Secret Cities Radiation Dosage Chart

Categories: Articles

It goes without saying that building the atomic bomb in the “Secret Cities” of the Manhattan Project involved working with high levels of radioactivity. At that time, the risks of radiation exposure were not as understood as they are today. Even now, there are debates about the safety of certain common forms of radiation, such as medical imaging, as well as less common sources, including stored radioactive waste.

By simplest definition, radiation is energy travelling through space. Sunshine is a familiar form of radiation, delivering light and heat. Of particular concern is ionizing radiation, which is a form of radiation that can damage cells in living things, posing potential health risks. Still, there are many forms of ionizing radiation that humans safely absorb every day.

So what’s the different between helpful and harmful radiation? Is it something we can avoid?

We talked to Secret Cities curator Martin Moeller to shine a light on the mysteries of radiation.

Is all radiation bad? Or at least is one radioactive object just as dangerous as another?

No. Nowadays, when people talk about radiation, they are typically referring to ionizing radiation, rather than just light or radio waves, for example. Even so, the potential health effects of ionizing radiation are variable. They depend on the distance from the radioactive source, duration of exposure, and any substances—clothing, for instance—that might block some of the radiation from reaching the body. There are also different types of ionizing radiation, each posing different kinds of risks—many people have heard the terms “alpha,” “beta,” and “gamma” used to refer to distinct forms of radiation.

There are some people who believe that low-level radiation exposure is not only harmless, but potentially even beneficial to human health. Others refute that, but what is clear is that we are all exposed to various forms of radiation every single day.

How does radiation dosage work? How does the chart (above) break down?

One common unit of measuring radiation dosage is the “sievert,” which is defined technical as one joule of energy per kilogram of recipient mass. That’s probably gobbledygook for most people, so let’s just say it is a specific amount of energy that is absorbed by, say, a person or animal. One sievert is actually a lot of energy, so we usually use smaller versions of the unit—the millisievert or microsievert, the equivalent of breaking meters into smaller units like millimeters. Since, as mentioned above, the duration of exposure is also critical, we might also talk in terms of, say, “millisieverts per hour.”

Bananas contain radioactive potassium—don’t stop eating bananas, though, because there is radiation in virtually everything you eat—and we can measure the radiation dosage in microsieverts (millionths of a sievert). That’s a tiny dose. As you move up into medical imaging, the dosage become more substantial. If your doctor says you really need a CT scan, then get a CT scan, but don’t go begging for one if you don’t need it—the dosage from a single CT scan is unlikely to cause any health problems, but multiple scans may slightly increase your future risk.

But one of the goals of this chart is to put risk in perspective. Many people travel by air all the time without thinking about it, but air travelers are subjected to higher ambient radiation during their flights because there is less atmosphere above them blocking solar radiation. The same is even true of people who live at very high elevations, but you never hear of people moving down the mountain to avoid radiation.

At what point does radiation become harmful to people?

Unfortunately, it is virtually impossible to establish an exact cut-off. After atomic bombs were dropped on Hiroshima and Nagasaki, hundreds of thousands of people received substantial radiation doses even if they survived the initial explosions and resulting fires. Some of these people died horrible deaths soon afterwards, others survived but went on to develop cancer or other possibly radiation-induced diseases later in life. Still others lived long lives seemingly without ill effects. Even minor differences in their locations could account for some, yet not all, of these differences.

Scientists and health professionals often talk about radiation risk in terms of populations rather than individuals. For example, under certain exposure circumstances, X number of people out of Y number of people might be expected to become ill as a result of the exposure. That is slightly different from saying that a given person has an X% greater chance of becoming ill.

For those working in the Manhattan Project cities, were workers able to protect themselves from higher dosages?

Manhattan Project leaders, of course, took many precautions to protect workers. As you might expect, protocols for radiation safety have changed a good deal since then. There is evidence that some Manhattan Project workers—particularly at Hanford—experienced higher levels of radiation-related illness in the years following the war. Based on the evidence I have seen, the current incidence of cancer and other potentially radiation-related illnesses does not appear to be appreciably different among residents of the former Secret Cities in comparison to other Americans, though some residents dispute that.

There are guidelines for maximum allowable dosage for radiation workers, and they are much higher than the typical radiation levels that most people receive over the course of their daily lives. There are still many questions about the health impacts of radiation exposure. Having said that, while no one should be blasé about it, most people have nothing to worry about in terms of their own radiation risk.

Secret Cities is now on view at the National Building Museum through March 3, 2019.