About 90,000 citizens of Ukraine, who were residents of the near zone of the Chernobyl nuclear power plant were evacuated during the first weeks after the accident due to the heavy contamination of the environment. Doses of this cohort were unknown. Retrospective reconstruction of external gamma exposure doses, based on the results of direct dose rate measurements performed during the accident and individual behavior/migration histories of the evacuees, was performed. Individual doses were reconstructed for 30,586 evacuees from the city of Prip'at and the settlements of the 30-km zone. The average effective dose H(E) due to external irradiation for this cohort was estimated to be 15 mSv, although individual values vary in an extremely wide range from 0.1 to 383 mSv. The collective dose of the whole evacuated population was found to be 1,300 person-Sv.

Some radiation-emergency countermeasures, including evacuation, were implemented in the settlements of the 30-km zone during the early phase of the accident at the Chernobyl Nuclear Power Plant. These countermeasures are described and compared with the international recommendations. An analysis of the effectiveness of the emergency countermeasures was conducted based upon the results of a wide-scale public survey. Quantitative assessments of the effectiveness (dose reduction) of the countermeasures were derived.