The vehicle gate and personnel exit from the radiation area at TRIUMF to the outside are monitored continuously to prevent any radioactivity from being taken off site. An alarm sounds if radiation is detected and the person or vehicle is then examined for contamination by the TRIUMF Safety Group (TSG) .
In order to detect the passage of low levels of gamma
activity , large and
sensitive detectors are required. These consist of two columns of liquid
scintillator , which are about 2 m high. The
walk-through monitor for personnel
has two columns separated by 1 m and the vehicle gate monitor has two columns
about 7 m apart. The sensitivity of the personnel monitor is such that it
will detect 
of
Co passing through at speeds much larger than
people can walk. The vehicle monitor is less sensitive because of the larger
spacing between the detectors.