Model 421NPPM

The major features of the 421NPPM include:

  • Automatic recycling dryer to measure tritium oxide specifically, immune to other radioisotopes, including all reactor gases as well as radon
  • Gamma compensated chamber design
  • Wire-grid ionization chambers are plate-out proof, eliminates tritium contamination and background zero drift
  • Completely drift free with automatic electronic zero
  • Unaffected by variations in temperature or humidity
  • Modular design allows you to configure a wide variety of alarms, controls, remote display units, and air sampling units
  • Computer compatible outputs to signal operational failure, including: loss of flow, pump failure, electrical failure (low voltage failure, high voltage failure, electrometer failure)
  • Upgraded heavy-duty pump system
  • NEMA-12 wall-mount enclosure

Optional air sampling units are available that allow you to remotely sample up to 24 different locations and can be customized according to your specific requirements.


The Model 421NPPM is a wide range ionization chamber tritium in air monitor configured for measuring tritium in the special environmental conditions associated with nuclear power plants, especially the CANDU type.  The 421NPPM is extremely accurate, stable, and has been designed to exhibit sensitivities commensurate with safety requirements for worker exposure in power plants with an unparalleled accuracy of ±2%.  Designed for measuring tritium oxide (HTO), even in the presence other radionuclides, through use of an automatic recycling dryer which includes two copper tube columns equipped with heating elements and containing desiccant; when one column is in use, the other is being automatically heated, purged, and cooled to regenerate the desiccant.  Includes an upgraded heavy-duty pump system and NEMA-12 wall-mount enclosure.

Choice of dual 2L or quad 2L ionization chambers, with the following typical measurement ranges:

Dual 2L Range:  1 to 199,999 µCi/m3 or 0.01 to 1,999.9 MBq/m3
Quad 2L Range: 0.1 to 19,999 µCi/m3 or 0.01 to 1,999.9 MBq/m3


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