Geant4 example rdecay02 radioactive particles do not travel far

Hi I am running geant4 examples in radioactivity. I am running rdecay02 example. I am studying how far radioactive particle travels if I use u238c.mac file.

for that I have added code which checks x,y,z position at each step along with A and Z. I kept the medium (Target and Detector) as Air. So that radioactive particles can travel as far as possible.

But I found out that although detector length is 20cm. all the radioactive particles travel only till around 20 micrometers (um).

Why is that?

The behavior you observed might be due to the physics processes included in the simulation. By default, the rdecay02 example uses the “QGSP_BIC” physics list, which includes a set of physics processes that might be limiting the range of particles in the simulation.

In addition, the “Detector” in the rdecay02 example is a thin foil, which might not be enough to stop high-energy particles. If you want to simulate the behavior of radioactive particles over a longer range, you might consider increasing the thickness of the detector or changing the material to a higher-density one.

You might also want to check the energy distribution of the radioactive particles in the u238c.mac file. If the energy is too low, the range of the particles will be limited due to energy loss processes like ionization, bremsstrahlung, and pair production.

Lastly, keep in mind that the behavior of radioactive particles in real-world scenarios is complex and depends on many factors, such as the type and energy of the radioactive source, the surrounding materials, and the geometry of the setup. A careful analysis of the problem and the physical processes involved is necessary to obtain accurate results.

Thank you so much for the reply. I am solving this problem by adding superficial velocity to the particle at each step until it reaches the boundary of geometry. I have two approaches to this:

  1. create a custom physics process that extends G4VContinuousProcess where the AlongStepDoIt() function I can add a small amount of velocity in current velocity in each step. But in this my particle is traveling all along my geometry I am not able to get time information. All localTime, globalTime, and PropertTime values are 0. One doubt is which property should I change: velocity, kinetic energy, or momentum as all the three are convertible to one another.

  2. directly adding extra velocity in stepping action. I am not able to figure out the exact reason for it. This does not work (changes are not applied to particles). The particle does not travel far.