[maryz]

". . . the maximum radiation dose received was equal to the amount of natural background radiation one would receive in one month from sources such as rocks, soil and the sun."

Anyone have any idea of how that compares to the dose of radiation in any medical or dental x-ray?

[driftdiver]

http://www.ada.org/2760.aspx

Dental xrays (full mouth) - .15 mSv
Lower GI x-ray - 4.060 mSv
Cosmic radiation - .510 mSv
Earth radiation - 3.0 mSv

[chimera]

A chest x-ray gives you about 30 millirem (old fashioned units). The natural background in my area is about 0.02 mrem/hr, so in 30 days I get about 14 millirem. So they were getting about this much per hour, or one x-ray every two hours.

That much isn't harmful, the trouble is, exposure is cumulative. If they had remained in the plume for a long time they might experience measurable effects. Changes in blood counts start at about 10 rems. Macroscopic effects start around 200-250 rem (nausea, hair loss). LD50/60 for humans without medical intervention is about 450 rem. So they were not close to that, but my guess is they wished to avoid any unnecessary exposure, so they moved away from the plume. A reasonable way to handle things, on balance.