radiation shielding materials

Nuclear Radiation Shielding Protection and Halving Thickness Values

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 and the energy thereof
  • properties of the shielding material (density is important)
  • the total thickness of the material used, based on radiation halving thickness values

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 radiation are of primary concern.

The ‘Alpha’ particle (another type of radiation from a nuclear explosion) is also 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 (fallout) 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 consider:

Time

The less time you spend exposed to radiation the lower your dose.

Distance

Radiation decreases with distance in accordance with the inverse square law. This means that the further away you are from the source of the radiation, the less radiation you’ll be exposed to.

Shielding

As ionizing radiation passes through matter, the intensity of the radiation is diminished. Therefore, to help protect yourself from radiation you use shielding. However, the material you use matters significantly; some materials reduce the intensity of radiation more than others…

Radiation Halving Thickness

Every material has a “halving thickness.” This is the thickness required to reduce the radiation intensity by half. 50%.

So if the halving thickness of a material is 1 inch, then a 1 inch thick sheet will cut the radiation to 50%. Two inches will cut the radiation to 25%, 3 inches to 12.5%, and so forth.

See radiation halving thickness materials chart below.

First, this…

Radiation Protection Factor

This brings us to radiation protection factor. Or protective factor.

A typical house will reduce the power of the radiation to one fifteenth of that outside – this is called a protective factor of 15. Shelters constructed of the right materials can give a much greater protective factor than this.

According to FEMA TR-87, Standards for Fallout Shelters, “The minimum level of protection for public fallout shelters is PF 40”.

CAUTION: Permanent home fallout and blast shelters described in widely available FEMA pamphlets have protection factors in line with the PF 40 minimum standard for public shelters in buildings. In heavy fallout areas a sizable fraction of the occupants of PF 40 shelters will receive radiation doses large enough to incapacitate or kill them later. Permanent shelters built specifically to protect against nuclear weapon effects should have PF values much higher than PF 40.

Gamma Radiation Shielding For Various Materials

How do we apply all this in order to get an approximate idea about gamma radiation shielding for various materials?

A halving thickness is the amount of material that will block half the gamma radiation passing through it. A halving thickness has a protection factor (PF) of 2.

If you add another ‘halving thickness’, the material will block half of the remaining gamma rays, leaving 1/4. 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.

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 PF1000 (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

Consider the following chart of materials which indicate their radiation halving thickness, and approximately how much to achieve PF40, PF300, and PF1000 protection.

I’ve sourced the (halving thickness) numbers from what I believe are reputable sources. Then, simply calculated the PF numbers. Note that some of these materials will certainly vary in density and therefore shift one way or the other. For example, wood. They vary in density. Concrete, same thing… depends on its density mix/profile.

Consult with a specialist for accurate determinations. This is for information only.

Radiation Halving Thickness Chart

MaterialHalving
Thickness
[inches] 
PF40
[inches]
PF300
[inches]
PF1000
[inches]
Lead 0.42.13.24.0
Iron 0.94.87.29.0
Steel 1.05.38.010.0
Stone 2.211.717.622.0
Concrete 2.412.719.224.0
Aluminum 2.714.321.627.0
Brickwork 2.814.822.428.0
Sand 2.915.423.229.0
Packed Soil 3.619.128.836.0
Water 7.238.257.672.0
Wood 11.058.388.0110.0

A few typical questions:

How Much Concrete To Stop Radiation?

Well, apparently, for typical concrete density, it would take about 24 inches (two feet) to achieve an approximate PF1000 modern-day protection factor (radiation reduced to one one-thousandth). It doesn’t ‘stop’ it. Rather, it’s greatly reduced.

How Much Dirt To Stop Radiation?

Based on the radiation halving thickness of packed soil, it would take about 36 inches, or 3 feet to achieve approximately PF1000.

Sources

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:

  • NRC.gov
  • Civil Defense League of Canada
  • Wikipedia

Nuclear War Survival Skills (Upgraded Edition) by Cresson Kearny
(amzn)

U.S. Armed Forces Nuclear, Biological And Chemical Survival Manual
(amzn)

Potassium Iodide Tablets

Anyone who is concerned about radiation fallout should have these:
>> iOSAT Potassium Iodide Tablets
(view on amzn)

does potassium iodide expire

Concerned about nuclear fallout and alpha particles? I recommend a CE / CBRN approved full face respirator mask. The following product from MIRA Safety is one good choice…

CBRN Full Face Reusable Respirator-Mask
(their storefront on amzn)

[ Read:

5 Nuclear Radiation Detector Choices

Gas Mask For Nuclear Fallout

U.S. Nuclear Power Plants – Safe Distance?

US Nuclear Target Map

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33 Comments

  1. A fallout shelter is a wonderful thing but now let’s look at the missing link. Now, let’s say you are in a shelter with a PF of 1000 for radiation and and everyone is still getting very sick from radiation. You then ask yourself what have I missed in my build? Answer: I forgot to properly filter the air circulating thru the shelter. The air filter is actually in the same room as we are and has become highly radioactive from filtering the contaminated air. The air filter system itself must also be isolated from the room containing the occupants.
    The final question I have to ask is how long must I keep my family in the shelter. The time to remain in the shelter is ————- the subject of another article—— Ken, let’s have it.

  2. So based on above a 12×12 room at the 24” thickness is ROM 240,000 lbs of concrete. That is a lot of trips to H0m3 Depot in the Prius.

        1. Can anyone point to information which clearly says what a safe distance is from fallout outside a building without any heavy shielding? 15ft? 20 ft? I would have thought this info would be easy to find… how far does the dangerous radiation project through air?… for instance.. if I used tarps to quickly build lean-to’s around a house… causing radioactive particles to accumulate 15 feet away from the house (instead of directly alongside the foundation) … there must be a safe distance without heavy shielding

  3. If I store food in my basement (with just wood frame house above for shielding), I assume the food becomes contaminated with radiation. Does the passage of time make it safe to use or is it dangerous forever?

    1. Radiation kills living cells. Cells that are dead are still the same atoms and thus food if they have no alpha or beta particles I.e., fallout dust in them. So any food in a container would be fine.

  4. Does the gamma radiation move in straight lines? If you are in a basement, below ground level, are you essentially safe from the radiation if the source of the radiation is at an angle that places the ground (> 36”) between you and the source?

    1. NJ74,
      Gamma rays pretty much travel in straight lines. Question arises when you try to pinpoint the source. If you look at a nuclear blast, your basement scenario might be good. But you also would be smart to take in the gamma emitters in any fallout afterwards. This is why a fallout shelter with 3′ of earth cover is smart.

    2. Gamma radiation travels in the same way as light does, since it is part of the same (electromagnetic) spectrum. Diffraction and refraction can be discounted and the result is still accurate enough in this case. If you take the radiation from the fallout as “shining” in straight lines, that is good enough to determine the shielding level you have in any particular direction. Downwards is the major problem, since the MASS between you and the radiation source determines the attenuation. Three feet of earth sounds great, but how do you get it above your head safely, without danger of collapse ?

  5. A basement is not really that safe (better than nothing) as the fallout that lands on your roof will mostly pass through your house unhindered and give you a dose in the basement. Presuming your house is standard wood frame residential home. You really need shielding over you, though the distance from the source (your roof) to the basement will reduce your exposure slightly as well as the slight amount of shielding you receive from the wood, drywall etc.

  6. This article prompted me to further reading on gamma radiation. As Ken mentioned, it is only one of several forms of radiation, and only one of the many sources of damage, from a nuclear blast. That blast has to be on or close to the ground to emit gamma radiation that will harm people on the ground. As Ken says, gamma radiation moves at the speed of light. Within one minute or less all the gamma radiation has been expended from the blast. Gamma radiation will hit and pass through you at the same time as you see the flash. Other blast waves – sound, force, wind – arrive later, if at all. A dose of ionizing gamma radiation at the threshold level for tissue damage, 150 cGy (centigray), is to be expected at 2.8 km (1-3/4 miles) from the detonation of a 1 MT (megaton) bomb blast. Farther away is safer. (End of part 1.)

  7. (Part 2.) Gamma radiation is a photon, a type of light energy. It is not a material particle like fallout, and it does not make anything radioactive/does not cause matter to become an emitter. A ground or near-ground blast will turn certain metals in the ground radioactive and as as the nucleus of the material decays it will give off gamma radiation. Most gamma radiation dissipates within about 500 feet. So it’s best to keep clear of ground zero. Cosmic gamma rays (mostly from stars going nova) are reflected back into space by Earth’s atmosphere. A high-altitude EMP detonation likewise will not send gamma rays to the surface. Here are two main sources for relevant information:

    nuke.fas.org/guide/usa/doctrine/dod/fm8-9/1ch3.htm .. .. and .. .. acq.osd.mil/ncbdp/nm/NMHB2020rev/chapters/chapter13.html

    1. ..Most Gamma radiation.. depends on the energy of the photon. Some cosmic rays go all the way to the ground and go deep into the ground.

  8. In nuclear weapons of the size commonly held by the nuclear powers, the initial radiation pulse is not a concern as far as civilian survival is concerned. The size of the device, even the 400kT MIRV devices, means that the blast radius likely to destroy non-hardened structures (thereby killing the occupants) exceeds the lethal initial radiation burst radius. Not exactly good news but it does put it into perspective. IF you are far enough away to survive the initial radiation burst, you may STILL be in the lethal blast range. Not exactly good news either. The most interesting, and problematic zone is the area where the blast is the problem, with the possibilty of being trapped in the debris etc.

  9. Further to my previous comment, NukeMap is a good tool to find out which “zone” you are likely to be in. This is a good starting point to draw the conclusions on which to base any preparations you choose to make.

  10. I have heard that an EMP bomb will usually be used prior to thermonuclear weapons, approximately 20 minutes before blast. Will this type of power outage automatically start transfer switches of generator powered equipment for air and water filtration? If I have to find radio tubes and non-circuit board equipment then I am in trouble. Better to have a stationary bike with generator for air filtration.

  11. Tax Man,
    EMP result of bomb, not a separate bomb. No, to second question, it will fry any and all non protected electronics, as far as I’m aware.

  12. From the dates, I a retired engineering boss, 24 nukes, add a few crude organizational thoughts to an excellent text. The three rules of survival are get out of the city, repeated. Some will be hit 10- 20 times, if we win. The keys are the size, bull’s eye errors, air burst (max damage radius) or ground burst (max fall out. Wind direction will be crucial). Most of the energy is expended in seconds; duck, cover, lay down facing away and protect your eyes from light much brighter than the sun. Make prior decisions with loved ones: coming to get you or not. We meet at X. Do not die struggling to meet some one who left town. Have a bug out bag with you. Alpha and beta particles are lethal inside but can be stopped by a face mask/T shirt. Never ingest them. They are in dust. Gamma rays are deeply penetrating, kill, but do not harm water or food. They all will come from fall out, sand and dust, depositing on all surfaces. Tape cracked windows, keep the dust out. Wipe it off, strip it off, wear a scarf, run to a distant trash can.

    Add 200 ft of air to the halfing dimensions against fall out, consider those shade trees leaves. Get in the basement, deep as you can for as long as you can, the first days after the last blast will define life or death. Dust on the roof is a problem for most single level homes. Electromagnetic Pulse is death on electronics but some small stuff may survive; wrap a few radios in aluminum foil, lay them about on different steel shelves.

    I pray a lot, for our nation.

  13. Can anyone point to information which clearly says what a safe distance is from fallout outside a building without any heavy shielding? 15ft? 20 ft? I would have thought this info would be easy to find… how far does the dangerous radiation project through air?… for instance.. if I used tarps to quickly build lean-to’s around a house… causing radioactive particles to accumulate 15 feet away from the house (instead of directly alongside the foundation) … there must be a safe distance without heavy shielding

  14. Downwind207, Catch my comment to this article re gamma radiation. That radiation hits you at the same time as you see the flash. For protection from radioactive particles, all depends. Type of fissile material used, type of detonator and warhead, distance from blast to ground level, type of material atomized by the blast, mineral content of the ground, weather, jet stream pattern, height that particulate matter reaches during blast, proximity of very tall buildings or mountains. Lots of variables. Best to do lots of reading if interested in the topic. Might invest in dosimeters or a Geiger counter.

  15. Downwind207 asks an important question but unfortunately it has a harsh answer. Fall out shielding is simply a matter of matter of the heavy density of common materials such as concrete, and earth and uncommon thicknesses of solid metals, inches. Radiation passes essentially unhindered downward through the roof of a normal house, providing a Protection Factor of 1 -2 where 500 – 1,000 is desired. (Multistory buildings increase this with every added floor.) The distances in air are football field lengths, miles, irrelevant in most assessments. Thus it is vital that the air born fall out, dust, be kept out of the shelter area.

    1. I still want to know… if a pile of radioactive fallout particles was in the middle of a football field… how far away would you have to be so there were no dangerous level? 10ft, 50ft?, 100ft?

      1. Downwind207, You’re not paying attention. Saying “radioactive” is like saying “mammal.” How far away from that mammal do you have to be to be safe? That depends, is it a mouse or a mountain lion? Does it have rabies, scabies, or hungry offspring to feed? With radioactivity it all depends, and on a complex, interlinked set of facts and circumstances. And you haven’t even asked “for how long.”

      2. Downwind207
        I agree with Anony Mee. That if you had a Geiger counter you will know that “safe” distance. Since the “dust” can be made of material emitting any of 4 types of radiation, the safe distance will vary.

        If the “contamination dust “ was only emitting Alpha an inch away would be plenty.

        If the “contamination dust “ was only Beta a few ft away would be enough ( with only a few exceptions of high energy beta).

        If the “contamination dust “ was only Gamma it could take that whole football field.

        If the “contamination dust “ was only Neutron it might take a mile.

        In addition the volume of “dust” makes a difference. So you can see why there is no way to know without a detector.
        What I can say is it is a much bigger hazard to your health if you breath it into your lungs then it is on your skin. Keep as much off of you as possible and keep everything out of your body.
        I know this doesn’t answer your question but it may give you a place to start looking.

  16. I grew up near the sub base in Groton CT. Every now and then we would get something in the mail about what to do if there were a nuke war… I still have a newsletter which explained one of the safest places to be in a fallout situation is in a boat in at least 6ft of water. It said just get out of the cabin once an hour and rinse the boat off… in 6ft of water the radiation is dispersed enough so it is not dangerous… it was presumed the boat would have both a canvas cover for the area behind the cabin (like to keep rain out… often fitted with snap buttons) and that there would be a pump and hose to rinse the fallout particles off the boat.

  17. Situation: Victorian stone cottage, Blue Lias stone. 18″ thick walls. Foundation concrete. No idea how thick but guess pretty sturdy. No basement. Only possible safe place in centre of house ground floor. Not large rooms. Furthest from outside possible: 13ft from front, and 7′ 6″ from side (18″ thick) stone wall. Behind safe space, another 18″ thick wall, leading to kitchen 8ft wide, with an additional 18″ thick wall on opposite side. Downside -1 wood door leading through to kitchen which is sadly 3/4″ thick only.
    If I put thick (non biodegradable) garbage bags filled with dense earth outside against the wall (the 7′ 6″ distance from safe place) to 5ft height, how thick should that be? 3FT thick?
    Behind safe place leading to kitchen, would 18″ thick outer wall and 8ft kitchen ‘air space’ plus something like earth bags again to shore up the sad 3/4″ kitchen door create a survivable barrier against fallout particles? Survivable meaning no radiation sickness?
    Above -1 storey only bedroom area plus loft space approx.6-7ft high. 1892 build. Will be leaky re: air, though not rain water. Never modernised. Not insulated. Not my fault. Peppercorn rent as I am pensioner and landlord never does anything to help. 2 lath-and-plaster ceilings between roof and safe place. What are the hopes of reducing roof fallout direct line to safe place downstairs to safer levels? Should I just kiss my ass goodbye?

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