MOSCOW (AP) — A senior executive at the Russian nuclear processing plant suspected of being behind a spike of radioactivity over Europe this fall admitted Wednesday that the isotope recorded does emerge as part of the plant's production cycle but said its levels are negligible.

Russian officials last month reported high levels of Ruthenium-106 in areas close to the Mayak nuclear plant in the Ural Mountains.

The environmental group Greenpeace alleged that Mayak could have been the source of a Ruthenium-106 leak, but the plant said it has not extracted the isotope or conducted any other operatio...