Appendix B EGS5 USER MANUAL
Contents
1. IBLOCK DATA SHOWER gt ELECTR BLOCK SET tsz orc il Defaults gt gt fareste NIZ gt MSCAT PEGS5 Create ji pe Media gt ANNIH Data sase i iii ni alai gt BHABHA cica gt MOLLER AZ hsec po gt BREMS HATCH hats l Access VA PEGS5 farta Data a gt UPH formation xtracted om Shower COMPT lt PHOTO lt gt PHOTON gt Figure B 1 EGS5 user code control and data flow diagram Table B 2 Variable descriptions for COMMON block BREMPR include file egs5_brempr f of the EGS5 distribution Flag for turning on 1 sampling of bremsstrahlung polar angle from default 0 implies angle given by m E Flag for specifying order of sampling of polar angles of pair electrons default 0 implies angles given by m E IBRSPL Flag for turning on 1 splitting of bremsstrahlung photons default 0 implies no splitting NBRSPL Number of bremsstrahlung photons for splitting when IBRSPL 1 B 4 Sequence of Actions Required of User Code MAIN The exact sequertce of procedures he specification and control of an EGS5 sin eps are provided in subseque Pre PEGS5 initializations PEGS5 call2. MAIN may now call PEGS5 to create material data files for the problem Specifications for the PEGS input is found in the PEGS User Manual Appendix C of SLAC R 730 KEK 2005 8 Note that the call to PEGS5 may be skipped if the working user code directory contains an existing PEGS data file generated with parameters compatible with the current EGS5 simulation specifications Checks for compatibility are performed in HATCH B 4 3 Pre HATCH Initializations Step 3 Users are strictly required to define the following variables prior to HATCH being called NREG the number of regions in the geometry MED an array containing the material numbers as set prior to the call to PEGS5 of each region and EMAXE the maximum total energy of any electron in the problem No other variables used by HATCH and then by the EGS5 system in simulating showers need be explicitly specified However if the user wishes to use any of the non default options or 14 features of EGS5 the appropriate flags for invoking such requests must be specified prior to the call to HATCH even if the data needed to execute such options has been generated by PEGS All of the variables processed by HATCH in setting up an EGS5 simulation are described below Variables required by HATCH EMAXE This variable the maximum energy of an electron in the problem is located in COMMON USERSC found in include egs5_usersc f and is used by HATCH to perform checks on the compati bili
3. Pre HATCH initializations Specification of incident particle parameters HATCH call Initializations for HOWFAR Initializations for AUSGAB SHOWER call Output of results Step Step Step Step Step Step Step Step Step O ON ODO KPWN Ee been prepared and properly links B 4 1 Pre PEGS5 Initializations Step 1 Prior to calling PEGS5 users must define certain variables and may at their discretion override some of the EGS5 parameter defaults As noted earlier all EGS5 variables are readily accessed through COMMON blocks which are imported into user code through include statements as in include include egs5_h f Main EGS header file include include egs5_bounds f bounds contains ecut and pcut include include egs5_edge f edge contains iedgfl Table B 3 Variable descriptions for COMMON block COUNTERS include file counters f of the EGS5 distribution All variables in COMMON block COUNTERS are initialized to 0 by a call to subroutine COUNTERS_OUT 0O with argument of 0 TANNIH umber of times calling subprogram ANNIH IAPHI umber of times calling subprogram APHI IBHABHA Number of times calling subprogram BHABHA a ee N imos calli N imes calli N i i N i i N i i N i i N i i N i i N ILAUGER Number of times calling subprogram LAUGER ITMXS Number of times requested multiple scattering step was truncated in ELECTR because pathlength was too long NOSCAT
4. header file include include egs5_epcont f COMMONs required by EGS5 code include include egs5_stack f include auxcommons lines f common totals esum 3 real 8 esum integer iarg Arguments 39 Add deposition energy if nlines 1t nwrite then write 6 1240 e np z np w np iq mp ir p iarg 1240 FORMAT 3G15 7 315 nlines nlines 1 end if return end Version 050701 1615 Reference SLAC R 730 KEK 2005 8 Appendix 2 subroutine howfar implicit none include include egs5_h f Main EGS header file include include egs5_epcont f COMMONs required by EGS5 code include include egs5_stack f common passit zthick real 8 zthick real 8 deltaz Local variables integer irnxt if ir mp ne 2 then idisc 1 return end if dnear np dmini z np zthick z np 40 Check forward plane first since shower heading that way most of the time if w mp gt 0 0 then deltaz zthick z np w np irnxt 3 else deltaz z np w np irnxt 1 end if if deltaz le ustep then ustep deltaz irnew irnxt end if return end 41
5. incohr i 0 S Z rejection iprofr i 0 Doppler broadening impacr i 0 Electron impact ionization end do estepe 0 10 estepe2 0 20 write 6 110 estepe estepe2 110 FORMAT 1X ESTEPE at EKMAX F10 5 estepe 1X ESTEPE at ECUT F10 5 estepe2 Random number seeds Must be defined before call hatch ins 1 2731 inseed 1 luxlev 1 ncases 1000 idinc 1 ei 1000 D0 ekin eitiqi RM 36 Step 5 hatch call Total energy of incident source particle must be defined before hatch Define posible maximum total energy of electron before hatch if igi ne 0 then emaxe ei charged particle else emaxe ei RM photon end if open UNIT KMPI FILE pgs5job pegs5dat STATUS old open UNIT KMPO FILE egs5job dummy STATUS unknown write 6 130 130 FORMAT HATCH call comes next close UNIT KMPI close UNIT KMPO write 6 140 140 FORMAT Quantities associated with each MEDIA do j 1 nmed write 6 150 media i j i 1 24 150 FORMAT 1X 24A1 write 6 160 rhom j rlcm j 160 FORMAT 5X rho G15 7 g cu cm rlc G15 7 cm write 6 170 ae j ue j 170 FORMAT 5X ae G15 7 MeV ue G15 7 MeV write 6 180 ap j up j 180 FORMAT 5X ap G15 7 MeV up G15 7 MeV end do zthick 3 0 37 plate is 3 cm thick do i 1l nreg esum i 0 D0O end do nlines 0
6. nwrite 15 tt etime tarray t0 tarray 1 write 6 190 190 format Shower Results 7X e 14X z 14X w 10X 1 iq 3X ir 2X iarg do i 1 ncases if nlines 1t nwrite then write 6 200 i ei zi wi igi iri idinc 200 format i2 3G15 7 315 nlines gt nlines 1 end if call shover igi ei xi yi zi ui vi wi iri wti end do tt etime tarray ti tarray 1 timecpu t1 t0 write 6 210 timecpu 210 format Elapsed Time sec 1PE12 5 totke ncases ekin write 6 220 ei zthick ncases 220 format Incident total energy of electron F12 1 MeV Iron slab thickness F6 3 cm Number of cases in run I7 Energy deposition summary etot 0 D0 38 do i 1 nreg etot etot esum i esum i esum i totke write 6 230 i esum i 230 format Fraction in region 13 F10 7 end do etot etot totke write 6 240 etot 240 FORMAT Total energy fraction in run G15 7 Which should be close to unity Version 050701 1615 Reference SLAC R 730 KEK 2005 8 Appendix 2 Required subroutine for use with the EGS5 Code System E e pa SSS oS as i a a ee ee ee ee eee A simple AUSGAB to 1 Score energy deposition 2 Print out stack information 3 Print out particle transport information if switch is turned on subroutine ausgab iarg implicit none include include egs5_h f Main EGS
7. Number of times multiple scattering was aborted in MSCAT because the pathlength was too small Note change in that NOSCAT has been moved here from EGS4 COMMON block MISC IBLOCK Number of times calling subprogram BLOCK_SET Table B 4 Variable descriptions for COMMON block EDGE2 include file egs5_edge f of the EGS5 distribution eal Table B 5 Variable descriptions for COMMON block EIICOM include file egs5_eiicom f of the EGS5 distribution IEISPL Flag for turning on 1 splitting of x rays generated by electron impact ionization default 0 implies no splitting NEISPL Number of electron impact ionization x rays for splitting when IEISPL 1 Table B 6 Variable descriptions for COMMON block EPCONT include file egs5_epcont f of the EGS5 distribution EDEP Energy deposited in MeV USTEP Actual total Multiple scattering step to be transported Note that because of the use of the random hinge transport mechanics in EGS5 the EGS4 variables TUSTEP wa and VSTEP are redundant and so have been removed as has the variable TSCAT RHOF Value of density scaling correction default 1 EOLD Charged particle total energy at beginning of step in MeV BETAZ User discard request flag to be set in HOWFAR IDISC gt 0 means user requests imme diate discard IDISC lt 0 means user requests discard after completion of transport and IDISC 0 default means no user discard requested IROLD Ind
8. deltaz irnew irnxt end if return end Note that a number of auxiliary geometry subprograms are distributed with the EGS5 Code System in order to make it easier to write HOWFAR For example subroutine PLAN2P could have been 29 sponding PEGS cutoff AE or AP respectively Particle is going to be Particle is going to be discarded because the user requested it in HOWFAR usually This situation occurs in one of the following 3 cases 1 A photoelectric interaction has occurred and the difference in the electron binding energy and the secondary particle X ray or Auger electron energy is deposited Compton interaction has occurred and the electron binding energy is deposited locally This is enabled only when the Doppler broadening option is turned on The K shell EII has occurred and the difference between the electron binding energy and the secondary particle K X ray energy is deposited This is enabled only when the EII option is turned on used in place of several lines above and the program would have been easier to read Example user codes which employ several of the auxiliary geometry subprograms are described in Chapter 4 of SLAC R 730 KEK 2005 8 B 6 Specifications for AUSGAB call ausgab iarg The argument TARG indicates the situation under which AUSGAB is being called IARG can take on 31 values starting from zero i e IARG 0 through IARG 30 although only the first five are called in the defau
9. in BLOCK_SET and assigned the default density of the medium by HATCH unless specified by the user prior to HATCH being called Flags and variables which may be set either before or after HATCH is called The following variables can be set either before or after the call to HATCH TMXSET When TMXSET is true any multiple scattering step whether selected by the user or determined by EGS5 using CHARD which violate the Bethe criteria for the maximum allowed step length see chapter 2 of SLAC R 730 KEK 2005 8 will be truncated in ELECTR to the maximum If the user wishes to over ride this limit TMXSET which is material dependent and part of COMMON MS and defaults to true can be set to false at any point in an EGS5 user code ESTEPR Electron energy hinge steps are scaled on a region dependent basis when users set non zero values of ESTEPR MXREG prior to a call to SHOWER Since energy hinge step sizes are determined in PEGS ESTEPR provides the user the capability to take smaller or larger steps in certain materials or regions for increased accuracy or efficiency respectively ESTEPR which is part of EGS5 COMMON USERSC is initialized to 0 0 in BLOCK_SET and ignored in ELECTR unless set by the user ESAVE The variable ESAVE dimensioned ESAVE MXREG and part of COMMON USERSC can be em ployed by users to speed computations for applications which involve the transport of electrons across boundaries between scoring and non scoring regions F
10. made in ELECTR Returned to ELECTR after a call to BHABHA was made 12 13 An in flight annihilation of the positron is to occur and a call to ANNIH is about to be made in ELECTR Returned to ELECTR after a call to ANNIH was made A positron has annihilated at rest 15 16 A pair production interaction is to occur and a call to PAIR is about to be made in PHOTON Returned to PHOTON after a call to PAIR was made A Compton interaction is to occur and a call to COMPT is about to be made in PHOTON Returned to PHOTON after a call to COMPT was made 19 20 A photoelectric interaction is to occur and a call to PHOTO is about to be made in PHOTON Returned to PHOTON after a call to PHOTO was made assuming NP is non zero Subroutine UPHI was just entered Subroutine UPHI was just exited A coherent Rayleigh interaction is about to occur A coherent Rayleigh interaction has just occurred Returned to MOLLER after a call to EII was made 32 B 7 UCSAMPL5 An Example of a Complete EGS5 User Code The following user code called UCSAMPL5 simulates electro magnetic cascade showers initiated by 1 GeV electrons that are incident normally on a 3 cm semi infinite slab of iron The upstream region of the slab is vacuum and the downstream region is air at NTP A particle is discarded whenever it leaves the slab on either side or whenever its total energy falls below a preset cutoff energy of 100 MeV Note that
11. on 1 sampling of angular distributions of photoelectrons in various regions default 0 implying isotropic emission include include egs5_epcont f epcont contains iausfl include include egs5_media f media contains the array media include include egs5_misc f misc contains med include include egs5_thresh f include include egs5_uphiot f include include egs5_useful f include include egs5_usersc f include include randomm f thresh contains ae and ap uphiot contains PI useful contains RM usersc contains emaxe Note that most of the variables accessed in a typical user code MAIN program can be found in the COMMON files referenced by the include statements in the above example Other variables which a user code might wish to access and the EGS5 include files which contain them were given in Tables B 1 through B 17 of the previous section Note that all EGS5 variables are explicitly declared all EGS5 subroutines and functions begin with the statement IMPLICT NONE and that all floating point variables except some of those used in the random number generator and in sample user codes which call intrinsic functions to compute CPU time are declared as REAL 8 Optional parameter modifications The EGS5 file include egs5_h f is different from the other files in the include directory in that it contains not COMMON blocks but rather declarations and specifications of the FORTRAN parameters
12. surface of current region Statistical weight of current particle default 1 0 Used in conjunction with variance reduction techniques as determined by user K1iRSD Scattering strength remaining after the current multiple scattering hinge to the nd of tne ur enmont pie nenea a a S O K1INIT Scattering strength from the end of the previous multiple scattering step to the EME Grent mite seg ie o o Na Stap e DENSTEP Energy loss remaining before the next energy loss hinge DERESID Energy loss remaining after the current energy loss hinge to the end of the full current energy loss step DEINITIAL Energy loss from the end of the previous energy loss step to the current energy loss hinge Latching variable LATCHI Initialization for latch i e the particle currently being pointed to Also the number of particles on the stack 10 Table B 12 Variable descriptions for COMMON block THRESH include file egs5_thresh f of the EGS5 distribution AE Array containing PEGS lower photon cutoff energy Tor each medium m MeV 0P Array containing PEGS upper photon cutoff energy for each medium in MeV i Array containing PEGS lower charged particle cutoff energy for each medium in MeV hall Array containing PEGS upper charged particle cutoff energy for each medium in MeV TE Same as AE except kinetic energy rather than total energy sd as AE Same as AE except kinetic energy rather than total energy sd kinetic energy
13. used by the other EGS5 include files to define array dimensions This is done so that users may trivially update the dimensions of all arrays throughout the EGS5 code system simply by changing the values of the appropriate variables in the PARAMETER statements of include egs5_h f The principal parameters defined in include egs5_h f which users may wish to adjust are MXMED the maximum number of media for the problem MXREG the maximum number of regions and MXSTACK the maximum stack size Most of the other parameters defined in include egs5_h f should be altered only under exceptional circumstances Some examples of parameter modifications are given in the comments in include egs5_h f as seen below 12 Maximum number of different media excluding vacuum integer MXMED parameter MXMED 4 parameter MXMED 10 Maximum number of regions allocated integer MXREG parameter MXREG 2000 parameter MXREG 2097153 Required initializations Two sets of initializations must be performed in the user s MAIN program First MAIN must call the EGS5 subroutine BLOCK_SET to initialize common block variables not defined in BLOCK DATA This is done simply by including the statement call block_set Initialize some general variables Also if the user is interested in tracking the number of calls to the various subroutines of EGS5 the counters in common block COUNTERS may also be initialized at this point by calling subroutine COUN
14. user calls RLUXINIT and supplies values of MKOUNT and KOUNT in addition to LUXLEV and INSEED the RANLUX will be restarted at exactly that point in the sequence defined by MKOUNT and KOUNT Alternatively the user may execute the following statement call rluxout at any time at which point integer representations of the current values of the seeds in RANLUX will be returned via the array ISDEXT of COMMON RLUXDAT A call to RLUXINIT at any time when the values of ISDEXT are non zero will result in a restart of RANLUX based on the seeds in ISDEXT Thus the restart options can be summarized as follows 1 A brute force method involves calling RLUXINIT with the values of the luxury level initial seed and number of delivered randoms up to the time of the desired restart The values of MKOUNT and KOUNT can be obtained at any time directly from COMMON RLUXDAT 2 A more elegant restart using the actual seeds can be done by passing the integer seeds at the time of the restart to RLUXINIT via ISDEXT in COMMON RLUXDAT The seeds in ISDEXT can be obtained for later restart at any convenient time such as the end of a shower or the end of a batch by a call to RLUXOUT B 4 4 Specification of Incident Particle Parameters Step 4 This step required in constructing a MAIN user code is self explanatory An example of suitable coding is given as follows igqi 1 Incident particle is an electron xi 0 IParticle coordinates yi 0 zi 0 ui 0 IDi
15. 1 whether given media uses Goudsmit Saunderson multiple scattering distribution Set by user code MAIN prior to HATCH call de fault 0 Note that in the current implementation it is a requirement that if one elects to use this option in one media one must use it in all media Table B 8 Variable descriptions for COMMON block MISC include file egs5_misc f of the EGS5 distribution NREG set by user code MAIN prior to HATCH call set by user code MAIN prior to HATCH call DUNIT The distance unit to be used DUNIT 1 default establishes all distances in cm e whereas DUNIT 2 54 establishes all distances in inches FORTRAN unit number default 12 from which to read material data KMPO FORTRAN unit number default 8 on which to echo material data e g printed output dummy output etc Array containing the density for each region g cm If this is different than the default density of the material in that region the cross sections and stopping powers with the exception of the density effect are scaled appropriately Array of flags forcing multiple scattering to be bypassed on 1 in subroutine MSCAT for various regions default 0 off in various regions default 0 in various regions default 0 in various regions default 0 in various regions default 0 K1HSCL of parameters for scaling region scattering strength at highest problem energy i set in user code MAIN prior to HATCH c
16. 23456789 123456789 123456789 12 include include egs5_h f Main EGS header file include include egs5_bounds f include include egs5_edge f include include egs5_media f include include egs5_misc f include include egs5_thresh f include include egs5_useful f include include egs5_usersc f include include egs5_userxt f include include randomm f include auxcommons lines f common passit zthick real 8 zthick common totals esum 3 real 8 esum real 8 ei ekin etot totke xi yi zi Arguments ui vi wi wti real tarray 2 real t0 t1 timecpu tt Local variables real etime integer i idinc igi iri j ncases character 24 medarr 2 open UNIT 6 FILE egs5job out STATUS unknown 34 nmed 2 medarr 1 FE RAYLEIGH 2 medarr 2 AIR AT NTP d do j 1 nmed do i 1 24 media i j medarr j i i end do end do chard 1 chard 2 write 6 100 FORMAT PEGS5 call comes next Step 3 Pre hatch call initialization med 1 0 med 2 1 med 3 2 Set of option flag for region 2 3 1 on O off 35 nreg 3 do i 2 nreg ecut i 100 0 egs cut off energy for electrons pcut i 100 0 egs cut off energy for photons iphter i 0 Switches for PE angle sampling iedgfl i 0 K amp L edge fluorescence iauger i 0 K amp L Auger iraylr i 0 Rayleigh scattering lpolar i 0 Linearly polarized photon scattering
17. Appendix B EGS5 USER MANUAL Hideo Hirayama and Yoshihito Namito Radiation Science Center Advanced Research Laboratory High Energy Accelerator Research Organization KEK 1 1 Oho Tsukuba shi Ibaraki ken 305 0801 JAPAN Alex F Bielajew and Scott J Wilderman Department of Nuclear Engineering and Radiological Sciences The University of Michigan 2355 Bonisteel Boulevard Ann Arbor MI 48109 USA Walter R Nelson Department Associate in the Radiation Physics Group retired Radiation Protection Department Stanford Linear Accelerator Center 2575 Sand Hill Road Menlo Park CA 94025 USA This EGS5 User Manual is Appendix B of a document called SLAC R 730 KEK 2005 8 which can be obtained from the SLAC and KEK web sites B 1 Introduction Version 5 of the EGS code system is written exclusively in FORTRAN marking a departure from the use of the MORTRAN programming language first introduced with Version 2 To retain some of the functionality and flexibility that MORTRAN provided EGS5 employs some common extensions of FORTRAN 77 most notably include statements which are used to import identical versions of all the EGS5 COMMON blocks into all appropriate subroutines Users can thus alter the values of parameters set in the COMMON block files which are included in the various source codes thus emulating the use of MORTRAN macros in specifying array dimensions Each of the COMMON block files contains the declarations for just one
18. COMMON block with all files containing EGS related COMMON blocks located in a directory named include and all PEGS related files in a directory called pegscommons Additionally many of the features and options in EGS4 which were invoked through MORTRAN macro substitutions have been retained in the base shower code in EGS5 and can be turned on by user specification of the appropriate flags and parameters B 2 General Description of Implementation As described in Chapter 2 of SLAC R 730 KEK 2005 8 The EGS5 Code System to use EGS the user must write a user code consisting of a MAIN program and subroutines HOWFAR and AUSGAB The user defines and controls an EGS5 shower simulation by initializing tallying and in some cases altering variables found in COMMON blocks shared by user code MAIN and a set of four EGS5 subroutines which MAIN must call BLOCK_SET PEGS5 HATCH and SHOWER The user can access and manipulate variables located in many additional COMMON blocks which are shared by EGS5 subroutines which call the user subroutines HOWFAR and AUSGAB at points in the simulation specified by the user The user s MAIN program first calls the EGS5 BLOCK_SET subroutine to set default values for variables in EGS5 COMMON blocks which are too large to be defined in BLOCK DATA MAIN also initializes variables needed by HOWFAR and defines the values of EGS5 COMMON block variables corresponding to such things as names of the media to be
19. EGS including any part of the user code requires a floating point random number taken uniformly from the interval 0 1 to be returned to a variable all EGS5 routines use the variable name RNNOW the following statement is required call randomset rnnow EGS5 employs the random number generator RANLUX implemented by James Depending on the input specification called the luxury level RANLUX provides random sequences which pass different levels of tests for randomness and execute at different speeds Independent random se quences for the same luxury level can be generated with RANLUX by simply specifying a different input seed any integer in the range from 1 to 23t The default luxury level as defined in the vari able LUXLEV of COMMON RLUXDAT in file include randomm f is 1 and the default seed INSEED is 314159265 RANLUX is initialized by HATCH using the defaults for LUXLEV and INSEED unless the user specifies different values prior to the HATCH call In addition users may initialize the generator themselves at any time by invoking call rluxinit after specifying LUXLEV and INSEED The user may also restart RANLUX at any desired point in a previously used sequence of random numbers using either of two ways RANLUX keeps a tally of the number of random numbers delivered 20 through the variables MKOUNT and KOUNT as MKOUNT 100000000 KOUNT and MKOUNT and KOUNT are accessible at all times through COMMON RLUXDAT If the
20. TERS_OUT with argument 0 as in Second because of the way PEGS and EGS are linked in EGS5 the specification of the names of the problem media prior to calling PEGS5 is now a requirement of EGS5 user codes pe An example of a typical method for filling the MEDIA array using lead steel and air at NTP as the media is shown below character 24 medarr 3 medarr 1 PB medarr 2 STEEL 13 medarr 3 AIR AT NTP nmed 3 Number of media used do j 1 nmed do i 1 24 media i j medarr i j end do end do One final variable which is optional but recommended must be set prior to PEGS5 being called if it is to be used As described in chapter 2 of SLAC R 730 KEK 2005 8 The method requires the input specification of a material dependent parameter CHARD dimensioned CHARD MXMED and related to the size in cm of the smallest scoring region for a given material Values in cm of CHARD which is part of COMMON MEDIA can be passed to PEGS5 simply by assigning values as in chard 1 optional but recommended to invoke chard 2 automatic step size control chard 3 If CHARD is not specified or is set to 0 the default for a given material PEGS5 will use a method for determining scattering strengths and hence step sizes for electron multiple scattering based on fractional energy losses also described in chapter 2 of the EGS5 Code System report B 4 2 PEGS5 Call Step 2
21. This can be illustrated by considering the four region example from above The statements do i 1 3 ecut i 10 0 15 pcut i 100 0 end do when put in Step 3 of the user code result in charged particle histories being terminated at 10 0 MeV total energy and photon histories being terminated at 100 0 MeV in the first three regions only In the fourth region the respective cutoffs will be determined by the values of AE and AP as established by PEGS ECUT and PCUT are elements of COMMON BOUNDS TRAYLR The elements of this array dimensioned IRAYLR MXREG and contained in COMMON MISC are set to 1 prior to calling HATCH when coherent Rayleigh scattering is to be modeled in particular regions Execution of EGS is terminated if Rayleigh scattering data is not included in the PEGS data file however INCOHR The elements of this array dimensioned INCOHR MXREG and found in COMMON MISC are set to 1 prior to calling HATCH when incoherent scattering functions are to be used in sampling Compton scattering angles in particular regions Execution of EGS5 is terminated if the appropriate incoherent scattering function data is not found in the PEGS data file being used however Note that when INCOHR 1 1 it is necessary to have used IBOUND 1 for the corresponding materials when PEGS was run IPROFR The elements of this array dimensioned IPROFR MXREG and accessed via COMMON MISC are set to 1 prior to ca
22. all K1LSCL Array of parameters for scaling region scattering strength at lowest problem energy set in user code MAIN prior to HATCH call default 0 Table B 9 Variable descriptions for COMMON block MS include file egs5_ms f of the EGS5 distri bution TMXSET Flag to force truncation of requested multiple scattering steps which violate Bethe criteria default true enforce limit Table B 10 Variable descriptions for COMMON block RLUXDAT include file randomm f of the EGS5 distribution LUXLEV Luxury level of random number generator RANLUX called RANDOMSET in EGS5 de TEYE fault 1 INSEED Initial seed used with RANLUX random number generator default 314159265 Number of random numbers delivered plus number skipped at any point in simula tion up to 10 MKOUNT Number of sets of 10 random numbers delivered at any point in simulation ISDEXT Array of integer representations of the current RANLUX seeds at any point in simu lation Table B 11 Variable descriptions for COMMON block STACK include file egs5_stack f of the EGS5 distribution This COMMON contains information about particles currently in the shower All vari ables are arrays except for NP LATCHI DEINITIAL DERESID and DENSTEP X Y Z Position of particle in units established by DUNIT Cd UF VF WF Electric field vectors of polarized photon DNEAR A lower bound on the distance from the coordinates X Y Z to nearest
23. arameter IPRDST determines the method used for determining the angles of electron and positron pairs resulting from photon pair production in the same way that IBRDST is used to select the sampling method for bremsstrahlung photon angles IPRDST which is part of COMMON BREMPR has a default value of 0 and controls pair electron angles relative to the incident photon direction as follows IPRDST Method for determining 0 fixed at 1 k sampled from Motz Olsen and Koch formula 3D 2000 sampled from Motz Olsen and Koch formula 3D 2003 TEISPL and NEISPL In order to speed up EGS5 simulations for applications involving x rays gen erated from electron impact_ionizations a method for creating additional x rays using the familiar Monte Carlo technique of splitting is provided see chapter 4 of SLAC R 730 KEK 2005 8 for the description of an EGS5 application involving splitting of particles If the flag IEISPL which is part of COMMON EIICOM and defaulted to 0 is set to be 1 each electron impact ionization event which leads to the production of a characteristic x ray will result in NEISPL appropriately weighted x rays being produced IBRSPL and NBRSPL The parameters IBRSPL and NBRSPL allow the user to improve the efficiencies of simulations in which low probability bremsstrahlung photon production is important by splitting the secondary particles The method is similar to that described above for splitting in x ray production following elec
24. article on the stack a straight line distance USTEP in the current media All of the parameters of the particle are available to the user via COMMON STACK as described earlier The user controls the transport upon return to EGS by altering one or more of the following variables USTEP IDISC IRNEW and DNEAR NP Except for DNEAR which is in COMMON STACK these are available to the user via COMMON EPCONT The ways in which these variables may be changed and the way EGS will interpret these changes is discussed in detail below Note flow diagrams for subroutines ELECTR and PHOTON have been included in Appendix A of SLAC R 730 KEK 2005 8 for the user who requires a more complete understanding of what actually takes place during particle transport IDISC Ifthe user decides that the current particle should be discarded then IDISC must be set nonzero the usual convention is to set IDISC 1 A positive value for IDISC will cause the particle to be discarded immediately A negative value for IDISC will cause EGS to discard the particle when it completes the transport EGS initializes IDISC to zero and if left zero no user requested discard will take place For example the easiest way to define an infinite homogeneous medium is with the HOWFAR routine subroutine howfar return end In this case particle transport will continue to take place until energy cutoffs are reached However a common procedure is to set IDISC 1 whenever the partic
25. cross regions in a variety of common geometries are provided with the EGS5 distribution The interaction between the user code and the EGS5 modules is best illustrated in Figure B 1 In summary the user controls an EGS5 simulation by means of Calls to subroutines PEGS5 to create media data HATCH to establish media data SHOWER to initiate the cascade Calls from EGS to user subroutines HOWFAR to specify the geometry AUSGAB to score and output the results Altering elements of COMMON blocks parameters inside EGS5 source code to set array dimensions variables inside user code to specify problem data The following sections discuss the above mechanisms in greater detail B 3 Variables in EGS5 COMMON Blocks Listed in Tables B 1 through B 17 are the variables in EGS5 COMMON blocks which may be relevant to the user along with a brief description of their functions Methods for manipulating these variables to either control EGS5 shower simulations or to retrieve results will be discussed in subsequent sections Note that an asterisk after a variable name in any of the tables indicates a change from the orginal EGS4 default User In Control E Data Fr l 4 MAIN HOWFAR 4 PIN ZIN aie i dea sosea tS 3545 l I pa
26. ct for the purposes of EGS by using different names for them in PEGS input files B 4 6 Initializations for HOWFAR Step 6 As stated previously HOWFAR is the routine that describes the translation of particles through the geometry of the various regions in the problem Note that initialization of data required by HOWFAR may be done at any step prior to calling SHOWER in Step 8 and that in fact for some trivial versions of HOWFAR no initializations are required at all For versions of HOWFAR which model realistic geometries however it is likely that some initialization will be required in MAIN or auxiliary user subprograms called by MAIN In such cases it will also be necessary that local auxiliary COMMON blocks be defined to pass geometry data to HOWFAR B 4 7 Initializations for AUSGAB Step 7 This step is similar to initialization for HOWFAR above in that it could actually be done anywhere in MAIN prior to SHOWER being called An example initialization based on a three region geometry is given here Suppose that we wish to know the total energy deposited in each of the three regions We could declare a scoring array ESUM in a COMMON block TOTALS in both MAIN and in AUSGAB as common totals esum 3 This array would be initialized in MAIN by the statements do i 1 3 esum i 0 0 end do Then the statement esum ir np esum ir np edep in AUSGAB would keep a running total of the energy deposited in each region under considerat
27. ero 2 Whenever a particle is actually moved by a straight line distance TVSTEP the path length transported is deducted from the DNEAR for the particle 3 Whenever a particle interacts the DNEAR values for the product particles are set from the DNEAR value of the parent particle 4 When EGS has decided it would like to transport the current particle by a distance USTEP which will be the distance to the next interaction subroutine HOWFAR will be called to get the user s permission to go that far only if USTEP is larger than DNEAR It is this feature which permits EGS to avoid potentially cumbersome geometry computations whenever possible In summary to take advantage of these efficiency features the user should set DNEAR NP equal to the perpendicular distance to the nearest region boundary from the particle s current position If it is easier for the user to compute some quick lower bound on the actual nearest distance this could be used to set DNEAR with time savings depending on how close the lower bound is to the actual nearest distance on the average It should be understood however that if the boundary separations are smaller than the mean step size subroutine HOWFAR will still be called and the overall efficiency will decrease as a result of having to perform the DNEAR calculation so many times Finally if the medium for a region is vacuum the user need not bother computing DNEAR as EGS will always transport to the next bou
28. ex of previous region IRNEW Index of new region TAUSFL Array of flags for turning on various calls to AUSGAB Table B 7 Variable descriptions for COMMON block MEDIA include file egs5_media f of the EGS5 distribution RLCM Array containing radiation lengths of the media in cm Note the name change P necessitated by combining EGS and PEGS RLDU Array containing radiation lengths of the media in distance units established by So E RHOM Array containing density of the media in g cm Note the name change necessitated by combining EGS and PEGS NMED Number of media being used default 1 S O MEDIA Array containing names of media default is NaI O IRAYLM Array of flags for turning on 1 coherent Rayleigh scattering in various media Set in HATCH based on values of IRAYLR INCOHM Array of flags for turning on 1 use of incoherent scattering function for Compton scattering angles in various media Set in HATCH based on values of INCOHR IPROFM Array of flags for turning on 1 Doppler broadening of Compton scattering ener gies in various media Set in HATCH based on values of IPROFR IMPACM Array of flags for turning on 1 electron impact ionization in various media Set in HATCH based on values of IMPACR in various media Set by user code MAIN prior to PEGS5 call to invoke automated electron step size selection USEGSD Array of flags indicating on
29. he specification of the photon electric field vector and the passing of that data to SHOWER Example 1 Completely linearly polarized photon source with electric vector along y direction ufi 0 0 vfi 1 0 wfi 0 0 do i i ncases uf 1 ufi vi 1 vfi wf 1 wfi call shower igi e xi yi zi ui vi wi iri wti end do 24 Example 2 Partially linearly polarized photon source with source propagation vector along the z direction and polarization vector along the y axis with P 0 85 P is the degree of linear polarization ui 0 0 vi 0 0 wi 1 0 pval 0 85 Degree of linear polarization pratio 0 5 pval 0 5 Ratio of y polarization do i i ncases call randomset value if value 1t pratio then ufi 0 0 vfi 1 0 wfi 0 0 else ufi 1 0 vfi 0 0 wfi 0 0 end if uf 1 ufi vf 1 vfi wf 1 wfi call shower igi e xi yi zi ui vi wi iri wti end do Example 3 Unpolarized photon source In a photon transport simulation modeling linear po larization an unpolarized photon source is automatically generated by setting uf 1 0 0 vf 1 0 0 wf 1 0 0 inside the shower call loop B 4 9 Output of Results Step 9 This step is self explanatory and is included only for the sake of completeness 25 B 5 Specifications for HOWFAR BGS calls user code HOWFAR when it reaches the point at which it has determined because of step size specifications and or interaction probabilities that it would like to transport the top p
30. ion Note that global auxiliary subroutines ECNSV1 and NTALLY are provided with the EGS5 distribution to facilitate scoring of energy deposition and the numbers of various types of events respectively 23 B 4 8 SHOWER Call Step 8 The calling sequence for SHOWER is call shower iqi ei xi yi zi ui vi wi iri wti All of the arguments in this call are declared real 8 in SHOWER except for iqi and iri which are integer These variables which can have any names the user wishes in MAIN specify the charge total energy position direction region index and statistical weight of the incident particle and are used to fill the corresponding stack variables see the listing in Table B 11 In a typical problem SHOWER is called repeatedly in a loop over a number of histories or cases as in do i 1 NCASES call shower iqi ei xi etc end do The statistical weight WTI of the incident particle is generally taken as unity unless variance reduc tion techniques are employed by the user Note that if IQI is assigned the value of 2 subroutine SHOWER recognizes this as a pi zero meson decay event and two photons are added to the stack with energies and direction cosines appropriately obtained by sampling Specification of electric vector of photon for SHOWER This is necessary only if the incident particle is a photon and the scattering of linearly polarized photons is being modeled The following 3 examples illustrate t
31. le reaches a discard region e g outside the problem geometry USTEP and IRNEW If immediate discard has not been requested then the HOWFAR should check to see whether transport by distance USTEP will cause a region boundary to be crossed If no boundary will be crossed then USTEP and IRNEW may be left as they are If a boundary will be crossed then USTEP should be set to the distance to the boundary from the current position along the current direction and IRNEW should be set to the region index of the region on the other side of the boundary For sophisticated geometries this is the most complex part of the user code DNEAR NP The setting of DNEAR NP by the user is optional However in many situations a sig nificant gain in efficiency will result by defining DNEAR NP in HOWFAR It is obvious that distance to boundary calculations are computationally expensive and should be avoided whenever possible For electrons traveling in regions in which their step sizes are much smaller than the region dimensions 26 interrogation of the problem geometry at each electron step can greatly slow the simulation In order to avoid this inefficiency each particle has stored on the stack a variable called DNEAR NP which is used by EGS to hold a lower bound on the distance from the particle s current position to the nearest region boundary This variable is used by EGS in the following ways 1 DNEAR for the incident particle is initialized to z
32. lling HATCH if Doppler broadening of the energies of Compton scattered photons is to be modeling in particular regions EGS5 execution is terminated if the Doppler broadening data is not found by HATCH in the PEGS data file being used however Note that when IPROFR 1 1 it is necessary to have set IBOUND 1 and INCOH 1 in the corresponding materials when PEGS was run and that MAIN must set INCOHR 1I 1 for the corresponding regions as well IMPACR The elements of this array dimensioned IMPACR MXREG and found in COMMON MISC are set to 1 prior to calling HATCH when electron impact ionization is to be simulated in particular regions Execution of EGS5 is terminated if the electron impact ionization data is not found in the PEGS data however IPHTER The elements of this array dimensioned IPHTER MXREG and located in COMMON USERXT are set to 1 if photoelectron angles are to be sampled in particular regions The default IPHTER 0 assumes isotropic emission TEDGFL The elements of this array dimensioned IEDGFL MXREG and passed in COMMON EDGE2 are set to 1 if K and L edge fluorescence is be explicitly modeling in specific regions 16 IAUGER The elements of this array dimensioned IAUGER MXREG and found in COMMON EDGE2 are set to 1 if K and L edge Auger electrons are to be generated in given regions LPOLAR The elements of this array dimensioned LPOLAR MXREG and contained in COMMON MISC are set to 1 if linearl
33. lt version of EGS The remaining 26 IARG situations must be switched on via specification of the array IAUSFL The 5 values of IARG which are turned on by default and the corresponding situations in which they initiate calls to user code AUSGAB are given in Table B 18 30 The above IARG values are the ones required in the majority of situations in which EGS5 is used to simulate electromagnetic cascade shower development In particular IARG 0 is useful whenever track lengths are being calculated or when charged particle ionization loss is being scored The large number of situations which initiate calls to AUSGAB for various IARG values allows the user to extract information about EGS5 simulations without making changes to the EGS code The user controls when AUSGAB is to be called by specifying in the user code values of the integer flag array IAUSFL J for J 1 through 31 IAUSFL J takes on values of 1 or 0 depending on whether AUSGAB is called or not respectively For J 1 through 5 which corresponds to IARG of 0 through 4 IAUSFL J is set to 1 by default and AUSGAB is always called for the situations listed in Table B 18 For the remaining values of J corresponding to IARG 5 through 31 IAUSFL J is set to 0 by default and the user must modify IAUSFL J in order to initiate any desired AUSGAB calls The value for IARG and the corresponding situations for this upper set of IARG values are shown in Table B 19 Note that the code statu
34. ndary in only one step in this case B 5 1 Sample HOWFAR User Code Consider as an example of how to write a HOWFAR subprogram the three region geometry in B 2 A particle is shown in Region 2 with coordinates X Y Z and direction cosines U V W We will assume that the slab of thickness ZTHICK is semi infinite x and y directions and that particles are immediately discarded whenever they go into Region 1 or Region 3 The following HOWFAR code correctly models this geometry subroutine howfar implicit none include include egs5_h f Main EGS header file include include egs5_epcont f COMMONs required by EGS5 code 27 Region Region Region 1 2 3 X Y Z x Vacuum Air at NTP Q gt Z Iron x U V W gt ZTHICK lt V Y into paper Figure B 2 A three region geometry for a HOWFAR example code 28 include include egs5_stack f common passit zthick real 8 zthick real 8 deltaz Local variables integer irnxt if ir mp ne 2 then idisc 1 return end if dnear np dmin1 z np zthick z np Particle going parallel to planes Check forward plane first since shower heading that way most of the time if w np gt 0 0 then deltaz zthick z np w np irnxt 3 else deltaz z np w np irnxt 1 end if if deltaz le ustep then ustep
35. ng strength at EMAXE is scaled by the factor K1HSCL and the scattering strength at ECUT for the region is scaled by K1LSCL Scaling at other electron ener gies is determined by logarithm interpolation K1HSCL MXREG and KiLSCL MXREG are found in COMMON MISC and are initialized to 0 0 in BLOCK_SET which implies no scaling USEGSD If the user wishes to use the Goudsmit Saunderson multiple scattering distribution func tion instead of the Moli re distribution function for a material USEGSD MXMED must be set to be non zero prior to the call to HATCH In addition the appropriate requests to pre compute the distribution function tables must have been specified in the PEGS input files prior to the call to PEGS5 or the appropriate data table files must exist in the working directory In the current version of EGS5 all regions must use the Goudsmit Saunderson distribution if any of them do USEGSD is a part of COMMON block MEDIA 17 RHOR Media of similar materials but with varying density in different regions can be defined by setting non zero values of the region density in the variable RHOR MXREG of COMMON MISC prior to calls to HATCH This feature eliminates the need for the user to create a distinct new media for each region which has a a given material but with a different density Values of RHOR should be specified in terms of the actual density in each region not the density relative to the reference density RHOR is initialized to 0
36. or example if a user is interested in energy deposition in a gas detector only those electrons which are energetic enough to escape the solid walls surrounding the gas of the detector have a chance to be scored Thus the simulation of the transport in the walls of electrons with ranges less than the closest normal distances to the outer walls adds nothing but CPU time to the simulation If however the user specifies a non zero value of ESAVE for a given region ELECTR will discard the electron if its energy is less than ESAVE and its range is less than DNEAR see below thus speeding the computation This technique is commonly called range rejection and is most effective when ESAVE is much larger than ECUT Note that the range of the electron is defined very crudely here as simply E NP divided by the stopping power of the medium This assures that the decision to discard a particle based on range rejection will be conservative as long as the stopping power of the medium increases at energies below ESAVE 18 IBRDST The parameter IBRDST which has a default value of 0 and is part of COMMON BREMPR determines the procedure for determining the angle of bremsstrahlung photons relative to the incident electrons as described below IBRDST Method for determining 0 0 fixed at m Ep 1 sampled from Koch and Motz formula 2BS Values of IBRDST set by the user apply to all media and regions in a simulation IPRDST The value of the p
37. rather than total energy aT Array containing the Meller threshold energy THMOLL AE TE for each medium in MeV Table B 13 Variable descriptions for COMMON block UPHIOT include file egs5_uphiot f of the EGS5 distribution JE Table B 14 Variable descriptions for COMMON block USEFUL include file egs5_useful f of the EGS5 distribution Index of current medium If vacuum then MEDIUM 0 Index of previous medium RM Electron rest mass energy in MeV IBLOBE Flag indicating if photon is below binding energy EBINDA after a photoelectric interaction yes 1 Table B 15 Variable descriptions for COMMON block USERSC include file egs5_usersc f of the EGS5 distribution ESTEPR Array of factors by which to scale the energy hinge steps in various regions de i fault 0 implying no scaling ESAVE Array of energies below which to discard electrons which have ranges less than the perpendicular distances to their current region boundaries default 0 implying no range based discard EMAXE Maximum total energy in MeV of any electron in the simulation 11 Table B 16 Variable descriptions for COMMON block USERVR include file egs5_uservr f of the EGS5 distribution Constant used in exponential transform of photon collision distance default 0 no transformation Table B 17 Variable descriptions for COMMON block USERXT include file egs5_userxt f of the EGS5 distribution Array of flags for turning
38. rection cosines vi 0 wi 1 iri 2 Region number 2 is the incident region wti 1 0 Weight factor in importance sampling ncases 10 Number of histories to run idinc 1 21 ei 1000 d0 Total energy MeV ekin eitiqi RM Incident kinetic energy Note that the variables initialized above are the ones passed to EGS5 subroutine SHOWER as de scribed below in step 8 B 4 5 HATCH Call Step 5 When the user code MAIN calls the EGS HATCH subroutine EGS is hatched by executing some necessary once only initializations and reading material data for the media from a data set that created by PEGS The required call is trivially Some examples of reports from HATCH are shown below The following is a typical output message when DUNIT has not been changed and Rayleigh data is included in the file RAYLEIGH DATA AVAILABLE FOR MEDIUM 1 BUT OPTION NOT REQUESTED EGS SUCCESSFULLY HATCHED FOR ONE MEDIUM For a non default specification of DUNIT DUNIT 2 54 for example the output report from HATCH would look like the following for two media and no Rayleigh data DUNIT REQUESTED amp USED ARE 2 54000E 00 2 54000E 00 CM EGS SUCCESSFULLY HATCHED FOR 2 MEDIA END OF FILE ON UNIT 12 PROGRAM STOPPED IN HATCH BECAUSE THE FOLLOWING NAMES WERE NOT RECOGNIZED list of names 22 Note that one cannot ask for the same medium twice though one can define two media which are physically identical to be distin
39. ses for IARG values from 0 to 3 and from 5 to 24 are the identical to those found in EGS4 A slight modification has been made in EGS5 for IARG of 4 and the situations in which IARG values of 25 through 30 initiate a call to AUSGAB are newly added in EGS5 As an example of how to write an AUSGAB subprogram consider the previous three region geometry of Figure B 2 Suppose that we wish to score only photons that emanate from Region 2 into Region 3 The AUSGAB subprogram that will accomplish this is given below in this example we print out the stack variables plus IARG subroutine ausgab iarg implicit none include include egs5_h f Main EGS header file include include egs5_stack f integer iarg Arguments if iarg eq 3 and iq np eq 0 and ir np eq 3 then write 6 1000 e np x np y np z np u np v np w np iq np ir np iarg end if 1000 format 7g15 7 3i5 return end 31 Table B 19 IARG values IAUSFL indices and program status for AUSGAB calls TARG TAUST o Bia 6l Particle has been transported by distance TVSTEP 7 A bremsstrahlung interaction is to occur and a call to BREMS is about to be pa made in ELECTR eh 8l Returned to ELECTR after a call to BREMS was made a A Maller interaction is to occur and a call to MOLLER is about to be made in ELECTR 9f ALO Returned to ELECTR after a call to MOLLER was made A Bhabha interaction is to occur and a call to BHABHA is about to be
40. the medium assigned to Region 3 is really not important in this example and was included solely for purposes of illustration Some of the stack variable information E NP Z NP W NP IQ NP IR NP plus the IARG value is printed out on the printer first 15 lines only for photons reaching Region 3 A total of 10 cases of incident electrons are run and the total energy fraction for each region is summed and printed out at the end of the run for an energy balance check The UCSAMPL5 user code is given below T akaka ak k ak 2k 2 k A 2 2 K EE KRA FK K FK K K K K FK K FK K K K K FK K K K FK K OK K KK K OK FKK K KK K K KK K K K K K ucsamplb f FA k kkk kk k A complete example of a EGS5 user code using a simple plane geometry For SLAC R 730 KEK Report 2005 8 This user code corresponds to ucsampl4 mor for egs4 The following shows the geometry LGC ACACIA CARI ICRI ICI KAI ICA I OK K A A 1K 2k 3 4 4 21 21 3 4 4 2k 2K 4 2K 2k electron 0 3 0 Po eee a a a a a a n a a a a a a a a a a a a ea 1 Dimensional Plane Z Geometry ucsampl5 example Po ee ee a a a a a a a a a a a a a a a a a a a a a a a ua Y X into page l Fe Air 1 GeV gt op gt Z 33 PRR RR RR RR RR RR RR RR RR RR RR AAA I A A Ak 1 2k 2k 2k 2k 2k 2k 2k 2 kkk k 123456789 123456789 123456789 123456789 1
41. tron impact ionization When the parameter IBRSPL which has a default value of 0 and is found in COMMON BREMPR is set to 1 each electron bremsstrahlung event will result in the generation of NBRSPL appropriately weighted photons CEXPTR The parameter CEXPTR found in COMMON USERVR is a scaling factor which can be used to either force or inhibit photon collisions in regions with cross section that are very small or very 19 large If A is the photon mean free path and we use C to represent the scaling factor CEXPTR we have for the interaction probability distribution B A a 1 Cue A t C ad where the overall multiplier 1 C u is introduced to ensure that the probability is correctly normal ized i e 9 P A dA 1 For C 0 we have the unbiased probability distribution e Ad One sees that for 0 lt C lt 1 the average distance to an interaction is stretched and for C lt 0 the average distance to the next interaction is shortened Note that the average number of mean free paths to an interaction A is given by A Joo AB A d ere NOMSCT The user may override all treatment of electron multiple scattering in a given region by setting the switch NOMSCT MXREG to be 1 for that region NOMSCT which is a part of COMMON MISC and is initialized 0 is used primarily as a debugging and code development tool and is included in this description for completeness only Random number generator initialization Whenever
42. ty of the EGS5 problem specification and the PEGS data file being used NREG HATCH uses the variable NREG when verifying and loading region dependent options for the problem materials MED The array MED dimensioned MED MXREG contains the medium indices for each region default values are 1 for all MXREG A medium index of zero means a region is vacuum Indices are defined by the order specified by the user and are independent of the order in which the materials are defined in the PEGS data file being used Consider the three media example above from the pre PEGS5 initialization section with vacuum defined as a fourth regions The EGS5 user code to accomplish this might look like First region is AIR AT NTP Second region is LEAD Third region is VACUUM Fourth region is STEEL Optional variables and flags processed by HATCH CUT and PCUT The ECUT and PCUT arrays contain the cutoff energies in MeV for the termi nation of the tracking of charged particles and photons respectively for each region They are dimensioned ECUT MXREG and PCUT MXREG and are initialized to 0 0 in BLOCK_SET Note that HATCH will override any user defined values of ECUT and PCUT if these values are lower than the threshold energies set in PEGS for the generation of secondary electrons and photons the param eters AE and AP Thus by assigning values of ECUT and PCUT prior to the HATCH call the user can raise but not lower the cutoff energies
43. used the desired cutoff energies and the distance unit to be used e g inches centimeters radiation lengths etc MAIN next calls EGS5 subroutine PEGS5 to create basic material data and then calls EGS5 subroutine HATCH which hatches EGS by reading the material data created by PEGS for the media in the given problem Once the initialization is complete MAIN then calls the EGS5 subroutine SHOWER with each call to SHOWER resulting in the simulation of one history often referred to as a case The arguments to SHOWER specify the parameters of the incident particle initiating the cascade The user subroutine HOWFAR is required for modeling the problem geometry which it does primarily by keeping track of and reporting to EGS the regions in which the particles lie while user subroutine AUSGAB is typically used to score the results of the simulation Table B 1 Variable descriptions for COMMON block BOUNDS include file egs5_bounds f of the EGS5 distribution ECUT Array of region dependent charged particle cutoff energies in MeV Array of region dependent photon cutoff energies in MeV VACDST Distance to transport in vacuum default 1 E8 In addition to MAIN HOWFAR and AUSGAB additional subprograms may be included in the user code to facilitate the geometry computations of HOWFAR among other things Sample auxiliary subroutines useful in performing distance to boundary computations and in moving particles a
44. y polarized photon scattering is to be modeled in specified regions DUNIT The parameter DUNIT defines the unit of distance to be used in the shower simulation the default is cm if DUNIT 1 On input to HATCH DUNIT is interpreted as follows 1 DUNIT gt 0 means that DUNIT is the length of the distance unit expressed in centimeters For example setting DUNIT 2 54 would mean that the distance unit would be one inch 2 DUNIT lt 0 means that the absolute value of DUNIT will be interpreted as a medium index The distance unit used will then be the radiation length for the medium and on exit from HATCH DUNIT will be equal to the radiation length of that medium in centimeters The obvious use of this feature is for the case of only one medium with DUNIT 1 which results in the shower being expressed entirely in radiation lengths of the first medium Note that the unit of distance used in PEGS is the radiation length After HATCH interprets DUNIT it scales all PEGS data by units of distance as specified by the user so that all subsequent operations in EGS will be performed with distances in units of DUNIT default value 1 0 cm K1HSCL and KiLSCL The parameters K1HSCL and K1iLSCL permit the user to apply energy dependent scaling of the material dependent scattering strength which is roughly proportional to the multiple scattering step size distance on a region by region basis When K1HSCL and K1LSCL are non zero for a region the scatteri
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