David Incorporated Esq.
Member
The radiation poisoning is different than the infection caused by the blue stuff. Alex says "but what if they are infected" and Naomi says something like "He wouldn't do that [come back on the ship infected]."
Aww Naomi <3 Holden
Hence why Julie also smashes all her TVs and lights when she's infected. She was either going crazy or started associating any form of radiation may be increasing her problem. She initially finds the blue stuff on the core of the ship, which is full of radiation, etc.
She could probably feel it kicking off in her body; she was sitting right under a lamp when she first freaked out.