Understanding Radioactive Fallout

Although the purpose of this article is to discuss the effects of radioactive fallout after a nuclear attack, it is appropriate first to briefly go over the other effects of these powerful weapons so that a good understanding of the situation leading to the necessity of sheltering from fallout can be had.

The primary effects of a nuclear detonation are:

• Heat (thermal radiation)
• EMP (Electro-Magnetic-Pulse)
• Initial Nuclear Radiation
• Blast
• Radioactive Fallout

Heat (thermal radiation) is an instant and intensely bright flash of light comparable to or exceeding the brightness of the sun, traveling at the speed of light away from the detonation site in all directions. This flash of visible and thermal energy results in the instant ignition of fires on combustable materials for as much as several miles in every direction surrounding the site of detonation. Combustible items shadowed from the flash by buildings, fences, or other opaque objects are unaffected for the moment.

U.S. Department of Energy photograph

EMP (Electro-Magnetic Pulse) When a nuclear weapon is detonated a tremendous surge of electromagnetic energy is released. This high-energy pulse induces current flow in any electrical conductor just as current flow is induced in the windings of an electric generator as they pass through the field of a magnet. Induced voltages can exceed the values that will destroy many electronic devices. Since there has been no high altitude testing of nuclear weapons since 1963, actual experimental knowledge is limited; however, the following information can be used as a guide in understanding its effects:

• The EMP effects of a ground burst are serious mostly within the same area of the blast radius over 2 PSI (the Moderate Damage Radius in the table below), but can be propagated by power and telephone lines, railrod tracks, pipelines, etc. (The effects will travel line of sight from the detonation site for the most part, but will travel along conductors beyond that.)
• The EMP effects of a high altitude burst can be serious at over 1000 miles.
• For a large area, a 1 megaton device is about the minimum yeild needed to produce a significant EMP event, but the effects of blast, heat, and radiation are more serious.
• From an EMP perspective, the larger the weapon and the higher the detonation altitude, the more effect it will have.
• In the case of a large EMP event, you can expect many or most solid-state semiconductor devices within the effected area to be damaged or destroyed. This includes transistors, diodes, and integrated circuits in computers, TV's, radios, digital watches, hearing aids, pacemakers, digital electronics in microwave ovens and refrigerators, electronic ignition systems in automobiles, power inverters, glass cockpits in aircraft, etc.
• The older vacuum tube based equipment will be unaffected. Backups of emergency solid-state equipment that are well shielded and stored underground should be unaffected.

If it is any comfort, a terrorist attacker would most likely use a very small weapon of say, 1 or 2 kilotons yeild (1/1000 of a megaton), employed in a ground burst scenario. EMP effects would not be serious beyond the immediate blast radius and would be a non-issue for people outside the blast area. Inside the blast area EMP would be the least of their worries.

Initial Nuclear Radiation travels from the burst site imperceptibly slower than the speed of light and is made up of the gamma rays and neutrons released by the detonation and continues for a minute or so after it. Persons near enough to the site to receive a fatal dose of this radiation will more than likely be killed by the heat or blast anyway (unless they are in an underground shelter, in which case they would probably be shielded from the initial radiation as well).

Blast: The blast wave expands from the detonation at a little over the speed of sound (roughly 800 MPH) and consists of a sudden increase in air pressure. The pressure near the detonation site will be well over 100 PSI but this figure decreases rapidly with distance. This is followed by extremely powerful winds (greatly exceeding 100 MPH) moving away from the detonation site. After a short time the wind will decrease and air pressure will drop to less than normal. The wind will then increase again, but this time blowing toward the detonation site as the surrounding air rushes to fill the vacuum left by the initial blast. Air pressure will then return to normal though the wind may persist for several minutes (spreading and feeding the fires started by the thermal component).

This photograph shows a railroad bridge destroyed by an over pressure of 40 PSI which severely distorted the interior structural girders. The bridge was about 1/3 mile from the 37 kiloton air burst pictured at the top of this article.

U.S. Department of Energy photograph

There is large variety in the types of nuclear weapons available. Some are quite small (1 or 2 kilotons yield) and were allegedly developed for use in large engineering projects such as highway and dam construction. Others of greater yield (10 to 40 kilotons) were developed as tactical devices deliverable via artillery or rocket, or as air defense weapons deliverable via ground-to-air missile. Warheads of this class are roughly comparable to the devices used at Hiroshima and Nagasaki in 1945. Larger devices exist that yeild energies measured in the hundreds of kilotons, but these are mere fractions of the large devices available that can yield blasts measured in the tens of MEGAtons (millions of tons of TNT equivalent) - in excess of 1000 times the yield of the Hiroshima device.

Pictured below are detonations of two devices. On the left is an 11 kiloton device detonated in the Nevada desert. On the right is an 11 megaton device (1000 times greater yield) detonated on Bikini atoll in the South Pacific ocean. Obviously, the photo of the 11 megaton device was taken from a much greater distance, but you get the general idea.

U.S. Department of Energy photographs

The following table gives some perspective on the size of the blast areas produced by the larger weapons.

Surface Detonation
Distances given in miles.

Megatons weapon yeild:	1	5	25
Fireball radius	0.7	0.83	2.5
Total destruction radius (over 12 PSI) 98% dead	1.7	3	5
Heavy damage radius (5-12 PSI) Severe damage to commercial bldgs. 90% casualties (50% dead + 40% injured)	3	5	8
*Moderate damage radius (2-5 PSI) Moderate damage to commercial bldgs. Severe dammage to small residences. 50% casualties (5% dead + 45% injured)	5	7	14
*Ignition radius (newspaper will catch fire)	5	9	14
Light damage radius (1-2 PSI) Light damage to commercial buildings. Moderate damage to small residences. 25% injured	7	9	22

*If the weapon is detonated at altitude to maximize the reach of the blast, the moderate damage radius and ignition radius (on a clear day) are almost doubled. For instance, the 1 megaton moderate damage radius is extened from 5 to 8 miles and the 25 megaton moderate damage radius is increased from 14 to 22 miles.

Bear in mind that these figures represent initial effects and do not include further effects caused by spreading fires, accidents, and problems caused by public panic. The figures in this table also represent heavy Cold War style weapons employed by a high-tech aggressor probably delivered by an intercontinental missile. A smaller weapon employed by a terrorist would probably have a low yield resulting in a total destruction area of little more than a few city blocks - but that may be a naive assumption.

Radioactive Fallout is the fifth and most insidious of the five primary effects of a nuclear detonation and is the main subject of this article. The first four primarily concern persons in the local area of the blast, but radioactive fallout will leave its effects on persons tens and hundreds of miles away from the site of weapon detonation and can result in slow and agonizing death over a period of time for those affected.

Understanding Fallout

What is it?

In a nuclear detonation dirt and shattered debris are sucked up into the radioactive cloud where they are melted and infused with radioactive elements and on which radioactive elements condense. The majority of these particles take the form of gritty sand or dust. The larger particles fall to the ground fastest and emit radiation the longest. The smaller particles stay suspended in the air longer and therefore disperse over a much wider area - as much as hundreds of miles - but lose much of their radiation before they have a chance to fall to the ground. A high altitude detonation results in mostly smaller particles, but fallout will be present in any event.

Smaller particles lose most of their radiation in 24 hours or so. Larger particles (sand-sized) may take 3 or 4 days or more for their radiation output to fall to safer levels. Bigger debris which falls closer to the blast area and in greater amounts may take much more time. Generally speaking, the first 24 hours after fallout begins to settle will be the most dangerous time for an area near or downwind from a detonation site.

The image on the left below is a 15 kiloton ground burst. The image at right is a small air burst. As you can see, even in the small air burst there is much debris sucked up into the nuclear cloud. In spite of altitude, air detonations are not immune from creating large amounts of radioactive fallout debris.

U.S. Department of Energy photographs

Below, at left we see an 11 kiloton device detonated at 1500 feet altitude. At right is another airburst of 74 kilotons.

U.S. Department of Energy photographs

So, what is this radiation and how do I quantify it?

There are several units of measurement commonly used to describe radioactivity and its effects, but for the purpose of this discussion (which deals with high dosage levels in the human body expected after a nuclear attack) I will use the roentgen (symbol: R).

A simple definition of the roentgen (pronounced rent' jen) is the amount of X-radiation (X-rays or gamma rays) producing one electrostatic unit of electric force in one cubic centimeter of dry air. A more precise measure of radiation when it affects the human body is the REM (Roentgen Equivalent Man), which is the amount of any radiation that has the same effect in the human body as 1 roentgen of X-rays or gamma rays. This equivalence conversion is necessary because of the varrying degrees of destructive effect that differing types of radiation have on the human body. Here is the formula:

Neutron energy is limited to the initial nuclear radiation at detonation and one minute following. If a person is close enough to the detonation to receive a lethal dose of initial neutron or gamma radiation then the probability is high that he would be killed by the other weapon effects of blast and heat, so it is moot. For survivors of the blast and heat, the radiation produced by radioactive fallout after the detonation is of primary concern.

As can be seen by the table above, alpha particles are the most destructive but are stopped by as little as a sheet of paper or two. Beta radiation is similarly stopped by thick clothing, so the threat posed by these two types is limited to accidentally ingesting or breathing contaminated particles. Gamma rays, however, will penetrate completely through the body leaving dead and dying cells in their path. It is the dead cells that result in radiation sickness, infection, and death.

The roentgen is the unit measured by the common home dosimeter, so in light of these facts the roentgen is the most practical unit to use for a discussion of radioactive fallout from nuclear attack.

Effects of Gamma Rays on the Human Body

How much is too much?

Normal background radiation from natural sources such as cosmic rays, rocks, food, air, and water amount to less than 1/2 a roentgen per YEAR (about 360millirem). A modern dental X-ray doses us with only 2 or 3 thousandths of a roentgen, and a complete set of mouth X-rays amounts to only about 1/25 of a roentgen (about 40 milliREM). When compared to the energy released by fresh radioactive fallout from a nuclear weapon this is nothing!

The human body can tolerate much, much more than this. There is a limit for everyone though, and long-term effects such as increased incidence of cancer and leukemia are not considered here. The very young or very old, or those that are sick or otherwise infirm will be much more susceptible to adverse long and short-term effects of radiation exposure. For this reason, no particular dosage level can be used to exactly quantify a standard effect. The following tables will give a good general understanding though.

It is good to remember that radiation sickness is NOT contagious - it is NOT spread from person to person, just as hotdogs heated in a microwave oven will not cook other hotdogs they come in contact with. Each hotdog is affected only by the dose it receives.

This first table gives some rough guidelines describing short-term, whole-body exposures (in roentgens) and probable effects for the average person. By "short-term" we mean a period of hours, days, or a couple of weeks. By "long-term" we mean periods of months or years. We are also referring to total accumulated exposure.

What this means is that for a dose of 100 roentgens received over a few day's time there will probably be no obvious effects, and you will be able to continue your normal routine. When the short-term exposure exceeds about 200 roentgens you will get sick and probably need medical attention. A short-term exposure of about 600 roentgens will probably kill you..

These effects are lessened considerably if the dose is received over a long period of time. A short-term dose of 600 roentgens would probably be fatal, but if the exposure were gradually acquired over a much longer period (months to years) it would probably have no noticeable effects. For instance, if a person's total dose is 200 roentgens for the first month, 25 roentgens per week for the next 5 months, and 10 roentgens per week thereafter for the next 6 months, they would have little if any radiation sickness. The body will heal and repair some of the damage if the exposure is received gradually, allowing larger total doses.

Here is a similar chart detailing dosage effects expected in a group of people as condensed from a 1967 Defense Department shelter management textbook:

Laying Low

The image below is a map of the fallout plume produced by a 15 Mt device set off on Bikini atoll in 1954 that drifted over the Marshall islands, but in this image the plume is superimposed over a map of the eastern US to give a perspective of scale. The contour lines depict the areas of cumulative radiation dose in roentgens during the first 96 hours. As we learned in the discussion above, a dose of 450 or 600 can be considered fatal.

In the event of nuclear detonation, it is wise to be conservative and assume that you are downwind from the site and that the debris cloud is approaching you at 50 MPH even if you are hundreds of miles from the site of detonation. If you do not have instruments to detect and measure the radioactivity, assume that sandy particles that collect on windowsills, roofs, cars, tables, and other surfaces are radioactive fallout and get to your private or public shelter and stay there.

How long do I remain in the shelter?

If you do not have a dosimeter and rate meter or other monitoring device, a portable radio stored in your shelter will give you a chance to find out from local official sources when the radiation level has decreased to safe levels. At least that was true when local governments had Civil Defense equipment back in the Cold War days. Most of that stuff is history now, though with the recent threats from terrorists and others, radiation measurement equipment is coming back in style. As a rule of thumb, plan for 2 weeks in the shelter (unless you are in a very unlucky area). The following discusion will help you to understand the process of radiation decay.

Half-life: The decay rate for a radioactive element is expressed as "half-life" - which is the period of time it takes a radioactive element to decrease to half its initial value. Example: iodine 131 has a half-life of 8 days, and therefore loses half of its radioactivity in 8 days. Half of the remaining radioactivity will be lost in the next 8 days, and so on

There are about 200 radioactive elements present in a nuclear detonation with half-lives ranging from a few seconds to many tens of years, so the overall decay rate will be a combination of the decay rates of these elements which are present in varrying amounts.

A rough estimate of decay rate can be made by the "7/10 rule" which states that for every sevenfold increase in elapsed time, the radiation dose rate will decrease by a factor of 10. Example: Assuming all fallout has fallen and accumulated (big assumption), if the dose rate is 500 roentgens per hour one hour after detonation, then 7 hours after detonation the rate will be 50 R/hr. 49 hours after detonation (7x7 hours) the dose rate will be 5 R/hr. 343 hours after detonation (49x7 - or about 2 weeks) the dose rate will be about 0.5 R/hr.

As mentioned above, a dose of radiation spread out over time is less deadly than the same dose received in a short time. The longer you stay in a protective shelter, the better off you will be. Here are some suggested limits for time spent outside of the shelter at various radiation levels after an attack.

Needless to say, it would be very desirable to have some kind of monitoring equipment on hand in the event of a nuclear incident, whether it is the result of an attack or an accident. There are a number of radiation monitoring devices available, new as well as on the surplus market. The advantage of the "Geiger Counter" type monitors is that they give an instant indication of radioactivity without having to wait for a reading to accumulate. The advantage of the dosimeter type monitors is that a running total of accumulated dosage is recorded. It would be handy to have both types in your shelter,

The photo below shows the contents of the Family Radiation Measurement Kit as produced by the Bendix Corporation during the height of the Cold War. The kit is virtually identical to the old Civil Defense kits, containing a charging unit flanked by a dosimeter (at left) and a ratemeter (at right). This is a very effective and inexpensive gamma radiation monitoring set for the home shelter. The charging unit is used to apply a high voltage charge to the interiors and zero the readings of the two meters. It is equipped with an internal light source so that the meter's scales can be read while zeroing, and runs on a single D-cell battery. The two meters can be read at any time by looking through them at a light source like a lamp, window, or the daytime sky. The meters are equipped with clips so they can be secured to a shirt pocket, etc.

The function of the dosimeter and ratemeter are basically the same. The difference is in sensitivity. The dosimeter is allowed to tally up the radiation dose over an extended period of time so that the wearer's total exposure in roentgents can be measured. The ratemeter is much more sensitive than the dosimeter and is designed to be read after a short, measured period of time so that a rate of exposure can be measured - roentgens per hour.

Think of the dosimeter as being like the odometer in your car, measuring the total miles the car has traveled. In similar fashion you can think of the ratemeter as being like the speedometer in your car, measuring how fast your car is going in miles per hour.

Pictured below are views through each instrument when in use. The dosimeter at left is recording a total of 125 roentgens received. The ratemeter at right, if read ten minutes (bottom scale) after zeroing on the charger is showing a rate of 3.3 roengtens per hour. If read 1 minute after zeroing (top scale) it shows a rate of 33 roentgens per hour.

It is a good idea to measure the rate during the first day or so at least once per hour. Keep a log. It is good to check various locations within the shelter periodically as well. Some spots will be safer than others.

In the absense of radiation monitoring equipment or a radio to receive news from official sources, you can place a white object like a dinner plate or painted piece of wood or metal outside. If it remains clear of dust particles after a period of hours you will at least know that the fallout has stopped accumulating. A bright flashlight directed into the air at night can indicate falling particles as well. When the fallout stops, remain buttoned up for two weeks as a safety measure.

Shielding Materials

A home shelter may save your life.

Some radiation protection is provided by home basements as they are, but if the walls and ceiling are not thick or dense enough some simple additions to the existing construction can turn them into very effective and comfortable shelters. Here is a little questionaire I lifted from a Defense Department publication that will give a general idea of the potential your house has of providing effective shelter space. Answer the questions and add the total points, then compare the score with the Shelter Potential table at the bottom of the questionaire.

1. How many stories are above the ground level?

One story	11 points
One and a half stories	9 points
Two stories	6 points
Three stories or more	3 points

2. What is the maximum exposure of any basement wall above the ground? (Exclude exterior entrance of 3 feet width or less.)

No basement (skip question 3)	15 points
3 feet or more	8 points
2 to 3 feet	3 points
1 to 2 feet	1 points
Less than 1 foot	0 points

3. What is the principal material in the basement walls?

Cinder block or concrete block	2 points
Stone, brick, or poured concrete	0 points

4. What is the principal material of the first story walls?

Solid brick, stone, and concrete	3 points
Other	5 points

5. Is the house attached to or closer than 10 feet to another home or homes of similar size and construction?

No	2 points
Yes, 1 side	1 point
Yes, 2 sides	0 points

TOTAL POINTS __________

The lowest number of points indicates the highest degree of fallout shielding. Shelter Potential:

Up to 13 points:	Adequate
14 - 19 points:	Improvable at low cost
20 or more points:	Low

Below is a chart giving the thickness of common materials that will attenuate gamma radiation to one tenth of its un-shielded value, or in other words, reduce the received dose rate by 90%:

It is interesting to note that aluminum is only slightly better than concrete - definitely not a good choice from the economic perspective! Concrete blocks and dirt prove to be excellent low-cost or improvised shelter material.

A layer of one or two feet of bricks or dirt is good shielding, assuming there is no line-of-sight path from where fallout particles land to the interior of your shelter. So build the entrance to your shelter such that you must go around a corner or two to enter.

Distance matters too.

Given a large flat area covered with fallout, a person receives 50% of their exposure from the area within a radius of 25 feet, 75% of their exposure comes from the fallout within a radius of 50 feet, and 25% of their dose comes from beyond 50 feet. So, given a tall building, better protection from outside ground contamination will be found on the upper floors than on the lower floors (though distance must be maintained from the contaminated roof as well).

It is evident then, that the most effective shelter design will include distance from the gamma ray producing particles in combination with shielding to provide the highest level of protection.

With this distance factor in mind, it follows that a boat can serve as an effective shelter. Remain a few hundred feet offshore to distance yourself from fallout on the ground. The majority of radiating particles falling on the water will sink below the surface. Be sure the boat is equipped with a broom and a pump and hose to wash particles from the cabin and deck periodically. A tarpaulin or sail stretched over as much of the cabin and deck as possible - like an umbrella - will help to efficiently shed and wash particles from the craft.

Besides shielding, the general strategy of dealing with radioactive fallout is to:

Remove it from the area near your shelter by sweeping or washing. A tarpaulin to cover a space can be removed and cleaned off then replaced, thereby eliminating that portion of the radioactive particles from proximity to your shelter area.
Cover it with shielding material like sand or dirt to be dealt with at a later time.
or Isolate it by other means.

What about personal decontamination?

Decontamination of persons is very simple and is simply the process of removing the fallout particles from your hair and clothes and leaving it outside the shelter. Comb or brush out the hair, brush or shake off the clothing, and keep the particles out of the shelter. If you must go outside while fallout is accumulating, it would be a good idea to wear a hat and a raincoat that can be shaken off and stored outside the shelter. A dust mask and goggles would not hurt either.

The following is a short list of items, based on a list published by the Department of Defense in 1977 (but heavily modified by me), that you may want to take with you in the event that you relocate to another area. Not all of the items (the large ones in particular) are practical to transport if you are using public transportation - use common sense. This is a good list of items to keep in your basement shelter too.

The list as published by the Defense Department made special mention of items NOT to take with you if you relocate, including:

• Firearms - (guns of any kind)
• Alcoholic beverages
• Narcotics

I must take exception to the first two items. Both belong in the shelter.

First of all, and of most importance, firearms are a right and a necessity to a free people and the means by which not only political power but public order is maintained. In this day and age rational or proper social behaviour can not be expected from many segments of our society. In the event of a large public emergecy the improper behavior of these segments can be expected to be enhanced dramatically and the services of public security personnel will be in short supply. Bear witness to the public reaction to hurricane Katrina in New Orleans in 2005. It is the right and duty of all free men to defend their selves, their families, and the defenseless by any means necessary.
Secondly, alcohol in strong beverage form is a necessary item in the first aid kit that serves as disinfectant, pain reliever, anesthetic, blood thinner, and even as a fuel, and is also a highly valuable trade item. Ask anyone who has lived for a time in an area where the tap is turned off - Saudi Arabia for instance. It is amazing how many people will crawl out of the woodwork seeking this item and what they will pay.

A personal note to the reader:

During the height of the Cold War, the information presented in this article was general knowledge. In the years since the "fall" of the Soviet Union, this information seems to have left the national consciousness and a whole new generation has grown up without the apparent impending threat of thermonuclear war. The public fallout shelters that once were found underneath almost every school, hospital, and other public building are no longer stocked with emergency food, water, and medical supplies and other rescue and radiological equipment. The sirens and other warning systems have been removed and are no longer tested or heard in most communities. How long has it been since you've seen one of these signs?

Despite the apparent political landscape, the weapons discussed in this article still exist in the world by the tens of thousands. There are rogue nations and well funded extremist groups that are extremely hostile to the western world and would pay any price to acquire these weapons. It is certain they would use them if and when they could aquire them.

There is the information. Do with it what you will.

- Sustinemus
April, 2005

Only 350 kilotons, about 1/100 the yeild of the most powerful available.