Isotopes in radioactive clouds

Dear Mr. Cerutti,
thank you for your suggestions for improvement. The sphere of 1mm was just to test the input file with an isotope-point-source. Goal of this simulation is to “see” different isotopes in a radioactive cloud, where the detector sits inside of this cloud (for example the isotopes in the atmosphere after the burnings in Tschernobyl in March 2020):
Are there important settings to consider?
And is it possible to detect only gammas? So no beta-rays (of the Cs-137/Ba-137 decay) will be detected?

Thanks in advance, i really appreciate your help

I understand that you will keep then a spatially extended ISOTOPE source, to be modeled by means of one of the volumetric BEAMPOS options as you already did. I’d perhaps consider to further lower the photon transport threshold from the PRECISIO default value of 33 keV, down to say 10 keV with the EMFCUT card. If the electron exclusion really makes sense to you, you can eliminate them thanks to the DISCARD card.