PROVIDENCE, Rhode Island< (AP) -- A Brown University graduate student has been charged with using a radioactive medical chemical to poison two other students -- one of them his former girlfriend, authorities said Sunday.

Neither of the poisoned students was harmed, said university spokesman Mark Nickel.

Cheng Gu, 24, placed a radioactive isotope of iodine in a dish of vegetables and chicken he gave to Yuanyuan Xiao, a fellow student in molecular pharmacology, said police Lt. Stephen Campbell. Yuanyuan's roommate, undergraduate James A. O'Brien, also ate the tainted food.

Cheng was arrested Friday and charged with poisoning, assault and larceny. He was freed on personal recognizance until his next court date.

The attack apparently was motivated by "some kind of love interest," said police Capt. John Ryan. Yuanyuan told police she had been Cheng's girlfriend in their native China and, for a time, in the United States.

The isotope, iodine-125, is used to diagnose and treat thyroid disorders, and the amount Yuanyuan and O'Brien received was about the same as that given in such diagnostic procedures, said Nickel.

Radiation alert

The contamination was discovered Wednesday when Yuanyuan arrived at Brown's pharmacology laboratory, where students routinely are tested for radiation. A Geiger counter showed that Yuanyuan was "hot," Campbell said.

Finding nothing amiss in the lab, safety personnel went to Yuanyuan's home and found radioactive contamination in Cheng's dish of chicken, tomatoes, string beans and a green leafy vegetable, Campbell said.

Although Cheng worked in the laboratory, he was not supposed to be working with iodine-125 and the isotope was secured with a combination lock, Campbell said.

Iodine-125 has a half-life of six months, meaning half of its radiation dissipates every six months.