|MadSci Network: Physics|
To begin answering your question, I will have to state that I am not a James Bond afficionado. However, I believe you are referring to the bomb in the movie “Goldfinger.” Seeing as how it was quite some time ago since I last watched the movie, I forgot a number of the important details about the bomb. However, there are several scientific theories we can utilize to help figure out exactly what this “dirty bomb” may leave behind. To address the effects of the bomb blast on the gold, I would imagine the shrapnel or bomb pieces could embed themselves in the gold, the shock wave would move or destroy things, and the heat possibly even melting some of the gold. But since this is a “dirty bomb”, I’m going to assume that there is not a neutron producing part of the bomb activating surrounding materials. This would make things a lot more complicated. A dirty bomb is nothing more than a device used to spread some substance over a specific area (namely a large area). This “substance” could be anything from radioactive material, to harmful biological substances (anthrax), or even harmful chemicals like nerve gas. I do not remember whether or not the device was a thermonuclear device. If it were, I would not know where to begin in answering your question. However, since your question states it was a dirty bomb with only two radioactive components, it will make answering your question a bit easier. First, I’m going to present a common rule of thumb used by many in the health physics or radiation protection field: less than 1% of a radioactive isotope is left behind after 7 to 10 half lives of natural radioactive decay. The number of half lives that occur or passed during a specific time period is a ratio of the time period to the radioactive half life of the isotope of interest: n = T / (t1/2) where n = number of half lives that have occurred or passed, T = time period, t1/2 = radioactive half life of isotope of interest. By using the above equation, we can search through a chart of various radionuclides and isotopes to identify the particular radioactive material by its unique half life and discover what particular isotope or radionuclide establishes the “irradiated for 58 years” statement in the movie. Lets start with the assumption that the only radioactive components to this dirty bomb are cobalt and iodine. To set up our equation, we’ll first use 7 half lives to have less than 1% remaining radioactive material and see what answers we get. We’ll need to use some algebra to rearrange the equation so that we are solving for the half life (t1/2). And after we do that, we get the following equation: t1/2 = T / n We know that the time period we are interested in (T) is 58 years and the number of half lives that has passed (n) is 7. t1/2 = 58 years / 7 = 8.29 years From here, I would look up in a chart of radionuclides or isotopes for an iodine or cobalt nuclide with a half life close to 8.29 years. There are a couple of Isotope and Nuclide Charts on the web, but the one I use most can be found at: http://ie.lbl.gov/education/ isotopes.htm When looking through this reference, I could not find a cobalt or iodine isotope with a half life close to 8.29 years. And before I give up, let’s try 10 half lives to get less than 1% and see what we get. t1/2 = 58 years / 10 = 5.8 years Going back to a chart of nuclides, I find that cobalt has an isotope close to 5.8 years. This isotope is Cobalt-60 with a half life of 5.2 years. A much older reference I blew dust off of (Radiological Health Handbook, Jan. 1970 Edition, US Dept. of Health, Education, and Welfare) has a half life for Cobalt-60 from 5.2 years to 5.8 years, depending on how the half life was measured. So, it appears the gold in For Nox would be mainly “irradiated” (exposed to the radiations emitted from the radionuclide) by the Cobalt-60 isotope in the dirty bomb for 58 years - providing it was just left there and no one touching it. This would mean the cobalt-60 would be producing radiation particles (electrons and gamma rays) as it decays and exposing individuals that got too close to the bomb’s fall out. These radiations would not affect the gold in any way other than keeping individuals away from it until the radiation levels dropped to a safe level. I believe this is the intent of the dirty bomb in the movie: to create a situation where individuals could not access the gold for a long period of time and cause economic problems. However, there are other assumptions that could have been made that would significantly affected the outcome if the bomb had exploded. Like, was this more than just a “cobalt” and “iodine” device? If there were other radioactive components, those components could have made the device more destructive by having even longer lived radionuclides or activating surrounding building materials. Thereby taking even longer to decay to less than 1%. Another assumption to consider is just how much material was in the device to begin with. Depending on this amount and how well the device was able to disperse it in Fort Nox, the amount distributed may be of such a level that it would be possible for a decontamination crew to come in days later and remove the radioactive material. However, if the device had sufficient material and kept it rather local (only on the gold), then it may take a little longer for the nuclides to decay to a safe level before a team could reasonably go in and decontaminate the gold. After spending several years working in the radiation protection field, I found it quite odd that the characters in the movie would wait 58 years before doing anything with the gold. I mean, most radionuclides can be completely decontaminated from most surfaces and disposed of safely. Even though there may have been a considerable amount of radioactive material, it would not take 58 years to have radiation levels decay down to a level that individuals could work with it. Radioactive material is at times dangerous, but when handled with care and respect, it can be dealt with long before they decay away to nothing. I hope this has answered your question.
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