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943-5 Process GM Tube Detector and Preamplifier

GM Tube Detector and Preamplifier

943-5 Process

The 943-5 Process GM Detector is designed for the direct measurement of beta and gamma noble gas activity inventilation or exhaust ducts.

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Key Features

  • Plug-in GM tube detector
  • Integral pulse conditioning and driving preamplifier
  • 30 to 40 mg/cm3 wall for beta and gamma detection
  • Operates from 15 in Hg to +15 psig
  • Provides up to 5,200 CPM/mR/h, 137Cs
  • Drives up to 1,500 ft of cable
  • Used with Model 942A UDR or Model 960 System


Federal and state regulations specify the concentration of radioactive isotopes that may be released into an unrestricted area. Facilities that use, or have the potential for the generation of, radioactive materials are required to monitor release points for radioactive noble gasses. The Model 943-5 Process Geiger-Mueller (GM) Detector has been designed for the direct measurement of beta and gamma noble gas activity in ventilation or exhaust ducts. The GM detector is a thin-walled, gas filled radiation detector. In low background areas, the GM tube may be installed directly into the ventilation or exhaust duct. In higher background areas, a lead shielded in-line or off-line process radiation monitor is recommended. Detector efficiency is a function of the sampling geometry and detector used, and ranges from approximately 1 x 103 to 1 x 107 CPM/µCi/cc.

  • Process Radiation Detector with Preamplifier
  • Beta and Gamma Radiation Detector
  • Detects and Measures Gaseous Radioactive Effluents
  • Measures Radioactivity in Ducts, In-line or Off-line Sampling Geometries


The Model 943-5 Process GM Detector, when directly mounted in the release path or used with the Model 940-4 In-Line Sampler or 841-334 Off-Line Sampler and a Model 942A Universal Digital Ratemeter (UDR) or Model 960 Digital Radiation Processor Controller, provides a radiation monitoring system for applications where the direct measurement of ionizing radiation in the release path is required. The Model 943-5 GM detector consists of a GM tube detector and a preamplifier. A Model 942A UDR or Model 960 Readout provides the high DC voltage necessary to operate the detector, the low DC voltage required to operate the preamplifier and the pulse counting electronics necessary to quantify the detector pulse output. The detector is a thin-walled electronic tube with a negative electrode (cathode) and a positive electrode (anode). A positive high voltage (HV) is applied across the anode and cathode. The tube is filled with a mixture of halogen, or noble gasses, and a quenching gas. When a radioactive particle penetrates the wall of the tube, an ionizing event occurs. The event produces an ion pair, which triggers the discharge of the tube, producing an avalanche of ion pairs and a current pulse. The current pulse, one per ionizing event, is independent of the energy of the initiating particle. Multiple discharges are eliminated via the use of a quenching gas in the tube. The resultant pulses are then coupled to the preamplifier. The preamplifier receives the pulses from the GM tube and amplifies the pulses to a nominal 5 VDC level. The preamplifier also includes signal conditioning and line driver circuitry capable of driving the pulses through a 50 ohm transmission line a distance of 1,500 feet without degradation. In the event the radiation field is greater than the maximum range of the detector, the tube will saturate, resulting in a relatively constant output from the preamplifier. This will result in the display of a radiation value that is much less than the actual radiation field. To prevent understating the radiation value, an anti-jam circuit is provided in the preamplifier. When the preamplifier detects a constant output condition, a square wave with a frequency equivalent to the maximum range of the detector is sent to the readout. The preamplifier is integrally mounted to the top of the detector. The preamplifier enclosure functions as a waterproof enclosure for preamplifier and provides a method for connecting the detector HV, signal and power cables to the control room readout. Field calibration of the detector is accomplished through the use secondary transfer button sources and a Model 943-5-100 Fixed Geometry Source Holder.


Fixed geometry source holder Fixed geometry source holder (part# 943-5-100)
Model number: 943-5-100
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