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Notes: The photodissociation of F2 in crystalline Kr is subject to only a minor cage effect—quantum yield of 0.5 at 308 nm, at T=12 K. Two-photon-induced harpooning in the same system leads to dissociation with near unit quantum efficiency; it is shown that this absorption is coherent with a giant cross section of 3(±2)×10−45 cm4 s at 275 nm. Excitation and emission spectra of charge-transfer transitions in solid Kr doped with F atoms, and solid Ar multiply doped with F/Kr are reported. The vertical excitation in F/Kr leads to a state delocalized over immediate neighbors—assigned to Kr+6F−. This state localizes on a subpicosecond time scale to the triatomic Kr+2F− configuration. The latter relaxes radiatively (τr=140 ns), to the repulsive wall of the ground state (∼1 eV above ground). The excitation in F:Kr/Ar solids shows the diatomic KrF(B←X) resonances. From the analysis of the spectrum, a harmonic frequency ω=75(±3) cm−1 is extracted for F atoms in the ground state, consistent with molecular-dynamics simulations of an octahedrally trapped F atom [ω=70(±1) cm−1]. The diatomic KrF(B) state relaxes on a time scale of 20 fs〈t〈500 fs to the mixed triatomic configuration, (ArKr)+F−, which then relaxes radiatively (τr=60 ns). The kinetic energy released upon the radiative dissociation of triatomic exciplexes generates acoustic waves, and defects, and leads to mass transport. The modes of propagation of the acoustic waves, their subsequent thermalization, and self-annealing of the solid, are directly monitored by spatially and temporally resolved transient scattering experiments. A transient loss (σ(approximately-equal-to)10−17 cm2), the origin of which is not fully understood, is observed for Kr2F isolated in solid Kr. The mass transport, and long-range migration of F atoms (∼10 lattice sites), is directly monitored in multiply doped Ar solids in which the shuttle of F atoms between Xe and Kr centers can be demonstrated.

Notes: Vacuum scanning tunneling microscopy has been used to investigate the hydrogen-terminated Si(111) surfaces obtained upon dissolution of the native oxide in HF and NH4F solutions. Whereas etching in aqueous HF acid produces an atomically rough surface, comparable treatment in NH4F results in atomically flat surfaces. These atomically flat surfaces are extremely well ordered and exhibit terraces which extend thousands of angstroms.

Notes: In the past, the doorstopper method has been used successfully for determining in situ tectonic stresses. Here an example is given about the application of the borehole slotter in the domain of tectonic stress determinations, which is an innovative strain relief technique without overcoring. Data are presented that test the reliability of the strain measurements by the borehole slotter under well-known stress conditions, that indicate the reproducibility of borehole slotter strain data compared with those from doorstopper measurements, and that demonstrate the utility of the borehole slotter even for the determination of weak tectonic strains. In northern Switzerland the borehole slotter was used in a horizontal borehole under lithostatic loading conditions only, in a rock slope area with very heterogeneous stress conditions, and in a vertical borehole where tectonic stress should be dominant. The results show that the borehole slotter is a reliable technique, which allows precise determination of in situ strains. In addition, borehole slotter measurements are less time-consuming and therefore less costly than most other stress-measuring techniques—an important aspect in a future of reduced research budgets.〈section xml:id="abs1-2"〉〈title type="main"〉SummaryThe borehole slotter is a strain relief technique, using a recoverable strain sensor that need not be glued to the rock surface and need not be overcored. It is quicker to use than most other stress or strain measuring techniques, especially in comparison to standard overcoring techniques (Fig. 14).The borehole slotter supplied convincing results with respect to principal stress orientations, in good agreement with:(i) principal stress orientations related to lithostatic stress conditions (Dittingen 2 site),(ii) palaeostress orientations during the main stage of Jura folding only 13 to 7 Ma (Laufen 1 site),(iii) the results of neighboring door-stopper measurements (Dittingen 1 site).The borehole slotter tests do not supply stress magnitudes directly. Thus, the elastic properties of the rock mass have to be determined independently. Stress ratios from borehole dotter tests in Dittingen 2 are realistic.In conclusion, the borehole slotter is a fully developed probe to measure in situ strains in boreholes. It allows the reliable determination of a large number of data within a short time even in weakly stressed rocks. This makes the borehole slotter a powerful tool for the determination of contemporary regional tectonic stress fields.

Notes: Book Reviews

Notes: Zusammenfassung Es wird die Einwirkung von α-Strahlen auf normale Selenphotoelemente verfolgt mit der Absicht, mit diesen intensiven Energieträgern im wesentlichen diejenige Zone — Randschicht — zu erfassen, welche für die charakteristischen Eigenschaften dieser Leiter-Halbleitersysteme als verantwortlich betrachtet wird und deren strukturelle Ergründung fortgesetzte Aufgabe des Experiments ist. Es findet sich, daß die α-Strahlung selbst in der verwandten Stärke keine meßbare elektromotorische Wirkung besitzt, daß sie aber die Photowirkung in einer Weise herabsetzt, die einer zeitlich schnell fortschreitenden, nahe vollständigen und nicht rückgängigen Zerstörung der für die Photowirkung maß-gebenden Bedingungen gleichkommt. Die Ursache dieser Erscheinung liegt, soweit bisher geprüft, weder in Veränderungen der optischen Eigenschaften, noch in groben Modifikationsänderungen des Selens. Auch sind elektrische Veränderungen im Gesamtmaterial des Halbleiters offenbar von nicht wesentlichem Einfluß, da die Wirkung ausschließlich der α-Strahlung zukommt, während intensive γ-Bestrahlung vergleichsweise bedeutungslos bleibt.

Notes: Zusammenfassung Es wird ein auf kleinsten Gehalt noch weit unterhalb 0,01 mg Ra-Äquiv. anwendbares Verfahren zur raschen quantitativen Bestimmung von Ra, MTh und Ra Th in einem beliebigen Gemisch dieser Stoffe beschrieben und seine Leistungsfähigkeit und Zuverlässigkeit durch eine eingehende systematische Untersuchung nachgewiesen. Dasselbe besteht in einer kombinierten Anwendung von Emanations-undγ-Strahlmessungen an Lösungen unter Berücksichtigung der besonderen Verhältnisse, welche die Gegenwart von Thor-Emanation mit sich bringt.