BRATISLAVA, Slovakia — A Slovak man has been sentenced to life imprisonment for sending envelopes that contained a radioactive substance to authorities.

The man identified as Stefan K. was convicted of terrorism by a court in the western town of Pezinok for sending the substance, americium, to several county courts, the Justice Ministry and a regional police headquarters in 2016 with a letter containing threats to judges, prosecutors and police officers. Nobody became ill.

Court spokeswoman Katarina Kudjakova says the man, who pleaded not guilty, immediately appealed. The case will be decided by the country's Supreme Court.

Americium is not available naturally in the environment. It is used in smoke detectors or in the medicine. Prosecutors said, without providing further details, that the man obtained the substance at his work.