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- Mancusi, Davide, 1980, et al.
(author)
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PHITS - benchmark of partial charge-changing cross sections for intermediate-mass systems
- 2007
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In: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 254:1, s. 30-38
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Journal article (peer-reviewed)abstract
- The PHITS (Particle and Heavy Ion Transport System) code is a three-dimensional Monte Carlo code that is able to simulate the transport of nuclei and other particles in complicated geometries and calculate fluxes, doses, energy-deposition distributions and many other observables. Among its many possible fields of application, it can be used e.g. to design and optimise radiation shields for space vessels. However, the reliability of the predictions of the code depends directly on the certified accuracy of the code components, i.e. the models the code uses to estimate the quantities necessary for the transport calculation. As a part of a comprehensive benchmarking program, we have investigated the possibility of using PHITS to calculate partial charge-changing cross sections and we have compared the results with measurements performed by some of us (CZ, LH, JM, SG). The results, although limited, suggest that the current reaction-cross-section models might be inadequate for use in space radioprotection; we therefore claim the need for a thorough benchmarking of the models and for new reaction-cross-section measurements and experimental techniques.
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- Tafoya, D., et al.
(author)
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Detection of HCO+ emission toward the planetary nebula K3-35
- 2007
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In: Astronomical Journal. - 1538-3881 .- 0004-6256. ; 133:2, s. 364-369
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Journal article (peer-reviewed)abstract
- We report the detection, for the first time, of HCO+(J = 1 -> 0) emission, as well as marginal CO(J = 1 -> 0) emission, toward the planetary nebula (PN) K3-35 as a result of a molecular survey carried out toward this source. We also report new observations of the previously detected CO( J 2 ! 1) and water maser emission, as well as upper limits for the emission of the SiO, (HCO+)-C-13, HNC, HCN, HC3OH, HC5N, CS, HC3N, (CO)-C-13, CN, and NH3 molecules. From the ratio of CO(J = 2 -> 1) to CO(J = 1 -> 0) emission we have estimated the kinetic temperature of the molecular gas, obtaining a value of similar or equal to 20 K. Using this result we have estimated a molecular mass for the envelope of similar or equal to 0.017M(circle dot) and an HCO+ abundance relative to H-2 of 6 x 10(-7), similar to the abundances found in other PNe. K3-35 is remarkable because it is one of the two PNe reported to exhibit water maser emission, which is present in the central region, as well as at a distance of similar or equal to 5000 AU from the center. The presence of molecular emission provides some clues that could help in understanding the persistence of water molecules in the envelope of K3-35. The HCO+ emission could be arising in dense molecular clumps, which may provide the shielding mechanism that protects water molecules in this source.
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- Winnberg, A., et al.
(author)
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CO in OH/IR stars close to the Galactic centre
- 2009
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 497, s. 177-181
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Journal article (peer-reviewed)abstract
- Aims: A pilot project has been carried out to measure circumstellar CO emission from three OH/IR stars close to the Galactic centre. The intention was to find out whether it would be possible to conduct a large-scale survey for mass-loss rates using, for example, the Atacama large millimeter array (ALMA). Such a survey would increase our understanding of the evolution of the Galactic bulge. Methods: Two millimetre-wave instruments were used: the Nobeyama Millimeter Array at 115 GHz and the Submillimeter Array at 230 GHz. An interferometer is necessary as a “spatial filter” in this region of space because of the confusion with interstellar CO emission. Results: Towards two of the stars, CO emission was detected with positions and radial velocities coinciding within the statistical errors with the corresponding data of the associated OH sources. However, for one of the stars the line profile is not what one expects for an unresolved expanding circumstellar envelope. We believe that this CO envelope is partially resolved and that this star therefore is a foreground star not belonging to the bulge. Conclusions: The results of the observations have shown that it is possible to detect line profiles of circumstellar CO from late-type stars both within and in the direction of the Galactic bulge. ALMA will be able to detect CO emission in short integrations with sensitivity sufficient to estimate mass-loss rates from a large number of such stars.
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