|Message: Why electron increases in energy when traveling in uniform magnetic field?||Not Logged In (login)|
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Dear GEANT4 experts,
before trying a simulation of detector in a combined electromagnetic field, I tried a simpler case I am interested in:
Particle: 1.0 MeV e- Field: Uniform magnetic field along x axis, 4.0 tesla Detector: 2mm silicon
I modify somewhat Em5 example, and also have a look at N04 novice example for the magnetic field definition.
My problem: the energy deposited in Si detector is greater then the starting kinetic energy of electron. I print out the kinetic energy of e- and its position at every step and see the electron gains energy in the uniform magnetic field. Is this a bug? I get the same behavior using
void Em5Field::GetFieldValue(const double Point,double *Bfield) const
to set a field value (as in N04), and
void Em5DetectorConstruction::SetMagField(G4double fieldValue)
to set a field value (as in Em5 example).
The increase in energy apparently depend on the initial momentum direction of e-.
I am trying to see what is a reason for (unphysical) boost in kinetic energy. Is this due to rounding errors in tracking or ...? Should I set some step size to a smaller value to increase a tracking precision?
Because I will be eventually interested in simulating the neutron beta decay electron (with a maximum energy 0.8 MeV) detected in a Si counter after traveling ca. 1.5 meters in ~4 tesla magnetic field, this behavior obviously renders the simulation unusable...
Am I missing something? Cheers, Emil email@example.com
P.S. Here is kinetic energy in MeV in first column followed by position of e- in mm, until e- stops in 2 mm of Si centered at x=150 cm Initial energy: 1.0 MeV, deposited energy: 1.08308 MeV
---> Begin of Event: 0 1 KinEn e- (0.70713,0.62626,0.28086) mm 1.0001 KinEn e- (1.4142,0.83297,0.93536) mm 1.0001 KinEn e- (2.1213,0.48164,1.525) mm 1.0002 KinEn e- (2.8284,-0.1924,1.6548) mm 1.0002 KinEn e- (3.5354,-0.73762,1.2377) mm 1.0003 KinEn e- (4.2424,-0.78879,0.55319) mm 1.0003 KinEn e- (4.9494,-0.31162,0.059663) mm 1.0003 KinEn e- (5.6564,0.37432,0.087722) mm 1.0004 KinEn e- (6.3634,0.80963,0.6186) mm 1.0004 KinEn e- (7.0703,0.70277,1.2968) mm 1.0005 KinEn e- (7.7772,0.12529,1.6681) mm 1.0005 KinEn e- (8.4841,-0.53615,1.484) mm 1.0005 KinEn e- (9.191,-0.83866,0.86757) mm 1.0006 KinEn e- (9.8978,-0.57967,0.23164) mm 1.0006 KinEn e- (10.605,0.067433,0.0019294) mm 1.0007 KinEn e- (11.311,0.66946,0.33224) mm 1.0007 KinEn e- (12.018,0.82339,1.0015) mm 1.0008 KinEn e- (12.725,0.42617,1.5617) mm 1.0008 KinEn e- (13.432,-0.25635,1.6379) mm 1.0008 KinEn e- (14.138,-0.76736,1.179) mm 1.0009 KinEn e- (14.845,-0.76485,0.49222) mm 1.0009 KinEn e- (15.552,-0.25048,0.037082) mm 1.001 KinEn e- (16.258,0.43157,0.11819) mm 1.001 KinEn e- (16.965,0.82489,0.68129) mm 1.001 KinEn e- (17.672,0.66631,1.3496) mm 1.0011 KinEn e- (18.378,0.061903,1.676) mm 1.0011 KinEn e- (19.085,-0.58398,1.4421) mm 1.0012 KinEn e- (19.791,-0.83925,0.80435) mm 1.0012 KinEn e- (20.498,-0.53312,0.18935) mm 1.0013 KinEn e- (21.204,0.12966,0.0084996) mm 1.0013 KinEn e- (21.911,0.70578,0.38279) mm 1.0013 KinEn e- (22.617,0.8099,1.0619) mm 1.0014 KinEn e- (23.324,0.37237,1.5917) mm 1.0014 KinEn e- (24.03,-0.31423,1.6178) mm 1.0015 KinEn e- (24.736,-0.79077,1.1228) mm 1.0015 KinEn e- (25.443,-0.73858,0.4376) mm 1.0015 KinEn e- (26.149,-0.19254,0.020422)
..... deleted .....
1.0831 KinEn e- (1498.4,0.51728,1.6226) mm 1.0831 KinEn e- (1499,-0.11084,1.7409) mm 0.83218 KinEn e- (1499.7,-0.36039,1.6732) mm 0.6459 KinEn e- (1499.9,-0.80863,1.2929) mm 0.43104 KinEn e- (1499.7,-0.49025,1.396) mm 0.27809 KinEn e- (1499.8,-0.70194,1.4364) mm 0.13182 KinEn e- (1499.9,-0.79351,1.544) mm 2.6926e-11 KinEn e- (1499.9,-0.8145,1.5381) mm Run terminated. Run Summary Number of events processed : 1 User=0.23s Real=0.29s Sys=0s ================== run summary ===================== end of Run TotNbofEvents = 1 mean charged track length in absorber=2.83012 +- 0 mm
mean energy deposit in absorber=1.08308 +- 0 MeV
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