It doesn't look that close to me

• Finland: lowest death rate on the southern coast, which is almost the country's highest Chernobyl exposure

• Poland: almost an inverse correlation within the country, not to mention that it got one of the highest doses overall but isn't particularly high on the death rates

• Bulgaria and Hungary: low exposures, very high death rates

• Turkiye and Georgia: high death rates, little to no exposure

Like, yes, there is a general correlation of more east = higher death rates and also higher doses, but there's too much other stuff going on in the details for that to be the explanation by itself