The Interstellar Environment of our Galaxy

We review the current knowledge and understanding of the interstellar medium of our galaxy. We first present each of the three basic constituents - ordinary matter, cosmic rays, and magnetic fields - of the interstellar medium, laying emphasis on their physical and chemical properties inferred from a broad range of observations. We then position the different interstellar constituents, both with respect to each other and with respect to stars, within the general galactic ecosystem.Comment: 39 pages, 12 figures (including 3 figures in 2 parts

Edge-on disk around the T Tauri star [MR81] Halpha 17 NE in CrA

Using the speckle camera SHARP at the 3.5m ESO NTT, K\"ohler and collaborators found an object ~3.5 mag fainter in K only 1.3" north-east of the T Tauri star [MR81] Ha 17 in the Corona Australis (CrA) star-forming region, which could be either a brown dwarf or a T Tauri star with an edge-on disk. We attempt to study this faint object in detail. We acquired deep VLT NACO near-infrared images at three epochs to determine, whether [MR81] Ha 17 and the nearby faint object are co-moving and to measure the infrared colors of both objects. We obtained optical and infrared spectra of both objects with the VLT using FORS and ISAAC, respectively, to determine spectral types and temperatures as well as ages and masses. The T Tauri star [MR81] Ha 17 and the faint nearby object have a projected separation of 1369.58 mas, i.e. 178 AU at 130 pc. They share the same proper motion (~5 sigma), so that they most certainly form a bound binary pair. The apparently fainter component [MR81] Ha 17 NE has a spectral type of M2e, while the apparently brighter component [MR81] Ha 17 SW, the previously known T Tauri star, has a spectral type of M4-5e. We can identify a nearly edge-on disk around [MR81] Ha 17 NE by visual inspection, which has a diameter of at least 30 to 50 AU. We are able to detect strong emission lines in [MR81] Ha 17 NE, which are almost certainly due to ongoing accretion. The NE object is detectable only by means of its scattered light. If both objects are coeval (2-3 Myr) and located at the same distance (~130 pc as CrA), then the apparently fainter [MR81] Ha 17 NE is more massive (primary) component with a nearly edge-on disk and the apparently brighter component [MR81] Ha 17 SW is less massive (com- panion). Both are low-mass T Tauri stars with masses of ~0.5 and 0.23 \pm 0.05 solar masses, respectively.Comment: A&A in pres

Reprocessing of nuclear fuels by fluoride volatilization with sulfur hexafluoride

A new procedure was developed for the reprocessing of nuclear fuels by fluoride volatilization, based on the fact that uranium or other uranium containing fuels can be fluorinated in a single step to uranium hexafluoride with sulfur hexafluoride at temperatures above 800° C. The essential reactions taking place can be represented by the following equations : U0 $_{2}$ + SF $_{6}$ - -> UF $_{6}$ + S0 $_{2}$ / UC $_{2}$ + SF $_{6}$ + 3O $_{2}$ - -> UF $_{6}$ + 2CO $_{2}$ + SO $_{2}$ / U + SF $_{6}$ + O $_{2}$ - -> UF $_{6}$ + SO $_{2}$ / Advantageous for the use of sulfur hexafluoride is its property to be noncorrosive up to temperatures of about 500° C. In order to perform the process, the fuels are first pulverized in a known manner and then fluorinated either with pure sulfur hexafluoride alone or together with oxidation agents like oxygen, air, manganese dioxide or others. The fluorination can be done in two steps. At first the starting material is fluorinated at temperatures between 700° C and 800° C, separating the non volatile uranyl fluoride from the easily volatile fission product fluorides. Afterwards, in the second step the U02 F is transformed to the easily volatile UF6 at about 900° C. For the reprocessing of coated particle containing fuels it has proved appropriate, either to crack and pulverize these particles prior to fluorination or to treat them at temperatures of about 900° C up to 1100° C with oxygen or a mixture of oxygen and sulfur hexafluoride, eventually in the presence of combustion catalysts. The fluorination can be achieved using either the fluidized bed or the conventional rotating oven technique. As contructing material for the ovens, besides others; especially pure alumina has stood the test. The advantages of the new procedure are not only its simplicity and economy, another important fact is the absolute untoxicity of sulfur hexafluoride. lt does not act corrosive on any part of the gas inlet system. Small amounts of fluorine contained in the off-gas stream may be reconverted into sulfur hexafluoride by reaction with sulfur. This adds another advantage of re-using the so formed sulfur rexafluoride. A required high factor of recontamination of the formed uranium hexafluoride may be achieved applying the known absorption-desorption technique on sodium fluoride columns