Unless you have a personal space to hang out in for a very extended period - a radiation shelter stocked with lots of food, water and other supplies - what is the use of a radiation detector? The knowledge to stay inside, stay shielded as best you can, etc. would be your guiding principles. Would a detector materially alter what you do?

A detector might tell you just how bad it is out there, but since there's nothing you can do about it, who cares? I would think a good reference book on how radiation spreads, how to protect yourself from it, etc. would be the better resource to have. Knowledge.