Hello,
you do not specify which Geant4 version you are using. In 10.4 and 10.5 my recommendation would to add radioactive decay physics on top of any physics list. For example:
QGSP_BIC* pl = new QGSP_BIC();
pl->AddPhysics(new G4RadioactiveDecayPhysics());
In 10.6 you need to check if radioctive decay physics is already enabled or not to avoid double definition. I also cannot recommend ShieldingLEND - cannot gurantee results.
VI