SANTA ANA, Calif. (AP) -- A chemist involved in a 1997 laboratory explosion was arrested after investigators found radioactive materials at his home.

Investigators said Egyptian-born Riad Mohamad Ahmed is not yet suspected of any terrorist activities. They would not say what he was doing with the radioactive materials or why they were in his home.

Ahmed, 62, was arrested Thursday and charged with illegal possession of radioactive material after investigators seized three briefcases, a suit and a desk all contaminated with radioactive carbon 14 at his home, said Tori Richards, a spokeswoman for the Orange County district attorney.

The radiation exceeded allowable levels outside a laboratory, but did not pose any danger, authorities said.

Ahmed could also face charges of violating probation stemming from the 1997 explosion at a laboratory in Gardena, said Daniel Wright, Los Angeles County deputy district attorney.

In that incident, Ahmed was working with carbon 14 at the California Bionuclear Corp. when a small explosion and fire occurred, Wright said. The building was contaminated and the federal government later labeled it a Superfund cleanup site.

``It was so contaminated, he had to take the building down to the studs,'' said Wright, who prosecuted Ahmed in that case.

Ahmed was also charged in 1986 with mishandling radioactive, flammable and explosives materials at another lab. He pleaded no contest, served 60 days in jail and was fined $15,000.

Ahmed told prosecutors he was born in Cairo, immigrated to the United States in the 1970s and earned a Ph.D. in bionuclear chemistry from the University of Southern California.