FLUKA dose and fluence simulations for CBM

experimentI.Kadenko, O.Bezshyyko, V.Pluyko, V.Shevchenko

National Taras Shevchenko University of Kiev

Introduction – Geant4 or Fluka ?

• GEANT4 is very quickly progressing toolkit for development of simulation projects in various areas of nuclear physics and HEP, but so far there are appreciable quantity of significant inconsistencies between experimental data and GEANT4 predictions. Therefore additional experimental tests and checking with use of other well tested simulation codes are not superfluous. One of these codes is FLUKA. Important advantage of FLUKA is advanced functionality for dose and irradiation calculations. Also authors of FLUKA plan to open source codes for noncommercial applications in near future.

VMC Concept• LHC collaborations (ALICE, ATLAS and other) have

developed tools for integrated work with GEANT3, GEANT4 and FLUKA. This packages very promising for combined Monte Carlo simulation of the passage of particles through matter (for example Virtual Monte Carlo – VMC) with GEANT4 and FLUKA. Unfortunately for the present moment many partly solved questions, restrictions or incompatibility of old toolkits versions with new versions of GEANT4 and FLUKA make difficulties for comfortable work in the environment of FLUKA package with use of geometry, built in GEANT4.

• Furthermore close integration of the work of FLUKA and GEANT4 together with advantages has significant shortcoming, especially in conditions of restricted access to FLUKA code. Work in debug modes is complicated, and possibility to make errors rises. More suitable way now, in our opinion, for checks and tracing of bugs is extraction of GEANT4 information about detector set geometry and other data (materials, magnet fields etc.) and forming of input files for FLUKA. FLUKA works full independently from GEANT4 or other wrapper tools in standard mode (without special additional subroutine calls). Clear checks and tests on every transformation step are possible without large efforts.

Geometry converting from VMC

• We have chosen such approach to use FLUKA for dose calculations in CBM detector set and to compare output data of GEANT4 with FLUKA results. File in the “gdml” format was used to obtain geometry and material information from GEANT4 (more exactly - converting from VMC "geo" form) and to form automatically geometry "cards" of FLUKA input file. VMC package has feature to convert geometry information in xml and “gdml” format. Information in “gdml” file is represented in clear and suitable form for checks and modifications.

Real source with UrQMD• Auxiliary utility was written to print this information after data

processing to FLUKA input file. User routine in FLUKA format was used for reading of data from output file of UrQMD to form real source, also user routines for set of magnet field and calculation of dose "surfaces" were used. As a result we have full set of input files and user routines for FLUKA, which is easy to check and modify. It is easy also to take account any change of CBM simulation geometry in the FLUKA input files in the semi-automatic mode. Fig.1- Fig.4 show various parts and slices of the simulation geometry for CBM experiment (information in “gdml” format). Distribution of energy density in relative units on STS station STS 7 (energy density for largest ring on the Fig.4 is represented – USRBIN option of code FLUKA and output file 00-03fm.100ev.f14 of UrQMD was used) are shown in Fig.5-7 in different projections.

Implemented geometry

Results – the energy density in STS