Cs-137 Decay Simulation

Particles, Track, Event, Run and Biasing
1

Dear, G4 User

I am analysing the detector signal using the Cs-137 source term.

I registered ‘RadioactiveDecayPhysics’ in the physics list and here is a snippet of the .mac file that defines Cs-137.

# Macro file: run.mac

/run/verbose 1
/tracking/verbose 1

# gps example (isotropic gamma point source, 1 MeV at origin)
/gps/particle ion
/gps/ion 55 137
/gps/pos/type Point
/gps/pos/centre 0 0 0 cm
/gps/direction 0 0 -1
/gps/ene/type Mono
/gps/ene/mono 0 eV 
#/gps/ang/type iso
#/gps/energy 3.0 MeV 

/run/beamOn 10

Currently, the process of Cs137 decaying to Ba137m and emitting 662 keV gamma can be observed ‘intermittently’ via verbose.

As far as I know, this decay process occurs 85% of the time, but 662 keV gamma rays are only observed occasionally.

Therefore, if we increase beamOn significantly and observe the fraction, we get 662 keV emitted, which is roughly 12%.

The physicslist I defined is shown below.

    // EM Physics
    RegisterPhysics(new G4EmStandardPhysics_option3()); 

    // Decay
    RegisterPhysics(new G4DecayPhysics());

    // Radioactive decay
    RegisterPhysics(new G4RadioactiveDecayPhysics());

Please share your knowledge and experience with this phenomenon.

Best

Junsung

Geant4 Version: geant4-10-07-patch-03
Operating System: window-WSL
Compiler/Version: 11.3.0
CMake Version: 3.22.1

2

Maybe you should add

/process/had/rdm/thresholdForVeryLongDecayTime 1.0e+60 year

in the macro file to set a long enough time so that all atoms can decay into stable nuclides.

3

@Dong-Minghao22

Thank you for your response.

When I added the code snippet you mentioned to the .mac, I got “Batch is interrupted!!” is printed.

I know it’s a hassle, but can you tell me how to add it to the .mac?

4

You can refer to the examples in /extended/radioactivedecay, just add the command after the initialization.

5

1- The command suggested by @Dong-Minghao22 is only for 11.2 and toward.
In 10.7p3 you must not put this command …

2- attached, a macro for rdecay01, its printout, and the plot of gamma.

cesium.mac.txt (416 Bytes)
cesium.out.txt (2.3 KB)

cesium
cesium698×475 26.9 KB

6

@Dong-Minghao22 and @maire1

Thank you for your response.

Thanks to your comments, we have identified the reason for this discrepancy.

If I don’t define the source energy, the initial Cs137 particle has 1 MeV (default).

So I set it to 0 keV to define a source, and this was the problem: when I annotated this snippet, I could observe 662 keV with 85% probability.

I also noticed that rdecay01 does not use the same snippet as above to define isotopes.

I now want to evaluate the impact on the initial energy (1 MeV).

Best

Junsung