A radioactive package bound for the US was seized in Kiev
The regional emergencies ministry said the package, discovered Tuesday, was emitting radiation at a rate thousands of times higher than the norm in Kiev of 0.05 milliroentgens an hour.
OK, here's a quick primer for the non-nukes out there. There are several types of radiation, alpha, beta, gamma and neutron. The amount of biological damage (REM) per unit exposure (roentgen) for each type of radiation varies. We use a number called the quality factor to determine the amount of biological damage for a given exposure to radiation. The quality factor for gamma and beta radiation is 1, for neutron radiation is 3-10, and 20 for alpha. While the article doesn't specify the type of radiation, we can rule out alpha and beta because the packaging materials, even if it were just cardboard and paper, would have shielded the radiation, and the package would not have been detected. That leaves us with gamma or neutron radiation, so our quality factor ranges from 1 to 10. We'll take the conservative (most limiting) approach and assume a QF of 10.
The article tells us that the radiation levels were "thousands of times higher than the norm in Kiev of 0.05 milli-roentgens per hour." (I'm assuming that the dose rate they're using was taken on contact with the package.) A milli-roentgen (mr) is 1/1000 of a roentgen. Again, we don't have a hard number, so we'll go conservative again and assume "thousands" to mean 10,000.
10,000 X 0.05 mr/hr = 500 mr/hr.
Apply the quality factor of 10 to get the biological dose (rem)
500mr/hr neutron radiation X 10 (QF) = 5000 mrem/hr or 5 rem/hr.
So, how does this compare to dose rates we accept as a matter of course?
Normal background exposure in the US runs at about 0.36 rem per year. A chest x-ray gives the recipient about .3 rem per exposure. A routine heart catheterization gives the recipient about 25 rem over 10 minutes.
By the way, the Health Physics society is a great resource for radiation information.
So what we have is a package that is hot, but how dangerous is it? Looked at as an acute exposure, that is, all at once, it's moderately dangerous. Assuming a whole body exposure, again, the most limiting case, after 20 hours of contact with the package, you could expect mild radiation sickness. After 60 hours, severe radiation sickness, and possibly death. 70 hours of whole body exposure would result in death in 50% of the cases without medical intervention. 120 hours would be fatal in almost every case. Remember, for these numbers to hold true, you would have to be in direct physical contact with the package the entire time. Simply moving three feet away from the package would drip the dose by an order of magnitude, in which case it would take 200 hours of constant exposure to get to a dose where you might expect some radiation sickness.
Remember, this is all based on worst case assumptions. Going the other way, assuming a gamma source (QF=1) and a radiation level of 5,000 times background, the dose rate drops to 250 mrem/hr. At that rate, you would have to hug the package for 400 hours to achieve a dose which might make you a little bit sick.
In short, this package is probably not a terror device of any sort. My guess is it's a calibration source that's been shipped improperly.
That's a helpful explanation for us "non-nukes." Without such context, reading that a package is emitting "thousands of times" more radiation than norm is a bit frightening.
Posted by: Brian A. on September 25, 2003 6:32 PMI have to wonder who would be importing a calibration source from Kiev...of all places. Not that it isn't possible. The link to the story is dead so I have nothing else to go on.
Your dose estimate information is good, but without explaining that typical whole body dose calculations are based on the fact that the entire body is exposed to the same gamma fluence, it's a bit overly simplistic. If a small area of the body is exposed, such as in a directional source, then a "weighting factor" can be used to determine the committed effective dose equivalent. The weighting factor will take into account the area of the body and what internal organs are exposed. This scenario would certainly present itself with a very interesting issue in regards to dosimetry problems and assigning the correct dose to the correct critical organ.
P.S. Using micro-R meters is patently silly. At those levels, you don't even need signage.