Trinity Site


Radiation levels in the fenced, Ground Zero area are very low. The maximum levels are only 10 times greater than the region’s natural background radiation. Many places on Earth are naturally more radioactive than Trinity Site.

A one-hour visit to the inner fenced area will result in a whole body exposure of one-half to one millirem. The levels vary from place to place, depending on the concentration of Trinitite buried at any one spot. Trinitite, the green glassy substance found in the ground zero area, contains several radioactive elements and is an alpha and beta particle emitter.

Comparative Sources of Radiation (in millirem)

The first chart shows different sources of radiation that people are subjected to. Note the different lengths of times in parenthesis. These radiation sources are from the Environmental Protection Agency.

The second chart shows the same radiation sources as the first chart, but this one compares those sources to levels that can result in radiation sickness and radiation poisoning. It is very important to note the different amounts of exposure time when comparing sources and doses of radiation. Data regarding radiation sickness are according to the Centers for Disease Control and Prevention’s Radiation Thermometer.

Radiation Frequently Asked Questions

Have questions about radiation? Take a look below to learn more about how radiation affects the human body. These questions and answers are from the Federal Emergency Management Agency’s (FEMA’s) Handbook on Radiation Safety.

What is Nuclear Radiation?

In the early 1900s, scientists discovered that certain materials eject three different kinds of energetic rays, which they named alpha, beta, and gamma rays. These rays, or radiation, can pass through certain thicknesses of air, liquids, and solids much like streams of tiny bullets, but at speeds many thousands of times faster than the fastest rifle bullet. The rays cannot be seen, heard, felt, smelled, or tasted.

Later, it was discovered that alpha and beta rays are very tiny particles with an electric charge that move more slowly and are less penetrating than gamma rays, which travel at the speed of light. Still later, it was found that gamma rays are packets of pure energy, called photons, that contain neither electrical charge nor matter. Because of this property of gamma radiation, it is more penetrating than alpha or beta radiation. Visible light and x-rays are also composed of photons, except that the photons of light have much less energy than the photons of gamma rays or x-rays. Alpha, beta, and gamma radiation originate from the nucleus, or central part, of a radioactive atom. This radiation is, therefore, called nuclear radiation.

All three kinds of radiation, alpha, beta, and gamma, are emitted from radioactive fallout particles produced by the explosion of nuclear weapons. Although alpha and beta radiation can be dangerous under certain conditions, the greatest threat to human life from fallout, and the most difficult to protect against, arises from gamma radiation.

How is Radioactive Fallout Produced?

When a nuclear weapon explodes near the ground, it makes a big pit or crater. Tons of earth in the crater are instantly changed from solids into hot gas and fine dust by the tremendous heat and pressure from the bomb explosion. This hot gas and dust, together with vaporized materials, form a giant fireball that rises rapidly in the air to high altitudes. It becomes the top part of the familiar mushroom cloud of a nuclear explosion.

Large volumes of dust and earth are sucked up with the fireball. some of this dust and heavier particles make up the stem of the mushroom cloud. The top of the cloud spreads out, cools, and forms a cloud of fine particles of earth and bomb materials. This dust cloud is carried for miles by the wind and drifts down to the earth as fallout. The dust in the stem and in the mushroom cloud becomes radioactive mostly from radioactive materials created in the nuclear explosion that become stuck to the dust particles.

The air around the particles does not become radioactive, and neither do the surface materials on which they settle. The heavier, large particles settle closer to the explosion than the small particles, which can be carried several hundred miles by the wind. Most of the fallout will come to the ground within 24 hours. Very small particles come down very slowly and may be spread over large areas of the earth’s surface, over periods of many days, even weeks. This delayed fallout is sometimes called “worldwide” fallout, although most of the fallout comes down in the hemisphere in which it is produced. Fallout that arrives within the first day or two after the explosion poses a much greater threat to human life than delayed fallout.

How Does Nuclear Radiation Harm Our Bodies?

Alpha radiation is stopped by the outer skin layers and isn’t harmful unless fallout particles are inhaled or swallowed. In this case, the alpha radiation may cause serious damage to the tissues inside the lungs or digestive tract. However, it is unlikely that anyone will breathe or swallow enough particles to become a casualty from alpha radiation during the emergency. The fallout particles are too large to pass through the respiratory tracts without being filtered or trapped, and it is unlikely that anyone will swallow large quantities of fallout particles except under bizarre circumstances. The average person does not need to be concerned about alpha radiation from fallout.

Beta radiation is much more penetrating than alpha radiation and may cause skin burns if a lot of fallout particles less than a few days old stay on the skin for a few hours. It may also be a greater hazard than alpha radiation if fallout particles are accidentally eaten or inhaled. If fallout particles are accidentally swallowed or inhaled, some of the radioactive atoms will find their way into the bones and organs of the body, where the alpha and beta radiation may possibly cause cancer years later. Again, it is unlikely that anyone will breathe or swallow enough fallout particles to become a casualty from beta radiation during an emergency, for the same reasons as given for alpha radiation.

Gamma radiation is the most dangerous of the three kinds of fallout radiation, because it can penetrate the entire body and cause cell damage to all parts, to the organs, blood, and bones. If enough cells in your body are damaged by gamma radiation, you will feel sick after awhile. Higher levels of exposure will cause death. Even if you are exposed to enough radiation to make you sick or possibly kill you later on, you may not feel anything while the radiation is causing damage. The reason you don’t feel anything is because the nerve cells are not directly stimulated by nuclear radiation as they are by pressure and temperature.

The hazard from nuclear radiation is much reduced within a few days after fallout has arrived because all radioactivity in fallout from nuclear weapons decays by natural processes. The rate of radioactive decay is most rapid during the first few days, and gradually slows as time goes on.

How do We Measure Quantities of Nuclear Radiation?

We cannot weigh nuclear radiation or collect it in a box, just as we cannot weigh or collect sunshine in a box. We must measure these things by the effects they cause. Unlike the part of sunshine that we can see, invisible nuclear radiation produces an electrical effect called ionization in the materials it passes through. This ionization can be measured by special instruments.

The roentgen (abbreviated R) is a unit of measurement for exposure to gamma and x-ray radiation. This unit is named after Professor Wilhelm Roentgen, who discovered x-rays in 1895. The harmful effects of nuclear radiation are related to the quantity of radiation to which a person is exposed. The quantity of radiation exposure will be given in units of roentgens. We use two kinds of instruments to measure nuclear radiation. One measures the total accumulated exposure to the radiation, and the other measures the rate of exposure, or how quickly radiation exposure is accumulated.

A dosimeter is a radiation detection instrument which gives its readings directly in units of roentgens. These instruments are called dosimeters because they measure the total “dose” or accumulated amount of radiation to which they are exposed.

Another kind of instrument, the survey meter, will measure the rate of exposure, in units of roentgens per hour (abbreviated R/hr). These instruments are called survey meters because they can be used to look over, or survey, an area to find out what the radiation levels are and find the spots where the nuclear radiation intensity is the highest or the lowest.

How Much Nuclear Radiation is Harmful?

Natural Background Levels. Low levels of nuclear radiation are a natural part of our surroundings. Radioactive elements in our own flesh and blood give off nuclear radiation, as they do in the foods we eat, the buildings we live in, and some of the water we drink. Nuclear radiation also comes from the sky and is called cosmic radiation. Nuclear radiation is part of all of our lives and has been present since the Earth was formed.

In the United States, the exposure per person to natural nuclear radiation during a whole year is seldom more than two-tenths of a roentgen. These background levels of nuclear radiation are too low to be measured by the radiological instruments provided for shelters. Levels of nuclear radiation from fallout will be thousands of times higher and will be measured in roentgens per hour (R/hr) instead of roentgens per year.

Symptoms of Radiation Injury. Although nuclear radiation from the natural background damages some cells in our bodies and destroys others, we do not notice this damage. Billions of cells in our bodies die natural deaths every hour and are replaced by normal growth and repair processes. We feel no injury or sickness from exposure to nuclear radiation at the levels which exist in our natural surroundings.

But if our bodies are exposed to gamma radiation from fallout, which is many thousands of times higher than the levels of natural background nuclear radiation, there will be so many cells damaged or destroyed that some of us may become sick, and some may even die. Some or all of the symptoms of injury may appear within the first three days after exposure. These symptoms include nausea, vomiting, diarrhea, fever, irritability, a lack of energy, and a feeling of being tired. The symptoms may disappear and then come back after a week to three weeks later, sometimes with diarrhea, sore throat, loss of hair, and a tendency to bleed easily. The greater the exposure, the earlier the symptoms will appear. They will also be more severe and last longer.

Chances of illness from infections are greater among those who are exposed to more than about 200 R, because the high radiation exposure damages the immune system in our bodies that helps fight diseases. In small children, the symptoms of radiation injury will appear at lower exposures than for adults. Even though a person may be severely affected by high radiation exposures, the person does not become radioactive from such exposure, and will not be a radiation hazard to anyone else.

Beta burns will result if a lot (enough to make you feel dirty or grimy) of fallout particles less than a few days old stay on the skin for several hours. Early symptoms of such skin contamination include itching and burning sensations. These may soon disappear. Darkened or raised skin areas or sores may appear within one or two weeks. After two weeks or more, there may be a temporary loss of hair (it will return in about six months). The greater the exposure, the earlier the symptoms will appear.

Beta burns will not be a problem if fallout particles are brushed or washed off promptly. Wearing clothing such as gloves, hats, scarves, face-masks, and long-sleeved garments will help to prevent fallout particles from collecting on the skin. Within a few days after fallout has arrived, its radioactivity will have decayed so much that beta radiation will not be a hazard under most circumstances. It may be a problem in the first few weeks if a person must lie or crawl on the ground, as may be necessary in rescue operations, and the skin is covered with dust which is not removed for many hours.

We are concerned mostly about radiation injury from gamma radiation from fallout particles on the ground, buildings, trees, and shrubs around us. This radiation is called external radiation because it comes from particles which are outside the body.

What is Brief Exposure and Radiation Sickness?

When people are exposed to gamma radiation from fallout, their entire bodies are exposed, including arms, legs, head, and trunk. This kind of exposure, called whole-body exposure, differs from medical exposures in which radiation may be concentrated on one small part of the body. A whole-body brief exposure to 50-200 R of gamma radiation may result in radiation sickness, but if only a part of the body such as the hand or foot is exposed to 50-200 R of gamma radiation, as in medical treatment, there will likely be no radiation sickness.

The human body has ways of repairing damage done to it. Because of these repair mechanisms, a whole-body radiation exposure of 600 R spread out uniformly over a period of 20 years would not cause any radiation sickness. But if this exposure were received over a period of a week or less, it would probably result in death.

Some people may become very sick within a few weeks after being exposed for a brief time (a week or less) to a certain amount of gamma radiation from fallout. Others may be exposed to the same dose and not feel any serious effects. If the exposure is less than 50 R, the injury from radiation should not produce symptoms in anyone. Some people irradiated in this dose range might experience loss of appetite and nausea, but this could also be the result of anxiety, uncertainty, and fear.

Doctors have described five levels of sickness which occur after brief whole-body exposure to 50 R or more of gamma radiation from fallout.

Exposure Range (roentgens)ResponseProbable Death Rate EstimateComments
0-50RNo symptoms0
50-200RRadiation Sickness Level 1Less than 5 percentDeath can occur in 60 or more days
200-450RRadiation Sickness Level 2Less than 50 percentDeath can occur within 30-60 days
450-600RRadiation Sickness Level 3More than 50 percentDeath can occur in about one month
<More than 600RRadiation Sickness Levels 4&5100 percentDeath will occur in two weeks or less
Levels of sickness and probable conditions of most people after brief whole-body exposure to gamma radiation.

Level 1, 50-200 R Exposure. Less than half of the people exposed to this much radiation experience nausea and vomiting within 24 hours. Afterwards, some people might tire easily, but otherwise there are no further symptoms. Less than five percent (one out of twenty) will need medical care. Any deaths that occur after radiation exposure are probably due to additional medical problems (complications) a person might have at the same time, such as infections and diseases, physical injuries, or other injuries caused by a nuclear explosion.

Level 2, 200-450 R Exposure. More than half of the people exposed to 200-450 R experience nausea and vomiting and are ill for a few days. This illness is followed by a period of one to three weeks when there are few if any symptoms, called a latent period. At the end of this latent period, more than half of those exposed experience loss of hair. A moderately severe illness develops which is often characterized by a sore throat. Radiation damage to the blood-forming organs results in a loss of white blood cells, increasing the chance of illness from infections. Most of the people in this group need medical care, but more than half will survive without treatment. The chances of living are better for those with smaller doses and those who get medical care. More than half are sick the first few days, but less than half die.

Level 3, 450-600 R Exposure. Most of the people exposed to 450-600 R experience severe nausea and vomiting and are very ill for several days. The latent period is shortened to one or two weeks. The main episode of illness which follows is characterized by bleeding from the mouth, throat, and skin, as well as loss of hair. Infections such as sore throat, pneumonia, and enteritis (inflammation of the small intestine) are common. People in this group need intensive medical care and hospitalization to survive. Fewer than half will survive in spite of the best care, the chances of survival being poorest for those who received the largest exposures.

Level 4, 600-1000 R Exposure. This level produces an accelerated version of the illness described for level 3. All the people in this group will begin to experience severe nausea and vomiting. Without medication, this condition can continue for several days or until death. Death can happen in less than two weeks, without the appearance of bleeding or loss of hair. It is unlikely, even with extensive medical care, that many can survive.

Level 5, Several Thousand Roentgens Exposure. Symptoms of rapidly progressing shock come on almost as soon as the dose has been received. Death occurs in a period from a few hours to a few days.

What are the Long-Term Effects of Radiation Exposure?

In addition to early sickness, exposure to nuclear radiation has some effects which may not show up for months or years. In the event of mass nuclear exposure, our first concerns will be with survival from the early effects. If the levels of nuclear radiation are low enough so that early radiation sickness is not a serious factor, then we become concerned with avoiding long-term effects. After a period of months to years has passed following an exposure to nuclear radiation levels many times higher than background levels, some of the people (less than a few percent) may develop various kinds of cancers. The probability of developing such late effects should not be used as a principal determining factor in decision-making during an emergency, but such effects can and should be minimized by keeping controllable exposures as low as practicable.

Can Radiation Contaminate Food and Water?

Food and water that have been exposed to nuclear radiation but are not contaminated by fallout particles are not harmed and are fit for human consumption, unless spoiled in some other manner. If food containers, fruits, vegetables, and grains become contaminated by the presence of radioactive fallout particles, they do not need to be thrown away. If the particles can be removed by washing, scrubbing, brushing, or peeling, the food is safe for consumption.

Water in covered containers and from underground sources will be safe. Water into which fallout particles have fallen may become unsafe to drink for awhile, because radioactive iodine dissolves in water. Water that is collected from rooftops or other flat areas into cisterns, tanks, or other reservoirs, may have much higher concentrations of radioiodine than other sources of water if there is a rainfall shortly after fallout has arrived. Rivers and streams that are fed mostly by water from the surface rather than from underground springs may also become contaminated by radioiodine if there is a rainfall in the first few days after fallout arrives. Water in large, deep lakes, reservoirs, and rivers will probably be safe to drink, although it could still be unsafe due to other pollutants, within several hours or days after fallout has arrived because of dilution of the radioiodine into large volumes of water.

The radioiodine problem will almost completely disappear in any water in a few weeks due to natural radioactive decay. The quantity of the radioactive iodine of greatest concern will become half as much every eight days, due to the half-life off radioactive iodine.

Radioisotopes that have dissolved in water cannot be removed by boiling or settling. The water can be purified by special filtering or chemical processes, one method being the filtration of water through several inches of soil or clay, but not sand. Water filtered through soil must be disinfected either by boiling or by adding chemicals such as chlorine or household iodine.