SLAC 265 Appendix 3
PEGS4 User Manual


About this document

This document is an HTML version of SLAC-265 Appendix 3 written by




                      Walter R. Nelson

              Stanford Linear Accelerator Center

                     Stanford University

                  Stanford, CA 94305, U.S.A.





                       Hideo Hirayama

      National Laboratory for High Energy Physics (KEK)

           Oho-machi, Tsukuba-gun, Ibaraki, Japan





                     David W. O. Rogers

             National Research Council of Canada

                   Ottawa K1A 0R6, Canada





                      31 December 1985




A3. PEGS4 USER MANUAL

A3.1 Introduction

The PEGS code (Preprocessor for EGS) is a stand alone utility program written in Mortran **. PEGS' purpose is to generate material data for the EGS code, and to provide other services for the user who is studying or simulating electro- magnetic interactions. The active operations of PEGS are functionals; that is, they are operations whose arguments are functions (the functions related to physics interactions). Included among these operations are:

Associated with these active functionals are other operations; namely,

Note: Those interested in preparing data sets for EGS4 can go directly to Section A3.3

* This manual is kept up-to-date on the EGS account at SLAC and is distributed along with other files on the EGS4 distribution tape.

** A. J. Cook, "Mortran3 User's Guide", SLAC Computation Research Group Technical Memorandum CGTM-209 (1983) [see also APPENDIX 4: "EGS4 Users Guide to Mortran3"].


A3.2 Structural Organization of PEGS

The PEGS code contains over 4200 Mortran source lines which are the source for a MAIN program, BLOCK DATA subpro- gram, 12 subroutines, and 83 functions. Despite the large number of subprograms, PEGS has a simple structure. Fig. A3.2.1 shows a flowchart of the MAIN program of PEGS. After the once-only initializations an option loop is entered. Each time through the option loop, an option is read (option names are four characters and are read as 4A1), numeric con- trol parameters are read (using NAMELIST/INP/), and then the option name is looked up in the option table. If not found, the job is aborted. If found, the appropriate code is exec- uted and return is passed to the beginning of the option loop. Normal exit from the loop is by selection of the STOP option, or detection of an End of File condition on the con- trol input file. The details for the use of the options are contained in Section A3.3.

Fig. A3.2.2 shows the subprogram relationships of PEGS. Boxed items are subprograms, and labels for option names (i.e., :CALL:) are used to show which subprograms correspond to which options. It can be seen that the physical routines are accessed directly for the PWLF option. For utility options (TEST, PLTN, PLTI, HPLT, and CALL) the physical routines are referenced using the function FI---the so-called "function multiplexer". Function FI has five arguments. The first argument (I) tells which physical function to invoke, and the other four arguments (X1, X2, X3, X4) are used as needed as arguments for the called function. FI then returns the value returned by the called function.

This method of implementing options that are functionals was selected to avoid the necessity of having a separate call to the associated utility routines for each physical function on which it might be desired to operate. It was also desired to be able to refer to the particular function symbolically, both at compile time and at run-time, and to know the number of arguments to each function. In order to have these conveniences and also allow easy insertion or deletion of functions to the list of functions accessible to FI, a Mortran macro ($FUNCTIONS) was written which takes a list of names of functions (each of which is immediately pre- ceded by the number of arguments it has) and generates other macros containing the desired information. In particular,




                         +------+

                         | PEGS |

                         +------+

                           |  |       +-------------+

               initialize  |  +------x| OPTION LOOP |x-----+

            +--------------+          +-------------+      A

            |                                |             |

            |                                |             |

            V                                V             |

+------------------------+          +-----------------+    |

|   Compute Physical &   |          |   Read Option   |    |

| Mathematical Constants |          |    Name (4A1)   |    |

+------------------------+          |        &        |    |

            |                       |   Read Control  |    |

            |                       |    Parameters   |    |

            V                       | (NAMELIST/INP/) |    |

+------------------------+          +-----------------+    |

| Read Pair Production & |                   |             |

|  Photo Cross Sections  |                   |             |

|    from File PHPRDAT   |                   |             |

+------------------------+                   |             |

                                             |             |

                                             V             |

               +------+     Yes      +--------------+      |

               | Stop |x------------ | End of File? |      |

               +------+              +--------------+      |

                                             |             |

                                             | No          |

                                             |             |

                                             V             |

     +-----------------------+       +---------------+     |

     | Illegal Option---Stop |x----- | Select Option |     |

     +-----------------------+       +---------------+     |

                                             |             |

                                             |             |

                                             V             |

  +x---------------------------------------- +             |

  |                                                        |

  V                                                        |

  *                                                        *

 * *                                                      * *

* 1 *                                                    * 2 *

 * *                                                      * *

  *                                                        *







     Fig. A3.2.1  Flowchart of the MAIN Program of PEGS

                         (continued)







  *                                                         *

 * *                                                       * *

* 1 *                                                     * 2 *

 * *                                                       * *

  *                                                         *

  |                                                         A

  |                                                         |

  |          +-----------------------+                      |

  +--x:ELEM: | Set Up Element Medium | -------------------x |

  |          +-----------------------+                      |

  |          +-----------------------+                      |

  +--x:MIXT: | Set Up Mixture Medium | -------------------x |

  |          +-----------------------+                      |

  |          +------------------------+                     |

  +--x:COMP: | Set Up Compound Medium | ------------------x |

  |          +------------------------+                     |

  |          +------------------------+                     |

  +--x:ENER: | Set Energy Cutoffs and | ------------------x |

  |          | Compute Thresholds     |                     |

  |          +------------------------+                     |

  |          +---------------------+                        |

  +--x:PLTN: | Plot Named Function | ---------------------x |

  |          +---------------------+                        |

  |          +-----------------------+                      |

  +--x:PLTI: | Plot Indexed Function | -------------------x |

  |          +-----------------------+                      |

  |          +-----------------------+                      |

  +--x:HPLT: | Histogram Theoretical | -------------------x |

  |          |  vs Sampled Spectrum  |                      |

  |          +-----------------------+                      |

  |          +-------------------------+                    |

  +--x:CALL: | Evaluate Named Function | -----------------x |

  |          +-------------------------+                    |

  |          +-----------------------------+                |

  +--x:TEST: | Plot Functions To Be Fitted | -------------x |

  |          +-----------------------------+                |

  |          +----------------------+                       |

  +--x:PWLF: | Piecewise Linear Fit | --------------------x |

  |          +----------------------+                       |

  |          +------------------------+                     |

  +--x:DECK: | Punch Deck of Material | ------------------x +

  |          | Dependent Data         |

  |          +------------------------+

  |          +------+

  +--x:STOP: | Stop |

             +------+





     Fig. A3.2.1  Flowchart of the MAIN Program of PEGS







    +------------+         +------+

    | BLOCK DATA |         | MAIN |

    +------------+         +------+

                               |

                               |

    + --- + -- + ----- + ----- + ----- + ----- + ---- + ---- +

    |     |            |       |       |       |      |      |

    |     |         :PWLF:  :DECK:  :TEST:  :HPLT: :CALL: :ENER:

    |     |            |       |    :PLTN:     |      |

    |     |            |     +---+  :PLTI:  +-----+   |

    |     |            |     |LAY|     |    |HPLT1|   |

    |     |            |     +---+     |    +-----+   |

    |     |            |            +----+     |      |

 +------+ |        +---+----+       |PLOT|     |      |

 |PMDCON| |        |        |       +----+     |      |

 +------+ |     +-----+  +-----+       |       |      |

          |     |EBIND|  |PWLF1|       +-----x | x--- +

          |     +-----+  +-----+               |

       :ELEM:               |                  |

       :MIXT:            +----+                |

       :COMP:            |QFIT|                *

          |              +----+               * *

  + ----- + ----- +         |                * 3 *

  |       |       |         |                 * *

+---+ +------+ +------+     |                  *

|MIX| |SPINIT| |DIFFER|     |

+---+ +------+ +------+     |

                            |

                            |

                       + -- + -- + --------------- +

                       |         |                 |

                    +-----+   +-----+           +-----+

                    |EFUNS|   |GFUNS|           |RFUNS|

                    +-----+   +-----+           +-----+

                       |         |                 |

   +-----+----+-----+--+---+---+ |   +------+   +-----+

   |     |    |     |      |   | +---|PHOTTE|   |AINTP|

+------+ | +------+ | +------+ | |   +------+   +-----+

|SPTOTP| | |ANIHTM| | |BHABTM| | |   +------+

+------+ | +------+ | +------+ | +---|COMPTM|

         |          |          | |   +------+

+------+ | +------+ | +------+ | |   +------+

|SPTOTE|-+ |AMOLTM|-+ |BREMTM|-+ +---|PAIRTU|

+------+   +------+   +------+   |   +------+

                                 |   +------+

                                 +---|COHETM|

                                     +------+





     Fig. A3.2.2  Subprogram Relationships of PEGS

                        (continued)






                              *

                             * *

                            * 3 *

                             * *

                              *

                              |

                              |

                              |

                              |

                 + ---------------------- +

                 |           FI           |

                 | "Function Multiplexer" |

                 + ---------------------- +

                              |

                              |

                              |

          + ------------------------------------- +

          |                                       |

          |   ALIN     APRIM    COMPFM   PAIRTE   |

          |   ALINI    BHABDM   COMPRM   PAIRTM   |

          |            BHABFM   COMPTM   PAIRTR   |

          |   ADFMOL   BHABRM   CRATIO   PAIRTU   |

          |   ADIMOL   BHABTM   EBIND    PAIRTZ   |

          |   ADDMOL   BREMDR   EBR1     PBR1     |

          |   ALOG     BREMFR   EDEDX    PBR2     |

          |   EXP      BREMDZ   ESIG     PDEDX    |

          |   AREC     BRMSDZ   FCOULC   PHOTTZ   |

          |   ALKE     BREMFZ   GBR1     PHOTTE   |

          |   ALKEI    BRMSFZ   GBR2     PSIG     |

          |   AMOLDM   BREMRR   GMFP     SPIONE   |

          |   AMOLFM   BREMRM   PAIRDR   SPIONP   |

          |   AMOLRM   BREMRZ   PAIRFR   SPTOTE   |

          |   AMOLTM   BREMTM   PAIRDZ   SPTOTP   |

          |   ANIHDM   BREMTR   PAIRFZ   TMXB     |

          |   ANIHFM   BRMSRM   PAIRRM   TMXS     |

          |   ANIHRM   BRMSRZ   PAIRRR   TMXDE2   |

          |   ANIHTM   BRMSTM   PAIRRZ   XSIF     |

          |            COHETM                     |

          |            COHETZ                     |

          |            COMPDM                     |

          + ------------------------------------- +







     Fig. A3.2.2  Subprogram Relationships of PEGS

                  (continued from previous page)

The following macros are defined:

$NFUNS - Gives the number of functions.

$FLIST$DATA(FNAME) - Generates a data statement init- alizing the array FNAME(6,$NFUNS) so that FNAME(i,j) has the ith character of the name of the jth function.

$FLIST$NARGS - Gives a list of the number of arguments for each function, which is used to initialize the run- time array NFARG($NFUNS).

$FLIST$FNUMS - Gives a list of numbers from 1 to $NFUNS, which is used to generate the computed GO TO in FI.

$FLIST$FCALLS - Generates the function calls in FI with the proper number of arguments for each function taken from the list X1, X2, X3, X4.

$FN(function name) - Gives the function index of the specified function.

$NA(function name) - Gives the number of arguments for the specified function.

It should also be noted that there are relationships between the functions shown in Fig. A3.2.2 that are not indicated there. We show the most complicated of these in Figs. A3.2.3a,b (Bremsstrahlung Related Functions) and in Figs. A3.2.4a,b (Pair Production Related Functions). One reason for the complexity of these is that the higher level forms of the cross sections must be obtained by numerical integration of the more differential forms.





                       +------+

                       |BREMTM|

                       +------+

                           |

                           V

                       +------+

                       |BREMRM|

                       +------+

                           |

                           V

+------+               +------+  initialize   +------+

|  QD  |x------------- |BREMRZ|-------------x |BREMDZ|

+------+               +------+    BREMFZ     +------+

   |                                              |

   V                                              |

+------+                                          |

|DCADRE|                                          |

+------+                                          |

   |                                              |

   V                                              V

+------+               +------+               +------+

|BREMFZ|-------------x |BRMSFZ|x------------- |BRMSDZ|

+------+               +------+               +------+

                           A                    A |

                           |                    | |   +------+

           +---------------+                    | +--x|APRIM |

           |                                    | |   +------+

       +------+        +------+   initialize    | |

       |DCADRE|   +----|BRMSRZ|---------------x + |   +------+

       +------+   |    +------+     BRMSFZ        +--x| XSIF |

           A      |        A                      |   +------+

           |      |        |                      |

       +------+   |    +------+                   |   +------+

       |  QD  |x--+    |BRMSRM|                   +--x|FCOULC|

       +------+        +------+                       +------+

                           A

                           |

                           |

  +------+             +------+             +------+

  |SPTOTE|-----------x |BRMSTM|x----------- |SPTOTP|

  +------+             +------+             +------+

     |                                          |

     |                                          |

     V                                          V

  +------+             +------+             +------+

  |SPIONE|-----------x |SPIONB|x----------- |SPIONP|

  +------+             +------+             +------+



    Fig. A3.2.3a  Bremsstrahlung Related Functions---Most

                 Accurate Form (Used to Produce the Total

                 Cross Sections and Stopping Power).









                            +------+

                            |BREMTR|

                            +------+

                                |

                                |

                                V

                            +------+

                            |BREMRR|

                            +------+

                                |

                                |

                     initialize V

                    + x---------+--------x +

                    |  BREMFR              |

                    |                      |

                    V                      V

                 +------+              +------+

                 |BREMDR|              |  QD  |

                 +------+              +------+

                    |                      |

                    |                      |

                    |                      V

                    |                  +------+

                    |                  |DCADRE|

                    |                  +------+

                    |                      |

                    |                      |

                    |                      |

                    |       +------+       |

                    + ----x |BREMFR| x---- +

                            +------+





    Fig. A3.2.3b  Bremsstrahlung Related Functions---With

                 Run-Time Approximations (For Comparison

                 with Sampled Spectra).





                        +------+

                        |PAIRTU|

                        +------+

                          |  |

   + x------------------- +  + -------------------x +

   |                                                |

   V                                                V

+------+                                        +------+

|PAIRTM|                                        |PAIRTE|

+------+                                        +------+

   |                                                |

   V                                                V

+------+                                        +------+

|PAIRRM|                                        |PAIRTZ|

+------+                                        +------+

   |                                                |

   V                                                V

+------+   initialize                           +------+

|PAIRRZ|-------------x +                        |AINTP |

+------+     PAIRFZ    |                        +------+

   |                   |

   |                   |

   |                   |

   |                   |

   V                   V

+------+            +------+            +------+

|  QD  |            |PAIRDZ|-----+----x | XSIF |

+------+            +------+     |      +------+

  |                    |         |

  |                    |         |      +------+

  |                    |         +----x |FCOULC|

  V                    V                +------+

+------+            +------+

|DCADRE|----------x |PAIRFZ|

+------+            +------+





    Fig. A3.2.4a  Pair Production Related Functions---Most

                 Accurate Form (Used to Produce the Total

                 Cross Sections and Stopping Power).







                            +------+

                            |PAIRTR|

                            +------+

                                |

                                |

                                V

                            +------+

                            |PAIRRR|

                            +------+

                                |

                                |

                     initialize V

                    + x-------- + -------x +

                    |  PAIRFR              |

                    |                      |

                    V                      V

                 +------+              +------+

                 |PAIRDR|              |  QD  |

                 +------+              +------+

                    |                      |

                    |                      |

                    |                      V

                    |                  +------+

                    |                  |DCADRE|

                    |                  +------+

                    |                      |

                    |                      |

                    |                      |

                    |       +------+       |

                    + ----x |PAIRFR| x---- +

                            +------+





    Fig. A3.2.4b  Pair Production Related Functions---With

                 Run-Time Approximations (For Comparison

                 with Sampled Spectra).


Table A3.2.1 lists the SUBROUTINES used in PEGS. A brief description of their use and page references for a fuller discussion is given.

Table A3.2.2 lists the FUNCTIONS used in PEGS along with their mathematical symbols, definitions, and locations in this report for a fuller discussion. The names of most of the functions have been chosen in a rather mnemonic way. The first three or four letters suggest the process being con- sidered. The last letter designates the form of the cross section (Z for element, M for mixture, and R for "run-time" mixture). The next to last letter describes either the part- icular form of the cross section (such as D for differential, T for total or R for range-integrated), or it indicates that only the secondary energy is to vary, with other data being passed through a common. The letter F is used in such cases and the data in common is initialized using the corresponding function that has a next to last letter of D. If the function word begins with an I through N (i.e., the FORTRAN integer convention) the word is prefixed with the letter A. A few examples are given below:

AMOLDM is the differential Moller cross section for a mixture of elements.

BREMDR is the differential bremsstrahlung cross section for a "run-time" mixture of elements.

BREMRM is the bremsstrahlung cross section, integrated over some energy range, for a mixture of elements.

BRMSTM is the soft bremsstrahlung total cross section for a mixture of elements.

PAIRRR is the pair production cross section, integrated over some energy range, for a "run-time" mixture of elements.

PAIRTZ is the total cross section for pair production for an element.

This method of naming is not strictly adhered to, however. For example, SPIONE is the ionization stopping power for an electron, PBR1 and PBR2 are positron branching ratios, and GMFP is the gamma-ray mean free path.


                        Table A3.2.1



                  SUBROUTINES Used In PEGS



-----------------------------------------------------------------

   NAME                 DESCRIPTION                   PAGES

-----------------------------------------------------------------

   DIFFER    Determines the various parameters       A3.2-4,

             needed for bremsstrahlung and pair      A3.3-11

             production energy sampling.



   EFUNS     Subprogram to compute electron          A3.2-4

             functions to be fit in a way

             that avoids repetition.



   GFUNS     Subprogram to compute photon            A3.2-4

             functions to be fit in a way

             that avoids repetition.



   HPLT1     Creates line printer plot comparisons   A3.2-4,

             of EGS-sampled data (UCTESTSR User      A3.3-20,21

             Code) and theoretical functions of PEGS.



   LAY       Subprogram to produce a deck of         A3.2-4,

             material dependent data (for sub-       A3.3-17

             sequent use by EGS).



   MIX       Computes Z-dependent paramaters         A3.2-4,

             that reside in COMMON/MOLVAR/.          A3.3-11



   MOLIER    Computes material independent           A3.2-4

             multiple scattering data (for

             EGS2 only).



   PLOT      Subprogram to plot a given function     A3.2-4

             (referenced by number).



   PMDCON    Determines the physical, mathematical,  A3.2-4

             and derived constants in a very

             mnemonic way.



   PWLF1     Subprogram to piecewise linearly fit    A3.2-4,19,

             up to 10 functions simultaneously on    A3.3-14

             an interval (XL,XU).



   RFUNS     Subprogram to compute Rayleigh          A3.2-4

             scattering functions to be fit in

             a way that avoids repetition.



   SPINIT    Initializes stopping power functions    A3.2-4,

             for a particular medium.                A3.3-11



   AFFACT    Atomic form factor (squared) for an

             element or mixture of elements.



   AINTP     Linear or log interpolation function.   A3.2-4,9



   ALKE      Log of kinetic energy (ALOG(E-RM)),     A3.2-5,

             used as a cumulative distribution       A3.3-20

             function for fits and plots.



   ALKEI     Inverse of ALKE (=EXP(X)+RM).           A3.2-5



   ALIN      Linear cumulative distribution func-    A3.2-5,

             tion for plots (ALIN(X)=X).             A3.3-20



   ALINI     Inverse of ALIN (=same as ALIN).        A3.2-5

             Used as inverse cumulative distri-

             bution function in plots.



   ADFMOL    Approximate cumulative distribution     A3.2-5,

             function for Moller and Bhabha cross    A3.3-20

             sections (ADFMOL(E)=-1/(E-RM)).



   ADIMOL    Inverse of ADFMOL.                      A3.2-5



   ADDMOL    Derivative of ADFMOL.                   A3.2-5



   AMOLDM    Moller differential cross section for   A3.2-5,11,14

             a mixture of elements.

   AMOLFM    "One argument" form of AMOLDM.          A3.2-5



   AMOLRM    Moller cross section, integrated over   A3.2-5

             some energy range, for a mixture of

             elements.



   AMOLTM    Moller total cross section for a        A3.2-4,5

             mixture of elements.



   ANIHDM    Annihilation differential cross         A3.2-5

             section for a mixture of elements.



   ANIHFM    "One argument" form of ANIHDM.          A3.2-5



   ANIHRM    Annihilation cross section, integrated  A3.2-5

             over some energy range, for a mixture

             of elements.



   ANIHTM    Annihilation total cross section for    A3.2-4,5

             a mixture of elements.



   APRIM     Empirical correction factor in          A3.2-5,7

             bremsstrahlung cross section.



   AREC      Reciprocal function (=derivative of     A3.2-5

             ALOG(X)).  Used as probability density

             function in log plots (AREC(X)=1/X).



   BHABDM    Bhabha differential cross section for   A3.2-5

             a mixture of elements.



   BHABFM    "One argument" form of BHABDM.          A3.2-5



   BHABRM    Bhabha cross section, integrated over   A3.2-5

             some energy range, for a mixture of

             elements.



   BHABTM    Bhabha total cross section for a        A3.2-4,5

             mixture of elements.



   BREMDR    Bremsstrahlung differential cross       A3.2,5,8,11

             section for a "run-time" mixture

             of elements.



   BREMFR    "One argument" form of BREMDR.          A3.2-5,8



   BREMDZ    Bremsstrahlung differential cross       A3.2-5,7

             section for an element.



   BREMFZ    "One argument" form of BREMDZ.          A3.2-5,7



   BREMRM    Bremsstrahlung cross section, inte-     A3.2-5,7,11

             grated over some energy range, for a

             mixture of elements.



   BREMRR    Bremsstrahlung cross section, inte-     A3.2-5,8

             grated over some energy range, for a

             "run-time" mixture of elements.



   BREMRZ    Bremsstrahlung cross section, inte-     A3.2-5,7

             grated over some energy range, for an

             element.



   BREMTM    Bremsstrahlung total cross section      A3.2-4,5,7

             for a mixture of elements.



   BREMTR    Bremsstrahlung total cross section      A3.2-5,8

             for a "run-time" mixture of elements.



   BRMSDZ    Soft bremsstrahlung differential        A3.2-5,7

             cross section for an element.



   BRMSFZ    "One argument" form of BRMSDZ.          A3.2-5,7



   BRMSRM    Soft bremsstrahlung cross section,      A3.2-5,7

             integrated over some energy range, for

             a mixture of elements.



   BRMSRZ    Soft bremsstrahlung cross section       A3.2-5,7,

             integrated over some energy range,      A3.3-19,20

             for an element.



   BRMSTM    Soft bremsstrahlung total cross         A3.2-5,7,11

             section for a mixture of elements.



   COHERTM   Coherent (Rayleigh) total cross         A3.2-4,5

             section for a mixture of elements.



   COHETZ    Coherent (Rayleigh) total cross         A3.2-5

             section for an element.



   COMPDM    Compton differential cross section      A3.2-5

             for a mixture of elements.



   COMPFM    "One argument" form for COMPDM.         A3.2-5



   COMPRM    Compton cross section, integrated over  A3.2-5

             some energy range, for a mixture of

             elements.



   COMPTM    Compton total cross section for a       A3.2-4,5

             mixture of elements.



   CRATIO    Coherent (Rayleigh) cross section ratio A3.2-5



   DCADRE    Quadrature routine to integrate         A3.2-7-10,19

             f(x) between a and b using cautious

             Romberg extrapolation.



   EBIND     Function to get an average photo-       A3.2-4,5

             electric binding energy.



   EBR1      Function to determine the electron(-)   A3.2-5

             branching ratio (Brem/Total).



   EDEDX     Evaluates SPTOTE with cutoff energies   A3.2-5

             of AE and AP.



   ESIG      Determines the total electron(-)        A3.2-5

             interaction cross section (prob-

             ability per radiation length).



   FCOULC    Coulomb correction term in pair         A3.2-5,7,9

             production and bremsstrahlung cross

             sections.



   FI        Function multiplexer.                   A3.2-1,5,6



   GBR1      Function to determine the gamma-ray     A3.2-5

             branching ratio (Pair/Total).



   GBR2      Function to determine the gamma-ray     A3.2-5

             branching ratio ((Pair+Compton)/Total).



   GMFP      Function to determine the gamma-ray     A3.2-5,11,

             mean free path.                         A3.3-18,19



   IFUNT     Given PEGS function name, it looks it

             up name in table and returns the

             function index.  Used by options that

             specify functions by name.



   PAIRDR    Pair production differential cross      A3.2-5,10,18

             section for a "run-time" mixture of

             elements.



   PAIRDZ    Pair production differential cross      A3.2-5,9,18

             section for an element.



   PAIRFR    "One argument" form of PAIRDR.          A3.2-5,10



   PAIRFZ    "One argument" form of PAIRDZ.          A3.2-5,10



   PAIRRM    Pair production cross section, inte-    A3.2-5,9

             grated over some energy range, for a

             mixture of elements.



   PAIRRR    Pair production cross section, inte-    A3.2-5,10,11

             grated over some energy range, for a

             "run-time" mixture of elements.



   PAIRRZ    Pair production cross section, inte-    A3.2-5,9

             grated over some energy range, for an

             element.



   PAIRTE    "Empirical" total pair production       A3.2-5,9

             production cross section for a

             mixture (=SUM(PZ(I)*PAIRTZ(Z(I))).



   PAIRTM    Pair production total cross section     A3.2-5,9

             for a mixture of elements, obtained

             by numerical integration of differ-

             ential cross section.



   PAIRTR    Pair production total cross section     A3.2-5,10

             for a "run-time" mixture of elements.



   PAIRTU    Pair production total cross section     A3.2-4,5,9

             actually "used".  Same as PAIRTE for

             primary energy less than 50 MeV;

             otherwise, same as PAIRTM.



   PAIRTZ    Computes contribution to empirical      A3.2-5,9,11

             pair production total cross section

             for an element assuming one atom per

             molecule.  It is obtained by log-linear

             interpolation of Israel-Storm data.



   PBR1      Function to determine the positron      A3.2-5,11

             branching ratio (Brem/Total).



   PBR2      Function to determine the positron      A3.2-5,11

             branching ratio ((Brem+Bhabha)/Total).



   PDEDX     Evaluates SPTOTP with cutoff energies   A3.2-5

             of AE and AP.



   PHOTTE    Determines the proper mix of PHOTTZ's   A3.2-4,5

             for a mixture.



   PHOTTZ    Determines the interpolated total       A3.2-5

             photoelectric cross section from

             tabulated data.



   PSIG      Determines the total positron           A3.2-5

             interaction cross section (prob-

             ability per radiation length).



   QD        Driver function for DCADRE, the         A3.2-7-10

             numerical integration routine.



   QFIT      Utility logical function for the        A3.2-4,

             piecewise linear fit subroutine, PWLF1. A3.3-14,15

             It returns .TRUE. if a given parti-

             tion gives a good fit.



   SPIONB    Does the work for SPIONE and SPIONP.    A3.2-7

             One argument tells whether to compute

             stopping power for electron or positron.



   SPIONE    Calculates the stopping power due to    A3.2-5,7

             ionization for electrons(-).



   SPIONP    Calculates the stopping power due to    A3.2-5,7

             ionization for positrons.



   SPTOTE    Calculates the total stopping power     A3.2-4,5,7

             (ionization plus soft bremsstrahlung)

             for electrons(-) for specified cutoffs.



   SPTOTP    Calculates the total stopping power     A3.2-4,5,7,19

             (ionization plus soft bremsstrahlung)

             for positrons for specified cutoffs.



   TMXB      Determines the maximum total step       A3.2-5

             length consistent with Bethe's

             criterion.



   TMXS      Determines the minimum of TMXB and      A3.2-5

             10 radiation lengths.



   TMXDE2    Included for possible future modifi-    A3.2-5

             cation purposes (=TMXB/(E**2*BETA**4)).

             It might be easier to fit this quantity

             than to fit TMXB and then apply the

             the denominator in EGS at run-time.



   XSIF      Function to account for bremsstrahlung  A3.2-5,7,9

             and pair production in the field of

             the atomic electrons.



   ZTBL      Given the atomic symbol for an element,

             it returns the atomic number.




A3.3 PEGS Options and Input Specifications


A3.4 Concluding Remarks

In the previous sections we have seen the various uses for PEGS. We summarize by giving the option sequences most generally used.


-----------------------------------------------------------------

  A. Minimal material data set creation (for use by EGS).

-----------------------------------------------------------------

         1.  ELEM (or MIXT, or COMP)

         2.  ENER

         3.  PWLF

         4.  DECK





-----------------------------------------------------------------

  B. Same as A. with default plots of all the functions

     that the PWLF option fits.

-----------------------------------------------------------------

         1.  ELEM (or MIXT, or COMP)

         2.  ENER

         3.  TEST

         4.  PWLF

         5.  DECK





-----------------------------------------------------------------

  C. Comparison of theoretical and sampled distributions

     by means of the HPLT option.

-----------------------------------------------------------------

         1.  ELEM (or MIXT, or COMP)

             Note: Data cards should agree with those used

                   with the UCTESTSR run.

         2.  HPLT

             Note: Output data from UCTESTSR run.





-----------------------------------------------------------------

  D. Selective plotting of various functions.

-----------------------------------------------------------------

         1.  ELEM (or MIXT, or COMP) - for material 1

         2.  PLTN  -  for function 1

         3.  PLTN  -  for function 2,....etc.

         4.  ELEM (or MIXT, or COMP) - for material 2,....etc.

         5.  PLTN  -  for function 1

         6.  PLTN  -  for function 2,....etc.




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