Back in the 80's, My dad was passionate about surviving a nuclear war. he was a civil instructor (for the military), teaching post nuclear detonation survival. He knew where where bombs would fall, blast radius size, what radiation, and how to build a shelter. He was a prodigy, and absolutely brilliant... But he could never apply himself or focus (ADHD?). Anyway, his passion to spread the word about survival led to his creating a role playing game called "Survive". I just found all his old manuscripts (printed on old library word processors, lol). I had it transcribed to modern documents, and am now in the process of testing the game for modern distribution. Why give this background? Because I'm going to copy and paste the RADEF section (not edited or updated from what my dad wrote in the 80's). This was my dad's life work, and is for entertainment purposes only. Use this info at your own risk, but my dad did know his stuff...
APPENDIX A: PRINCIPLES OF RADIOLOGICAL DEFENSE (RADEF)
Fallout radiation is one of the least understood hazards that will be faced following any nuclear exchange. Fallout radiation is not a gas. Fallout comes from the tons of earth, rock, and concrete vaporized in a nuclear surface burst. The vaporized material is carried upward as the fireball rises to form the toroidal “mushroom” cloud. Churned and mixed with the 80 or so radioactive isotopes produced in the nuclear fission of the warhead (the fusion portion is “clean”), this material cools and condenses first into molten globs, and then particles, ranging in size from fine sand to small marbles. The isotopes within these particles give off the radiation that is so hazardous.
Each of the 80 odd isotopes gives off one of three types of radiation. Alpha particles are very low energy, and are only a threat if the fallout particle is inhaled or ingested. Beta particles are of a slightly higher level of energy, and can also cause “Beta burns” from fallout in contact with the skin. Gamma rays are very high energy, and very penetrating. A Gamma ray can pass through the entire body, destroying or damaging many of the cells it contacts. Enough exposure to Gamma radiation will kill enough cells to make a person ill for weeks. A larger exposure can kill or leave one disabled for months or even years.
Each of the isotopes mixed up in the fallout particles decays (loses radioactivity) at it’s own rate. The time it takes for any given isotope to lose half its radioactivity is the “half-life” of that isotope. The isotopes with the shortest half lives will emit radiation at a much higher rate, and those with the longest will emit at lower rates, thus being far less of a threat unless ingested or inhaled. Since the rough distribution of isotopes and their decay rates are known, an overall decay curve can be determined. This curve is expressed in the “Seven-Ten Rule”; For every SEVENFOLD increase in TIME, there will be a TENFOLD decrease in the rate at which radiation will be emitted. Thus, if the rate at H+1 hour was 250 rad per hour, then at H+7 hours, the rate would be 25 rad per hour, at H+49 hours (2 days) it would be 2.5 rad per hour, and at 2 weeks the rate would be down to .25 rad per hour. At this rate (.25 rad per hour) emergence from a shelter may be safely accomplished wearing a respiratory filter or gas mask and clothing to prevent contact with the skin (an anticontamination “RAD” suit). At this point, the job of rebuilding civilization can begin.
Protection from fallout (until TIME has reduced the hazard) can be provided by either MASS or DISTANCE (or a combination of BOTH). MASS attenuates (lessons) radiation because a Gamma ray must “spend” energy to get through. The thickness of any shielding material that will only allow half of the exposure is called the “half thickness” (HT) of that material. For example, one HT will allow half the radiation through, a second HT will allow only half of THAT radiation, a third HT will only allow half of the radiation that passes through the second, and so on. Thus, one HT gives a Protection Factor (PF) of two; two HT gives a PF of four; three HT will yield a PF of eight; four HT gives PF-16, and so on. Each additional HT of any material added to the shielding will DOUBLE the PF that is provided. (See PF table at the end of this appendix).
Distance attenuates radiation of all kinds according to the inverse square law. If the intensity of any radiation at any given base distance from its source is know, the intensity at any multiple of that base will be 1 over (fractional) the square of that multiple. The standard RADEF base distance is 3 feet, this at 6 feet (multiple of 2) there would be 1/3x3 or 1/9; at 12 feet (multiple of 4) intensity would be 1/4x4 of 1/16 of base. A chart showing the distances at which PF is achieved is as follows:
INSERT: Half Thickness Charts.