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.

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The article proposes an empirical method for constructing a universal calibration for a scintillation gamma spectrometer, which allows determining the activity and specific activity of 137Cs with an accuracy of no more than 15% in counting samples of arbitrary density and volume in cylindrical containers with a volume of 250 ml and 500 ml. To construct calibration ratios, measurements of 137Cs sample media prepared on the basis of materials of different densities (quartz sand, plastic granules and sawdust) were performed. The calibration was carried out by preparing samples from the listed materials with a volume of 50 to 250 ml in increments of 50 ml for a 250 ml container and 100-500 ml in increments of 100 ml for a 500 ml container. Along with taking into account the volume of the counting sample, its weighing was also carried out. The result of the measurements performed for each material was the ratio of the activity of the counting sample to the counting intensity in the 137Cs window, depending on the volume. The universal calibration factor is obtained by taking into account the counting rate from the mass and volume of the sample for the corresponding measuring vessel.