放射線を大量に浴びたら、すぐに嘔吐と下痢が始まります。

、。

If you're exposed to a large dose of radiation, vomiting and diarrhea begin almost immediately.

Literal

Radiation [object-を] large-quantity [object-を] be-exposed-[if-たら], immediately vomiting [and-と] diarrhea [subject-が] begin.

A medical/emergency reference. 放射線 (ほうしゃせん) 'radiation' (ionizing). 浴びる ('to bathe in, be exposed to') is commonly used for radiation exposure as well as for sunlight and praise. 嘔吐 (おうと) 'vomiting' and 下痢 (げり) 'diarrhea' are both formal medical terms. The sentence describes acute radiation syndrome symptoms.