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Radiation Exposure

I keep hearing that no amount of radiation is safe. Now this document says that some of it is. Which is it?

Low levels of radiation exposure are safe. The exposure does carry some risk, and the level of risk is the same or less than other day-to-day activities we consider safe or acceptable.

Whether something is truly safe is based on how each individual sees it. Every day we face risks of various sorts without much consideration. The reason? The risk is so very low that we just don’t think about it or the risk is something we are willing to take because of benefits we see (like driving your car or walking across a busy street). It is the same with a dose of radiation. When the calculated risk from radiation exposure is the same as risks we routinely take and consider acceptable, we then say that amount of radiation exposure is also acceptable.

Why are there so many different terms when it comes to radiation? Rem, rad, curie, gray . . . what are they all for?

One reason for so many different terms is that the United States uses traditional radiation units while the rest of the world uses an international system of units (very similar to the United States using inches and other countries using centimeters). In the international system, we use sievert, gray, becquerel, and coulombs/kilogram, for example, while in traditional units we use rem (= 0.01 sievert), rad (= 0.01 gray), curie (= 3.7 x 10 10 becquerel), and roentgen (= 2.5 x 10 -4 coulombs/kilogram).

Another reason for all the different types of units is our need, as scientists, to be precise and accurate when we are describing radiation interactions and energy left behind.

How do we know about the effects at large doses, like skin reddening or cataracts or cancer?

While there have been animal studies, much of our information does come from actual human radiation exposure that was due to accidents and events. Some of the information came from the first people working with radiation, who were unaware there might be possible harmful effects and in some cases were exposed to too much radiation. Some became sick or suffered severe damage to their hands. There also has been follow-up on patients undergoing radiation therapy treatments, research focusing on people exposed to large amounts of radiation by accident, and studies of health effects in the Japanese atomic bomb survivors during World War II and in underground uranium miners.

Does the information on this site apply to children?

The information obtained about high-dose radiation exposures in adults does apply to children. Children are more sensitive to radiation than adults. Generally, when cells, organs or tissues are developing, as they are in children, they are more likely to be affected if radiation interacts with them. When considering radiation exposure to children, it is important to weigh the benefits (diagnosing a broken arm or appendicitis) against the risks (is there enough radiation exposure to increase the cancer risk?). 

How can I tell good radiation exposure from bad radiation exposure?

The detemination of radiation exposure being good or bad has more to do with how we each judge its benefit. Is it bad radiation exposure if you have an arm x ray and it shows that no bones are broken? Or is that a good thing because now you know it is only a sprain? The reason for a person to receive a radiation dose from any source should be justified based on the expectation that the activity causing the radiation will benefit the individual exposed or society. 

What about women who are pregnant and exposed to radiation?

This is such an important topic that we’ve chosen to go into more detail in another section. You can also go to the Health Physics Society Web site for information sheets, Q & A pages, and radiation doses to the embryo/fetus from medical exams involving radiation (

If I had x rays periodically when I was young (broken arm, sprained ankle, chest x ray, and more), do I need to be concerned?

No, there is no reason to be concerned about having a variety of routine diagnostic x-ray exams. The total radiation exposure you received is low and well within the lower radiation dose ranges that we call safe.

How do we know that the radiation exposure we received isn’t going to cause cancer?

We can't precisely predict whether any one individual will get cancer from radiation exposure. It’s like getting in a car to drive to work. We can’t predict whether any one individual will be in an accident or not. Even if the person drives very carefully, doing all the right things, we still don’t know what will happen. With radiation exposure, it is the same. At lower radiation dose levels, the chance of developing cancer or observing other effects is very low.

Who regulates radiation?

There are many regulators in the United States for various aspects of radiation uses and types of exposures. The Food and Drug Administration (FDA) regulates the manufacture and sale of devices that emit radiation (such as x-ray machines) and state health departments regulate the manufacture and sale of these devices, the use of radioactive materials and releases of radioactive material that could expose the public. The states, the Nuclear Regulatory Commission (NRC), and the Department of Energy (DOE) regulate how people work with various devices and radioactive materials and how much radiation exposure workers can receive.

How do I protect myself?

Before we talk about protection, let’s talk about need and benefit because we think it all goes together. We each need to be careful in considering what we are doing or are about to do. If we hurt, we finally decide to go to the doctor who, often, can help us with some type of pill. If we read the package insert for that pill, we will see that there are a number of side effects that can occur if we take it. We choose to take that pill anyway because it will make us feel better and we are either willing to risk the side effects or we have decided that the chance of them occurring is small.

That is how we assess the need and benefit of taking a risk. I need the pill because I hurt, the pill will benefit me by taking away my pain, and I’ve decided any of the side effects of the pill aren’t worthy of my concern. We need to give the same considerations to the various potential radiation situations. Some situations are easier to consider than others because the benefit is more obvious. We fall out of a tree and have an x ray to see if we broke our leg or just hurt it badly. Here, the benefit is obvious—the x ray will show right away if the bone is broken or not and, with that information, we can decide if we need to do anything else. Sometimes the benefit is obvious, like the bone x ray, and sometimes it is more difficult to determine what the benefit might be. Often, a benefit might be for our society as a whole, but not for us personally.

When something carries a risk that may affect us personally and we have the opportunity to say yes or no to it, it is considered a voluntary risk. Something that carries a risk but is a benefit to society might be considered an involuntary risk if it does not benefit us and we might not be able to say yes or no to it. For example, we voluntarily accept the risks associated with the production and disposal of batteries, computers, carpets, or plastics whether we use them or not because we know of their beneficial purposes. Although their improper disposal has the potential to release harmful products to the environment, we have decided that the benefits outweigh the risks. It can often be that way with nuclear technologies such as the production of electricity using nuclear power plants. There are benefits to society—a cleaner source of electricity to light and heat our homes and the reduction of our dependency on foreign oil—and potential risks if the radioactive waste generated at these plants is not disposed of properly.

To best assess the beneficial uses that might expose you to radiation: (1) be informed, (2) learn why you are going to receive a dose of radiation and what the dose is likely to be, (3) evaluate the concern with that level of radiation, and (4) if the level warrants, evaluate whether there are ways to lower the radiation dose.