I'm having a hard time figuring the Nuclear Protection Factor. Math isn't my stronge point and this halving has me a little confused. I just want to make sure I'm figuring it right. OK, so for an underground shelter with a 12" concrete ceiling and 8" concrete walls (which has a PF of 40 or 70%), how much earth should be on top to have 100% radiation absorbtion (not a PF of 100, which is 90%)?
Thanks, Denise