Hi Dear geant4 user!
What is the difference between total energy and total energy deposit?
for example:
G4double energy = step->GetTotalEnergyDeposit();
and
G4double energy = preStepPoint->GetTotalEnergy();
Thanks for any answers.
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TotalEnergy = relativist energy of the particle at that point = kinetic energy + energy_mass
EnergyDeposit = “continuous” energy lost by the particle along the step = stepLength*stoppingPower
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Would EnergyDeposit() also be the energy a particle deposits in a detector?
Yes : the energy deposit in the present step
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Thank you!
When a particle enters a detector and I’m interested in how much energy the particle deposits there in total. Would this be one single step or is it more a sum of steps?
To specify even further: When the SetTrackStatus() is set to fStopAndKill, would there even be several steps?
But what is the difference between DeltaEnergy and DepositedEnergy? They should be equal, since energy which is transferred to secondaries is taken into account in both if I understand it correctly.
However, what I recently observed in a simulation is that the change in KineticEnergy per step of incident electrons stopping in a detector is different from the DepositedEnergy of the step in some cases. Can somebody explain why?
That’s not correct. The delta energy (change in kinetic energy) does, correctly, include both energy loss from deposits and energy transferred to secondaries. However, EnergyDeposit does not include secondaries at all. If it did, you would end up double counting because those secondaries themselves would go on and deposit energy.
Thank you for your reply! That means that one also has to keep track of the produced secondaries’ energy deposit then, if the total energy of the incident parent particle should be obtained. This corresponds to summing up the deposition of all (including secondaries) particles (approach 1).
According to the Book for Application Developers - Release 10.3:
Total energy deposited during the step - this is the sum of
– the energy deposited by the energy loss process, and
– the energy lost by secondaries which have NOT been generated because each of their energies was below the cut threshold
On the other hand, the total energy could equally be obtained by stepwise adding up the DeltaKineticEnergy (without secondary kinetic energies) of the parent particle and the TotalKineticEnergy at its last step (approach 2).
When using approach 2, of course I obtain the total energy as expected.
But with approach 1, I observe a minor fraction of events with total deposited energies well below the total initial energy (until almost 0).
Since no secondaries that are NOT generated carry energy away, I am wondering where this energy is left. (No escaping photons are produced in the investigated setup).
Why is there still a discrepancy between both approaches (why is the total energy deposit below the energy of the stopped particle)?
First, are you sure that you don’t have any escaping particles of any kind? Not just photons, but electrons, neutrinos, etc.?
Are you doing a simple electromagnetic simulation (electron beam, X-rays, etc.)? If there’s any hadronic physics involved (neutrons, proton beam), then you can have transmutation, and the binding energy difference isn’t something you’ll see. That can lead to both “missing” energy and also potentially large “excess” energy (e.g., a few tens of eV neutron captured onto Ge-70 will make Ge-71, which then decays with a 10.331 keV gamma).
Hey! I have a question about the TotalEnergyDeposit.
You correctly wrote that it is obtained multiplying the stopping power times the spe lenght, but my question is: how is the stopping power obtained? Do they use the Seltzer and Berger tables or do they integrate the cross sections obtained from the processes of MyPhysicsList?
thank you!
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Troncaded Berger-Seltzer or Bethe-Bloch formulae.
At least for standard electromagnetic physics .
For Livermore and Penelope, I do not remember exactly …
For detailed description, see Geant4 doc : Physics Reference Manual
or Geant4 Electromagnetic Physics courses
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