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

Motivation From Geant4 side, From Geant4 side, In Geant4, various activities trying to implement additional physics processes based on different/more-detailed models are still going. In Geant4, various activities trying to implement additional physics processes based on different/more-detailed models are still going. Such variety of physics processes implemented is one of the most important functionalities as simulation system. Such variety of physics processes implemented is one of the most important functionalities as simulation system. From EGS4 side, From EGS4 side, There are many EGS4 users especially in medical and space field. There are many EGS4 users especially in medical and space field. But, EGS4 has some difficulties; But, EGS4 has some difficulties; Implementing users ’ geometry is hard work, which makes them difficult; Implementing users ’ geometry is hard work, which makes them difficult; to implement complex geometries. to implement complex geometries. to track particles in electromagnetic fields. to track particles in electromagnetic fields. It is written in MORTRAN/FORTRAN. It is written in MORTRAN/FORTRAN.

Our Goal Taking advantages of Geant4: Taking advantages of Geant4: The Geant4 framework has rich flexibility and expansibility. The Geant4 framework has rich flexibility and expansibility. physics processes, geometry, user interface,... physics processes, geometry, user interface,... Geant4 is designed to allow users to implement new processes in a generic/general way. Geant4 is designed to allow users to implement new processes in a generic/general way. We try to use EGS4 as a module of physics process in Geant4. We try to use EGS4 as a module of physics process in Geant4. We can provide an easy-to-use system of EGS4 under the Geant4 framework. We can provide an easy-to-use system of EGS4 under the Geant4 framework. 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 ’ application level. A common environment for comparison tests between EGS4 and Geant4 especially in users ’ application level.

Co-Workers Persons involved Persons involved K.Murakami (KEK, K.Murakami (KEK, K.Amako (KEK) K.Amako (KEK) T.Sasaki (KEK) T.Sasaki (KEK) M.Asai (SLAC) M.Asai (SLAC) T.Koi (SLAC) T.Koi (SLAC) and EGS4 developers (technical advice and benchmark) H.Hirayama (KEK) H.Hirayama (KEK) Y.Namito (KEK) Y.Namito (KEK)

II. System Analysis

Analysis of EGS4 System - in terms of difference from Geant4- We first carried out analysis of EGS4 system in terms of difference from Geant4. We first carried out analysis of 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: Determination of step size and process selection Issue-1: Determination 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. Then, which process will occur is chosen at the rate of branching fraction. In EGS4, the next step size is calculated based on the total cross section. Then, which process will occur is chosen at the rate of branching fraction. Good!! In principle, these are performed in the same manner. Good!! In principle, these are performed in the same manner.

Analysis of EGS4 System (Cont ’ d) Issue-2: The scheme of describing material information Issue-2: The scheme of describing material information In Geant4, material information can be given in users ’ code. In Geant4, material information can be given in users ’ code. In EGS4, users have to prepare a material file to be read in by executing PEGS, which is an external program, preceding to execution of a EGS4 program. In EGS4, users have to prepare a material file to be read in 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 in material. Additional information related to “ processes ” (cutoff, parameters/coefficients of formulas) are described in material. We gave up treating materials of EGS4 under the G4 system. We gave up treating materials of EGS4 under the G4 system. Users have to execute PEGS externally to prepare materials to be used in EGS4. Users have to execute PEGS externally to prepare materials to be used in EGS4. Our interface manages materials listed in the PEGS output file. Our interface manages materials listed in the PEGS output file. A material is described/instantiated in terms of both Geant4 and EGS4. A material is described/instantiated in terms of both Geant4 and EGS4. Issue-3: Cutoff scheme Issue-3: Cutoff scheme In Geant4, there is no cutoff energy. Particles basically will be transported until they have zero kinetic energy. In Geant4, there is no cutoff energy. Particles basically will be transported until they have zero kinetic energy. An idea of production cut is in stead introduced. An idea of production cut is in stead introduced. In EGS4, an idea of cutoff energy is applied. Particles below cutoff energy will be discarded. In EGS4, an idea of cutoff energy is applied. Particles below cutoff energy will be discarded. Each material has its own cutoff energy for electron/photon. Each material has its own cutoff energy for electron/photon. We should not change the EGS4 treatments in order to get the same output as obtained by EGS4 itself. (Our Policy) We should not change the EGS4 treatments in order to get the same output as obtained by EGS4 itself. (Our Policy) We don ’ t disturb the cutoff treatment carried out in EGS4. We don ’ t disturb the cutoff treatment carried out in EGS4.

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

Decomposition of EGS4 System Materials DATA (PEGS output file) PEGS input files HATCH Block DATA Stack SHOWER ELECTR PHOTON Physics Process Engine A set of subroutines HOWFAR transportation user input EGS4 subroutine replaced with G4 transportation Materials reuse as-is Tracking/Stepping replaced with G4 stepping and G4 processes PEGS external program data managed as EGS4 material

III. Implementation

Materials G4Material EGS Material PEGS Material Geant4 WorldEGS4 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 assigned to A EGSMaterial by users. A G4Material is assigned to A EGSMaterial by users. A G4Material is converted to a EGSMaterial through a map at tracking time. A G4Material is converted to a EGSMaterial through a map at tracking time. If no EGSMaterial is assigned, run-time exception occurs. If no EGSMaterial is assigned, run-time exception occurs.

How to work 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. 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

Process List 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 Note: As the first target, we started with interfacing with a plain EGS4 package. So, some extension components like PRESTA is not included yet. Electron processes Electron processes multiple scattering multiple scattering (momentum flip only) (momentum flip only) 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)

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 code. Users don ’ t have to modify any existing Geant4 geometry code. Users have to make assignment of a Geant4 material to a EGS4 material. Users have to make assignment of a Geant4 material to a EGS4 material. Cross Section Table: Cross Section Table: Users have to execute PEGS by themselves. Users have to execute PEGS by themselves. 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 8.1 / RedHat x.x /...) Linux (SuSE 8.1 / RedHat x.x /...) gcc/g77 ver. 3.2 (2.95.2/3) gcc/g77 ver. 3.2 (2.95.2/3) Geant4 ver (patch01) Geant4 ver (patch01) 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 plan comparisons We plan comparisons between EGS4 itself and EGS2G4. between EGS4 itself and EGS2G4. between EGS4 and EGS2G4 on a common environment. between EGS4 and EGS2G4 on a common environment. Information/documentation is being prepared on WWW. Information/documentation is being prepared on WWW. Technical studies for including extensive components like PRESTA are planned for fairer comparisons. Technical studies for including extensive components like PRESTA are planned for fairer comparisons.

Summary We have successfully developed the first version of an interface between Geant4 and EGS4 based on OO- approach. We have successfully developed the first version of an interface between Geant4 and EGS4 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. We also plan to include some extension components so that as much functionalities as possible can be available. We also plan to include some extension components so that as much functionalities as possible can be available.