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1 *
2 * $Id$
3 *
4 * $Log$
5 * Revision 1.1.1.1  1995/10/24 10:21:19  cernlib
6 * Geant
7 *
8 *
9 #include "geant321/pilot.h"
10 #if defined(CERNLIB_DOC)
11 *CMZ :  3.21/02 29/03/94  15.41.21  by  S.Giani
12 *-- Author :
13 *
14 ************************************************************************
15 *                                                                      *
16 *                  Introduction to the section PHYS                    *
17 *                  --------------------------------                    *
18 *                                                                      *
19 *                                                                      *
20 * THE PHYSICS PROCESSES                                                *
21 *                                                                      *
22 *  The processes  currently implemented in GEANT3  can be classified   *
23 * as follows:                                                          *
24 *                                                                      *
25 * - Decays in flight                                                   *
26 * - Multiple scattering (Gaussian or Moliere)                          *
27 * - Continuous electromagnetic processes                               *
28 * - Discrete electromagnetic processes                                 *
29 * - Hadronic interactions                                              *
30 * - Muon nucleus-interactions.                                         *
31 *                                                                      *
32 *  The  fist  two  are  controlled  by  the  routines  GDECAY  which   *
33 * generates the decay products and  GMULTS which computes the change   *
34 * in  the angle  due to  multiple scattering  over a  given tracking   *
35 * step.   The  others  are  reviewed  separately  in  the  following   *
36 * paragraphs.                                                          *
37 *  For  convenience the  particles are  given a  'tracking type'  in   *
38 * GEANT, depending on their interaction with matter:                   *
39 *                                                                      *
40 *   ITRTYP = 1  photon                                                 *
41 *            2  electron and positron                                  *
42 *            3  neutral particles                                      *
43 *            4  charged hadrons                                        *
44 *            5  muon                                                   *
45 *            6  'Geantino'                                             *
46 *            7  Cerenkov photon                                        *
47 *            8  Ion                                                    *
48 *                                                                      *
49 *  The  paragraph  5  gives  a  summary  of  the  physics  processes   *
50 * activated for  each type  of particle with  the momentum  range of   *
51 * validity when relevant.  GPHYSI controls the initialisation of the   *
52 * various processes.                                                   *
53 *                                                                      *
54 * CONTINUOUS ELECTROMAGNETIC PROCESSES                                 *
55 *                                                                      *
56 * GMOLI     Initializes Moliere scattering                             *
57 * GPROBI    initializes material 'constants'  used for computing the   *
58 *           probability of various interactions.                       *
59 * GDRELA    Control routine  to fill   DE/DX tables for  energy loss   *
60 *           due to ionisation.                                         *
61 * GDRELP    Calculates  energy loss  due to  ionisation for  charged   *
62 *           particles other than electrons and positrons.              *
63 * GDRELE    Calculates energy  loss due to ionisation  for electrons   *
64 *           and  positrons.  As  Moller  and  Bhabba scattering  are   *
65 *           treated  as discrete  processes the  energy loss  due to   *
66 *           ionisation is a function  of the electron kinetic energy   *
67 *           cut-off DCUTE below which these processes are treated as   *
68 *           a continuous energy loss [BASE 030, common /GCPHYS/].      *
69 * GBRELA    Initializes   Bremsstrahlung  cross-section   and  fills   *
70 *           energy  loss tables  for Bremsstrahlung.   Both formulae   *
71 *           depend on  the photon  energy cut-off BCUTE  below which   *
72 *           Bremsstrahlung is  treated as  a continuous  energy loss   *
73 *           [BASE 030, common /GCPHYS/].                               *
74 * GPRELA    Fills  DE/DX  tables  for  energy loss  by  direct  pair   *
75 *           production  for high  energy  muons.  The  corresponding   *
76 *           discrete process is not considered.                        *
77 * GRANGI    Calculates    the    stopping     range    tables    for   *
78 *           electron/positron, muon and proton.                        *
79 * GMULOF    Calculates the tables for the maximum step allowed to to   *
80 *           continuous processes: Bending  in magnetic field, energy   *
81 *           loss and multiple scattering.                              *
82 * GCOEFF    Calculates  the   interpolation  coefficients   for  the   *
83 *           energy/Range relation  to be used in  the calculation of   *
84 *           the energy loss.                                           *
85 *                                                                      *
86 * DISCRETE ELECTROMAGNETIC PROCESSES                                   *
87 *                                                                      *
88 *   For the simulation of each  given discrete physics process three   *
89 * tasks have to be performed:                                          *
90 *                                                                      *
91 * - The evaluation  of the step  length.  This is computed  from the   *
92 *   updated  probability for  the  occurrence of  the process.   The   *
93 *   corresponding code  has been  inserted directly in  the tracking   *
94 *   routines for each tracking type as appropriate.                    *
95 * - After transport  of the  particle, the  generation of  the final   *
96 *   state particles (GEANT routines GPHOT, GCOMP, etc.)                *
97 * - If the  particle survives  after the interaction,  recompute the   *
98 *   probability.                                                       *
99 *                                                                      *
100 *   It should be outlined that the  evaluation of the step length is   *
101 * made independently  for each  process which  can occur,  the final   *
102 * step  size  being the  minimum  of  all  and the  process  finally   *
103 * considered being the corresponding one.                              *
104 *                                                                      *
105 * GPHOTI    Tabulates  cross-section  for photo-electric  effect  at   *
106 *           initialisation time                                        *
107 * GPHOT     Simulates photo-electric mechanism                         *
108 * GCOMPI    Tabulates  cross-section  for  Compton  intersection  at   *
109 *           initialisation time                                        *
110 * GCOMP     Simulates Compton scattering                               *
111 * GPRSGA    Tabulates   cross-section   for   pair   production   at   *
112 *           initialisation time                                        *
113 * GPAIRG    Simulates electron pair production by photons              *
114 * GBRSGA    Tabulates    cross-section    for   Bremsstrahlung    at   *
115 *           initialisation time                                        *
116 * GBREME    Simulates  hard  Bremsstrahlung   by  electrons.  -  see   *
117 *           cut-off BCUTE in routine GBRELA above                      *
118 * GDRSGA    Tabulates cross-section for  delta-ray at initialisation   *
119 *           time                                                       *
120 * GDRAY     Simulates delta rays (Moller or Bhabba scattering) - see   *
121 *           cut-off DCUTE in routine GDRELE above                      *
122 * GANNII    Tabulates  cross-section  for positron  annihilation  at   *
123 *           initialisation time                                        *
124 * GANNI     Simulates positron annihilation in flight                  *
125 * GANNIR    Simulates positron annihilation at rest.                   *
126 * GPFISI    Tabulates cross-section for photo-fission                  *
127 * GPFIS     Simulates photo-fission                                    *
128 *                                                                      *
129 * HADRONIC PROCESSES                                                   *
130 *                                                                      *
131 *   For GHEISHA:                                                       *
132 * GPGHEI    returns the hadronic cross section                         *
133 * GHEISH    Simulates  hadronic  interactions, program  GHEISHA  (H.   *
134 *           Fesefeldt) in GEANH file.                                  *
135 *                                                                      *
136 *   For FLUKA:                                                         *
137 * FLDIST    returns the hadronic cross section                         *
138 * FLUFIN    Simulates    hadronic   interactions,    program   FLUKA   *
139 *           (A.Ferrari et al.) in GEANH file.                          *
140 *                                                                      *
141 * MUON INTERACTION                                                     *
142 *                                                                      *
143 * GBRELM    Tabulates energy loss by soft Bremsstrahlung               *
144 * GBRSGM    Tabulates cross-section for hard Bremsstrahlung            *
145 * GBREMM    Generates hard Bremsstrahlung                              *
146 * GPAIRI    Tabulates cross-section for direct pair production         *
147 * GPAIRM    Generate direct pair production                            *
148 * GMUNUI    Tabulates cross-section for nuclear interaction            *
149 * GMUNU     Generates nuclear interaction                              *
150 * GDRELM    Tabulates energy loss by soft delta rays                   *
151 * GDRSGA    Tabulates cross-section for hard delta rays                *
152 * GDRAY     Generates delta rays                                       *
153 *                                                                      *
154 ************************************************************************
155 #endif