What Determines Whether Radiation Passes Through Materials?

In summary: Water is also an effective moderator of neutrons, helping to control the nuclear reaction.In summary, water is used as a shielding material for nuclear waste because it is cheap, non-toxic, and can easily be handled. It is not as efficient as other materials, but by having a sufficient thickness, it can effectively reduce the radiation. Water is also a good moderator of neutrons, helping to control the nuclear reaction. The ability of a chemical to block high frequency radiation depends on the availability of transitions between energy levels and its ability to ionize molecules.
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Stephen22
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I've read that nuclear waste is stored in Olympic-sized swimming pools, but what is it about water that so effectively stops radiation? And apparently, this shielding effect of water is so powerful that one could literally stand right next to the pool (and according to some things I've read, they could even accidentally fall in) without suffering any ill effects whatsoever. But why? Water, chemically is h2o of course, but what is it about this compound that would be able to block such powerful rays that are capable of traveling through solid objects? Because X-rays (which are also emitted by nuclear waste if I'm not mistaken) are capable of traveling through the body and even through cargo in airports. These objects are solid, yet water is a liquid and stops them. Also, why is it that visible light is able to extend through water, but not the higher spectrum stuff (e.g. x rays and gamma rays)? Because one can see the waste at the bottom of the pool clearly, yet the radiation cannot reach the top of the pool in any substantial quantities?

Also, I'm aware that ozone (in trace amounts in the upper atomsphere) blocks a large amount of high frequency radiation (UV light) despite being present in the thin levels of the stratosphere. What is it about ozone that has protective qualities? And in general, what determines if a chemical is likely to block high frequency radiation or if it is likely to pass through it?
 
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The human body absorbs some part of the x-rays, that's how the x-ray images are created. Human bodies filling the same volume would give about the same shielding properties (especially as humans are mainly water anyway) but they can't be used in nuclear power plants for obvious reasons.
Concrete would give similar shielding, steel and lead would give better shielding. Mercury would give better shielding. But all these materials would make handling the material more difficult. Water is cheap, it is not toxic and it makes handling the material inside easy.

> Also, why is it that visible light is able to extend through water, but not the higher spectrum stuff (e.g. x rays and gamma rays)?

There are no excitations of water molecules with transition energies in the energy range of visible light, and visible light doesn't have the energy to ionize water molecules either.

> And in general, what determines if a chemical is likely to block high frequency radiation or if it is likely to pass through it?

Available transitions between energy levels and the ability to ionize the molecule.
 
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Stephen22 said:
I've read that nuclear waste is stored in Olympic-sized swimming pools, but what is it about water that so effectively stops radiation?

It is not particularly efficient. You need about 10 cm layer of water of reduce gamma radiation by half. To the first approximation, gamma shielding is proportional to mass. Denser materials have more mass per unit of thickness. Thus, denser materials are "more efficient" if efficiency is measured by thickness.

Water shielding in spent fuel pools is achieved by having sufficient thickness of water. 1 meter gives you about ~1000 fold attenuation. 2 meters - one million. 3 meters - one billion. IIRC fuel pools have ~7 meters of water above fuel assemblies. That gives attenuation of ~10^21.
 
  • #4
nikkkom said:
That gives attenuation of ~10^21.
Be careful with extrapolations. The attenuation is not completely independent of the energy, and the energies with the weakest attenuation will dominate after a meter. Just continuing the exponential approach will massively overestimate the attenuation.
 
  • #5
mfb said:
Be careful with extrapolations. The attenuation is not completely independent of the energy

Right. It's actually very much energy-dependent. IIRC the worst are ~2-5MeV gammas.
 
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it is cheap and free
 

Related to What Determines Whether Radiation Passes Through Materials?

What Determines Whether Radiation Passes Through Materials?

1. What is radiation?
Radiation refers to the emission or transmission of energy in the form of waves or particles through space or a material medium. There are different types of radiation, including electromagnetic radiation (such as radio waves, visible light, and X-rays) and particle radiation (such as alpha and beta particles).2. What are the factors that determine whether radiation can pass through materials?
The factors that determine whether radiation can pass through materials include the type and energy of the radiation, the type and thickness of the material, and the density and composition of the material. Different materials have different abilities to absorb and block radiation, which can also depend on the energy and type of radiation.3. How do different materials affect the penetration of radiation?
Different materials have different properties that determine their ability to block or absorb radiation. Materials with high density and atomic number, such as lead and concrete, are more effective at blocking radiation than materials with lower density and atomic number, such as air or water. The thickness of a material can also affect its ability to block radiation, as thicker materials provide more obstacles for the radiation to pass through.4. Can radiation pass through all materials?
No, radiation cannot pass through all materials. Some materials, such as lead and thick concrete, are highly effective at blocking most types of radiation. However, even these materials may not completely block all types of radiation. For example, gamma rays can still penetrate through several feet of lead.5. What are some examples of materials that are commonly used to block radiation?
Lead, concrete, and steel are commonly used to block radiation in various applications. For example, lead is used to line X-ray rooms in hospitals, concrete is used to shield nuclear reactors, and steel is used in the construction of nuclear power plants. Other materials that can be used to block radiation include water, plastic, and glass, depending on the type and energy of the radiation.

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