BAI 9100 D Moving Filter Monitor

The Moving Filter Monitor BAI 9100 D measures α and β particulates activity in stack or environmental monitoring applications.


  • Filter transport can be continuous or stepwise
  • The detector is mounted directly over the dust collection area and promptly measures the particulates radioactivity
  • The dust collection and detector assembly is shielded by an enveloping 4 pi lead shield
  • The large collection area allows a high flow rate of 25 m³/h hence low detection limits
  • Beta plastic scintillator detector BAI 9300 B with high dynamic range (standard version)
  • Alpha-/Beta scintillator detector BAI 9300 AB to detect simultaneously in separated counting channels Alpha and Beta activities (optional)
  • A delayed measurement which measures the activity on the filter 120 h (5 days) after collection for virtually eliminating any Radon progeny influence from the result which results in Detection limits for artificial Beta activities lower than 1 mBq/m³ is possible (optional)
  • With the Alpha-Beta measurement the influence of natural radioactivity is compensated by the Alpha/Beta ratio method or optional the Alpha-Beta pseudo-coincidence method (ABPD)
  • The Monitor can be combined with an Iodine and/or Noble gas monitor in the same 19’’ cabinet



The particulates monitor BAI 9100 D is used to measure airborne Alpha-/Beta particulates in the presence of naturally occurring (Radon) activity and fluctuating gamma backgrounds.

The monitor consists of following main building blocks:

Dust collection unit BAI 9100 D: Allows the prompt measurement of radioactive Beta or Alpha-/Beta particles as well as the prompt Gamma measurement. The Beta or Alpha/Beta detector is mounted on the top of the dust collection area in order that no delay occurs in the evaluation. The sample air is drawn in via a flat nozzle through the glass fiber filter. Additionally a delayed measurement position is available with up to 120 h delay, depending on the filter speed.

Prompt Beta detector BAI 9300 B: with plastic scintillator and integrated preamplifier BAI9207-1. The Detector delivers digital norm pulses that are fed to the evaluation electronics.


Prompt Alpha-Beta detector BAI 9300 AB: with ZnS coated plastic scintillator and preamplifier unit LB2030 for simultaneous and separate Alpha and Beta activity measurement. The Analog signal from the detector is converted into digital norm pulses in the preamplifier LB2030 which are fed to the evaluation electronics.

Cassette: made of aluminum (optional stainless steel) with protection degree IP68 envelopes the dust collection unit, filter supply and take-up spools. On the back side of the cassette the capstan drive mechanism and filter tape sensors are mounted. The capstan drive mechanism ensures a virtually tension free filter advance and makes it less prone to filter rupture even with a humid filter tape. A plexi-glass front door envelopes the medium wetted parts and allows visual inspection of the filter supply on the feed spool. The cassette is built to 19’’ standard and is suited for mounting into a 19’’ enclosure.

PLC Unit: to drive and monitor the Stepper motor filter advance mechanism.

Pump Unit: equipped with a maintenance free lateral blower pump, suited for temperatures up to 45 °C and designed for a sample airflow of 25 m³/h with flow sensor or an optional flow meter.

Evaluation electronics: depending on the application field (room or process gas, environmental or stack monitoring): LB 5340 or LB 9000 Data Logger.


All applications where airborne Alpha and Beta particulates radioactivity has to be measured to prevent personnel exposure and to measure release rates in ducts and stacks

  • Decommissioning
  • Nuclear power
  • Source manufacturing
  • Industrial safety
  • Research
Product Information
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