Answer to Question #7986 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Surveys and Measurements (SM)

The following question was answered by an expert in the appropriate field:

Q
Is it possible to detect radioactivity from a satellite of a nuclear bomb that detonated on the ground in the 1940s (say for example at Hiroshima or Nagasaki)? Is there satellite imagery that a civilian can scrutinize?

I would assume that due to the radioactive half-life of the fission products of a tactical nuclear weapon, it would still be possible to detect residual radiation (239Pu or 235U) from over 60 years ago. Is this so?

If it is not possible for a civilian to view Department of Defense satellite imagery, then what about taking soil core samples at an actual site and having them tested? How would I go about attempting this?

Finally, what about snow layers in locales such as Greenland, Antarctica, etc.? I would imagine that it would be difficult to pinpoint a date from this a type of sample.

A

To my knowledge there is no technology that would allow satellite detection of radioactivity remaining on earth from the second world war nuclear bombings, and there are no images available to scrutinize. You are correct in your assumption that some radioactivity from the use of those weapons does remain in the environment.

Such radioactivity includes some longer-lived fission products such as 137Cs and 90Sr, uranium isotopes and transuranic radionuclides, such as 239Pu, and some radioactive species that were produced by irradiation of stable elements with neutrons produced during the fission process. Examples of the latter activation products are 252Eu, 36Cl, and 60Co. The presence of these radionuclides is well known and numerous measurements have been made.

Some of the bomb products, such as the likely fission products and transuranic nuclides, are the same as products present naturally in the earth and/or products produced when atmospheric testing of nuclear bombs was being conducted; products of this testing have been deposited as fallout around the world. These facts somewhat confound attempts to evaluate the amounts of such materials that represent residual activity from the bombings. Researchers have gotten around this problem, in part, by looking at ratios of particular isotopes, such as 234U/238U, which tend to be higher in the Japanese bomb fallout areas compared to other locations not influenced by the war bombings. This ratio can be correlated with certain fission product activity, such as 137Cs, and this has been used to associate excess levels of 137Cs in some sections of Japan with the bombing events. Techniques using ratios of plutonium isotopes and ratios of plutonium to certain fission products have also been used to identify residual soil activity associated with the bombings of Nagasaki and Hiroshima.

You can find references to a variety of work that has been carried out by searching the Internet, using an inquiry such as “residual radioactivity Japan” or “activation products Hiroshima.” There has been an ongoing interest among the governments and scientists in Japan, the United States, and other countries as to the consequences of the World War II bombings of Nagasaki and Hiroshima, and many environmental samples have been taken and analyzed for radioactivity content. In addition to usual media, such as soil, these samples include many taken from buildings and structural materials to be analyzed for neutron activation products, which are especially useful in attempting to reconstruct the neutron doses received by victims of the bombings. Since many of the results of such work are generally available to anyone with an interest in this area, I would not think you would want to pursue independent analytical work unless you are equipped through training and/or acquired expertise, have considerable financial backing, and have a plan to generate new data that will add to present knowledge. Your chances of pursuing studies in this area would be enhanced if you had some background in this type of work and could contact one or more researchers involved in analyses of this sort. The Radiation Effects Research Foundation (RERF) is a Japan-United States cooperative organization that studies health effects of atomic bomb radiation. You may find it helpful to learn more about RERF and the research programs that it is pursuing.

Regarding your last question about snow layers, I am not quite sure I fully understand your question. You refer to pinpointing a date. If your reference is to some aspects of geological dating, there are some effects of snow cover that do have an impact on some aspects of age dating—e.g., significant snow and ice cover reduce the penetration of cosmic neutrons, thus reducing the production of certain nuclear species through neutron interactions with nuclei in the earth. A specific example relates to ratios of 26Al to 10Be, two radioactive species produced at a more or less constant rate through cosmic neutrons interacting in the earth. When production of these species ceases or is reduced, the ratio changes compared to what would be observed under constant production. In fact, the ratio is used to make estimates of ages of layers of earth/sediment that have been buried by subsequent deposition of additional material. When heavy deposits of snow/ice have been present for long periods, the cosmic neutron fluence will be reduced, and the surface concentrations of these radionuclides will be less than would otherwise be expected, and this may have to be considered in some analyses.

Hope this is helpful. Good luck in your pursuits.

George Chabot, PhD, CHP

 
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