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16} Special source: cosmic rays


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Cosmic ray calculations can be done with FLUKA using the input commands GCR-SPE (for initialisation purposes) and SPECSOUR. In addition, several auxiliary stand-alone programs need to be used to prepare the geometry and material cards to be inserted into the input file. Command SPECSOUR does not define only cosmic ray sources, but also a number of other pre-defined complex sources that cannot be described by the simple keywords BEAM, BEAMPOSit, BEAMAXES and HI-PROPErt. To avoid confusion, SPECSOUR input related to cosmic rays is described separately in this Chapter, in 16.7}. A complete calculation to determine particle fluxes in the atmosphere requires: - the determination of the spectrum and composition of cosmic rays at the local interstellar medium, - the determination of changing conditions in the solar wind magnetic field and the resulting interaction with the inward flow of galactic cosmic rays from the local interstellar medium, - the determination of the trajectories of cosmic rays through the Earth's geomagnetic field, - the transport of the surviving incident cosmic rays through the Earth's atmosphere to various depths. The following options are available concerning the simulation of cosmic ray interactions in FLUKA: - Superposition model. In this approach primary nuclei are split into equivalent independent nucleons. See card PHYSICS with
SDUM
= IONSPLITti. - DPMJET interaction model [Ran95,Roe01]. This model simulates the nucleus-nucleus collision above 5 GeV/nucleon. In case DPMJET is chosen for cosmic ray application, it is suggested to avoid the otherwise recommended DPMJET-III choice and to use instead the DPMJET-II.5 version (linking with the script $FLUPRO/flutil/ldpm2qmd). The DMPJET and the superposition model can also be used together, by setting the respective energy ranges with the PHYSICS card. A number of tools and packages have been developed for the FLUKA environment to simulate the production of secondary particles by primary cosmic rays interacting with the Earth's atmosphere. These tools, in different stand-alone versions, have already been successfully used for fundamental physics research [Bat00,Bat03a]. ' The set of FLUKA tools for cosmic ray simulation includes a set of core routines to manage event generation, geomagnetic effects and particle scoring, and the following stand-alone data files and programs : - file atmomat.cards: it contains the material definitions for the density profile of the US Standard Atmosphere. These cards must be inserted (or the file included with the #include directive) into the FLUKA input file. -file atmogeo.cards: it contains an example of a 3D geometrical description of the Earth atmosphere, generated in according with the previous data cards (and corresponding density profile). This geometry includes the whole Earth - program atmloc_2011.f: it prepares the description of the local atmosphere geometry with the atmospheric shells initialised by option GCR-SPE. This geometry includes only a slice of the Earth geometry, centered around the geomagnetic latitude input by the user - <iz>phi<MV>.spc: GCR All-Particle-Spectra for the iz_th ion species (iz=1,...,28), modulated for the solar activity corresponding to a Phi parameter <Mv> MegVolt. Phi=500 MV roughly corresponds to solar minimum, while Phi=1400 MV roughly corresponds to solar maximum - allnucok.dat: GCR All-Nucleon Spectra - sep20jan2005.spc: spectra for the Solar Particle Event of Jan 20th, 2005 - sep28oct2003.spc: spectra for the Solar Particle Event of Oct 28th, 2008

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