Dallas ? Two vials of radioactive material missing in Texas for three weeks do not contain enough radiation to cause serious health problems if used in a “dirty bomb,” experts say.

Explosives meant to spread radiation would cause more harm than the radiation itself, they say. But any possibility of radioactive exposure could be enough to scare people – terrorism’s real purpose.

“It plays into people’s psychology,” said Ivan Oelrich, a nuclear specialist with the Federation of American Scientists, based in Washington, D.C.

There’s no indication that the missing antimony-124, which disappeared during a trip across Texas this month, is in the hands of terrorists. However, no one knows who has it or where it might be despite searches by the FBI, the Department of Homeland Security and, most recently, the government’s top nuclear emergency team.

Since last weekend, a helicopter from the National Nuclear Security Administration, a semi-autonomous arm of the Energy Department, has joined in the search.

The agency produces and guards U.S. nuclear weapons and their radioactive components, works to prevent nuclear terrorism and responds to radiation emergencies.

The helicopter flies at 150 feet, sweeping the ground for unusual readings. “The helicopter is staffed with specialists who are trained to find different types of radiation,” agency spokesman Bryan Wilkes said.

The helicopter and its ground-based crew have finished checking Tyler and are searching now around Dallas.

Antimony-124 is used as a tracer in oil and gas exploration.