This is the average of the 60 previous counts per second values, updated once per second CPM BKRD: background subtract setpoint, current in CPM Ka: CPM to ♜i/cc constant setpoint. The equation for the radioactive concentration is: ♜i/cc = (CPM - CPM BKRD) x Ka where: ♜i/cc: Concentration, ♜i per cubic centimeter CPM: detector output, counts per minute. The ♜i/cc calculation is a measurement of the radioactivity seen by the detector. Secondary standard solid source sets and a standard field calibration fixture are available for on-site re-calibrations. By applying the detector unique correction factor to the counts per minute (CPM) to ♜i/cc conversion constant, the variations between detectors are eliminated. To accommodate these differences, each GM detector is subjected to a primary calibration to determine a unique correction factor. Because the GM detector operates on a limited plateau, manufacturing differences between detectors can have a significant effect on detector response. In addition, the junction box provides a method to interconnect the detector to the control room cable. The Model 843-252 Junction Box includes a pulse shaping and cable driving preamplifier. The GM detector is housed in a phenolic tube to reduce the potential for damage during handling. The detector is provided with a 6 ft cable with a triax connector for termination in a Model 843-252 Junction Box. The detector is a Model 843-251 Series GM tube gamma detector. A radioactive check source is installed in the shield weldment to verify detector operation Thermal insulation may be installed between the steam line and the shield (where required) to reduce the temperature at the detector. The shield should be located to reduce potential interference that may result from other steam lines in the area. The shield also provides a convenient location to mount the detector junction box. The distance between the detector and the main steam line is based on the size of the line, the fission product activity expected and the response of the GM tube detector. ![]() The detector tube intersects a viewing port that positions the GM detector to view the main steam line directly. A “seal grip” type adaptor is used to seal the detector entry port and prevent moisture from damaging the detector. Because of the small size of the GM detector, it is inserted into the shield through a stainless steel tube welded to the shield frame. The purpose of the shielding is to reduce the induced background due to the low energy fission products present in the steam line, thereby increasing the monitor sensitivity. The shield is designed to mount on a platform or pedestal, adjacent to the main steam line. ![]() The face of the shield is designed to match the diameter of the main steam line, which affects its overall size and weight. ![]() Reduce radiation exposure through equipment modificationĪ Model 841-7, “adjacent to the line” or “on-line” shield assembly, with 7 inches of 4 Pi virgin lead shielding is provided.Reduce radiation exposure through behavior.LANDAUER Radiation Measurement Services.Victoreen Calibration Equipment and Accessories.Victoreen Liquid, Duct, Process Radiation Monitors.Victoreen Particulate, Iodine, Noble Gas Monitoring Systems.Nuclear Power Radiation Monitoring Systems.
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