If the initial amount of iridium-192 produces radiation at 1,000 times the safe level, how long will it take before radiation levels drop below the safe level? reddit

To cause death within hours of exposure to radiation, the dose needs to be very high, 10Gy or higher, while 4-5Gy will kill within 60 days, and less than 1.5-2Gy will not be lethal in the short term. However all doses, no matter how small, carry a finite risk of cancer and other diseases. Patients exposed to radiation between 8 to 30 Gy experience nausea and severe diarrhea within an hour, and they die between 2 days and 2 weeks after exposure. Absorbed doses greater than 30 Gy cause neurological damage