Olaf asks: I'd like to write a novel concerning a radiation leak at a hospital. How would the leak be detected? How would they determine which patients need to be evacuated?
The inspiration for his story came from this real life incident. A radiation leak at a hospital in Hawaii.
You can read about that story here.
The first thing to understand is that there are two different types of devices that make radiation. One is for radiation based oncology called a linear accelerator. For chemotherapy-- it's different. The dosimeter that rad techs wear would actually be a poor way to detect the leak as they are only read every two months or so.
There are radiation detectors all around the linear accelerator so this would likely be how it would be picked up. On a gieger counter (Geiger Mueler reader) a reading over 2mR/hr is considered dangerous. It depends on the extent of the leak to determine who would need to be evacuated.
Patients exposed to the radiation would need to be decontaminated. Here are a few links to read about how to decontaminate patients from radiation exposure.