Hi, all:
I am simulating a pi+ particle with 50GeV energy in the water medium, using FTFP_BERT physics module.
I found there some some chances that geant4 will produce a ~1e-5 MeV energy gamma particle (via pi- hBertiniCaptureAtRest process). This extrem low energy gamma will continue to be rayleigh scattered and will never be absorbed. Thus the simulation is caught in endless loop.
Here are some excerpts of the simulation output:
G4WT0 > *********************************************************************************************************
G4WT0 > * G4Track Information: Particle = pi-, Track ID = 5435, Parent ID = 5225
G4WT0 > *********************************************************************************************************
G4WT0 >
G4WT0 > Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName
G4WT0 > 0 2.66e+03 74.3 712 141 0 0 0 World initStep
G4WT0 > 1 2.66e+03 78 707 139 1.19 6.35 6.35 World hIoni
G4WT0 > 2 2.66e+03 91.1 688 134 4.77 23.2 29.5 World hIoni
G4WT0 > 3 2.66e+03 96 681 131 1.79 8.67 38.2 World hIoni
G4WT0 > 4 2.66e+03 111 659 125 5.27 26.2 64.4 World hIoni
G4WT0 > 5 2.66e+03 121 645 121 3.77 17.4 81.8 World hIoni
G4WT0 > 6 2.67e+03 153 600 108 12.5 55.6 137 World hIoni
G4WT0 > 7 2.67e+03 163 588 104 3.24 15.3 153 World hIoni
G4WT0 > 8 2.67e+03 182 561 96.3 6.85 33.3 186 World hIoni
G4WT0 > 9 2.67e+03 199 537 89.1 6.64 28.5 215 World hIoni
G4WT0 > 10 2.67e+03 199 536 88.6 0.256 1.45 216 World hIoni
G4WT0 > 11 2.67e+03 214 517 81.5 6.24 24.2 240 World hIoni
G4WT0 > 12 2.67e+03 216 513 79.6 1.5 4.87 245 World hIoni
G4WT0 > 13 2.67e+03 227 498 74 4.5 18 263 World hIoni
G4WT0 > 14 2.66e+03 236 485 69.3 3.99 15.5 279 World hIoni
G4WT0 > 15 2.66e+03 242 476 65.1 3.04 11.2 290 World hIoni
G4WT0 > 16 2.66e+03 255 457 58.1 6.56 23.4 313 World hIoni
G4WT0 > 17 2.66e+03 269 437 51.2 6.92 24.6 338 World hIoni
G4WT0 > 18 2.66e+03 280 420 44.4 6.48 19.7 357 World hIoni
G4WT0 > 19 2.66e+03 288 407 39.3 5.15 15.8 373 World hIoni
G4WT0 > 20 2.66e+03 293 401 36.2 2.78 7.62 381 World hIoni
G4WT0 > 21 2.66e+03 299 392 31.7 4.44 11.1 392 World hIoni
G4WT0 > 22 2.66e+03 300 391 31 0.36 1.09 393 World hIoni
G4WT0 > 23 2.66e+03 304 384 27.5 3.48 8.58 402 World hIoni
G4WT0 > 24 2.66e+03 308 378 24.1 3.47 7 409 World hIoni
G4WT0 > 25 2.65e+03 310 374 21.4 2.34 4.02 413 World hIoni
G4WT0 > 26 2.65e+03 312 370 18.9 2.46 4.56 417 World hIoni
G4WT0 > 27 2.65e+03 314 367 16.7 2.22 3.71 421 World hIoni
G4WT0 > 28 2.65e+03 316 365 14.6 2.14 3 424 World hIoni
G4WT0 > 29 2.65e+03 317 363 12.7 1.84 2.39 426 World hIoni
G4WT0 > 30 2.65e+03 318 362 10.9 1.82 1.91 428 World hIoni
G4WT0 > 31 2.65e+03 319 360 9.52 1.41 1.49 430 World hIoni
G4WT0 > 32 2.65e+03 320 359 8.12 1.4 1.2 431 World hIoni
G4WT0 > 33 2.65e+03 320 359 6.99 1.13 0.939 432 World hIoni
G4WT0 > 34 2.65e+03 321 358 5.89 1.09 0.753 433 World hIoni
G4WT0 > 35 2.65e+03 321 358 4.96 0.934 0.595 433 World hIoni
G4WT0 > 36 2.65e+03 321 357 4.23 0.726 0.476 434 World hIoni
G4WT0 > 37 2.65e+03 321 357 3.48 0.759 0.395 434 World hIoni
G4WT0 > 38 2.65e+03 322 357 2.57 0.908 0.319 434 World hIoni
G4WT0 > 39 2.65e+03 322 356 1.83 0.735 0.242 435 World hIoni
G4WT0 > 40 2.65e+03 322 356 0.994 0.84 0.184 435 World hIoni
G4WT0 > 41 2.65e+03 322 356 0.066 0.928 0.0909 435 World hIoni
G4WT0 > 42 2.65e+03 322 356 0 0.066 0.00164 435 World hIoni
G4WT0 > 43 2.65e+03 322 356 0 0 0 435 World hBertiniCaptureAtRest
G4WT0 > Track (trackID 5435, parentID 5225) is processed with stopping code 2
...
...
SOME OTHER SECONDERIES PROCESSING
...
...
G4WT0 > *********************************************************************************************************
G4WT0 > * G4Track Information: Particle = gamma, Track ID = 5589, Parent ID = 5435
G4WT0 > *********************************************************************************************************
G4WT0 >
G4WT0 > Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName
G4WT0 > 0 2.65e+03 322 356 1.21e-05 0 0 0 World initStep
G4WT0 > 1 2.65e+03 321 357 1.21e-05 0 1.18 1.18 World Rayl
G4WT0 > 2 2.65e+03 321 356 1.21e-05 0 0.652 1.83 World Rayl
G4WT0 > 3 2.65e+03 317 353 1.21e-05 0 6.84 8.68 World Rayl
G4WT0 > 4 2.67e+03 307 327 1.21e-05 0 34.6 43.3 World Rayl
G4WT0 > 5 2.65e+03 294 327 1.21e-05 0 21.4 64.7 World Rayl
G4WT0 > 6 2.64e+03 281 336 1.21e-05 0 18.4 83.1 World Rayl
G4WT0 > 7 2.64e+03 279 337 1.21e-05 0 2.88 85.9 World Rayl
G4WT0 > 8 2.64e+03 277 341 1.21e-05 0 5.92 91.9 World Rayl
G4WT0 > 9 2.64e+03 278 341 1.21e-05 0 3.25 95.1 World Rayl
G4WT0 > 10 2.64e+03 278 343 1.21e-05 0 3.31 98.4 World Rayl
G4WT0 > 11 2.66e+03 268 348 1.21e-05 0 21.9 120 World Rayl
G4WT0 > 12 2.66e+03 269 347 1.21e-05 0 1.76 122 World Rayl
G4WT0 > 13 2.66e+03 268 346 1.21e-05 0 1.61 124 World Rayl
G4WT0 > 14 2.67e+03 268 341 1.21e-05 0 7.35 131 World Rayl
G4WT0 > 15 2.67e+03 265 340 1.21e-05 0 3.01 134 World Rayl
G4WT0 > 16 2.66e+03 264 337 1.21e-05 0 5.25 139 World Rayl
G4WT0 > 17 2.66e+03 263 338 1.21e-05 0 1.05 140 World Rayl
...
...
CONTINUE SCATTERING
...
...
I am wondering why pi- capture at rest will produce such a low energy gamma particle and why this particle is not absorbed.
Thanks