NEW YORK, june 28: The New York City police department has installed four radiation detectors to prevent terrorists armed with radioactive material from entering their offices.

Called radiation portal monitors, the detectors consists of two upright black poles placed two metres or more apart through which people must walk to enter the police headquarters and its garage. Two other units are to be used by the Emergency Service Unit and the bomb squad department.

“They are easily deployable,” a police official told The New York Times, calling the detectors a precautionary measure. He said there was no specific warning that prompted the installation.

“There was no trigger, it’s just another counter-terrorism response,” he was quoted as saying.

The Bush administration has warned that terrorists might use radioactive materials to build a so-called “dirty bomb” - one which would spew radioactive waste over a limited area - or launch a strike at nuclear plants that could cause a dispersion of deadly radioactive clouds in populated areas.—dpa