Since 1986, a thousand square miles of eastern Europe is off-limits to average people. That is because of the nuclear accident at Chernobyl. Ironically, the fact that people aren't allowed in the Chernobyl Exclusion Zone is what turns the zone into a sanctuary for wildlife, most notably in the Red Forest:

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One of the Red Forest's immediate concerns is that when the reactor failed, it contaminated the soil, water and air with 20 times as much radioactive material as the bombings of Hiroshima and Nagasaki.

In this alternate scenario, there is a different Red Forest, caused not by the meltdown of a nuclear power plant, but by the nearby explosion of a nuclear explosion. As the title suggests, we will be using the Tsar Bomba for a demonstration, for there was no greater nuclear bomb in human history. The explosion had a blast yield of 50 megatons of dynamite, almost 2400 times the size of the explosion that destroyed Nagasaki and more than 3,000 times the size of the one that destroyed Hiroshima! And to make matters worse, there were plans for a Tsar Bomba big enough to blast off 100 megatons of TNT!

Let's say that was exactly what happened--a 100-megaton explosion annihilated a city. A Red Forest soon sprouted from the barren, radioactive crater. Animals that were endangered elsewhere are now abundant in this one spot. Compared to the Red Forest of Chernobyl, how much radiation from the explosion would the trees of this Red Forest store?

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    $\begingroup$ In which conditions did the bomb explode? The tsar bomb was one of the cleanest explosions with respect to their energy, because it exploded mid air $\endgroup$ – L.Dutch - Reinstate Monica Mar 31 at 3:53
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    $\begingroup$ High yield thermonuclear explosive devices generally produce very low amount of radioactive pollution relative to their yield. There's added complexity here, that should RDS-220 had been detonated with uranium tamper instead of lead, it would have produced many times the fallout. But either way it is not comparable to fission reactor meltdown. $\endgroup$ – void_ptr Mar 31 at 5:28
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    $\begingroup$ So, this is quite a difficult question to answer, principally because the type of fallout from a nuclear bomb is very different from the type of fallout from a nuclear reactor. The latter has far more long lived isotopes, making the fallout less immediately deadly but longer lasting. I think that if you wanted to exclude people from an area for a long period, you'd need to use a salted bomb to deliberately generate large amounts of longer-lived radioactive isotopes. $\endgroup$ – Starfish Prime Mar 31 at 7:01
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    $\begingroup$ Please clarify at least the meaning of "how much radiation would this area store". I don't immediately see a meaning for "stored radiation". And you might have noticed that Hiroshima and Nagasaki are large thriving cities, with no exclusion zones whatsoever. $\endgroup$ – AlexP Mar 31 at 10:51
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    $\begingroup$ Radiation (alpha particles, electrons, or gamma photons) cannot be "stored". It hits, does its effects, and then it's gone. You probably mean radioactive material. Nuclear bombs don't produce that much of that, for the reason that they are designed to produce as little long lasting damage as possible; nobody wants to conquer a wasteland. Even the Bikini Atoll, where the U.S.A. detonated 23 rather primitive nuclear devices from 1946 to 1958, is already in a state where it could be made safe for human occupation if so desired. $\endgroup$ – AlexP Mar 31 at 21:43