BAI 9109-4 Beta-Gasmonitor

The Beta-Gasmonitor BAI 9109-4 provides the opportunity to monitor radioactive gases such as Krypton-85, Argon-41, Xenon-133, Carbon-11 and Fluorine-18 in rooms and discharched air with low minimal detectable activities.


  • 1 to 4 large area proportional counter tubes, xenon sealed
  • Integrated preamplifier and high voltage supply
  • Measuring chamber with 11.45 l volume
  • Lead shield, all sides with 2 cm thickness in 4π geometry
  • Different data acquisition systems available depending on the application: Data Logger LB 112, Data Logger LB 5340, Data Logger LB 9000

The measuring chamber of the BAI 9109-4 can be equipped with 1 to 4 large area proportional counter tubes, xenon sealed, whereas one detector can be used as a compensation detector.

The sample air being measured will be directed via a prefilter by means of a pump. Disturbing particles within the sample air will be removed and the air will be directed to the measuring chamber.

The measuring chamber has a volume of 11.45 l and is equipped with a lead shield all sides with 2 cm thickness in 4π geometry to minimize the background as much as possible.



Measuring Chamber BAI 9109-4
Construction MaterialPVC
Volume11.45 l
Pump                               max. nominal flow rate thorough the vessel 15 m³/h





Lead Shield
Type96 % Pb + 4 % Sb
Geometry4π - all sided with 2 cm thickness
Construction6 plates
Weight                approx. 185 kg (lead only)






Type                                   sealed xenon large area proportional counter tubes LB 6350-11
Sensitive detector area230 cm²
Backgroundtypical approx. 4 cps per detector in 2 cm lead shield
Measurement range1 kBq/m³ to 100 MBq/m³
Gamma-sensitivitymeasured in 137Cs isotropic dose rate field
 1 Detector110 cps per µSv/h
 2 Detectors220 cps per µSv/h
 3 Detectors330 cps per µSv/h
 4 Detectors440 cps per µSv/h
Protectiondouble protection grid for protection against pressure fluctuations up to 0.2 bar and prefilter
ElectronicsIntegrated preamplifier and high voltage supply LB 2022-22













Ambient Conditions
BAI 9109-4                              Temperature0°C to +40 °C
 Humidity10 % to 95 % (non-condensing)
Sample AirTemperature-5°C to +50 °C
 Humidity10 % to 95 % (non-condensing)
 Max. flow15 m³/h
 Max. differential pressure0.2 bar absolute
 Sample must be free of caustic and acid vapours and solvents








  • Monitoring of radioactive gases in rooms and discharched air
  • Measurement of beta- and beta+ (positrons) nuclides
Format Size
BAI 9109-4 en PDF 288.82 KB