A federal judge sentenced a retired University of Tennessee professor to four years in prison Wednesday for passing sensitive information from a U.S. Air Force contract to two research assistants from China and Iran.

Plasma physics expert J. Reece Roth was found guilty in September on all 18 counts of conspiracy, fraud and violating the Arms Export Control Act.

The case marked the first time the government used the export control act to crack down on the distribution of restricted data, not hardware, to foreigners in a university setting.

Prosecutors said Roth allowed the two graduate students to see sensitive information while they researched a plasma-guidance system for unmanned aircraft.

Roth, 71, testified at trial that he didn't believe he broke the law because the research had yet to produce anything tangible. He said he received only about $6,000 from the contract.

Roth, who is appealing his conviction, faced a maximum of 160 years in prison and more than $1.5 million in fines.

The charges involved work performed from 2004 to 2006 on two Air Force contracts by Roth; graduate students Xin Dai of China and Sirous Nourgostar of Iran; and university spinoff company Atmospheric Glow Technologies Inc. of Knoxville.

Prosecutors presented several documents suggesting research by Roth's university laboratory and Atmospheric Glow Technologies was restricted. Roth attempted to keep the sensitive research with an American graduate student and the rest with a foreign student, but eventually the data was shared.

Roth also was accused of taking reports and related studies in his laptop to China during a lecture tour in 2006, and having one report e-mailed to him there through a Chinese professor's Internet connection.

Atmospheric Glow Technologies has pleaded guilty to 10 counts of exporting defense-related materials, and Roth protege Daniel Sherman has pleaded guilty to conspiracy.