What kinds of radiation? Alpha, beta, gamma? gamma rays & X-rays? All of it? How does it block radiation. i assume it absorbs the energy and puts electrons in a higher orbital but why don’t any other elements block radiation.
if lead absorbs radiation by kicking up electrons do the electrons go back into a low energy level and give off the energy as something else or do the electrons stay at the higher energy level? if they are brought back down what is the energy given off as (visible light, UV, etc), and if the electrons stay at a higher energy point will lead reach a point where it becomes saturated with high energy electrons and cannot block radiation anymore.
Any material blocks alpha and beta fairly easily. Metals attenuates gamma and X-rays most effectively. An effective attenuator has a lot of electrons for the photons to interact with. Lead has a high atomic number and is dense, resulting in large numbers of electrons per unit volume. At the same time it is relatively inexpensive, readily available, and easily shaped and formed, and so is a preferred metal for shielding.
Photons interact in several ways (pair production, Compton effect, and photoelectric effect), the ultimate result of which are electrons ejected from the shield atoms creating heat. The lead will never become saturated, and the amount of radiation required to cause it to melt would be astronomical. Even melted it would still shield as long as it could be held in place.
I deal with radiation sensitive electronics all the time, and have to account for the different kinds of radiation and contrive ways to block them sometimes.
First, lead blocks radiation because it’s dense. The higher the density, e.g., grams per square centimeter of shielding, the more nuclei there are in a given volume of material, and thus, the more effective it will shield against gamma radiation (high energy photons).
Notice I said grams per square centimeter. Mass per unit area, rather than per unit volume. The third dimension is left unconstrained because in practice, you will vary the thickness of the shield depending on the available materials.
So if you need 10 grams per square centimeter of shielding, you can either use a sheet of 4cm thick aluminum, 1 cm thick lead, or 0.5 cm thick iridium. (Approximate, from densities listed here.)
That effectively answers the OP’s question.
But there is lots more detail… enough to keep our engineers constantly busy on radiation analyses. For instance, in very high energy radiation environments more shielding can create more problems than they solve by nature of secondary radiation produced by interactions of primary radiation with the shield material…
Electromagnetic radiation is attentuated mainly by three types of photointeraction. Basically, high energy photons are converted into lower energy photons, or to more easily attenuated charged particles.
Alpha and Beta radiation, being made of chraged particles, will undergo electrostatic interaction as it passes through a material (like charges repel, opposites attract), passing some of the kinetic energy of the particles to the atoms of the material. Eventually they slow down enough to no longer deserve the moniker radiation. Alphas have double the charge of a beta, interact more strongly, and are more easily stopped.
Why lead you ask?
Well, how good a material is at attenuating radiation depends a fair bit on the energy of the radiation. Aluminum and steel, for example, are very good at blocking radiation in very narrow bands of energies, but kind of suck at it elsewhere. Lead is pretty good all around and relatively cheap.
Folks have pretty much handled [symbol]a, b, [/symbol] and [symbol]g[/symbol] radiation.
If you find yourself needing to stop neutrons, though, lead will only get you part of the way. Once a neutron has less than a few MeV of kinetic energy, a big ol’ lead atom doesn’t do anything: the electrons are useless since the neutron is neutral, and the nucleus is so heavy that the neutron just bounces off elastically, losing very little energy. (At higher energies, a neutron can lose energy by either exciting the nucleus to a higher energy level (analogous to atomic energy levels) or by actually breaking the nucleus apart. Below an MeV, though, none of the energy levels is accessible – the lowest excited state is several MeV above the ground state. So to the neutron, the nucleus looks like a perfectly rigid object that is much heavier that it is.)
So to stop slow neutrons, you want low atomic numbers. Hydrogen is best since its nucleus (a single proton) matches the neutron in mass pretty well. (A slow neutron will transfer about half it’s energy to a struck proton.) In practice, one uses a variety of polymers / hydrocarbons to stop slow neutrons.
Oh, and a 1 MeV neutron is traveling at 14 million meters per second (4.6% of c), so it’s not that slow.
This is a very important issue. I’m a nuclear medicine technologist and, in the hospitals I’ve worked in, when we used beta-emitting isotopes like Strontium-90 or Phosphorus-32, we wouldn’t use lead at all, because of the secondary, scattered radiation. In these cases we used a plastic shield with an aluminum foil coating. This would be much more effective at protecting us from the beta and secondary emissions.
Yea, I wasn’t gonna go there, but since you opened that can of baryons…
Traditional nuclear reactors use a combination of Hi-Z and Low-Z shielding, to block both the gamma rays and the neutron radiation. (Do that and you get the alphas, betas, and protons pretty much for free…)
When I worked at the University of Colorado Nuclear Physics Lab, we were building detectors for the high energy physics department to be installed at cyclotrons run by other institutions. The lab did once have a linear accelerator, but it had been decommissioned years ago. We had to wear dosimeter badges when inside the building because there was still a bunch of mildly radioactive stuff lying around… mostly dust, but a few tools and ancient pieces of test equipment and stuff.
As an undergrad, I got the crap jobs quite frequently. Like cleaning out the basement, which included an area known as “the vault.” It was a shielded room in the basement where they stored everything that was too hot to just discard. Right outside the vault was the storage area I was asked to clean out. Stacked just outside the door to the vault were stacks of bricks, about 50, which were clearly lead blocks, coated in about 2cm of paraffin wax.
Not knowing what the were, or where to move these lead bricks, I grabbed one in each hand and carried them upstairs to the engineer’s office. Being lead bricks, my arms were hanging by my side by the time I made it to his office. “Jack, what are these?” I knew Jack would know. Jack knew everything, and loved to demonstrate it. He’d have made a great Doper.
“Those are shielding blocks. We used those to block radiation that might emit from targets we hit with the beam. The lead blocked everything but neutrons, which is what the wax is for. Hydrogen atoms block neutrons best, and there’s lotsa hydrogen in paraffin. Water has even more, but it’s hard to make it stick to the bricks for very long.”
As I’m absorbing this, I realized I was probably also absorbing whatever residual radiation was emitting from the bricks. “Are they hot?”
“Probably,” said Jack. In the lab, hot meant that they should be stored in the vault, not necessarily dangerous.
I looked down at the bricks hanging at the ends of my arms. And then realized what valuable and particularly sensitive part of my anatomy is closest to the bricks.
And I walked quickly back down the stairs holding the bricks out at arms length.
Not even. At typical neutrino energies, it’d take lead shielding a lightyear thick to stop even half the radiation. The core of a star will produce significant attenuation, and a few kilometers of neutronium would pretty effectively stop them.
Fortunately, however, for the exact same reason that it’s so difficult to shield neutrinos, it’s also unnecessary. If they don’t interact significantly with the shielding, then they also won’t interact with your body, or with your experiment, or with whatever else you would want to shield.