MPE Compton Telescope observations of MeV radiation from the direction of the Galactic Center result in constraints on the central gamma-ray source in the Galaxy: The extent of 1.8 MeV line emission from 26Al suggests an 26Al production process with pronounced concentration towards the Galactic Center. The absence of other gamma-ray lines constrains nucleosynthesis and cosmic ray excitation parameters in the Galaxy. Calculations demonstrate that time variable Galactic Center annihilation radiation may be related to a central 26Al source.

We estimate the 1.8 MeV luminosity of the Sco-Cen association due to radioactive decay of 26A1 to (4 – 15) 10−5ph cm−2 s−1. We propose a low surface brightness, limb brightened bubble for the 1.8 MeV intensity distribution. The detectibility of this distribution with existing γ-ray telescopes is discussed.

The Compton Gamma-Ray Observatory (C-GRO) has completed a full-sky survey during which the number of known γ-ray pulsars has more than doubled. COMPTEL has observed the classical pulsars Crab and Vela on several occasions and has derived detailed pulse patterns and spectral parameters in the 0.7-30 MeV energy interval. The new C-GRO γ-ray pulsars have different properties in terms of energy spectra and light-curve shapes, and, in fact, only the Crab is seen by all four C-GRO instruments. This raises intriguing questions about the particle acceleration processes and beaming taking place in the neutron magnetosphere. We have examined the COMPTEL data to add information on these objects in the 0.7-30 MeV energy interval and present evidence for the detection of one of them, PSR B1509-58. We have also undertaken a search for candidate radio pulsars whose ephemerides are well defined. The results of these analyses are presented.

Subject headings: gamma rays: observations — pulsars: general

26Al radioactivity is believed to originate predominantly from massive stars, ejected into interstellar medium in wind phases and/or supernova events. With its million-year decay time, penetrating γ-rays from 26Al decay measure the massive-star history averaged over a time scale of ≃million years, thus extending times cales accessible otherwise. The COMPTEL 1.809 MeV all-sky data from 5 years of observations show irregularities and features at intermediate latitudes, which may have a more local origin (≃ 1 kpc). We find that the large scale emission can be characterized by a Galactic scale height of ≃ 130 pc, and a Galactocentric scale radius of ≃ 5 kpc, with features from spiral structure. Catalogues from massive-star related objects do not significantly improve the description of COMPTEL data above this. Emission associated with nearby structures such as the Gould Belt, Loop I, or stellar aggregates, is indicated, yet cannot be clearly detected. Combined with our imaging results, this suggests that 26A1 yields from massive star ensembles depend on specifics of those stars and their history. Further 26A1 γ-ray studies are underway to help mapping of the massive star history in the solar vicinity.

This article looks at the first five years of reconstruction in Nagasaki City after the atomic bombing of 9 August 1945, elucidating how the municipal vision of reconstruction shaped the city's post-war urban identity, especially in comparison to Hiroshima. From early on, city officials envisioned the future of Nagasaki as a restored ‘international cultural city’, not solely as a centre of atomic memory, while Hiroshima made the atomic experience the centre of its urban identity. This article seeks to revive Nagasaki as a subject of historical inquiry in order to balance scholarly, as well as popular, literature on the bombings, which has favoured Hiroshima for nearly seven decades. In short, the story of Nagasaki sheds a different light on bombing and aftermath, not only in comparison with Hiroshima but with other cities that have suffered mass destruction and the course of their subsequent reconstruction.

We summarize the results presented in Krause et al. (2012a, K12) on the impact of supernova-driven shells and dark-remnant accretion on gas expulsion in globular cluster infancy.

We have used thermal desorption spectroscopy to carry out a comparative study of potassium adsorption on Al(111) and on the fivefold Al-Pd-Mn surface. Potassium adsorption on the quasicrystal was found to be different than on Al(111). The potassium monolayer desorbed from fivefold Al-Pd-Mn at lower temperatures than from Al(111). Potassium is known to form a dense monolayer on Al(111), with an ideal coverage of 0.33, but for the monolayer on fivefold Al Pd Mn we find that the saturation coverage is only one twelfth.

The effect of variation of the preparation parameters filament temperature Tfil, gas pressure p and hydrogen dilution (H2/SiH4-flow ratio) on the absorption spectra of microcrystalline silicon deposited by the hot-wire technique (hw-μc-Si:H) has been studied by means of Photothermal Deflection Spectroscopy (PDS). We find an enhanced absorption of the μc-Si:H compared to crystalline silicon in the band gap (defect absorption) as well as in the interband transition region. An increase of absorption has already been reported for μc-Si:H films prepared by different techniques. In the case of hw-pc-Si:H we observe a relation between the absorption enhancement and the crystallite size. Increasing the gas pressure from 35 to 400 mTorr (Tfil=1850°C) or the filament temperature from 1750°C to 1950°C (p=100mTorr) the crystallite sizes, deduced from X-ray diffraction measuements, range from 10 to 60 nm. An alteration of the hydrogen dilution by varying the flow ratio between 2.5 and 25 does not affect the crystallite size and the optical absorption remains constant. In our opinion the enhancement cannot be described by a simple superposition of an amorphous and a crystalline absorption coefficient weighted by the volume fractions of the amorphous and crystalline phase, respectively. The possible reasons for the enhanced absorption will be discussed. The variation of the crystallite size with deposition conditions offers the possibility to control the optical absorption of μc-Si:H which is important for incorporating the material either as window layers or intrinsic layers in solar cells.

The phenomenon of enhanced optical absorption in hot wire microcrystalline silicon (hw-μ-Si:H) has been investigated with respect to the structural properties of the as deposited as well as annealed films. The influence of the structural properties on the absorption behavior is explained within the framework of a model. In this model the μc-Si:H is assumed to consist of crystalline grains surrounded by grain boundaries embedded into an amorphous matrix. Because of the relaxation of the k-selection rule the absorption is supposed to be higher for the disordered grain boundaries than for the crystalline grains. The absorption coefficient α is derived from the superposition of the absorption coefficients for the amorphous, crystalline and grain boundary regions weighted by their appropriate volume fractions. According to experimental results it is furthermore assumed that the absorption of the grain boundary regions correlates with the hydrogen content of the films. The model is proven and confirmed by crucial experiments especially concerning the influence of the hydrogen content on the absorption coefficient. Other possible reasons that might influence the enhanced optical absorption such as strain induced changes of α and light scattering effects are also discussed and explicitely excluded by appropriate experiments to be the essential enhancement reasons.

Deposition of a rare earth salt layer on a silicon substrate with subsequent spark processing yields a porous Si layer and SiO 2 cap doped with the rare earth ion. We have characterized luminescent Er-doped porous SiO2 on Si by scanning electron microscopy, energy dispersive Xray spectroscopy, as well as visible and near IR photoluminescence (PL) spectroscopies. Energydispersive x-ray maps indicate that the erbium concentration in the porous layer can be controlled by varying the molarity of the erbium solution deposited on the substrate prior to spark processing. Visible PL measurements reveal that the concentration of Er3+ is proportional to the resultant intensity of the visible fluorescence transitions; however, for the near IR fluorescence peak at 1.54 gim, self-quenching due to erbium clustering occurs at higher concentrations. Erbium-doped porous silicon layers can also be obtained by diffusion of an erbium salt into porous silicon formed by anodic etching of Si in hydrofluoric acid. Densification of the porous Si layers through high temperature oxidation after erbium diffusion forms erbium-doped SiO2 layers.

The five-fold surface of the Al70 Pd21 Mn9 quasicrystal has been studied using STM, LEED and AES. STM images from surfaces which have been sputtered and annealed to 875 K reveal 20-30 Å protrusions that have been identified by others as Mackay-type clusters. Higher-resolution images reveal substructures in these clusters having dimensions 2-3 Å. Longer annealing times at 875 K produced large areas having flat terraces which were imaged with atomic resolution. The LEED pattern from this surface has sharp spots on a low background, and AES indicates that the surface is deficient in Mn relative to the bulk. For surfaces annealed to 1050 K for less than 2 hours, STM images indicate that cluster and terrace phases coexist, and a third phase having aligned arrays of clusters is identified which appears to be intermediate between the cluster and terrace phases.

InN continues to be a topic of great interest, particularly with respect to the issues surrounding its bandgap energy. To further explore this material and its properties, we have grown 200–300 nm InN films by a plasma-assisted molecular beam epitaxy (PAMBE) technique on a variety of substrates, including (0001) sapphire, (100) InAs, and both (100) and (111) YSZ. Single-crystal films regardless of quality all show the commonly reported broad luminescence feature in the range of 0.7 to 0.8 eV, although we have also observed this feature in polycrystalline films. Growth on (100) InAs and (100) YSZ was motivated by a desire to explore cubic InN; in both cases growth appears to be initially cubic, but a mixture of hexagonal and cubic phases is detected in the final layer.

The end of the cold war has signaled a dramatic increase in the number and forms of United Nations (UN) intervention into ongoing conflicts. Yet, this larger UN role has not always translated into success. Short-term failures are evident, but the long-term effects of UN efforts are not readily apparent. We explore this longer-term impact by examining the incidence of recurring conflict between state dyads following a crisis. Overall, UN intervention has proved ineffective in inhibiting, delaying, or lessening the severity of future conflicts, independent of the level of violence in the precipitating crisis, the relative capabilities of the two states, the states' history of conflict, and the form of crisis outcome; nor were UN efforts successful in deterring future conflict. These sobering results suggest that changes in long-term strategy may be in order.

Nuclear reactions occur in cosmic environments in the cores of stars and in stellar explosions. Nuclear energy production is a key agent in these objects; the production of new isotopes drives the chemical evolution of gas throughout the universe and of the objects which form from this gas over cosmic times. Radioactive isotopes, ejected into interstellar space by cosmic nucleosynthesis events, are observed with new space telescopes. Gamma-ray lines from the radioactive ejecta of such cosmic nuclear reactors need to be sufficiently bright so they can be observed with current telescopes; this limits all gamma-ray astronomy studies to present and nearby nucleosynthesis processes, i.e. out to few Mpc in distance and back a few million years in time. The Compton Observatory had provided a first sky survey for the isotopes 56Co, 22Na, 44Ti, and 26Al, detecting supernova radioactivity and the diffuse glow of long-lived radioactivity from massive stars in the Galaxy. High-resolution spectroscopy is now being exploited with Ge detectors, which allows to measure Doppler broadenings and line shape details of these cosmic gamma-ray lines. Current results include an all-sky map and line shape measurement of positron annihilation emission, 26Al emission from the inner Galaxy and from the Cygnus region, a detection of 60Fe gamma-rays, and limits on 44Tiemission from Cas A and other candidate young supernova remnants; 22Na from novae still has not been seen. In this paper we discuss the experimental methods for such cosmic gamma-ray spectroscopy, and the corresponding astrophysical implications.

Polarimetry in gamma-rays has the capability to enhance our understanding of compact object emission in our galaxy. In particular this diagnostic method could provide useful insight into the geometrical arrangement of these emitting objects and the roles that magnetic fields play in their emisson mechanisms. Gamma Ray Bursts have been studied in this way but the results, perhaps indicating a high degree of polarisation, remain unverified [Coburn & Boggs (2003), Wigger et al. (2004), Willis et al. (2005)]. The nature of GRBs solve many instrumental problems in polarimetry, however their true nature is less well defined and so a study of a better understood object such as the Crab Pulsar, for now, may reveal more as to the physics of the system.

The ESA observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory) is dedicated to fine imaging and spectroscopy in the energy range 15 keV to 10 Mev with concurrent X-ray (3-35 keV) and optical monitoring. It was launched on October 17, 2002 and has been succesfully operating ever since. Its two main instruments the spectrometer SPI – optimized for high resolution spectroscopy – and the imager IBIS – optimized for for high resolution imaging – are complemented by the X-ray monitor JEM-X and the optical monitor OMC. All the high energy instruments use coded mask techniques, allowing imaging in the gamma-ray range and combining wide fields of view with high spatial resolution. The presentation gives an overview of the unique properties of INTEGRAL.