*Some Nuke Facts*
Gamma radiation intensity decreases by the square of the distance from the source.. that's a fact I know for sure from College Physics, we did the experiments several times in Labs.... It's also backed up by several Gov pamphlets...
Cresson Kearny, in his book "Nuclear War Survival Skills", says that it takes 36 inches of dirt to stop the ray from a fallout particle.. but several other sources on the web say 7 inches of dirt..
one US Gov document I found says:
Every 3.6 inches of packed earth will cut the gamma rays in half. The HVT (half value thickness) of dirt packed is 3.6 inches. To be protected from gamma radiation you need two (2) feet of earth....
This can't be right since you need 10 half thickness of dirt for a protection factor of 1024 (You want 1000 to 1024 Protection factor) so 3.6 x 10 HVT = 36 inches of dirt, not 24 inches...
Another US Gov document says:
The required shielding can be accomplished with 10 halving-thicknesses of any material. Shields that reduce gamma ray intensity by 50% (1/2) include 1cm (0.4 inches) of lead, 6cm (2.4 inches) of concrete, 9cm (3.6 inches) of packed dirt or 150m (500 ft) of air. When multiple thicknesses are built, the shielding multiplies. Thus, a practical fallout shield is ten halving-thicknesses of packed dirt. This reduces gamma rays by a factor of 1024, which is 1/2 multiplied by itself ten times. This multiplies out to 90cm (3ft) of dirt.
This corresponds to what I know to be true (mathematically) about radiation.
There are three ways to protect against fallout.. Time, Shielding and Distance...
Meaning that you'd need to put 5000 feet of open air between you and the Gamma emitting particle...
The "Most frequent" number(s) I come up with for total shielding against gamma are:
4 inches of lead
24 inches of concrete
36 inches of packed dirt
After doing the math with what I "know" to be true from College experiments using different radioactive samples, I accept the above numbers as correct (Or as close as possible to correct).
Now.. How much radiation can the body stand? Again the numbers are all over the board.. but the CDC and Kearny agree here:
Fortunately, the human body can repair most radiation damage if the daily radiation doses are not too large. A person who is healthy and has not been exposed in the past two weeks to a total radiation dose of more than 100 R can receive a dose of 6 R each day for at least two months without being incapacitated.
All the texts also agree that if you are in the worst of the fallout area, you'd have to be in shelter for 2 weeks before the radiation levels would be down to 1 Rad/Hour. Which means then you could be outside for up to 6 hours a day... But most people think "It's safe to abandon the shelter in 2 weeks".. this is NOT the case.. you'd have to stay in shelter 3-4 WEEKS before abandoning it if your initial radiation reading was 1000Rads per Hour (R/H)
This would be reduced of course if you were in an area not so hard hit by fallout.
This also follows the "7/10 rule" that says every 7 fold time periods that go by from the first measurement means a 10 fold reduction in R/H of Radiation. So in 7 hours an initial reading of 1000R/H would be reduced to 100 R/H... in 49 hours (7x7) you'd have 10R/H, in 343 hours (7x7x7= 343 or about 14 days) you'd have 1R/H.. meaning that you could go outside for 6 hour per day after 14 days.
This is assuming that you started out at 1000R/H.. if your area was getting only 10R/H to start out then in 7 hours that would reduce to 1R/H... meaning that in 49 hours you could safely abandon the shelter (I'd give it a week to be SURE).
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So.. I think what I accept as fact, and what I NEED to know is this:
* For a protection factor of 1024, I need:
4 inches of lead, or
24 inches of concrete, or
36 inches of packed dirt
*Length of time I need to be sheltered is:
a 10 fold reduction in R/H for every 7 fold time increase... meaning that I can divide the radiation reading by 10 for every time I multiply the time by 7.
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That's the meat of the matter... and that's the "cheat sheet" I am printing and taping to my Rad gear..
Cresson Kearny's "Nuclear War Survival Skills", and this FEMA document, seem to be the reliable sources to read
http://www.radmeters4u.com/FEMA_book/Contents.htm
Warlord
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