4/1/2023 0 Comments Walls on radiation island![]() Included furnishing and installing 12" of steel on the linac vault ceiling. Included furnishing and installing lead lined plywood with lead angles for the seams and penetrations, one lead lined solid core wood door with matching frame, and a lead lined view window frame are, "higher-order" electromagnetic processes such as Compton scattering from individual electrons in the material, become important, and these materials, due to the fact of being dense, have lots of electrons in any given volume to provide lots of chances for a gamma ray to interact.Included furnishing and installing interlocking lead bricks, lead lined plywood, sheet lead on walls and ceiling and lead lined solid core wood doors and frames. The reason for this is that while the radiations are well above the metal plasma frequency and so are not going to be affected the same way, say, light, radio waves, etc. Insofar as to how to more effectively shield gamma radiation - the basic answer is to use some high-density and also high-atomic-number material, typically lead, but also bismuth (much less toxic than lead, but more expensive and a bit less dense), tungsten (very dense but not so good due to lower atomic number), and even uranium (that may seem a bit counterproductive, but natural and much less "depleted" uranium is actually a lot less radioactive than you might be thinking, and when you're resorting to this, whatever you've got inside is typically WAY "hotter".). But, as said, the chief danger would be fallout particles getting through the cracks and hence delivering the radiation directly to you, bypassing the walls altogether. These radiations are considerably easier to stop than EM radiation, and in fact your house walls typically can resist them. I want to emphasize, however, that the above discussion pretty much only is about specifically EM radiation, and radioactive materials also emit particle radiation: massive particles that are typically electrons, positrons (though these are effectively instantly converted to gamma rays via annihilation with an electron) and "alpha particles" (fast-moving helium-4 nuclei). And inhaled or ingested radioactive material is generally the worst since it spreads throughout your body and irradiates it internally. These have the problem that, as essentially dusts, they can seep in through various cracks in your house and you can then breathe them. If a nuclear explosion is lit off far enough away from your house though as to avoid the immediate blast, heat, and prompt radiation, the kind of "radiation" you will be more concerned about will be that emitted by radioactive fallout: finely divided radioactive materials transported from the bomb site to your home on the wind. ![]() On the other hand, it COULD be a concern with a VERY small (not a mistake - as the devices get larger, blast and heat effects increase their lethal distance much faster than prompt radiation effects) device, like that a terrorist might use. ![]() That is, they will "stop" them, just not stop very many, and probably not stop enough if, say, there was a nuclear blast outside close enough to be in the prompt gamma range, however in most cases that also means you are close enough the house and you will be vaporized in the heat and blast wave and hence you aren't going to worry about this (or anything else, for that matter). However, they are not absolutely so: while their optical depth may be "large", it is not infinite and hence some gamma rays will be absorbed. the optical depth is very large and considerably in excess of the typical wall thicknes. Your house's walls, if made of wood, are generally speaking very transparent to most gamma radiation, i.e. greater than 1000 PHz, and typically more than $10^5$ PHz, and hence transmitted. This frequency is around the petahertz (PHz) range, while gamma rays are in the exahertz (EHz) range or higher, i.e. Effectively, the reason the metals absorb radiation at lower frequencies is their copious highly mobile electrons are very responsive to the stimulation from the EM waves, but above a certain point, they are unable to move fast enough to keep up with the high-frequency oscillations and let it through. But, above a certain point, which is called the metal's plasma frequency, the ability to absorb the radiation drops precipitously. As you surmise, it depends on both material and on the frequency of radiation directed thereat, but what also holds is that all EM radiation will penetrate most everything to at least some depth which depends on both the frequency and the material type, which is characterized by a parameter known as the optical depth and, moreover, this depth is not all-or-nothing either: if $\mathrm(m, f)$) is a decreasing function of the frequency $f$, i.e. ![]() Whether or not a material stops or admits EM radiation is not an all-or-nothing affair. ![]()
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