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## Step time calculation

Forum: Event and Track Management
Date: 27 Aug, 2013
From: Benjamin F <Benjamin F>

 Hello, I am finding problems with calculating the step time in G4. I generate a primary particle (37K +1 ion) with essentially zero initial velocity (10^-5 mm/ns) and watch it propagate in a uniform electric field before striking a detector and recording the local time (or global time). Given the step length, final and initial velocities it should be simple to calculate the step time (and this is confirmed in the Geant Physics Reference Manual). I have tried various electric field stepper types but none work satisfactorily. Below is the output when I turn on tracking/verbose/3. You can see that the expected time difference based on the formula in the reference manual is 468.4 ns and the reported time is 470.3 ns. (This is just one event; other events are similarly off but not by exactly the same ratio or amount). The stepper here used is G4CashKarpRKF45. ```>>AlongStepDoIt (after all invocations): ++List of invoked processes 1) Transportation 2) msc 3) ionIoni``` ``` ++G4Step Information Address of G4Track : 0x1a7f310 Step Length (mm) : 10 Energy Deposit (MeV) : 1.187306976999772e-11 ----------------------------------------------------------------------- StepPoint Information PreStep PostStep ----------------------------------------------------------------------- Position - x (mm) : 00.002694155277345721 Position - y (mm) : 0 9.999934290837558 Position - z (mm) : 0-0.002315248395075974 Global Time (ns) : 0 470.3252800447956 Local Time (ns) : 0 470.3252800447956 Proper Time (ns) : 0 470.3252800447954 Momentum Direct - x : 0.72757967933865550.0001333171207950369 Momentum Direct - y : -0.2822887763974083 0.9999999845504328 Momentum Direct - z : -0.6252526344874632-0.0001145673571795582 Momentum - x (MeV/c): 0.00065797370979303850.0006579736987469881 Momentum - y (MeV/c): -0.0002552828215432984 4.935402779911176 Momentum - z (MeV/c): -0.000565436071339341-0.0005654360618468107 Total Energy (MeV) : 34439.98428241977 34439.98463605234 Kinetic Energy (MeV): 1.187306976999772e-110.000353632583392034 Velocity (mm/ns) : 7.872011835876924e-06 0.04296159156586455 Volume Name : world_phys world_phys Safety (mm) : 00.002250170179225464 Polarization - x : 0 0 Polarization - y : 0 0 Polarization - Z : 0 0 Weight : 1 1 Step Status : Undefined PostStep Proc Process defined Step: Undefined StepLimiter -----------------------------------------------------------------------``` ` ++List of secondaries generated (x,y,z,kE,t,PID): No. of secodaries = 0` ``` Thanks in advance for your help! ```

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