That is a rather unsatisfactory answer though. So here is an alternative way.
Since GSIM is a collection of 3 dimensional volumes, it is not an easy question to answer even with complete knowledge of the code. An easier question to answer is "What materials does an electron of 2 GeV at 40 degrees traverse?". This question can be answered by asking the code:
Here is a very simple way to get a "quick" list of the volumes that a particle traverses:
Use FFREAD cards: NOSEC 'ALL' so that you get only ONE track (else you will get several hundred secondaries in the EC).
Start interactive GSIM, gsim_int and give the following commands ( after # is my comment, don't type it):
next
dcut clas 2 0 10 10 0.015 0.015
# Draw pictue of sector 1 and 4.
swit 1 3
# Set interactive debug level to 3
kine 3 3 2. 2. 40. 40. 0. 0.
# electron (3) of 2 GeV at 40 degrees theta, 0 phi.
trig 1
You should see a track drawn on the picture, and a long list of GSIM info on the screen:
=====> TRACK 1 STACK NR
0 NTMULT= 1
ELECTRON
TOFG = 0.000 NS
X
Y Z
R NAME NUMBER SLENG
STEP DESTEP GEKIN
MECHANISMS
0.0000 0.0000
0.0000 0.0000 TARG 1
0.0000 0.0000 0.0 eV
1.999 GeV NULL
0.2493 0.0000
0.2971 0.2493 TARG 1
0.3878 0.3878 99.0 keV
1.999 GeV FIEL LOSS MULS
0.4300 -0.0002
0.5128 0.4300 TARG 1
0.6692 0.2814 52.3 keV
1.999 GeV FIEL NEXT LOSS MULS
0.4300 -0.0002
0.5128 0.4300 TGCL 1
0.6692 0.0000 0.0 eV
1.999 GeV NULL
0.4420 -0.0002
0.5271 0.4420 TGCL 1
0.6879 0.0187 61.5 keV
1.999 GeV NEXT LOSS MULS
0.4420 -0.0002
0.5271 0.4420 TG
1 0.6879 0.0000
0.0 eV 1.999 GeV NULL
0.7630 -0.0006
0.9105 0.7630 TG
1 1.1879 0.5000
0.0 eV 1.999 GeV FIEL SMAX
1.0841 -0.0010
1.2938 1.0841 TG
1 1.6879 0.5000
0.0 eV 1.999 GeV FIEL SMAX
1.4051 -0.0014
1.6771 1.4051 TG
1 2.1879 0.5000
0.0 eV 1.999 GeV FIEL SMAX
1.6303 -0.0017
1.9461 1.6303 TG
1 2.5388 0.3508
0.0 eV 1.999 GeV FIEL NEXT
1.6303 -0.0017
1.9461 1.6303 TGSI 1
2.5388 0.0000 0.0 eV
1.999 GeV NULL
1.6500 -0.0017
1.9696 1.6500 TGSI 1
2.5694 0.0307 123.0 keV 1.999
GeV NEXT LOSS MULS
1.6500 -0.0017
1.9696 1.6500 TG
1 2.5694 0.0000
0.0 eV 1.999 GeV NULL
1.9711 -0.0021
2.3529 1.9711 TG
1 3.0694 0.5000
0.0 eV 1.999 GeV FIEL SMAX
2.2923 -0.0024
2.7361 2.2923 TG
1 3.5694 0.5000
0.0 eV 1.999 GeV FIEL SMAX
2.6134 -0.0028
3.1194 2.6134 TG
1 4.0694 0.5000
0.0 eV 1.999 GeV FIEL SMAX
2.9345 -0.0032
3.5026 2.9345 TG
1 4.5694 0.5000
0.0 eV 1.999 GeV FIEL SMAX
3.2556 -0.0035
3.8859 3.2556 TG
1 5.0694 0.5000
0.0 eV 1.999 GeV FIEL SMAX
3.5767 -0.0039
4.2691 3.5767 TG
1 5.5694 0.5000
0.0 eV 1.999 GeV FIEL SMAX
3.8979 -0.0043
4.6524 3.8979 TG
1 6.0694 0.5000
0.0 eV 1.999 GeV FIEL SMAX
4.2190 -0.0047
5.0356 4.2190 TG
1 6.5694 0.5000
0.0 eV 1.999 GeV FIEL SMAX
4.4303 -0.0049
5.2879 4.4303 TG
1 6.8985 0.3291
0.0 eV 1.999 GeV FIEL NEXT
4.4303 -0.0049
5.2879 4.4303 GAS2 1
6.8985 0.0000 0.0 eV
1.999 GeV NULL
4.7514 -0.0053
5.6711 4.7514 GAS2 1
7.3985 0.5000 35.9 eV
1.999 GeV FIEL LOSS MULS SMAX
5.0726 -0.0056
6.0544 5.0726 GAS2 1
7.8985 0.5000 164.8 eV
1.999 GeV FIEL LOSS MULS SMAX
5.2078 -0.0058
6.2157 5.2078 GAS2 1
8.1090 0.2105 0.0 eV
1.999 GeV FIEL NEXT LOSS MULS
5.2078 -0.0058
6.2157 5.2078 FOI2 1
8.1090 0.0000 0.0 eV
1.999 GeV NULL
5.5289 -0.0062
6.5990 5.5289 FOI2 1
8.6090 0.5000 971.9 eV
1.999 GeV FIEL LOSS MULS SMAX
5.8500 -0.0066
6.9822 5.8500 FOI2 1
9.1090 0.5000 1.0 keV
1.999 GeV FIEL LOSS MULS SMAX
6.1711 -0.0069
7.3655 6.1711 FOI2 1
9.6090 0.5000 1.8 keV
1.999 GeV FIEL LOSS MULS SMAX
6.3744 -0.0072
7.6081 6.3744 FOI2 1
9.9256 0.3166 358.5 eV
1.999 GeV FIEL NEXT LOSS MULS
6.3744 -0.0072
7.6081 6.3744 WIND 1
9.9256 0.0000 0.0 eV
1.999 GeV NULL
6.3834 -0.0072
7.6189 6.3834 WIND 1
9.9396 0.0140 33.8 keV
1.999 GeV FIEL NEXT LOSS MULS
6.3834 -0.0072
7.6189 6.3834 FOI2 1
9.9396 0.0000 0.0 eV
1.999 GeV NULL
6.7045 -0.0076
8.0022 6.7045 FOI2 1
10.4396 0.5000 1.1 keV
1.999 GeV FIEL LOSS MULS SMAX
7.0256 -0.0081
8.3854 7.0256 FOI2 1
10.9396 0.5000 2.2 keV
1.999 GeV FIEL LOSS MULS SMAX
7.3466 -0.0086
8.7687 7.3466 FOI2 1
11.4396 0.5000 1.2 keV
1.999 GeV FIEL LOSS MULS SMAX
7.6677 -0.0091
9.1520 7.6677 FOI2 1
11.9396 0.5000 1.8 keV
1.999 GeV FIEL LOSS MULS SMAX
7.9888 -0.0096
9.5353 7.9888 FOI2 1
12.4396 0.5000 867.8 eV
1.999 GeV FIEL LOSS MULS SMAX
8.3098 -0.0101
9.9186 8.3098 FOI2 1
12.9396 0.5000 601.4 eV
1.999 GeV FIEL LOSS MULS SMAX
8.6309 -0.0105
10.3019 8.6309 FOI2 1
13.4396 0.5000 1.4 keV
1.999 GeV FIEL LOSS MULS SMAX
8.9520 -0.0110
10.6852 8.9520 FOI2 1
13.9396 0.5000 1.3 keV
1.999 GeV FIEL LOSS MULS SMAX
I guess it is fairly obvious what it prints out, you get the coordinates
of each "step", the volume it is in, the amount of energy lost and the
physics process that was applied to the particle (multiple scattering,
energy loss, magnetic field bending etc.)
A different printout is obtained from the "track_debugger" in clas_step.c
in the gsim code. This routine can be easily modified to include more information.
You turn it on with "swit 3 1". First turn off the other printout (swit
1 0) so you don't get both (which may be usefull, but is too much now.)
Printout:
[Trk# partname ] Volumes
Materials
(step# ) [ Pathlen, Delta ] Kin_e
Processes.
[ 1 0 ELECTRON ]: CLAS FOIL
GAS2 VOLM VH_4
CLAS L_He3
( 0) [ 0.0000, 0.0000] E: 1999.489
MeV
GUSER_STEP I: *** Default version of guser_step called
***
[ 1 0 ELECTRON ]: CLAS FOIL
GAS2 VOLM VH_4
CLAS L_He3
( 1) [ 0.5629, 0.5629] E: 1999.413
MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS FOIL
GAS2 VOLM VM_4
CLAS Mylar
( 2) [ 0.5683, 0.0053] E: 1999.401
MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS FOIL
GAS2 VOLM
CLAS Vacuum (
3) [ 0.9012, 0.3329] E: 1999.401 MeV FIEL NEXT
[ 1 0 ELECTRON ]: CLAS FOIL
GAS2 VOLM VM_3
CLAS Mylar
( 4) [ 0.9273, 0.0261] E: 1999.338
MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS FOIL
GAS2 VOLM
CLAS Vacuum (
7) [ 5.8743, 4.9471] E: 1999.338 MeV FIEL NEXT
[ 1 0 ELECTRON ]: CLAS FOIL
GAS2
CLAS He
( 9) [ 8.1056, 2.2313] E: 1999.337
MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS FOIL
FOI1 FOI2
CLAS Air
( 10) [ 9.9218, 1.8161] E: 1999.332 MeV FIEL
NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS FOIL
FOI1 FOI2 WIND
CLAS Mylar
( 11) [ 9.9358, 0.0140] E: 1999.299 MeV FIEL
NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS FOIL
FOI1 FOI2
CLAS Air
( 31) [ 46.7897, 36.8539] E: 1999.209 MeV FIEL NEXT LOSS
MULS
[ 1 0 ELECTRON ]: CLAS
CLAS Air
( 40) [ 63.3557, 16.5660] E: 1999.167 MeV FIEL NEXT LOSS
MULS
[ 1 0 ELECTRON ]: CLAS DC1A
ARG/CO2 90:10 (
43) [ 65.9700, 2.6143] E: 1999.161 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS1A
ARG/CO2 90:10 (
44) [ 65.9842, 0.0142] E: 1999.161 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS1A DW1A
ARG/CO2 90:10 (
46) [ 67.2593, 1.2751] E: 1999.157 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS1A
ARG/CO2 90:10 (
47) [ 67.2805, 0.0212] E: 1999.157 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS1A DW1A
ARG/CO2 90:10 (
49) [ 68.5675, 1.2870] E: 1999.154 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS1A
ARG/CO2 90:10 (
50) [ 68.5746, 0.0071] E: 1999.154 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS1A DW1A
ARG/CO2 90:10 (
52) [ 69.8734, 1.2988] E: 1999.151 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS1A DW1A
ARG/CO2 90:10 (
54) [ 71.1771, 1.3037] E: 1999.117 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
ARG/CO2 90:10 (
57) [ 73.9236, 2.7465] E: 1999.110 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS2A
ARG/CO2 90:10 (
58) [ 73.9366, 0.0130] E: 1999.110 MeV FIEL NEXT LOSS MULS
[ 1 0 ELECTRON ]: CLAS DC1A
DS2A DW2A
ARG/CO2 90:10 (
60) [ 75.1937, 1.2572] E: 1999.105 MeV FIEL NEXT LOSS MULS
Note that the information is similar, with the main difference that
the entire hiarchy of the volumes is given. It gives you a more exact idea
of where you are in the code.
To get the *material* that the particle steps through, either modify
the clas_step.c routine to add it in the printout, or look up the material
in the GSIM code.
If you need to customize the information in that is printed out, you want to do this in the routine: track_debugger in clas_step.c. If you need help, send an email to holtrop (at) jlab.org