Model RS400-HTO


  • High performance portable tritium air monitor
  • HTO only measurement (noble gas compensation)
  • Cruciform gamma compensation (400cc volume) with virtually no offset in fields up to 10 mR/h
  • Sensitivity: 2 µCi/m3, 0.1 MBq/m3
  • Range: 1 to 19,999 µCi/m3 or 0.1 to 1,999.9 MBq/m3 (DAC, MPCa, and µSv/h also available)
  • Audible and visual alarm indicators for low flow, low battery, and signal level
  • High voltage power supply malfunction alarm
  • Alpha pulse suppression, radon rejection
  • Includes RS-232 Data Output
  • No long-term drift, no manual zero adjustments
  • Offset potentiometer control included
  • CE Marked


The Model RS400-HTO lightweight portable tritium in air monitor is designed to measure tritium oxide (HTO) only, even in the presence of other radioactive gases (such as noble gases) and background gamma.  Four 200cc ion chambers arranged in a cruciform geometry provide nearly perfect gamma compensation regardless of photon energy, flux gradient, or flux direction.  Two ion chambers are used for measurement (400cc total) and two for gamma compensation (400cc total).  The Model RS400-HTO includes RS-232 data output.

The Model RS400-HTO includes 6 hose connections which can be adjusted for two operating modes to measure either:

  • Total Tritium (HT, HTO, including any other radioactive gases present), or
  • Tritium Oxide (HTO) only, ignoring all other airborne radionuclides such as noble gases and gamma fields.

For HTO measurement, an external desiccant column is interposed between the measurement and compensation chambers which absorbs and removes the HTO to provide a differential measurement that is proportional to HTO only [HTO + other radionuclide – (other radionuclide) = HTO].

Power is supplied by a pair of “D” size batteries in your choice of alkaline or NiMH rechargeable.  Onset of the battery depletion is signaled by illumination of an LED located next to the meter face.  This same LED will also signal red when there is a malfunction with the high voltage power supply.  A nine-position alarm level stepped attenuator, adjustable over partial scale (2 to 1,000 µCi/m3) is located on the front panel.  A steady tone is emitted by an acoustic signaler if the measurement exceeds the alarm set-point (illuminates red LED), or if the sample airflow has been interrupted and is too low (illuminates yellow LED).  The alarms are non-latching.

Zero adjustment is unnecessary, the electrometer is completely temperature stable and shows zero drift from 0° C to 50° C due to special design and careful selection of an ultra-high impedance semiconductor with low internal current leakage and long-term DC stability.  The RS400-HTO can reliably measure currents as low as 10-16 amperes and the span calibration is permanently stable.  The ionization chamber polarizing voltage is supplied by an electronic low-noise regulated dual high-voltage power supply (±80VDC).  The RS400-HTO includes proprietary radon recognition and elimination circuitry to provide accurate, fast, and drift-free measurement.

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