Model 945A

Area monitors are used for the detection of x-ray or gamma radiation in selected areas. The monitor should be used in any location where personnel may be exposed to an adverse amount of radiation. Applications include nuclear reactors, accelerators, hot cells, irradiators and any area where radiation sources are handled. These monitors can be used as single channel monitors or grouped together as a multichannel area monitoring system.

The Model 977-210 Wide Range Ion Chamber Detector is a gamma sensitive radiation detection device, which measures radiation in the range of 10^-1 mR/h to 10⁷ mR/h with an energy dependence of less than ± 10% from 55 keV to 3 MeV. The preamp is housed in a gasket sealed enclosure. Interconnection between the detector and preamplifier is accomplished via two five foot cables, encased in a flexible conduit. The wide-range ion chamber detector design includes a dual, concentric ion chamber with a volume of approximately 1000 cc. The chamber walls are made of tissue equivalent plastic. An outer wall, made of aluminum, is provided to protect the ion chamber and to mechanically interface with the Model 848-8 Field Test Source. The ion chamber is biased at a nominal 500 volts and produces an output current proportional to radiation absorbed in the chamber. The current is approximately 8 x 10^-11 A/R/h. The ion chamber assembly makes use of a double seal design, where the actual ion chamber is filled with nitrogen at atmospheric pressure. The connector area is sealed against moisture and particulates through the use of a sealed, liquid tight flexible conduit between the detector and preamplifier electronics.

The preamplifier contains a microprocessor controlled, auto-zeroing, integrating electrometer, a programmable gain amplifier, an analog-to-digital converter, an asynchronous serial communication interface, an electronic check source and the detector high voltage power supply. Communications with the UDR is accomplished via the optically isolated serial communication loop driver/receiver circuitry.

Standard features for the instrument consist of a three digit display of the radiation value and a multicolored bargraph indicator which covers the entire range of the detector. The bargraph will change color in the event of an alarm condition (green for normal, amber for warning and red for high). Front panel alarm indicators and rear panel output relays for alarm annunciation are also included. Front panel pushbuttons are provided to apply power, to display alarm limit setpoints, for alarm acknowledgment and for the activation of a check source function.