In April 26, 1986, Reactor #4 of the Chernobyl Nuclear Power Plant in Ukraine exploded, contaminating an area of more than 200 000 km2 in Europe with above 0.04 MBq of 137Cs/m2  as well as other radioactive particles (IAEA,06). Most contaminated in Ukraine is an area of 260,000 hectares known as the Chernobyl Exclusion Zone (CEZ) that was contaminated with 90Sr, 137Cs, 154Eu, 238Pu,239,240Pu, and 241Am. This CEZ was evacuated and cordoned off for limited activities and access.

This area is known as the Chernobyl Exclusion Zone (CEZ).  Radioactive contamination was unevenly spread in the CEZ.