i'm gonna have to call shens on this:
"The initial three stage design was capable of approximately 100 Mt (Megatons), but at a cost of too much radioactive fallout. To limit fallout, the third stage, and possibly the second stage, had a lead tamper instead of a uranium-238 fusion tamper (which greatly amplifies the reaction by fissioning uranium atoms with fast neutrons from the fusion reaction). This eliminated fast fission by the fusion-stage neutrons, so that approximately 97% of the total energy resulted from fusion alone (as such, it was one of the "cleanest" nuclear bombs ever created, generating a very low amount of fallout relative to its yield). There was a strong incentive for this modification since most of the fallout from a test of the bomb would fall on populated Soviet territory."
everything i've read and seen on Tsar Bomba says it was a 50ishMT prototype of a 100MT design, but the soviets were not capable of producing the 100MT version. itwas a propaganda piece from the beginning.
since when did the soviets give a flying F about any kind of polution? Tsar Bomba sprinkled plutonium over every inch of the planet.
edit:
from the excellent "Trinity and Beyond"
http://www.liveleak.com/view?i=f93_1176808864