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Excellent Source of Nuclear Preparedness Information: KI4U

Q: What are the Nuclear Radiation and Fallout Effects?

A: All nuclear explosions release radiation, both initial radiation and residual or fallout radiation. The initial radiation makes up about 5% of the total energy released by a nuclear explosion and is released well within the first minute following the detonation. The threat of exposure to injurious levels of this initial radiation are confined typically to within a radius of about 1.50 miles from the nuclear detonation of anything less than a 1 MT bomb. Within this range, and out in the open and exposed without blast and thermal pulse protection, you most likely would also suffer lethal injuries from the blast impact and burns.


Nuclear Blast Distance Effects

One other effect of the initial radiation that is of concern only from very high altitude nuclear explosions is called the Electromagnetic Pulse or EMP. This very brief, but powerful electrical field is expected to disable electric power and communications on the ground as well as satellites. While it causes no direct harm to people when detonated at its high altitude optimum heights, it is expected by the DoD to be the first shot fired to effectively knock out the electrical grid and communications below it. Even one large correctly placed nuclear explosion over the center of the U.S. could severely disable most all the electrical power and communications from coast-to-coast. More information on EMP effects can be found in the Nuclear War Survival Skills book.

What will be of concern to the greatest number of people, though, is the remaining 10% of the energy unleashed by a nuclear explosion, the residual or fallout radiation. Any nuclear detonation on the ground, or where an airburst was low enough that the fireball touched the ground, will create tons of radioactive materials that will be sucked up into the classical mushroom shaped cloud to then be spread far downwind. These radioactive particles carried by the wind then later fall out many miles away from ground zero and are the source of what we know as radioactive fallout. Each of these trillions of contaminated particles continuously gives off invisible radiation while in the mushroom cloud, while descending, and after having fallen to earth.

If you remember the dust and ash that had covered many parts of the U.S. hundreds of miles away from the eruption of Mount St. Helens, then you have an idea of how far and wide thousands of tons of radioactive fallout sucked miles high into the atmosphere can then later be deposited well away from its initial ground zero source. This radioactive fallout, spread by the winds and eventually covering hundreds of square miles, has the potential to kill many more people downwind than those unfortunate enough to have been too close to ground zero.

Few realize, too, that surface nuclear tests conducted in the Soviet Union and China have covered much of the U.S. with low levels of radioactive fallout in the past. Many are concerned that a serious nuclear exchange in the Mid-East, Korea, or between India and Pakistan could, at the minimum, result in serious contamination of milk and other foodstuffs here in the U.S., too. See/Read Trans-Pacific Fallout for more details.


Nuclear Blast Distance Effects

The heaviest particles normally fall closest to ground zero and at the other extreme the smallest of the particles, invisible to the naked eye, can travel thousands of miles on the winds and some of it will stay suspended for decades. The larger the bomb the higher the mushroom cloud and the likelihood of the fallout being dispersed and suspended longer in the upper atmosphere. But, with rain showers, all sized radioactive fallout particles can be brought down much sooner and can create localized 'hot spots'. However, at any one place where the fallout from a single explosion is being deposited on the ground in concentrations strong enough to require the use of protective shelters, this deposition will usually be completed within a few hours.


Nuclear Blast Distance Effects

The above 15 mph fallout pattern examples do not reflect that the winds are often moving in different directions and at different speeds at different altitudes. Only generalizations should be inferred from them. The maps do show that the highest levels of radioactive fallout can be expected closest to ground zero and then trail off with distance. One exception, though, would be from rain showers creating hotspots downwind.

Bottom Line: While the blast, shock wave and thermal effects are nearest ground zero, the residual radiation effects via fallout can endanger thousands more and for 100's of miles downwind. It is this radiation hazard carried on the winds that holds the potential to sicken and kill the greatest number of people. As seen above, the fallout radiation, measured in R/hr, is highest nearest to ground zero. But, as Chernobyl proved with documented cases of thyroid cancer 500 km (310 miles) downwind, the danger zone truly is extensive. (See the Potassium Iodide Anti-Radiation Pill FAQ for more details on thyroid cancer creating radioactive iodine.) Next, we'll explore the different kinds of radiation, their measurement units and, finally, how much is too much.


Q: What's the Difference Between Alpha, Beta and Gamma Radiation?

A: Everything in nature would prefer to be in a relaxed, or stable state. Unstable atoms undergo nuclear processes that cause them to become more stable. One such process involves emitting excess energy from the nucleus. This process is called radioactivity or radioactive decay. "Radiation" and "radioactivity" are often confused, the proper relationship is that "radioactive atoms emit radiation."

The three main types of nuclear radiation emitted from radioactive atoms and included in all fallout are:

Bottom Line: All three of the primary types of radiation above can be a hazard if emitted from radioactive fallout that was inhaled or ingested. Protected food and water and even a simple inexpensive dust protector face mask can go a long ways to denying this route of entry. However, for the penetrating gamma rays, it is essential to be able to identify the best protected shielding and distance options available. More information on the specific physical damage caused by gamma radiation is below in the section below entitled: How Much Radiation Is Too Much?


Q: What's the Difference Between Roentgen, Rad and Rem Radiation Measurements?

A: Since nuclear radiation affects people, we must be able to measure its presence. We also need to relate the amount of radiation received by the body to its physiological effects. Two terms used to relate the amount of radiation received by the body are exposure and dose. When you are exposed to radiation, your body absorbs a dose of radiation.

As in most measurement quantities, certain units are used to properly express the measurement. For radiation measurements they are...


  • Roentgen: The roentgen measures the energy produced by gamma radiation in a cubic centimeter of air. It is usually abbreviated with the capital letter "R". A milliroentgen, or "mR", is equal to one one-thousandth of a roentgen. An exposure of 50 roentgens would be written "50 R".


  • Rad: Or, Radiation Absorbed Dose recognizes that different materials that receive the same exposure may not absorb the same amount of energy. A rad measures the amount of radiation energy transferred to some mass of material, typically humans. One roentgen of gamma radiation exposure results in about one rad of absorbed dose.


  • Rem: Or, Roentgen Equivalent Man is a unit that relates the dose of any radiation to the biological effect of that dose. To relate the absorbed dose of specific types of radiation to their biological effect, a "quality factor" must be multiplied by the dose in rad, which then shows the dose in rems. For gamma rays and beta particles, 1 rad of exposure results in 1 rem of dose.

Other measurement terms: Standard International (SI) units which may be used in place of the rem and the rad are the sievert (Sv) and the gray (Gy). These units are related as follows: 1Sv = 100 rem, 1Gy = 100 rad. Two other terms which refer to the rate of radioactive decay of a radioactive material are curie (Ci) and becquerel (Bq).

Bottom Line: Fortunately, cutting through the above confusion, for purposes of practical radiation protection in humans, most experts agree (including FEMA Emergency Management Institute) that Roentgen, Rad and Rem can all be considered equivalent. The exposure rates and doses you'll usually see will be expressed simply in terms of roentgen (R) or milliroentgen (mR). Remember, too, a milliroentgen, or "mR", is equal to one one-thousandth of a roentgen "R". For details on how much is too much "R", see the next Q&A section below entitled: How Much Radiation Is Too Much?


Q: How Much Radiation Is Too Much?

A: Before you can begin formulating a radiation protection shelter strategy you need to first understand and then determine the levels of radiation exposure one should be most concerned about in a nuclear emergency. Then the correct strategy best suited for the job will begin to reveal itself.

The following is compiled from FM 3-7. NBC Field Handbook, 1994. FM 8-9. NATO Handbook on the Medical Aspects of NBC Defensive Operations, 1996. FM 8-10-7. Health Services Support in a Nuclear, Biological, and Chemical Environment, 1996. It is instructive in outlining the levels of radiation and their health effects.


Expected health effects assuming the cumulative total radiation exposure was all received within a week.



30 to 70 R	From 6-12 hours: none to slight incidence of transient headache and nausea; 
		vomiting in up to 5 percent of personnel in upper part of dose range. Mild 
		lymphocyte depression within 24 hours. Full recovery expected.

70 to 150 R	From 2-20 hours: transient mild nausea and vomiting in 5 to 30 percent of 
		personnel. Potential for delayed traumatic and surgical wound healing, 
		minimal clinical effect. Moderate drop in lymphocycte, platelet, and 
		granulocyte counts. Increased susceptibility to opportunistic pathogens. 
		Full recovery expected.

150 to 300 R	From 2 hours to three days: transient to moderate nausea and vomiting in 
		20 to 70 percent; mild to moderate fatigability and weakness in 25 to 60 
		percent of personnel. At 3 to 5 weeks: medical care required for 10 to 50%. 
		At high end of range, death may occur to maximum 10%. Anticipated medical 
		problems include infection, bleeding, and fever. Wounding or burns will 
		geometrically increase morbidity and mortality.

300 to 530 R	From 2 hours to three days: transient to moderate nausea and vomiting in 50 
		to 90 percent; mild to moderate fatigability in 50 to 90 percent of personnel. 
		At 2 to 5 weeks: medical care required for 10 to 80%. At low end of range, 
		less than 10% deaths; at high end, death may occur for more than 50%. 
		Anticipated medical problems include frequent diarrheal stools, anorexia, 
		increased fluid loss, ulceration. Increased infection susceptibility during 
		immunocompromised time-frame.  Moderate to severe loss of lymphocytes. 
		Hair loss after 14 days.

530 to 830 R	From 2 hours to two days: moderate to severe nausea and vomiting in 80 to 
		100 percent of personnel; From 2 hours to six weeks: moderate to severe 
		fatigability and weakness in 90 to 100 percent of personnel. At 10 days to 
		5 weeks: medical care required for 50 to 100%. At low end of range, death 
		may occur for more than 50% at six weeks. At high end, death may occur 
		for 99% of personnel. Anticipated medical problems include developing 
		pathogenic and opportunistic infections, bleeding, fever, loss of appetite, 
		GI ulcerations, bloody diarrhea, severe fluid and electrolyte shifts, capillary 
		leak, hypotension. Combined with any significant physical trauma, survival 
		rates will approach zero.

830 R Plus	From 30 minutes to 2 days: severe nausea, vomiting, fatigability, weakness, 
		dizziness, and disorientation; moderate to severe fluid imbalance and headache. 
		Bone marrow total depletion within days. CNS symptoms are predominant at 
		higher radiation levels. Few, if any, survivors even with aggressive and 
		immediate medical attention.


The effects from the above radiation dose levels assume that the total dose was received over a short period of time of a week or less.

The response to radiation varies widely amongst people and the longer the time frame over which a specific dose is accumulated the better your body can respond to, and recover from, the radiation damage. In other words, a normally fatal (to 50% of a group exposed to it) cumulative dose of 530 R, if received all within a week, would create few noticeable ill health effects at all if it was received and spread out over a years time at the rate of about 10 R per week. Think of the difference in acquiring a suntan gradually over a years time at a rate of about an half hour per day compared to packing that years worth of sun exposure (182 hours) all into one solid non-stop week, night and day, for 24/7. The health effect difference is obviously very dramatic.


Nuclear Blast Distance Effects

Remember, promptly removing yourself from the radiation source would have you no longer absorbing and adding to that cumulative dose. And, that can make all the difference between absorbing a dangerous radiation dose or getting only a tiny fraction you might not even be able to later notice.

With all of the above lethal radiation exposure ranges in mind, review again the typical fallout distribution patterns and levels of radioactivity likely to be encountered at different distances from ground zero...


Nuclear Blast Distance Effects

When you see an area above such as 50R/hr, understand that that means if you stayed exposed in that region for 4 hours you would have received a total dose of 200R. Or, if you promptly left the area or got into a good shelter within half an hour you would only have received a total dose of 25R. (Actually less in both cases, once the fallout has stopped arriving, because it loses much of its initial intensity quickly. More on that 'good news' later below.)

It should be readily apparent now, too, that an essential tool to knowing and thus minimizing your family exposure to radioactive fallout is both acquiring and learning the proper operation of a radiation meter. Cresson H. Kearny, the author of Nuclear War Survival Skills, by Oak Ridge National Laboratory, a Facility of the U.S. Department of Energy states in Chapter 10 - Fallout Radiation Meters:


    A survivor in a shelter that does not have a dependable meter to measure fallout radiation or that has one but lacks someone who knows how to use it will face a prolonged nightmare of uncertainties. Human beings cannot feel, smell, taste, hear, or see fallout radiation.

    Which parts of the shelter give the best protection? How large is the radiation dose being received by each person? When is it safe to leave the shelter for a few minutes? When can one leave for an hour's walk to get desperately needed water? As the fallout continues to decay, how long can one safely work each day outside the shelter? When can the shelter be left for good? Only an accurate, dependable fallout meter will enable survivors to answer these life-or-death questions.

    With a reliable dose rate meter you can quite quickly determine how great the radiation dangers are in different places, and then promptly act to reduce your exposure to these unseen, unfelt dangers. For example, if you go outside an excellent fallout shelter and learn by reading your dose rate meter that you are being exposed to 30 R/hr, you know that if you stay there for one hour you will receive a dose of 30 R. But if you go back inside your excellent shelter after 2 minutes, then while outside you will have received a dose of only 1 R.

Bottom Line: Clearly, as seen above, there are high enough levels of radiation from fallout to kill unsheltered people many miles downwind from ground zero of a nuclear explosion. (The probability that you are currently at, or downwind of, future 'ground zeros' is explored in the next Q&A section.) If you ever discover yourself to likely be downwind of a future nuclear explosion, to where the winds could later be depositing radioactive fallout on your location, you will have only three options:

#1 - Prompt evacuation to an area you are confident will not have fallout deposited onto it also, but only if you know that you have time to do so. (Of course, if the fallout has already begun to arrive or likely will be shortly, attempting evacuation could be very risky, especially with incomplete information as to what locations would really be safer. Don't count on having nice drawings like the above overlaid on your regions map and airing on TV accompanied by evacuation directions from the TV weatherman.)

Or, #2 - have already prepared a fallout shelter for your family where they usually are, at home.