MadSci Network: Physics

Re: What effects would the a cobalt-iodine atomic device have on gold?

Date: Mon Mar 10 17:30:51 2003
Posted By: Bernadette Baca, Health Physicist, Division of Reactor Safety
Area of science: Physics
ID: 1046642849.Ph

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:

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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