dbeeksci, you might as well forget about the Potassium Iodide, it's more of a band-aid fix in a situation that requires a tornoquet.
As the other guys said, two major hazards:
Particulate: Alpha and Beta particles, commonly called fallout. Keeping the dust and ash in a "Magic Mushroom" scenario is imperative, but very difficult depending upon the density (CPM's) and extent of the contamination. A rain suit with hood, boots and some creative use of duct tape works fine. For repiratory under 10K CPM, you need a very high efficiency filter on a full face mask, taped to your hood to form a seal. Over 10K CPM, you need Positive Pressure Full Face SCBA or supplied air, at that rate, it's so thick, it will clog a filter. In our "dirty" training room in Albuquerque, the stuff looks like talcum powder, and just fills the air from walking around in it, it's like a fog. Granted, Alpha particles can usually be just washed and brushed off. We recently have dropped the "sand scrub" technique recently in lieu of "duct tape patting", I'm not sure wich one sucks worse. The upside to sand or cornmeal scrubbing is if you are alone (or not within a CCA) you can get the vast majority of material off of yourself, the downside is that if any is left, you are just grinding it into your skin deeper. We use the tape pat because we usually have medical support handy to remove said material. Beta particles on the other hand are pretty nasty and leave some vicious "burns". They are still so hot, that they are still producing quite a large quantity of X-ray and Neutron radiation, so they are just killing cells, getting them off of you is a priority, knowing that it's there before it's too late is the hard part, Tape pat and medical are your best bet. The good part is that the stuff is so heavy that it cant usually move around, so it at least stays where it is, no breezes taking it across town like Alpha.

Transient or "Hard" radiation are another story. Gamma, Neutron, and X-Ray are all by products of nuclear material. You cant see it, smell it, or hear it. If you catch a pulse and see that "blue flash", just grab a good bottle of Scotch Whisky pull off your mask, have a seat, and relax, it won't be long. We joke about this in our teams SOP.
"The contaminated individual is required to step into a contamination collection bag and hand out all personal items for decon, then all government property for reissue, load pistol and ensure that assistant has control of the lanyard, fill out own hazardous material shipping label and hand to assistant, pull bag over head and use pistol, ensuring trajectory of bullet will not exit contamination control bag. Assistant then removes and safes pistol for decon, applies label and seals bag, repeat as necessary."
Gallows humor, gotta love it.

Seriously, if you get a good pulse, all those little pocket detectors are good for is letting you know it, because when you're bit, then you're bit, end of story. As stated, find some train tracks and look for the pretty blue train to step in front of.
The positive side is that you pretty much need a "Magic Mushroom Maker" to produce significant(fatal) ammounts of "hard" energy, not to many of those out there thank goodness. An RDD, or Radiation Dispersal Device (dirty bomb) is just a device to spread the particulate contamination around. They are more hype than most think, fairly small area, and not that much dirty material leads to news panic and only a couple hundred contaminated people. Not much in the grand scheme. Not panicking, and going through decon as soon as possible will save one nine times out of ten. If you inhaled any particulat, just be glad they have made some wonderful advances in cancer research lately.
If you want to see why you need to step in the way of that train, I have copies of the pictures from the accident in Los Alamos during the "Manhattan" project. I'll send them to you, but I won't post them, they are pretty graphic. Basically, a ball park frank in the microwave!

"The old father wove the skein of your life long ago, hide in a hole if you like, you won't live one second longer"

Have a nice day folks!