I have no deep sources in English, but Wikipedia has some references:
https://en.wikipedia.org/wiki/Brazil_and_weapons_of_mass_destruction
https://en.wikipedia.org/wiki/Argentina_and_weapons_of_mass_destruction
Argentina’s last dictatorship was extremely afraid of Brazil attacking them.






That one was about the official nuclear program, that wasn’t intended to create nuclear weapons. The Brazilian nuclear weapons program was a secret out of the clearance level of the official nuclear program so there was never any interaction between them.
And yes, it was in the later 80s, when Brazil was trying to repair the damaged relations with Argentina.