Re:This is bullshit and I can PROVE it. (Score 1)

As a working physicist, I routinely run radiation transport codes: both photons and particles with mass(neutrons and ions). I just found out about the Demron claims late last Friday and bumped into these posts while trying to find some sign of outrage on the Internet. Lots of pseudoscience and bogus hi-tech gets on the market but rarely is it so uncritically touted in the "mainstream" news like this. Yes, this stuff is bogus IF the claim is that an equivalent thickness of low-Z material(low atomic number, like plastic) attenuates x rays (soft gammas) in the 20 to 200 keV range as well as lead or other high-Z materials. Your calculation of the attenuation of Co-57 photons (at 122 keV) by 0.5mm lead is about right -- you say it should be about 90% and I calculate 84% with my simple x-ray transport code. If Demron is essentially PVC, the highest Z in it is Chlorine. But there's not enough to do much good. My code says that the absorption from 0.43mm of PVC, would be about 0.5% -- Demron should be terrible at absorbing 122 keV gammas! The reason it must be THAT terrible is something that Einstein got a Noble Prize for: the photoelectric effect. X rays (soft gammas) below a few hundred keV interact with matter primarily through the photoelectric effect. Photons at or just above the binding energy of electrons are absorbed by a quantum mechanical effect of the atom+electron+photon system. The cross section for the interaction is very dependent on the Z of the material. For photons around 100 keV, you need to introduce the x rays to material with a very tightly bound inner shell electron -- gold or lead for example -- in order to get a very large cross section. Well, lead has a 100x larger cross section than PVC at 122 keV. A beam of photons gets absorbed by this factor: exp(-cross section in cm^2/g * density in g/cm^3 * thickness in cm). So differences in DENSITY and THICKNESS are also important! Now, if you go above 1 MeV, cross sections for absorptions for all materials all start to converge. The photoelectric effect is no longer important -- now the Compton effect takes over, and over 10 MeV, the dominant process is pair production. The high energy photons mainly care about how many electrons per cubic cm are in their way, and as you folks already have pointed out, that tends to be proportional to material density. So fine, for a 2 MeV gamma, 10 g/cm^2 of Demron works just as well as 10 g/cm^2 lead, and note I said g/cm^2, so you need a 5x thicker Demron layer. So big deal -- Demron should be useless for absorbing 20-200 keV photons. Dental x rays run about 60 keV, as an example of the "medical" x rays that are supposed to be blocked. I think I still prefer that lead apron, if you don't mind. I don't care what goes into arranging the "electron cloud" in the Demron fabric, since any games with the chemistry of the material are irrelevant. The properties that determine absorption are the atomic number (Z) of the material and the density (how many of those atoms are crammed into the material per unit volume). Since I can estimate the probable mix of Z's in Demron and they state the density at less than 3 g/cm^3, it is not possible for this stuff to efficiently absorb 20 to 200 keV x rays. The only question is how fast Demron customers wise up.