PhysicsList for ionizing radiation shielding

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_Geant4 Version: 11.1.0
_Operating System: Windows 10
_Compiler/Version: Visual Studio 17.9
_CMake Version: 3.25.1

Hello everybody,

I am simulating the mass attenuation coefficient for different compounds using gamma radiation at various energy ranges.

Which physics lists should I use to ensure accurate results?

Thanks in advanced

To calculate mass attenuation coefficient you must calculate as a counter of the gammas with and without target.
I = no of gammas after target
I0 = no. of gammas hitting target

You can use
#include “Shielding.hh”

as it already includes “G4EmStandardPhysics_option4.hh” or else you can choose only

Source: Shielding Physics List Description


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Thank you for your response.

Do you mean I need to count number of photons reach the detector with and without the target? For example if I start with 100000 primaries this will be Io and I will be the number of gamma reaches the detector. Is that correct?

Second thing, is “Shielding.hh” is enough for low gamma energy such as 0.511 MeV?

I appreciate your responses.

The most current documentation can be found here:

and in particular the Electromagnetic options are here:

Have a read and confirm they cover the energy range you are interested in.


Thank you all.

I just want to confirm if all I need is to record the “number” of photons with and without a shielding material. Is that correct or should I record something else?

Best regards


Yes only photons with ParentID()==1
Kill all secondaries.


Thank you. Very helpful

Hi again,

Should ParentID()==1 or 0 ? To my understanding, if ParentID()==0 then this is a primary, otherwise it is a secondary.

Am I correct?
Thank you for your response and collaboration


Yes … parent_ID = 0 indicates a primary particle


Hi again
I shoot 1000 gamma photons with 0.511 MeV to the NaI detector. The target is to count how many photons reach the detector. Every time I get 6644577 photons reach the detector.
I am attaching some of my files: (1.8 KB) (706 Bytes) (974 Bytes) (1.9 KB)

Any idea or guidance will be highly appreciated

@drvijayraj any help please?
Should I construct a sensitive detector to get an accurate number?
I also gun 1 photon and get 4 in the detector.

Thanks in advance

Dear @OdaiSuad

If you check example B1 then you can have an idea how you can have integrated counts in a scoring volume [detector/target/both].
Score at the end of event or at end of run via PostUserTrackingAction.

Since you are not doing any Physics for creating secondaries therefore you may opt em_op1.

PhysicsList = new G4EmStandardPhysics_option1();

Scoring …


In generating particles you can restrict it to 1 in PGA [better choice];

fParticleGun = new G4ParticleGun(1);

Add eventID when scoring.

Please look testem0 and em1 example for further understanding

Hi Dear @drvijayraj

I am a newcomer and would like to understand how to count the number of particles based on recorded energy deposition. Could you please explain the underlying logic? :pray:

Dear @saimegemenyucel ,

please do not hijack someone else’s thread. To get your question read by the people in the forum please create your own.


I did not mean to hijack. I already post my own questions but still could not figure this. Since my question is related I wanted to ask also here. Maybe this can also help to question owner too I believe.

Dear @saimegemenyucel

Please look example B1, testem0 and testem1. It will help you to know how to count particles.

If you check testem1 TrackingAction lines 89 to 96

  if (aTrack->GetDefinition()->GetPDGCharge() == 0.) {
  } else {

This is how you will have counts in scoring volume.

The same you can do at the end of eventaction.

Please follow examples as said.

1 Like