragter Gamma-Peak tritt auf bei der Energie 0.53 MeV. Er klingt ab mit einer Halbwertszeit von 1.6 h und ist vermut· lich auf ein Element der Tablettierhilfsstoffe zurUckzufUhren. Vom strahlenphysikalischen Gesichtspunkt ist das Praparat fUr die Human. medizin gut geeignet.</p

Physikalische grund-lagen und medizinische anwendungen des siemens-unterrichts reaktors SUR 100

Die physikalischen Grundlagen eines Kernreaktors werden beschrieben. Als spezielles Beispiel wird Aufbau, Kontrolle und Betrieb des Siemens-Unterrichtsreaktors SUR 100 beschrieben. Dieser homogene polyathylenmoderierte Nullleistungsreaktor hat eine Leistung von nur 100 mW. Trotzdem-oder gerade deswegen-ist dieser Reaktor fur Ausbildungszwecke und als Ubungsmoglichkeit auf dem Gebiet der Reaktortheorie und der Kernenergie sehr gut geeignet, denn die Leistungsbeschrankung erlaubt eine einfache Installierung und Betriebsweise des Reaktors. Neben seiner Verwendung als Ausbildungsinstrument kann dieser Reaktor aber auch als Strahlenquelle benutzt werden. Hiermit wurden verschiedene medizinische Praparate, die auch im Strahlenschutz Verwendung finden, bestrahlt, und anschlieBend ihre Dosisrate bestimmt. AuBerdem werden noch weitere Anwendungsmoglichkeiten des Siemens-Unterrichtsreaktors SUR 100 deschrieben.</p

Competitive ion-exchange of manganese and gadolinium in titanate nanotubes

Homogeneous Mn2+ and Gd3+ intercalation of scroll-type trititanate nanotubes using a post-synthesis ion exchange method is reported. Compared to Mn2+, Gd3+ ion-exchange shows larger saturation intercalation levels. Upon co-doping, weak interactions between the dopant ions were found to modify the incorporated concentrations. Electron spin resonance (ESR) measurements, performed at several frequencies, confirmed the homogeneous distribution of Mn2+ and Gd3+. Detailed simulation of ESR spectra identified a large spread of the local structural distortions of the occupied sites as a result of a wide range of curvature radii of the titanate nanotubes. (C) 2016 Elsevier B.V. All rights reserved

Tuning ferromagnetism at room temperature by visible light

Most digital information today is encoded in the magnetization of ferromagnetic domains. The demand for ever-increasing storage space fuels continuous research for energy-efficient manipulation of magnetism at smaller and smaller length scales. Writing a bit is usually achieved by rotating the magnetization of domains of the magnetic medium, which relies on effective magnetic fields. An alternative approach is to change the magnetic state directly by acting on the interaction between magnetic moments. Correlated oxides are ideal materials for this because the effects of a small external control parameter are amplified by the electronic correlations. Here, we present a radical method for reversible, light-induced tuning of ferromagnetism at room temperature using a halide perovskite/oxide perovskite heterostructure. We demonstrate that photoinduced charge carriers from the CH3NH3PbI3 photovoltaic perovskite efficiently dope the thin La0.7Sr0.3MnO3 film and decrease the magnetization of the ferromagnetic state, allowing rapid rewriting of the magnetic bit. This manipulation could be accomplished at room temperature; hence this opens avenues for magnetooptical memory devices

Anisotropic Elliott-Yafet theory and application to KC8 potassium intercalated graphite

We report electron spin resonance (ESR) measurements on stage-I potassium intercalated graphite (KC8). Angular dependent measurements show that the spin-lattice relaxation time is longer when the magnetic field is perpendicular to the graphene layer as compared to when the magnetic field is in the plane. This anisotropy is analyzed in the framework of the Elliott-Yafet theory of spin-relaxation in metals. The analysis considers an anisotropic spin-orbit Hamiltonian and the first order perturbative treatment of Elliott is reproduced for this model Hamiltonian. The result provides an experimental input for the first-principles theories of spin-orbit interaction in layered carbon and thus to a better understanding of spin-relaxation phenomena in graphene and in other layered materials as well

Density of states deduced from ESR measurements on low-dimensional nanostructures; benchmarks to identify the ESR signals of graphene and SWCNTs

Electron spin resonance (ESR) spectroscopy is an important tool to characterize the ground state of conduction electrons and to measure their spin-relaxation times. Observing ESR of the itinerant electrons is thus of great importance in graphene and in single-wall carbon nanotubes. Often, the identification of CESR signal is based on two facts: the apparent asymmetry of the ESR signal (known as a Dysonian lineshape) and on the temperature independence of the ESR signal intensity. We argue that these are insufficient as benchmarks and instead the ESR signal intensity (when calibrated against an intensity reference) yields an accurate characterization. We detail the method to obtain the density of states from an ESR signal, which can be compared with theoretical estimates. We demonstrate the success of the method for K doped graphite powder. We give a benchmark for the observation of ESR in graphene

Improved Alkali Intercalation of Carbonaceous Materials in Ammonia Solution

Alkali-intercalated graphite compounds represent a compelling modification of carbon with significant application potential and various fundamentally important phases. The intercalation of graphite with alkali atoms (Li and K) using liquid ammonia solution as a mediating agent is reported. Alkali atoms dissolve well in liquid ammonia, which simplifies and speeds up the intercalation process, and it also avoids the high temperature formation of alkali carbides. Optical microscopy, Raman, and electron spin-resonance spectroscopy attest that the prepared samples are highly and homogeneously intercalated to a level approaching stage-I intercalation compounds. The method and the synthesis route may serve as a starting point for the various forms of alkali-atom-intercalated carbon compounds (including carbon nanotubes and graphene), which can be exploited in energy storage and further chemical modifications