Your intake depends entirely on proximity to the detonation, as well as the amount of contaminant released. In calm weather, fallout doesn't linger, but eventually "falls" to surfaces. You cannot hear it, taste it, feel it, smell it, and the bits are often too small to be seen with the naked eye. Rain helps clean the air of the particles, and water runoff helps clean the land. Of course these also tend to foul water supplies and, if it's a light rain, the water will soaks into the soil without runoff and the particles stay, irradiating the ground.

The best way to know when to come out into the open is to "hope" a local emergency radio transmitter is up and running (I know the radio bands in the U.S.A. used to be AM 640 & 1240, and AM ‘cause an AM radio was about the limit for your new car) -- and your radio's batteries aren't dead. You’ll receive reports for your area, which should be broken down to tell you how long you can stay exposed per day. Radiation is cumulative, so if the report says not more than 45 minutes -- and you really, really, really need to go outside (can’t think of a reason myself) -- don’t test it. Get back under cover within 20 to 30 minutes. And if you do go out, wash yourself off when you return.

For shelters, the basement is the best place for protection. The next best would be an inside room at the middle of the house, which provides additional walls to help absorb radiation. They say you should have a 3 to 4 week supply of nonperishable foods and water (including an emergency supply of scrub-water for periods of exposure) on hand, as well as battery-powered accessories (radio, lamps), also a small generator (your rechargeable batteries will like these things) and a kerosene heater would be handy for cold months. And don’t forget something the read!! 3 to 4 weeks staring at a cinder block wall with your family ain’t quite the same as a cable hookup. The rest would be up to your own imagination. It would also be a good idea to test the place, perhaps having a day or week that the family sleeps in the shelter. Doing this helps acclimate the family to the possibility, and brings flaws to your shelter to light.

Complicated, but a doable project. There are sites out there today that can help you set up a sound shelter, and give steps for proper radiological decontamination.

Still a ‘60s-man,
Dan (no, I don’t have a fallout shelter -- but it’d be cool!)