Lost Cesium-137 Leads to Tightened Security : Safety: A small vial of the radioactive substance was recovered, but a state investigation is continuing.

An oil exploration firm has taken new security measures after the alleged theft of potentially lethal radioactive material last month, the head of the company said.

However, a state health official said Flo-Log Inc. has been ordered to stop using sealed radioactive materials until the state completes its investigation of the incident.

A cigarette lighter-size vial of cesium-137 was discovered missing from the South Gate company Feb. 17, setting off a search that extended to an oil field near Willows in Northern California, where the material had last been used.

An anonymous telephone tip led company officials Feb. 25 to an area beside the Firestone Boulevard on-ramp of the Long Beach Freeway, where the missing container of the powdery substance was found.

“They did an outstanding job in searching for this thing once they lost it, but that doesn’t placate the fact that they lost it,” said Donald Bunn, the state Department of Health Services official in charge of radioactive material. “We are telling them that they have to . . . come in with a better control plan.”

Cesium-137 is an isotope used in medicine to treat certain cancers and in oil exploration, where it can tell researchers whether a well is plugged by sand.

Prolonged exposure--through touching, eating or inhaling--is potentially lethal, causing burns, bleeding, vomiting and diarrhea, and increasing the risk of cancer.

Alan Cassiano, Flo-Log’s chief executive officer, said visual inspections will be required of all materials delivered to and removed from the South Gate facility.

Access to the radiation room where cesium and other radioactive substances are stored has been reduced from six people to two: Cassiano and a radiation safety officer. Until the alleged theft, four field engineers also had access to the room, Cassiano said.

In addition, Cassiano said he or the safety officer must be present when anyone enters the room, and combination locks to the building and the room have been changed.

The company is conducting an internal investigation of the incident, including polygraph tests for all workers, he said.

“We would hate to see something like that happen again,” Cassiano said. “We’re not sure who it was, but we are obviously asking everyone here, going right down the line.”

In addition to cesium-137, Flo-Log is authorized to handle americium-beryllium and radium-226, radioactive materials that are also used in oil exploration, Bunn said.

The state Health Services Department is conducting its own investigation.

Depending on the outcome, the department will either require additional security measures or refer the matter to the state attorney general’s office, which could modify or revoke Flo-Log’s license, Bunn said.

The South Gate Police Department is investigating possible criminal wrongdoing.

In a 1990 inspection, the firm was cited for seven violations, Bunn said.