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, the properties of the shielding material, and the shielding strength or thickness of that material.
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“.
X-ray and Gamma photons are essentially identical.
The ‘Alpha’ particle however (another type of nuclear radiation from an 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. To protect yourself from gamma radiation resulting from a nuclear explosion, there are three things to remember:
Time, Distance, Shielding.
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. If a certain thickness will block half of the incoming radiation, then adding the same thickness again will block half of what’s left (leaving only 1/4 or the original gamma ray intensity), and so on.
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.
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).
Radiation Shielding Materials
To achieve a protection factor of 1,000 the following chart of materials and thicknesses must be used. We’ve saved you the trouble and have factored the proper ‘halving thickness’ values of each material in order to achieve a protection factor of 1,000.
As a rule-of-thumb, for a protection factor of 1000, you want about 375 pounds of mass per square foot of area that you’re shielding (this is not a linear function, but this approximation is accurate for a protection factor of 1,000).
It appears that the most practical and economical means to achieve this protection factor is to use the absorption properties of packed dirt. So long as you’re at least 3 feet underground, you’re apparently safe (enough)…