Yeah, that's mainly 'Neutron induced radiation' and high energy gamma ray secondary effects, but for that to produce really dangerous levels of radiation, the thing, place, or person concerned pretty much has to be directly exposed to an unshielded reactor or be well inside the 'Total destruction' radius of a nuclear blast (The latter, of course, not being much of a treatment problem for medical care providers as far as radioactive patients are concerned).
500 rads is generally considered to be about the lethal dose, though technically it's the '50 percent of those exposed to it are going to die within two weeks' dose. Rads and REMs aren't used that much anymore, for the last couple of decades radiation hazards have been discussed in different units, 'Centigrays,' one of which is the same as one Rad for purposes of how much ionizing radiation they measure.
Yup--5 Sv is equal to 500 Rem, which is what is called the LD50/30, meaning 50 percent exposed to that amount would die within 30 days.
And the amount of exposure they'd have to take to emit SIGNIFICANT (>0.1 mr/hr or 1 microSv/hr) radiation would be massive, as DAT stated--think THOUSANDS, if not tens of thousands of Rem (or 10-100 Sv.)
Gray is to Sievert as Rad was to Rem--Rad doesn't take into account biological damage, of which alpha is by far the worst if the material is ingested or inhaled. However, Co-60 is a beta/gamma emitter.
To put it into perspective, my LIFETIME exposure is about 1.5 Rem, or 0.015 Sv, of which I got about 50 mr (500 microSv) over the seven years I was at Seabrook.
