Development of an Interface for Using EGS4 Physics Processes in Geant4 K.Murakami (KEK) 27/Mar./ Conference for Computing in High Energy and Nuclear Physics

Outline I. Introduction II. System Analysis III. Implementation IV. Status and Summary

I. Introduction

Introduction By means of this interface, By means of this interface, EGS4 users can share Geant4 powerful resources, such as geometry description, tracking etc. EGS4 users can share Geant4 powerful resources, such as geometry description, tracking etc. A common environment for comparison tests between EGS4 and Geant4 especially in users ’ realistic application level. A common environment for comparison tests between EGS4 and Geant4 especially in users ’ realistic application level. Geant4 has rich flexibility and expansibility for adding physics processes, in addition to its powerful geometry description. Geant4 has rich flexibility and expansibility for adding physics processes, in addition to its powerful geometry description. It is not easy to describe complicated/realistic geometry for EGS4 users. It is not easy to describe complicated/realistic geometry for EGS4 users. Taking advantage of the capabilities of Geant4 as a framework, we developed an interface for using EGS4 as a module of physics process in Geant4. Taking advantage of the capabilities of Geant4 as a framework, we developed an interface for using EGS4 as a module of physics process in Geant4.

Co-Workers Persons involved Persons involved K.Murakami (KEK, K.Murakami (KEK, K.Amako (KEK) K.Amako (KEK) H.Hirayama (KEK) H.Hirayama (KEK) Y.Namito (KEK) Y.Namito (KEK) T.Sasaki (KEK) T.Sasaki (KEK) M.Asai (SLAC) M.Asai (SLAC) T.Koi (SLAC) T.Koi (SLAC)

II. System Analysis

Analysis of EGS4 System - in terms of difference from Geant4- We first carried out analysis of the EGS4 system in terms of difference from Geant4. We first carried out analysis of the EGS4 system in terms of difference from Geant4. Our policy is that we should care for NOT to change algorithms and prescriptions which are used in the EGS4 system. Our policy is that we should care for NOT to change algorithms and prescriptions which are used in the EGS4 system. Issue-1: A way of calculation of step size and process selection Issue-1: A way of calculation of step size and process selection In Geant4, each process has its own fate in terms of NIL (N of Interaction Length). Then, a process having minimum fate will occur. In Geant4, each process has its own fate in terms of NIL (N of Interaction Length). Then, a process having minimum fate will occur. In EGS4, the next step size is calculated based on the total cross section of a particle. Then, which process will occur is chosen at the rate of branching fraction of a process. In EGS4, the next step size is calculated based on the total cross section of a particle. Then, which process will occur is chosen at the rate of branching fraction of a process. In principle, these work in the same manner. Good!! In principle, these work in the same manner. Good!! We implement the EGS physics processes as single Geant4 processes for electron/photon respectively. We implement the EGS physics processes as single Geant4 processes for electron/photon respectively.

Analysis of EGS4 System (Cont ’ d) Issue-2: Scheme of describing material information Issue-2: Scheme of describing material information In Geant4, In Geant4, Material information has only properties of material itself (atomic number/mass, density, composition...) Material information has only properties of material itself (atomic number/mass, density, composition...) Cross section tables are calculated at initialization time. Cross section tables are calculated at initialization time. In EGS4, In EGS4, Users have to prepare a material (cross section) file by executing PEGS, which is an external program, preceding to execution of a EGS4 program. Users have to prepare a material (cross section) file by executing PEGS, which is an external program, preceding to execution of a EGS4 program. Additional information related to “ processes ” (cutoff, parameters/coefficients of formulas) are described as material. Additional information related to “ processes ” (cutoff, parameters/coefficients of formulas) are described as material. We manage material information in terms of both of Geant4 and EGS4. We manage material information in terms of both of Geant4 and EGS4. Users have to execute PEGS externally and our interface manages material information listed in a PEGS output file. Users have to execute PEGS externally and our interface manages material information listed in a PEGS output file. A mapping table between G4 materials and EGS4 materials is prepared. A mapping table between G4 materials and EGS4 materials is prepared. Issue-3: Cutoff scheme Issue-3: Cutoff scheme In Geant4, In Geant4, There is no cutoff energy. Particles basically will be transported until they have zero kinetic energy. There is no cutoff energy. Particles basically will be transported until they have zero kinetic energy. An idea of production cut is introduced to avoid infrared divergence. An idea of production cut is introduced to avoid infrared divergence. In EGS4, In EGS4, An idea of cutoff energy is applied. Particles below cutoff energy will be discarded. An idea of cutoff energy is applied. Particles below cutoff energy will be discarded. According to our policy, we don ’ t disturb the EGS4 treatments in order to obtain the same output as obtained by EGS4 itself. According to our policy, we don ’ t disturb the EGS4 treatments in order to obtain the same output as obtained by EGS4 itself. Each material has its own cutoff energy for electron/photon. Each material has its own cutoff energy for electron/photon.

Table of Components – Which package is used – Control Framework :EGS4Geant4 Control Framework :EGS4Geant4 Tracking :EGS4Geant4 Tracking :EGS4Geant4 Geometry : EGS4Geant4 Geometry : EGS4Geant4 Materials :EGS4Geant4 Materials :EGS4Geant4 Cross Section Table:EGS4Geant4 Cross Section Table:EGS4Geant4 (PEGS) (PEGS) Physics Process :EGS4Geant4 Physics Process :EGS4Geant4 Cutoff Scheme :EGS4Geant4 Cutoff Scheme :EGS4Geant4

III. Implementation

Functional Mapping Geant4 Class tracking manager stepping manager single process for electron single process for photon GPIL() (GetPhysicalInteractionLength) calculating the next interaction point DoIt() describing a reaction G4 geometry G4 transportation (as a process) reused as-is wrapped with FORTRAN-C++ interface EGS4 Flow  SHOWER  (tracking controller) ELECTOR  PHOTON (controller for stepping and process invocation) HOWFAR  (geometry and navigation, user code) each Physics Process  COMPT BREMS... EGS4 subroutines

How It Works In the EGS4 world, a single virtual volume with In the EGS4 world, a single virtual volume with no dimensions (transportation is a G4 job) no dimensions (transportation is a G4 job) empty medium (dynamically updated) empty medium (dynamically updated) is prepared. is prepared. At tracking time, At tracking time, 1. Medium information of the EGS4 volume is updated at every step though the material map from G4 to EGS4. 2. Kinematical information in the EGS4 stack is updated from G4 track 3. A EGS4 process is invoked. 4. The stack information of EGS4 is evacuated to a G4 particle-change. A virtual volume with no dimensions empty media g4mate g4-egs material map egsmate g4track egs stack g4change egs stack evacuation update

Material Description G4Material EGS Material PEGS Material Geant4 World EGS4 World There are three classes describing materials: There are three classes describing materials: PEGS Material: PEGS Material: It describes materials defined in a PEGS output. It describes materials defined in a PEGS output. EGS Material: EGS Material: It has a PEGSMaterial. It has a PEGSMaterial. In addition, it has information, such as In addition, it has information, such as user cutoffs, user density, user flags,... user cutoffs, user density, user flags,... G4 Material: G4 Material: A G4Material is related to a EGSMaterial by users at initialization time. A G4Material is related to a EGSMaterial by users at initialization time. A G4Material is translated to a EGSMaterial through the map at tracking time. A G4Material is translated to a EGSMaterial through the map at tracking time. G4-EGS Material Map

Process List Currently Covered Photon processes Photon processes Rayleigh scattering Rayleigh scattering pair production pair production photo-electric effect photo-electric effect w/ subsequent fluorescence w/ subsequent fluorescence Compton scattering Compton scattering Electron processes Electron processes multiple scattering multiple scattering momentum flip only. momentum flip only. lateral displacement is not included. lateral displacement is not included. PRESTA is not included. PRESTA is not included. continuous energy loss continuous energy loss Bremsstrahlung Bremsstrahlung M ø ller scattering (e-) M ø ller scattering (e-) BhaBha(e+) BhaBha(e+) positron annihilation (e+) positron annihilation (e+) (in-flight / at-rest) (in-flight / at-rest) As the first target, we started with interfacing with a plain EGS4 (distributed as a KEK version).

View from Users’ Side User Physics List: User Physics List: An alternative EM-physics list is provided as a modular “ Physics List ” for EM w/ EGS4 processes. An alternative EM-physics list is provided as a modular “ Physics List ” for EM w/ EGS4 processes. User Detector Construction (Geometry): User Detector Construction (Geometry): Users don ’ t have to modify any existing Geant4 geometry codes. Users don ’ t have to modify any existing Geant4 geometry codes. Users make assignment of a Geant4 material to a EGS4 material by hands. Users make assignment of a Geant4 material to a EGS4 material by hands. Cross Section Table: Cross Section Table: Users have to execute PEGS externally. Users have to execute PEGS externally. define PEGS materials in PEGS input files. define PEGS materials in PEGS input files. execute PEGS to generate a cross section file (so-called PEGS output). execute PEGS to generate a cross section file (so-called PEGS output). All operations can be performed via G4 command line interface interactively. All operations can be performed via G4 command line interface interactively. assigning G4Material to EGSMaterial assigning G4Material to EGSMaterial setting users parameters setting users parameters initialization,... initialization,...

IV. Status and Summary

5 electrons with E k =50 MeV into a slab geometry composed of several materials. (w/ cutoff E k =10 keV) 5 electrons with E k =50 MeV into a slab geometry composed of several materials. (w/ cutoff E k =10 keV) red: electron green: photon Sample Event Display

Benchmarks Development environment Development environment Linux (SuSE / RedHat /...) Linux (SuSE / RedHat /...) gcc/g77 ver. 3.2 (2.95.2/3) gcc/g77 ver. 3.2 (2.95.2/3) Geant4 ver.5.0 (patch01) Geant4 ver.5.0 (patch01) EGS4 (distributed as a KEK version) EGS4 (distributed as a KEK version) Robustness Robustness several-M events in a simple geometry were successfully generated without crush. several-M events in a simple geometry were successfully generated without crush. Detail benchmark tests were just started. Detail benchmark tests were just started.

Current Status and Plans First implementation was finished. First implementation was finished. Detail system check and benchmark tests are started as the next target. Detail system check and benchmark tests are started as the next target. We have plans of comparisons; We have plans of comparisons; between EGS4 itself and the EGS4-G4 interface. between EGS4 itself and the EGS4-G4 interface. between G4 and EGS4(w/ the interface) on common geometries. between G4 and EGS4(w/ the interface) on common geometries. Technical study for treating PRESTA is planned for more precise simulation. Technical study for treating PRESTA is planned for more precise simulation. The treatment of multiple scattering is closely coupled with geometry (boundary). The treatment of multiple scattering is closely coupled with geometry (boundary).

Summary We have successfully developed the first version of an interface between EGS4 and Geant4 based on OO-approach. We have successfully developed the first version of an interface between EGS4 and Geant4 based on OO-approach. This work is a proof of flexibility and expansibility of the Geant4 framework. This work is a proof of flexibility and expansibility of the Geant4 framework. By means of this interface, EGS4 users will be able to share Geant4 powerful resources, such as geometry description, tracking etc. By means of this interface, EGS4 users will be able to share Geant4 powerful resources, such as geometry description, tracking etc. Further detail benchmarks are on going. Further detail benchmarks are on going.