After setting a cobalt 60 radioactive source in the rdecay01 example and typing the command /run/beamOn 10 nothing happens, why?

Considering the extended example rdecay01, why after setting a Cobalt 60 radioactive source with commands in the user interface neither secondary particles (trajectories) nor radioactive decays are observed?; That is, after opening the executable file for example rdecay01, I set the primary particle to be an ion, then I set the ion to be Coablt 60. Then I type the command /run/beamOn 10, but nothing happens , Why does this happen?. Then I do the same, but this time, before typing the command /run/beamOn 10, I also type the command /process/had/rdm/thresholdForVeryLongDecayTime 1.0e+60 year, then I type the command /run/beamOn 10, and now I do observe secondary particles and trajectories and I also observe radioactive decays. Why does this happen? What is the reason for this difference?

_Geant4 Version:_11.2.1
_Operating System:_Windows 10
_Compiler/Version:_Visual Studio 2022
_CMake Version:_3.29.0-rc2


Hi Alfredo,

There was a change in the defaults introduced in version 11.2. From the release notes:

Hadronic physics

The default value of the time threshold for radioactive decays of ions - above which these decays are ignored - has been changed, from 10^27 ns (i.e. about twice the age of the universe) to 1 year. For applications where radioactive decays of ions do play an important role, it is recommended to increase the default time threshold of these decays to a very high value, e.g. 1.0e+60 years. This can be done in either one of the following three ways:
    Via UI command, e.g. /process/had/rdm/thresholdForVeryLongDecayTime 1.0e+60 year, (command to be used after /run/initialization);
    Via C++ interface, e.g. G4HadronicParameters::Instance()->SetTimeThresholdForRadioactiveDecay( 1.0e+60*CLHEP::year ) (to be placed in the main program before run initialization);
    Via the second parameter of the constructor of the class G4RadioactiveDecay (for analogue mode only) or G4Radioactivation (for both analogue or biased mode), e.g. G4RadioactiveDecay( "RadioactiveDecay", 1.0e+60*CLHEP::year ) or G4Radioactivation( "Radioactivation", 1.0e+60*CLHEP::year ) (this is for custom physics lists, before run initialization).
In the examples, the first method is adopted.

Best,
Alvaro

1 Like

Ok Alvaro, thanks for your reply. Now I understand things better