# How to define a isotope radioactive γ source？

Dear Fluka experts,
I am trying to define a γ source. But most γ source have a few energy branches such as 60Co and 133Ba, how to define them?

Dear @shusheng,

you can define an radioactive isotope as a source using the ISOTOPE particle type on the BEAM card, in conjunction with the HI-PROPE card. Furthermore, you need to activate the radioactive decay with the RADDECAY card (semi analogue mode), and associate the scorings with a DCYSCORE card.

For an example see slide 24 of the following lecture:

Cheers,
David

A post was split to a new topic: ISOTOPE beam decay data

Dear Dávid Horváth,