Radiation shielding is a mass of absorbing material placed between yourself and the source of radiation in order to reduce the radiation to a level that is safer for humans.
The effectiveness of the material depends on:
– the type of radiation itself
– properties of the shielding material
– the shielding strength or thickness of that material.
(UPDATED) More Shielding Materials Listed Below
Different types of radiation behave in different ways:
According to the NATO Handbook On The Medical Aspects Of NBC Defensive Operations,
“Gamma or X radiation constitutes the principal casualty producing form of ionizing electromagnetic radiation associated with nuclear explosions”.
In other words, Gamma and X-ray are of primary concern.
The ‘Alpha’ particle (another type of radiation from a nuclear explosion) is also highly dangerous but is hardly penetrable. It can be stopped by a single piece of paper, or an air filter (think of it as a heavy dust particle). It is carried by the wind currents and eventually falls to the ground and ‘decays’.
Gamma radiation though travels at the speed of light.
Nuclear Radiation Shielding – Gamma & X-ray
To protect yourself from gamma radiation resulting from a nuclear explosion, there are three things to remember:
Time & Distance – Get as far away as quickly as you can.
Shielding between you and the radiation source – Knowing how much of what type of material is enough to protect you.
It is the ‘mass’ of the shielding material that does the blocking.
The more shielding, the better.
Shielding is measured by the fraction of gamma rays that it blocks.
A halving thickness is the amount of material that will block half the gamma rays passing through it. A halving thickness ( 1/2 ) has a protection factor (PF) of 2.
If you add another ‘halving thickness’ it will block half of the remaining gamma rays, so now 1/4 are getting through. This is a protection factor (PF) of 4.
Another layer of ‘halving thickness’ brings it down to 1/8 or PF 8. And so on.
Were’ looking for PF 1000. Here’s how it works:
Protection Factor (PF) layers
A radiation shield is characterized by its total ‘protection factor’. For example, a shield that only lets 1/1,000 (one one-thousandth) of the gamma rays through, has a protection factor of 1000 (the modern day standard).
1 layer = PF 2
2 layers = PF 4
3 layers = PF 8
4 layers = PF 16
5 layers = PF 32
6 layers = PF 64
7 layers = PF 128
8 layers = PF 256
9 layers = PF 512
10 layers = PF 1024
Radiation shielding materials are commonly categorized by their ‘halving thickness’, which is the thickness of that material required to block half of the incoming gamma rays.
If we know the halving thickness, then multiply it by 10 for PF of about 1000 (1024).
Radiation Shielding Materials
To achieve a protection factor of 1,000 consider the following chart of materials and thicknesses. I have researched the data that I could find on this, and have assembled a table which I’ve factored the halving thicknesses to PF 1000 values.
Obviously, some of these materials are not practical when considering radiation protection! But it’s interesting nonetheless.
The asterisk* indicates where I have extrapolated halving thickness from a materials correlation (to concrete). Some of my sources listed below.
Radiation Shielding Mass
Typical mixed concrete has a density of about 150 pounds per cubic foot. 24 inches of concrete provides a approximate PF of 1000. So you might say a typical density of materials for radiation shielding might be a density of about 300 pounds per cubic foot (or equivalent stack of layers).
PF 1000 correlates to ~ 300 lbs/cubic-foot density
I went through the list of materials above, and of the 14 listed I found 11 with density data. I averaged them all and it came out to 295 pounds per cubic foot for PF 1000.
With lead, it only takes 4 inches. But water, it takes 6 feet. Both of which stack up to about 300 pounds per cubic foot.
As a rule-of-thumb, for a protection factor of 1000, you want about 300 pounds of mass per foot for your shield – however thick it stacks (layers) up.
Most Practical Gamma Radiation Shielding
It appears that the most practical and economical means to achieve this protection factor is to use concrete or packed earth. 2 feet of concrete or 3 feet of packed soil and you’re good to go…
Dirt’s cheap. Dig a hole, put a bunker down there. The trick is supporting at least 3 feet of packed dirt above you! Maybe a shipping container bomb shelter? Well, that’s another set of articles…
While searching for data in this regard, I noticed that there are some discrepancies out there. However I have gleaned what I believe to be accurate for this report.
Some of my sources include the following:
During a nuclear disaster, consider these:
iOSAT Potassium Iodide Tablets, 130 mg (14 Tablets)
Also, a Geiger counter / nuclear radiation detector will be an important asset!
Related article: 5 Nuclear Radiation Detector Choices
I originally published this article during 2012. However I have updated it several times, including this last 2019 update. Hopefully some of you may find it informative.
Continue reading: U.S. Nuclear Power Plants – Safe Distance?